1 // Copyright 2014 The Rust Project Developers. See the COPYRIGHT
2 // file at the top-level directory of this distribution and at
3 // http://rust-lang.org/COPYRIGHT.
5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
8 // option. This file may not be copied, modified, or distributed
9 // except according to those terms.
13 //! ## The threading model
15 //! An executing Rust program consists of a collection of native OS threads,
16 //! each with their own stack and local state. Threads can be named, and
17 //! provide some built-in support for low-level synchronization.
19 //! Communication between threads can be done through
20 //! [channels], Rust's message-passing types, along with [other forms of thread
21 //! synchronization](../../std/sync/index.html) and shared-memory data
22 //! structures. In particular, types that are guaranteed to be
23 //! threadsafe are easily shared between threads using the
24 //! atomically-reference-counted container, [`Arc`].
26 //! Fatal logic errors in Rust cause *thread panic*, during which
27 //! a thread will unwind the stack, running destructors and freeing
28 //! owned resources. While not meant as a 'try/catch' mechanism, panics
29 //! in Rust can nonetheless be caught (unless compiling with `panic=abort`) with
30 //! [`catch_unwind`](../../std/panic/fn.catch_unwind.html) and recovered
31 //! from, or alternatively be resumed with
32 //! [`resume_unwind`](../../std/panic/fn.resume_unwind.html). If the panic
33 //! is not caught the thread will exit, but the panic may optionally be
34 //! detected from a different thread with [`join`]. If the main thread panics
35 //! without the panic being caught, the application will exit with a
36 //! non-zero exit code.
38 //! When the main thread of a Rust program terminates, the entire program shuts
39 //! down, even if other threads are still running. However, this module provides
40 //! convenient facilities for automatically waiting for the termination of a
41 //! child thread (i.e., join).
43 //! ## Spawning a thread
45 //! A new thread can be spawned using the [`thread::spawn`][`spawn`] function:
50 //! thread::spawn(move || {
55 //! In this example, the spawned thread is "detached" from the current
56 //! thread. This means that it can outlive its parent (the thread that spawned
57 //! it), unless this parent is the main thread.
59 //! The parent thread can also wait on the completion of the child
60 //! thread; a call to [`spawn`] produces a [`JoinHandle`], which provides
61 //! a `join` method for waiting:
66 //! let child = thread::spawn(move || {
70 //! let res = child.join();
73 //! The [`join`] method returns a [`thread::Result`] containing [`Ok`] of the final
74 //! value produced by the child thread, or [`Err`] of the value given to
75 //! a call to [`panic!`] if the child panicked.
77 //! ## Configuring threads
79 //! A new thread can be configured before it is spawned via the [`Builder`] type,
80 //! which currently allows you to set the name and stack size for the child thread:
83 //! # #![allow(unused_must_use)]
86 //! thread::Builder::new().name("child1".to_string()).spawn(move || {
87 //! println!("Hello, world!");
91 //! ## The `Thread` type
93 //! Threads are represented via the [`Thread`] type, which you can get in one of
96 //! * By spawning a new thread, e.g. using the [`thread::spawn`][`spawn`]
97 //! function, and calling [`thread`][`JoinHandle::thread`] on the [`JoinHandle`].
98 //! * By requesting the current thread, using the [`thread::current`] function.
100 //! The [`thread::current`] function is available even for threads not spawned
101 //! by the APIs of this module.
103 //! ## Thread-local storage
105 //! This module also provides an implementation of thread-local storage for Rust
106 //! programs. Thread-local storage is a method of storing data into a global
107 //! variable that each thread in the program will have its own copy of.
108 //! Threads do not share this data, so accesses do not need to be synchronized.
110 //! A thread-local key owns the value it contains and will destroy the value when the
111 //! thread exits. It is created with the [`thread_local!`] macro and can contain any
112 //! value that is `'static` (no borrowed pointers). It provides an accessor function,
113 //! [`with`], that yields a shared reference to the value to the specified
114 //! closure. Thread-local keys allow only shared access to values, as there would be no
115 //! way to guarantee uniqueness if mutable borrows were allowed. Most values
116 //! will want to make use of some form of **interior mutability** through the
117 //! [`Cell`] or [`RefCell`] types.
119 //! ## Naming threads
121 //! Threads are able to have associated names for identification purposes. By default, spawned
122 //! threads are unnamed. To specify a name for a thread, build the thread with [`Builder`] and pass
123 //! the desired thread name to [`Builder::name`]. To retrieve the thread name from within the
124 //! thread, use [`Thread::name`]. A couple examples of where the name of a thread gets used:
126 //! * If a panic occurs in a named thread, the thread name will be printed in the panic message.
127 //! * The thread name is provided to the OS where applicable (e.g. `pthread_setname_np` in
128 //! unix-like platforms).
132 //! The default stack size for spawned threads is 2 MiB, though this particular stack size is
133 //! subject to change in the future. There are two ways to manually specify the stack size for
136 //! * Build the thread with [`Builder`] and pass the desired stack size to [`Builder::stack_size`].
137 //! * Set the `RUST_MIN_STACK` environment variable to an integer representing the desired stack
138 //! size (in bytes). Note that setting [`Builder::stack_size`] will override this.
140 //! Note that the stack size of the main thread is *not* determined by Rust.
142 //! [channels]: ../../std/sync/mpsc/index.html
143 //! [`Arc`]: ../../std/sync/struct.Arc.html
144 //! [`spawn`]: ../../std/thread/fn.spawn.html
145 //! [`JoinHandle`]: ../../std/thread/struct.JoinHandle.html
146 //! [`JoinHandle::thread`]: ../../std/thread/struct.JoinHandle.html#method.thread
147 //! [`join`]: ../../std/thread/struct.JoinHandle.html#method.join
148 //! [`Result`]: ../../std/result/enum.Result.html
149 //! [`Ok`]: ../../std/result/enum.Result.html#variant.Ok
150 //! [`Err`]: ../../std/result/enum.Result.html#variant.Err
151 //! [`panic!`]: ../../std/macro.panic.html
152 //! [`Builder`]: ../../std/thread/struct.Builder.html
153 //! [`Builder::stack_size`]: ../../std/thread/struct.Builder.html#method.stack_size
154 //! [`Builder::name`]: ../../std/thread/struct.Builder.html#method.name
155 //! [`thread::current`]: ../../std/thread/fn.current.html
156 //! [`thread::Result`]: ../../std/thread/type.Result.html
157 //! [`Thread`]: ../../std/thread/struct.Thread.html
158 //! [`park`]: ../../std/thread/fn.park.html
159 //! [`unpark`]: ../../std/thread/struct.Thread.html#method.unpark
160 //! [`Thread::name`]: ../../std/thread/struct.Thread.html#method.name
161 //! [`thread::park_timeout`]: ../../std/thread/fn.park_timeout.html
162 //! [`Cell`]: ../cell/struct.Cell.html
163 //! [`RefCell`]: ../cell/struct.RefCell.html
164 //! [`thread_local!`]: ../macro.thread_local.html
165 //! [`with`]: struct.LocalKey.html#method.with
167 #![stable(feature = "rust1", since = "1.0.0")]
170 use cell::UnsafeCell;
171 use ffi::{CStr, CString};
177 use sync::{Mutex, Condvar, Arc};
178 use sync::atomic::AtomicUsize;
179 use sync::atomic::Ordering::SeqCst;
180 use sys::thread as imp;
181 use sys_common::mutex;
182 use sys_common::thread_info;
183 use sys_common::thread;
184 use sys_common::{AsInner, IntoInner};
187 ////////////////////////////////////////////////////////////////////////////////
188 // Thread-local storage
189 ////////////////////////////////////////////////////////////////////////////////
191 #[macro_use] mod local;
193 #[stable(feature = "rust1", since = "1.0.0")]
194 pub use self::local::{LocalKey, AccessError};
196 // The types used by the thread_local! macro to access TLS keys. Note that there
197 // are two types, the "OS" type and the "fast" type. The OS thread local key
198 // type is accessed via platform-specific API calls and is slow, while the fast
199 // key type is accessed via code generated via LLVM, where TLS keys are set up
200 // by the elf linker. Note that the OS TLS type is always available: on macOS
201 // the standard library is compiled with support for older platform versions
202 // where fast TLS was not available; end-user code is compiled with fast TLS
203 // where available, but both are needed.
205 #[unstable(feature = "libstd_thread_internals", issue = "0")]
206 #[cfg(target_arch = "wasm32")]
207 #[doc(hidden)] pub use self::local::statik::Key as __StaticLocalKeyInner;
208 #[unstable(feature = "libstd_thread_internals", issue = "0")]
209 #[cfg(target_thread_local)]
210 #[doc(hidden)] pub use self::local::fast::Key as __FastLocalKeyInner;
211 #[unstable(feature = "libstd_thread_internals", issue = "0")]
212 #[doc(hidden)] pub use self::local::os::Key as __OsLocalKeyInner;
214 ////////////////////////////////////////////////////////////////////////////////
216 ////////////////////////////////////////////////////////////////////////////////
218 /// Thread factory, which can be used in order to configure the properties of
221 /// Methods can be chained on it in order to configure it.
223 /// The two configurations available are:
225 /// - [`name`]: specifies an [associated name for the thread][naming-threads]
226 /// - [`stack_size`]: specifies the [desired stack size for the thread][stack-size]
228 /// The [`spawn`] method will take ownership of the builder and create an
229 /// [`io::Result`] to the thread handle with the given configuration.
231 /// The [`thread::spawn`] free function uses a `Builder` with default
232 /// configuration and [`unwrap`]s its return value.
234 /// You may want to use [`spawn`] instead of [`thread::spawn`], when you want
235 /// to recover from a failure to launch a thread, indeed the free function will
236 /// panick where the `Builder` method will return a [`io::Result`].
243 /// let builder = thread::Builder::new();
245 /// let handler = builder.spawn(|| {
249 /// handler.join().unwrap();
252 /// [`thread::spawn`]: ../../std/thread/fn.spawn.html
253 /// [`stack_size`]: ../../std/thread/struct.Builder.html#method.stack_size
254 /// [`name`]: ../../std/thread/struct.Builder.html#method.name
255 /// [`spawn`]: ../../std/thread/struct.Builder.html#method.spawn
256 /// [`io::Result`]: ../../std/io/type.Result.html
257 /// [`unwrap`]: ../../std/result/enum.Result.html#method.unwrap
258 /// [naming-threads]: ./index.html#naming-threads
259 /// [stack-size]: ./index.html#stack-size
260 #[stable(feature = "rust1", since = "1.0.0")]
263 // A name for the thread-to-be, for identification in panic messages
264 name: Option<String>,
265 // The size of the stack for the spawned thread in bytes
266 stack_size: Option<usize>,
270 /// Generates the base configuration for spawning a thread, from which
271 /// configuration methods can be chained.
278 /// let builder = thread::Builder::new()
279 /// .name("foo".into())
282 /// let handler = builder.spawn(|| {
286 /// handler.join().unwrap();
288 #[stable(feature = "rust1", since = "1.0.0")]
289 pub fn new() -> Builder {
296 /// Names the thread-to-be. Currently the name is used for identification
297 /// only in panic messages.
299 /// The name must not contain null bytes (`\0`).
301 /// For more information about named threads, see
302 /// [this module-level documentation][naming-threads].
309 /// let builder = thread::Builder::new()
310 /// .name("foo".into());
312 /// let handler = builder.spawn(|| {
313 /// assert_eq!(thread::current().name(), Some("foo"))
316 /// handler.join().unwrap();
319 /// [naming-threads]: ./index.html#naming-threads
320 #[stable(feature = "rust1", since = "1.0.0")]
321 pub fn name(mut self, name: String) -> Builder {
322 self.name = Some(name);
326 /// Sets the size of the stack (in bytes) for the new thread.
328 /// The actual stack size may be greater than this value if
329 /// the platform specifies minimal stack size.
331 /// For more information about the stack size for threads, see
332 /// [this module-level documentation][stack-size].
339 /// let builder = thread::Builder::new().stack_size(32 * 1024);
342 /// [stack-size]: ./index.html#stack-size
343 #[stable(feature = "rust1", since = "1.0.0")]
344 pub fn stack_size(mut self, size: usize) -> Builder {
345 self.stack_size = Some(size);
349 /// Spawns a new thread by taking ownership of the `Builder`, and returns an
350 /// [`io::Result`] to its [`JoinHandle`].
352 /// The spawned thread may outlive the caller (unless the caller thread
353 /// is the main thread; the whole process is terminated when the main
354 /// thread finishes). The join handle can be used to block on
355 /// termination of the child thread, including recovering its panics.
357 /// For a more complete documentation see [`thread::spawn`][`spawn`].
361 /// Unlike the [`spawn`] free function, this method yields an
362 /// [`io::Result`] to capture any failure to create the thread at
365 /// [`spawn`]: ../../std/thread/fn.spawn.html
366 /// [`io::Result`]: ../../std/io/type.Result.html
367 /// [`JoinHandle`]: ../../std/thread/struct.JoinHandle.html
371 /// Panics if a thread name was set and it contained null bytes.
378 /// let builder = thread::Builder::new();
380 /// let handler = builder.spawn(|| {
384 /// handler.join().unwrap();
386 #[stable(feature = "rust1", since = "1.0.0")]
387 pub fn spawn<F, T>(self, f: F) -> io::Result<JoinHandle<T>> where
388 F: FnOnce() -> T, F: Send + 'static, T: Send + 'static
390 let Builder { name, stack_size } = self;
392 let stack_size = stack_size.unwrap_or_else(thread::min_stack);
394 let my_thread = Thread::new(name);
395 let their_thread = my_thread.clone();
397 let my_packet : Arc<UnsafeCell<Option<Result<T>>>>
398 = Arc::new(UnsafeCell::new(None));
399 let their_packet = my_packet.clone();
402 if let Some(name) = their_thread.cname() {
403 imp::Thread::set_name(name);
406 thread_info::set(imp::guard::current(), their_thread);
407 #[cfg(feature = "backtrace")]
408 let try_result = panic::catch_unwind(panic::AssertUnwindSafe(|| {
409 ::sys_common::backtrace::__rust_begin_short_backtrace(f)
411 #[cfg(not(feature = "backtrace"))]
412 let try_result = panic::catch_unwind(panic::AssertUnwindSafe(f));
413 *their_packet.get() = Some(try_result);
417 Ok(JoinHandle(JoinInner {
419 Some(imp::Thread::new(stack_size, Box::new(main))?)
422 packet: Packet(my_packet),
427 ////////////////////////////////////////////////////////////////////////////////
429 ////////////////////////////////////////////////////////////////////////////////
431 /// Spawns a new thread, returning a [`JoinHandle`] for it.
433 /// The join handle will implicitly *detach* the child thread upon being
434 /// dropped. In this case, the child thread may outlive the parent (unless
435 /// the parent thread is the main thread; the whole process is terminated when
436 /// the main thread finishes). Additionally, the join handle provides a [`join`]
437 /// method that can be used to join the child thread. If the child thread
438 /// panics, [`join`] will return an [`Err`] containing the argument given to
441 /// This will create a thread using default parameters of [`Builder`], if you
442 /// want to specify the stack size or the name of the thread, use this API
445 /// As you can see in the signature of `spawn` there are two constraints on
446 /// both the closure given to `spawn` and its return value, let's explain them:
448 /// - The `'static` constraint means that the closure and its return value
449 /// must have a lifetime of the whole program execution. The reason for this
450 /// is that threads can `detach` and outlive the lifetime they have been
452 /// Indeed if the thread, and by extension its return value, can outlive their
453 /// caller, we need to make sure that they will be valid afterwards, and since
454 /// we *can't* know when it will return we need to have them valid as long as
455 /// possible, that is until the end of the program, hence the `'static`
457 /// - The [`Send`] constraint is because the closure will need to be passed
458 /// *by value* from the thread where it is spawned to the new thread. Its
459 /// return value will need to be passed from the new thread to the thread
460 /// where it is `join`ed.
461 /// As a reminder, the [`Send`] marker trait expresses that it is safe to be
462 /// passed from thread to thread. [`Sync`] expresses that it is safe to have a
463 /// reference be passed from thread to thread.
467 /// Panics if the OS fails to create a thread; use [`Builder::spawn`]
468 /// to recover from such errors.
472 /// Creating a thread.
477 /// let handler = thread::spawn(|| {
481 /// handler.join().unwrap();
484 /// As mentioned in the module documentation, threads are usually made to
485 /// communicate using [`channels`], here is how it usually looks.
487 /// This example also shows how to use `move`, in order to give ownership
488 /// of values to a thread.
492 /// use std::sync::mpsc::channel;
494 /// let (tx, rx) = channel();
496 /// let sender = thread::spawn(move || {
497 /// tx.send("Hello, thread".to_owned())
498 /// .expect("Unable to send on channel");
501 /// let receiver = thread::spawn(move || {
502 /// let value = rx.recv().expect("Unable to receive from channel");
503 /// println!("{}", value);
506 /// sender.join().expect("The sender thread has panicked");
507 /// receiver.join().expect("The receiver thread has panicked");
510 /// A thread can also return a value through its [`JoinHandle`], you can use
511 /// this to make asynchronous computations (futures might be more appropriate
517 /// let computation = thread::spawn(|| {
518 /// // Some expensive computation.
522 /// let result = computation.join().unwrap();
523 /// println!("{}", result);
526 /// [`channels`]: ../../std/sync/mpsc/index.html
527 /// [`JoinHandle`]: ../../std/thread/struct.JoinHandle.html
528 /// [`join`]: ../../std/thread/struct.JoinHandle.html#method.join
529 /// [`Err`]: ../../std/result/enum.Result.html#variant.Err
530 /// [`panic`]: ../../std/macro.panic.html
531 /// [`Builder::spawn`]: ../../std/thread/struct.Builder.html#method.spawn
532 /// [`Builder`]: ../../std/thread/struct.Builder.html
533 /// [`Send`]: ../../std/marker/trait.Send.html
534 /// [`Sync`]: ../../std/marker/trait.Sync.html
535 #[stable(feature = "rust1", since = "1.0.0")]
536 pub fn spawn<F, T>(f: F) -> JoinHandle<T> where
537 F: FnOnce() -> T, F: Send + 'static, T: Send + 'static
539 Builder::new().spawn(f).unwrap()
542 /// Gets a handle to the thread that invokes it.
546 /// Getting a handle to the current thread with `thread::current()`:
551 /// let handler = thread::Builder::new()
552 /// .name("named thread".into())
554 /// let handle = thread::current();
555 /// assert_eq!(handle.name(), Some("named thread"));
559 /// handler.join().unwrap();
561 #[stable(feature = "rust1", since = "1.0.0")]
562 pub fn current() -> Thread {
563 thread_info::current_thread().expect("use of std::thread::current() is not \
564 possible after the thread's local \
565 data has been destroyed")
568 /// Cooperatively gives up a timeslice to the OS scheduler.
570 /// This is used when the programmer knows that the thread will have nothing
571 /// to do for some time, and thus avoid wasting computing time.
573 /// For example when polling on a resource, it is common to check that it is
574 /// available, and if not to yield in order to avoid busy waiting.
576 /// Thus the pattern of `yield`ing after a failed poll is rather common when
577 /// implementing low-level shared resources or synchronization primitives.
579 /// However programmers will usually prefer to use, [`channel`]s, [`Condvar`]s,
580 /// [`Mutex`]es or [`join`] for their synchronization routines, as they avoid
581 /// thinking about thread scheduling.
583 /// Note that [`channel`]s for example are implemented using this primitive.
584 /// Indeed when you call `send` or `recv`, which are blocking, they will yield
585 /// if the channel is not available.
592 /// thread::yield_now();
595 /// [`channel`]: ../../std/sync/mpsc/index.html
596 /// [`spawn`]: ../../std/thread/fn.spawn.html
597 /// [`join`]: ../../std/thread/struct.JoinHandle.html#method.join
598 /// [`Mutex`]: ../../std/sync/struct.Mutex.html
599 /// [`Condvar`]: ../../std/sync/struct.Condvar.html
600 #[stable(feature = "rust1", since = "1.0.0")]
602 imp::Thread::yield_now()
605 /// Determines whether the current thread is unwinding because of panic.
607 /// A common use of this feature is to poison shared resources when writing
608 /// unsafe code, by checking `panicking` when the `drop` is called.
610 /// This is usually not needed when writing safe code, as [`Mutex`es][Mutex]
611 /// already poison themselves when a thread panics while holding the lock.
613 /// This can also be used in multithreaded applications, in order to send a
614 /// message to other threads warning that a thread has panicked (e.g. for
615 /// monitoring purposes).
622 /// struct SomeStruct;
624 /// impl Drop for SomeStruct {
625 /// fn drop(&mut self) {
626 /// if thread::panicking() {
627 /// println!("dropped while unwinding");
629 /// println!("dropped while not unwinding");
636 /// let a = SomeStruct;
641 /// let b = SomeStruct;
646 /// [Mutex]: ../../std/sync/struct.Mutex.html
648 #[stable(feature = "rust1", since = "1.0.0")]
649 pub fn panicking() -> bool {
650 panicking::panicking()
653 /// Puts the current thread to sleep for the specified amount of time.
655 /// The thread may sleep longer than the duration specified due to scheduling
656 /// specifics or platform-dependent functionality.
658 /// # Platform-specific behavior
660 /// On Unix platforms this function will not return early due to a
661 /// signal being received or a spurious wakeup.
668 /// // Let's sleep for 2 seconds:
669 /// thread::sleep_ms(2000);
671 #[stable(feature = "rust1", since = "1.0.0")]
672 #[rustc_deprecated(since = "1.6.0", reason = "replaced by `std::thread::sleep`")]
673 pub fn sleep_ms(ms: u32) {
674 sleep(Duration::from_millis(ms as u64))
677 /// Puts the current thread to sleep for the specified amount of time.
679 /// The thread may sleep longer than the duration specified due to scheduling
680 /// specifics or platform-dependent functionality.
682 /// # Platform-specific behavior
684 /// On Unix platforms this function will not return early due to a
685 /// signal being received or a spurious wakeup. Platforms which do not support
686 /// nanosecond precision for sleeping will have `dur` rounded up to the nearest
687 /// granularity of time they can sleep for.
692 /// use std::{thread, time};
694 /// let ten_millis = time::Duration::from_millis(10);
695 /// let now = time::Instant::now();
697 /// thread::sleep(ten_millis);
699 /// assert!(now.elapsed() >= ten_millis);
701 #[stable(feature = "thread_sleep", since = "1.4.0")]
702 pub fn sleep(dur: Duration) {
703 imp::Thread::sleep(dur)
706 // constants for park/unpark
707 const EMPTY: usize = 0;
708 const PARKED: usize = 1;
709 const NOTIFIED: usize = 2;
711 /// Blocks unless or until the current thread's token is made available.
713 /// A call to `park` does not guarantee that the thread will remain parked
714 /// forever, and callers should be prepared for this possibility.
716 /// # park and unpark
718 /// Every thread is equipped with some basic low-level blocking support, via the
719 /// [`thread::park`][`park`] function and [`thread::Thread::unpark`][`unpark`]
720 /// method. [`park`] blocks the current thread, which can then be resumed from
721 /// another thread by calling the [`unpark`] method on the blocked thread's
724 /// Conceptually, each [`Thread`] handle has an associated token, which is
725 /// initially not present:
727 /// * The [`thread::park`][`park`] function blocks the current thread unless or
728 /// until the token is available for its thread handle, at which point it
729 /// atomically consumes the token. It may also return *spuriously*, without
730 /// consuming the token. [`thread::park_timeout`] does the same, but allows
731 /// specifying a maximum time to block the thread for.
733 /// * The [`unpark`] method on a [`Thread`] atomically makes the token available
734 /// if it wasn't already. Because the token is initially absent, [`unpark`]
735 /// followed by [`park`] will result in the second call returning immediately.
737 /// In other words, each [`Thread`] acts a bit like a spinlock that can be
738 /// locked and unlocked using `park` and `unpark`.
740 /// The API is typically used by acquiring a handle to the current thread,
741 /// placing that handle in a shared data structure so that other threads can
742 /// find it, and then `park`ing. When some desired condition is met, another
743 /// thread calls [`unpark`] on the handle.
745 /// The motivation for this design is twofold:
747 /// * It avoids the need to allocate mutexes and condvars when building new
748 /// synchronization primitives; the threads already provide basic
749 /// blocking/signaling.
751 /// * It can be implemented very efficiently on many platforms.
757 /// use std::time::Duration;
759 /// let parked_thread = thread::Builder::new()
761 /// println!("Parking thread");
763 /// println!("Thread unparked");
767 /// // Let some time pass for the thread to be spawned.
768 /// thread::sleep(Duration::from_millis(10));
770 /// // There is no race condition here, if `unpark`
771 /// // happens first, `park` will return immediately.
772 /// println!("Unpark the thread");
773 /// parked_thread.thread().unpark();
775 /// parked_thread.join().unwrap();
778 /// [`Thread`]: ../../std/thread/struct.Thread.html
779 /// [`park`]: ../../std/thread/fn.park.html
780 /// [`unpark`]: ../../std/thread/struct.Thread.html#method.unpark
781 /// [`thread::park_timeout`]: ../../std/thread/fn.park_timeout.html
783 // The implementation currently uses the trivial strategy of a Mutex+Condvar
784 // with wakeup flag, which does not actually allow spurious wakeups. In the
785 // future, this will be implemented in a more efficient way, perhaps along the lines of
786 // http://cr.openjdk.java.net/~stefank/6989984.1/raw_files/new/src/os/linux/vm/os_linux.cpp
787 // or futuxes, and in either case may allow spurious wakeups.
788 #[stable(feature = "rust1", since = "1.0.0")]
790 let thread = current();
792 // If we were previously notified then we consume this notification and
794 if thread.inner.state.compare_exchange(NOTIFIED, EMPTY, SeqCst, SeqCst).is_ok() {
798 // Otherwise we need to coordinate going to sleep
799 let mut m = thread.inner.lock.lock().unwrap();
800 match thread.inner.state.compare_exchange(EMPTY, PARKED, SeqCst, SeqCst) {
803 thread.inner.state.store(EMPTY, SeqCst);
805 } // should consume this notification, so prohibit spurious wakeups in next park.
806 Err(_) => panic!("inconsistent park state"),
809 m = thread.inner.cvar.wait(m).unwrap();
810 match thread.inner.state.compare_exchange(NOTIFIED, EMPTY, SeqCst, SeqCst) {
811 Ok(_) => return, // got a notification
812 Err(_) => {} // spurious wakeup, go back to sleep
817 /// Use [`park_timeout`].
819 /// Blocks unless or until the current thread's token is made available or
820 /// the specified duration has been reached (may wake spuriously).
822 /// The semantics of this function are equivalent to [`park`] except
823 /// that the thread will be blocked for roughly no longer than `dur`. This
824 /// method should not be used for precise timing due to anomalies such as
825 /// preemption or platform differences that may not cause the maximum
826 /// amount of time waited to be precisely `ms` long.
828 /// See the [park documentation][`park`] for more detail.
830 /// [`park_timeout`]: fn.park_timeout.html
831 /// [`park`]: ../../std/thread/fn.park.html
832 #[stable(feature = "rust1", since = "1.0.0")]
833 #[rustc_deprecated(since = "1.6.0", reason = "replaced by `std::thread::park_timeout`")]
834 pub fn park_timeout_ms(ms: u32) {
835 park_timeout(Duration::from_millis(ms as u64))
838 /// Blocks unless or until the current thread's token is made available or
839 /// the specified duration has been reached (may wake spuriously).
841 /// The semantics of this function are equivalent to [`park`][park] except
842 /// that the thread will be blocked for roughly no longer than `dur`. This
843 /// method should not be used for precise timing due to anomalies such as
844 /// preemption or platform differences that may not cause the maximum
845 /// amount of time waited to be precisely `dur` long.
847 /// See the [park documentation][park] for more details.
849 /// # Platform-specific behavior
851 /// Platforms which do not support nanosecond precision for sleeping will have
852 /// `dur` rounded up to the nearest granularity of time they can sleep for.
856 /// Waiting for the complete expiration of the timeout:
859 /// use std::thread::park_timeout;
860 /// use std::time::{Instant, Duration};
862 /// let timeout = Duration::from_secs(2);
863 /// let beginning_park = Instant::now();
865 /// let mut timeout_remaining = timeout;
867 /// park_timeout(timeout_remaining);
868 /// let elapsed = beginning_park.elapsed();
869 /// if elapsed >= timeout {
872 /// println!("restarting park_timeout after {:?}", elapsed);
873 /// timeout_remaining = timeout - elapsed;
877 /// [park]: fn.park.html
878 #[stable(feature = "park_timeout", since = "1.4.0")]
879 pub fn park_timeout(dur: Duration) {
880 let thread = current();
882 // Like `park` above we have a fast path for an already-notified thread, and
883 // afterwards we start coordinating for a sleep.
885 if thread.inner.state.compare_exchange(NOTIFIED, EMPTY, SeqCst, SeqCst).is_ok() {
888 let m = thread.inner.lock.lock().unwrap();
889 match thread.inner.state.compare_exchange(EMPTY, PARKED, SeqCst, SeqCst) {
892 thread.inner.state.store(EMPTY, SeqCst);
894 } // should consume this notification, so prohibit spurious wakeups in next park.
895 Err(_) => panic!("inconsistent park_timeout state"),
898 // Wait with a timeout, and if we spuriously wake up or otherwise wake up
899 // from a notification we just want to unconditionally set the state back to
900 // empty, either consuming a notification or un-flagging ourselves as
902 let (_m, _result) = thread.inner.cvar.wait_timeout(m, dur).unwrap();
903 match thread.inner.state.swap(EMPTY, SeqCst) {
904 NOTIFIED => {} // got a notification, hurray!
905 PARKED => {} // no notification, alas
906 n => panic!("inconsistent park_timeout state: {}", n),
910 ////////////////////////////////////////////////////////////////////////////////
912 ////////////////////////////////////////////////////////////////////////////////
914 /// A unique identifier for a running thread.
916 /// A `ThreadId` is an opaque object that has a unique value for each thread
917 /// that creates one. `ThreadId`s are not guaranteed to correspond to a thread's
918 /// system-designated identifier. A `ThreadId` can be retrieved from the [`id`]
919 /// method on a [`Thread`].
926 /// let other_thread = thread::spawn(|| {
927 /// thread::current().id()
930 /// let other_thread_id = other_thread.join().unwrap();
931 /// assert!(thread::current().id() != other_thread_id);
934 /// [`id`]: ../../std/thread/struct.Thread.html#method.id
935 /// [`Thread`]: ../../std/thread/struct.Thread.html
936 #[stable(feature = "thread_id", since = "1.19.0")]
937 #[derive(Eq, PartialEq, Clone, Copy, Hash, Debug)]
938 pub struct ThreadId(u64);
941 // Generate a new unique thread ID.
942 fn new() -> ThreadId {
943 // We never call `GUARD.init()`, so it is UB to attempt to
944 // acquire this mutex reentrantly!
945 static GUARD: mutex::Mutex = mutex::Mutex::new();
946 static mut COUNTER: u64 = 0;
949 let _guard = GUARD.lock();
951 // If we somehow use up all our bits, panic so that we're not
952 // covering up subtle bugs of IDs being reused.
953 if COUNTER == ::u64::MAX {
954 panic!("failed to generate unique thread ID: bitspace exhausted");
965 ////////////////////////////////////////////////////////////////////////////////
967 ////////////////////////////////////////////////////////////////////////////////
969 /// The internal representation of a `Thread` handle
971 name: Option<CString>, // Guaranteed to be UTF-8
974 // state for thread park/unpark
981 #[stable(feature = "rust1", since = "1.0.0")]
982 /// A handle to a thread.
984 /// Threads are represented via the `Thread` type, which you can get in one of
987 /// * By spawning a new thread, e.g. using the [`thread::spawn`][`spawn`]
988 /// function, and calling [`thread`][`JoinHandle::thread`] on the
990 /// * By requesting the current thread, using the [`thread::current`] function.
992 /// The [`thread::current`] function is available even for threads not spawned
993 /// by the APIs of this module.
995 /// There is usually no need to create a `Thread` struct yourself, one
996 /// should instead use a function like `spawn` to create new threads, see the
997 /// docs of [`Builder`] and [`spawn`] for more details.
999 /// [`Builder`]: ../../std/thread/struct.Builder.html
1000 /// [`JoinHandle::thread`]: ../../std/thread/struct.JoinHandle.html#method.thread
1001 /// [`JoinHandle`]: ../../std/thread/struct.JoinHandle.html
1002 /// [`thread::current`]: ../../std/thread/fn.current.html
1003 /// [`spawn`]: ../../std/thread/fn.spawn.html
1010 // Used only internally to construct a thread object without spawning
1011 // Panics if the name contains nuls.
1012 pub(crate) fn new(name: Option<String>) -> Thread {
1013 let cname = name.map(|n| {
1014 CString::new(n).expect("thread name may not contain interior null bytes")
1017 inner: Arc::new(Inner {
1019 id: ThreadId::new(),
1020 state: AtomicUsize::new(EMPTY),
1021 lock: Mutex::new(()),
1022 cvar: Condvar::new(),
1027 /// Atomically makes the handle's token available if it is not already.
1029 /// Every thread is equipped with some basic low-level blocking support, via
1030 /// the [`park`][park] function and the `unpark()` method. These can be
1031 /// used as a more CPU-efficient implementation of a spinlock.
1033 /// See the [park documentation][park] for more details.
1038 /// use std::thread;
1039 /// use std::time::Duration;
1041 /// let parked_thread = thread::Builder::new()
1043 /// println!("Parking thread");
1045 /// println!("Thread unparked");
1049 /// // Let some time pass for the thread to be spawned.
1050 /// thread::sleep(Duration::from_millis(10));
1052 /// println!("Unpark the thread");
1053 /// parked_thread.thread().unpark();
1055 /// parked_thread.join().unwrap();
1058 /// [park]: fn.park.html
1059 #[stable(feature = "rust1", since = "1.0.0")]
1060 pub fn unpark(&self) {
1062 match self.inner.state.compare_exchange(EMPTY, NOTIFIED, SeqCst, SeqCst) {
1063 Ok(_) => return, // no one was waiting
1064 Err(NOTIFIED) => return, // already unparked
1065 Err(PARKED) => {} // gotta go wake someone up
1066 _ => panic!("inconsistent state in unpark"),
1069 // Coordinate wakeup through the mutex and a condvar notification
1070 let _lock = self.inner.lock.lock().unwrap();
1071 match self.inner.state.compare_exchange(PARKED, NOTIFIED, SeqCst, SeqCst) {
1072 Ok(_) => return self.inner.cvar.notify_one(),
1073 Err(NOTIFIED) => return, // a different thread unparked
1074 Err(EMPTY) => {} // parked thread went away, try again
1075 _ => panic!("inconsistent state in unpark"),
1080 /// Gets the thread's unique identifier.
1085 /// use std::thread;
1087 /// let other_thread = thread::spawn(|| {
1088 /// thread::current().id()
1091 /// let other_thread_id = other_thread.join().unwrap();
1092 /// assert!(thread::current().id() != other_thread_id);
1094 #[stable(feature = "thread_id", since = "1.19.0")]
1095 pub fn id(&self) -> ThreadId {
1099 /// Gets the thread's name.
1101 /// For more information about named threads, see
1102 /// [this module-level documentation][naming-threads].
1106 /// Threads by default have no name specified:
1109 /// use std::thread;
1111 /// let builder = thread::Builder::new();
1113 /// let handler = builder.spawn(|| {
1114 /// assert!(thread::current().name().is_none());
1117 /// handler.join().unwrap();
1120 /// Thread with a specified name:
1123 /// use std::thread;
1125 /// let builder = thread::Builder::new()
1126 /// .name("foo".into());
1128 /// let handler = builder.spawn(|| {
1129 /// assert_eq!(thread::current().name(), Some("foo"))
1132 /// handler.join().unwrap();
1135 /// [naming-threads]: ./index.html#naming-threads
1136 #[stable(feature = "rust1", since = "1.0.0")]
1137 pub fn name(&self) -> Option<&str> {
1138 self.cname().map(|s| unsafe { str::from_utf8_unchecked(s.to_bytes()) } )
1141 fn cname(&self) -> Option<&CStr> {
1142 self.inner.name.as_ref().map(|s| &**s)
1146 #[stable(feature = "rust1", since = "1.0.0")]
1147 impl fmt::Debug for Thread {
1148 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
1149 fmt::Debug::fmt(&self.name(), f)
1153 ////////////////////////////////////////////////////////////////////////////////
1155 ////////////////////////////////////////////////////////////////////////////////
1157 /// A specialized [`Result`] type for threads.
1159 /// Indicates the manner in which a thread exited.
1161 /// A thread that completes without panicking is considered to exit successfully.
1166 /// use std::thread;
1169 /// fn copy_in_thread() -> thread::Result<()> {
1170 /// thread::spawn(move || { fs::copy("foo.txt", "bar.txt").unwrap(); }).join()
1174 /// match copy_in_thread() {
1175 /// Ok(_) => println!("this is fine"),
1176 /// Err(_) => println!("thread panicked"),
1181 /// [`Result`]: ../../std/result/enum.Result.html
1182 #[stable(feature = "rust1", since = "1.0.0")]
1183 pub type Result<T> = ::result::Result<T, Box<dyn Any + Send + 'static>>;
1185 // This packet is used to communicate the return value between the child thread
1186 // and the parent thread. Memory is shared through the `Arc` within and there's
1187 // no need for a mutex here because synchronization happens with `join()` (the
1188 // parent thread never reads this packet until the child has exited).
1190 // This packet itself is then stored into a `JoinInner` which in turns is placed
1191 // in `JoinHandle` and `JoinGuard`. Due to the usage of `UnsafeCell` we need to
1192 // manually worry about impls like Send and Sync. The type `T` should
1193 // already always be Send (otherwise the thread could not have been created) and
1194 // this type is inherently Sync because no methods take &self. Regardless,
1195 // however, we add inheriting impls for Send/Sync to this type to ensure it's
1196 // Send/Sync and that future modifications will still appropriately classify it.
1197 struct Packet<T>(Arc<UnsafeCell<Option<Result<T>>>>);
1199 unsafe impl<T: Send> Send for Packet<T> {}
1200 unsafe impl<T: Sync> Sync for Packet<T> {}
1202 /// Inner representation for JoinHandle
1203 struct JoinInner<T> {
1204 native: Option<imp::Thread>,
1209 impl<T> JoinInner<T> {
1210 fn join(&mut self) -> Result<T> {
1211 self.native.take().unwrap().join();
1213 (*self.packet.0.get()).take().unwrap()
1218 /// An owned permission to join on a thread (block on its termination).
1220 /// A `JoinHandle` *detaches* the associated thread when it is dropped, which
1221 /// means that there is no longer any handle to thread and no way to `join`
1224 /// Due to platform restrictions, it is not possible to [`Clone`] this
1225 /// handle: the ability to join a thread is a uniquely-owned permission.
1227 /// This `struct` is created by the [`thread::spawn`] function and the
1228 /// [`thread::Builder::spawn`] method.
1232 /// Creation from [`thread::spawn`]:
1235 /// use std::thread;
1237 /// let join_handle: thread::JoinHandle<_> = thread::spawn(|| {
1238 /// // some work here
1242 /// Creation from [`thread::Builder::spawn`]:
1245 /// use std::thread;
1247 /// let builder = thread::Builder::new();
1249 /// let join_handle: thread::JoinHandle<_> = builder.spawn(|| {
1250 /// // some work here
1254 /// Child being detached and outliving its parent:
1257 /// use std::thread;
1258 /// use std::time::Duration;
1260 /// let original_thread = thread::spawn(|| {
1261 /// let _detached_thread = thread::spawn(|| {
1262 /// // Here we sleep to make sure that the first thread returns before.
1263 /// thread::sleep(Duration::from_millis(10));
1264 /// // This will be called, even though the JoinHandle is dropped.
1265 /// println!("♫ Still alive ♫");
1269 /// original_thread.join().expect("The thread being joined has panicked");
1270 /// println!("Original thread is joined.");
1272 /// // We make sure that the new thread has time to run, before the main
1273 /// // thread returns.
1275 /// thread::sleep(Duration::from_millis(1000));
1278 /// [`Clone`]: ../../std/clone/trait.Clone.html
1279 /// [`thread::spawn`]: fn.spawn.html
1280 /// [`thread::Builder::spawn`]: struct.Builder.html#method.spawn
1281 #[stable(feature = "rust1", since = "1.0.0")]
1282 pub struct JoinHandle<T>(JoinInner<T>);
1284 #[stable(feature = "joinhandle_impl_send_sync", since = "1.29.0")]
1285 unsafe impl<T> Send for JoinHandle<T> {}
1286 #[stable(feature = "joinhandle_impl_send_sync", since = "1.29.0")]
1287 unsafe impl<T> Sync for JoinHandle<T> {}
1289 impl<T> JoinHandle<T> {
1290 /// Extracts a handle to the underlying thread.
1295 /// use std::thread;
1297 /// let builder = thread::Builder::new();
1299 /// let join_handle: thread::JoinHandle<_> = builder.spawn(|| {
1300 /// // some work here
1303 /// let thread = join_handle.thread();
1304 /// println!("thread id: {:?}", thread.id());
1306 #[stable(feature = "rust1", since = "1.0.0")]
1307 pub fn thread(&self) -> &Thread {
1311 /// Waits for the associated thread to finish.
1313 /// In terms of [atomic memory orderings], the completion of the associated
1314 /// thread synchronizes with this function returning. In other words, all
1315 /// operations performed by that thread are ordered before all
1316 /// operations that happen after `join` returns.
1318 /// If the child thread panics, [`Err`] is returned with the parameter given
1321 /// [`Err`]: ../../std/result/enum.Result.html#variant.Err
1322 /// [`panic`]: ../../std/macro.panic.html
1323 /// [atomic memory orderings]: ../../std/sync/atomic/index.html
1327 /// This function may panic on some platforms if a thread attempts to join
1328 /// itself or otherwise may create a deadlock with joining threads.
1333 /// use std::thread;
1335 /// let builder = thread::Builder::new();
1337 /// let join_handle: thread::JoinHandle<_> = builder.spawn(|| {
1338 /// // some work here
1340 /// join_handle.join().expect("Couldn't join on the associated thread");
1342 #[stable(feature = "rust1", since = "1.0.0")]
1343 pub fn join(mut self) -> Result<T> {
1348 impl<T> AsInner<imp::Thread> for JoinHandle<T> {
1349 fn as_inner(&self) -> &imp::Thread { self.0.native.as_ref().unwrap() }
1352 impl<T> IntoInner<imp::Thread> for JoinHandle<T> {
1353 fn into_inner(self) -> imp::Thread { self.0.native.unwrap() }
1356 #[stable(feature = "std_debug", since = "1.16.0")]
1357 impl<T> fmt::Debug for JoinHandle<T> {
1358 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
1359 f.pad("JoinHandle { .. }")
1363 fn _assert_sync_and_send() {
1364 fn _assert_both<T: Send + Sync>() {}
1365 _assert_both::<JoinHandle<()>>();
1366 _assert_both::<Thread>();
1369 ////////////////////////////////////////////////////////////////////////////////
1371 ////////////////////////////////////////////////////////////////////////////////
1373 #[cfg(all(test, not(target_os = "emscripten")))]
1376 use sync::mpsc::{channel, Sender};
1378 use super::{Builder};
1383 // !!! These tests are dangerous. If something is buggy, they will hang, !!!
1384 // !!! instead of exiting cleanly. This might wedge the buildbots. !!!
1387 fn test_unnamed_thread() {
1388 thread::spawn(move|| {
1389 assert!(thread::current().name().is_none());
1390 }).join().ok().unwrap();
1394 fn test_named_thread() {
1395 Builder::new().name("ada lovelace".to_string()).spawn(move|| {
1396 assert!(thread::current().name().unwrap() == "ada lovelace".to_string());
1397 }).unwrap().join().unwrap();
1402 fn test_invalid_named_thread() {
1403 let _ = Builder::new().name("ada l\0velace".to_string()).spawn(|| {});
1407 fn test_run_basic() {
1408 let (tx, rx) = channel();
1409 thread::spawn(move|| {
1410 tx.send(()).unwrap();
1416 fn test_join_panic() {
1417 match thread::spawn(move|| {
1420 result::Result::Err(_) => (),
1421 result::Result::Ok(()) => panic!()
1426 fn test_spawn_sched() {
1427 let (tx, rx) = channel();
1429 fn f(i: i32, tx: Sender<()>) {
1430 let tx = tx.clone();
1431 thread::spawn(move|| {
1433 tx.send(()).unwrap();
1445 fn test_spawn_sched_childs_on_default_sched() {
1446 let (tx, rx) = channel();
1448 thread::spawn(move|| {
1449 thread::spawn(move|| {
1450 tx.send(()).unwrap();
1457 fn avoid_copying_the_body<F>(spawnfn: F) where F: FnOnce(Box<dyn Fn() + Send>) {
1458 let (tx, rx) = channel();
1460 let x: Box<_> = box 1;
1461 let x_in_parent = (&*x) as *const i32 as usize;
1463 spawnfn(Box::new(move|| {
1464 let x_in_child = (&*x) as *const i32 as usize;
1465 tx.send(x_in_child).unwrap();
1468 let x_in_child = rx.recv().unwrap();
1469 assert_eq!(x_in_parent, x_in_child);
1473 fn test_avoid_copying_the_body_spawn() {
1474 avoid_copying_the_body(|v| {
1475 thread::spawn(move || v());
1480 fn test_avoid_copying_the_body_thread_spawn() {
1481 avoid_copying_the_body(|f| {
1482 thread::spawn(move|| {
1489 fn test_avoid_copying_the_body_join() {
1490 avoid_copying_the_body(|f| {
1491 let _ = thread::spawn(move|| {
1498 fn test_child_doesnt_ref_parent() {
1499 // If the child refcounts the parent thread, this will stack overflow when
1500 // climbing the thread tree to dereference each ancestor. (See #1789)
1501 // (well, it would if the constant were 8000+ - I lowered it to be more
1502 // valgrind-friendly. try this at home, instead..!)
1503 const GENERATIONS: u32 = 16;
1504 fn child_no(x: u32) -> Box<dyn Fn() + Send> {
1505 return Box::new(move|| {
1506 if x < GENERATIONS {
1507 thread::spawn(move|| child_no(x+1)());
1511 thread::spawn(|| child_no(0)());
1515 fn test_simple_newsched_spawn() {
1516 thread::spawn(move || {});
1520 fn test_try_panic_message_static_str() {
1521 match thread::spawn(move|| {
1522 panic!("static string");
1525 type T = &'static str;
1526 assert!(e.is::<T>());
1527 assert_eq!(*e.downcast::<T>().unwrap(), "static string");
1534 fn test_try_panic_message_owned_str() {
1535 match thread::spawn(move|| {
1536 panic!("owned string".to_string());
1540 assert!(e.is::<T>());
1541 assert_eq!(*e.downcast::<T>().unwrap(), "owned string".to_string());
1548 fn test_try_panic_message_any() {
1549 match thread::spawn(move|| {
1550 panic!(box 413u16 as Box<dyn Any + Send>);
1553 type T = Box<dyn Any + Send>;
1554 assert!(e.is::<T>());
1555 let any = e.downcast::<T>().unwrap();
1556 assert!(any.is::<u16>());
1557 assert_eq!(*any.downcast::<u16>().unwrap(), 413);
1564 fn test_try_panic_message_unit_struct() {
1567 match thread::spawn(move|| {
1570 Err(ref e) if e.is::<Juju>() => {}
1571 Err(_) | Ok(()) => panic!()
1576 fn test_park_timeout_unpark_before() {
1578 thread::current().unpark();
1579 thread::park_timeout(Duration::from_millis(u32::MAX as u64));
1584 fn test_park_timeout_unpark_not_called() {
1586 thread::park_timeout(Duration::from_millis(10));
1591 fn test_park_timeout_unpark_called_other_thread() {
1593 let th = thread::current();
1595 let _guard = thread::spawn(move || {
1596 super::sleep(Duration::from_millis(50));
1600 thread::park_timeout(Duration::from_millis(u32::MAX as u64));
1605 fn sleep_ms_smoke() {
1606 thread::sleep(Duration::from_millis(2));
1610 fn test_thread_id_equal() {
1611 assert!(thread::current().id() == thread::current().id());
1615 fn test_thread_id_not_equal() {
1616 let spawned_id = thread::spawn(|| thread::current().id()).join().unwrap();
1617 assert!(thread::current().id() != spawned_id);
1620 // NOTE: the corresponding test for stderr is in run-pass/thread-stderr, due
1621 // to the test harness apparently interfering with stderr configuration.