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.
18 //! Communication between threads can be done through
19 //! [channels](../../std/sync/mpsc/index.html), Rust's message-passing
20 //! 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,
25 //! [`Arc`](../../std/sync/struct.Arc.html).
27 //! Fatal logic errors in Rust cause *thread panic*, during which
28 //! a thread will unwind the stack, running destructors and freeing
29 //! owned resources. Thread panic is unrecoverable from within
30 //! the panicking thread (i.e. there is no 'try/catch' in Rust), but
31 //! the panic may optionally be detected from a different thread. If
32 //! the main thread panics, the application will exit with a non-zero
35 //! When the main thread of a Rust program terminates, the entire program shuts
36 //! down, even if other threads are still running. However, this module provides
37 //! convenient facilities for automatically waiting for the termination of a
38 //! child thread (i.e., join).
40 //! ## The `Thread` type
42 //! Threads are represented via the `Thread` type, which you can
43 //! get in one of two ways:
45 //! * By spawning a new thread, e.g. using the `thread::spawn` function.
46 //! * By requesting the current thread, using the `thread::current` function.
48 //! Threads can be named, and provide some built-in support for low-level
49 //! synchronization (described below).
51 //! The `thread::current()` function is available even for threads not spawned
52 //! by the APIs of this module.
54 //! ## Spawning a thread
56 //! A new thread can be spawned using the `thread::spawn` function:
61 //! thread::spawn(move || {
66 //! In this example, the spawned thread is "detached" from the current
67 //! thread. This means that it can outlive its parent (the thread that spawned
68 //! it), unless this parent is the main thread.
70 //! The parent thread can also wait on the completion of the child
71 //! thread; a call to `spawn` produces a `JoinHandle`, which provides
72 //! a `join` method for waiting:
77 //! let child = thread::spawn(move || {
81 //! let res = child.join();
84 //! The `join` method returns a `Result` containing `Ok` of the final
85 //! value produced by the child thread, or `Err` of the value given to
86 //! a call to `panic!` if the child panicked.
88 //! ## Configuring threads
90 //! A new thread can be configured before it is spawned via the `Builder` type,
91 //! which currently allows you to set the name and stack size for the child thread:
94 //! # #![allow(unused_must_use)]
97 //! thread::Builder::new().name("child1".to_string()).spawn(move || {
98 //! println!("Hello, world!");
102 //! ## Blocking support: park and unpark
104 //! Every thread is equipped with some basic low-level blocking support, via the
105 //! `park` and `unpark` functions.
107 //! Conceptually, each `Thread` handle has an associated token, which is
108 //! initially not present:
110 //! * The `thread::park()` function blocks the current thread unless or until
111 //! the token is available for its thread handle, at which point it atomically
112 //! consumes the token. It may also return *spuriously*, without consuming the
113 //! token. `thread::park_timeout()` does the same, but allows specifying a
114 //! maximum time to block the thread for.
116 //! * The `unpark()` method on a `Thread` atomically makes the token available
117 //! if it wasn't already.
119 //! In other words, each `Thread` acts a bit like a semaphore with initial count
120 //! 0, except that the semaphore is *saturating* (the count cannot go above 1),
121 //! and can return spuriously.
123 //! The API is typically used by acquiring a handle to the current thread,
124 //! placing that handle in a shared data structure so that other threads can
125 //! find it, and then `park`ing. When some desired condition is met, another
126 //! thread calls `unpark` on the handle.
128 //! The motivation for this design is twofold:
130 //! * It avoids the need to allocate mutexes and condvars when building new
131 //! synchronization primitives; the threads already provide basic blocking/signaling.
133 //! * It can be implemented very efficiently on many platforms.
135 //! ## Thread-local storage
137 //! This module also provides an implementation of thread local storage for Rust
138 //! programs. Thread local storage is a method of storing data into a global
139 //! variable which each thread in the program will have its own copy of.
140 //! Threads do not share this data, so accesses do not need to be synchronized.
142 //! At a high level, this module provides two variants of storage:
144 //! * Owned thread-local storage. This is a type of thread local key which
145 //! owns the value that it contains, and will destroy the value when the
146 //! thread exits. This variant is created with the `thread_local!` macro and
147 //! can contain any value which is `'static` (no borrowed pointers).
149 //! * Scoped thread-local storage. This type of key is used to store a reference
150 //! to a value into local storage temporarily for the scope of a function
151 //! call. There are no restrictions on what types of values can be placed
154 //! Both forms of thread local storage provide an accessor function, `with`,
155 //! which will yield a shared reference to the value to the specified
156 //! closure. Thread-local keys only allow shared access to values as there is no
157 //! way to guarantee uniqueness if a mutable borrow was allowed. Most values
158 //! will want to make use of some form of **interior mutability** through the
159 //! `Cell` or `RefCell` types.
161 #![stable(feature = "rust1", since = "1.0.0")]
166 use cell::UnsafeCell;
169 use sync::{Mutex, Condvar, Arc};
170 use sys::thread as imp;
171 use sys_common::thread_info;
172 use sys_common::unwind;
173 use sys_common::util;
174 use sys_common::{AsInner, IntoInner};
177 ////////////////////////////////////////////////////////////////////////////////
178 // Thread-local storage
179 ////////////////////////////////////////////////////////////////////////////////
181 #[macro_use] mod local;
182 #[macro_use] mod scoped_tls;
184 #[stable(feature = "rust1", since = "1.0.0")]
185 pub use self::local::{LocalKey, LocalKeyState};
187 #[unstable(feature = "scoped_tls",
188 reason = "scoped TLS has yet to have wide enough use to fully \
189 consider stabilizing its interface",
192 pub use self::scoped_tls::ScopedKey;
194 #[unstable(feature = "libstd_thread_internals", issue = "0")]
195 #[cfg(target_thread_local)]
196 #[doc(hidden)] pub use self::local::elf::Key as __ElfLocalKeyInner;
197 #[unstable(feature = "libstd_thread_internals", issue = "0")]
198 #[doc(hidden)] pub use self::local::os::Key as __OsLocalKeyInner;
199 #[unstable(feature = "libstd_thread_internals", issue = "0")]
200 #[doc(hidden)] pub use self::scoped_tls::__KeyInner as __ScopedKeyInner;
202 ////////////////////////////////////////////////////////////////////////////////
204 ////////////////////////////////////////////////////////////////////////////////
206 /// Thread configuration. Provides detailed control over the properties
207 /// and behavior of new threads.
208 #[stable(feature = "rust1", since = "1.0.0")]
210 // A name for the thread-to-be, for identification in panic messages
211 name: Option<String>,
212 // The size of the stack for the spawned thread
213 stack_size: Option<usize>,
217 /// Generates the base configuration for spawning a thread, from which
218 /// configuration methods can be chained.
219 #[stable(feature = "rust1", since = "1.0.0")]
220 pub fn new() -> Builder {
227 /// Names the thread-to-be. Currently the name is used for identification
228 /// only in panic messages.
229 #[stable(feature = "rust1", since = "1.0.0")]
230 pub fn name(mut self, name: String) -> Builder {
231 self.name = Some(name);
235 /// Sets the size of the stack for the new thread.
236 #[stable(feature = "rust1", since = "1.0.0")]
237 pub fn stack_size(mut self, size: usize) -> Builder {
238 self.stack_size = Some(size);
242 /// Spawns a new thread, and returns a join handle for it.
244 /// The child thread may outlive the parent (unless the parent thread
245 /// is the main thread; the whole process is terminated when the main
246 /// thread finishes). The join handle can be used to block on
247 /// termination of the child thread, including recovering its panics.
251 /// Unlike the `spawn` free function, this method yields an
252 /// `io::Result` to capture any failure to create the thread at
254 #[stable(feature = "rust1", since = "1.0.0")]
255 pub fn spawn<F, T>(self, f: F) -> io::Result<JoinHandle<T>> where
256 F: FnOnce() -> T, F: Send + 'static, T: Send + 'static
258 let Builder { name, stack_size } = self;
260 let stack_size = stack_size.unwrap_or(util::min_stack());
262 let my_thread = Thread::new(name);
263 let their_thread = my_thread.clone();
265 let my_packet : Arc<UnsafeCell<Option<Result<T>>>>
266 = Arc::new(UnsafeCell::new(None));
267 let their_packet = my_packet.clone();
270 if let Some(name) = their_thread.name() {
271 imp::Thread::set_name(name);
274 thread_info::set(imp::guard::current(), their_thread);
275 let mut output = None;
277 let ptr = &mut output;
278 unwind::try(move || *ptr = Some(f()))
280 *their_packet.get() = Some(try_result.map(|()| {
286 Ok(JoinHandle(JoinInner {
288 Some(try!(imp::Thread::new(stack_size, Box::new(main))))
291 packet: Packet(my_packet),
296 ////////////////////////////////////////////////////////////////////////////////
298 ////////////////////////////////////////////////////////////////////////////////
300 /// Spawns a new thread, returning a `JoinHandle` for it.
302 /// The join handle will implicitly *detach* the child thread upon being
303 /// dropped. In this case, the child thread may outlive the parent (unless
304 /// the parent thread is the main thread; the whole process is terminated when
305 /// the main thread finishes.) Additionally, the join handle provides a `join`
306 /// method that can be used to join the child thread. If the child thread
307 /// panics, `join` will return an `Err` containing the argument given to
312 /// Panics if the OS fails to create a thread; use `Builder::spawn`
313 /// to recover from such errors.
314 #[stable(feature = "rust1", since = "1.0.0")]
315 pub fn spawn<F, T>(f: F) -> JoinHandle<T> where
316 F: FnOnce() -> T, F: Send + 'static, T: Send + 'static
318 Builder::new().spawn(f).unwrap()
321 /// Gets a handle to the thread that invokes it.
322 #[stable(feature = "rust1", since = "1.0.0")]
323 pub fn current() -> Thread {
324 thread_info::current_thread().expect("use of std::thread::current() is not \
325 possible after the thread's local \
326 data has been destroyed")
329 /// Cooperatively gives up a timeslice to the OS scheduler.
330 #[stable(feature = "rust1", since = "1.0.0")]
332 imp::Thread::yield_now()
335 /// Determines whether the current thread is unwinding because of panic.
337 #[stable(feature = "rust1", since = "1.0.0")]
338 pub fn panicking() -> bool {
342 /// Puts the current thread to sleep for the specified amount of time.
344 /// The thread may sleep longer than the duration specified due to scheduling
345 /// specifics or platform-dependent functionality. Note that on unix platforms
346 /// this function will not return early due to a signal being received or a
348 #[stable(feature = "rust1", since = "1.0.0")]
349 #[rustc_deprecated(since = "1.6.0", reason = "replaced by `std::thread::sleep`")]
350 pub fn sleep_ms(ms: u32) {
351 sleep(Duration::from_millis(ms as u64))
354 /// Puts the current thread to sleep for the specified amount of time.
356 /// The thread may sleep longer than the duration specified due to scheduling
357 /// specifics or platform-dependent functionality.
359 /// # Platform behavior
361 /// On Unix platforms this function will not return early due to a
362 /// signal being received or a spurious wakeup. Platforms which do not support
363 /// nanosecond precision for sleeping will have `dur` rounded up to the nearest
364 /// granularity of time they can sleep for.
365 #[stable(feature = "thread_sleep", since = "1.4.0")]
366 pub fn sleep(dur: Duration) {
367 imp::Thread::sleep(dur)
370 /// Blocks unless or until the current thread's token is made available.
372 /// Every thread is equipped with some basic low-level blocking support, via
373 /// the `park()` function and the [`unpark()`][unpark] method. These can be
374 /// used as a more CPU-efficient implementation of a spinlock.
376 /// [unpark]: struct.Thread.html#method.unpark
378 /// The API is typically used by acquiring a handle to the current thread,
379 /// placing that handle in a shared data structure so that other threads can
380 /// find it, and then parking (in a loop with a check for the token actually
383 /// A call to `park` does not guarantee that the thread will remain parked
384 /// forever, and callers should be prepared for this possibility.
386 /// See the [module documentation][thread] for more detail.
388 /// [thread]: index.html
390 // The implementation currently uses the trivial strategy of a Mutex+Condvar
391 // with wakeup flag, which does not actually allow spurious wakeups. In the
392 // future, this will be implemented in a more efficient way, perhaps along the lines of
393 // http://cr.openjdk.java.net/~stefank/6989984.1/raw_files/new/src/os/linux/vm/os_linux.cpp
394 // or futuxes, and in either case may allow spurious wakeups.
395 #[stable(feature = "rust1", since = "1.0.0")]
397 let thread = current();
398 let mut guard = thread.inner.lock.lock().unwrap();
400 guard = thread.inner.cvar.wait(guard).unwrap();
405 /// Blocks unless or until the current thread's token is made available or
406 /// the specified duration has been reached (may wake spuriously).
408 /// The semantics of this function are equivalent to `park()` except that the
409 /// thread will be blocked for roughly no longer than *ms*. This method
410 /// should not be used for precise timing due to anomalies such as
411 /// preemption or platform differences that may not cause the maximum
412 /// amount of time waited to be precisely *ms* long.
414 /// See the module doc for more detail.
415 #[stable(feature = "rust1", since = "1.0.0")]
416 #[rustc_deprecated(since = "1.6.0", reason = "replaced by `std::thread::park_timeout`")]
417 pub fn park_timeout_ms(ms: u32) {
418 park_timeout(Duration::from_millis(ms as u64))
421 /// Blocks unless or until the current thread's token is made available or
422 /// the specified duration has been reached (may wake spuriously).
424 /// The semantics of this function are equivalent to `park()` except that the
425 /// thread will be blocked for roughly no longer than *dur*. This method
426 /// should not be used for precise timing due to anomalies such as
427 /// preemption or platform differences that may not cause the maximum
428 /// amount of time waited to be precisely *dur* long.
430 /// See the module doc for more detail.
432 /// # Platform behavior
434 /// Platforms which do not support nanosecond precision for sleeping will have
435 /// `dur` rounded up to the nearest granularity of time they can sleep for.
436 #[stable(feature = "park_timeout", since = "1.4.0")]
437 pub fn park_timeout(dur: Duration) {
438 let thread = current();
439 let mut guard = thread.inner.lock.lock().unwrap();
441 let (g, _) = thread.inner.cvar.wait_timeout(guard, dur).unwrap();
447 ////////////////////////////////////////////////////////////////////////////////
449 ////////////////////////////////////////////////////////////////////////////////
451 /// The internal representation of a `Thread` handle
453 name: Option<String>,
454 lock: Mutex<bool>, // true when there is a buffered unpark
459 #[stable(feature = "rust1", since = "1.0.0")]
460 /// A handle to a thread.
466 // Used only internally to construct a thread object without spawning
467 fn new(name: Option<String>) -> Thread {
469 inner: Arc::new(Inner {
471 lock: Mutex::new(false),
472 cvar: Condvar::new(),
477 /// Atomically makes the handle's token available if it is not already.
479 /// See the module doc for more detail.
480 #[stable(feature = "rust1", since = "1.0.0")]
481 pub fn unpark(&self) {
482 let mut guard = self.inner.lock.lock().unwrap();
485 self.inner.cvar.notify_one();
489 /// Gets the thread's name.
490 #[stable(feature = "rust1", since = "1.0.0")]
491 pub fn name(&self) -> Option<&str> {
492 self.inner.name.as_ref().map(|s| &**s)
496 #[stable(feature = "rust1", since = "1.0.0")]
497 impl fmt::Debug for Thread {
498 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
499 fmt::Debug::fmt(&self.name(), f)
503 // a hack to get around privacy restrictions
504 impl thread_info::NewThread for Thread {
505 fn new(name: Option<String>) -> Thread { Thread::new(name) }
508 ////////////////////////////////////////////////////////////////////////////////
510 ////////////////////////////////////////////////////////////////////////////////
512 /// Indicates the manner in which a thread exited.
514 /// A thread that completes without panicking is considered to exit successfully.
515 #[stable(feature = "rust1", since = "1.0.0")]
516 pub type Result<T> = ::result::Result<T, Box<Any + Send + 'static>>;
518 // This packet is used to communicate the return value between the child thread
519 // and the parent thread. Memory is shared through the `Arc` within and there's
520 // no need for a mutex here because synchronization happens with `join()` (the
521 // parent thread never reads this packet until the child has exited).
523 // This packet itself is then stored into a `JoinInner` which in turns is placed
524 // in `JoinHandle` and `JoinGuard`. Due to the usage of `UnsafeCell` we need to
525 // manually worry about impls like Send and Sync. The type `T` should
526 // already always be Send (otherwise the thread could not have been created) and
527 // this type is inherently Sync because no methods take &self. Regardless,
528 // however, we add inheriting impls for Send/Sync to this type to ensure it's
529 // Send/Sync and that future modifications will still appropriately classify it.
530 struct Packet<T>(Arc<UnsafeCell<Option<Result<T>>>>);
532 unsafe impl<T: Send> Send for Packet<T> {}
533 unsafe impl<T: Sync> Sync for Packet<T> {}
535 /// Inner representation for JoinHandle
536 struct JoinInner<T> {
537 native: Option<imp::Thread>,
542 impl<T> JoinInner<T> {
543 fn join(&mut self) -> Result<T> {
544 self.native.take().unwrap().join();
546 (*self.packet.0.get()).take().unwrap()
551 /// An owned permission to join on a thread (block on its termination).
553 /// A `JoinHandle` *detaches* the child thread when it is dropped.
555 /// Due to platform restrictions, it is not possible to `Clone` this
556 /// handle: the ability to join a child thread is a uniquely-owned
558 #[stable(feature = "rust1", since = "1.0.0")]
559 pub struct JoinHandle<T>(JoinInner<T>);
561 impl<T> JoinHandle<T> {
562 /// Extracts a handle to the underlying thread
563 #[stable(feature = "rust1", since = "1.0.0")]
564 pub fn thread(&self) -> &Thread {
568 /// Waits for the associated thread to finish.
570 /// If the child thread panics, `Err` is returned with the parameter given
572 #[stable(feature = "rust1", since = "1.0.0")]
573 pub fn join(mut self) -> Result<T> {
578 impl<T> AsInner<imp::Thread> for JoinHandle<T> {
579 fn as_inner(&self) -> &imp::Thread { self.0.native.as_ref().unwrap() }
582 impl<T> IntoInner<imp::Thread> for JoinHandle<T> {
583 fn into_inner(self) -> imp::Thread { self.0.native.unwrap() }
586 fn _assert_sync_and_send() {
587 fn _assert_both<T: Send + Sync>() {}
588 _assert_both::<JoinHandle<()>>();
589 _assert_both::<Thread>();
592 ////////////////////////////////////////////////////////////////////////////////
594 ////////////////////////////////////////////////////////////////////////////////
601 use sync::mpsc::{channel, Sender};
603 use super::{Builder};
608 // !!! These tests are dangerous. If something is buggy, they will hang, !!!
609 // !!! instead of exiting cleanly. This might wedge the buildbots. !!!
612 fn test_unnamed_thread() {
613 thread::spawn(move|| {
614 assert!(thread::current().name().is_none());
615 }).join().ok().unwrap();
619 fn test_named_thread() {
620 Builder::new().name("ada lovelace".to_string()).spawn(move|| {
621 assert!(thread::current().name().unwrap() == "ada lovelace".to_string());
622 }).unwrap().join().unwrap();
626 fn test_run_basic() {
627 let (tx, rx) = channel();
628 thread::spawn(move|| {
629 tx.send(()).unwrap();
635 fn test_join_panic() {
636 match thread::spawn(move|| {
639 result::Result::Err(_) => (),
640 result::Result::Ok(()) => panic!()
645 fn test_spawn_sched() {
648 let (tx, rx) = channel();
650 fn f(i: i32, tx: Sender<()>) {
652 thread::spawn(move|| {
654 tx.send(()).unwrap();
666 fn test_spawn_sched_childs_on_default_sched() {
667 let (tx, rx) = channel();
669 thread::spawn(move|| {
670 thread::spawn(move|| {
671 tx.send(()).unwrap();
678 fn avoid_copying_the_body<F>(spawnfn: F) where F: FnOnce(Box<Fn() + Send>) {
679 let (tx, rx) = channel();
681 let x: Box<_> = box 1;
682 let x_in_parent = (&*x) as *const i32 as usize;
684 spawnfn(Box::new(move|| {
685 let x_in_child = (&*x) as *const i32 as usize;
686 tx.send(x_in_child).unwrap();
689 let x_in_child = rx.recv().unwrap();
690 assert_eq!(x_in_parent, x_in_child);
694 fn test_avoid_copying_the_body_spawn() {
695 avoid_copying_the_body(|v| {
696 thread::spawn(move || v());
701 fn test_avoid_copying_the_body_thread_spawn() {
702 avoid_copying_the_body(|f| {
703 thread::spawn(move|| {
710 fn test_avoid_copying_the_body_join() {
711 avoid_copying_the_body(|f| {
712 let _ = thread::spawn(move|| {
719 fn test_child_doesnt_ref_parent() {
720 // If the child refcounts the parent thread, this will stack overflow when
721 // climbing the thread tree to dereference each ancestor. (See #1789)
722 // (well, it would if the constant were 8000+ - I lowered it to be more
723 // valgrind-friendly. try this at home, instead..!)
724 const GENERATIONS: u32 = 16;
725 fn child_no(x: u32) -> Box<Fn() + Send> {
726 return Box::new(move|| {
728 thread::spawn(move|| child_no(x+1)());
732 thread::spawn(|| child_no(0)());
736 fn test_simple_newsched_spawn() {
737 thread::spawn(move || {});
741 fn test_try_panic_message_static_str() {
742 match thread::spawn(move|| {
743 panic!("static string");
746 type T = &'static str;
747 assert!(e.is::<T>());
748 assert_eq!(*e.downcast::<T>().unwrap(), "static string");
755 fn test_try_panic_message_owned_str() {
756 match thread::spawn(move|| {
757 panic!("owned string".to_string());
761 assert!(e.is::<T>());
762 assert_eq!(*e.downcast::<T>().unwrap(), "owned string".to_string());
769 fn test_try_panic_message_any() {
770 match thread::spawn(move|| {
771 panic!(box 413u16 as Box<Any + Send>);
774 type T = Box<Any + Send>;
775 assert!(e.is::<T>());
776 let any = e.downcast::<T>().unwrap();
777 assert!(any.is::<u16>());
778 assert_eq!(*any.downcast::<u16>().unwrap(), 413);
785 fn test_try_panic_message_unit_struct() {
788 match thread::spawn(move|| {
791 Err(ref e) if e.is::<Juju>() => {}
792 Err(_) | Ok(()) => panic!()
797 fn test_park_timeout_unpark_before() {
799 thread::current().unpark();
800 thread::park_timeout(Duration::from_millis(u32::MAX as u64));
805 fn test_park_timeout_unpark_not_called() {
807 thread::park_timeout(Duration::from_millis(10));
812 fn test_park_timeout_unpark_called_other_thread() {
814 let th = thread::current();
816 let _guard = thread::spawn(move || {
817 super::sleep(Duration::from_millis(50));
821 thread::park_timeout(Duration::from_millis(u32::MAX as u64));
826 fn sleep_ms_smoke() {
827 thread::sleep(Duration::from_millis(2));
830 // NOTE: the corresponding test for stderr is in run-pass/thread-stderr, due
831 // to the test harness apparently interfering with stderr configuration.