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/comm/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 //! 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), described below.
40 //! ## The `Thread` type
42 //! Already-running 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` constructor;
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:
59 //! use std::thread::Thread;
61 //! let guard = Thread::spawn(move || {
62 //! println!("Hello, World!");
63 //! // some computation here
65 //! let result = guard.join();
68 //! The `spawn` function doesn't return a `Thread` directly; instead, it returns
69 //! a *join guard* from which a `Thread` can be extracted. The join guard is an
70 //! RAII-style guard that will automatically join the child thread (block until
71 //! it terminates) when it is dropped. You can join the child thread in advance
72 //! by calling the `join` method on the guard, which will also return the result
73 //! produced by the thread.
75 //! If you instead wish to *detach* the child thread, allowing it to outlive its
76 //! parent, you can use the `detach` method on the guard,
78 //! A handle to the thread itself is available via the `thread` method on the
81 //! ## Configuring threads
83 //! A new thread can be configured before it is spawned via the `Builder` type,
84 //! which currently allows you to set the name, stack size, and writers for
85 //! `println!` and `panic!` for the child thread:
90 //! thread::Builder::new().name("child1".to_string()).spawn(move || {
91 //! println!("Hello, world!")
95 //! ## Blocking support: park and unpark
97 //! Every thread is equipped with some basic low-level blocking support, via the
98 //! `park` and `unpark` functions.
100 //! Conceptually, each `Thread` handle has an associated token, which is
101 //! initially not present:
103 //! * The `Thread::park()` function blocks the current thread unless or until
104 //! the token is available for its thread handle, at which point It atomically
105 //! consumes the token. It may also return *spuriously*, without consuming the
108 //! * The `unpark()` method on a `Thread` atomically makes the token available
109 //! if it wasn't already.
111 //! In other words, each `Thread` acts a bit like a semaphore with initial count
112 //! 0, except that the semaphore is *saturating* (the count cannot go above 1),
113 //! and can return spuriously.
115 //! The API is typically used by acquiring a handle to the current thread,
116 //! placing that handle in a shared data structure so that other threads can
117 //! find it, and then `park`ing. When some desired condition is met, another
118 //! thread calls `unpark` on the handle.
120 //! The motivation for this design is twofold:
122 //! * It avoids the need to allocate mutexes and condvars when building new
123 //! synchronization primitives; the threads already provide basic blocking/signaling.
125 //! * It can be implemented highly efficiently on many platforms.
130 use cell::UnsafeCell;
132 use kinds::{Send, Sync};
133 use ops::{Drop, FnOnce};
134 use option::Option::{mod, Some, None};
135 use result::Result::{Err, Ok};
136 use sync::{Mutex, Condvar, Arc};
139 use rt::{mod, unwind};
140 use io::{Writer, stdio};
143 use sys::thread as imp;
144 use sys_common::{stack, thread_info};
146 /// Thread configuation. Provides detailed control over the properties
147 /// and behavior of new threads.
149 // A name for the thread-to-be, for identification in panic messages
150 name: Option<String>,
151 // The size of the stack for the spawned thread
152 stack_size: Option<uint>,
153 // Thread-local stdout
154 stdout: Option<Box<Writer + Send>>,
155 // Thread-local stderr
156 stderr: Option<Box<Writer + Send>>,
160 /// Generate the base configuration for spawning a thread, from which
161 /// configuration methods can be chained.
162 pub fn new() -> Builder {
171 /// Name the thread-to-be. Currently the name is used for identification
172 /// only in panic messages.
173 pub fn name(mut self, name: String) -> Builder {
174 self.name = Some(name);
178 /// Deprecated: use `name` instead
179 #[deprecated = "use name instead"]
180 pub fn named<T: IntoCow<'static, String, str>>(self, name: T) -> Builder {
181 self.name(name.into_cow().into_owned())
184 /// Set the size of the stack for the new thread.
185 pub fn stack_size(mut self, size: uint) -> Builder {
186 self.stack_size = Some(size);
190 /// Redirect thread-local stdout.
191 #[experimental = "Will likely go away after proc removal"]
192 pub fn stdout(mut self, stdout: Box<Writer + Send>) -> Builder {
193 self.stdout = Some(stdout);
197 /// Redirect thread-local stderr.
198 #[experimental = "Will likely go away after proc removal"]
199 pub fn stderr(mut self, stderr: Box<Writer + Send>) -> Builder {
200 self.stderr = Some(stderr);
204 /// Spawn a new joinable thread, and return a JoinGuard guard for it.
206 /// See `Thead::spawn` and the module doc for more details.
207 pub fn spawn<T, F>(self, f: F) -> JoinGuard<T> where
208 T: Send, F: FnOnce() -> T, F: Send
210 self.spawn_inner(Thunk::new(f))
213 fn spawn_inner<T: Send>(self, f: Thunk<(), T>) -> JoinGuard<T> {
214 let my_packet = Packet(Arc::new(UnsafeCell::new(None)));
215 let their_packet = Packet(my_packet.0.clone());
217 let Builder { name, stack_size, stdout, stderr } = self;
219 let stack_size = stack_size.unwrap_or(rt::min_stack());
220 let my_thread = Thread::new(name);
221 let their_thread = my_thread.clone();
223 // Spawning a new OS thread guarantees that __morestack will never get
224 // triggered, but we must manually set up the actual stack bounds once
225 // this function starts executing. This raises the lower limit by a bit
226 // because by the time that this function is executing we've already
227 // consumed at least a little bit of stack (we don't know the exact byte
228 // address at which our stack started).
229 let main = move |:| {
230 let something_around_the_top_of_the_stack = 1;
231 let addr = &something_around_the_top_of_the_stack as *const int;
232 let my_stack_top = addr as uint;
233 let my_stack_bottom = my_stack_top - stack_size + 1024;
235 stack::record_os_managed_stack_bounds(my_stack_bottom,
237 thread_info::set(imp::guard::current(), their_thread);
240 let mut output = None;
241 let f: Thunk<(), T> = if stdout.is_some() || stderr.is_some() {
242 Thunk::new(move |:| {
243 let _ = stdout.map(stdio::set_stdout);
244 let _ = stderr.map(stdio::set_stderr);
252 let ptr = &mut output;
254 // There are two primary reasons that general try/catch is
255 // unsafe. The first is that we do not support nested
256 // try/catch. The fact that this is happening in a newly-spawned
257 // thread suffices. The second is that unwinding while unwinding
258 // is not defined. We take care of that by having an
259 // 'unwinding' flag in the thread itself. For these reasons,
260 // this unsafety should be ok.
262 unwind::try(move || *ptr = Some(f.invoke(())))
266 *their_packet.0.get() = Some(match (output, try_result) {
267 (Some(data), Ok(_)) => Ok(data),
268 (None, Err(cause)) => Err(cause),
275 native: unsafe { imp::create(stack_size, Thunk::new(main)) },
284 name: Option<String>,
285 lock: Mutex<bool>, // true when there is a buffered unpark
289 unsafe impl Sync for Inner {}
292 /// A handle to a thread.
297 unsafe impl Sync for Thread {}
300 // Used only internally to construct a thread object without spawning
301 fn new(name: Option<String>) -> Thread {
303 inner: Arc::new(Inner {
305 lock: Mutex::new(false),
306 cvar: Condvar::new(),
311 /// Spawn a new joinable thread, returning a `JoinGuard` for it.
313 /// The join guard can be used to explicitly join the child thread (via
314 /// `join`), returning `Result<T>`, or it will implicitly join the child
315 /// upon being dropped. To detach the child, allowing it to outlive the
316 /// current thread, use `detach`. See the module documentation for additional details.
317 pub fn spawn<T, F>(f: F) -> JoinGuard<T> where
318 T: Send, F: FnOnce() -> T, F: Send
320 Builder::new().spawn(f)
323 /// Gets a handle to the thread that invokes it.
324 pub fn current() -> Thread {
325 thread_info::current_thread()
328 /// Cooperatively give up a timeslice to the OS scheduler.
330 unsafe { imp::yield_now() }
333 /// Determines whether the current thread is panicking.
335 pub fn panicking() -> bool {
339 /// Block unless or until the current thread's token is made available (may wake spuriously).
341 /// See the module doc for more detail.
343 // The implementation currently uses the trivial strategy of a Mutex+Condvar
344 // with wakeup flag, which does not actually allow spurious wakeups. In the
345 // future, this will be implemented in a more efficient way, perhaps along the lines of
346 // http://cr.openjdk.java.net/~stefank/6989984.1/raw_files/new/src/os/linux/vm/os_linux.cpp
347 // or futuxes, and in either case may allow spurious wakeups.
349 let thread = Thread::current();
350 let mut guard = thread.inner.lock.lock().unwrap();
352 guard = thread.inner.cvar.wait(guard).unwrap();
357 /// Atomically makes the handle's token available if it is not already.
359 /// See the module doc for more detail.
360 pub fn unpark(&self) {
361 let mut guard = self.inner.lock.lock().unwrap();
364 self.inner.cvar.notify_one();
368 /// Get the thread's name.
369 pub fn name(&self) -> Option<&str> {
370 self.inner.name.as_ref().map(|s| s.as_slice())
374 // a hack to get around privacy restrictions
375 impl thread_info::NewThread for Thread {
376 fn new(name: Option<String>) -> Thread { Thread::new(name) }
379 /// Indicates the manner in which a thread exited.
381 /// A thread that completes without panicking is considered to exit successfully.
382 pub type Result<T> = ::result::Result<T, Box<Any + Send>>;
384 struct Packet<T>(Arc<UnsafeCell<Option<Result<T>>>>);
386 unsafe impl<T:'static+Send> Send for Packet<T> {}
387 unsafe impl<T> Sync for Packet<T> {}
390 /// An RAII-style guard that will block until thread termination when dropped.
392 /// The type `T` is the return type for the thread's main function.
393 pub struct JoinGuard<T> {
394 native: imp::rust_thread,
400 unsafe impl<T: Send> Sync for JoinGuard<T> {}
402 impl<T: Send> JoinGuard<T> {
403 /// Extract a handle to the thread this guard will join on.
404 pub fn thread(&self) -> &Thread {
408 /// Wait for the associated thread to finish, returning the result of the thread's
411 /// If the child thread panics, `Err` is returned with the parameter given
413 pub fn join(mut self) -> Result<T> {
414 assert!(!self.joined);
415 unsafe { imp::join(self.native) };
418 (*self.packet.0.get()).take().unwrap()
422 /// Detaches the child thread, allowing it to outlive its parent.
423 pub fn detach(mut self) {
424 unsafe { imp::detach(self.native) };
425 self.joined = true; // avoid joining in the destructor
430 impl<T: Send> Drop for JoinGuard<T> {
433 unsafe { imp::join(self.native) };
441 use any::{Any, AnyRefExt};
444 use std::io::{ChanReader, ChanWriter};
446 use super::{Thread, Builder};
448 // !!! These tests are dangerous. If something is buggy, they will hang, !!!
449 // !!! instead of exiting cleanly. This might wedge the buildbots. !!!
452 fn test_unnamed_thread() {
453 Thread::spawn(move|| {
454 assert!(Thread::current().name().is_none());
455 }).join().map_err(|_| ()).unwrap();
459 fn test_named_thread() {
460 Builder::new().name("ada lovelace".to_string()).spawn(move|| {
461 assert!(Thread::current().name().unwrap() == "ada lovelace".to_string());
462 }).join().map_err(|_| ()).unwrap();
466 fn test_run_basic() {
467 let (tx, rx) = channel();
468 Thread::spawn(move|| {
475 fn test_join_success() {
476 match Thread::spawn(move|| -> String {
477 "Success!".to_string()
478 }).join().as_ref().map(|s| s.as_slice()) {
479 result::Result::Ok("Success!") => (),
485 fn test_join_panic() {
486 match Thread::spawn(move|| {
489 result::Result::Err(_) => (),
490 result::Result::Ok(()) => panic!()
495 fn test_spawn_sched() {
498 let (tx, rx) = channel();
500 fn f(i: int, tx: Sender<()>) {
502 Thread::spawn(move|| {
516 fn test_spawn_sched_childs_on_default_sched() {
517 let (tx, rx) = channel();
519 Thread::spawn(move|| {
520 Thread::spawn(move|| {
528 fn avoid_copying_the_body<F>(spawnfn: F) where F: FnOnce(Thunk) {
529 let (tx, rx) = channel::<uint>();
532 let x_in_parent = (&*x) as *const int as uint;
534 spawnfn(Thunk::new(move|| {
535 let x_in_child = (&*x) as *const int as uint;
539 let x_in_child = rx.recv();
540 assert_eq!(x_in_parent, x_in_child);
544 fn test_avoid_copying_the_body_spawn() {
545 avoid_copying_the_body(|v| {
546 Thread::spawn(move || v.invoke(())).detach();
551 fn test_avoid_copying_the_body_thread_spawn() {
552 avoid_copying_the_body(|f| {
553 Thread::spawn(move|| {
560 fn test_avoid_copying_the_body_join() {
561 avoid_copying_the_body(|f| {
562 let _ = Thread::spawn(move|| {
569 fn test_child_doesnt_ref_parent() {
570 // If the child refcounts the parent task, this will stack overflow when
571 // climbing the task tree to dereference each ancestor. (See #1789)
572 // (well, it would if the constant were 8000+ - I lowered it to be more
573 // valgrind-friendly. try this at home, instead..!)
574 static GENERATIONS: uint = 16;
575 fn child_no(x: uint) -> Thunk {
576 return Thunk::new(move|| {
578 Thread::spawn(move|| child_no(x+1).invoke(())).detach();
582 Thread::spawn(|| child_no(0).invoke(())).detach();
586 fn test_simple_newsched_spawn() {
587 Thread::spawn(move || {}).detach();
591 fn test_try_panic_message_static_str() {
592 match Thread::spawn(move|| {
593 panic!("static string");
596 type T = &'static str;
597 assert!(e.is::<T>());
598 assert_eq!(*e.downcast::<T>().unwrap(), "static string");
605 fn test_try_panic_message_owned_str() {
606 match Thread::spawn(move|| {
607 panic!("owned string".to_string());
611 assert!(e.is::<T>());
612 assert_eq!(*e.downcast::<T>().unwrap(), "owned string".to_string());
619 fn test_try_panic_message_any() {
620 match Thread::spawn(move|| {
621 panic!(box 413u16 as Box<Any + Send>);
624 type T = Box<Any + Send>;
625 assert!(e.is::<T>());
626 let any = e.downcast::<T>().unwrap();
627 assert!(any.is::<u16>());
628 assert_eq!(*any.downcast::<u16>().unwrap(), 413u16);
635 fn test_try_panic_message_unit_struct() {
638 match Thread::spawn(move|| {
641 Err(ref e) if e.is::<Juju>() => {}
642 Err(_) | Ok(()) => panic!()
648 let (tx, rx) = channel();
649 let mut reader = ChanReader::new(rx);
650 let stdout = ChanWriter::new(tx);
652 let r = Builder::new().stdout(box stdout as Box<Writer + Send>).spawn(move|| {
653 print!("Hello, world!");
657 let output = reader.read_to_string().unwrap();
658 assert_eq!(output, "Hello, world!".to_string());
661 // NOTE: the corresponding test for stderr is in run-pass/task-stderr, due
662 // to the test harness apparently interfering with stderr configuration.