Use a concurrent timer task to expire semaphores and unblock executions

This task is managed by the scheduler and uses its same polling interval to
run.

app/models/solid_queue/blocked_execution.rb

@@ -4,7 +4,7 @@ class BlockedExecution < SolidQueue::Execution
 
     has_one :semaphore, foreign_key: :concurrency_key, primary_key: :concurrency_key
 
-    scope :releasable, -> { left_outer_joins(:execution_semaphore).merge(Semaphore.available.or(Semaphore.where(id: nil))) }
+    scope :releasable, -> { left_outer_joins(:semaphore).merge(Semaphore.available.or(Semaphore.where(id: nil))) }
     scope :ordered, -> { order(priority: :asc) }
 
     class << self

app/models/solid_queue/semaphore.rb

@@ -1,6 +1,7 @@
 class SolidQueue::Semaphore < SolidQueue::Record
   scope :available, -> { where("value > 0") }
   scope :locked, -> { where(value: 0) }
+  scope :expired, -> { where(expires_at: ...Time.current)}
 
   class << self
     def wait_for(concurrency_key, limit, duration)

lib/solid_queue/process_registration.rb

@@ -9,7 +9,7 @@ module ProcessRegistration
       define_callbacks :start, :run, :shutdown
 
       set_callback :start, :before, :register
-      set_callback :start, :before, :start_heartbeat
+      set_callback :start, :before, :launch_heartbeat
 
       set_callback :run, :after, -> { stop unless registered? }
 
@@ -43,7 +43,7 @@ def registered?
         process.persisted?
       end
 
-      def start_heartbeat
+      def launch_heartbeat
         @heartbeat_task = Concurrent::TimerTask.new(execution_interval: SolidQueue.process_heartbeat_interval) { heartbeat }
         @heartbeat_task.execute
       end

lib/solid_queue/scheduler.rb

@@ -1,34 +1,55 @@
 # frozen_string_literal: true
 
-class SolidQueue::Scheduler
-  include SolidQueue::Runner
+module SolidQueue
+  class Scheduler
+    include Runner
 
-  attr_accessor :batch_size, :polling_interval
+    attr_accessor :batch_size, :polling_interval
 
-  def initialize(**options)
-    options = options.dup.with_defaults(SolidQueue::Configuration::SCHEDULER_DEFAULTS)
+    set_callback :start, :before, :launch_concurrency_maintenance
 
-    @batch_size = options[:batch_size]
-    @polling_interval = options[:polling_interval]
-  end
+    def initialize(**options)
+      options = options.dup.with_defaults(SolidQueue::Configuration::SCHEDULER_DEFAULTS)
+
+      @batch_size = options[:batch_size]
+      @polling_interval = options[:polling_interval]
+    end
 
-  private
-    def run
-      with_polling_volume do
-        batch = SolidQueue::ScheduledExecution.next_batch(batch_size)
+    private
+      def run
+        with_polling_volume do
+          batch = SolidQueue::ScheduledExecution.next_batch(batch_size).tap(&:load)
 
-        if batch.size > 0
-          procline "preparing #{batch.size} jobs for execution"
+          if batch.size > 0
+            procline "preparing #{batch.size} jobs for execution"
 
-          SolidQueue::ScheduledExecution.prepare_batch(batch)
-        else
-          procline "waiting"
-          interruptible_sleep(polling_interval)
+            SolidQueue::ScheduledExecution.prepare_batch(batch)
+          else
+            procline "waiting"
+            interruptible_sleep(polling_interval)
+          end
         end
       end
-    end
 
-    def metadata
-      super.merge(batch_size: batch_size, polling_interval: polling_interval)
-    end
+      def launch_concurrency_maintenance
+        @concurrency_maintenance_task = Concurrent::TimerTask.new(run_now: true, execution_interval: polling_interval) do
+          expire_semaphores
+          unblock_blocked_executions
+        end
+
+        @concurrency_maintenance_task.execute
+      end
+
+      def expire_semaphores
+        Semaphore.expired.in_batches(of: batch_size, &:delete_all)
+      end
+
+      def unblock_blocked_executions
+        BlockedExecution.unblock(batch_size)
+      end
+
+      def metadata
+        super.merge(batch_size: batch_size, polling_interval: polling_interval)
+      end
+  end
 end

test/integration/concurrency_controls_test.rb

@@ -10,7 +10,9 @@ class ConcurrencyControlsTest < ActiveSupport::TestCase
     @result = JobResult.create!(queue_name: "default", status: "seq: ")
 
     default_worker = { queues: "default", polling_interval: 1, processes: 3, threads: 2 }
-    @pid = run_supervisor_as_fork(load_configuration_from: { workers: [ default_worker ] })
+    scheduler = { polling_interval: 1, batch_size: 200 }
+
+    @pid = run_supervisor_as_fork(mode: :all, load_configuration_from: { workers: [ default_worker ], scheduler: scheduler })
 
     wait_for_registered_processes(4, timeout: 0.2.second) # 3 workers working the default queue + supervisor
   end
@@ -80,9 +82,7 @@ class ConcurrencyControlsTest < ActiveSupport::TestCase
     assert_stored_sequence @result, [ "B", "D", "F" ] + ("G".."K").to_a
   end
 
-  test "rely on worker to unblock blocked executions with an available semaphore" do
-    skip "Moving this task to the supervisor"
-
+  test "rely on scheduler to unblock blocked executions with an available semaphore" do
     # Simulate a scenario where we got an available semaphore and some stuck jobs
     job = SequentialUpdateResultJob.perform_later(@result, name: "A")
 
@@ -115,9 +115,7 @@ class ConcurrencyControlsTest < ActiveSupport::TestCase
     assert_stored_sequence @result, ("A".."K").to_a, [ "A", "C", "B" ] + ("D".."K").to_a
   end
 
-  test "rely on worker to unblock blocked executions with a missing semaphore" do
-    skip "Moving this task to the supervisor"
-
+  test "rely on scheduler to unblock blocked executions with an expired semaphore" do
     # Simulate a scenario where we got an available semaphore and some stuck jobs
     job = SequentialUpdateResultJob.perform_later(@result, name: "A")
     wait_for_jobs_to_finish_for(2.seconds)
@@ -135,10 +133,10 @@ class ConcurrencyControlsTest < ActiveSupport::TestCase
       end
     end
 
-    # Then delete the semaphore, as if we had cleared it
-    SolidQueue::Semaphore.find_by(concurrency_key: job.concurrency_key).destroy!
+    # Simulate semaphore expiration
+    SolidQueue::Semaphore.find_by(concurrency_key: job.concurrency_key).update(expires_at: 1.hour.ago)
 
-    # And wait for workers to release the jobs
+    # And wait for scheduler to release the jobs
     wait_for_jobs_to_finish_for(2.seconds)
     assert_no_pending_jobs