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;
170 use ffi::{CStr, CString};
171 use sync::{Mutex, Condvar, Arc};
172 use sys::thread as imp;
173 use sys_common::thread_info;
174 use sys_common::unwind;
175 use sys_common::util;
176 use sys_common::{AsInner, IntoInner};
179 ////////////////////////////////////////////////////////////////////////////////
180 // Thread-local storage
181 ////////////////////////////////////////////////////////////////////////////////
183 #[macro_use] mod local;
184 #[macro_use] mod scoped_tls;
186 #[stable(feature = "rust1", since = "1.0.0")]
187 pub use self::local::{LocalKey, LocalKeyState};
189 #[unstable(feature = "scoped_tls",
190 reason = "scoped TLS has yet to have wide enough use to fully \
191 consider stabilizing its interface",
194 pub use self::scoped_tls::ScopedKey;
196 #[unstable(feature = "libstd_thread_internals", issue = "0")]
197 #[cfg(target_thread_local)]
198 #[doc(hidden)] pub use self::local::elf::Key as __ElfLocalKeyInner;
199 #[unstable(feature = "libstd_thread_internals", issue = "0")]
200 #[doc(hidden)] pub use self::local::os::Key as __OsLocalKeyInner;
201 #[unstable(feature = "libstd_thread_internals", issue = "0")]
202 #[doc(hidden)] pub use self::scoped_tls::__KeyInner as __ScopedKeyInner;
204 ////////////////////////////////////////////////////////////////////////////////
206 ////////////////////////////////////////////////////////////////////////////////
208 /// Thread configuration. Provides detailed control over the properties
209 /// and behavior of new threads.
210 #[stable(feature = "rust1", since = "1.0.0")]
212 // A name for the thread-to-be, for identification in panic messages
213 name: Option<String>,
214 // The size of the stack for the spawned thread
215 stack_size: Option<usize>,
219 /// Generates the base configuration for spawning a thread, from which
220 /// configuration methods can be chained.
221 #[stable(feature = "rust1", since = "1.0.0")]
222 pub fn new() -> Builder {
229 /// Names the thread-to-be. Currently the name is used for identification
230 /// only in panic messages.
231 #[stable(feature = "rust1", since = "1.0.0")]
232 pub fn name(mut self, name: String) -> Builder {
233 self.name = Some(name);
237 /// Sets the size of the stack for the new thread.
238 #[stable(feature = "rust1", since = "1.0.0")]
239 pub fn stack_size(mut self, size: usize) -> Builder {
240 self.stack_size = Some(size);
244 /// Spawns a new thread, and returns a join handle for it.
246 /// The child thread may outlive the parent (unless the parent thread
247 /// is the main thread; the whole process is terminated when the main
248 /// thread finishes). The join handle can be used to block on
249 /// termination of the child thread, including recovering its panics.
253 /// Unlike the `spawn` free function, this method yields an
254 /// `io::Result` to capture any failure to create the thread at
256 #[stable(feature = "rust1", since = "1.0.0")]
257 pub fn spawn<F, T>(self, f: F) -> io::Result<JoinHandle<T>> where
258 F: FnOnce() -> T, F: Send + 'static, T: Send + 'static
260 let Builder { name, stack_size } = self;
262 let stack_size = stack_size.unwrap_or(util::min_stack());
264 let my_thread = Thread::new(name);
265 let their_thread = my_thread.clone();
267 let my_packet : Arc<UnsafeCell<Option<Result<T>>>>
268 = Arc::new(UnsafeCell::new(None));
269 let their_packet = my_packet.clone();
272 if let Some(name) = their_thread.cname() {
273 imp::Thread::set_name(name);
276 thread_info::set(imp::guard::current(), their_thread);
277 let mut output = None;
279 let ptr = &mut output;
280 unwind::try(move || *ptr = Some(f()))
282 *their_packet.get() = Some(try_result.map(|()| {
288 Ok(JoinHandle(JoinInner {
290 Some(imp::Thread::new(stack_size, Box::new(main))?)
293 packet: Packet(my_packet),
298 ////////////////////////////////////////////////////////////////////////////////
300 ////////////////////////////////////////////////////////////////////////////////
302 /// Spawns a new thread, returning a `JoinHandle` for it.
304 /// The join handle will implicitly *detach* the child thread upon being
305 /// dropped. In this case, the child thread may outlive the parent (unless
306 /// the parent thread is the main thread; the whole process is terminated when
307 /// the main thread finishes.) Additionally, the join handle provides a `join`
308 /// method that can be used to join the child thread. If the child thread
309 /// panics, `join` will return an `Err` containing the argument given to
314 /// Panics if the OS fails to create a thread; use `Builder::spawn`
315 /// to recover from such errors.
316 #[stable(feature = "rust1", since = "1.0.0")]
317 pub fn spawn<F, T>(f: F) -> JoinHandle<T> where
318 F: FnOnce() -> T, F: Send + 'static, T: Send + 'static
320 Builder::new().spawn(f).unwrap()
323 /// Gets a handle to the thread that invokes it.
324 #[stable(feature = "rust1", since = "1.0.0")]
325 pub fn current() -> Thread {
326 thread_info::current_thread().expect("use of std::thread::current() is not \
327 possible after the thread's local \
328 data has been destroyed")
331 /// Cooperatively gives up a timeslice to the OS scheduler.
332 #[stable(feature = "rust1", since = "1.0.0")]
334 imp::Thread::yield_now()
337 /// Determines whether the current thread is unwinding because of panic.
339 #[stable(feature = "rust1", since = "1.0.0")]
340 pub fn panicking() -> bool {
344 /// Puts the current thread to sleep for the specified amount of time.
346 /// The thread may sleep longer than the duration specified due to scheduling
347 /// specifics or platform-dependent functionality. Note that on unix platforms
348 /// this function will not return early due to a signal being received or a
350 #[stable(feature = "rust1", since = "1.0.0")]
351 #[rustc_deprecated(since = "1.6.0", reason = "replaced by `std::thread::sleep`")]
352 pub fn sleep_ms(ms: u32) {
353 sleep(Duration::from_millis(ms as u64))
356 /// Puts the current thread to sleep for the specified amount of time.
358 /// The thread may sleep longer than the duration specified due to scheduling
359 /// specifics or platform-dependent functionality.
361 /// # Platform behavior
363 /// On Unix platforms this function will not return early due to a
364 /// signal being received or a spurious wakeup. Platforms which do not support
365 /// nanosecond precision for sleeping will have `dur` rounded up to the nearest
366 /// granularity of time they can sleep for.
367 #[stable(feature = "thread_sleep", since = "1.4.0")]
368 pub fn sleep(dur: Duration) {
369 imp::Thread::sleep(dur)
372 /// Blocks unless or until the current thread's token is made available.
374 /// Every thread is equipped with some basic low-level blocking support, via
375 /// the `park()` function and the [`unpark()`][unpark] method. These can be
376 /// used as a more CPU-efficient implementation of a spinlock.
378 /// [unpark]: struct.Thread.html#method.unpark
380 /// The API is typically used by acquiring a handle to the current thread,
381 /// placing that handle in a shared data structure so that other threads can
382 /// find it, and then parking (in a loop with a check for the token actually
385 /// A call to `park` does not guarantee that the thread will remain parked
386 /// forever, and callers should be prepared for this possibility.
388 /// See the [module documentation][thread] for more detail.
390 /// [thread]: index.html
392 // The implementation currently uses the trivial strategy of a Mutex+Condvar
393 // with wakeup flag, which does not actually allow spurious wakeups. In the
394 // future, this will be implemented in a more efficient way, perhaps along the lines of
395 // http://cr.openjdk.java.net/~stefank/6989984.1/raw_files/new/src/os/linux/vm/os_linux.cpp
396 // or futuxes, and in either case may allow spurious wakeups.
397 #[stable(feature = "rust1", since = "1.0.0")]
399 let thread = current();
400 let mut guard = thread.inner.lock.lock().unwrap();
402 guard = thread.inner.cvar.wait(guard).unwrap();
407 /// Blocks unless or until the current thread's token is made available or
408 /// the specified duration has been reached (may wake spuriously).
410 /// The semantics of this function are equivalent to `park()` except that the
411 /// thread will be blocked for roughly no longer than *ms*. This method
412 /// should not be used for precise timing due to anomalies such as
413 /// preemption or platform differences that may not cause the maximum
414 /// amount of time waited to be precisely *ms* long.
416 /// See the module doc for more detail.
417 #[stable(feature = "rust1", since = "1.0.0")]
418 #[rustc_deprecated(since = "1.6.0", reason = "replaced by `std::thread::park_timeout`")]
419 pub fn park_timeout_ms(ms: u32) {
420 park_timeout(Duration::from_millis(ms as u64))
423 /// Blocks unless or until the current thread's token is made available or
424 /// the specified duration has been reached (may wake spuriously).
426 /// The semantics of this function are equivalent to `park()` except that the
427 /// thread will be blocked for roughly no longer than *dur*. This method
428 /// should not be used for precise timing due to anomalies such as
429 /// preemption or platform differences that may not cause the maximum
430 /// amount of time waited to be precisely *dur* long.
432 /// See the module doc for more detail.
434 /// # Platform behavior
436 /// Platforms which do not support nanosecond precision for sleeping will have
437 /// `dur` rounded up to the nearest granularity of time they can sleep for.
438 #[stable(feature = "park_timeout", since = "1.4.0")]
439 pub fn park_timeout(dur: Duration) {
440 let thread = current();
441 let mut guard = thread.inner.lock.lock().unwrap();
443 let (g, _) = thread.inner.cvar.wait_timeout(guard, dur).unwrap();
449 ////////////////////////////////////////////////////////////////////////////////
451 ////////////////////////////////////////////////////////////////////////////////
453 /// The internal representation of a `Thread` handle
455 name: Option<CString>, // Guaranteed to be UTF-8
456 lock: Mutex<bool>, // true when there is a buffered unpark
461 #[stable(feature = "rust1", since = "1.0.0")]
462 /// A handle to a thread.
468 // Used only internally to construct a thread object without spawning
469 fn new(name: Option<String>) -> Thread {
470 let cname = name.map(|n| CString::new(n).unwrap_or_else(|_| {
471 panic!("thread name may not contain interior null bytes")
474 inner: Arc::new(Inner {
476 lock: Mutex::new(false),
477 cvar: Condvar::new(),
482 /// Atomically makes the handle's token available if it is not already.
484 /// See the module doc for more detail.
485 #[stable(feature = "rust1", since = "1.0.0")]
486 pub fn unpark(&self) {
487 let mut guard = self.inner.lock.lock().unwrap();
490 self.inner.cvar.notify_one();
494 /// Gets the thread's name.
495 #[stable(feature = "rust1", since = "1.0.0")]
496 pub fn name(&self) -> Option<&str> {
497 self.cname().map(|s| unsafe { str::from_utf8_unchecked(s.to_bytes()) } )
500 fn cname(&self) -> Option<&CStr> {
501 self.inner.name.as_ref().map(|s| &**s)
505 #[stable(feature = "rust1", since = "1.0.0")]
506 impl fmt::Debug for Thread {
507 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
508 fmt::Debug::fmt(&self.name(), f)
512 // a hack to get around privacy restrictions
513 impl thread_info::NewThread for Thread {
514 fn new(name: Option<String>) -> Thread { Thread::new(name) }
517 ////////////////////////////////////////////////////////////////////////////////
519 ////////////////////////////////////////////////////////////////////////////////
521 /// Indicates the manner in which a thread exited.
523 /// A thread that completes without panicking is considered to exit successfully.
524 #[stable(feature = "rust1", since = "1.0.0")]
525 pub type Result<T> = ::result::Result<T, Box<Any + Send + 'static>>;
527 // This packet is used to communicate the return value between the child thread
528 // and the parent thread. Memory is shared through the `Arc` within and there's
529 // no need for a mutex here because synchronization happens with `join()` (the
530 // parent thread never reads this packet until the child has exited).
532 // This packet itself is then stored into a `JoinInner` which in turns is placed
533 // in `JoinHandle` and `JoinGuard`. Due to the usage of `UnsafeCell` we need to
534 // manually worry about impls like Send and Sync. The type `T` should
535 // already always be Send (otherwise the thread could not have been created) and
536 // this type is inherently Sync because no methods take &self. Regardless,
537 // however, we add inheriting impls for Send/Sync to this type to ensure it's
538 // Send/Sync and that future modifications will still appropriately classify it.
539 struct Packet<T>(Arc<UnsafeCell<Option<Result<T>>>>);
541 unsafe impl<T: Send> Send for Packet<T> {}
542 unsafe impl<T: Sync> Sync for Packet<T> {}
544 /// Inner representation for JoinHandle
545 struct JoinInner<T> {
546 native: Option<imp::Thread>,
551 impl<T> JoinInner<T> {
552 fn join(&mut self) -> Result<T> {
553 self.native.take().unwrap().join();
555 (*self.packet.0.get()).take().unwrap()
560 /// An owned permission to join on a thread (block on its termination).
562 /// A `JoinHandle` *detaches* the child thread when it is dropped.
564 /// Due to platform restrictions, it is not possible to `Clone` this
565 /// handle: the ability to join a child thread is a uniquely-owned
567 #[stable(feature = "rust1", since = "1.0.0")]
568 pub struct JoinHandle<T>(JoinInner<T>);
570 impl<T> JoinHandle<T> {
571 /// Extracts a handle to the underlying thread
572 #[stable(feature = "rust1", since = "1.0.0")]
573 pub fn thread(&self) -> &Thread {
577 /// Waits for the associated thread to finish.
579 /// If the child thread panics, `Err` is returned with the parameter given
581 #[stable(feature = "rust1", since = "1.0.0")]
582 pub fn join(mut self) -> Result<T> {
587 impl<T> AsInner<imp::Thread> for JoinHandle<T> {
588 fn as_inner(&self) -> &imp::Thread { self.0.native.as_ref().unwrap() }
591 impl<T> IntoInner<imp::Thread> for JoinHandle<T> {
592 fn into_inner(self) -> imp::Thread { self.0.native.unwrap() }
595 fn _assert_sync_and_send() {
596 fn _assert_both<T: Send + Sync>() {}
597 _assert_both::<JoinHandle<()>>();
598 _assert_both::<Thread>();
601 ////////////////////////////////////////////////////////////////////////////////
603 ////////////////////////////////////////////////////////////////////////////////
610 use sync::mpsc::{channel, Sender};
612 use super::{Builder};
617 // !!! These tests are dangerous. If something is buggy, they will hang, !!!
618 // !!! instead of exiting cleanly. This might wedge the buildbots. !!!
621 fn test_unnamed_thread() {
622 thread::spawn(move|| {
623 assert!(thread::current().name().is_none());
624 }).join().ok().unwrap();
628 fn test_named_thread() {
629 Builder::new().name("ada lovelace".to_string()).spawn(move|| {
630 assert!(thread::current().name().unwrap() == "ada lovelace".to_string());
631 }).unwrap().join().unwrap();
636 fn test_invalid_named_thread() {
637 let _ = Builder::new().name("ada l\0velace".to_string()).spawn(|| {});
641 fn test_run_basic() {
642 let (tx, rx) = channel();
643 thread::spawn(move|| {
644 tx.send(()).unwrap();
650 fn test_join_panic() {
651 match thread::spawn(move|| {
654 result::Result::Err(_) => (),
655 result::Result::Ok(()) => panic!()
660 fn test_spawn_sched() {
663 let (tx, rx) = channel();
665 fn f(i: i32, tx: Sender<()>) {
667 thread::spawn(move|| {
669 tx.send(()).unwrap();
681 fn test_spawn_sched_childs_on_default_sched() {
682 let (tx, rx) = channel();
684 thread::spawn(move|| {
685 thread::spawn(move|| {
686 tx.send(()).unwrap();
693 fn avoid_copying_the_body<F>(spawnfn: F) where F: FnOnce(Box<Fn() + Send>) {
694 let (tx, rx) = channel();
696 let x: Box<_> = box 1;
697 let x_in_parent = (&*x) as *const i32 as usize;
699 spawnfn(Box::new(move|| {
700 let x_in_child = (&*x) as *const i32 as usize;
701 tx.send(x_in_child).unwrap();
704 let x_in_child = rx.recv().unwrap();
705 assert_eq!(x_in_parent, x_in_child);
709 fn test_avoid_copying_the_body_spawn() {
710 avoid_copying_the_body(|v| {
711 thread::spawn(move || v());
716 fn test_avoid_copying_the_body_thread_spawn() {
717 avoid_copying_the_body(|f| {
718 thread::spawn(move|| {
725 fn test_avoid_copying_the_body_join() {
726 avoid_copying_the_body(|f| {
727 let _ = thread::spawn(move|| {
734 fn test_child_doesnt_ref_parent() {
735 // If the child refcounts the parent thread, this will stack overflow when
736 // climbing the thread tree to dereference each ancestor. (See #1789)
737 // (well, it would if the constant were 8000+ - I lowered it to be more
738 // valgrind-friendly. try this at home, instead..!)
739 const GENERATIONS: u32 = 16;
740 fn child_no(x: u32) -> Box<Fn() + Send> {
741 return Box::new(move|| {
743 thread::spawn(move|| child_no(x+1)());
747 thread::spawn(|| child_no(0)());
751 fn test_simple_newsched_spawn() {
752 thread::spawn(move || {});
756 fn test_try_panic_message_static_str() {
757 match thread::spawn(move|| {
758 panic!("static string");
761 type T = &'static str;
762 assert!(e.is::<T>());
763 assert_eq!(*e.downcast::<T>().unwrap(), "static string");
770 fn test_try_panic_message_owned_str() {
771 match thread::spawn(move|| {
772 panic!("owned string".to_string());
776 assert!(e.is::<T>());
777 assert_eq!(*e.downcast::<T>().unwrap(), "owned string".to_string());
784 fn test_try_panic_message_any() {
785 match thread::spawn(move|| {
786 panic!(box 413u16 as Box<Any + Send>);
789 type T = Box<Any + Send>;
790 assert!(e.is::<T>());
791 let any = e.downcast::<T>().unwrap();
792 assert!(any.is::<u16>());
793 assert_eq!(*any.downcast::<u16>().unwrap(), 413);
800 fn test_try_panic_message_unit_struct() {
803 match thread::spawn(move|| {
806 Err(ref e) if e.is::<Juju>() => {}
807 Err(_) | Ok(()) => panic!()
812 fn test_park_timeout_unpark_before() {
814 thread::current().unpark();
815 thread::park_timeout(Duration::from_millis(u32::MAX as u64));
820 fn test_park_timeout_unpark_not_called() {
822 thread::park_timeout(Duration::from_millis(10));
827 fn test_park_timeout_unpark_called_other_thread() {
829 let th = thread::current();
831 let _guard = thread::spawn(move || {
832 super::sleep(Duration::from_millis(50));
836 thread::park_timeout(Duration::from_millis(u32::MAX as u64));
841 fn sleep_ms_smoke() {
842 thread::sleep(Duration::from_millis(2));
845 // NOTE: the corresponding test for stderr is in run-pass/thread-stderr, due
846 // to the test harness apparently interfering with stderr configuration.