RedisQueuedLocks ·

Distributed locks with "prioritized lock acquisition queue" capabilities based on the Redis Database.

Each lock request is put into the request queue (each lock is hosted by it's own queue separately from other queues) and processed in order of their priority (FIFO). Each lock request lives some period of time (RTTL) (with requeue capabilities) which guarantees the request queue will never be stacked.

In addition to the classic queued (FIFO) strategy RQL supports random (RANDOM) lock obtaining strategy when any acquirer from the lock queue can obtain the lock regardless the position in the queue.

Provides flexible invocation flow, parametrized limits (lock request ttl, lock ttl, queue ttl, lock attempts limit, fast failing, etc), logging and instrumentation.

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Table of Contents

• Requirements
• Experience
• Algorithm
• Installation
• Setup
• Configuration
• Usage
  • lock
  • lock!
  • lock_info
  • queue_info
  • locked?
  • queued?
  • unlock
  • clear_locks
  • extend_lock_ttl
  • locks
  • queues
  • keys
  • locks_info
  • queues_info
  • clear_dead_requests
  • current_acquirer_id
  • current_host_id
  • possible_host_ids
• Swarm Mode and Zombie Locks
  • work and usage preview (temporary example-based docs)
  • How to Swarm
    • configuration
    • swarm_status
    • swarm_info
    • swarmize!
    • deswarmize!
    • probe_hosts
    • flush_zobmies
  • zombies_info
  • zombie_locks
  • zombie_hosts
  • zombie_acquiers
• Lock Access Strategies
  • queued
  • random
• Deadlocks and Reentrant locks
• Logging
  • Logging Configuration
• Instrumentation
  • Instrumentation Configuration
  • Instrumentation Events
• Roadmap
• Contributing
• License
• Authors

---

Requirements

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• Redis Version: ~> 7.x;
• Redis Protocol: RESP3;
• gem redis-client: ~> 0.20;
• Ruby: >= 3.1;

---

Experience

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• Battle-tested on huge ruby projects in production: ~3000 locks-per-second are obtained and released on an ongoing basis;
• Works well with hiredis driver enabled (it is enabled by default on our projects where redis_queued_locks are used);

---

Algorithm

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Each lock request is put into the request queue (each lock is hosted by it's own queue separately from other queues) and processed in order of their priority (FIFO). Each lock request lives some period of time (RTTL) which guarantees that the request queue will never be stacked.

In addition to the classic "queued" (FIFO) strategy RQL supports "random" (RANDOM) lock obtaining strategy when any acquirer from the lock queue can obtain the lock regardless the position in the queue.

Soon: detailed explanation.

---

Installation

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gem 'redis_queued_locks'

bundle install
# --- or ---
gem install redis_queued_locks

require 'redis_queued_locks'

---

Setup

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require 'redis_queued_locks'

# Step 1: initialize RedisClient instance
redis_client = RedisClient.config.new_pool # NOTE: provide your own RedisClient instance

# Step 2: initialize RedisQueuedLock::Client instance
rq_lock_client = RedisQueuedLocks::Client.new(redis_client) do |config|
  # NOTE:
  #   - some your application-related configs;
  #   - for documentation see <Configuration> section in readme;
end

# Step 3: start to work with locks :)
rq_lock_client.lock("some-lock") { puts "Hello, lock!" }

---

Configuration

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redis_client = RedisClient.config.new_pool # NOTE: provide your own RedisClient instance

clinet = RedisQueuedLocks::Client.new(redis_client) do |config|
  # (default: 3) (supports nil)
  # - nil means "infinite retries" and you are only limited by the "try_to_lock_timeout" config;
  config.retry_count = 3

  # (milliseconds) (default: 200)
  config.retry_delay = 200

  # (milliseconds) (default: 25)
  config.retry_jitter = 25

  # (seconds) (supports nil)
  # - nil means "no timeout" and you are only limited by "retry_count" config;
  config.try_to_lock_timeout = 10

  # (milliseconds) (default: 5_000)
  # - lock's time to live
  config.default_lock_ttl = 5_000

  # (seconds) (default: 15)
  # - lock request timeout. after this timeout your lock request in queue will be requeued with new position (at the end of the queue);
  config.default_queue_ttl = 15

  # (boolean) (default: false)
  # - should be all blocks of code are timed by default;
  config.is_timed_by_default = false

  # (boolean) (default: false)
  # - When the lock acquirement try reached the acquirement time limit (:timeout option) the
  #   `RedisQueuedLocks::LockAcquirementTimeoutError` is raised (when `raise_errors` option
  #   of the #lock method is set to `true`). The error message contains the lock key name and
  #   the timeout value).
  # - <true> option adds the additional details to the error message:
  #   - current lock queue state (you can see which acquirer blocks your request and
  #     how much acquirers are in queue);
  #   - current lock data stored inside (for example: you can check the current acquirer and
  #     the lock meta state if you store some additional data there);
  # - Realized as an option because of the additional lock data requires two additional Redis
  #   queries: (1) get the current lock from redis and (2) fetch the lock queue state;
  # - These two additional Redis queries has async nature so you can receive
  #   inconsistent data of the lock and of the lock queue in your error emssage because:
  #   - required lock can be released after the error moment and before the error message build;
  #   - required lock can be obtained by other process after the error moment and
  #     before the error message build;
  #   - required lock queue can reach a state when the blocking acquirer start to obtain the lock
  #     and moved from the lock queue after the error moment and before the error message build;
  # - You should consider the async nature of this error message and should use received data
  #   from error message correspondingly;
  config.detailed_acq_timeout_error = false

  # (symbol) (default: :queued)
  # - Defines the way in which the lock should be obitained;
  # - By default it is configured to obtain a lock in classic `queued` way:
  #   you should wait your position in queue in order to obtain a lock;
  # - Can be customized in methods `#lock` and `#lock!` via `:access_strategy` attribute (see method signatures of #lock and #lock! methods);
  # - Supports different strategies:
  #   - `:queued` (FIFO): the classic queued behavior (default), your lock will be obitaned if you are first in queue and the required lock is free;
  #   - `:random` (RANDOM): obtain a lock without checking the positions in the queue (but with checking the limist,
  #     retries, timeouts and so on). if lock is free to obtain - it will be obtained;
  config.default_access_strategy = :queued

  # (symbol) (default: :wait_for_lock)
  # - Global default conflict strategy mode;
  # - Can be customized in methods `#lock` and `#lock!` via `:conflict_strategy` attribute (see method signatures of #lock and #lock! methods);
  # - Conflict strategy is a logical behavior for cases when the process that obtained the lock want to acquire this lock again;
  # - Realizes "reentrant locks" abstraction (same process conflict / same process deadlock);
  # - By default uses `:wait_for_lock` strategy (classic way);
  # - Strategies:
  #   - `:work_through` - continue working under the lock <without> lock's TTL extension;
  #   - `:extendable_work_through` - continue working under the lock <with> lock's TTL extension;
  #   - `:wait_for_lock` - (default) - work in classic way (with timeouts, retry delays, retry limits, etc - in classic way :));
  #   - `:dead_locking` - fail with deadlock exception;
  # - See "Dead locks and Reentrant Locks" documentation section in REDME.md for details;
  config.default_conflict_strategy = :wait_for_lock

  # (default: 100)
  # - how many items will be released at a time in #clear_locks and in #clear_dead_requests (uses SCAN);
  # - affects the performance of your Redis and Ruby Application (configure thoughtfully);
  config.lock_release_batch_size = 100

  # (default: 500)
  # - how many items should be extracted from redis during the #locks, #queues, #keys
  #   #locks_info, and #queues_info operations (uses SCAN);
  # - affects the performance of your Redis and Ruby Application (configure thoughtfully;)
  config.key_extraction_batch_size = 500

  # (default: 1 day)
  # - the default period of time (in milliseconds) after which a lock request is considered dead;
  # - used for `#clear_dead_requests` as default vaule of `:dead_ttl` option;
  config.dead_request_ttl = (1 * 24 * 60 * 60 * 1000) # one day in milliseconds

  # (default: RedisQueuedLocks::Instrument::VoidNotifier)
  # - instrumentation layer;
  # - you can provide your own instrumenter that should realize `#notify(event, payload = {})` interface:
  #   - event: <string> requried;
  #   - payload: <hash> requried;
  # - disabled by default via `VoidNotifier`;
  config.instrumenter = RedisQueuedLocks::Instrument::ActiveSupport

  # (default: -> { RedisQueuedLocks::Resource.calc_uniq_identity })
  # - uniqude idenfitier that is uniq per process/pod;
  # - prevents potential lock-acquirement collisions bettween different process/pods
  #   that have identical process_id/thread_id/fiber_id/ractor_id (identivcal acquier ids);
  # - it is calculated once per `RedisQueudLocks::Client` instance;
  # - expects the proc object;
  # - `SecureRandom.hex(8)` by default;
  config.uniq_identifier = -> { RedisQueuedLocks::Resource.calc_uniq_identity }

  # (default: RedisQueuedLocks::Logging::VoidLogger)
  # - the logger object;
  # - should implement `debug(progname = nil, &block)` (minimal requirement) or be an instance of Ruby's `::Logger` class/subclass;
  # - supports `SemanticLogger::Logger` (see "semantic_logger" gem)
  # - at this moment the only debug logs are realised in following cases:
  #   - "[redis_queued_locks.start_lock_obtaining]" (logs "lock_key", "queue_ttl", "acq_id", "hst_id", "acs_strat");
  #   - "[redis_queued_locks.start_try_to_lock_cycle]" (logs "lock_key", "queue_ttl", "acq_id", "hst_id", "acs_strat");
  #   - "[redis_queued_locks.dead_score_reached__reset_acquier_position]" (logs "lock_key", "queue_ttl", "acq_id", "hst_id", "acs_strat");
  #   - "[redis_queued_locks.lock_obtained]" (logs "lock_key", "queue_ttl", "acq_id", "hst_id", "acq_time", "acs_strat");
  #   - "[redis_queued_locks.extendable_reentrant_lock_obtained]" (logs "lock_key", "queue_ttl", "acq_id", "hst_id", "acq_time", "acs_strat");
  #   - "[redis_queued_locks.reentrant_lock_obtained]" (logs "lock_key", "queue_ttl", "acq_id", "hst_id", "acq_time", "acs_strat");
  #   - "[redis_queued_locks.fail_fast_or_limits_reached_or_deadlock__dequeue]" (logs "lock_key", "queue_ttl", "acq_id", "hst_id", "acs_strat");
  #   - "[redis_queued_locks.expire_lock]" (logs "lock_key", "queue_ttl", "acq_id", "hst_id", "acs_strat");
  #   - "[redis_queued_locks.decrease_lock]" (logs "lock_key", "decreased_ttl", "queue_ttl", "acq_id", "hst_id", "acs_strat");
  # - by default uses VoidLogger that does nothing;
  config.logger = RedisQueuedLocks::Logging::VoidLogger

  # (default: false)
  # - adds additional debug logs;
  # - enables additional logs for each internal try-retry lock acquiring (a lot of logs can be generated depending on your retry configurations);
  # - it adds following debug logs in addition to the existing:
  #   - "[redis_queued_locks.try_lock.start]" (logs "lock_key", "queue_ttl", "acq_id", "hst_id", "acs_strat");
  #   - "[redis_queued_locks.try_lock.rconn_fetched]" (logs "lock_key", "queue_ttl", "acq_id", "hst_id", "acs_strat");
  #   - "[redis_queued_locks.try_lock.same_process_conflict_detected]" (logs "lock_key", "queue_ttl", "acq_id", "hst_id", "acs_strat");
  #   - "[redis_queued_locks.try_lock.same_process_conflict_analyzed]" (logs "lock_key", "queue_ttl", "acq_id", "hst_id", "acs_strat", "spc_status");
  #   - "[redis_queued_locks.try_lock.reentrant_lock__extend_and_work_through]" (logs "lock_key", "queue_ttl", "acq_id", "hst_id", "acs_strat", "spc_status", "last_ext_ttl", "last_ext_ts");
  #   - "[redis_queued_locks.try_lock.reentrant_lock__work_through]" (logs "lock_key", "queue_ttl", "acq_id", "hst_id", "acs_strat", "spc_status", last_spc_ts);
  #   - "[redis_queued_locks.try_lock.acq_added_to_queue]" (logs "lock_key", "queue_ttl", "acq_id", "hst_id", "acs_strat")";
  #   - "[redis_queued_locks.try_lock.remove_expired_acqs]" (logs "lock_key", "queue_ttl", "acq_id", "hst_id", "acs_strat");
  #   - "[redis_queued_locks.try_lock.get_first_from_queue]" (logs "lock_key", "queue_ttl", "acq_id", "hst_id", "acs_strat", "first_acq_id_in_queue");
  #   - "[redis_queued_locks.try_lock.exit__queue_ttl_reached]" (logs "lock_key", "queue_ttl", "acq_id", "hst_id", "acs_strat");
  #   - "[redis_queued_locks.try_lock.exit__no_first]" (logs "lock_key", "queue_ttl", "acq_id", "hst_id", "acs_strat", "first_acq_id_in_queue", "<current_lock_data>");
  #   - "[redis_queued_locks.try_lock.exit__lock_still_obtained]" (logs "lock_key", "queue_ttl", "acq_id", "hst_id", "acs_strat", "first_acq_id_in_queue", "locked_by_acq_id", "<current_lock_data>");
  #   - "[redis_queued_locks.try_lock.obtain__free_to_acquire]" (logs "lock_key", "queue_ttl", "acq_id", "hst_id", "acs_strat");
  config.log_lock_try = false

  # (default: false)
  # - enables <log sampling>: only the configured percent of RQL cases will be logged;
  # - disabled by default;
  # - works in tandem with <config.log_sampling_percent> and <log.sampler> configs;
  config.log_sampling_enabled = false

  # (default: 15)
  # - the percent of cases that should be logged;
  # - take an effect when <config.log_sampling_enalbed> is true;
  # - works in tandem with <config.log_sampling_enabled> and <config.log_sampler> configs;
  config.log_sampling_percent = 15

  # (default: RedisQueuedLocks::Logging::Sampler)
  # - percent-based log sampler that decides should be RQL case logged or not;
  # - works in tandem with <config.log_sampling_enabled> and <config.log_sampling_percent> configs;
  # - based on the ultra simple percent-based (weight-based) algorithm that uses SecureRandom.rand
  #   method so the algorithm error is ~(0%..13%);
  # - you can provide your own log sampler with bettter algorithm that should realize
  #   `sampling_happened?(percent) => boolean` interface (see `RedisQueuedLocks::Logging::Sampler` for example);
  config.log_sampler = RedisQueuedLocks::Logging::Sampler

  # (default: false)
  # - enables <instrumentaion sampling>: only the configured percent of RQL cases will be instrumented;
  # - disabled by default;
  # - works in tandem with <config.instr_sampling_percent and <log.instr_sampler>;
  config.instr_sampling_enabled = false

  # (default: 15)
  # - the percent of cases that should be instrumented;
  # - take an effect when <config.instr_sampling_enalbed> is true;
  # - works in tandem with <config.instr_sampling_enabled> and <config.instr_sampler> configs;
  config.instr_sampling_percent = 15

  # (default: RedisQueuedLocks::Instrument::Sampler)
  # - percent-based log sampler that decides should be RQL case instrumented or not;
  # - works in tandem with <config.instr_sampling_enabled> and <config.instr_sampling_percent> configs;
  # - based on the ultra simple percent-based (weight-based) algorithm that uses SecureRandom.rand
  #   method so the algorithm error is ~(0%..13%);
  # - you can provide your own log sampler with bettter algorithm that should realize
  #   `sampling_happened?(percent) => boolean` interface (see `RedisQueuedLocks::Instrument::Sampler` for example);
  config.instr_sampler = RedisQueuedLocks::Instrument::Sampler
end

---

Usage

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• lock
• lock!
• lock_info
• queue_info
• locked?
• queued?
• unlock
• clear_locks
• extend_lock_ttl
• locks
• queues
• keys
• locks_info
• queues_info
• clear_dead_requests
• current_acquirer_id
• current_host_id
• possible_host_ids

---

#lock - obtain a lock

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• #lock - obtain a lock;
• If block is passed:
  • the obtained lock will be released after the block execution or the lock's ttl (what will happen first);
    • if you want to timeout (fail with timeout) the block execution with lock's TTL use timed: true option;
  • the block's result will be returned;
• If block is not passed:
  • the obtained lock will be released after lock's ttl;
  • the lock information will be returned (hash with technical info that contains: lock key, acquier identifier, acquirement timestamp, lock's ttl, type of obtaining process, etc);

def lock(
  lock_name,
  ttl: config[:default_lock_ttl],
  queue_ttl: config[:default_queue_ttl],
  timeout: config[:try_to_lock_timeout],
  timed: config[:is_timed_by_default],
  retry_count: config[:retry_count],
  retry_delay: config[:retry_delay],
  retry_jitter: config[:retry_jitter],
  raise_errors: false,
  fail_fast: false,
  conflict_strategy: config[:default_conflict_strategy],
  access_strategy: config[:default_access_strategy],
  identity: uniq_identity, # (attr_accessor) calculated during client instantiation via config[:uniq_identifier] proc;
  meta: nil,
  detailed_acq_timeout_error: config[:detailed_acq_timeout_error],
  instrument: nil,
  instrumenter: config[:instrumenter],
  logger: config[:logger],
  log_lock_try: config[:log_lock_try],
  log_sampling_enabled: config[:log_sampling_enabled],
  log_sampling_percent: config[:log_sampling_percent],
  log_sampler: config[:log_sampler],
  log_sample_this: false,
  instr_sampling_enabled: config[:instr_sampling_enabled],
  instr_sampling_percent: config[:instr_sampling_percent],
  instr_sampler: config[:instr_sampler],
  instr_sample_this: false,
  &block
)

• lock_name - (required) [String]
  • Lock name to be obtained.
• ttl - (optional) - [Integer]
  • Lock's time to live (in milliseconds);
  • pre-configured in config[:default_lock_ttl];
• queue_ttl - (optional) [Integer]
  • Lifetime of the acuier's lock request. In seconds.
  • pre-configured in config[:default_queue_ttl];
• timeout - (optional) [Integer,NilClass]
  • Time period a client should try to acquire the lock (in seconds). Nil means "without timeout".
  • pre-configured in config[:try_to_lock_timeout];
• timed - (optiona) [Boolean]
  • Limit the invocation time period of the passed block of code by the lock's TTL.
  • pre-configured in config[:is_timed_by_default];
  • false by default;
• retry_count - (optional) [Integer,NilClass]
  • How many times we should try to acquire a lock. Nil means "infinite retries".
  • pre-configured in config[:retry_count];
• retry_delay - (optional) [Integer]
  • A time-interval between the each retry (in milliseconds).
  • pre-configured in config[:retry_delay];
• retry_jitter - (optional) [Integer]
  • Time-shift range for retry-delay (in milliseconds);
  • pre-configured in config[:retry_jitter];
• instrumenter - (optional) [#notify]
  • See RedisQueuedLocks::Instrument::ActiveSupport for example;
  • See Instrumentation section of docs;
  • pre-configured in config[:isntrumenter] with void notifier (RedisQueuedLocks::Instrumenter::VoidNotifier);
• instrument - (optional) [NilClass,Any]
  • Custom instrumentation data wich will be passed to the instrumenter's payload with :instrument key;
  • nil by default (means "no custom instrumentation data");
• raise_errors - (optional) [Boolean]
  • Raise errors on library-related limits (such as timeout or retry count limit) and on lock conflicts (such as same-process dead locks);
  • false by default;
• fail_fast - (optional) [Boolean]
  • Should the required lock to be checked before the try and exit immidietly if lock is already obtained;
  • Should the logic exit immidietly after the first try if the lock was obtained by another process while the lock request queue was initially empty;
  • false by default;
• access_strategy - (optional) - [Symbol]
  • Defines the way in which the lock should be obitained (in queued way, in random way and so on);
  • By default it is configured to obtain a lock in classic :queued way: you should wait your position in queue in order to obtain a lock;
  • Supports following strategies:
    • :queued (FIFO): (default) the classic queued behavior, your lock will be obitaned if you are first in queue and the required lock is free;
    • :random (RANDOM): obtain a lock without checking the positions in the queue (but with checking the limist, retries, timeouts and so on). if lock is free to obtain - it will be obtained;
  • pre-configured in config[:default_access_strategy];
  • See Lock Access Strategies documentation section for details;
• conflict_strategy - (optional) - [Symbol]
  • The conflict strategy mode for cases when the process that obtained the lock want to acquire this lock again;
  • By default uses :wait_for_lock strategy;
  • pre-confured in config[:default_conflict_strategy];
  • Strategies:
    • :work_through - continue working under the lock without lock's TTL extension;
    • :extendable_work_through - continue working under the lock with lock's TTL extension;
    • :wait_for_lock - (default) - work in classic way (with timeouts, retry delays, retry limits, etc - in classic way :));
    • :dead_locking - fail with deadlock exception;
  • See Deadlocks and Reentrant locks documentation section for details;
• identity - (optional) [String]
  • An unique string that is unique per RedisQueuedLock::Client instance. Resolves the collisions between the same process_id/thread_id/fiber_id/ractor_id identifiers on different pods or/and nodes of your application;
  • It is calculated once during RedisQueuedLock::Client instantiation and stored in @uniq_identity ivar (accessed via uniq_dentity accessor method);
  • Identity calculator is pre-configured in config[:uniq_identifier];
• meta - (optional) [NilClass,Hash<String|Symbol,Any>]
  • A custom metadata wich will be passed to the lock data in addition to the existing data;
  • Custom metadata can not contain reserved lock data keys (such as lock_key, acq_id, ts, ini_ttl, rem_ttl);
  • nil by default (means "no metadata");
• detailed_acq_timeout_error - (optional) [Boolean]
  • When the lock acquirement try reached the acquirement time limit (:timeout option) the RedisQueuedLocks::LockAcquirementTimeoutError is raised (when raise_errors option set to true). The error message contains the lock key name and the timeout value).
  • option adds the additional details to the error message:
    • current lock queue state (you can see which acquirer blocks your request and how much acquirers are in queue);
    • current lock data stored inside (for example: you can check the current acquirer and the lock meta state if you store some additional data there);
  • Realized as an option because of the additional lock data requires two additional Redis queries: (1) get the current lock from redis and (2) fetch the lock queue state;
  • These two additional Redis queries has async nature so you can receive inconsistent data of the lock and of the lock queue in your error emssage because:
    • required lock can be released after the error moment and before the error message build;
    • required lock can be obtained by other process after the error moment and before the error message build;
    • required lock queue can reach a state when the blocking acquirer start to obtain the lock and moved from the lock queue after the error moment and before the error message build;
  • You should consider the async nature of this error message and should use received data from error message correspondingly;
  • pre-configred in config[:detailed_acq_timeout_error];
• logger - (optional) [::Logger,#debug]
  • Logger object used for loggin internal mutation oeprations and opertioan results / process progress;
  • pre-configured in config[:logger] with void logger RedisQueuedLocks::Logging::VoidLogger;
• log_lock_try - (optional) [Boolean]
  • should be logged the each try of lock acquiring (a lot of logs can be generated depending on your retry configurations);
  • pre-configured in config[:log_lock_try];
  • false by default;
• log_sampling_enabled - (optional) [Boolean]
  • enables log sampling: only the configured percent of RQL cases will be logged;
  • disabled by default;
  • works in tandem with log_sampling_percent and log_sampler options;
  • pre-configured in config[:log_sampling_enabled];
• log_sampling_percent - (optional) [Integer]
  • the percent of cases that should be logged;
  • take an effect when log_sampling_enalbed is true;
  • works in tandem with log_sampling_enabled and log_sampler options;
  • pre-configured in config[:log_sampling_percent];
• log_sampler - (optional) [#sampling_happened?,Module<RedisQueuedLocks::Logging::Sampler>]
  • percent-based log sampler that decides should be RQL case logged or not;
  • works in tandem with log_sampling_enabled and log_sampling_percent options;
  • based on the ultra simple percent-based (weight-based) algorithm that uses SecureRandom.rand method so the algorithm error is ~(0%..13%);
  • you can provide your own log sampler with bettter algorithm that should realize sampling_happened?(percent) => boolean interface (see RedisQueuedLocks::Logging::Sampler for example);
  • pre-configured in config[:log_sampler];
• log_sample_this - (optional) [Boolean]
  • marks the method that everything should be logged despite the enabled log sampling;
  • makes sense when log sampling is enabled;
  • false by default;
• instr_sampling_enabled - (optional) [Boolean]
  • enables instrumentaion sampling: only the configured percent of RQL cases will be instrumented;
  • disabled by default;
  • works in tandem with instr_sampling_percent and instr_sampler options;
  • pre-configured in config[:instr_sampling_enabled];
• instr_sampling_percent - (optional) [Integer]
  • the percent of cases that should be instrumented;
  • take an effect when instr_sampling_enalbed is true;
  • works in tandem with instr_sampling_enabled and instr_sampler options;
  • pre-configured in config[:instr_sampling_percent];
• instr_sampler - (optional) [#sampling_happened?,Module<RedisQueuedLocks::Instrument::Sampler>]
  • percent-based log sampler that decides should be RQL case instrumented or not;
  • works in tandem with instr_sampling_enabled and instr_sampling_percent options;
  • based on the ultra simple percent-based (weight-based) algorithm that uses SecureRandom.rand method so the algorithm error is ~(0%..13%);
  • you can provide your own log sampler with bettter algorithm that should realize sampling_happened?(percent) => boolean interface (see RedisQueuedLocks::Instrument::Sampler for example);
  • pre-configured in config[:instr_sampler];
• instr_sample_this - (optional) [Boolean]
  • marks the method that everything should be instrumneted despite the enabled instrumentation sampling;
  • makes sense when instrumentation sampling is enabled;
  • false by default;
• block - (optional) [Block]
  • A block of code that should be executed after the successfully acquired lock.
  • If block is passed the obtained lock will be released after the block execution or it's ttl (what will happen first);
  • If block is not passed the obtained lock will be released after it's ttl;
  • If you want the block to have a TTL too and this TTL to be the same as TTL of the lock use timed: true option (rql.lock("my_lock", timed: true, ttl: 5_000) { ... })

Return value:

• If block is passed the block's yield result will be returned:

  result = rql.lock("my_lock") { 1 + 1 }
  result # => 2

• If block is not passed the lock information will be returned:

  result = rql.lock("my_lock")
  result # =>
  {
    ok: true,
    result: {
      lock_key: "rql:lock:my_lock",
      acq_id: "rql:acq:26672/2280/2300/2320/70ea5dbf10ea1056",
      ts: 1711909612.653696,
      ttl: 10000,
      process: :lock_obtaining
    }
  }

• Lock information result:

  • Signature: [yield, Hash<Symbol,Boolean|Hash<Symbol,Numeric|String>>]

  • Format: { ok: true/false, result: <Symbol|Hash<Symbol,Hash>> };

  • Includes the :process key that describes a logical type of the lock obtaining process. Possible values:

    • :lock_obtaining - classic lock obtaining proces. Default behavior (conflict_strategy: :wait_for_lock);
    • :extendable_conflict_work_through - reentrant lock acquiring process with lock's TTL extension. Suitable for conflict_strategy: :extendable_work_through;
    • :conflict_work_through - reentrant lock acquiring process without lock's TTL extension. Suitable for conflict_strategy: :work_through;
    • :dead_locking - current process tries to acquire a lock that is already acquired by them. Suitalbe for conflict_startegy: :dead_locking;
    • For more details see Deadlocks and Reentrant locks readme section;

  • For successful lock obtaining:

    {
      ok: true,
      result: {
        lock_key: String, # acquierd lock key ("rql:lock:your_lock_name")
        acq_id: String, # acquier identifier ("process_id/thread_id/fiber_id/ractor_id/identity")
        hst_id: String, # host identifier ("process_id/thread_id/ractor_id/identity")
        ts: Float, # time (epoch) when lock was obtained (float, Time#to_f)
        ttl: Integer, # lock's time to live in milliseconds (integer)
        process: Symbol # which logical process has acquired the lock (:lock_obtaining, :extendable_conflict_work_through, :conflict_work_through, :conflict_dead_lock)
      }
    }

    # example:
    {
      ok: true,
      result: {
        lock_key: "rql:lock:my_lock",
        acq_id: "rql:acq:26672/2280/2300/2320/70ea5dbf10ea1056",
        acq_id: "rql:acq:26672/2280/2320/70ea5dbf10ea1056",
        ts: 1711909612.653696,
        ttl: 10000,
        process: :lock_obtaining # for custom conflict strategies may be: :conflict_dead_lock, :conflict_work_through, :extendable_conflict_work_through
      }
    }

  • For failed lock obtaining:

    { ok: false, result: :timeout_reached }
    { ok: false, result: :retry_count_reached }
    { ok: false, result: :conflict_dead_lock } # see <conflict_strategy> option for details (:dead_locking strategy)
    { ok: false, result: :fail_fast_no_try } # see <fail_fast> option
    { ok: false, result: :fail_fast_after_try } # see <fail_fast> option
    { ok: false, result: :unknown }

Examples:

• obtain a lock:

rql.lock("my_lock") { print "Hello!" }

• obtain a lock with custom lock TTL:

rql.lock("my_lock", ttl: 5_000) { print "Hello!" } # for 5 seconds

• obtain a lock and limit the passed block of code TTL with lock's TTL:

rql.lock("my_lock", ttl: 5_000, timed: true) { sleep(4) }
# => OK

rql.lock("my_lock", ttl: 5_000, timed: true) { sleep(6) }
# => fails with RedisQueuedLocks::TimedLockTimeoutError

• infinite lock obtaining (no retry limit, no timeout limit):

rql.lock("my_lock", retry_count: nil, timeout: nil)

• try to obtain with a custom waiting timeout:

# First Ruby Process:
rql.lock("my_lock", ttl: 5_000) { sleep(4) } # acquire a long living lock

# Another Ruby Process:
rql.lock("my_lock", timeout: 2) # try to acquire but wait for a 2 seconds maximum
# =>
{ ok: false, result: :timeout_reached }

• obtain a lock and immediatly continue working (the lock will live in the background in Redis with the passed ttl)

rql.lock("my_lock", ttl: 6_500) # blocks execution until the lock is obtained
puts "Let's go" # will be called immediately after the lock is obtained

• add custom metadata to the lock (via :meta option):

rql.lock("my_lock", ttl: 123456, meta: { "some" => "data", key: 123.456 })

rql.lock_info("my_lock")
# =>
{
  "lock_key" => "rql:lock:my_lock",
  "acq_id" => "rql:acq:123/456/567/678/374dd74324",
  "hst_id" => "rql:acq:123/456/678/374dd74324",
  "ts" => 123456789,
  "ini_ttl" => 123456,
  "rem_ttl" => 123440,
  "some" => "data",
  "key" => "123.456" # NOTE: returned as a raw string directly from Redis
}

• (:queue_ttl) setting a short limit of time to the lock request queue position (if a process fails to acquire the lock within this period of time (and before timeout/retry_count limits occurs of course) - it's lock request will be moved to the end of queue):

rql.lock("my_lock", queue_ttl: 5, timeout: 10_000, retry_count: nil)
# "queue_ttl: 5": 5 seconds time slot before the lock request moves to the end of queue;
# "timeout" and "retry_count" is used as "endless lock try attempts" example to show the lock queue behavior;

# lock queue: =>
[
 "rql:acq:123/456/567/676/374dd74324",
 "rql:acq:123/456/567/677/374dd74322", # <- long living lock
 "rql:acq:123/456/567/679/374dd74321",
 "rql:acq:123/456/567/683/374dd74322", # <== we are here
 "rql:acq:123/456/567/685/374dd74329", # some other waiting process
]

# ... some period of time (2 seconds later)
# lock queue: =>
[
 "rql:acq:123/456/567/677/374dd74322", # <- long living lock
 "rql:acq:123/456/567/679/374dd74321",
 "rql:acq:123/456/567/683/374dd74322", # <== we are here
 "rql:acq:123/456/567/685/374dd74329", # some other waiting process
]

# ... some period of time (3 seconds later)
# ... queue_ttl time limit is reached
# lock queue: =>
[
 "rql:acq:123/456/567/685/374dd74329", # some other waiting process
 "rql:acq:123/456/567/683/374dd74322", # <== we are here (moved to the end of the queue)
]

• obtain a lock in :random way (with :random strategy): in :random strategy any acquirer from the lcok queue can obtain the lock regardless of the position in the lock queue;

# Current Process (process#1)
rql.lock('my_lock', ttl: 2_000, access_strategy: :random)
# => holds the lock

# Another Process (process#2)
rql.lock('my_lock', retry_delay: 7000, ttl: 4000, access_strategy: :random)
# => the lock is not free, stay in a queue and retry...

# Another Process (process#3)
rql.lock('my_lock', retry_delay: 3000, ttl: 3000, access_strategy: :random)
# => the lock is not free, stay in a queue and retry...

# lock queue:
[
 "rql:acq:123/456/567/677/374dd74322", # process#1 (holds the lock)
 "rql:acq:123/456/567/679/374dd74321", # process#2 (waiting for the lock, in retry)
 "rql:acq:123/456/567/683/374dd74322", # process#3 (waiting for the lock, in retry)
]

# ... some period of time
# -> process#1 => released the lock;
# -> process#2 => delayed retry, waiting;
# -> process#3 => preparing for retry (the delay is over);
# lock queue:
[
 "rql:acq:123/456/567/679/374dd74321", # process#2 (waiting for the lock, DELAYED)
 "rql:acq:123/456/567/683/374dd74322", # process#3 (trying to obtain the lock, RETRYING now)
]

# ... some period of time
# -> process#2 => didn't have time to obtain the lock, delayed retry;
# -> process#3 => holds the lock;
# lock queue:
[
 "rql:acq:123/456/567/679/374dd74321", # process#2 (waiting for the lock, DELAYED)
 "rql:acq:123/456/567/683/374dd74322", # process#3 (holds the lock)
]

# `process#3` is the last in queue, but has acquired the lock because his lock request "randomly" came first;

---

#lock! - exceptional lock obtaining

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• #lock! - exceptional lock obtaining;
• fails when (and with):
  • (RedisQueuedLocks::LockAlreadyObtainedError) when fail_fast is true and lock is already obtained;
  • (RedisQueuedLocks::LockAcquiermentTimeoutError) timeout limit reached before lock is obtained;
  • (RedisQueuedLocks::LockAcquiermentRetryLimitError) retry_count limit reached before lock is obtained;
  • (RedisQueuedLocks::ConflictLockObtainError) when conflict_strategy: :dead_locking is used and the "same-process-dead-lock" is happened (see Deadlocks and Reentrant locks for details);

def lock!(
  lock_name,
  ttl: config[:default_lock_ttl],
  queue_ttl: config[:default_queue_ttl],
  timeout: config[:try_to_lock_timeout],
  timed: config[:is_timed_by_default],
  retry_count: config[:retry_count],
  retry_delay: config[:retry_delay],
  retry_jitter: config[:retry_jitter],
  fail_fast: false,
  identity: uniq_identity,
  meta: nil,
  detailed_acq_timeout_error: config[:detailed_acq_timeout_error]
  logger: config[:logger],
  log_lock_try: config[:log_lock_try],
  instrument: nil,
  instrumenter: config[:instrumenter],
  access_strategy: config[:default_access_strategy],
  conflict_strategy: config[:default_conflict_strategy],
  log_sampling_enabled: config[:log_sampling_enabled],
  log_sampling_percent: config[:log_sampling_percent],
  log_sampler: config[:log_sampler],
  log_sample_this: false,
  instr_sampling_enabled: config[:instr_sampling_enabled],
  instr_sampling_percent: config[:instr_sampling_percent],
  instr_sampler: config[:instr_sampler],
  instr_sample_this: false,
  &block
)

See #lock method documentation.

---

#lock_info

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• get the lock information;
• returns nil if lock does not exist;
• lock data (Hash<String,String|Integer>):
  • "lock_key" - string - lock key in redis;
  • "acq_id" - string - acquier identifier (process_id/thread_id/fiber_id/ractor_id/identity);
  • "hst_id" - string - host identifier (process_id/thread_id/ractor_id/identity);
  • "ts" - numeric/epoch - the time when lock was obtained;
  • "init_ttl" - integer - (milliseconds) initial lock key ttl;
  • "rem_ttl" - integer - (milliseconds) remaining lock key ttl;
  • <custom metadata>- string/integer - custom metadata passed to the lock/lock! methods via meta: keyword argument (see lock method documentation);
  • additional keys for reentrant locks and extendable reentrant locks:
    • for any type of reentrant locks:
      • "spc_cnt" - integer - how many times the lock was obtained as reentrant lock;
    • for non-extendable reentrant locks:
      • "l_spc_ts" - numeric/epoch - timestamp of the last non-extendable reentrant lock obtaining;
    • for extendalbe reentrant locks:
      • "spc_ext_ttl" - integer - (milliseconds) sum of TTL of the each extendable reentrant lock (the total TTL extension time);
      • "l_spc_ext_ini_ttl" - integer - (milliseconds) TTL of the last reentrant lock;
      • "l_spc_ext_ts" - numeric/epoch - timestamp of the last extendable reentrant lock obtaining;

# <without custom metadata>
rql.lock_info("your_lock_name")

# =>
{
  "lock_key" => "rql:lock:your_lock_name",
  "acq_id" => "rql:acq:123/456/567/678/374dd74324",
  "hst_id" => "rql:acq:123/456/678/374dd74324",
  "ts" => 123456789.12345,
  "ini_ttl" => 5_000,
  "rem_ttl" => 4_999
}

# <with custom metadata>
rql.lock("your_lock_name", meta: { "kek" => "pek", "bum" => 123 })
rql.lock_info("your_lock_name")

# =>
{
  "lock_key" => "rql:lock:your_lock_name",
  "acq_id" => "rql:acq:123/456/567/678/374dd74324",
  "hst_id" => "rql:acq:123/456/678/374dd74324",
  "ts" => 123456789.12345,
  "ini_ttl" => 5_000,
  "rem_ttl" => 4_999,
  "kek" => "pek",
  "bum" => "123" # NOTE: returned as a raw string directly from Redis
}

# <for reentrant locks>
# (see `conflict_strategy:` kwarg attribute of #lock/#lock! methods and `config.default_conflict_strategy` config)

rql.lock("your_lock_name", ttl: 5_000)
rql.lock("your_lock_name", ttl: 3_000)
rql.lock("your_lock_name", ttl: 2_000)
rql.lock_info("your_lock_name")

# =>
{
  "lock_key" => "rql:lock:your_lock_name",
  "acq_id" => "rql:acq:123/456/567/678/374dd74324",
  "hst_id" => "rql:acq:123/456/678/374dd74324",
  "ts" => 123456789.12345,
  "ini_ttl" => 5_000,
  "rem_ttl" => 9_444,
  # ==> keys for any type of reentrant lock:
  "spc_count" => 2, # how many times the lock was obtained as reentrant lock
  # ==> keys for extendable reentarnt locks with `:extendable_work_through` strategy:
  "spc_ext_ttl" => 5_000, # sum of TTL of the each <extendable> reentrant lock (3_000 + 2_000)
  "l_spc_ext_ini_ttl" => 2_000, # TTL of the last <extendable> reentrant lock
  "l_spc_ext_ts" =>  123456792.12345, # timestamp of the last <extendable> reentrant lock obtaining
  # ==> keys for non-extendable locks with `:work_through` strategy:
  "l_spc_ts" => 123456.789 # timestamp of the last <non-extendable> reentrant lock obtaining
}

---

#queue_info

^{[back to top]}

Returns an information about the required lock queue by the lock name. The result represnts the ordered lock request queue that is ordered by score (Redis Sets) and shows lock acquirers and their position in queue. Async nature with redis communcation can lead the situation when the queue becomes empty during the queue data extraction. So sometimes you can receive the lock queue info with empty queue value (an empty array).

• get the lock queue information;
• queue represents the ordered set of lock key reqests:
  • set is ordered by score in ASC manner (inside the Redis Set);
  • score is represented as a timestamp when the lock request was made;
  • represents the acquier identifier and their score as an array of hashes;
• returns nil if lock queue does not exist;
• lock queue data (Hash<String,String|Array<Hash<String|Numeric>>):
  • "lock_queue" - string - lock queue key in redis;
  • "queue" - array - an array of lock requests (array of hashes):
    • "acq_id" - string - acquier identifier (process_id/thread_id/fiber_id/ractor_id/identity by default);
    • "score" - float/epoch - time when the lock request was made (epoch);

rql.queue_info("your_lock_name")

# =>
{
  "lock_queue" => "rql:lock_queue:your_lock_name",
  "queue" => [
    { "acq_id" => "rql:acq:123/456/567/678/fa76df9cc2", "score" => 1711606640.540842},
    { "acq_id" => "rql:acq:123/567/456/679/c7bfcaf4f9", "score" => 1711606640.540906},
    { "acq_id" => "rql:acq:555/329/523/127/7329553b11", "score" => 1711606640.540963},
    # ...etc
  ]
}

---

#locked?

^{[back to top]}

• is the lock obtaied or not?

rql.locked?("your_lock_name") # => true/false

---

#queued?

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• is the lock queued for obtain / has requests for obtain?

rql.queued?("your_lock_name") # => true/false

---

#unlock - release a lock

^{[back to top]}

• release the concrete lock with lock request queue;
• queue will be relased first;
• has an alias: #release_lock;
• accepts:
  • lock_name - (required) [String] - the lock name that should be released.
  • :logger - (optional) [::Logger,#debug]
    • custom logger object;
    • pre-configured in config[:logger];
  • :instrumenter - (optional) [#notify]
    • custom instrumenter object;
    • pre-configured in config[:instrumetner];
  • :instrument - (optional) [NilClass,Any];
    • custom instrumentation data wich will be passed to the instrumenter's payload with :instrument key;
    • nil by default (no additional data);
  • :log_sampling_enabled - (optional) [Boolean]
    • enables log sampling;
    • pre-configured in config[:log_sampling_enabled];
  • :log_sampling_percent - (optional) [Integer]
    • log sampling:the percent of cases that should be logged;
    • pre-configured in config[:log_sampling_percent];
  • :log_sampler - (optional) [#sampling_happened?,Module<RedisQueuedLocks::Logging::Sampler>]
    • log sampling: percent-based log sampler that decides should be RQL case logged or not;
    • pre-configured in config[:log_sampler];
  • log_sample_this - (optional) [Boolean]
    • marks the method that everything should be logged despite the enabled log sampling;
    • makes sense when log sampling is enabled;
    • false by default;
  • :instr_sampling_enabled - (optional) [Boolean]
    • enables instrumentaion sampling;
    • pre-configured in config[:instr_sampling_enabled];
  • instr_sampling_percent - (optional) [Integer]
    • the percent of cases that should be instrumented;
    • pre-configured in config[:instr_sampling_percent];
  • instr_sampler - (optional) [#sampling_happened?,Module<RedisQueuedLocks::Instrument::Sampler>]
    • percent-based log sampler that decides should be RQL case instrumented or not;
    • pre-configured in config[:instr_sampler];
  • instr_sample_this - (optional) [Boolean]
    • marks the method that everything should be instrumneted despite the enabled instrumentation sampling;
    • makes sense when instrumentation sampling is enabled;
    • false by default;
• if you try to unlock non-existent lock you will receive ok: true result with operation timings and :nothing_to_release result factor inside;

Return:

• [Hash<Symbol,Boolean|Hash<Symbol,Numeric|String|Symbol>>] ({ ok: true/false, result: Hasn });
• :result format;
  • :rel_time - Float - time spent to process redis commands (in seconds);
  • :rel_key - String - released lock key (RedisQueudLocks-internal lock key name from Redis);
  • :rel_queue - String - released lock queue key (RedisQueuedLocks-internal queue key name from Redis);
  • :queue_res - Symbol - :released (or :nothing_to_release if the required queue does not exist);
  • :lock_res - Symbol - :released (or :nothing_to_release if the required lock does not exist);

Consider that lock_res and queue_res can have different value because of the async nature of invoked Redis'es commands.

rql.unlock("your_lock_name")

# =>
{
  ok: true,
  result: {
    rel_time: 0.02, # time spent to lock release (in seconds)
    rel_key: "rql:lock:your_lock_name", # released lock key
    rel_queue: "rql:lock_queue:your_lock_name", # released lock key queue
    queue_res: :released, # or :nothing_to_release
    lock_res: :released # or :nothing_to_release
  }
}

---

#clear_locks - release all locks and lock queues

^{[back to top]}

• release all obtained locks and related lock request queues;
• queues will be released first;
• has an alias: #release_locks;
• accepts:
  • :batch_size - (optional) [Integer]
    • the size of batch of locks and lock queus that should be cleared under the one pipelined redis command at once;
    • pre-configured in config[:lock_release_batch_size];
  • :logger - (optional) [::Logger,#debug]
    • custom logger object;
    • pre-configured value in config[:logger];
  • :instrumenter - (optional) [#notify]
    • custom instrumenter object;
    • pre-configured value in config[:isntrumenter];
  • :instrument - (optional) [NilClass,Any]
    • custom instrumentation data wich will be passed to the instrumenter's payload with :instrument key;
  • :log_sampling_enabled - (optional) [Boolean]
    • enables log sampling;
    • pre-configured in config[:log_sampling_enabled];
  • :log_sampling_percent - (optional) [Integer]
    • log sampling:the percent of cases that should be logged;
    • pre-configured in config[:log_sampling_percent];
  • :log_sampler - (optional) [#sampling_happened?,Module<RedisQueuedLocks::Logging::Sampler>]
    • log sampling: percent-based log sampler that decides should be RQL case logged or not;
    • pre-configured in config[:log_sampler];
  • log_sample_this - (optional) [Boolean]
    • marks the method that everything should be logged despite the enabled log sampling;
    • makes sense when log sampling is enabled;
    • false by default;
  • :instr_sampling_enabled - (optional) [Boolean]
    • enables instrumentaion sampling;
    • pre-configured in config[:instr_sampling_enabled];
  • instr_sampling_percent - (optional) [Integer]
    • the percent of cases that should be instrumented;
    • pre-configured in config[:instr_sampling_percent];
  • instr_sampler - (optional) [#sampling_happened?,Module<RedisQueuedLocks::Instrument::Sampler>]
    • percent-based log sampler that decides should be RQL case instrumented or not;
    • pre-configured in config[:instr_sampler];
  • instr_sample_this - (optional) [Boolean]
    • marks the method that everything should be instrumneted despite the enabled instrumentation sampling;
    • makes sense when instrumentation sampling is enabled;
    • false by default;
• returns:
  • [Hash<Symbol,Numeric>] - Format: { ok: true, result: Hash<Symbol,Numeric> };
  • result data:
    • :rel_time - Numeric - time spent to release all locks and related queus;
    • :rel_key_cnt - Integer - the number of released Redis keys (queues+locks);

rql.clear_locks

# =>
{
  ok: true,
  result: {
    rel_time: 3.07,
    rel_key_cnt: 1234
  }
}

---

#extend_lock_ttl

^{[back to top]}

• extends lock ttl by the required number of milliseconds;
• expects the lock name and the number of milliseconds;
• accepts:
  • lock_name - (required) [String]
    • the lock name which ttl should be extended;
  • milliseconds - (required) [Integer]
    • how many milliseconds should be added to the lock's TTL;
  • :instrumenter - (optional) [#notify]
    • custom instrumenter object;
    • pre-configured in config[:instrumetner];
  • :instrument - (optional) [NilClass,Any];
    • custom instrumentation data wich will be passed to the instrumenter's payload with :instrument key;
    • nil by default (no additional data);
  • :logger - (optional) [::Logger,#debug]
    • custom logger object;
    • pre-configured in config[:logger];
  • :log_sampling_enabled - (optional) [Boolean]
    • enables log sampling;
    • pre-configured in config[:log_sampling_enabled];
  • :log_sampling_percent - (optional) [Integer]
    • log sampling:the percent of cases that should be logged;
    • pre-configured in config[:log_sampling_percent];
  • :log_sampler - (optional) [#sampling_happened?,Module<RedisQueuedLocks::Logging::Sampler>]
    • log sampling: percent-based log sampler that decides should be RQL case logged or not;
    • pre-configured in config[:log_sampler];
  • log_sample_this - (optional) [Boolean]
    • marks the method that everything should be logged despite the enabled log sampling;
    • makes sense when log sampling is enabled;
    • false by default;
  • :instr_sampling_enabled - (optional) [Boolean]
    • enables instrumentaion sampling;
    • pre-configured in config[:instr_sampling_enabled];
  • instr_sampling_percent - (optional) [Integer]
    • the percent of cases that should be instrumented;
    • pre-configured in config[:instr_sampling_percent];
  • instr_sampler - (optional) [#sampling_happened?,Module<RedisQueuedLocks::Instrument::Sampler>]
    • percent-based log sampler that decides should be RQL case instrumented or not;
    • pre-configured in config[:instr_sampler];
  • instr_sample_this - (optional) [Boolean]
    • marks the method that everything should be instrumneted despite the enabled instrumentation sampling;
    • makes sense when instrumentation sampling is enabled;
    • false by default;
• returns { ok: true, result: :ttl_extended } when ttl is extended;
• returns { ok: false, result: :async_expire_or_no_lock } when a lock not found or a lock is already expired during some steps of invocation (see Important section below);
• Important:
  • the method is non-atomic cuz redis does not provide an atomic function for TTL/PTTL extension;
  • the method consists of two commands:
    • (1) read current pttl;
    • (2) set new ttl that is calculated as "current pttl + additional milliseconds";
  • the method uses Redis'es CAS (check-and-set) behavior;
  • what can happen during these steps:
    • lock is expired between commands or before the first command;
    • lock is expired before the second command;
    • lock is expired AND newly acquired by another process (so you will extend the totally new lock with fresh PTTL);
  • use it at your own risk and consider the async nature when calling this method;

rql.extend_lock_ttl("my_lock", 5_000) # NOTE: add 5_000 milliseconds

# => `ok` case
{ ok: true, result: :ttl_extended }

# => `failed` case
{ ok: false, result: :async_expire_or_no_lock }

---

#locks - get list of obtained locks

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• get list of obtained locks;
• uses redis SCAN under the hood;
• accepts:
  • :scan_size - Integer - (config[:key_extraction_batch_size] by default);
  • :with_info - Boolean - false by default (for details see #locks_info);
• returns:
  • Set<String> (for with_info: false);
  • Set<Hash<Symbol,Any>> (for with_info: true). See #locks_info for details;

rql.locks # or rql.locks(scan_size: 123)

=>
#<Set:
 {"rql:lock:locklock75",
  "rql:lock:locklock9",
  "rql:lock:locklock108",
  "rql:lock:locklock7",
  "rql:lock:locklock48",
  "rql:lock:locklock104",
  "rql:lock:locklock13",
  "rql:lock:locklock62",
  "rql:lock:locklock80",
  "rql:lock:locklock28",
  ...}>

---

#queues - get list of lock request queues

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• get list of lock request queues;
• uses redis SCAN under the hood;
• accepts
  • :scan_size - Integer - (config[:key_extraction_batch_size] by default);
  • :with_info - Boolean - false by default (for details see #queues_info);
• returns:
  • Set<String> (for with_info: false);
  • Set<Hash<Symbol,Any>> (for with_info: true). See #locks_info for details;

rql.queues # or rql.queues(scan_size: 123)

=>
#<Set:
 {"rql:lock_queue:locklock75",
  "rql:lock_queue:locklock9",
  "rql:lock_queue:locklock108",
  "rql:lock_queue:locklock7",
  "rql:lock_queue:locklock48",
  "rql:lock_queue:locklock104",
  "rql:lock_queue:locklock13",
  "rql:lock_queue:locklock62",
  "rql:lock_queue:locklock80",
  "rql:lock_queue:locklock28",
  ...}>

---

#keys - get list of taken locks and queues

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• get list of taken locks and queues;
• uses redis SCAN under the hood;
• accepts: :scan_size - Integer - (config[:key_extraction_batch_size] by default);
• returns: Set<String>

rql.keys # or rql.keys(scan_size: 123)

=>
#<Set:
 {"rql:lock_queue:locklock75",
  "rql:lock_queue:locklock9",
  "rql:lock:locklock9",
  "rql:lock_queue:locklock108",
  "rql:lock_queue:locklock7",
  "rql:lock:locklock7",
  "rql:lock_queue:locklock48",
  "rql:lock_queue:locklock104",
  "rql:lock:locklock104",
  "rql:lock_queue:locklock13",
  "rql:lock_queue:locklock62",
  "rql:lock_queue:locklock80",
  "rql:lock:locklock80",
  "rql:lock_queue:locklock28",
  ...}>

---

#locks_info - get list of locks with their info

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• get list of locks with their info;
• uses redis SCAN under the hod;
• accepts scan_size:/Integer option (config[:key_extraction_batch_size] by default);
• returns Set<Hash<Symbol,Any>> (see #lock_info and examples below for details).
  • contained data: { lock: String, status: Symbol, info: Hash<String,Any> };
  • :lock - String - lock key in Redis;
  • :status - Symbol- :released or :alive
    • the lock may become relased durign the lock info extraction process;
    • :info for :released keys is empty ({});
  • :info - Hash<String,Any>
    • lock data stored in the lock key in Redis;
    • See #lock_info for details;

rql.locks_info # or rql.locks_info(scan_size: 123)

# =>
=> #<Set:
 {{:lock=>"rql:lock:some-lock-123",
   :status=>:alive,
   :info=>{
    "acq_id"=>"rql:acq:41478/4320/4340/4360/848818f09d8c3420",
    "hst_id"=>"rql:hst:41478/4320/4360/848818f09d8c3420"
    "ts"=>1711607112.670343,
    "ini_ttl"=>15000,
    "rem_ttl"=>13998}},
  {:lock=>"rql:lock:some-lock-456",
   :status=>:released,
   :info=>{},
  ...}>

---

#queues_info - get list of queues with their info

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• get list of queues with their info;
• uses redis SCAN under the hod;
• accepts scan_size:/Integer option (config[:key_extraction_batch_size] by default);
• returns Set<Hash<Symbol,Any>> (see #queue_info and examples below for details).
  • contained data: { queue: String, requests: Array<Hash<String,Any>> }
  • :queue - String - lock key queue in Redis;
  • :requests - Array<Hash<String,Any>> - lock requests in the que with their acquier id and score.

rql.queues_info # or rql.qeuues_info(scan_size: 123)

=> #<Set:
 {{:queue=>"rql:lock_queue:some-lock-123",
   :requests=>
    [{"acq_id"=>"rql:acq:38529/4500/4520/4360/66093702f24a3129", "score"=>1711606640.540842},
     {"acq_id"=>"rql:acq:38529/4580/4600/4360/66093702f24a3129", "score"=>1711606640.540906},
     {"acq_id"=>"rql:acq:38529/4620/4640/4360/66093702f24a3129", "score"=>1711606640.5409632}]},
  {:queue=>"rql:lock_queue:some-lock-456",
   :requests=>
    [{"acq_id"=>"rql:acq:38529/4380/4400/4360/66093702f24a3129", "score"=>1711606640.540722},
     {"acq_id"=>"rql:acq:38529/4420/4440/4360/66093702f24a3129", "score"=>1711606640.5407748},
     {"acq_id"=>"rql:acq:38529/4460/4480/4360/66093702f24a3129", "score"=>1711606640.540808}]},
  ...}>

---

#clear_dead_requests

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In some cases your lock requests may become "dead". It means that your lock request lives in lock queue in Redis without any processing. It can happen when your processs that are enqueeud to the lock queue is failed unexpectedly (for some reason) before the lock acquire moment occurs and when no any other process does not need this lock anymore. For this case your lock reuquest will be cleared only when any process will try to acquire this lock again (cuz lock acquirement triggers the removement of expired requests).

In order to help with these dead requests you may periodically call #clear_dead_requests with corresponding :dead_ttl option, that is pre-configured by default via config[:dead_request_ttl].

:dead_ttl option is required because of it is no any fast and resource-free way to understand which request is dead now and is it really dead cuz each request queue can host their requests with a custom queue ttl for each request differently.

Accepts:

• :dead_ttl - (optional) [Integer]
  • lock request ttl after which a lock request is considered dead;
  • has a preconfigured value in config[:dead_request_ttl] (1 day by default);
• :sacn_size - (optional) [Integer]
  • the batch of scanned keys for Redis'es SCAN command;
  • has a preconfigured valie in config[:lock_release_batch_size];
• :logger - (optional) [::Logger,#debug]
  • custom logger object;
  • pre-configured in config[:logger];
• :instrumenter - (optional) [#notify]
  • custom instrumenter object;
  • pre-configured in config[:isntrumenter];
• :instrument - (optional) [NilClass,Any]
  • custom instrumentation data wich will be passed to the instrumenter's payload with :instrument key;
  • nil by default (no additional data);
• :log_sampling_enabled - (optional) [Boolean]
  • enables log sampling;
  • pre-configured in config[:log_sampling_enabled];
• :log_sampling_percent - (optional) [Integer]
  • log sampling:the percent of cases that should be logged;
  • pre-configured in config[:log_sampling_percent];
• :log_sampler - (optional) [#sampling_happened?,Module<RedisQueuedLocks::Logging::Sampler>]
  • log sampling: percent-based log sampler that decides should be RQL case logged or not;
  • pre-configured in config[:log_sampler];
• log_sample_this - (optional) [Boolean]
  • marks the method that everything should be logged despite the enabled log sampling;
  • makes sense when log sampling is enabled;
  • false by default;
• :instr_sampling_enabled - (optional) [Boolean]
  • enables instrumentaion sampling;
  • pre-configured in config[:instr_sampling_enabled];
• instr_sampling_percent - (optional) [Integer]
  • the percent of cases that should be instrumented;
  • pre-configured in config[:instr_sampling_percent];
• instr_sampler - (optional) [#sampling_happened?,Module<RedisQueuedLocks::Instrument::Sampler>]
  • percent-based log sampler that decides should be RQL case instrumented or not;
  • pre-configured in config[:instr_sampler];
• instr_sample_this - (optional) [Boolean]
  • marks the method that everything should be instrumneted despite the enabled instrumentation sampling;
  • makes sense when instrumentation sampling is enabled;
  • false by default;

Returns: { ok: true, processed_queues: Set<String> } returns the list of processed lock queues;

rql.clear_dead_requests(dead_ttl: 60 * 60 * 1000) # 1 hour in milliseconds

# =>
{
  ok: true,
  processed_queues: [
    "rql:lock_queue:some-lock-123",
    "rql:lock_queue:some-lock-456",
    "rql:lock_queue:your-other-lock",
    ...
  ]
}

---

#current_acquirer_id

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• get the current acquirer identifier in RQL notation that you can use for debugging purposes during the lock analyzation;
• acquirer identifier format:

    "rql:acq:#{process_id}/#{thread_id}/#{fiber_id}/#{ractor_id}/#{identity}"

• because of the moment that #lock/#lock! gives you a possibility to customize process_id, fiber_id, thread_id, ractor_id and unique identity identifiers the #current_acquirer_id method provides this possibility too;

Accepts:

• process_id: - (optional) [Integer,Any]
  • ::Process.pid by default;
• thread_id: - (optional) [Integer,Any];
  • ::Thread.current.object_id by default;
• fiber_id: - (optional) [Integer,Any];
  • ::Fiber.current.object_id by default;
• ractor_id: - (optional) [Integer,Any];
  • ::Ractor.current.object_id by default;
• identity: - (optional) [String,Any];
  • this value is calculated once during RedisQueuedLock::Client instantiation and stored in @uniq_identity;
  • this value can be accessed from RedisQueuedLock::Client#uniq_identity;
  • Configuration documentation: see config[:uniq_identifier];
  • #lock method documentation: see uniq_identifier;

rql.current_acquirer_id

# =>
"rql:acq:38529/4500/4520/4360/66093702f24a3129"

---

#current_host_id

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• get a current host identifier in RQL notation that you can use for debugging purposes during the lock analyzis;
• the host is a ruby worker (a combination of process/thread/ractor/identity) that is alive and can obtain locks;
• the host is limited to process/thread/ractor (without fiber) combination cuz we have no abilities to extract all fiber objects from the current ruby process when at least one ractor object is defined (ObjectSpace loses abilities to extract Fiber and Thread objects after the any ractor is created) (Thread objects are analyzed via Thread.list API which does not lose their abilites);
• host identifier format:

    "rql:hst:#{process_id}/#{thread_id}/#{ractor_id}/#{uniq_identity}"

• because of the moment that #lock/#lock! gives you a possibility to customize process_id, fiber_id, thread_id, ractor_id and unique identity identifiers the #current_host_id method provides this possibility too (except the fiber_id correspondingly);

Accepts:

• process_id: - (optional) [Integer,Any]
  • ::Process.pid by default;
• thread_id: - (optional) [Integer,Any];
  • ::Thread.current.object_id by default;
• ractor_id: - (optional) [Integer,Any];
  • ::Ractor.current.object_id by default;
• identity: - (optional) [String];
  • this value is calculated once during RedisQueuedLock::Client instantiation and stored in @uniq_identity;
  • this value can be accessed from RedisQueuedLock::Client#uniq_identity;
  • Configuration documentation: see config[:uniq_identifier];
  • #lock method documentation: see uniq_identifier;

rql.current_host_id

# =>
"rql:acq:38529/4500/4360/66093702f24a3129"

---

#possible_host_ids

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• return the list (Array<String>) of possible host identifiers that can be reached from the current ractor;
• the host is a ruby worker (a combination of process/thread/ractor/identity) that is alive and can obtain locks;
• the host is limited to process/thread/ractor (without fiber) combination cuz we have no abilities to extract all fiber objects from the current ruby process when at least one ractor object is defined (ObjectSpace loses abilities to extract Fiber and Thread objects after the any ractor is created) (Thread objects are analyzed via Thread.list API which does not lose their abilites);
• host identifier format:

    "rql:hst:#{process_id}/#{thread_id}/#{ractor_id}/#{uniq_identity}"

Accepts:

• identity - (optional) [String];
  • this value is calculated once during RedisQueuedLock::Client instantiation and stored in @uniq_identity;
  • this value can be accessed from RedisQueuedLock::Client#uniq_identity;
  • Configuration documentation: see config[:uniq_identifier];
  • #lock method documentation: see uniq_identifier;

rql.possible_host_ids

# =>
[
  "rql:hst:18814/2300/2280/5ce0c4582fc59c06", # process id / thread id / ractor id / uniq identity
  "rql:hst:18814/2320/2280/5ce0c4582fc59c06", # ...
  "rql:hst:18814/2340/2280/5ce0c4582fc59c06", # ...
  "rql:hst:18814/2360/2280/5ce0c4582fc59c06", # ...
  "rql:hst:18814/2380/2280/5ce0c4582fc59c06", # ...
  "rql:hst:18814/2400/2280/5ce0c4582fc59c06"
]

---

Swarm Mode and Zombie Locks

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Eliminate zombie locks with a swarm.

This documentation section is in progress! (see the changelog and the usage preview for details at this moment)

(work and usage preview (temporary example-based docs))

• How to Swarm
  • configuration
  • swarm_status
  • swarm_info
  • swarmize!
  • deswarmize!
  • probe_hosts
  • flush_zobmies
• zombies_info
• zombie_locks
• zombie_hosts
• zombie_acquiers

---

Work and Usage Preview (temporary example-based docs)

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configuration

redis_client = RedisClient.config.new_pool # NOTE: provide your own RedisClient instance

clinet = RedisQueuedLocks::Client.new(redis_client) do |config|
  # NOTE: auto-swarm your RQL client after initalization (run swarm elements and their supervisor)
  config.swarm.auto_swarm = false

  # supervisor configs
  config.swarm.supervisor.liveness_probing_period = 2 # NOTE: in seconds

  # (probe_hosts) host probing configuration
  config.swarm.probe_hosts.enabled_for_swarm = true # NOTE: run host-probing from or not
  config.swarm.probe_hosts.probe_period = 2 # NOTE: (in seconds) the period of time when the probing process is triggered
  # (probe_hosts) individual redis config
  config.swarm.probe_hosts.redis_config.sentinel = false # NOTE: individual redis config
  config.swarm.probe_hosts.redis_config.pooled = false # NOTE: individual redis config
  config.swarm.probe_hosts.redis_config.config = {} # NOTE: individual redis config
  config.swarm.probe_hosts.redis_config.pool_config = {} # NOTE: individual redis config

  # (flush_zombies) zombie flushing configuration
  config.swarm.flush_zombies.enabled_for_swarm = true # NOTE: run zombie flushing or not
  config.swarm.flush_zombies.zombie_flush_period = 10 # NOTE: (in seconds) period of time when the zombie flusher is triggered
  config.swarm.flush_zombies.zombie_ttl = 15_000 # NOTE: (in milliseconds) when the lock/host/acquier is considered a zombie
  config.swarm.flush_zombies.zombie_lock_scan_size = 500 # NOTE: scan sizec during zombie flushing
  config.swarm.flush_zombies.zombie_queue_scan_size = 500 # NOTE: scan sizec during zombie flushing
  # (flush_zombies) individual redis config
  config.swarm.flush_zombies.redis_config.sentinel = false # NOTE: individual redis config
  config.swarm.flush_zombies.redis_config.pooled = false # NOTE: individual redis config
  config.swarm.flush_zombies.redis_config.config = {} # NOTE: individual redis config
  config.swarm.flush_zombies.redis_config.pool_config = {} # NOTE: individual redis config
end

seed a zombie

• obtain some long living lock and kill the host process which will lead the lock becoming a zombie:

daiver => ~/Projects/redis_queued_locks  master [$]
➜ bin/console
[1] pry(main)> rql = RedisQueuedLocks::Client.new(RedisClient.new);
[2] pry(main)> rql.swarmize!
/Users/daiver/Projects/redis_queued_locks/lib/redis_queued_locks/swarm/flush_zombies.rb:107: warning: Ractor is experimental, and the behavior may change in future versions of Ruby! Also there are many implementation issues.
=> {:ok=>true, :result=>:swarming}
[3] pry(main)> rql.lock('kekpek', ttl: 1111111111)
=> {:ok=>true,
 :result=>
  {:lock_key=>"rql:lock:kekpek",
   :acq_id=>"rql:acq:17580/2260/2380/2280/3f16b93973612580",
   :hst_id=>"rql:hst:17580/2260/2280/3f16b93973612580",
   :ts=>1720305351.069259,
   :ttl=>1111111111,
   :process=>:lock_obtaining}}
[4] pry(main)> exit

find zombies

• start another process, fetch the swarm info, see that our last process is a zombie now and their hosted lock is a zombie too:

daiver => ~/Projects/redis_queued_locks  master [$] took 27.2s
➜ bin/console
[1] pry(main)> rql = RedisQueuedLocks::Client.new(RedisClient.new);
[2] pry(main)> rql.swarm_info
=> {"rql:hst:17580/2260/2280/3f16b93973612580"=>{:zombie=>true, :last_probe_time=>2024-07-07 01:35:53 12897/262144 +0300, :last_probe_score=>1720305353.0491982},
 "rql:hst:17580/2300/2280/3f16b93973612580"=>{:zombie=>true, :last_probe_time=>2024-07-07 01:35:53 211107/4194304 +0300, :last_probe_score=>1720305353.0503318},
 "rql:hst:17580/2320/2280/3f16b93973612580"=>{:zombie=>true, :last_probe_time=>2024-07-07 01:35:53 106615/2097152 +0300, :last_probe_score=>1720305353.050838},
 "rql:hst:17580/2260/2340/3f16b93973612580"=>{:zombie=>true, :last_probe_time=>2024-07-07 01:35:53 26239/524288 +0300, :last_probe_score=>1720305353.050047},
 "rql:hst:17580/2300/2340/3f16b93973612580"=>{:zombie=>true, :last_probe_time=>2024-07-07 01:35:53 106359/2097152 +0300, :last_probe_score=>1720305353.050716},
 "rql:hst:17580/2320/2340/3f16b93973612580"=>{:zombie=>true, :last_probe_time=>2024-07-07 01:35:53 213633/4194304 +0300, :last_probe_score=>1720305353.050934},
 "rql:hst:17580/2360/2280/3f16b93973612580"=>{:zombie=>true, :last_probe_time=>2024-07-07 01:35:53 214077/4194304 +0300, :last_probe_score=>1720305353.05104},
 "rql:hst:17580/2360/2340/3f16b93973612580"=>{:zombie=>true, :last_probe_time=>2024-07-07 01:35:53 214505/4194304 +0300, :last_probe_score=>1720305353.051142},
 "rql:hst:17580/2400/2280/3f16b93973612580"=>{:zombie=>true, :last_probe_time=>2024-07-07 01:35:53 53729/1048576 +0300, :last_probe_score=>1720305353.05124},
 "rql:hst:17580/2400/2340/3f16b93973612580"=>{:zombie=>true, :last_probe_time=>2024-07-07 01:35:53 3365/65536 +0300, :last_probe_score=>1720305353.0513458}}
[3] pry(main)> rql.swarm_status
=> {:auto_swarm=>false,
 :supervisor=>{:running=>false, :state=>"non_initialized", :observable=>"non_initialized"},
 :probe_hosts=>{:enabled=>true, :thread=>{:running=>false, :state=>"non_initialized"}, :main_loop=>{:running=>false, :state=>"non_initialized"}},
 :flush_zombies=>{:enabled=>true, :ractor=>{:running=>false, :state=>"non_initialized"}, :main_loop=>{:running=>false, :state=>"non_initialized"}}}
[4] pry(main)> rql.zombies_info
=> {:zombie_hosts=>
  #<Set:
   {"rql:hst:17580/2260/2280/3f16b93973612580",
    "rql:hst:17580/2300/2280/3f16b93973612580",
    "rql:hst:17580/2320/2280/3f16b93973612580",
    "rql:hst:17580/2260/2340/3f16b93973612580",
    "rql:hst:17580/2300/2340/3f16b93973612580",
    "rql:hst:17580/2320/2340/3f16b93973612580",
    "rql:hst:17580/2360/2280/3f16b93973612580",
    "rql:hst:17580/2360/2340/3f16b93973612580",
    "rql:hst:17580/2400/2280/3f16b93973612580",
    "rql:hst:17580/2400/2340/3f16b93973612580"}>,
 :zombie_acquirers=>#<Set: {"rql:acq:17580/2260/2380/2280/3f16b93973612580"}>,
 :zombie_locks=>#<Set: {"rql:lock:kekpek"}>}
[5] pry(main)> rql.zombie_locks
=> #<Set: {"rql:lock:kekpek"}>
[6] pry(main)> rql.zombie_acquiers
=> #<Set: {"rql:acq:17580/2260/2380/2280/3f16b93973612580"}>
[7] pry(main)> rql.zombie_hosts
=> #<Set:
 {"rql:hst:17580/2260/2280/3f16b93973612580",
  "rql:hst:17580/2300/2280/3f16b93973612580",
  "rql:hst:17580/2320/2280/3f16b93973612580",
  "rql:hst:17580/2260/2340/3f16b93973612580",
  "rql:hst:17580/2300/2340/3f16b93973612580",
  "rql:hst:17580/2320/2340/3f16b93973612580",
  "rql:hst:17580/2360/2280/3f16b93973612580",
  "rql:hst:17580/2360/2340/3f16b93973612580",
  "rql:hst:17580/2400/2280/3f16b93973612580",
  "rql:hst:17580/2400/2340/3f16b93973612580"}>

kill zombies in a background

• swarmize the new current ruby process that should run the flush zombies element that will drop zombie locks, zombie hosts and their lock requests in a background:

[8] pry(main)> rql.swarmize!
/Users/daiver/Projects/redis_queued_locks/lib/redis_queued_locks/swarm/flush_zombies.rb:107: warning: Ractor is experimental, and the behavior may change in future versions of Ruby! Also there are many implementation issues.
=> {:ok=>true, :result=>:swarming}
[9] pry(main)> rql.swarm_info
=> {"rql:hst:17752/2260/2280/89beef198021f16d"=>{:zombie=>false, :last_probe_time=>2024-07-07 01:36:39 4012577/4194304 +0300, :last_probe_score=>1720305399.956673},
 "rql:hst:17752/2300/2280/89beef198021f16d"=>{:zombie=>false, :last_probe_time=>2024-07-07 01:36:39 4015233/4194304 +0300, :last_probe_score=>1720305399.9573061},
 "rql:hst:17752/2320/2280/89beef198021f16d"=>{:zombie=>false, :last_probe_time=>2024-07-07 01:36:39 4016755/4194304 +0300, :last_probe_score=>1720305399.957669},
 "rql:hst:17752/2260/2340/89beef198021f16d"=>{:zombie=>false, :last_probe_time=>2024-07-07 01:36:39 1003611/1048576 +0300, :last_probe_score=>1720305399.957118},
 "rql:hst:17752/2300/2340/89beef198021f16d"=>{:zombie=>false, :last_probe_time=>2024-07-07 01:36:39 2008027/2097152 +0300, :last_probe_score=>1720305399.957502},
 "rql:hst:17752/2320/2340/89beef198021f16d"=>{:zombie=>false, :last_probe_time=>2024-07-07 01:36:39 2008715/2097152 +0300, :last_probe_score=>1720305399.95783},
 "rql:hst:17752/2360/2280/89beef198021f16d"=>{:zombie=>false, :last_probe_time=>2024-07-07 01:36:39 4018063/4194304 +0300, :last_probe_score=>1720305399.9579809},
 "rql:hst:17752/2360/2340/89beef198021f16d"=>{:zombie=>false, :last_probe_time=>2024-07-07 01:36:39 1004673/1048576 +0300, :last_probe_score=>1720305399.9581308}}
[10] pry(main)> rql.swarm_status
=> {:auto_swarm=>false,
 :supervisor=>{:running=>true, :state=>"sleep", :observable=>"initialized"},
 :probe_hosts=>{:enabled=>true, :thread=>{:running=>true, :state=>"sleep"}, :main_loop=>{:running=>true, :state=>"sleep"}},
 :flush_zombies=>{:enabled=>true, :ractor=>{:running=>true, :state=>"running"}, :main_loop=>{:running=>true, :state=>"sleep"}}}
[11] pry(main)> rql.zombies_info
=> {:zombie_hosts=>#<Set: {}>, :zombie_acquirers=>#<Set: {}>, :zombie_locks=>#<Set: {}>}
[12] pry(main)> rql.zombie_acquiers
=> #<Set: {}>
[13] pry(main)> rql.zombie_hosts
=> #<Set: {}>
[14] pry(main)>

swarm hosts key in Redis

"rql:swarm:hsts"

---

Lock Access Strategies

^{[back to top]}

• this documentation section is in progress;
• (little details for a context of the current implementation and feautres):
  • defines the way in which the lock should be obitained;
  • by default it is configured to obtain a lock in classic queued way: you should wait your position in queue in order to obtain a lock;
  • can be customized in methods #lock and #lock! via :access_strategy attribute (see method signatures of #lock and #lock! methods);
  • supports different strategies:
    • :queued (FIFO): the classic queued behavior (default), your lock will be obitaned if you are first in queue and the required lock is free;
    • :random (RANDOM): obtain a lock without checking the positions in the queue (but with checking the limist, retries, timeouts and so on). if lock is free to obtain - it will be obtained;
  • for current implementation detalis check:
    • Configuration documentation: see config.default_access_strategy config docs;
    • #lock method documentation: see access_strategy attribute docs;

---

Deadlocks and Reentrant locks

^{[back to top]}

• this documentation section is in progress;
• (little details for a context of the current implementation and feautres):
  • at this moment we support only reentrant locks: they works via customizable conflict strategy behavior (:wait_for_lock (default), :work_through, :extendable_work_through, :dead_locking);
  • by default behavior (:wait_for_lock) your lock obtaining process will work in a classic way (limits, retries, etc);
  • :work_through, :extendable_work_through works with limits too (timeouts, delays, etc), but the decision of "is your lock are obtained or not" is made as you work with reentrant locks (your process continues to use the lock without/with lock's TTL extension accordingly);
  • for current implementation details check:
    • Configuration documentation: see config.default_conflict_strategy config docs;
    • #lock method documentation: see conflict_strategy attribute docs and the method result data;

---

Logging

^{[back to top]}

• Logging Configuration

• default logs (raised from #lock/#lock!):

"[redis_queued_locks.start_lock_obtaining]" # (logs "lock_key", "queue_ttl", "acq_id", "hst_id", "acs_strat");
"[redis_queued_locks.start_try_to_lock_cycle]" # (logs "lock_key", "queue_ttl", "acq_id", "hst_id", "acs_strat");
"[redis_queued_locks.dead_score_reached__reset_acquier_position]" # (logs "lock_key", "queue_ttl", "acq_id", "hst_id", "acs_strat");
"[redis_queued_locks.lock_obtained]" # (logs "lock_key", "queue_ttl", "acq_id", "hst_id", "acq_time");
"[redis_queued_locks.extendable_reentrant_lock_obtained]" # (logs "lock_key", "queue_ttl", "acq_id", "hst_id", "acs_strat", "acq_time");
"[redis_queued_locks.reentrant_lock_obtained]" # (logs "lock_key", "queue_ttl", "acq_id", "hst_id", "acs_strat", "acq_time");
"[redis_queued_locks.fail_fast_or_limits_reached_or_deadlock__dequeue]" # (logs "lock_key", "queue_ttl", "acq_id", "hst_id", "acs_strat");
"[redis_queued_locks.expire_lock]" # (logs "lock_key", "queue_ttl", "acq_id", "hst_id", "acs_strat");
"[redis_queued_locks.decrease_lock]" # (logs "lock_key", "decreased_ttl", "queue_ttl", "acq_id", "hst_id", "acs_strat");

• additional logs (raised from #lock/#lock! with confg[:log_lock_try] == true):

"[redis_queued_locks.try_lock.start]" # (logs "lock_key", "queue_ttl", "acq_id", "hst_id", "acs_strat");
"[redis_queued_locks.try_lock.rconn_fetched]" # (logs "lock_key", "queue_ttl", "acq_id", "hst_id", "acs_strat");
"[redis_queued_locks.try_lock.same_process_conflict_detected]" # (logs "lock_key", "queue_ttl", "acq_id", "hst_id", "acs_strat");
"[redis_queued_locks.try_lock.same_process_conflict_analyzed]" # (logs "lock_key", "queue_ttl", "acq_id", "hst_id", "acs_strat", "spc_status");
"[redis_queued_locks.try_lock.reentrant_lock__extend_and_work_through]" # (logs "lock_key", "queue_ttl", "acq_id", "hst_id", "acs_strat", "spc_status", "last_ext_ttl", "last_ext_ts");
"[redis_queued_locks.try_lock.reentrant_lock__work_through]" # (logs "lock_key", "queue_ttl", "acq_id", "hst_id", "acs_strat", "spc_status", last_spc_ts);
"[redis_queued_locks.try_lock.single_process_lock_conflict__dead_lock]" # (logs "lock_key", "queue_ttl", "acq_id", "hst_id", "acs_strat", "spc_status", "last_spc_ts");
"[redis_queued_locks.try_lock.acq_added_to_queue]" # (logs "lock_key", "queue_ttl", "acq_id", "hst_id", "acs_strat");
"[redis_queued_locks.try_lock.remove_expired_acqs]" # (logs "lock_key", "queue_ttl", "acq_id", "hst_id", "acs_strat");
"[redis_queued_locks.try_lock.get_first_from_queue]" # (logs "lock_key", "queue_ttl", "acq_id", "hst_id", "acs_strat", "first_acq_id_in_queue");
"[redis_queued_locks.try_lock.exit__queue_ttl_reached]" # (logs "lock_key", "queue_ttl", "acq_id", "hst_id", "acs_strat");
"[redis_queued_locks.try_lock.exit__no_first]" # (logs "lock_key", "queue_ttl", "acq_id", "hst_id", "acs_strat", "first_acq_id_in_queue", "<current_lock_data>");
"[redis_queued_locks.try_lock.exit__lock_still_obtained]" # (logs "lock_key", "queue_ttl", "acq_id", "hst_id", "acs_strat", "first_acq_id_in_queue", "locked_by_acq_id", "<current_lock_data>");
"[redis_queued_locks.try_lock.obtain__free_to_acquire]" # (logs "lock_key", "queue_ttl", "acq_id", "hst_id", "acs_strat");

---

Logging Configuration

^{[back to top]}

NOTICE: logging can be sampled via:

• config.log_samplign_enabled = true (false by default);
• config.log_sampler = RedisQueuedLocks::Logging::Sampler (used by default);
• see RedisQueuedLocks::Logging::Sampler implementation in source code for customization details;

# (default: RedisQueuedLocks::Logging::VoidLogger)
# - the logger object;
# - should implement `debug(progname = nil, &block)` (minimal requirement) or be an instance of Ruby's `::Logger` class/subclass;
# - supports `SemanticLogger::Logger` (see "semantic_logger" gem)
# - at this moment the only debug logs are realised in following cases:
#   - "[redis_queued_locks.start_lock_obtaining]" (logs "lock_key", "queue_ttl", "acq_id", "hst_id", "acs_strat");
#   - "[redis_queued_locks.start_try_to_lock_cycle]" (logs "lock_key", "queue_ttl", "acq_id", "hst_id", "acs_strat");
#   - "[redis_queued_locks.dead_score_reached__reset_acquier_position]" (logs "lock_key", "queue_ttl", "acq_id", "hst_id", "acs_strat");
#   - "[redis_queued_locks.lock_obtained]" (logs "lock_key", "queue_ttl", "acq_id", "hst_id", "acq_time", "acs_strat");
#   - "[redis_queued_locks.extendable_reentrant_lock_obtained]" (logs "lock_key", "queue_ttl", "acq_id", "hst_id", "acq_time", "acs_strat");
#   - "[redis_queued_locks.reentrant_lock_obtained]" (logs "lock_key", "queue_ttl", "acq_id", "hst_id", "acq_time", "acs_strat");
#   - "[redis_queued_locks.fail_fast_or_limits_reached_or_deadlock__dequeue]" (logs "lock_key", "queue_ttl", "acq_id", "hst_id", "acs_strat");
#   - "[redis_queued_locks.expire_lock]" (logs "lock_key", "queue_ttl", "acq_id", "hst_id", "acs_strat");
#   - "[redis_queued_locks.decrease_lock]" (logs "lock_key", "decreased_ttl", "queue_ttl", "acq_id", "hst_id", "acs_strat");
# - by default uses VoidLogger that does nothing;
config.logger = RedisQueuedLocks::Logging::VoidLogger

# (default: false)
# - adds additional debug logs;
# - enables additional logs for each internal try-retry lock acquiring (a lot of logs can be generated depending on your retry configurations);
# - it adds following debug logs in addition to the existing:
#   - "[redis_queued_locks.try_lock.start]" (logs "lock_key", "queue_ttl", "acq_id", "hst_id", "acs_strat");
#   - "[redis_queued_locks.try_lock.rconn_fetched]" (logs "lock_key", "queue_ttl", "acq_id", "hst_id", "acs_strat");
#   - "[redis_queued_locks.try_lock.same_process_conflict_detected]" (logs "lock_key", "queue_ttl", "acq_id", "hst_id", "acs_strat");
#   - "[redis_queued_locks.try_lock.same_process_conflict_analyzed]" (logs "lock_key", "queue_ttl", "acq_id", "hst_id", "acs_strat", "spc_status");
#   - "[redis_queued_locks.try_lock.reentrant_lock__extend_and_work_through]" (logs "lock_key", "queue_ttl", "acq_id", "hst_id", "acs_strat", "spc_status", "last_ext_ttl", "last_ext_ts");
#   - "[redis_queued_locks.try_lock.reentrant_lock__work_through]" (logs "lock_key", "queue_ttl", "acq_id", "hst_id", "acs_strat", "spc_status", last_spc_ts);
#   - "[redis_queued_locks.try_lock.acq_added_to_queue]" (logs "lock_key", "queue_ttl", "acq_id", "hst_id", "acs_strat")";
#   - "[redis_queued_locks.try_lock.remove_expired_acqs]" (logs "lock_key", "queue_ttl", "acq_id", "hst_id", "acs_strat");
#   - "[redis_queued_locks.try_lock.get_first_from_queue]" (logs "lock_key", "queue_ttl", "acq_id", "hst_id", "acs_strat", "first_acq_id_in_queue");
#   - "[redis_queued_locks.try_lock.exit__queue_ttl_reached]" (logs "lock_key", "queue_ttl", "acq_id", "hst_id", "acs_strat");
#   - "[redis_queued_locks.try_lock.exit__no_first]" (logs "lock_key", "queue_ttl", "acq_id", "hst_id", "acs_strat", "first_acq_id_in_queue", "<current_lock_data>");
#   - "[redis_queued_locks.try_lock.exit__lock_still_obtained]" (logs "lock_key", "queue_ttl", "acq_id", "hst_id", "acs_strat", "first_acq_id_in_queue", "locked_by_acq_id", "<current_lock_data>");
#   - "[redis_queued_locks.try_lock.obtain__free_to_acquire]" (logs "lock_key", "queue_ttl", "acq_id", "hst_id", "acs_strat");
config.log_lock_try = false

# (default: false)
# - enables <log sampling>: only the configured percent of RQL cases will be logged;
# - disabled by default;
# - works in tandem with <config.log_sampling_percent> and <log.sampler> configs;
config.log_sampling_enabled = false

# (default: 15)
# - the percent of cases that should be logged;
# - take an effect when <config.log_sampling_enalbed> is true;
# - works in tandem with <config.log_sampling_enabled> and <config.log_sampler> configs;
config.log_sampling_percent = 15

# (default: RedisQueuedLocks::Logging::Sampler)
# - percent-based log sampler that decides should be RQL case logged or not;
# - works in tandem with <config.log_sampling_enabled> and <config.log_sampling_percent> configs;
# - based on the ultra simple percent-based (weight-based) algorithm that uses SecureRandom.rand
#   method so the algorithm error is ~(0%..13%);
# - you can provide your own log sampler with bettter algorithm that should realize
#   `sampling_happened?(percent) => boolean` interface (see `RedisQueuedLocks::Logging::Sampler` for example);
config.log_sampler = RedisQueuedLocks::Logging::Sampler

---

Instrumentation

^{[back to top]}

• Instrumentation Events
• Instrumentation Configuration

An instrumentation layer is incapsulated in instrumenter object stored in config (RedisQueuedLocks::Client#config[:instrumenter]).

Instrumentation can be sampled. See Instrumentation Configuration section for details.

Instrumenter object should provide notify(event, payload) method with the following signarue:

• event - string;
• payload - hash<Symbol,Any>;

redis_queued_locks provides two instrumenters:

• RedisQueuedLocks::Instrument::ActiveSupport - ActiveSupport::Notifications instrumenter that instrument events via ActiveSupport::Notifications API;
• RedisQueuedLocks::Instrument::VoidNotifier - instrumenter that does nothing;

By default RedisQueuedLocks::Client is configured with the void notifier (which means "instrumentation is disabled").

---

Instrumentation Configuration

^{[back to top]}

NOTICE: instrumentation can be sampled via:

• config.instr_sampling_enabled = true (false by default);
• config.instr_sampler = RedisQueuedLocks::Instrument::Sampler (used by default);
• see RedisQueuedLocks::Instrument::Sampler implementation in source code for customization details;

# (default: RedisQueuedLocks::Instrument::VoidNotifier)
# - instrumentation layer;
# - you can provide your own instrumenter that should realize `#notify(event, payload = {})` interface:
#   - event: <string> requried;
#   - payload: <hash> requried;
# - disabled by default via `VoidNotifier`;
config.instrumenter = RedisQueuedLocks::Instrument::ActiveSupport

# (default: false)
# - enables <instrumentaion sampling>: only the configured percent of RQL cases will be instrumented;
# - disabled by default;
# - works in tandem with <config.instr_sampling_percent and <log.instr_sampler>;
config.instr_sampling_enabled = false

# (default: 15)
# - the percent of cases that should be instrumented;
# - take an effect when <config.instr_sampling_enalbed> is true;
# - works in tandem with <config.instr_sampling_enabled> and <config.instr_sampler> configs;
config.instr_sampling_percent = 15

# (default: RedisQueuedLocks::Instrument::Sampler)
# - percent-based log sampler that decides should be RQL case instrumented or not;
# - works in tandem with <config.instr_sampling_enabled> and <config.instr_sampling_percent> configs;
# - based on the ultra simple percent-based (weight-based) algorithm that uses SecureRandom.rand
#   method so the algorithm error is ~(0%..13%);
# - you can provide your own log sampler with bettter algorithm that should realize
#   `sampling_happened?(percent) => boolean` interface (see `RedisQueuedLocks::Instrument::Sampler` for example);
config.instr_sampler = RedisQueuedLocks::Instrument::Sampler

---

Instrumentation Events

^{[back to top]}

List of instrumentation events

• redis_queued_locks.lock_obtained;
• redis_queued_locks.extendable_reentrant_lock_obtained;
• redis_queued_locks.reentrant_lock_obtained;
• redis_queued_locks.lock_hold_and_release;
• redis_queued_locks.reentrant_lock_hold_completes;
• redis_queued_locks.explicit_lock_release;
• redis_queued_locks.explicit_all_locks_release;

Detalized event semantics and payload structure:

• "redis_queued_locks.lock_obtained"

  • a moment when the lock was obtained;
  • raised from #lock/#lock!;
  • payload:
    • :ttl - integer/milliseconds - lock ttl;
    • :acq_id - string - lock acquier identifier;
    • :hst_id - string - lock's host identifier;
    • :lock_key - string - lock name;
    • :ts - numeric/epoch - the time when the lock was obtaiend;
    • :acq_time - float/milliseconds - time spent on lock acquiring;
    • :instrument - nil/Any - custom data passed to the #lock/#lock! method as :instrument attribute;

• "redis_queued_locks.extendable_reentrant_lock_obtained"

  • an event signalizes about the "extendable reentrant lock" obtaining is happened;
  • raised from #lock/#lock! when the lock was obtained as reentrant lock;
  • payload:
    • :lock_key - string - lock name;
    • :ttl - integer/milliseconds - last lock ttl by reentrant locking;
    • :acq_id - string - lock acquier identifier;
    • :hst_id - string - lock's host identifier;
    • :ts - numeric/epoch - the time when the lock was obtaiend as extendable reentrant lock;
    • :acq_time - float/milliseconds - time spent on lock acquiring;
    • :instrument - nil/Any - custom data passed to the #lock/#lock! method as :instrument attribute;

• "redis_queued_locks.reentrant_lock_obtained"

  • an event signalizes about the "reentrant lock" obtaining is happened (without TTL extension);
  • raised from #lock/#lock! when the lock was obtained as reentrant lock;
  • payload:
    • :lock_key - string - lock name;
    • :ttl - integer/milliseconds - last lock ttl by reentrant locking;
    • :acq_id - string - lock acquier identifier;
    • :hst_id - string - lock's host identifier;
    • :ts - numeric/epoch - the time when the lock was obtaiend as reentrant lock;
    • :acq_time - float/milliseconds - time spent on lock acquiring;
    • :instrument - nil/Any - custom data passed to the #lock/#lock! method as :instrument attribute;

• "redis_queued_locks.lock_hold_and_release"

  • an event signalizes about the "hold+and+release" process is finished;
  • raised from #lock/#lock! when invoked with a block of code;
  • payload:
    • :hold_time - float/milliseconds - lock hold time;
    • :ttl - integer/milliseconds - lock ttl;
    • :acq_id - string - lock acquier identifier;
    • :hst_id - string - lock's host identifier;
    • :lock_key - string - lock name;
    • :ts - numeric/epoch - the time when lock was obtained;
    • :acq_time - float/milliseconds - time spent on lock acquiring;
    • :instrument - nil/Any - custom data passed to the #lock/#lock! method as :instrument attribute;

• "redis_queued_locks.reentrant_lock_hold_completes"

  • an event signalizes about the "reentrant lock hold" is complete (both extendable and non-extendable);
  • lock re-entering can happen many times and this event happens for each of them separately;
  • raised from #lock/#lock! when the lock was obtained as reentrant lock;
  • payload:
    • :hold_time - float/milliseconds - lock hold time;
    • :ttl - integer/milliseconds - last lock ttl by reentrant locking;
    • :acq_id - string - lock acquier identifier;
    • :hst_id - string - lock's host identifier;
    • :ts - numeric/epoch - the time when the lock was obtaiend as reentrant lock;
    • :lock_key - string - lock name;
    • :acq_time - float/milliseconds - time spent on lock acquiring;
    • :instrument - nil/Any - custom data passed to the #lock/#lock! method as :instrument attribute;

• "redis_queued_locks.explicit_lock_release"

  • an event signalizes about the explicit lock release (invoked via RedisQueuedLock#unlock);
  • raised from #unlock;
  • payload:
    • :at - float/epoch - the time when the lock was released;
    • :rel_time - float/milliseconds - time spent on lock releasing;
    • :lock_key - string - released lock (lock name);
    • :lock_key_queue - string - released lock queue (lock queue name);

• "redis_queued_locks.explicit_all_locks_release"

  • an event signalizes about the explicit all locks release (invoked via RedisQueuedLock#clear_locks);
  • raised from #clear_locks;
  • payload:
    • :rel_time - float/milliseconds - time spent on "realese all locks" operation;
    • :at - float/epoch - the time when the operation has ended;
    • :rel_keys - integer - released redis keys count (released queue keys + released lock keys);

---

Roadmap

^{[back to top]}

• Major:
  • Swarm:
    • circuit-breaker for long-living failures of your infrastructure inside the swarm elements and supervisor: the supervisor will stop (for some period of time or while the some factor will return true) trying to ressurect unexpectedly terminated swarm elements, and will notify about this;
    • swarm logs (thread/ractor has some limitations so the initial implementation does not include swarm logging);
    • swarm instrumentation (thread/ractor has some limitations so the initial implementation does not include swarm instrumentation);
  • isolated timeouts which are independent of internal Ruby's timeout implementation (where all timeouts are hostend inside the global "timeout request" queue and managed by a single global "timeout wathcer" thread). it should prevent any logic and timeout intersections, some GVL-related things and problem situations when the global watcher thread is "dead";
  • lock request prioritization;
  • strict redlock algorithm support (support for many RedisClient instances that are fully independent (distributed redis instances));
  • #lock_series - acquire a series of locks:

    rql.lock_series('lock_a', 'lock_b', 'lock_c') { puts 'locked' }

  • light mode: an ability to work without any debug and instrumentation logic and data (totally reduced debugging and instrumenting possibilities, but better performance);
• Minor:
  • Support for detailed OpenTelemetry tracing;
  • support for Dragonfly database backend (https://github.com/dragonflydb/dragonfly) (https://www.dragonflydb.io/);
  • (research) GVL-isolation for lock acquirement logic (try to bypass Ruby's "context-switching" in order to prevent any time-based affects on lock-acquirement logic);
  • Semantic error objects for unexpected Redis errors;
  • Experimental feature: (non-timed locks): per-ruby-block-holding-the-lock sidecar Ractor and in progress queue in RedisDB that will extend the acquired lock for long-running blocks of code (that invoked "under" the lock whose ttl may expire before the block execution completes). It makes sense for non-timed locks only;
  • sized lock queues (with an ability of dynamically growing size);
  • better code stylization (+ some refactorings);
  • RedisQueuedLocks::Acquier::Try.try_to_lock - detailed successful result analization;
  • Support for LIFO strategy;
  • better specs with 100% test coverage (total specs rework);
  • statistics with UI;
  • JSON log formatter;
  • RBS type signatures;
  • automatic deadlock detection;
  • go-lang implementation;
  • (research) simplification and speedup of the internal "redis-communuication-and-data-storing"-based algorithms;

---

Contributing

^{[back to top]}

• Fork it ( https://github.com/0exp/redis_queued_locks )
• Create your feature branch (git checkout -b feature/my-new-feature)
• Commit your changes (git commit -am '[feature_context] Add some feature')
• Push to the branch (git push origin feature/my-new-feature)
• Create new Pull Request

License

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Released under MIT License.

Authors

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Rustam Ibragimov