From 8902488fed90f7c2251720ed5b9334ca7ff47bab Mon Sep 17 00:00:00 2001 From: Mahmut Bulut Date: Sun, 27 Oct 2019 03:07:01 +0100 Subject: [PATCH] Stack representation --- bastion-executor/Cargo.toml | 4 + bastion-executor/src/distributor.rs | 14 +- bastion-executor/src/lib.rs | 4 + bastion-executor/src/load_balancer.rs | 27 + bastion-executor/src/placement.rs | 46 +- bastion-executor/src/pool.rs | 32 +- bastion-executor/src/run_queue.rs | 2161 +++++++++++++++++++++++++ bastion-executor/src/sleepers.rs | 52 + bastion-executor/src/worker.rs | 88 + 9 files changed, 2397 insertions(+), 31 deletions(-) create mode 100644 bastion-executor/src/load_balancer.rs create mode 100644 bastion-executor/src/run_queue.rs create mode 100644 bastion-executor/src/sleepers.rs create mode 100644 bastion-executor/src/worker.rs diff --git a/bastion-executor/Cargo.toml b/bastion-executor/Cargo.toml index 44da19f5..3474159e 100644 --- a/bastion-executor/Cargo.toml +++ b/bastion-executor/Cargo.toml @@ -9,6 +9,10 @@ edition = "2018" [dependencies] +crossbeam-utils = "0.6" +crossbeam-epoch = "0.7" lazy_static = "1.4" libc = "0.2" num_cpus = "1.10" + +lightproc = { "path" = "../lightproc" } diff --git a/bastion-executor/src/distributor.rs b/bastion-executor/src/distributor.rs index 8c556983..d7f0282b 100644 --- a/bastion-executor/src/distributor.rs +++ b/bastion-executor/src/distributor.rs @@ -1,6 +1,8 @@ -use crate::placement; -use crate::placement::CoreId; +use super::placement; +use super::placement::CoreId; use std::thread; +use super::run_queue::{Worker, Stealer}; +use lightproc::prelude::*; pub(crate) struct Distributor { pub round: usize, @@ -17,13 +19,17 @@ impl Distributor { } } - pub fn assign

(mut self, thunk: P) + pub fn assign

(mut self, thunk: P) -> Vec> where P: Fn() + Send + Sync + Copy + 'static, { + let mut stealers = Vec::>::new(); for core in self.cores { self.round = core.id; + let worker = Worker::new_fifo(); + stealers.push(worker.stealer()); + thread::Builder::new() .name("bastion-async-thread".to_string()) .spawn(move || { @@ -35,5 +41,7 @@ impl Distributor { }) .expect("cannot start the thread for running proc"); } + + stealers } } diff --git a/bastion-executor/src/lib.rs b/bastion-executor/src/lib.rs index 8cf4b57b..d4af3a66 100644 --- a/bastion-executor/src/lib.rs +++ b/bastion-executor/src/lib.rs @@ -3,3 +3,7 @@ pub mod distributor; pub mod placement; pub mod pool; pub mod thread_recovery; +pub mod load_balancer; +pub mod run_queue; +pub mod sleepers; +pub mod worker; diff --git a/bastion-executor/src/load_balancer.rs b/bastion-executor/src/load_balancer.rs new file mode 100644 index 00000000..5f648727 --- /dev/null +++ b/bastion-executor/src/load_balancer.rs @@ -0,0 +1,27 @@ +use lazy_static::*; +use std::thread; + +pub struct LoadBalancer(); + +impl LoadBalancer { + pub fn trigger() { + unimplemented!() + } +} + +#[inline] +pub(crate) fn launch() -> &'static LoadBalancer { + lazy_static! { + static ref LOAD_BALANCER: LoadBalancer = { + thread::Builder::new() + .name("load-balancer-thread".to_string()) + .spawn(|| { + + }) + .expect("load-balancer couldn't start"); + + LoadBalancer() + }; + } + &*LOAD_BALANCER +} diff --git a/bastion-executor/src/placement.rs b/bastion-executor/src/placement.rs index fa866625..48a5ac31 100644 --- a/bastion-executor/src/placement.rs +++ b/bastion-executor/src/placement.rs @@ -288,30 +288,30 @@ mod macos { use super::CoreId; - type kern_return_t = c_int; - type integer_t = c_int; - type natural_t = c_uint; - type thread_t = c_uint; - type thread_policy_flavor_t = natural_t; - type mach_msg_type_number_t = natural_t; + type KernReturnT = c_int; + type IntegerT = c_int; + type NaturalT = c_uint; + type ThreadT = c_uint; + type ThreadPolicyFlavorT = NaturalT; + type MachMsgTypeNumberT = NaturalT; #[repr(C)] - struct thread_affinity_policy_data_t { - affinity_tag: integer_t, + struct ThreadAffinityPolicyDataT { + affinity_tag: IntegerT, } - type thread_policy_t = *mut thread_affinity_policy_data_t; + type ThreadPolicyT = *mut ThreadAffinityPolicyDataT; - const THREAD_AFFINITY_POLICY: thread_policy_flavor_t = 4; + const THREAD_AFFINITY_POLICY: ThreadPolicyFlavorT = 4; #[link(name = "System", kind = "framework")] extern "C" { fn thread_policy_set( - thread: thread_t, - flavor: thread_policy_flavor_t, - policy_info: thread_policy_t, - count: mach_msg_type_number_t, - ) -> kern_return_t; + thread: ThreadT, + flavor: ThreadPolicyFlavorT, + policy_info: ThreadPolicyT, + count: MachMsgTypeNumberT, + ) -> KernReturnT; } pub fn get_core_ids() -> Option> { @@ -324,20 +324,20 @@ mod macos { } pub fn set_for_current(core_id: CoreId) { - let THREAD_AFFINITY_POLICY_COUNT: mach_msg_type_number_t = - mem::size_of::() as mach_msg_type_number_t - / mem::size_of::() as mach_msg_type_number_t; + let thread_affinity_policy_count: MachMsgTypeNumberT = + mem::size_of::() as MachMsgTypeNumberT + / mem::size_of::() as MachMsgTypeNumberT; - let mut info = thread_affinity_policy_data_t { - affinity_tag: core_id.id as integer_t, + let mut info = ThreadAffinityPolicyDataT { + affinity_tag: core_id.id as IntegerT, }; unsafe { thread_policy_set( - pthread_self() as thread_t, + pthread_self() as ThreadT, THREAD_AFFINITY_POLICY, - &mut info as thread_policy_t, - THREAD_AFFINITY_POLICY_COUNT, + &mut info as ThreadPolicyT, + thread_affinity_policy_count, ); } } diff --git a/bastion-executor/src/pool.rs b/bastion-executor/src/pool.rs index 0d3f69ff..1a86aff5 100644 --- a/bastion-executor/src/pool.rs +++ b/bastion-executor/src/pool.rs @@ -1,19 +1,41 @@ -use crate::distributor::Distributor; +use super::distributor::Distributor; +use super::run_queue::{Worker, Injector, Stealer}; use lazy_static::*; +use lightproc::prelude::*; +use super::sleepers::Sleepers; -pub struct Pool {} +pub struct Pool { + pub injector: Injector, + pub stealers: Vec>, + pub sleepers: Sleepers, +} + +impl Pool { + /// Error recovery for the fallen threads + pub fn recover_async_thread() { + unimplemented!() + } + + pub fn fetch_proc(&self, local: &Worker) -> Option { + // Pop only from the local queue with full trust + local.pop() + } +} #[inline] pub fn get() -> &'static Pool { lazy_static! { static ref POOL: Pool = { let distributor = Distributor::new(); - - distributor.assign(|| { + let stealers = distributor.assign(|| { println!("1,2,3"); }); - Pool {} + Pool { + injector: Injector::new(), + stealers, + sleepers: Sleepers::new(), + } }; } &*POOL diff --git a/bastion-executor/src/run_queue.rs b/bastion-executor/src/run_queue.rs new file mode 100644 index 00000000..613b3846 --- /dev/null +++ b/bastion-executor/src/run_queue.rs @@ -0,0 +1,2161 @@ +//! Concurrent work-stealing deques. +//! +//! These data structures are most commonly used in work-stealing schedulers. The typical setup +//! involves a number of threads, each having its own FIFO or LIFO queue (*worker*). There is also +//! one global FIFO queue (*injector*) and a list of references to *worker* queues that are able to +//! steal tasks (*stealers*). +//! +//! We spawn a new task onto the scheduler by pushing it into the *injector* queue. Each worker +//! thread waits in a loop until it finds the next task to run and then runs it. To find a task, it +//! first looks into its local *worker* queue, and then into the *injector* and *stealers*. +//! +//! # Queues +//! +//! [`Injector`] is a FIFO queue, where tasks are pushed and stolen from opposite ends. It is +//! shared among threads and is usually the entry point for new tasks. +//! +//! [`Worker`] has two constructors: +//! +//! * [`new_fifo()`] - Creates a FIFO queue, in which tasks are pushed and popped from opposite +//! ends. +//! * [`new_lifo()`] - Creates a LIFO queue, in which tasks are pushed and popped from the same +//! end. +//! +//! Each [`Worker`] is owned by a single thread and supports only push and pop operations. +//! +//! Method [`stealer()`] creates a [`Stealer`] that may be shared among threads and can only steal +//! tasks from its [`Worker`]. Tasks are stolen from the end opposite to where they get pushed. +//! +//! # Stealing +//! +//! Steal operations come in three flavors: +//! +//! 1. [`steal()`] - Steals one task. +//! 2. [`steal_batch()`] - Steals a batch of tasks and moves them into another worker. +//! 3. [`steal_batch_and_pop()`] - Steals a batch of tasks, moves them into another queue, and pops +//! one task from that worker. +//! +//! In contrast to push and pop operations, stealing can spuriously fail with [`Steal::Retry`], in +//! which case the steal operation needs to be retried. +//! +//! # Examples +//! +//! Suppose a thread in a work-stealing scheduler is idle and looking for the next task to run. To +//! find an available task, it might do the following: +//! +//! 1. Try popping one task from the local worker queue. +//! 2. Try stealing a batch of tasks from the global injector queue. +//! 3. Try stealing one task from another thread using the stealer list. +//! +//! An implementation of this work-stealing strategy: +//! +//! ``` +//! use crossbeam_deque::{Injector, Steal, Stealer, Worker}; +//! use std::iter; +//! +//! fn find_task( +//! local: &Worker, +//! global: &Injector, +//! stealers: &[Stealer], +//! ) -> Option { +//! // Pop a task from the local queue, if not empty. +//! local.pop().or_else(|| { +//! // Otherwise, we need to look for a task elsewhere. +//! iter::repeat_with(|| { +//! // Try stealing a batch of tasks from the global queue. +//! global.steal_batch_and_pop(local) +//! // Or try stealing a task from one of the other threads. +//! .or_else(|| stealers.iter().map(|s| s.steal()).collect()) +//! }) +//! // Loop while no task was stolen and any steal operation needs to be retried. +//! .find(|s| !s.is_retry()) +//! // Extract the stolen task, if there is one. +//! .and_then(|s| s.success()) +//! }) +//! } +//! ``` +//! +//! [`Worker`]: struct.Worker.html +//! [`Stealer`]: struct.Stealer.html +//! [`Injector`]: struct.Injector.html +//! [`Steal::Retry`]: enum.Steal.html#variant.Retry +//! [`new_fifo()`]: struct.Worker.html#method.new_fifo +//! [`new_lifo()`]: struct.Worker.html#method.new_lifo +//! [`stealer()`]: struct.Worker.html#method.stealer +//! [`steal()`]: struct.Stealer.html#method.steal +//! [`steal_batch()`]: struct.Stealer.html#method.steal_batch +//! [`steal_batch_and_pop()`]: struct.Stealer.html#method.steal_batch_and_pop + +extern crate crossbeam_epoch as epoch; +extern crate crossbeam_utils as utils; + +use std::cell::{Cell, UnsafeCell}; +use std::cmp; +use std::fmt; +use std::iter::FromIterator; +use std::marker::PhantomData; +use std::mem::{self, ManuallyDrop}; +use std::ptr; +use std::sync::atomic::{self, AtomicIsize, AtomicPtr, AtomicUsize, Ordering}; +use std::sync::Arc; + +use epoch::{Atomic, Owned}; +use utils::{Backoff, CachePadded}; + +// Minimum buffer capacity. +const MIN_CAP: usize = 64; +// Maximum number of tasks that can be stolen in `steal_batch()` and `steal_batch_and_pop()`. +const MAX_BATCH: usize = 32; +// If a buffer of at least this size is retired, thread-local garbage is flushed so that it gets +// deallocated as soon as possible. +const FLUSH_THRESHOLD_BYTES: usize = 1 << 10; + +/// A buffer that holds tasks in a worker queue. +/// +/// This is just a pointer to the buffer and its length - dropping an instance of this struct will +/// *not* deallocate the buffer. +struct Buffer { + /// Pointer to the allocated memory. + ptr: *mut T, + + /// Capacity of the buffer. Always a power of two. + cap: usize, +} + +unsafe impl Send for Buffer {} + +impl Buffer { + /// Allocates a new buffer with the specified capacity. + fn alloc(cap: usize) -> Buffer { + debug_assert_eq!(cap, cap.next_power_of_two()); + + let mut v = Vec::with_capacity(cap); + let ptr = v.as_mut_ptr(); + mem::forget(v); + + Buffer { ptr, cap } + } + + /// Deallocates the buffer. + unsafe fn dealloc(self) { + drop(Vec::from_raw_parts(self.ptr, 0, self.cap)); + } + + /// Returns a pointer to the task at the specified `index`. + unsafe fn at(&self, index: isize) -> *mut T { + // `self.cap` is always a power of two. + self.ptr.offset(index & (self.cap - 1) as isize) + } + + /// Writes `task` into the specified `index`. + /// + /// This method might be concurrently called with another `read` at the same index, which is + /// technically speaking a data race and therefore UB. We should use an atomic store here, but + /// that would be more expensive and difficult to implement generically for all types `T`. + /// Hence, as a hack, we use a volatile write instead. + unsafe fn write(&self, index: isize, task: T) { + ptr::write_volatile(self.at(index), task) + } + + /// Reads a task from the specified `index`. + /// + /// This method might be concurrently called with another `write` at the same index, which is + /// technically speaking a data race and therefore UB. We should use an atomic load here, but + /// that would be more expensive and difficult to implement generically for all types `T`. + /// Hence, as a hack, we use a volatile write instead. + unsafe fn read(&self, index: isize) -> T { + ptr::read_volatile(self.at(index)) + } +} + +impl Clone for Buffer { + fn clone(&self) -> Buffer { + Buffer { + ptr: self.ptr, + cap: self.cap, + } + } +} + +impl Copy for Buffer {} + +/// Internal queue data shared between the worker and stealers. +/// +/// The implementation is based on the following work: +/// +/// 1. [Chase and Lev. Dynamic circular work-stealing deque. SPAA 2005.][chase-lev] +/// 2. [Le, Pop, Cohen, and Nardelli. Correct and efficient work-stealing for weak memory models. +/// PPoPP 2013.][weak-mem] +/// 3. [Norris and Demsky. CDSchecker: checking concurrent data structures written with C/C++ +/// atomics. OOPSLA 2013.][checker] +/// +/// [chase-lev]: https://dl.acm.org/citation.cfm?id=1073974 +/// [weak-mem]: https://dl.acm.org/citation.cfm?id=2442524 +/// [checker]: https://dl.acm.org/citation.cfm?id=2509514 +struct Inner { + /// The front index. + front: AtomicIsize, + + /// The back index. + back: AtomicIsize, + + /// The underlying buffer. + buffer: CachePadded>>, +} + +impl Drop for Inner { + fn drop(&mut self) { + // Load the back index, front index, and buffer. + let b = self.back.load(Ordering::Relaxed); + let f = self.front.load(Ordering::Relaxed); + + unsafe { + let buffer = self.buffer.load(Ordering::Relaxed, epoch::unprotected()); + + // Go through the buffer from front to back and drop all tasks in the queue. + let mut i = f; + while i != b { + ptr::drop_in_place(buffer.deref().at(i)); + i = i.wrapping_add(1); + } + + // Free the memory allocated by the buffer. + buffer.into_owned().into_box().dealloc(); + } + } +} + +/// Worker queue flavor: FIFO or LIFO. +#[derive(Clone, Copy, Debug, Eq, PartialEq)] +enum Flavor { + /// The first-in first-out flavor. + Fifo, + + /// The last-in first-out flavor. + Lifo, +} + +/// A worker queue. +/// +/// This is a FIFO or LIFO queue that is owned by a single thread, but other threads may steal +/// tasks from it. Task schedulers typically create a single worker queue per thread. +/// +/// # Examples +/// +/// A FIFO worker: +/// +/// ``` +/// use crossbeam_deque::{Steal, Worker}; +/// +/// let w = Worker::new_fifo(); +/// let s = w.stealer(); +/// +/// w.push(1); +/// w.push(2); +/// w.push(3); +/// +/// assert_eq!(s.steal(), Steal::Success(1)); +/// assert_eq!(w.pop(), Some(2)); +/// assert_eq!(w.pop(), Some(3)); +/// ``` +/// +/// A LIFO worker: +/// +/// ``` +/// use crossbeam_deque::{Steal, Worker}; +/// +/// let w = Worker::new_lifo(); +/// let s = w.stealer(); +/// +/// w.push(1); +/// w.push(2); +/// w.push(3); +/// +/// assert_eq!(s.steal(), Steal::Success(1)); +/// assert_eq!(w.pop(), Some(3)); +/// assert_eq!(w.pop(), Some(2)); +/// ``` +pub struct Worker { + /// A reference to the inner representation of the queue. + inner: Arc>>, + + /// A copy of `inner.buffer` for quick access. + buffer: Cell>, + + /// The flavor of the queue. + flavor: Flavor, + + /// Indicates that the worker cannot be shared among threads. + _marker: PhantomData<*mut ()>, // !Send + !Sync +} + +unsafe impl Send for Worker {} + +impl Worker { + /// Creates a FIFO worker queue. + /// + /// Tasks are pushed and popped from opposite ends. + /// + /// # Examples + /// + /// ``` + /// use crossbeam_deque::Worker; + /// + /// let w = Worker::::new_fifo(); + /// ``` + pub fn new_fifo() -> Worker { + let buffer = Buffer::alloc(MIN_CAP); + + let inner = Arc::new(CachePadded::new(Inner { + front: AtomicIsize::new(0), + back: AtomicIsize::new(0), + buffer: CachePadded::new(Atomic::new(buffer)), + })); + + Worker { + inner, + buffer: Cell::new(buffer), + flavor: Flavor::Fifo, + _marker: PhantomData, + } + } + + /// Creates a LIFO worker queue. + /// + /// Tasks are pushed and popped from the same end. + /// + /// # Examples + /// + /// ``` + /// use crossbeam_deque::Worker; + /// + /// let w = Worker::::new_lifo(); + /// ``` + pub fn new_lifo() -> Worker { + let buffer = Buffer::alloc(MIN_CAP); + + let inner = Arc::new(CachePadded::new(Inner { + front: AtomicIsize::new(0), + back: AtomicIsize::new(0), + buffer: CachePadded::new(Atomic::new(buffer)), + })); + + Worker { + inner, + buffer: Cell::new(buffer), + flavor: Flavor::Lifo, + _marker: PhantomData, + } + } + + /// Creates a stealer for this queue. + /// + /// The returned stealer can be shared among threads and cloned. + /// + /// # Examples + /// + /// ``` + /// use crossbeam_deque::Worker; + /// + /// let w = Worker::::new_lifo(); + /// let s = w.stealer(); + /// ``` + pub fn stealer(&self) -> Stealer { + Stealer { + inner: self.inner.clone(), + flavor: self.flavor, + } + } + + /// Resizes the internal buffer to the new capacity of `new_cap`. + #[cold] + unsafe fn resize(&self, new_cap: usize) { + // Load the back index, front index, and buffer. + let b = self.inner.back.load(Ordering::Relaxed); + let f = self.inner.front.load(Ordering::Relaxed); + let buffer = self.buffer.get(); + + // Allocate a new buffer and copy data from the old buffer to the new one. + let new = Buffer::alloc(new_cap); + let mut i = f; + while i != b { + ptr::copy_nonoverlapping(buffer.at(i), new.at(i), 1); + i = i.wrapping_add(1); + } + + let guard = &epoch::pin(); + + // Replace the old buffer with the new one. + self.buffer.replace(new); + let old = + self.inner + .buffer + .swap(Owned::new(new).into_shared(guard), Ordering::Release, guard); + + // Destroy the old buffer later. + guard.defer_unchecked(move || old.into_owned().into_box().dealloc()); + + // If the buffer is very large, then flush the thread-local garbage in order to deallocate + // it as soon as possible. + if mem::size_of::() * new_cap >= FLUSH_THRESHOLD_BYTES { + guard.flush(); + } + } + + /// Reserves enough capacity so that `reserve_cap` tasks can be pushed without growing the + /// buffer. + fn reserve(&self, reserve_cap: usize) { + if reserve_cap > 0 { + // Compute the current length. + let b = self.inner.back.load(Ordering::Relaxed); + let f = self.inner.front.load(Ordering::SeqCst); + let len = b.wrapping_sub(f) as usize; + + // The current capacity. + let cap = self.buffer.get().cap; + + // Is there enough capacity to push `reserve_cap` tasks? + if cap - len < reserve_cap { + // Keep doubling the capacity as much as is needed. + let mut new_cap = cap * 2; + while new_cap - len < reserve_cap { + new_cap *= 2; + } + + // Resize the buffer. + unsafe { + self.resize(new_cap); + } + } + } + } + + /// Returns `true` if the queue is empty. + /// + /// ``` + /// use crossbeam_deque::Worker; + /// + /// let w = Worker::new_lifo(); + /// + /// assert!(w.is_empty()); + /// w.push(1); + /// assert!(!w.is_empty()); + /// ``` + pub fn is_empty(&self) -> bool { + let b = self.inner.back.load(Ordering::Relaxed); + let f = self.inner.front.load(Ordering::SeqCst); + b.wrapping_sub(f) <= 0 + } + + /// Pushes a task into the queue. + /// + /// # Examples + /// + /// ``` + /// use crossbeam_deque::Worker; + /// + /// let w = Worker::new_lifo(); + /// w.push(1); + /// w.push(2); + /// ``` + pub fn push(&self, task: T) { + // Load the back index, front index, and buffer. + let b = self.inner.back.load(Ordering::Relaxed); + let f = self.inner.front.load(Ordering::Acquire); + let mut buffer = self.buffer.get(); + + // Calculate the length of the queue. + let len = b.wrapping_sub(f); + + // Is the queue full? + if len >= buffer.cap as isize { + // Yes. Grow the underlying buffer. + unsafe { + self.resize(2 * buffer.cap); + } + buffer = self.buffer.get(); + } + + // Write `task` into the slot. + unsafe { + buffer.write(b, task); + } + + atomic::fence(Ordering::Release); + + // Increment the back index. + // + // This ordering could be `Relaxed`, but then thread sanitizer would falsely report data + // races because it doesn't understand fences. + self.inner.back.store(b.wrapping_add(1), Ordering::Release); + } + + /// Pops a task from the queue. + /// + /// # Examples + /// + /// ``` + /// use crossbeam_deque::Worker; + /// + /// let w = Worker::new_fifo(); + /// w.push(1); + /// w.push(2); + /// + /// assert_eq!(w.pop(), Some(1)); + /// assert_eq!(w.pop(), Some(2)); + /// assert_eq!(w.pop(), None); + /// ``` + pub fn pop(&self) -> Option { + // Load the back and front index. + let b = self.inner.back.load(Ordering::Relaxed); + let f = self.inner.front.load(Ordering::Relaxed); + + // Calculate the length of the queue. + let len = b.wrapping_sub(f); + + // Is the queue empty? + if len <= 0 { + return None; + } + + match self.flavor { + // Pop from the front of the queue. + Flavor::Fifo => { + // Try incrementing the front index to pop the task. + let f = self.inner.front.fetch_add(1, Ordering::SeqCst); + let new_f = f.wrapping_add(1); + + if b.wrapping_sub(new_f) < 0 { + self.inner.front.store(f, Ordering::Relaxed); + return None; + } + + unsafe { + // Read the popped task. + let buffer = self.buffer.get(); + let task = buffer.read(f); + + // Shrink the buffer if `len - 1` is less than one fourth of the capacity. + if buffer.cap > MIN_CAP && len <= buffer.cap as isize / 4 { + self.resize(buffer.cap / 2); + } + + Some(task) + } + } + + // Pop from the back of the queue. + Flavor::Lifo => { + // Decrement the back index. + let b = b.wrapping_sub(1); + self.inner.back.store(b, Ordering::Relaxed); + + atomic::fence(Ordering::SeqCst); + + // Load the front index. + let f = self.inner.front.load(Ordering::Relaxed); + + // Compute the length after the back index was decremented. + let len = b.wrapping_sub(f); + + if len < 0 { + // The queue is empty. Restore the back index to the original task. + self.inner.back.store(b.wrapping_add(1), Ordering::Relaxed); + None + } else { + // Read the task to be popped. + let buffer = self.buffer.get(); + let mut task = unsafe { Some(buffer.read(b)) }; + + // Are we popping the last task from the queue? + if len == 0 { + // Try incrementing the front index. + if self + .inner + .front + .compare_exchange( + f, + f.wrapping_add(1), + Ordering::SeqCst, + Ordering::Relaxed, + ) + .is_err() + { + // Failed. We didn't pop anything. + mem::forget(task.take()); + } + + // Restore the back index to the original task. + self.inner.back.store(b.wrapping_add(1), Ordering::Relaxed); + } else { + // Shrink the buffer if `len` is less than one fourth of the capacity. + if buffer.cap > MIN_CAP && len < buffer.cap as isize / 4 { + unsafe { + self.resize(buffer.cap / 2); + } + } + } + + task + } + } + } + } +} + +impl fmt::Debug for Worker { + fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result { + f.pad("Worker { .. }") + } +} + +/// A stealer handle of a worker queue. +/// +/// Stealers can be shared among threads. +/// +/// Task schedulers typically have a single worker queue per worker thread. +/// +/// # Examples +/// +/// ``` +/// use crossbeam_deque::{Steal, Worker}; +/// +/// let w = Worker::new_lifo(); +/// w.push(1); +/// w.push(2); +/// +/// let s = w.stealer(); +/// assert_eq!(s.steal(), Steal::Success(1)); +/// assert_eq!(s.steal(), Steal::Success(2)); +/// assert_eq!(s.steal(), Steal::Empty); +/// ``` +pub struct Stealer { + /// A reference to the inner representation of the queue. + inner: Arc>>, + + /// The flavor of the queue. + flavor: Flavor, +} + +unsafe impl Send for Stealer {} +unsafe impl Sync for Stealer {} + +impl Stealer { + /// Returns `true` if the queue is empty. + /// + /// ``` + /// use crossbeam_deque::Worker; + /// + /// let w = Worker::new_lifo(); + /// let s = w.stealer(); + /// + /// assert!(s.is_empty()); + /// w.push(1); + /// assert!(!s.is_empty()); + /// ``` + pub fn is_empty(&self) -> bool { + let f = self.inner.front.load(Ordering::Acquire); + atomic::fence(Ordering::SeqCst); + let b = self.inner.back.load(Ordering::Acquire); + b.wrapping_sub(f) <= 0 + } + + /// Steals a task from the queue. + /// + /// # Examples + /// + /// ``` + /// use crossbeam_deque::{Steal, Worker}; + /// + /// let w = Worker::new_lifo(); + /// w.push(1); + /// w.push(2); + /// + /// let s = w.stealer(); + /// assert_eq!(s.steal(), Steal::Success(1)); + /// assert_eq!(s.steal(), Steal::Success(2)); + /// ``` + pub fn steal(&self) -> Steal { + // Load the front index. + let f = self.inner.front.load(Ordering::Acquire); + + // A SeqCst fence is needed here. + // + // If the current thread is already pinned (reentrantly), we must manually issue the + // fence. Otherwise, the following pinning will issue the fence anyway, so we don't + // have to. + if epoch::is_pinned() { + atomic::fence(Ordering::SeqCst); + } + + let guard = &epoch::pin(); + + // Load the back index. + let b = self.inner.back.load(Ordering::Acquire); + + // Is the queue empty? + if b.wrapping_sub(f) <= 0 { + return Steal::Empty; + } + + // Load the buffer and read the task at the front. + let buffer = self.inner.buffer.load(Ordering::Acquire, guard); + let task = unsafe { buffer.deref().read(f) }; + + // Try incrementing the front index to steal the task. + if self + .inner + .front + .compare_exchange(f, f.wrapping_add(1), Ordering::SeqCst, Ordering::Relaxed) + .is_err() + { + // We didn't steal this task, forget it. + mem::forget(task); + return Steal::Retry; + } + + // Return the stolen task. + Steal::Success(task) + } + + /// Steals a batch of tasks and pushes them into another worker. + /// + /// How many tasks exactly will be stolen is not specified. That said, this method will try to + /// steal around half of the tasks in the queue, but also not more than some constant limit. + /// + /// # Examples + /// + /// ``` + /// use crossbeam_deque::Worker; + /// + /// let w1 = Worker::new_fifo(); + /// w1.push(1); + /// w1.push(2); + /// w1.push(3); + /// w1.push(4); + /// + /// let s = w1.stealer(); + /// let w2 = Worker::new_fifo(); + /// + /// s.steal_batch(&w2); + /// assert_eq!(w2.pop(), Some(1)); + /// assert_eq!(w2.pop(), Some(2)); + /// ``` + pub fn steal_batch(&self, dest: &Worker) -> Steal<()> { + // Load the front index. + let mut f = self.inner.front.load(Ordering::Acquire); + + // A SeqCst fence is needed here. + // + // If the current thread is already pinned (reentrantly), we must manually issue the + // fence. Otherwise, the following pinning will issue the fence anyway, so we don't + // have to. + if epoch::is_pinned() { + atomic::fence(Ordering::SeqCst); + } + + let guard = &epoch::pin(); + + // Load the back index. + let b = self.inner.back.load(Ordering::Acquire); + + // Is the queue empty? + let len = b.wrapping_sub(f); + if len <= 0 { + return Steal::Empty; + } + + // Reserve capacity for the stolen batch. + let batch_size = cmp::min((len as usize + 1) / 2, MAX_BATCH); + dest.reserve(batch_size); + let mut batch_size = batch_size as isize; + + // Get the destination buffer and back index. + let dest_buffer = dest.buffer.get(); + let mut dest_b = dest.inner.back.load(Ordering::Relaxed); + + // Load the buffer. + let buffer = self.inner.buffer.load(Ordering::Acquire, guard); + + match self.flavor { + // Steal a batch of tasks from the front at once. + Flavor::Fifo => { + // Copy the batch from the source to the destination buffer. + match dest.flavor { + Flavor::Fifo => { + for i in 0..batch_size { + unsafe { + let task = buffer.deref().read(f.wrapping_add(i)); + dest_buffer.write(dest_b.wrapping_add(i), task); + } + } + } + Flavor::Lifo => { + for i in 0..batch_size { + unsafe { + let task = buffer.deref().read(f.wrapping_add(i)); + dest_buffer.write(dest_b.wrapping_add(batch_size - 1 - i), task); + } + } + } + } + + // Try incrementing the front index to steal the batch. + if self + .inner + .front + .compare_exchange( + f, + f.wrapping_add(batch_size), + Ordering::SeqCst, + Ordering::Relaxed, + ) + .is_err() + { + return Steal::Retry; + } + + dest_b = dest_b.wrapping_add(batch_size); + } + + // Steal a batch of tasks from the front one by one. + Flavor::Lifo => { + for i in 0..batch_size { + // If this is not the first steal, check whether the queue is empty. + if i > 0 { + // We've already got the current front index. Now execute the fence to + // synchronize with other threads. + atomic::fence(Ordering::SeqCst); + + // Load the back index. + let b = self.inner.back.load(Ordering::Acquire); + + // Is the queue empty? + if b.wrapping_sub(f) <= 0 { + batch_size = i; + break; + } + } + + // Read the task at the front. + let task = unsafe { buffer.deref().read(f) }; + + // Try incrementing the front index to steal the task. + if self + .inner + .front + .compare_exchange(f, f.wrapping_add(1), Ordering::SeqCst, Ordering::Relaxed) + .is_err() + { + // We didn't steal this task, forget it and break from the loop. + mem::forget(task); + batch_size = i; + break; + } + + // Write the stolen task into the destination buffer. + unsafe { + dest_buffer.write(dest_b, task); + } + + // Move the source front index and the destination back index one step forward. + f = f.wrapping_add(1); + dest_b = dest_b.wrapping_add(1); + } + + // If we didn't steal anything, the operation needs to be retried. + if batch_size == 0 { + return Steal::Retry; + } + + // If stealing into a FIFO queue, stolen tasks need to be reversed. + if dest.flavor == Flavor::Fifo { + for i in 0..batch_size / 2 { + unsafe { + let i1 = dest_b.wrapping_sub(batch_size - i); + let i2 = dest_b.wrapping_sub(i + 1); + let t1 = dest_buffer.read(i1); + let t2 = dest_buffer.read(i2); + dest_buffer.write(i1, t2); + dest_buffer.write(i2, t1); + } + } + } + } + } + + atomic::fence(Ordering::Release); + + // Update the back index in the destination queue. + // + // This ordering could be `Relaxed`, but then thread sanitizer would falsely report data + // races because it doesn't understand fences. + dest.inner.back.store(dest_b, Ordering::Release); + + // Return with success. + Steal::Success(()) + } + + /// Steals a batch of tasks, pushes them into another worker, and pops a task from that worker. + /// + /// How many tasks exactly will be stolen is not specified. That said, this method will try to + /// steal around half of the tasks in the queue, but also not more than some constant limit. + /// + /// # Examples + /// + /// ``` + /// use crossbeam_deque::{Steal, Worker}; + /// + /// let w1 = Worker::new_fifo(); + /// w1.push(1); + /// w1.push(2); + /// w1.push(3); + /// w1.push(4); + /// + /// let s = w1.stealer(); + /// let w2 = Worker::new_fifo(); + /// + /// assert_eq!(s.steal_batch_and_pop(&w2), Steal::Success(1)); + /// assert_eq!(w2.pop(), Some(2)); + /// ``` + pub fn steal_batch_and_pop(&self, dest: &Worker) -> Steal { + // Load the front index. + let mut f = self.inner.front.load(Ordering::Acquire); + + // A SeqCst fence is needed here. + // + // If the current thread is already pinned (reentrantly), we must manually issue the + // fence. Otherwise, the following pinning will issue the fence anyway, so we don't + // have to. + if epoch::is_pinned() { + atomic::fence(Ordering::SeqCst); + } + + let guard = &epoch::pin(); + + // Load the back index. + let b = self.inner.back.load(Ordering::Acquire); + + // Is the queue empty? + let len = b.wrapping_sub(f); + if len <= 0 { + return Steal::Empty; + } + + // Reserve capacity for the stolen batch. + let batch_size = cmp::min((len as usize - 1) / 2, MAX_BATCH - 1); + dest.reserve(batch_size); + let mut batch_size = batch_size as isize; + + // Get the destination buffer and back index. + let dest_buffer = dest.buffer.get(); + let mut dest_b = dest.inner.back.load(Ordering::Relaxed); + + // Load the buffer + let buffer = self.inner.buffer.load(Ordering::Acquire, guard); + + // Read the task at the front. + let mut task = unsafe { buffer.deref().read(f) }; + + match self.flavor { + // Steal a batch of tasks from the front at once. + Flavor::Fifo => { + // Copy the batch from the source to the destination buffer. + match dest.flavor { + Flavor::Fifo => { + for i in 0..batch_size { + unsafe { + let task = buffer.deref().read(f.wrapping_add(i + 1)); + dest_buffer.write(dest_b.wrapping_add(i), task); + } + } + } + Flavor::Lifo => { + for i in 0..batch_size { + unsafe { + let task = buffer.deref().read(f.wrapping_add(i + 1)); + dest_buffer.write(dest_b.wrapping_add(batch_size - 1 - i), task); + } + } + } + } + + // Try incrementing the front index to steal the batch. + if self + .inner + .front + .compare_exchange( + f, + f.wrapping_add(batch_size + 1), + Ordering::SeqCst, + Ordering::Relaxed, + ) + .is_err() + { + // We didn't steal this task, forget it. + mem::forget(task); + return Steal::Retry; + } + + dest_b = dest_b.wrapping_add(batch_size); + } + + // Steal a batch of tasks from the front one by one. + Flavor::Lifo => { + // Try incrementing the front index to steal the task. + if self + .inner + .front + .compare_exchange(f, f.wrapping_add(1), Ordering::SeqCst, Ordering::Relaxed) + .is_err() + { + // We didn't steal this task, forget it. + mem::forget(task); + return Steal::Retry; + } + + // Move the front index one step forward. + f = f.wrapping_add(1); + + // Repeat the same procedure for the batch steals. + for i in 0..batch_size { + // We've already got the current front index. Now execute the fence to + // synchronize with other threads. + atomic::fence(Ordering::SeqCst); + + // Load the back index. + let b = self.inner.back.load(Ordering::Acquire); + + // Is the queue empty? + if b.wrapping_sub(f) <= 0 { + batch_size = i; + break; + } + + // Read the task at the front. + let tmp = unsafe { buffer.deref().read(f) }; + + // Try incrementing the front index to steal the task. + if self + .inner + .front + .compare_exchange(f, f.wrapping_add(1), Ordering::SeqCst, Ordering::Relaxed) + .is_err() + { + // We didn't steal this task, forget it and break from the loop. + mem::forget(tmp); + batch_size = i; + break; + } + + // Write the previously stolen task into the destination buffer. + unsafe { + dest_buffer.write(dest_b, mem::replace(&mut task, tmp)); + } + + // Move the source front index and the destination back index one step forward. + f = f.wrapping_add(1); + dest_b = dest_b.wrapping_add(1); + } + + // If stealing into a FIFO queue, stolen tasks need to be reversed. + if dest.flavor == Flavor::Fifo { + for i in 0..batch_size / 2 { + unsafe { + let i1 = dest_b.wrapping_sub(batch_size - i); + let i2 = dest_b.wrapping_sub(i + 1); + let t1 = dest_buffer.read(i1); + let t2 = dest_buffer.read(i2); + dest_buffer.write(i1, t2); + dest_buffer.write(i2, t1); + } + } + } + } + } + + atomic::fence(Ordering::Release); + + // Update the back index in the destination queue. + // + // This ordering could be `Relaxed`, but then thread sanitizer would falsely report data + // races because it doesn't understand fences. + dest.inner.back.store(dest_b, Ordering::Release); + + // Return with success. + Steal::Success(task) + } + + pub fn steal_batch_and_pop_with_amount(&self, dest: &Worker, amount: usize) -> Steal { + // Load the front index. + let mut f = self.inner.front.load(Ordering::Acquire); + + // A SeqCst fence is needed here. + // + // If the current thread is already pinned (reentrantly), we must manually issue the + // fence. Otherwise, the following pinning will issue the fence anyway, so we don't + // have to. + if epoch::is_pinned() { + atomic::fence(Ordering::SeqCst); + } + + let guard = &epoch::pin(); + + // Load the back index. + let b = self.inner.back.load(Ordering::Acquire); + + // Is the queue empty? + let len = b.wrapping_sub(f); + if len <= 0 { + return Steal::Empty; + } + + // Reserve capacity for the stolen batch. + let batch_size = cmp::min(amount, MAX_BATCH - 1); + dest.reserve(batch_size); + let mut batch_size = batch_size as isize; + + // Get the destination buffer and back index. + let dest_buffer = dest.buffer.get(); + let mut dest_b = dest.inner.back.load(Ordering::Relaxed); + + // Load the buffer + let buffer = self.inner.buffer.load(Ordering::Acquire, guard); + + // Read the task at the front. + let mut task = unsafe { buffer.deref().read(f) }; + + match self.flavor { + // Steal a batch of tasks from the front at once. + Flavor::Fifo => { + // Copy the batch from the source to the destination buffer. + match dest.flavor { + Flavor::Fifo => { + for i in 0..batch_size { + unsafe { + let task = buffer.deref().read(f.wrapping_add(i + 1)); + dest_buffer.write(dest_b.wrapping_add(i), task); + } + } + } + Flavor::Lifo => { + for i in 0..batch_size { + unsafe { + let task = buffer.deref().read(f.wrapping_add(i + 1)); + dest_buffer.write(dest_b.wrapping_add(batch_size - 1 - i), task); + } + } + } + } + + // Try incrementing the front index to steal the batch. + if self + .inner + .front + .compare_exchange( + f, + f.wrapping_add(batch_size + 1), + Ordering::SeqCst, + Ordering::Relaxed, + ) + .is_err() + { + // We didn't steal this task, forget it. + mem::forget(task); + return Steal::Retry; + } + + dest_b = dest_b.wrapping_add(batch_size); + } + + // Steal a batch of tasks from the front one by one. + Flavor::Lifo => { + // Try incrementing the front index to steal the task. + if self + .inner + .front + .compare_exchange(f, f.wrapping_add(1), Ordering::SeqCst, Ordering::Relaxed) + .is_err() + { + // We didn't steal this task, forget it. + mem::forget(task); + return Steal::Retry; + } + + // Move the front index one step forward. + f = f.wrapping_add(1); + + // Repeat the same procedure for the batch steals. + for i in 0..batch_size { + // We've already got the current front index. Now execute the fence to + // synchronize with other threads. + atomic::fence(Ordering::SeqCst); + + // Load the back index. + let b = self.inner.back.load(Ordering::Acquire); + + // Is the queue empty? + if b.wrapping_sub(f) <= 0 { + batch_size = i; + break; + } + + // Read the task at the front. + let tmp = unsafe { buffer.deref().read(f) }; + + // Try incrementing the front index to steal the task. + if self + .inner + .front + .compare_exchange(f, f.wrapping_add(1), Ordering::SeqCst, Ordering::Relaxed) + .is_err() + { + // We didn't steal this task, forget it and break from the loop. + mem::forget(tmp); + batch_size = i; + break; + } + + // Write the previously stolen task into the destination buffer. + unsafe { + dest_buffer.write(dest_b, mem::replace(&mut task, tmp)); + } + + // Move the source front index and the destination back index one step forward. + f = f.wrapping_add(1); + dest_b = dest_b.wrapping_add(1); + } + + // If stealing into a FIFO queue, stolen tasks need to be reversed. + if dest.flavor == Flavor::Fifo { + for i in 0..batch_size / 2 { + unsafe { + let i1 = dest_b.wrapping_sub(batch_size - i); + let i2 = dest_b.wrapping_sub(i + 1); + let t1 = dest_buffer.read(i1); + let t2 = dest_buffer.read(i2); + dest_buffer.write(i1, t2); + dest_buffer.write(i2, t1); + } + } + } + } + } + + atomic::fence(Ordering::Release); + + // Update the back index in the destination queue. + // + // This ordering could be `Relaxed`, but then thread sanitizer would falsely report data + // races because it doesn't understand fences. + dest.inner.back.store(dest_b, Ordering::Release); + + // Return with success. + Steal::Success(task) + } +} + +impl Clone for Stealer { + fn clone(&self) -> Stealer { + Stealer { + inner: self.inner.clone(), + flavor: self.flavor, + } + } +} + +impl fmt::Debug for Stealer { + fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result { + f.pad("Stealer { .. }") + } +} + +// Bits indicating the state of a slot: +// * If a task has been written into the slot, `WRITE` is set. +// * If a task has been read from the slot, `READ` is set. +// * If the block is being destroyed, `DESTROY` is set. +const WRITE: usize = 1; +const READ: usize = 2; +const DESTROY: usize = 4; + +// Each block covers one "lap" of indices. +const LAP: usize = 64; +// The maximum number of values a block can hold. +const BLOCK_CAP: usize = LAP - 1; +// How many lower bits are reserved for metadata. +const SHIFT: usize = 1; +// Indicates that the block is not the last one. +const HAS_NEXT: usize = 1; + +/// A slot in a block. +struct Slot { + /// The task. + task: UnsafeCell>, + + /// The state of the slot. + state: AtomicUsize, +} + +impl Slot { + /// Waits until a task is written into the slot. + fn wait_write(&self) { + let backoff = Backoff::new(); + while self.state.load(Ordering::Acquire) & WRITE == 0 { + backoff.snooze(); + } + } +} + +/// A block in a linked list. +/// +/// Each block in the list can hold up to `BLOCK_CAP` values. +struct Block { + /// The next block in the linked list. + next: AtomicPtr>, + + /// Slots for values. + slots: [Slot; BLOCK_CAP], +} + +impl Block { + /// Creates an empty block that starts at `start_index`. + fn new() -> Block { + unsafe { mem::zeroed() } + } + + /// Waits until the next pointer is set. + fn wait_next(&self) -> *mut Block { + let backoff = Backoff::new(); + loop { + let next = self.next.load(Ordering::Acquire); + if !next.is_null() { + return next; + } + backoff.snooze(); + } + } + + /// Sets the `DESTROY` bit in slots starting from `start` and destroys the block. + unsafe fn destroy(this: *mut Block, count: usize) { + // It is not necessary to set the `DESTROY` bit in the last slot because that slot has + // begun destruction of the block. + for i in (0..count).rev() { + let slot = (*this).slots.get_unchecked(i); + + // Mark the `DESTROY` bit if a thread is still using the slot. + if slot.state.load(Ordering::Acquire) & READ == 0 + && slot.state.fetch_or(DESTROY, Ordering::AcqRel) & READ == 0 + { + // If a thread is still using the slot, it will continue destruction of the block. + return; + } + } + + // No thread is using the block, now it is safe to destroy it. + drop(Box::from_raw(this)); + } +} + +/// A position in a queue. +struct Position { + /// The index in the queue. + index: AtomicUsize, + + /// The block in the linked list. + block: AtomicPtr>, +} + +/// An injector queue. +/// +/// This is a FIFO queue that can be shared among multiple threads. Task schedulers typically have +/// a single injector queue, which is the entry point for new tasks. +/// +/// # Examples +/// +/// ``` +/// use crossbeam_deque::{Injector, Steal}; +/// +/// let q = Injector::new(); +/// q.push(1); +/// q.push(2); +/// +/// assert_eq!(q.steal(), Steal::Success(1)); +/// assert_eq!(q.steal(), Steal::Success(2)); +/// assert_eq!(q.steal(), Steal::Empty); +/// ``` +pub struct Injector { + /// The head of the queue. + head: CachePadded>, + + /// The tail of the queue. + tail: CachePadded>, + + /// Indicates that dropping a `Injector` may drop values of type `T`. + _marker: PhantomData, +} + +unsafe impl Send for Injector {} +unsafe impl Sync for Injector {} + +impl Injector { + /// Creates a new injector queue. + /// + /// # Examples + /// + /// ``` + /// use crossbeam_deque::Injector; + /// + /// let q = Injector::::new(); + /// ``` + pub fn new() -> Injector { + let block = Box::into_raw(Box::new(Block::::new())); + Injector { + head: CachePadded::new(Position { + block: AtomicPtr::new(block), + index: AtomicUsize::new(0), + }), + tail: CachePadded::new(Position { + block: AtomicPtr::new(block), + index: AtomicUsize::new(0), + }), + _marker: PhantomData, + } + } + + /// Pushes a task into the queue. + /// + /// # Examples + /// + /// ``` + /// use crossbeam_deque::Injector; + /// + /// let w = Injector::new(); + /// w.push(1); + /// w.push(2); + /// ``` + pub fn push(&self, task: T) { + let backoff = Backoff::new(); + let mut tail = self.tail.index.load(Ordering::Acquire); + let mut block = self.tail.block.load(Ordering::Acquire); + let mut next_block = None; + + loop { + // Calculate the offset of the index into the block. + let offset = (tail >> SHIFT) % LAP; + + // If we reached the end of the block, wait until the next one is installed. + if offset == BLOCK_CAP { + backoff.snooze(); + tail = self.tail.index.load(Ordering::Acquire); + block = self.tail.block.load(Ordering::Acquire); + continue; + } + + // If we're going to have to install the next block, allocate it in advance in order to + // make the wait for other threads as short as possible. + if offset + 1 == BLOCK_CAP && next_block.is_none() { + next_block = Some(Box::new(Block::::new())); + } + + let new_tail = tail + (1 << SHIFT); + + // Try advancing the tail forward. + match self.tail.index.compare_exchange_weak( + tail, + new_tail, + Ordering::SeqCst, + Ordering::Acquire, + ) { + Ok(_) => unsafe { + // If we've reached the end of the block, install the next one. + if offset + 1 == BLOCK_CAP { + let next_block = Box::into_raw(next_block.unwrap()); + let next_index = new_tail.wrapping_add(1 << SHIFT); + + self.tail.block.store(next_block, Ordering::Release); + self.tail.index.store(next_index, Ordering::Release); + (*block).next.store(next_block, Ordering::Release); + } + + // Write the task into the slot. + let slot = (*block).slots.get_unchecked(offset); + slot.task.get().write(ManuallyDrop::new(task)); + slot.state.fetch_or(WRITE, Ordering::Release); + + return; + }, + Err(t) => { + tail = t; + block = self.tail.block.load(Ordering::Acquire); + backoff.spin(); + } + } + } + } + + /// Steals a task from the queue. + /// + /// # Examples + /// + /// ``` + /// use crossbeam_deque::{Injector, Steal}; + /// + /// let q = Injector::new(); + /// q.push(1); + /// q.push(2); + /// + /// assert_eq!(q.steal(), Steal::Success(1)); + /// assert_eq!(q.steal(), Steal::Success(2)); + /// assert_eq!(q.steal(), Steal::Empty); + /// ``` + pub fn steal(&self) -> Steal { + let mut head; + let mut block; + let mut offset; + + let backoff = Backoff::new(); + loop { + head = self.head.index.load(Ordering::Acquire); + block = self.head.block.load(Ordering::Acquire); + + // Calculate the offset of the index into the block. + offset = (head >> SHIFT) % LAP; + + // If we reached the end of the block, wait until the next one is installed. + if offset == BLOCK_CAP { + backoff.snooze(); + } else { + break; + } + } + + let mut new_head = head + (1 << SHIFT); + + if new_head & HAS_NEXT == 0 { + atomic::fence(Ordering::SeqCst); + let tail = self.tail.index.load(Ordering::Relaxed); + + // If the tail equals the head, that means the queue is empty. + if head >> SHIFT == tail >> SHIFT { + return Steal::Empty; + } + + // If head and tail are not in the same block, set `HAS_NEXT` in head. + if (head >> SHIFT) / LAP != (tail >> SHIFT) / LAP { + new_head |= HAS_NEXT; + } + } + + // Try moving the head index forward. + if self + .head + .index + .compare_exchange_weak(head, new_head, Ordering::SeqCst, Ordering::Acquire) + .is_err() + { + return Steal::Retry; + } + + unsafe { + // If we've reached the end of the block, move to the next one. + if offset + 1 == BLOCK_CAP { + let next = (*block).wait_next(); + let mut next_index = (new_head & !HAS_NEXT).wrapping_add(1 << SHIFT); + if !(*next).next.load(Ordering::Relaxed).is_null() { + next_index |= HAS_NEXT; + } + + self.head.block.store(next, Ordering::Release); + self.head.index.store(next_index, Ordering::Release); + } + + // Read the task. + let slot = (*block).slots.get_unchecked(offset); + slot.wait_write(); + let m = slot.task.get().read(); + let task = ManuallyDrop::into_inner(m); + + // Destroy the block if we've reached the end, or if another thread wanted to destroy + // but couldn't because we were busy reading from the slot. + if offset + 1 == BLOCK_CAP { + Block::destroy(block, offset); + } else if slot.state.fetch_or(READ, Ordering::AcqRel) & DESTROY != 0 { + Block::destroy(block, offset); + } + + Steal::Success(task) + } + } + + /// Steals a batch of tasks and pushes them into a worker. + /// + /// How many tasks exactly will be stolen is not specified. That said, this method will try to + /// steal around half of the tasks in the queue, but also not more than some constant limit. + /// + /// # Examples + /// + /// ``` + /// use crossbeam_deque::{Injector, Worker}; + /// + /// let q = Injector::new(); + /// q.push(1); + /// q.push(2); + /// q.push(3); + /// q.push(4); + /// + /// let w = Worker::new_fifo(); + /// q.steal_batch(&w); + /// assert_eq!(w.pop(), Some(1)); + /// assert_eq!(w.pop(), Some(2)); + /// ``` + pub fn steal_batch(&self, dest: &Worker) -> Steal<()> { + let mut head; + let mut block; + let mut offset; + + let backoff = Backoff::new(); + loop { + head = self.head.index.load(Ordering::Acquire); + block = self.head.block.load(Ordering::Acquire); + + // Calculate the offset of the index into the block. + offset = (head >> SHIFT) % LAP; + + // If we reached the end of the block, wait until the next one is installed. + if offset == BLOCK_CAP { + backoff.snooze(); + } else { + break; + } + } + + let mut new_head = head; + let advance; + + if new_head & HAS_NEXT == 0 { + atomic::fence(Ordering::SeqCst); + let tail = self.tail.index.load(Ordering::Relaxed); + + // If the tail equals the head, that means the queue is empty. + if head >> SHIFT == tail >> SHIFT { + return Steal::Empty; + } + + // If head and tail are not in the same block, set `HAS_NEXT` in head. Also, calculate + // the right batch size to steal. + if (head >> SHIFT) / LAP != (tail >> SHIFT) / LAP { + new_head |= HAS_NEXT; + // We can steal all tasks till the end of the block. + advance = (BLOCK_CAP - offset).min(MAX_BATCH); + } else { + let len = (tail - head) >> SHIFT; + // Steal half of the available tasks. + advance = ((len + 1) / 2).min(MAX_BATCH); + } + } else { + // We can steal all tasks till the end of the block. + advance = (BLOCK_CAP - offset).min(MAX_BATCH); + } + + new_head += advance << SHIFT; + let new_offset = offset + advance; + + // Try moving the head index forward. + if self + .head + .index + .compare_exchange_weak(head, new_head, Ordering::SeqCst, Ordering::Acquire) + .is_err() + { + return Steal::Retry; + } + + // Reserve capacity for the stolen batch. + let batch_size = new_offset - offset; + dest.reserve(batch_size); + + // Get the destination buffer and back index. + let dest_buffer = dest.buffer.get(); + let dest_b = dest.inner.back.load(Ordering::Relaxed); + + unsafe { + // If we've reached the end of the block, move to the next one. + if new_offset == BLOCK_CAP { + let next = (*block).wait_next(); + let mut next_index = (new_head & !HAS_NEXT).wrapping_add(1 << SHIFT); + if !(*next).next.load(Ordering::Relaxed).is_null() { + next_index |= HAS_NEXT; + } + + self.head.block.store(next, Ordering::Release); + self.head.index.store(next_index, Ordering::Release); + } + + // Copy values from the injector into the destination queue. + match dest.flavor { + Flavor::Fifo => { + for i in 0..batch_size { + // Read the task. + let slot = (*block).slots.get_unchecked(offset + i); + slot.wait_write(); + let m = slot.task.get().read(); + let task = ManuallyDrop::into_inner(m); + + // Write it into the destination queue. + dest_buffer.write(dest_b.wrapping_add(i as isize), task); + } + } + + Flavor::Lifo => { + for i in 0..batch_size { + // Read the task. + let slot = (*block).slots.get_unchecked(offset + i); + slot.wait_write(); + let m = slot.task.get().read(); + let task = ManuallyDrop::into_inner(m); + + // Write it into the destination queue. + dest_buffer.write(dest_b.wrapping_add((batch_size - 1 - i) as isize), task); + } + } + } + + atomic::fence(Ordering::Release); + + // Update the back index in the destination queue. + // + // This ordering could be `Relaxed`, but then thread sanitizer would falsely report + // data races because it doesn't understand fences. + dest.inner + .back + .store(dest_b.wrapping_add(batch_size as isize), Ordering::Release); + + // Destroy the block if we've reached the end, or if another thread wanted to destroy + // but couldn't because we were busy reading from the slot. + if new_offset == BLOCK_CAP { + Block::destroy(block, offset); + } else { + for i in offset..new_offset { + let slot = (*block).slots.get_unchecked(i); + + if slot.state.fetch_or(READ, Ordering::AcqRel) & DESTROY != 0 { + Block::destroy(block, offset); + break; + } + } + } + + Steal::Success(()) + } + } + + /// Steals a batch of tasks, pushes them into a worker, and pops a task from that worker. + /// + /// How many tasks exactly will be stolen is not specified. That said, this method will try to + /// steal around half of the tasks in the queue, but also not more than some constant limit. + /// + /// # Examples + /// + /// ``` + /// use crossbeam_deque::{Injector, Steal, Worker}; + /// + /// let q = Injector::new(); + /// q.push(1); + /// q.push(2); + /// q.push(3); + /// q.push(4); + /// + /// let w = Worker::new_fifo(); + /// assert_eq!(q.steal_batch_and_pop(&w), Steal::Success(1)); + /// assert_eq!(w.pop(), Some(2)); + /// ``` + pub fn steal_batch_and_pop(&self, dest: &Worker) -> Steal { + let mut head; + let mut block; + let mut offset; + + let backoff = Backoff::new(); + loop { + head = self.head.index.load(Ordering::Acquire); + block = self.head.block.load(Ordering::Acquire); + + // Calculate the offset of the index into the block. + offset = (head >> SHIFT) % LAP; + + // If we reached the end of the block, wait until the next one is installed. + if offset == BLOCK_CAP { + backoff.snooze(); + } else { + break; + } + } + + let mut new_head = head; + let advance; + + if new_head & HAS_NEXT == 0 { + atomic::fence(Ordering::SeqCst); + let tail = self.tail.index.load(Ordering::Relaxed); + + // If the tail equals the head, that means the queue is empty. + if head >> SHIFT == tail >> SHIFT { + return Steal::Empty; + } + + // If head and tail are not in the same block, set `HAS_NEXT` in head. + if (head >> SHIFT) / LAP != (tail >> SHIFT) / LAP { + new_head |= HAS_NEXT; + // We can steal all tasks till the end of the block. + advance = (BLOCK_CAP - offset).min(MAX_BATCH + 1); + } else { + let len = (tail - head) >> SHIFT; + // Steal half of the available tasks. + advance = ((len + 1) / 2).min(MAX_BATCH + 1); + } + } else { + // We can steal all tasks till the end of the block. + advance = (BLOCK_CAP - offset).min(MAX_BATCH + 1); + } + + new_head += advance << SHIFT; + let new_offset = offset + advance; + + // Try moving the head index forward. + if self + .head + .index + .compare_exchange_weak(head, new_head, Ordering::SeqCst, Ordering::Acquire) + .is_err() + { + return Steal::Retry; + } + + // Reserve capacity for the stolen batch. + let batch_size = new_offset - offset - 1; + dest.reserve(batch_size); + + // Get the destination buffer and back index. + let dest_buffer = dest.buffer.get(); + let dest_b = dest.inner.back.load(Ordering::Relaxed); + + unsafe { + // If we've reached the end of the block, move to the next one. + if new_offset == BLOCK_CAP { + let next = (*block).wait_next(); + let mut next_index = (new_head & !HAS_NEXT).wrapping_add(1 << SHIFT); + if !(*next).next.load(Ordering::Relaxed).is_null() { + next_index |= HAS_NEXT; + } + + self.head.block.store(next, Ordering::Release); + self.head.index.store(next_index, Ordering::Release); + } + + // Read the task. + let slot = (*block).slots.get_unchecked(offset); + slot.wait_write(); + let m = slot.task.get().read(); + let task = ManuallyDrop::into_inner(m); + + match dest.flavor { + Flavor::Fifo => { + // Copy values from the injector into the destination queue. + for i in 0..batch_size { + // Read the task. + let slot = (*block).slots.get_unchecked(offset + i + 1); + slot.wait_write(); + let m = slot.task.get().read(); + let task = ManuallyDrop::into_inner(m); + + // Write it into the destination queue. + dest_buffer.write(dest_b.wrapping_add(i as isize), task); + } + } + + Flavor::Lifo => { + // Copy values from the injector into the destination queue. + for i in 0..batch_size { + // Read the task. + let slot = (*block).slots.get_unchecked(offset + i + 1); + slot.wait_write(); + let m = slot.task.get().read(); + let task = ManuallyDrop::into_inner(m); + + // Write it into the destination queue. + dest_buffer.write(dest_b.wrapping_add((batch_size - 1 - i) as isize), task); + } + } + } + + atomic::fence(Ordering::Release); + + // Update the back index in the destination queue. + // + // This ordering could be `Relaxed`, but then thread sanitizer would falsely report + // data races because it doesn't understand fences. + dest.inner + .back + .store(dest_b.wrapping_add(batch_size as isize), Ordering::Release); + + // Destroy the block if we've reached the end, or if another thread wanted to destroy + // but couldn't because we were busy reading from the slot. + if new_offset == BLOCK_CAP { + Block::destroy(block, offset); + } else { + for i in offset..new_offset { + let slot = (*block).slots.get_unchecked(i); + + if slot.state.fetch_or(READ, Ordering::AcqRel) & DESTROY != 0 { + Block::destroy(block, offset); + break; + } + } + } + + Steal::Success(task) + } + } + + /// Returns `true` if the queue is empty. + /// + /// # Examples + /// + /// ``` + /// use crossbeam_deque::Injector; + /// + /// let q = Injector::new(); + /// + /// assert!(q.is_empty()); + /// q.push(1); + /// assert!(!q.is_empty()); + /// ``` + pub fn is_empty(&self) -> bool { + let head = self.head.index.load(Ordering::SeqCst); + let tail = self.tail.index.load(Ordering::SeqCst); + head >> SHIFT == tail >> SHIFT + } +} + +impl Drop for Injector { + fn drop(&mut self) { + let mut head = self.head.index.load(Ordering::Relaxed); + let mut tail = self.tail.index.load(Ordering::Relaxed); + let mut block = self.head.block.load(Ordering::Relaxed); + + // Erase the lower bits. + head &= !((1 << SHIFT) - 1); + tail &= !((1 << SHIFT) - 1); + + unsafe { + // Drop all values between `head` and `tail` and deallocate the heap-allocated blocks. + while head != tail { + let offset = (head >> SHIFT) % LAP; + + if offset < BLOCK_CAP { + // Drop the task in the slot. + let slot = (*block).slots.get_unchecked(offset); + ManuallyDrop::drop(&mut *(*slot).task.get()); + } else { + // Deallocate the block and move to the next one. + let next = (*block).next.load(Ordering::Relaxed); + drop(Box::from_raw(block)); + block = next; + } + + head = head.wrapping_add(1 << SHIFT); + } + + // Deallocate the last remaining block. + drop(Box::from_raw(block)); + } + } +} + +impl fmt::Debug for Injector { + fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result { + f.pad("Worker { .. }") + } +} + +/// Possible outcomes of a steal operation. +/// +/// # Examples +/// +/// There are lots of ways to chain results of steal operations together: +/// +/// ``` +/// use crossbeam_deque::Steal::{self, Empty, Retry, Success}; +/// +/// let collect = |v: Vec>| v.into_iter().collect::>(); +/// +/// assert_eq!(collect(vec![Empty, Empty, Empty]), Empty); +/// assert_eq!(collect(vec![Empty, Retry, Empty]), Retry); +/// assert_eq!(collect(vec![Retry, Success(1), Empty]), Success(1)); +/// +/// assert_eq!(collect(vec![Empty, Empty]).or_else(|| Retry), Retry); +/// assert_eq!(collect(vec![Retry, Empty]).or_else(|| Success(1)), Success(1)); +/// ``` +#[must_use] +#[derive(PartialEq, Eq, Copy, Clone)] +pub enum Steal { + /// The queue was empty at the time of stealing. + Empty, + + /// At least one task was successfully stolen. + Success(T), + + /// The steal operation needs to be retried. + Retry, +} + +impl Steal { + /// Returns `true` if the queue was empty at the time of stealing. + /// + /// # Examples + /// + /// ``` + /// use crossbeam_deque::Steal::{Empty, Retry, Success}; + /// + /// assert!(!Success(7).is_empty()); + /// assert!(!Retry::.is_empty()); + /// + /// assert!(Empty::.is_empty()); + /// ``` + pub fn is_empty(&self) -> bool { + match self { + Steal::Empty => true, + _ => false, + } + } + + /// Returns `true` if at least one task was stolen. + /// + /// # Examples + /// + /// ``` + /// use crossbeam_deque::Steal::{Empty, Retry, Success}; + /// + /// assert!(!Empty::.is_success()); + /// assert!(!Retry::.is_success()); + /// + /// assert!(Success(7).is_success()); + /// ``` + pub fn is_success(&self) -> bool { + match self { + Steal::Success(_) => true, + _ => false, + } + } + + /// Returns `true` if the steal operation needs to be retried. + /// + /// # Examples + /// + /// ``` + /// use crossbeam_deque::Steal::{Empty, Retry, Success}; + /// + /// assert!(!Empty::.is_retry()); + /// assert!(!Success(7).is_retry()); + /// + /// assert!(Retry::.is_retry()); + /// ``` + pub fn is_retry(&self) -> bool { + match self { + Steal::Retry => true, + _ => false, + } + } + + /// Returns the result of the operation, if successful. + /// + /// # Examples + /// + /// ``` + /// use crossbeam_deque::Steal::{Empty, Retry, Success}; + /// + /// assert_eq!(Empty::.success(), None); + /// assert_eq!(Retry::.success(), None); + /// + /// assert_eq!(Success(7).success(), Some(7)); + /// ``` + pub fn success(self) -> Option { + match self { + Steal::Success(res) => Some(res), + _ => None, + } + } + + /// If no task was stolen, attempts another steal operation. + /// + /// Returns this steal result if it is `Success`. Otherwise, closure `f` is invoked and then: + /// + /// * If the second steal resulted in `Success`, it is returned. + /// * If both steals were unsuccessful but any resulted in `Retry`, then `Retry` is returned. + /// * If both resulted in `None`, then `None` is returned. + /// + /// # Examples + /// + /// ``` + /// use crossbeam_deque::Steal::{Empty, Retry, Success}; + /// + /// assert_eq!(Success(1).or_else(|| Success(2)), Success(1)); + /// assert_eq!(Retry.or_else(|| Success(2)), Success(2)); + /// + /// assert_eq!(Retry.or_else(|| Empty), Retry::); + /// assert_eq!(Empty.or_else(|| Retry), Retry::); + /// + /// assert_eq!(Empty.or_else(|| Empty), Empty::); + /// ``` + pub fn or_else(self, f: F) -> Steal + where + F: FnOnce() -> Steal, + { + match self { + Steal::Empty => f(), + Steal::Success(_) => self, + Steal::Retry => { + if let Steal::Success(res) = f() { + Steal::Success(res) + } else { + Steal::Retry + } + } + } + } +} + +impl fmt::Debug for Steal { + fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result { + match self { + Steal::Empty => f.pad("Empty"), + Steal::Success(_) => f.pad("Success(..)"), + Steal::Retry => f.pad("Retry"), + } + } +} + +impl FromIterator> for Steal { + /// Consumes items until a `Success` is found and returns it. + /// + /// If no `Success` was found, but there was at least one `Retry`, then returns `Retry`. + /// Otherwise, `Empty` is returned. + fn from_iter(iter: I) -> Steal + where + I: IntoIterator>, + { + let mut retry = false; + for s in iter { + match &s { + Steal::Empty => {} + Steal::Success(_) => return s, + Steal::Retry => retry = true, + } + } + + if retry { + Steal::Retry + } else { + Steal::Empty + } + } +} diff --git a/bastion-executor/src/sleepers.rs b/bastion-executor/src/sleepers.rs new file mode 100644 index 00000000..4e701295 --- /dev/null +++ b/bastion-executor/src/sleepers.rs @@ -0,0 +1,52 @@ +use std::sync::atomic::{AtomicBool, Ordering}; +use std::sync::{Condvar, Mutex}; + +/// The place where worker threads go to sleep. +/// +/// Similar to how thread parking works, if a notification comes up while no threads are sleeping, +/// the next thread that attempts to go to sleep will pick up the notification immediately. +pub struct Sleepers { + /// How many threads are currently a sleep. + sleep: Mutex, + + /// A condvar for notifying sleeping threads. + wake: Condvar, + + /// Set to `true` if a notification came up while nobody was sleeping. + notified: AtomicBool, +} + +impl Sleepers { + /// Creates a new `Sleepers`. + pub fn new() -> Sleepers { + Sleepers { + sleep: Mutex::new(0), + wake: Condvar::new(), + notified: AtomicBool::new(false), + } + } + + /// Puts the current thread to sleep. + pub fn wait(&self) { + let mut sleep = self.sleep.lock().unwrap(); + + if !self.notified.swap(false, Ordering::SeqCst) { + *sleep += 1; + let _ = self.wake.wait(sleep).unwrap(); + } + } + + /// Notifies one thread. + pub fn notify_one(&self) { + if !self.notified.load(Ordering::SeqCst) { + let mut sleep = self.sleep.lock().unwrap(); + + if *sleep > 0 { + *sleep -= 1; + self.wake.notify_one(); + } else { + self.notified.store(true, Ordering::SeqCst); + } + } + } +} diff --git a/bastion-executor/src/worker.rs b/bastion-executor/src/worker.rs new file mode 100644 index 00000000..c4eda515 --- /dev/null +++ b/bastion-executor/src/worker.rs @@ -0,0 +1,88 @@ +use std::cell::Cell; +use std::ptr; + +use super::pool; +use lightproc::prelude::*; +use super::run_queue::Worker; + +pub fn current() -> ProcStack { + get_proc_stack(|proc| proc.clone()) + .expect("`proc::current()` called outside the context of the proc") +} + +thread_local! { + static STACK: Cell<*const ProcStack> = Cell::new(ptr::null_mut()); +} + +pub(crate) fn set_stack(stack: *const ProcStack, f: F) -> R + where + F: FnOnce() -> R, +{ + struct ResetStack<'a>(&'a Cell<*const ProcStack>); + + impl Drop for ResetStack<'_> { + fn drop(&mut self) { + self.0.set(ptr::null()); + } + } + + STACK.with(|st| { + st.set(stack); + let _guard = ResetStack(st); + + f() + }) +} + +pub(crate) fn get_proc_stack(f: F) -> Option + where + F: FnOnce(&ProcStack) -> R, +{ + let res = STACK.try_with(|st| unsafe { + st.get().as_ref().map(f) + }); + + match res { + Ok(Some(val)) => Some(val), + Ok(None) | Err(_) => None, + } +} + +thread_local! { + static IS_WORKER: Cell = Cell::new(false); + static QUEUE: Cell>> = Cell::new(None); +} + +pub(crate) fn is_worker() -> bool { + IS_WORKER.with(|is_worker| is_worker.get()) +} + +fn get_queue) -> T, T>(f: F) -> T { + QUEUE.with(|queue| { + let q = queue.take().unwrap(); + let ret = f(&q); + queue.set(Some(q)); + ret + }) +} + +pub(crate) fn schedule(proc: LightProc) { + if is_worker() { + get_queue(|q| q.push(proc)); + } else { + pool::get().injector.push(proc); + } + pool::get().sleepers.notify_one(); +} + +pub(crate) fn main_loop(worker: Worker) { + IS_WORKER.with(|is_worker| is_worker.set(true)); + QUEUE.with(|queue| queue.set(Some(worker))); + + loop { + match get_queue(|q| pool::get().fetch_proc(q)) { + Some(proc) => set_stack(proc.stack(), || proc.run()), + None => pool::get().sleepers.wait(), + } + } +}