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. Thread panic is unrecoverable from within
29 //! the panicking thread (i.e. there is no 'try/catch' in Rust), but
30 //! the panic may optionally be detected from a different thread. If
31 //! the main thread panics, the application will exit with a non-zero
34 //! When the main thread of a Rust program terminates, the entire program shuts
35 //! down, even if other threads are still running. However, this module provides
36 //! convenient facilities for automatically waiting for the termination of a
37 //! child thread (i.e., join).
39 //! ## Spawning a thread
41 //! A new thread can be spawned using the [`thread::spawn`][`spawn`] function:
46 //! thread::spawn(move || {
51 //! In this example, the spawned thread is "detached" from the current
52 //! thread. This means that it can outlive its parent (the thread that spawned
53 //! it), unless this parent is the main thread.
55 //! The parent thread can also wait on the completion of the child
56 //! thread; a call to [`spawn`] produces a [`JoinHandle`], which provides
57 //! a `join` method for waiting:
62 //! let child = thread::spawn(move || {
66 //! let res = child.join();
69 //! The [`join`] method returns a [`thread::Result`] containing [`Ok`] of the final
70 //! value produced by the child thread, or [`Err`] of the value given to
71 //! a call to [`panic!`] if the child panicked.
73 //! ## Configuring threads
75 //! A new thread can be configured before it is spawned via the [`Builder`] type,
76 //! which currently allows you to set the name and stack size for the child thread:
79 //! # #![allow(unused_must_use)]
82 //! thread::Builder::new().name("child1".to_string()).spawn(move || {
83 //! println!("Hello, world!");
87 //! ## The `Thread` type
89 //! Threads are represented via the [`Thread`] type, which you can get in one of
92 //! * By spawning a new thread, e.g. using the [`thread::spawn`][`spawn`]
93 //! function, and calling [`thread`][`JoinHandle::thread`] on the [`JoinHandle`].
94 //! * By requesting the current thread, using the [`thread::current`] function.
96 //! The [`thread::current`] function is available even for threads not spawned
97 //! by the APIs of this module.
99 //! ## Thread-local storage
101 //! This module also provides an implementation of thread-local storage for Rust
102 //! programs. Thread-local storage is a method of storing data into a global
103 //! variable that each thread in the program will have its own copy of.
104 //! Threads do not share this data, so accesses do not need to be synchronized.
106 //! A thread-local key owns the value it contains and will destroy the value when the
107 //! thread exits. It is created with the [`thread_local!`] macro and can contain any
108 //! value that is `'static` (no borrowed pointers). It provides an accessor function,
109 //! [`with`], that yields a shared reference to the value to the specified
110 //! closure. Thread-local keys allow only shared access to values, as there would be no
111 //! way to guarantee uniqueness if mutable borrows were allowed. Most values
112 //! will want to make use of some form of **interior mutability** through the
113 //! [`Cell`] or [`RefCell`] types.
115 //! [channels]: ../../std/sync/mpsc/index.html
116 //! [`Arc`]: ../../std/sync/struct.Arc.html
117 //! [`spawn`]: ../../std/thread/fn.spawn.html
118 //! [`JoinHandle`]: ../../std/thread/struct.JoinHandle.html
119 //! [`JoinHandle::thread`]: ../../std/thread/struct.JoinHandle.html#method.thread
120 //! [`join`]: ../../std/thread/struct.JoinHandle.html#method.join
121 //! [`Result`]: ../../std/result/enum.Result.html
122 //! [`Ok`]: ../../std/result/enum.Result.html#variant.Ok
123 //! [`Err`]: ../../std/result/enum.Result.html#variant.Err
124 //! [`panic!`]: ../../std/macro.panic.html
125 //! [`Builder`]: ../../std/thread/struct.Builder.html
126 //! [`thread::current`]: ../../std/thread/fn.current.html
127 //! [`thread::Result`]: ../../std/thread/type.Result.html
128 //! [`Thread`]: ../../std/thread/struct.Thread.html
129 //! [`park`]: ../../std/thread/fn.park.html
130 //! [`unpark`]: ../../std/thread/struct.Thread.html#method.unpark
131 //! [`thread::park_timeout`]: ../../std/thread/fn.park_timeout.html
132 //! [`Cell`]: ../cell/struct.Cell.html
133 //! [`RefCell`]: ../cell/struct.RefCell.html
134 //! [`thread_local!`]: ../macro.thread_local.html
135 //! [`with`]: struct.LocalKey.html#method.with
137 #![stable(feature = "rust1", since = "1.0.0")]
140 use cell::UnsafeCell;
141 use ffi::{CStr, CString};
147 use sync::{Mutex, Condvar, Arc};
148 use sys::thread as imp;
149 use sys_common::mutex;
150 use sys_common::thread_info;
151 use sys_common::util;
152 use sys_common::{AsInner, IntoInner};
155 ////////////////////////////////////////////////////////////////////////////////
156 // Thread-local storage
157 ////////////////////////////////////////////////////////////////////////////////
159 #[macro_use] mod local;
161 #[stable(feature = "rust1", since = "1.0.0")]
162 pub use self::local::{LocalKey, LocalKeyState};
164 // The types used by the thread_local! macro to access TLS keys. Note that there
165 // are two types, the "OS" type and the "fast" type. The OS thread local key
166 // type is accessed via platform-specific API calls and is slow, while the fast
167 // key type is accessed via code generated via LLVM, where TLS keys are set up
168 // by the elf linker. Note that the OS TLS type is always available: on macOS
169 // the standard library is compiled with support for older platform versions
170 // where fast TLS was not available; end-user code is compiled with fast TLS
171 // where available, but both are needed.
173 #[unstable(feature = "libstd_thread_internals", issue = "0")]
174 #[cfg(target_thread_local)]
175 #[doc(hidden)] pub use sys::fast_thread_local::Key as __FastLocalKeyInner;
176 #[unstable(feature = "libstd_thread_internals", issue = "0")]
177 #[doc(hidden)] pub use self::local::os::Key as __OsLocalKeyInner;
179 ////////////////////////////////////////////////////////////////////////////////
181 ////////////////////////////////////////////////////////////////////////////////
183 /// Thread factory, which can be used in order to configure the properties of
186 /// Methods can be chained on it in order to configure it.
188 /// The two configurations available are:
190 /// - [`name`]: allows to give a name to the thread which is currently
191 /// only used in `panic` messages.
192 /// - [`stack_size`]: specifies the desired stack size. Note that this can
193 /// be overriden by the OS.
195 /// If the [`stack_size`] field is not specified, the stack size
196 /// will be the `RUST_MIN_STACK` environment variable. If it is
197 /// not specified either, a sensible default will be set.
199 /// If the [`name`] field is not specified, the thread will not be named.
201 /// The [`spawn`] method will take ownership of the builder and create an
202 /// [`io::Result`] to the thread handle with the given configuration.
204 /// The [`thread::spawn`] free function uses a `Builder` with default
205 /// configuration and [`unwrap`]s its return value.
207 /// You may want to use [`spawn`] instead of [`thread::spawn`], when you want
208 /// to recover from a failure to launch a thread, indeed the free function will
209 /// panick where the `Builder` method will return a [`io::Result`].
216 /// let builder = thread::Builder::new();
218 /// let handler = builder.spawn(|| {
222 /// handler.join().unwrap();
225 /// [`thread::spawn`]: ../../std/thread/fn.spawn.html
226 /// [`stack_size`]: ../../std/thread/struct.Builder.html#method.stack_size
227 /// [`name`]: ../../std/thread/struct.Builder.html#method.name
228 /// [`spawn`]: ../../std/thread/struct.Builder.html#method.spawn
229 /// [`io::Result`]: ../../std/io/type.Result.html
230 /// [`unwrap`]: ../../std/result/enum.Result.html#method.unwrap
231 #[stable(feature = "rust1", since = "1.0.0")]
234 // A name for the thread-to-be, for identification in panic messages
235 name: Option<String>,
236 // The size of the stack for the spawned thread in bytes
237 stack_size: Option<usize>,
241 /// Generates the base configuration for spawning a thread, from which
242 /// configuration methods can be chained.
249 /// let builder = thread::Builder::new()
250 /// .name("foo".into())
253 /// let handler = builder.spawn(|| {
257 /// handler.join().unwrap();
259 #[stable(feature = "rust1", since = "1.0.0")]
260 pub fn new() -> Builder {
267 /// Names the thread-to-be. Currently the name is used for identification
268 /// only in panic messages.
275 /// let builder = thread::Builder::new()
276 /// .name("foo".into());
278 /// let handler = builder.spawn(|| {
279 /// assert_eq!(thread::current().name(), Some("foo"))
282 /// handler.join().unwrap();
284 #[stable(feature = "rust1", since = "1.0.0")]
285 pub fn name(mut self, name: String) -> Builder {
286 self.name = Some(name);
290 /// Sets the size of the stack (in bytes) for the new thread.
292 /// The actual stack size may be greater than this value if
293 /// the platform specifies minimal stack size.
300 /// let builder = thread::Builder::new().stack_size(32 * 1024);
302 #[stable(feature = "rust1", since = "1.0.0")]
303 pub fn stack_size(mut self, size: usize) -> Builder {
304 self.stack_size = Some(size);
308 /// Spawns a new thread by taking ownership of the `Builder`, and returns an
309 /// [`io::Result`] to its [`JoinHandle`].
311 /// The spawned thread may outlive the caller (unless the caller thread
312 /// is the main thread; the whole process is terminated when the main
313 /// thread finishes). The join handle can be used to block on
314 /// termination of the child thread, including recovering its panics.
316 /// For a more complete documentation see [`thread::spawn`][`spawn`].
320 /// Unlike the [`spawn`] free function, this method yields an
321 /// [`io::Result`] to capture any failure to create the thread at
324 /// [`spawn`]: ../../std/thread/fn.spawn.html
325 /// [`io::Result`]: ../../std/io/type.Result.html
326 /// [`JoinHandle`]: ../../std/thread/struct.JoinHandle.html
333 /// let builder = thread::Builder::new();
335 /// let handler = builder.spawn(|| {
339 /// handler.join().unwrap();
341 #[stable(feature = "rust1", since = "1.0.0")]
342 pub fn spawn<F, T>(self, f: F) -> io::Result<JoinHandle<T>> where
343 F: FnOnce() -> T, F: Send + 'static, T: Send + 'static
345 let Builder { name, stack_size } = self;
347 let stack_size = stack_size.unwrap_or(util::min_stack());
349 let my_thread = Thread::new(name);
350 let their_thread = my_thread.clone();
352 let my_packet : Arc<UnsafeCell<Option<Result<T>>>>
353 = Arc::new(UnsafeCell::new(None));
354 let their_packet = my_packet.clone();
357 if let Some(name) = their_thread.cname() {
358 imp::Thread::set_name(name);
361 thread_info::set(imp::guard::current(), their_thread);
362 #[cfg(feature = "backtrace")]
363 let try_result = panic::catch_unwind(panic::AssertUnwindSafe(|| {
364 ::sys_common::backtrace::__rust_begin_short_backtrace(f)
366 #[cfg(not(feature = "backtrace"))]
367 let try_result = panic::catch_unwind(panic::AssertUnwindSafe(f));
368 *their_packet.get() = Some(try_result);
372 Ok(JoinHandle(JoinInner {
374 Some(imp::Thread::new(stack_size, Box::new(main))?)
377 packet: Packet(my_packet),
382 ////////////////////////////////////////////////////////////////////////////////
384 ////////////////////////////////////////////////////////////////////////////////
386 /// Spawns a new thread, returning a [`JoinHandle`] for it.
388 /// The join handle will implicitly *detach* the child thread upon being
389 /// dropped. In this case, the child thread may outlive the parent (unless
390 /// the parent thread is the main thread; the whole process is terminated when
391 /// the main thread finishes). Additionally, the join handle provides a [`join`]
392 /// method that can be used to join the child thread. If the child thread
393 /// panics, [`join`] will return an [`Err`] containing the argument given to
396 /// This will create a thread using default parameters of [`Builder`], if you
397 /// want to specify the stack size or the name of the thread, use this API
400 /// As you can see in the signature of `spawn` there are two constraints on
401 /// both the closure given to `spawn` and its return value, let's explain them:
403 /// - The `'static` constraint means that the closure and its return value
404 /// must have a lifetime of the whole program execution. The reason for this
405 /// is that threads can `detach` and outlive the lifetime they have been
407 /// Indeed if the thread, and by extension its return value, can outlive their
408 /// caller, we need to make sure that they will be valid afterwards, and since
409 /// we *can't* know when it will return we need to have them valid as long as
410 /// possible, that is until the end of the program, hence the `'static`
412 /// - The [`Send`] constraint is because the closure will need to be passed
413 /// *by value* from the thread where it is spawned to the new thread. Its
414 /// return value will need to be passed from the new thread to the thread
415 /// where it is `join`ed.
416 /// As a reminder, the [`Send`] marker trait, expresses that it is safe to be
417 /// passed from thread to thread. [`Sync`] expresses that it is safe to have a
418 /// reference be passed from thread to thread.
422 /// Panics if the OS fails to create a thread; use [`Builder::spawn`]
423 /// to recover from such errors.
427 /// Creating a thread.
432 /// let handler = thread::spawn(|| {
436 /// handler.join().unwrap();
439 /// As mentioned in the module documentation, threads are usually made to
440 /// communicate using [`channels`], here is how it usually looks.
442 /// This example also shows how to use `move`, in order to give ownership
443 /// of values to a thread.
447 /// use std::sync::mpsc::channel;
449 /// let (tx, rx) = channel();
451 /// let sender = thread::spawn(move || {
452 /// let _ = tx.send("Hello, thread".to_owned());
455 /// let receiver = thread::spawn(move || {
456 /// println!("{}", rx.recv().unwrap());
459 /// let _ = sender.join();
460 /// let _ = receiver.join();
463 /// A thread can also return a value through its [`JoinHandle`], you can use
464 /// this to make asynchronous computations (futures might be more appropriate
470 /// let computation = thread::spawn(|| {
471 /// // Some expensive computation.
475 /// let result = computation.join().unwrap();
476 /// println!("{}", result);
479 /// [`channels`]: ../../std/sync/mpsc/index.html
480 /// [`JoinHandle`]: ../../std/thread/struct.JoinHandle.html
481 /// [`join`]: ../../std/thread/struct.JoinHandle.html#method.join
482 /// [`Err`]: ../../std/result/enum.Result.html#variant.Err
483 /// [`panic`]: ../../std/macro.panic.html
484 /// [`Builder::spawn`]: ../../std/thread/struct.Builder.html#method.spawn
485 /// [`Builder`]: ../../std/thread/struct.Builder.html
486 /// [`Send`]: ../../std/marker/trait.Send.html
487 /// [`Sync`]: ../../std/marker/trait.Sync.html
488 #[stable(feature = "rust1", since = "1.0.0")]
489 pub fn spawn<F, T>(f: F) -> JoinHandle<T> where
490 F: FnOnce() -> T, F: Send + 'static, T: Send + 'static
492 Builder::new().spawn(f).unwrap()
495 /// Gets a handle to the thread that invokes it.
499 /// Getting a handle to the current thread with `thread::current()`:
504 /// let handler = thread::Builder::new()
505 /// .name("named thread".into())
507 /// let handle = thread::current();
508 /// assert_eq!(handle.name(), Some("named thread"));
512 /// handler.join().unwrap();
514 #[stable(feature = "rust1", since = "1.0.0")]
515 pub fn current() -> Thread {
516 thread_info::current_thread().expect("use of std::thread::current() is not \
517 possible after the thread's local \
518 data has been destroyed")
521 /// Cooperatively gives up a timeslice to the OS scheduler.
523 /// This is used when the programmer knows that the thread will have nothing
524 /// to do for some time, and thus avoid wasting computing time.
526 /// For example when polling on a resource, it is common to check that it is
527 /// available, and if not to yield in order to avoid busy waiting.
529 /// Thus the pattern of `yield`ing after a failed poll is rather common when
530 /// implementing low-level shared resources or synchronization primitives.
532 /// However programmers will usualy prefer to use, [`channel`]s, [`Condvar`]s,
533 /// [`Mutex`]es or [`join`] for their synchronisation routines, as they avoid
534 /// thinking about thread schedulling.
536 /// Note that [`channel`]s for example are implemented using this primitive.
537 /// Indeed when you call `send` or `recv`, which are blocking, they will yield
538 /// if the channel is not available.
545 /// thread::yield_now();
548 /// [`channel`]: ../../std/sync/mpsc/index.html
549 /// [`spawn`]: ../../std/thread/fn.spawn.html
550 /// [`join`]: ../../std/thread/struct.JoinHandle.html#method.join
551 /// [`Mutex`]: ../../std/sync/struct.Mutex.html
552 /// [`Condvar`]: ../../std/sync/struct.Condvar.html
553 #[stable(feature = "rust1", since = "1.0.0")]
555 imp::Thread::yield_now()
558 /// Determines whether the current thread is unwinding because of panic.
560 /// A common use of this feature is to poison shared resources when writing
561 /// unsafe code, by checking `panicking` when the `drop` is called.
563 /// This is usually not needed when writing safe code, as [`Mutex`es][Mutex]
564 /// already poison themselves when a thread panics while holding the lock.
566 /// This can also be used in multithreaded applications, in order to send a
567 /// message to other threads warning that a thread has panicked (e.g. for
568 /// monitoring purposes).
575 /// struct SomeStruct;
577 /// impl Drop for SomeStruct {
578 /// fn drop(&mut self) {
579 /// if thread::panicking() {
580 /// println!("dropped while unwinding");
582 /// println!("dropped while not unwinding");
589 /// let a = SomeStruct;
594 /// let b = SomeStruct;
599 /// [Mutex]: ../../std/sync/struct.Mutex.html
601 #[stable(feature = "rust1", since = "1.0.0")]
602 pub fn panicking() -> bool {
603 panicking::panicking()
606 /// Puts the current thread to sleep for the specified amount of time.
608 /// The thread may sleep longer than the duration specified due to scheduling
609 /// specifics or platform-dependent functionality.
611 /// # Platform behavior
613 /// On Unix platforms this function will not return early due to a
614 /// signal being received or a spurious wakeup.
621 /// // Let's sleep for 2 seconds:
622 /// thread::sleep_ms(2000);
624 #[stable(feature = "rust1", since = "1.0.0")]
625 #[rustc_deprecated(since = "1.6.0", reason = "replaced by `std::thread::sleep`")]
626 pub fn sleep_ms(ms: u32) {
627 sleep(Duration::from_millis(ms as u64))
630 /// Puts the current thread to sleep for the specified amount of time.
632 /// The thread may sleep longer than the duration specified due to scheduling
633 /// specifics or platform-dependent functionality.
635 /// # Platform behavior
637 /// On Unix platforms this function will not return early due to a
638 /// signal being received or a spurious wakeup. Platforms which do not support
639 /// nanosecond precision for sleeping will have `dur` rounded up to the nearest
640 /// granularity of time they can sleep for.
645 /// use std::{thread, time};
647 /// let ten_millis = time::Duration::from_millis(10);
648 /// let now = time::Instant::now();
650 /// thread::sleep(ten_millis);
652 /// assert!(now.elapsed() >= ten_millis);
654 #[stable(feature = "thread_sleep", since = "1.4.0")]
655 pub fn sleep(dur: Duration) {
656 imp::Thread::sleep(dur)
659 /// Blocks unless or until the current thread's token is made available.
661 /// A call to `park` does not guarantee that the thread will remain parked
662 /// forever, and callers should be prepared for this possibility.
664 /// # park and unpark
666 /// Every thread is equipped with some basic low-level blocking support, via the
667 /// [`thread::park`][`park`] function and [`thread::Thread::unpark`][`unpark`]
668 /// method. [`park`] blocks the current thread, which can then be resumed from
669 /// another thread by calling the [`unpark`] method on the blocked thread's
672 /// Conceptually, each [`Thread`] handle has an associated token, which is
673 /// initially not present:
675 /// * The [`thread::park`][`park`] function blocks the current thread unless or
676 /// until the token is available for its thread handle, at which point it
677 /// atomically consumes the token. It may also return *spuriously*, without
678 /// consuming the token. [`thread::park_timeout`] does the same, but allows
679 /// specifying a maximum time to block the thread for.
681 /// * The [`unpark`] method on a [`Thread`] atomically makes the token available
682 /// if it wasn't already.
684 /// In other words, each [`Thread`] acts a bit like a spinlock that can be
685 /// locked and unlocked using `park` and `unpark`.
687 /// The API is typically used by acquiring a handle to the current thread,
688 /// placing that handle in a shared data structure so that other threads can
689 /// find it, and then `park`ing. When some desired condition is met, another
690 /// thread calls [`unpark`] on the handle.
692 /// The motivation for this design is twofold:
694 /// * It avoids the need to allocate mutexes and condvars when building new
695 /// synchronization primitives; the threads already provide basic
696 /// blocking/signaling.
698 /// * It can be implemented very efficiently on many platforms.
704 /// use std::time::Duration;
706 /// let parked_thread = thread::Builder::new()
708 /// println!("Parking thread");
710 /// println!("Thread unparked");
714 /// // Let some time pass for the thread to be spawned.
715 /// thread::sleep(Duration::from_millis(10));
717 /// println!("Unpark the thread");
718 /// parked_thread.thread().unpark();
720 /// parked_thread.join().unwrap();
723 /// [`Thread`]: ../../std/thread/struct.Thread.html
724 /// [`park`]: ../../std/thread/fn.park.html
725 /// [`unpark`]: ../../std/thread/struct.Thread.html#method.unpark
726 /// [`thread::park_timeout`]: ../../std/thread/fn.park_timeout.html
728 // The implementation currently uses the trivial strategy of a Mutex+Condvar
729 // with wakeup flag, which does not actually allow spurious wakeups. In the
730 // future, this will be implemented in a more efficient way, perhaps along the lines of
731 // http://cr.openjdk.java.net/~stefank/6989984.1/raw_files/new/src/os/linux/vm/os_linux.cpp
732 // or futuxes, and in either case may allow spurious wakeups.
733 #[stable(feature = "rust1", since = "1.0.0")]
735 let thread = current();
736 let mut guard = thread.inner.lock.lock().unwrap();
738 guard = thread.inner.cvar.wait(guard).unwrap();
743 /// Use [`park_timeout`].
745 /// Blocks unless or until the current thread's token is made available or
746 /// the specified duration has been reached (may wake spuriously).
748 /// The semantics of this function are equivalent to [`park`] except
749 /// that the thread will be blocked for roughly no longer than `dur`. This
750 /// method should not be used for precise timing due to anomalies such as
751 /// preemption or platform differences that may not cause the maximum
752 /// amount of time waited to be precisely `ms` long.
754 /// See the [park documentation][`park`] for more detail.
756 /// [`park_timeout`]: fn.park_timeout.html
757 /// [`park`]: ../../std/thread/fn.park.html
758 #[stable(feature = "rust1", since = "1.0.0")]
759 #[rustc_deprecated(since = "1.6.0", reason = "replaced by `std::thread::park_timeout`")]
760 pub fn park_timeout_ms(ms: u32) {
761 park_timeout(Duration::from_millis(ms as u64))
764 /// Blocks unless or until the current thread's token is made available or
765 /// the specified duration has been reached (may wake spuriously).
767 /// The semantics of this function are equivalent to [`park`][park] except
768 /// that the thread will be blocked for roughly no longer than `dur`. This
769 /// method should not be used for precise timing due to anomalies such as
770 /// preemption or platform differences that may not cause the maximum
771 /// amount of time waited to be precisely `dur` long.
773 /// See the [park dococumentation][park] for more details.
775 /// # Platform behavior
777 /// Platforms which do not support nanosecond precision for sleeping will have
778 /// `dur` rounded up to the nearest granularity of time they can sleep for.
782 /// Waiting for the complete expiration of the timeout:
785 /// use std::thread::park_timeout;
786 /// use std::time::{Instant, Duration};
788 /// let timeout = Duration::from_secs(2);
789 /// let beginning_park = Instant::now();
791 /// let mut timeout_remaining = timeout;
793 /// park_timeout(timeout_remaining);
794 /// let elapsed = beginning_park.elapsed();
795 /// if elapsed >= timeout {
798 /// println!("restarting park_timeout after {:?}", elapsed);
799 /// timeout_remaining = timeout - elapsed;
803 /// [park]: fn.park.html
804 #[stable(feature = "park_timeout", since = "1.4.0")]
805 pub fn park_timeout(dur: Duration) {
806 let thread = current();
807 let mut guard = thread.inner.lock.lock().unwrap();
809 let (g, _) = thread.inner.cvar.wait_timeout(guard, dur).unwrap();
815 ////////////////////////////////////////////////////////////////////////////////
817 ////////////////////////////////////////////////////////////////////////////////
819 /// A unique identifier for a running thread.
821 /// A `ThreadId` is an opaque object that has a unique value for each thread
822 /// that creates one. `ThreadId`s are not guaranteed to correspond to a thread's
823 /// system-designated identifier.
828 /// #![feature(thread_id)]
832 /// let other_thread = thread::spawn(|| {
833 /// thread::current().id()
836 /// let other_thread_id = other_thread.join().unwrap();
837 /// assert!(thread::current().id() != other_thread_id);
839 #[unstable(feature = "thread_id", issue = "21507")]
840 #[derive(Eq, PartialEq, Clone, Copy, Hash, Debug)]
841 pub struct ThreadId(u64);
844 // Generate a new unique thread ID.
845 fn new() -> ThreadId {
846 static GUARD: mutex::Mutex = mutex::Mutex::new();
847 static mut COUNTER: u64 = 0;
852 // If we somehow use up all our bits, panic so that we're not
853 // covering up subtle bugs of IDs being reused.
854 if COUNTER == ::u64::MAX {
856 panic!("failed to generate unique thread ID: bitspace exhausted");
869 ////////////////////////////////////////////////////////////////////////////////
871 ////////////////////////////////////////////////////////////////////////////////
873 /// The internal representation of a `Thread` handle
875 name: Option<CString>, // Guaranteed to be UTF-8
877 lock: Mutex<bool>, // true when there is a buffered unpark
882 #[stable(feature = "rust1", since = "1.0.0")]
883 /// A handle to a thread.
885 /// Threads are represented via the `Thread` type, which you can get in one of
888 /// * By spawning a new thread, e.g. using the [`thread::spawn`][`spawn`]
889 /// function, and calling [`thread`][`JoinHandle::thread`] on the
891 /// * By requesting the current thread, using the [`thread::current`] function.
893 /// The [`thread::current`] function is available even for threads not spawned
894 /// by the APIs of this module.
896 /// There is usualy no need to create a `Thread` struct yourself, one
897 /// should instead use a function like `spawn` to create new threads, see the
898 /// docs of [`Builder`] and [`spawn`] for more details.
900 /// [`Builder`]: ../../std/thread/struct.Builder.html
901 /// [`spawn`]: ../../std/thread/fn.spawn.html
908 // Used only internally to construct a thread object without spawning
909 pub(crate) fn new(name: Option<String>) -> Thread {
910 let cname = name.map(|n| {
911 CString::new(n).expect("thread name may not contain interior null bytes")
914 inner: Arc::new(Inner {
917 lock: Mutex::new(false),
918 cvar: Condvar::new(),
923 /// Atomically makes the handle's token available if it is not already.
925 /// Every thread is equipped with some basic low-level blocking support, via
926 /// the [`park`][park] function and the `unpark()` method. These can be
927 /// used as a more CPU-efficient implementation of a spinlock.
929 /// See the [park documentation][park] for more details.
935 /// use std::time::Duration;
937 /// let parked_thread = thread::Builder::new()
939 /// println!("Parking thread");
941 /// println!("Thread unparked");
945 /// // Let some time pass for the thread to be spawned.
946 /// thread::sleep(Duration::from_millis(10));
948 /// println!("Unpark the thread");
949 /// parked_thread.thread().unpark();
951 /// parked_thread.join().unwrap();
954 /// [park]: fn.park.html
955 #[stable(feature = "rust1", since = "1.0.0")]
956 pub fn unpark(&self) {
957 let mut guard = self.inner.lock.lock().unwrap();
960 self.inner.cvar.notify_one();
964 /// Gets the thread's unique identifier.
969 /// #![feature(thread_id)]
973 /// let other_thread = thread::spawn(|| {
974 /// thread::current().id()
977 /// let other_thread_id = other_thread.join().unwrap();
978 /// assert!(thread::current().id() != other_thread_id);
980 #[unstable(feature = "thread_id", issue = "21507")]
981 pub fn id(&self) -> ThreadId {
985 /// Gets the thread's name.
989 /// Threads by default have no name specified:
994 /// let builder = thread::Builder::new();
996 /// let handler = builder.spawn(|| {
997 /// assert!(thread::current().name().is_none());
1000 /// handler.join().unwrap();
1003 /// Thread with a specified name:
1006 /// use std::thread;
1008 /// let builder = thread::Builder::new()
1009 /// .name("foo".into());
1011 /// let handler = builder.spawn(|| {
1012 /// assert_eq!(thread::current().name(), Some("foo"))
1015 /// handler.join().unwrap();
1017 #[stable(feature = "rust1", since = "1.0.0")]
1018 pub fn name(&self) -> Option<&str> {
1019 self.cname().map(|s| unsafe { str::from_utf8_unchecked(s.to_bytes()) } )
1022 fn cname(&self) -> Option<&CStr> {
1023 self.inner.name.as_ref().map(|s| &**s)
1027 #[stable(feature = "rust1", since = "1.0.0")]
1028 impl fmt::Debug for Thread {
1029 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
1030 fmt::Debug::fmt(&self.name(), f)
1034 ////////////////////////////////////////////////////////////////////////////////
1036 ////////////////////////////////////////////////////////////////////////////////
1038 /// A specialized [`Result`] type for threads.
1040 /// Indicates the manner in which a thread exited.
1042 /// A thread that completes without panicking is considered to exit successfully.
1047 /// use std::thread;
1050 /// fn copy_in_thread() -> thread::Result<()> {
1051 /// thread::spawn(move || { fs::copy("foo.txt", "bar.txt").unwrap(); }).join()
1055 /// match copy_in_thread() {
1056 /// Ok(_) => println!("this is fine"),
1057 /// Err(_) => println!("thread panicked"),
1062 /// [`Result`]: ../../std/result/enum.Result.html
1063 #[stable(feature = "rust1", since = "1.0.0")]
1064 pub type Result<T> = ::result::Result<T, Box<Any + Send + 'static>>;
1066 // This packet is used to communicate the return value between the child thread
1067 // and the parent thread. Memory is shared through the `Arc` within and there's
1068 // no need for a mutex here because synchronization happens with `join()` (the
1069 // parent thread never reads this packet until the child has exited).
1071 // This packet itself is then stored into a `JoinInner` which in turns is placed
1072 // in `JoinHandle` and `JoinGuard`. Due to the usage of `UnsafeCell` we need to
1073 // manually worry about impls like Send and Sync. The type `T` should
1074 // already always be Send (otherwise the thread could not have been created) and
1075 // this type is inherently Sync because no methods take &self. Regardless,
1076 // however, we add inheriting impls for Send/Sync to this type to ensure it's
1077 // Send/Sync and that future modifications will still appropriately classify it.
1078 struct Packet<T>(Arc<UnsafeCell<Option<Result<T>>>>);
1080 unsafe impl<T: Send> Send for Packet<T> {}
1081 unsafe impl<T: Sync> Sync for Packet<T> {}
1083 /// Inner representation for JoinHandle
1084 struct JoinInner<T> {
1085 native: Option<imp::Thread>,
1090 impl<T> JoinInner<T> {
1091 fn join(&mut self) -> Result<T> {
1092 self.native.take().unwrap().join();
1094 (*self.packet.0.get()).take().unwrap()
1099 /// An owned permission to join on a thread (block on its termination).
1101 /// A `JoinHandle` *detaches* the associated thread when it is dropped, which
1102 /// means that there is no longer any handle to thread and no way to `join`
1105 /// Due to platform restrictions, it is not possible to [`Clone`] this
1106 /// handle: the ability to join a thread is a uniquely-owned permission.
1108 /// This `struct` is created by the [`thread::spawn`] function and the
1109 /// [`thread::Builder::spawn`] method.
1113 /// Creation from [`thread::spawn`]:
1116 /// use std::thread;
1118 /// let join_handle: thread::JoinHandle<_> = thread::spawn(|| {
1119 /// // some work here
1123 /// Creation from [`thread::Builder::spawn`]:
1126 /// use std::thread;
1128 /// let builder = thread::Builder::new();
1130 /// let join_handle: thread::JoinHandle<_> = builder.spawn(|| {
1131 /// // some work here
1135 /// Child being detached and outliving its parent:
1138 /// use std::thread;
1139 /// use std::time::Duration;
1141 /// let original_thread = thread::spawn(|| {
1142 /// let _detached_thread = thread::spawn(|| {
1143 /// // Here we sleep to make sure that the first thread returns before.
1144 /// thread::sleep(Duration::from_millis(10));
1145 /// // This will be called, even though the JoinHandle is dropped.
1146 /// println!("♫ Still alive ♫");
1150 /// let _ = original_thread.join();
1151 /// println!("Original thread is joined.");
1153 /// // We make sure that the new thread has time to run, before the main
1154 /// // thread returns.
1156 /// thread::sleep(Duration::from_millis(1000));
1159 /// [`Clone`]: ../../std/clone/trait.Clone.html
1160 /// [`thread::spawn`]: fn.spawn.html
1161 /// [`thread::Builder::spawn`]: struct.Builder.html#method.spawn
1162 #[stable(feature = "rust1", since = "1.0.0")]
1163 pub struct JoinHandle<T>(JoinInner<T>);
1165 impl<T> JoinHandle<T> {
1166 /// Extracts a handle to the underlying thread.
1171 /// #![feature(thread_id)]
1173 /// use std::thread;
1175 /// let builder = thread::Builder::new();
1177 /// let join_handle: thread::JoinHandle<_> = builder.spawn(|| {
1178 /// // some work here
1181 /// let thread = join_handle.thread();
1182 /// println!("thread id: {:?}", thread.id());
1184 #[stable(feature = "rust1", since = "1.0.0")]
1185 pub fn thread(&self) -> &Thread {
1189 /// Waits for the associated thread to finish.
1191 /// If the child thread panics, [`Err`] is returned with the parameter given
1194 /// [`Err`]: ../../std/result/enum.Result.html#variant.Err
1195 /// [`panic`]: ../../std/macro.panic.html
1200 /// use std::thread;
1202 /// let builder = thread::Builder::new();
1204 /// let join_handle: thread::JoinHandle<_> = builder.spawn(|| {
1205 /// // some work here
1207 /// join_handle.join().expect("Couldn't join on the associated thread");
1209 #[stable(feature = "rust1", since = "1.0.0")]
1210 pub fn join(mut self) -> Result<T> {
1215 impl<T> AsInner<imp::Thread> for JoinHandle<T> {
1216 fn as_inner(&self) -> &imp::Thread { self.0.native.as_ref().unwrap() }
1219 impl<T> IntoInner<imp::Thread> for JoinHandle<T> {
1220 fn into_inner(self) -> imp::Thread { self.0.native.unwrap() }
1223 #[stable(feature = "std_debug", since = "1.16.0")]
1224 impl<T> fmt::Debug for JoinHandle<T> {
1225 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
1226 f.pad("JoinHandle { .. }")
1230 fn _assert_sync_and_send() {
1231 fn _assert_both<T: Send + Sync>() {}
1232 _assert_both::<JoinHandle<()>>();
1233 _assert_both::<Thread>();
1236 ////////////////////////////////////////////////////////////////////////////////
1238 ////////////////////////////////////////////////////////////////////////////////
1240 #[cfg(all(test, not(target_os = "emscripten")))]
1243 use sync::mpsc::{channel, Sender};
1245 use super::{Builder};
1250 // !!! These tests are dangerous. If something is buggy, they will hang, !!!
1251 // !!! instead of exiting cleanly. This might wedge the buildbots. !!!
1254 fn test_unnamed_thread() {
1255 thread::spawn(move|| {
1256 assert!(thread::current().name().is_none());
1257 }).join().ok().unwrap();
1261 fn test_named_thread() {
1262 Builder::new().name("ada lovelace".to_string()).spawn(move|| {
1263 assert!(thread::current().name().unwrap() == "ada lovelace".to_string());
1264 }).unwrap().join().unwrap();
1269 fn test_invalid_named_thread() {
1270 let _ = Builder::new().name("ada l\0velace".to_string()).spawn(|| {});
1274 fn test_run_basic() {
1275 let (tx, rx) = channel();
1276 thread::spawn(move|| {
1277 tx.send(()).unwrap();
1283 fn test_join_panic() {
1284 match thread::spawn(move|| {
1287 result::Result::Err(_) => (),
1288 result::Result::Ok(()) => panic!()
1293 fn test_spawn_sched() {
1294 let (tx, rx) = channel();
1296 fn f(i: i32, tx: Sender<()>) {
1297 let tx = tx.clone();
1298 thread::spawn(move|| {
1300 tx.send(()).unwrap();
1312 fn test_spawn_sched_childs_on_default_sched() {
1313 let (tx, rx) = channel();
1315 thread::spawn(move|| {
1316 thread::spawn(move|| {
1317 tx.send(()).unwrap();
1324 fn avoid_copying_the_body<F>(spawnfn: F) where F: FnOnce(Box<Fn() + Send>) {
1325 let (tx, rx) = channel();
1327 let x: Box<_> = box 1;
1328 let x_in_parent = (&*x) as *const i32 as usize;
1330 spawnfn(Box::new(move|| {
1331 let x_in_child = (&*x) as *const i32 as usize;
1332 tx.send(x_in_child).unwrap();
1335 let x_in_child = rx.recv().unwrap();
1336 assert_eq!(x_in_parent, x_in_child);
1340 fn test_avoid_copying_the_body_spawn() {
1341 avoid_copying_the_body(|v| {
1342 thread::spawn(move || v());
1347 fn test_avoid_copying_the_body_thread_spawn() {
1348 avoid_copying_the_body(|f| {
1349 thread::spawn(move|| {
1356 fn test_avoid_copying_the_body_join() {
1357 avoid_copying_the_body(|f| {
1358 let _ = thread::spawn(move|| {
1365 fn test_child_doesnt_ref_parent() {
1366 // If the child refcounts the parent thread, this will stack overflow when
1367 // climbing the thread tree to dereference each ancestor. (See #1789)
1368 // (well, it would if the constant were 8000+ - I lowered it to be more
1369 // valgrind-friendly. try this at home, instead..!)
1370 const GENERATIONS: u32 = 16;
1371 fn child_no(x: u32) -> Box<Fn() + Send> {
1372 return Box::new(move|| {
1373 if x < GENERATIONS {
1374 thread::spawn(move|| child_no(x+1)());
1378 thread::spawn(|| child_no(0)());
1382 fn test_simple_newsched_spawn() {
1383 thread::spawn(move || {});
1387 fn test_try_panic_message_static_str() {
1388 match thread::spawn(move|| {
1389 panic!("static string");
1392 type T = &'static str;
1393 assert!(e.is::<T>());
1394 assert_eq!(*e.downcast::<T>().unwrap(), "static string");
1401 fn test_try_panic_message_owned_str() {
1402 match thread::spawn(move|| {
1403 panic!("owned string".to_string());
1407 assert!(e.is::<T>());
1408 assert_eq!(*e.downcast::<T>().unwrap(), "owned string".to_string());
1415 fn test_try_panic_message_any() {
1416 match thread::spawn(move|| {
1417 panic!(box 413u16 as Box<Any + Send>);
1420 type T = Box<Any + Send>;
1421 assert!(e.is::<T>());
1422 let any = e.downcast::<T>().unwrap();
1423 assert!(any.is::<u16>());
1424 assert_eq!(*any.downcast::<u16>().unwrap(), 413);
1431 fn test_try_panic_message_unit_struct() {
1434 match thread::spawn(move|| {
1437 Err(ref e) if e.is::<Juju>() => {}
1438 Err(_) | Ok(()) => panic!()
1443 fn test_park_timeout_unpark_before() {
1445 thread::current().unpark();
1446 thread::park_timeout(Duration::from_millis(u32::MAX as u64));
1451 fn test_park_timeout_unpark_not_called() {
1453 thread::park_timeout(Duration::from_millis(10));
1458 fn test_park_timeout_unpark_called_other_thread() {
1460 let th = thread::current();
1462 let _guard = thread::spawn(move || {
1463 super::sleep(Duration::from_millis(50));
1467 thread::park_timeout(Duration::from_millis(u32::MAX as u64));
1472 fn sleep_ms_smoke() {
1473 thread::sleep(Duration::from_millis(2));
1477 fn test_thread_id_equal() {
1478 assert!(thread::current().id() == thread::current().id());
1482 fn test_thread_id_not_equal() {
1483 let spawned_id = thread::spawn(|| thread::current().id()).join().unwrap();
1484 assert!(thread::current().id() != spawned_id);
1487 // NOTE: the corresponding test for stderr is in run-pass/thread-stderr, due
1488 // to the test harness apparently interfering with stderr configuration.