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use crate::enter;
use crate::unpark_mutex::UnparkMutex;
use futures_core::future::Future;
use futures_core::task::{Context, Poll};
use futures_task::{waker_ref, ArcWake};
use futures_task::{FutureObj, Spawn, SpawnError};
use futures_util::future::FutureExt;
use std::cmp;
use std::fmt;
use std::io;
use std::sync::atomic::{AtomicUsize, Ordering};
use std::sync::mpsc;
use std::sync::{Arc, Mutex};
use std::thread;
/// A general-purpose thread pool for scheduling tasks that poll futures to
/// completion.
///
/// The thread pool multiplexes any number of tasks onto a fixed number of
/// worker threads.
///
/// This type is a clonable handle to the threadpool itself.
/// Cloning it will only create a new reference, not a new threadpool.
///
/// This type is only available when the `thread-pool` feature of this
/// library is activated.
#[cfg_attr(docsrs, doc(cfg(feature = "thread-pool")))]
pub struct ThreadPool {
state: Arc<PoolState>,
}
/// Thread pool configuration object.
///
/// This type is only available when the `thread-pool` feature of this
/// library is activated.
#[cfg_attr(docsrs, doc(cfg(feature = "thread-pool")))]
pub struct ThreadPoolBuilder {
pool_size: usize,
stack_size: usize,
name_prefix: Option<String>,
after_start: Option<Arc<dyn Fn(usize) + Send + Sync>>,
before_stop: Option<Arc<dyn Fn(usize) + Send + Sync>>,
}
trait AssertSendSync: Send + Sync {}
impl AssertSendSync for ThreadPool {}
struct PoolState {
tx: Mutex<mpsc::Sender<Message>>,
rx: Mutex<mpsc::Receiver<Message>>,
cnt: AtomicUsize,
size: usize,
}
impl fmt::Debug for ThreadPool {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
f.debug_struct("ThreadPool").field("size", &self.state.size).finish()
}
}
impl fmt::Debug for ThreadPoolBuilder {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
f.debug_struct("ThreadPoolBuilder")
.field("pool_size", &self.pool_size)
.field("name_prefix", &self.name_prefix)
.finish()
}
}
enum Message {
Run(Task),
Close,
}
impl ThreadPool {
/// Creates a new thread pool with the default configuration.
///
/// See documentation for the methods in
/// [`ThreadPoolBuilder`](ThreadPoolBuilder) for details on the default
/// configuration.
pub fn new() -> Result<Self, io::Error> {
ThreadPoolBuilder::new().create()
}
/// Create a default thread pool configuration, which can then be customized.
///
/// See documentation for the methods in
/// [`ThreadPoolBuilder`](ThreadPoolBuilder) for details on the default
/// configuration.
pub fn builder() -> ThreadPoolBuilder {
ThreadPoolBuilder::new()
}
/// Spawns a future that will be run to completion.
///
/// > **Note**: This method is similar to `Spawn::spawn_obj`, except that
/// > it is guaranteed to always succeed.
pub fn spawn_obj_ok(&self, future: FutureObj<'static, ()>) {
let task = Task {
future,
wake_handle: Arc::new(WakeHandle { exec: self.clone(), mutex: UnparkMutex::new() }),
exec: self.clone(),
};
self.state.send(Message::Run(task));
}
/// Spawns a task that polls the given future with output `()` to
/// completion.
///
/// ```
/// # {
/// use futures::executor::ThreadPool;
///
/// let pool = ThreadPool::new().unwrap();
///
/// let future = async { /* ... */ };
/// pool.spawn_ok(future);
/// # }
/// # std::thread::sleep(std::time::Duration::from_millis(500)); // wait for background threads closed: https://github.com/rust-lang/miri/issues/1371
/// ```
///
/// > **Note**: This method is similar to `SpawnExt::spawn`, except that
/// > it is guaranteed to always succeed.
pub fn spawn_ok<Fut>(&self, future: Fut)
where
Fut: Future<Output = ()> + Send + 'static,
{
self.spawn_obj_ok(FutureObj::new(Box::new(future)))
}
}
impl Spawn for ThreadPool {
fn spawn_obj(&self, future: FutureObj<'static, ()>) -> Result<(), SpawnError> {
self.spawn_obj_ok(future);
Ok(())
}
}
impl PoolState {
fn send(&self, msg: Message) {
self.tx.lock().unwrap().send(msg).unwrap();
}
fn work(
&self,
idx: usize,
after_start: Option<Arc<dyn Fn(usize) + Send + Sync>>,
before_stop: Option<Arc<dyn Fn(usize) + Send + Sync>>,
) {
let _scope = enter().unwrap();
if let Some(after_start) = after_start {
after_start(idx);
}
loop {
let msg = self.rx.lock().unwrap().recv().unwrap();
match msg {
Message::Run(task) => task.run(),
Message::Close => break,
}
}
if let Some(before_stop) = before_stop {
before_stop(idx);
}
}
}
impl Clone for ThreadPool {
fn clone(&self) -> Self {
self.state.cnt.fetch_add(1, Ordering::Relaxed);
Self { state: self.state.clone() }
}
}
impl Drop for ThreadPool {
fn drop(&mut self) {
if self.state.cnt.fetch_sub(1, Ordering::Relaxed) == 1 {
for _ in 0..self.state.size {
self.state.send(Message::Close);
}
}
}
}
impl ThreadPoolBuilder {
/// Create a default thread pool configuration.
///
/// See the other methods on this type for details on the defaults.
pub fn new() -> Self {
Self {
pool_size: cmp::max(1, num_cpus::get()),
stack_size: 0,
name_prefix: None,
after_start: None,
before_stop: None,
}
}
/// Set size of a future ThreadPool
///
/// The size of a thread pool is the number of worker threads spawned. By
/// default, this is equal to the number of CPU cores.
///
/// # Panics
///
/// Panics if `pool_size == 0`.
pub fn pool_size(&mut self, size: usize) -> &mut Self {
assert!(size > 0);
self.pool_size = size;
self
}
/// Set stack size of threads in the pool, in bytes.
///
/// By default, worker threads use Rust's standard stack size.
pub fn stack_size(&mut self, stack_size: usize) -> &mut Self {
self.stack_size = stack_size;
self
}
/// Set thread name prefix of a future ThreadPool.
///
/// Thread name prefix is used for generating thread names. For example, if prefix is
/// `my-pool-`, then threads in the pool will get names like `my-pool-1` etc.
///
/// By default, worker threads are assigned Rust's standard thread name.
pub fn name_prefix<S: Into<String>>(&mut self, name_prefix: S) -> &mut Self {
self.name_prefix = Some(name_prefix.into());
self
}
/// Execute the closure `f` immediately after each worker thread is started,
/// but before running any tasks on it.
///
/// This hook is intended for bookkeeping and monitoring.
/// The closure `f` will be dropped after the `builder` is dropped
/// and all worker threads in the pool have executed it.
///
/// The closure provided will receive an index corresponding to the worker
/// thread it's running on.
pub fn after_start<F>(&mut self, f: F) -> &mut Self
where
F: Fn(usize) + Send + Sync + 'static,
{
self.after_start = Some(Arc::new(f));
self
}
/// Execute closure `f` just prior to shutting down each worker thread.
///
/// This hook is intended for bookkeeping and monitoring.
/// The closure `f` will be dropped after the `builder` is dropped
/// and all threads in the pool have executed it.
///
/// The closure provided will receive an index corresponding to the worker
/// thread it's running on.
pub fn before_stop<F>(&mut self, f: F) -> &mut Self
where
F: Fn(usize) + Send + Sync + 'static,
{
self.before_stop = Some(Arc::new(f));
self
}
/// Create a [`ThreadPool`](ThreadPool) with the given configuration.
pub fn create(&mut self) -> Result<ThreadPool, io::Error> {
let (tx, rx) = mpsc::channel();
let pool = ThreadPool {
state: Arc::new(PoolState {
tx: Mutex::new(tx),
rx: Mutex::new(rx),
cnt: AtomicUsize::new(1),
size: self.pool_size,
}),
};
for counter in 0..self.pool_size {
let state = pool.state.clone();
let after_start = self.after_start.clone();
let before_stop = self.before_stop.clone();
let mut thread_builder = thread::Builder::new();
if let Some(ref name_prefix) = self.name_prefix {
thread_builder = thread_builder.name(format!("{}{}", name_prefix, counter));
}
if self.stack_size > 0 {
thread_builder = thread_builder.stack_size(self.stack_size);
}
thread_builder.spawn(move || state.work(counter, after_start, before_stop))?;
}
Ok(pool)
}
}
impl Default for ThreadPoolBuilder {
fn default() -> Self {
Self::new()
}
}
/// A task responsible for polling a future to completion.
struct Task {
future: FutureObj<'static, ()>,
exec: ThreadPool,
wake_handle: Arc<WakeHandle>,
}
struct WakeHandle {
mutex: UnparkMutex<Task>,
exec: ThreadPool,
}
impl Task {
/// Actually run the task (invoking `poll` on the future) on the current
/// thread.
fn run(self) {
let Self { mut future, wake_handle, mut exec } = self;
let waker = waker_ref(&wake_handle);
let mut cx = Context::from_waker(&waker);
// Safety: The ownership of this `Task` object is evidence that
// we are in the `POLLING`/`REPOLL` state for the mutex.
unsafe {
wake_handle.mutex.start_poll();
loop {
let res = future.poll_unpin(&mut cx);
match res {
Poll::Pending => {}
Poll::Ready(()) => return wake_handle.mutex.complete(),
}
let task = Self { future, wake_handle: wake_handle.clone(), exec };
match wake_handle.mutex.wait(task) {
Ok(()) => return, // we've waited
Err(task) => {
// someone's notified us
future = task.future;
exec = task.exec;
}
}
}
}
}
}
impl fmt::Debug for Task {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
f.debug_struct("Task").field("contents", &"...").finish()
}
}
impl ArcWake for WakeHandle {
fn wake_by_ref(arc_self: &Arc<Self>) {
if let Ok(task) = arc_self.mutex.notify() {
arc_self.exec.state.send(Message::Run(task))
}
}
}
#[cfg(test)]
mod tests {
use super::*;
use std::sync::mpsc;
#[test]
fn test_drop_after_start() {
{
let (tx, rx) = mpsc::sync_channel(2);
let _cpu_pool = ThreadPoolBuilder::new()
.pool_size(2)
.after_start(move |_| tx.send(1).unwrap())
.create()
.unwrap();
// After ThreadPoolBuilder is deconstructed, the tx should be dropped
// so that we can use rx as an iterator.
let count = rx.into_iter().count();
assert_eq!(count, 2);
}
std::thread::sleep(std::time::Duration::from_millis(500)); // wait for background threads closed: https://github.com/rust-lang/miri/issues/1371
}
}