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.
129 use cell::UnsafeCell;
131 use kinds::{Send, Sync};
132 use ops::{Drop, FnOnce};
133 use option::Option::{self, Some, None};
134 use result::Result::{Err, Ok};
135 use sync::{Mutex, Condvar, Arc};
138 use rt::{self, unwind};
139 use io::{Writer, stdio};
142 use sys::thread as imp;
143 use sys_common::{stack, thread_info};
145 /// Thread configuation. Provides detailed control over the properties
146 /// and behavior of new threads.
148 // A name for the thread-to-be, for identification in panic messages
149 name: Option<String>,
150 // The size of the stack for the spawned thread
151 stack_size: Option<uint>,
152 // Thread-local stdout
153 stdout: Option<Box<Writer + Send>>,
154 // Thread-local stderr
155 stderr: Option<Box<Writer + Send>>,
159 /// Generate the base configuration for spawning a thread, from which
160 /// configuration methods can be chained.
161 pub fn new() -> Builder {
170 /// Name the thread-to-be. Currently the name is used for identification
171 /// only in panic messages.
172 pub fn name(mut self, name: String) -> Builder {
173 self.name = Some(name);
177 /// Set the size of the stack for the new thread.
178 pub fn stack_size(mut self, size: uint) -> Builder {
179 self.stack_size = Some(size);
183 /// Redirect thread-local stdout.
184 #[experimental = "Will likely go away after proc removal"]
185 pub fn stdout(mut self, stdout: Box<Writer + Send>) -> Builder {
186 self.stdout = Some(stdout);
190 /// Redirect thread-local stderr.
191 #[experimental = "Will likely go away after proc removal"]
192 pub fn stderr(mut self, stderr: Box<Writer + Send>) -> Builder {
193 self.stderr = Some(stderr);
197 /// Spawn a new joinable thread, and return a JoinGuard guard for it.
199 /// See `Thead::spawn` and the module doc for more details.
200 pub fn spawn<T, F>(self, f: F) -> JoinGuard<T> where
201 T: Send, F: FnOnce() -> T, F: Send
203 self.spawn_inner(Thunk::new(f))
206 fn spawn_inner<T: Send>(self, f: Thunk<(), T>) -> JoinGuard<T> {
207 let my_packet = Packet(Arc::new(UnsafeCell::new(None)));
208 let their_packet = Packet(my_packet.0.clone());
210 let Builder { name, stack_size, stdout, stderr } = self;
212 let stack_size = stack_size.unwrap_or(rt::min_stack());
213 let my_thread = Thread::new(name);
214 let their_thread = my_thread.clone();
216 // Spawning a new OS thread guarantees that __morestack will never get
217 // triggered, but we must manually set up the actual stack bounds once
218 // this function starts executing. This raises the lower limit by a bit
219 // because by the time that this function is executing we've already
220 // consumed at least a little bit of stack (we don't know the exact byte
221 // address at which our stack started).
222 let main = move |:| {
223 let something_around_the_top_of_the_stack = 1;
224 let addr = &something_around_the_top_of_the_stack as *const int;
225 let my_stack_top = addr as uint;
226 let my_stack_bottom = my_stack_top - stack_size + 1024;
228 stack::record_os_managed_stack_bounds(my_stack_bottom, my_stack_top);
231 (my_stack_bottom, my_stack_top),
232 unsafe { imp::guard::current() },
236 let mut output = None;
237 let f: Thunk<(), T> = if stdout.is_some() || stderr.is_some() {
238 Thunk::new(move |:| {
239 let _ = stdout.map(stdio::set_stdout);
240 let _ = stderr.map(stdio::set_stderr);
248 let ptr = &mut output;
250 // There are two primary reasons that general try/catch is
251 // unsafe. The first is that we do not support nested
252 // try/catch. The fact that this is happening in a newly-spawned
253 // thread suffices. The second is that unwinding while unwinding
254 // is not defined. We take care of that by having an
255 // 'unwinding' flag in the thread itself. For these reasons,
256 // this unsafety should be ok.
258 unwind::try(move || *ptr = Some(f.invoke(())))
262 *their_packet.0.get() = Some(match (output, try_result) {
263 (Some(data), Ok(_)) => Ok(data),
264 (None, Err(cause)) => Err(cause),
271 native: unsafe { imp::create(stack_size, Thunk::new(main)) },
280 name: Option<String>,
281 lock: Mutex<bool>, // true when there is a buffered unpark
285 unsafe impl Sync for Inner {}
288 /// A handle to a thread.
293 unsafe impl Sync for Thread {}
296 // Used only internally to construct a thread object without spawning
297 fn new(name: Option<String>) -> Thread {
299 inner: Arc::new(Inner {
301 lock: Mutex::new(false),
302 cvar: Condvar::new(),
307 /// Spawn a new joinable thread, returning a `JoinGuard` for it.
309 /// The join guard can be used to explicitly join the child thread (via
310 /// `join`), returning `Result<T>`, or it will implicitly join the child
311 /// upon being dropped. To detach the child, allowing it to outlive the
312 /// current thread, use `detach`. See the module documentation for additional details.
313 pub fn spawn<T, F>(f: F) -> JoinGuard<T> where
314 T: Send, F: FnOnce() -> T, F: Send
316 Builder::new().spawn(f)
319 /// Gets a handle to the thread that invokes it.
320 pub fn current() -> Thread {
321 thread_info::current_thread()
324 /// Cooperatively give up a timeslice to the OS scheduler.
326 unsafe { imp::yield_now() }
329 /// Determines whether the current thread is panicking.
331 pub fn panicking() -> bool {
335 /// Block unless or until the current thread's token is made available (may wake spuriously).
337 /// See the module doc for more detail.
339 // The implementation currently uses the trivial strategy of a Mutex+Condvar
340 // with wakeup flag, which does not actually allow spurious wakeups. In the
341 // future, this will be implemented in a more efficient way, perhaps along the lines of
342 // http://cr.openjdk.java.net/~stefank/6989984.1/raw_files/new/src/os/linux/vm/os_linux.cpp
343 // or futuxes, and in either case may allow spurious wakeups.
345 let thread = Thread::current();
346 let mut guard = thread.inner.lock.lock().unwrap();
348 guard = thread.inner.cvar.wait(guard).unwrap();
353 /// Atomically makes the handle's token available if it is not already.
355 /// See the module doc for more detail.
356 pub fn unpark(&self) {
357 let mut guard = self.inner.lock.lock().unwrap();
360 self.inner.cvar.notify_one();
364 /// Get the thread's name.
365 pub fn name(&self) -> Option<&str> {
366 self.inner.name.as_ref().map(|s| s.as_slice())
370 // a hack to get around privacy restrictions
371 impl thread_info::NewThread for Thread {
372 fn new(name: Option<String>) -> Thread { Thread::new(name) }
375 /// Indicates the manner in which a thread exited.
377 /// A thread that completes without panicking is considered to exit successfully.
378 pub type Result<T> = ::result::Result<T, Box<Any + Send>>;
380 struct Packet<T>(Arc<UnsafeCell<Option<Result<T>>>>);
382 unsafe impl<T:'static+Send> Send for Packet<T> {}
383 unsafe impl<T> Sync for Packet<T> {}
386 /// An RAII-style guard that will block until thread termination when dropped.
388 /// The type `T` is the return type for the thread's main function.
389 pub struct JoinGuard<T> {
390 native: imp::rust_thread,
396 unsafe impl<T: Send> Sync for JoinGuard<T> {}
398 impl<T: Send> JoinGuard<T> {
399 /// Extract a handle to the thread this guard will join on.
400 pub fn thread(&self) -> &Thread {
404 /// Wait for the associated thread to finish, returning the result of the thread's
407 /// If the child thread panics, `Err` is returned with the parameter given
409 pub fn join(mut self) -> Result<T> {
410 assert!(!self.joined);
411 unsafe { imp::join(self.native) };
414 (*self.packet.0.get()).take().unwrap()
418 /// Detaches the child thread, allowing it to outlive its parent.
419 pub fn detach(mut self) {
420 unsafe { imp::detach(self.native) };
421 self.joined = true; // avoid joining in the destructor
426 impl<T: Send> Drop for JoinGuard<T> {
429 unsafe { imp::join(self.native) };
439 use sync::mpsc::{channel, Sender};
442 use std::io::{ChanReader, ChanWriter};
443 use super::{Thread, Builder};
446 // !!! These tests are dangerous. If something is buggy, they will hang, !!!
447 // !!! instead of exiting cleanly. This might wedge the buildbots. !!!
450 fn test_unnamed_thread() {
451 Thread::spawn(move|| {
452 assert!(Thread::current().name().is_none());
453 }).join().map_err(|_| ()).unwrap();
457 fn test_named_thread() {
458 Builder::new().name("ada lovelace".to_string()).spawn(move|| {
459 assert!(Thread::current().name().unwrap() == "ada lovelace".to_string());
460 }).join().map_err(|_| ()).unwrap();
464 fn test_run_basic() {
465 let (tx, rx) = channel();
466 Thread::spawn(move|| {
467 tx.send(()).unwrap();
473 fn test_join_success() {
474 match Thread::spawn(move|| -> String {
475 "Success!".to_string()
476 }).join().as_ref().map(|s| s.as_slice()) {
477 result::Result::Ok("Success!") => (),
483 fn test_join_panic() {
484 match Thread::spawn(move|| {
487 result::Result::Err(_) => (),
488 result::Result::Ok(()) => panic!()
493 fn test_spawn_sched() {
496 let (tx, rx) = channel();
498 fn f(i: int, tx: Sender<()>) {
500 Thread::spawn(move|| {
502 tx.send(()).unwrap();
514 fn test_spawn_sched_childs_on_default_sched() {
515 let (tx, rx) = channel();
517 Thread::spawn(move|| {
518 Thread::spawn(move|| {
519 tx.send(()).unwrap();
526 fn avoid_copying_the_body<F>(spawnfn: F) where F: FnOnce(Thunk) {
527 let (tx, rx) = channel::<uint>();
530 let x_in_parent = (&*x) as *const int as uint;
532 spawnfn(Thunk::new(move|| {
533 let x_in_child = (&*x) as *const int as uint;
534 tx.send(x_in_child).unwrap();
537 let x_in_child = rx.recv().unwrap();
538 assert_eq!(x_in_parent, x_in_child);
542 fn test_avoid_copying_the_body_spawn() {
543 avoid_copying_the_body(|v| {
544 Thread::spawn(move || v.invoke(())).detach();
549 fn test_avoid_copying_the_body_thread_spawn() {
550 avoid_copying_the_body(|f| {
551 Thread::spawn(move|| {
558 fn test_avoid_copying_the_body_join() {
559 avoid_copying_the_body(|f| {
560 let _ = Thread::spawn(move|| {
567 fn test_child_doesnt_ref_parent() {
568 // If the child refcounts the parent task, this will stack overflow when
569 // climbing the task tree to dereference each ancestor. (See #1789)
570 // (well, it would if the constant were 8000+ - I lowered it to be more
571 // valgrind-friendly. try this at home, instead..!)
572 static GENERATIONS: uint = 16;
573 fn child_no(x: uint) -> Thunk {
574 return Thunk::new(move|| {
576 Thread::spawn(move|| child_no(x+1).invoke(())).detach();
580 Thread::spawn(|| child_no(0).invoke(())).detach();
584 fn test_simple_newsched_spawn() {
585 Thread::spawn(move || {}).detach();
589 fn test_try_panic_message_static_str() {
590 match Thread::spawn(move|| {
591 panic!("static string");
594 type T = &'static str;
595 assert!(e.is::<T>());
596 assert_eq!(*e.downcast::<T>().unwrap(), "static string");
603 fn test_try_panic_message_owned_str() {
604 match Thread::spawn(move|| {
605 panic!("owned string".to_string());
609 assert!(e.is::<T>());
610 assert_eq!(*e.downcast::<T>().unwrap(), "owned string".to_string());
617 fn test_try_panic_message_any() {
618 match Thread::spawn(move|| {
619 panic!(box 413u16 as Box<Any + Send>);
622 type T = Box<Any + Send>;
623 assert!(e.is::<T>());
624 let any = e.downcast::<T>().unwrap();
625 assert!(any.is::<u16>());
626 assert_eq!(*any.downcast::<u16>().unwrap(), 413u16);
633 fn test_try_panic_message_unit_struct() {
636 match Thread::spawn(move|| {
639 Err(ref e) if e.is::<Juju>() => {}
640 Err(_) | Ok(()) => panic!()
646 let (tx, rx) = channel();
647 let mut reader = ChanReader::new(rx);
648 let stdout = ChanWriter::new(tx);
650 let r = Builder::new().stdout(box stdout as Box<Writer + Send>).spawn(move|| {
651 print!("Hello, world!");
655 let output = reader.read_to_string().unwrap();
656 assert_eq!(output, "Hello, world!".to_string());
659 // NOTE: the corresponding test for stderr is in run-pass/task-stderr, due
660 // to the test harness apparently interfering with stderr configuration.