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// Copyright 2014 The Rust Project Developers. See the COPYRIGHT // file at the top-level directory of this distribution and at // http://rust-lang.org/COPYRIGHT. // // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your // option. This file may not be copied, modified, or distributed // except according to those terms. //! Native threads. //! //! ## The threading model //! //! An executing Rust program consists of a collection of native OS threads, //! each with their own stack and local state. Threads can be named, and //! provide some built-in support for low-level synchronization. //! //! Communication between threads can be done through //! [channels], Rust's message-passing types, along with [other forms of thread //! synchronization](../../std/sync/index.html) and shared-memory data //! structures. In particular, types that are guaranteed to be //! threadsafe are easily shared between threads using the //! atomically-reference-counted container, [`Arc`]. //! //! Fatal logic errors in Rust cause *thread panic*, during which //! a thread will unwind the stack, running destructors and freeing //! owned resources. Thread panic is unrecoverable from within //! the panicking thread (i.e. there is no 'try/catch' in Rust), but //! the panic may optionally be detected from a different thread. If //! the main thread panics, the application will exit with a non-zero //! exit code. //! //! When the main thread of a Rust program terminates, the entire program shuts //! down, even if other threads are still running. However, this module provides //! convenient facilities for automatically waiting for the termination of a //! child thread (i.e., join). //! //! ## Spawning a thread //! //! A new thread can be spawned using the [`thread::spawn`][`spawn`] function: //! //! ```rust //! use std::thread; //! //! thread::spawn(move || { //! // some work here //! }); //! ``` //! //! In this example, the spawned thread is "detached" from the current //! thread. This means that it can outlive its parent (the thread that spawned //! it), unless this parent is the main thread. //! //! The parent thread can also wait on the completion of the child //! thread; a call to [`spawn`] produces a [`JoinHandle`], which provides //! a `join` method for waiting: //! //! ```rust //! use std::thread; //! //! let child = thread::spawn(move || { //! // some work here //! }); //! // some work here //! let res = child.join(); //! ``` //! //! The [`join`] method returns a [`Result`] containing [`Ok`] of the final //! value produced by the child thread, or [`Err`] of the value given to //! a call to [`panic!`] if the child panicked. //! //! ## Configuring threads //! //! A new thread can be configured before it is spawned via the [`Builder`] type, //! which currently allows you to set the name and stack size for the child thread: //! //! ```rust //! # #![allow(unused_must_use)] //! use std::thread; //! //! thread::Builder::new().name("child1".to_string()).spawn(move || { //! println!("Hello, world!"); //! }); //! ``` //! //! ## The `Thread` type //! //! Threads are represented via the [`Thread`] type, which you can get in one of //! two ways: //! //! * By spawning a new thread, e.g. using the [`thread::spawn`][`spawn`] //! function, and calling [`thread()`] on the [`JoinHandle`]. //! * By requesting the current thread, using the [`thread::current()`] function. //! //! The [`thread::current()`] function is available even for threads not spawned //! by the APIs of this module. //! //! ## Blocking support: park and unpark //! //! Every thread is equipped with some basic low-level blocking support, via the //! [`thread::park()`][`park()`] function and [`thread::Thread::unpark()`][`unpark()`] //! method. [`park()`] blocks the current thread, which can then be resumed from //! another thread by calling the [`unpark()`] method on the blocked thread's handle. //! //! Conceptually, each [`Thread`] handle has an associated token, which is //! initially not present: //! //! * The [`thread::park()`][`park()`] function blocks the current thread unless or until //! the token is available for its thread handle, at which point it atomically //! consumes the token. It may also return *spuriously*, without consuming the //! token. [`thread::park_timeout()`] does the same, but allows specifying a //! maximum time to block the thread for. //! //! * The [`unpark()`] method on a [`Thread`] atomically makes the token available //! if it wasn't already. //! //! In other words, each [`Thread`] acts a bit like a semaphore with initial count //! 0, except that the semaphore is *saturating* (the count cannot go above 1), //! and can return spuriously. //! //! The API is typically used by acquiring a handle to the current thread, //! placing that handle in a shared data structure so that other threads can //! find it, and then `park`ing. When some desired condition is met, another //! thread calls [`unpark()`] on the handle. //! //! The motivation for this design is twofold: //! //! * It avoids the need to allocate mutexes and condvars when building new //! synchronization primitives; the threads already provide basic blocking/signaling. //! //! * It can be implemented very efficiently on many platforms. //! //! ## Thread-local storage //! //! This module also provides an implementation of thread-local storage for Rust //! programs. Thread-local storage is a method of storing data into a global //! variable that each thread in the program will have its own copy of. //! Threads do not share this data, so accesses do not need to be synchronized. //! //! A thread-local key owns the value it contains and will destroy the value when the //! thread exits. It is created with the [`thread_local!`] macro and can contain any //! value that is `'static` (no borrowed pointers). It provides an accessor function, //! [`with`], that yields a shared reference to the value to the specified //! closure. Thread-local keys allow only shared access to values, as there would be no //! way to guarantee uniqueness if mutable borrows were allowed. Most values //! will want to make use of some form of **interior mutability** through the //! [`Cell`] or [`RefCell`] types. //! //! [channels]: ../../std/sync/mpsc/index.html //! [`Arc`]: ../../std/sync/struct.Arc.html //! [`spawn`]: ../../std/thread/fn.spawn.html //! [`JoinHandle`]: ../../std/thread/struct.JoinHandle.html //! [`thread()`]: ../../std/thread/struct.JoinHandle.html#method.thread //! [`join`]: ../../std/thread/struct.JoinHandle.html#method.join //! [`Result`]: ../../std/result/enum.Result.html //! [`Ok`]: ../../std/result/enum.Result.html#variant.Ok //! [`Err`]: ../../std/result/enum.Result.html#variant.Err //! [`panic!`]: ../../std/macro.panic.html //! [`Builder`]: ../../std/thread/struct.Builder.html //! [`thread::current()`]: ../../std/thread/fn.spawn.html //! [`Thread`]: ../../std/thread/struct.Thread.html //! [`park()`]: ../../std/thread/fn.park.html //! [`unpark()`]: ../../std/thread/struct.Thread.html#method.unpark //! [`thread::park_timeout()`]: ../../std/thread/fn.park_timeout.html //! [`Cell`]: ../cell/struct.Cell.html //! [`RefCell`]: ../cell/struct.RefCell.html //! [`thread_local!`]: ../macro.thread_local.html //! [`with`]: struct.LocalKey.html#method.with #![stable(feature = "rust1", since = "1.0.0")] use any::Any; use cell::UnsafeCell; use ffi::{CStr, CString}; use fmt; use io; use panic; use panicking; use str; use sync::{Mutex, Condvar, Arc}; use sys::thread as imp; use sys_common::mutex; use sys_common::thread_info; use sys_common::util; use sys_common::{AsInner, IntoInner}; use time::Duration; //////////////////////////////////////////////////////////////////////////////// // Thread-local storage //////////////////////////////////////////////////////////////////////////////// #[macro_use] mod local; #[stable(feature = "rust1", since = "1.0.0")] pub use self::local::{LocalKey, LocalKeyState}; // The types used by the thread_local! macro to access TLS keys. Note that there // are two types, the "OS" type and the "fast" type. The OS thread local key // type is accessed via platform-specific API calls and is slow, while the fast // key type is accessed via code generated via LLVM, where TLS keys are set up // by the elf linker. Note that the OS TLS type is always available: on macOS // the standard library is compiled with support for older platform versions // where fast TLS was not available; end-user code is compiled with fast TLS // where available, but both are needed. #[unstable(feature = "libstd_thread_internals", issue = "0")] #[cfg(target_thread_local)] #[doc(hidden)] pub use sys::fast_thread_local::Key as __FastLocalKeyInner; #[unstable(feature = "libstd_thread_internals", issue = "0")] #[doc(hidden)] pub use self::local::os::Key as __OsLocalKeyInner; //////////////////////////////////////////////////////////////////////////////// // Builder //////////////////////////////////////////////////////////////////////////////// /// Thread configuration. Provides detailed control over the properties /// and behavior of new threads. /// /// # Examples /// /// ``` /// use std::thread; /// /// let builder = thread::Builder::new(); /// /// let handler = builder.spawn(|| { /// // thread code /// }).unwrap(); /// /// handler.join().unwrap(); /// ``` #[stable(feature = "rust1", since = "1.0.0")] #[derive(Debug)] pub struct Builder { // A name for the thread-to-be, for identification in panic messages name: Option<String>, // The size of the stack for the spawned thread stack_size: Option<usize>, } impl Builder { /// Generates the base configuration for spawning a thread, from which /// configuration methods can be chained. /// /// # Examples /// /// ``` /// use std::thread; /// /// let builder = thread::Builder::new() /// .name("foo".into()) /// .stack_size(10); /// /// let handler = builder.spawn(|| { /// // thread code /// }).unwrap(); /// /// handler.join().unwrap(); /// ``` #[stable(feature = "rust1", since = "1.0.0")] pub fn new() -> Builder { Builder { name: None, stack_size: None, } } /// Names the thread-to-be. Currently the name is used for identification /// only in panic messages. /// /// # Examples /// /// ``` /// use std::thread; /// /// let builder = thread::Builder::new() /// .name("foo".into()); /// /// let handler = builder.spawn(|| { /// assert_eq!(thread::current().name(), Some("foo")) /// }).unwrap(); /// /// handler.join().unwrap(); /// ``` #[stable(feature = "rust1", since = "1.0.0")] pub fn name(mut self, name: String) -> Builder { self.name = Some(name); self } /// Sets the size of the stack for the new thread. /// /// # Examples /// /// ``` /// use std::thread; /// /// let builder = thread::Builder::new().stack_size(10); /// ``` #[stable(feature = "rust1", since = "1.0.0")] pub fn stack_size(mut self, size: usize) -> Builder { self.stack_size = Some(size); self } /// Spawns a new thread, and returns a join handle for it. /// /// The child thread may outlive the parent (unless the parent thread /// is the main thread; the whole process is terminated when the main /// thread finishes). The join handle can be used to block on /// termination of the child thread, including recovering its panics. /// /// # Errors /// /// Unlike the [`spawn`] free function, this method yields an /// [`io::Result`] to capture any failure to create the thread at /// the OS level. /// /// [`spawn`]: ../../std/thread/fn.spawn.html /// [`io::Result`]: ../../std/io/type.Result.html /// /// # Examples /// /// ``` /// use std::thread; /// /// let builder = thread::Builder::new(); /// /// let handler = builder.spawn(|| { /// // thread code /// }).unwrap(); /// /// handler.join().unwrap(); /// ``` #[stable(feature = "rust1", since = "1.0.0")] pub fn spawn<F, T>(self, f: F) -> io::Result<JoinHandle<T>> where F: FnOnce() -> T, F: Send + 'static, T: Send + 'static { let Builder { name, stack_size } = self; let stack_size = stack_size.unwrap_or(util::min_stack()); let my_thread = Thread::new(name); let their_thread = my_thread.clone(); let my_packet : Arc<UnsafeCell<Option<Result<T>>>> = Arc::new(UnsafeCell::new(None)); let their_packet = my_packet.clone(); let main = move || { if let Some(name) = their_thread.cname() { imp::Thread::set_name(name); } unsafe { thread_info::set(imp::guard::current(), their_thread); let try_result = panic::catch_unwind(panic::AssertUnwindSafe(f)); *their_packet.get() = Some(try_result); } }; Ok(JoinHandle(JoinInner { native: unsafe { Some(imp::Thread::new(stack_size, Box::new(main))?) }, thread: my_thread, packet: Packet(my_packet), })) } } //////////////////////////////////////////////////////////////////////////////// // Free functions //////////////////////////////////////////////////////////////////////////////// /// Spawns a new thread, returning a [`JoinHandle`] for it. /// /// The join handle will implicitly *detach* the child thread upon being /// dropped. In this case, the child thread may outlive the parent (unless /// the parent thread is the main thread; the whole process is terminated when /// the main thread finishes). Additionally, the join handle provides a [`join`] /// method that can be used to join the child thread. If the child thread /// panics, [`join`] will return an [`Err`] containing the argument given to /// [`panic`]. /// /// # Panics /// /// Panics if the OS fails to create a thread; use [`Builder::spawn`] /// to recover from such errors. /// /// [`JoinHandle`]: ../../std/thread/struct.JoinHandle.html /// [`join`]: ../../std/thread/struct.JoinHandle.html#method.join /// [`Err`]: ../../std/result/enum.Result.html#variant.Err /// [`panic`]: ../../std/macro.panic.html /// [`Builder::spawn`]: ../../std/thread/struct.Builder.html#method.spawn /// /// # Examples /// /// ``` /// use std::thread; /// /// let handler = thread::spawn(|| { /// // thread code /// }); /// /// handler.join().unwrap(); /// ``` #[stable(feature = "rust1", since = "1.0.0")] pub fn spawn<F, T>(f: F) -> JoinHandle<T> where F: FnOnce() -> T, F: Send + 'static, T: Send + 'static { Builder::new().spawn(f).unwrap() } /// Gets a handle to the thread that invokes it. /// /// # Examples /// /// Getting a handle to the current thread with `thread::current()`: /// /// ``` /// use std::thread; /// /// let handler = thread::Builder::new() /// .name("named thread".into()) /// .spawn(|| { /// let handle = thread::current(); /// assert_eq!(handle.name(), Some("named thread")); /// }) /// .unwrap(); /// /// handler.join().unwrap(); /// ``` #[stable(feature = "rust1", since = "1.0.0")] pub fn current() -> Thread { thread_info::current_thread().expect("use of std::thread::current() is not \ possible after the thread's local \ data has been destroyed") } /// Cooperatively gives up a timeslice to the OS scheduler. /// /// # Examples /// /// ``` /// use std::thread; /// /// thread::yield_now(); /// ``` #[stable(feature = "rust1", since = "1.0.0")] pub fn yield_now() { imp::Thread::yield_now() } /// Determines whether the current thread is unwinding because of panic. /// /// # Examples /// /// ```should_panic /// use std::thread; /// /// struct SomeStruct; /// /// impl Drop for SomeStruct { /// fn drop(&mut self) { /// if thread::panicking() { /// println!("dropped while unwinding"); /// } else { /// println!("dropped while not unwinding"); /// } /// } /// } /// /// { /// print!("a: "); /// let a = SomeStruct; /// } /// /// { /// print!("b: "); /// let b = SomeStruct; /// panic!() /// } /// ``` #[inline] #[stable(feature = "rust1", since = "1.0.0")] pub fn panicking() -> bool { panicking::panicking() } /// Puts the current thread to sleep for the specified amount of time. /// /// The thread may sleep longer than the duration specified due to scheduling /// specifics or platform-dependent functionality. /// /// # Platform behavior /// /// On Unix platforms this function will not return early due to a /// signal being received or a spurious wakeup. /// /// # Examples /// /// ```no_run /// use std::thread; /// /// // Let's sleep for 2 seconds: /// thread::sleep_ms(2000); /// ``` #[stable(feature = "rust1", since = "1.0.0")] #[rustc_deprecated(since = "1.6.0", reason = "replaced by `std::thread::sleep`")] pub fn sleep_ms(ms: u32) { sleep(Duration::from_millis(ms as u64)) } /// Puts the current thread to sleep for the specified amount of time. /// /// The thread may sleep longer than the duration specified due to scheduling /// specifics or platform-dependent functionality. /// /// # Platform behavior /// /// On Unix platforms this function will not return early due to a /// signal being received or a spurious wakeup. Platforms which do not support /// nanosecond precision for sleeping will have `dur` rounded up to the nearest /// granularity of time they can sleep for. /// /// # Examples /// /// ```no_run /// use std::{thread, time}; /// /// let ten_millis = time::Duration::from_millis(10); /// let now = time::Instant::now(); /// /// thread::sleep(ten_millis); /// /// assert!(now.elapsed() >= ten_millis); /// ``` #[stable(feature = "thread_sleep", since = "1.4.0")] pub fn sleep(dur: Duration) { imp::Thread::sleep(dur) } /// Blocks unless or until the current thread's token is made available. /// /// Every thread is equipped with some basic low-level blocking support, via /// the `park()` function and the [`unpark()`][unpark] method. These can be /// used as a more CPU-efficient implementation of a spinlock. /// /// [unpark]: struct.Thread.html#method.unpark /// /// The API is typically used by acquiring a handle to the current thread, /// placing that handle in a shared data structure so that other threads can /// find it, and then parking (in a loop with a check for the token actually /// being acquired). /// /// A call to `park` does not guarantee that the thread will remain parked /// forever, and callers should be prepared for this possibility. /// /// See the [module documentation][thread] for more detail. /// /// [thread]: index.html // // The implementation currently uses the trivial strategy of a Mutex+Condvar // with wakeup flag, which does not actually allow spurious wakeups. In the // future, this will be implemented in a more efficient way, perhaps along the lines of // http://cr.openjdk.java.net/~stefank/6989984.1/raw_files/new/src/os/linux/vm/os_linux.cpp // or futuxes, and in either case may allow spurious wakeups. #[stable(feature = "rust1", since = "1.0.0")] pub fn park() { let thread = current(); let mut guard = thread.inner.lock.lock().unwrap(); while !*guard { guard = thread.inner.cvar.wait(guard).unwrap(); } *guard = false; } /// Use [park_timeout]. /// /// Blocks unless or until the current thread's token is made available or /// the specified duration has been reached (may wake spuriously). /// /// The semantics of this function are equivalent to `park()` except that the /// thread will be blocked for roughly no longer than `ms`. This method /// should not be used for precise timing due to anomalies such as /// preemption or platform differences that may not cause the maximum /// amount of time waited to be precisely `ms` long. /// /// See the [module documentation][thread] for more detail. /// /// [thread]: index.html /// [park_timeout]: fn.park_timeout.html #[stable(feature = "rust1", since = "1.0.0")] #[rustc_deprecated(since = "1.6.0", reason = "replaced by `std::thread::park_timeout`")] pub fn park_timeout_ms(ms: u32) { park_timeout(Duration::from_millis(ms as u64)) } /// Blocks unless or until the current thread's token is made available or /// the specified duration has been reached (may wake spuriously). /// /// The semantics of this function are equivalent to `park()` except that the /// thread will be blocked for roughly no longer than `dur`. This method /// should not be used for precise timing due to anomalies such as /// preemption or platform differences that may not cause the maximum /// amount of time waited to be precisely `dur` long. /// /// See the module doc for more detail. /// /// # Platform behavior /// /// Platforms which do not support nanosecond precision for sleeping will have /// `dur` rounded up to the nearest granularity of time they can sleep for. /// /// # Example /// /// Waiting for the complete expiration of the timeout: /// /// ```rust,no_run /// use std::thread::park_timeout; /// use std::time::{Instant, Duration}; /// /// let timeout = Duration::from_secs(2); /// let beginning_park = Instant::now(); /// park_timeout(timeout); /// /// while beginning_park.elapsed() < timeout { /// println!("restarting park_timeout after {:?}", beginning_park.elapsed()); /// let timeout = timeout - beginning_park.elapsed(); /// park_timeout(timeout); /// } /// ``` #[stable(feature = "park_timeout", since = "1.4.0")] pub fn park_timeout(dur: Duration) { let thread = current(); let mut guard = thread.inner.lock.lock().unwrap(); if !*guard { let (g, _) = thread.inner.cvar.wait_timeout(guard, dur).unwrap(); guard = g; } *guard = false; } //////////////////////////////////////////////////////////////////////////////// // ThreadId //////////////////////////////////////////////////////////////////////////////// /// A unique identifier for a running thread. /// /// A `ThreadId` is an opaque object that has a unique value for each thread /// that creates one. `ThreadId`s do not correspond to a thread's system- /// designated identifier. /// /// # Examples /// /// ``` /// #![feature(thread_id)] /// /// use std::thread; /// /// let handler = thread::Builder::new() /// .spawn(|| { /// let thread = thread::current(); /// let thread_id = thread.id(); /// }) /// .unwrap(); /// /// handler.join().unwrap(); /// ``` #[unstable(feature = "thread_id", issue = "21507")] #[derive(Eq, PartialEq, Copy, Clone)] pub struct ThreadId(u64); impl ThreadId { // Generate a new unique thread ID. fn new() -> ThreadId { static GUARD: mutex::Mutex = mutex::Mutex::new(); static mut COUNTER: u64 = 0; unsafe { GUARD.lock(); // If we somehow use up all our bits, panic so that we're not // covering up subtle bugs of IDs being reused. if COUNTER == ::u64::MAX { GUARD.unlock(); panic!("failed to generate unique thread ID: bitspace exhausted"); } let id = COUNTER; COUNTER += 1; GUARD.unlock(); ThreadId(id) } } } #[stable(feature = "std_debug", since = "1.15.0")] impl fmt::Debug for ThreadId { fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result { f.pad("ThreadId { .. }") } } //////////////////////////////////////////////////////////////////////////////// // Thread //////////////////////////////////////////////////////////////////////////////// /// The internal representation of a `Thread` handle struct Inner { name: Option<CString>, // Guaranteed to be UTF-8 id: ThreadId, lock: Mutex<bool>, // true when there is a buffered unpark cvar: Condvar, } #[derive(Clone)] #[stable(feature = "rust1", since = "1.0.0")] /// A handle to a thread. /// /// # Examples /// /// ``` /// use std::thread; /// /// let handler = thread::Builder::new() /// .name("foo".into()) /// .spawn(|| { /// let thread = thread::current(); /// println!("thread name: {}", thread.name().unwrap()); /// }) /// .unwrap(); /// /// handler.join().unwrap(); /// ``` pub struct Thread { inner: Arc<Inner>, } impl Thread { // Used only internally to construct a thread object without spawning fn new(name: Option<String>) -> Thread { let cname = name.map(|n| { CString::new(n).expect("thread name may not contain interior null bytes") }); Thread { inner: Arc::new(Inner { name: cname, id: ThreadId::new(), lock: Mutex::new(false), cvar: Condvar::new(), }) } } /// Atomically makes the handle's token available if it is not already. /// /// See the module doc for more detail. /// /// # Examples /// /// ``` /// use std::thread; /// /// let handler = thread::Builder::new() /// .spawn(|| { /// let thread = thread::current(); /// thread.unpark(); /// }) /// .unwrap(); /// /// handler.join().unwrap(); /// ``` #[stable(feature = "rust1", since = "1.0.0")] pub fn unpark(&self) { let mut guard = self.inner.lock.lock().unwrap(); if !*guard { *guard = true; self.inner.cvar.notify_one(); } } /// Gets the thread's unique identifier. /// /// # Examples /// /// ``` /// #![feature(thread_id)] /// /// use std::thread; /// /// let handler = thread::Builder::new() /// .spawn(|| { /// let thread = thread::current(); /// println!("thread id: {:?}", thread.id()); /// }) /// .unwrap(); /// /// handler.join().unwrap(); /// ``` #[unstable(feature = "thread_id", issue = "21507")] pub fn id(&self) -> ThreadId { self.inner.id } /// Gets the thread's name. /// /// # Examples /// /// Threads by default have no name specified: /// /// ``` /// use std::thread; /// /// let builder = thread::Builder::new(); /// /// let handler = builder.spawn(|| { /// assert!(thread::current().name().is_none()); /// }).unwrap(); /// /// handler.join().unwrap(); /// ``` /// /// Thread with a specified name: /// /// ``` /// use std::thread; /// /// let builder = thread::Builder::new() /// .name("foo".into()); /// /// let handler = builder.spawn(|| { /// assert_eq!(thread::current().name(), Some("foo")) /// }).unwrap(); /// /// handler.join().unwrap(); /// ``` #[stable(feature = "rust1", since = "1.0.0")] pub fn name(&self) -> Option<&str> { self.cname().map(|s| unsafe { str::from_utf8_unchecked(s.to_bytes()) } ) } fn cname(&self) -> Option<&CStr> { self.inner.name.as_ref().map(|s| &**s) } } #[stable(feature = "rust1", since = "1.0.0")] impl fmt::Debug for Thread { fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result { fmt::Debug::fmt(&self.name(), f) } } // a hack to get around privacy restrictions impl thread_info::NewThread for Thread { fn new(name: Option<String>) -> Thread { Thread::new(name) } } //////////////////////////////////////////////////////////////////////////////// // JoinHandle //////////////////////////////////////////////////////////////////////////////// /// Indicates the manner in which a thread exited. /// /// A thread that completes without panicking is considered to exit successfully. #[stable(feature = "rust1", since = "1.0.0")] pub type Result<T> = ::result::Result<T, Box<Any + Send + 'static>>; // This packet is used to communicate the return value between the child thread // and the parent thread. Memory is shared through the `Arc` within and there's // no need for a mutex here because synchronization happens with `join()` (the // parent thread never reads this packet until the child has exited). // // This packet itself is then stored into a `JoinInner` which in turns is placed // in `JoinHandle` and `JoinGuard`. Due to the usage of `UnsafeCell` we need to // manually worry about impls like Send and Sync. The type `T` should // already always be Send (otherwise the thread could not have been created) and // this type is inherently Sync because no methods take &self. Regardless, // however, we add inheriting impls for Send/Sync to this type to ensure it's // Send/Sync and that future modifications will still appropriately classify it. struct Packet<T>(Arc<UnsafeCell<Option<Result<T>>>>); unsafe impl<T: Send> Send for Packet<T> {} unsafe impl<T: Sync> Sync for Packet<T> {} /// Inner representation for JoinHandle struct JoinInner<T> { native: Option<imp::Thread>, thread: Thread, packet: Packet<T>, } impl<T> JoinInner<T> { fn join(&mut self) -> Result<T> { self.native.take().unwrap().join(); unsafe { (*self.packet.0.get()).take().unwrap() } } } /// An owned permission to join on a thread (block on its termination). /// /// A `JoinHandle` *detaches* the child thread when it is dropped. /// /// Due to platform restrictions, it is not possible to [`Clone`] this /// handle: the ability to join a child thread is a uniquely-owned /// permission. /// /// This `struct` is created by the [`thread::spawn`] function and the /// [`thread::Builder::spawn`] method. /// /// # Examples /// /// Creation from [`thread::spawn`]: /// /// ``` /// use std::thread; /// /// let join_handle: thread::JoinHandle<_> = thread::spawn(|| { /// // some work here /// }); /// ``` /// /// Creation from [`thread::Builder::spawn`]: /// /// ``` /// use std::thread; /// /// let builder = thread::Builder::new(); /// /// let join_handle: thread::JoinHandle<_> = builder.spawn(|| { /// // some work here /// }).unwrap(); /// ``` /// /// [`Clone`]: ../../std/clone/trait.Clone.html /// [`thread::spawn`]: fn.spawn.html /// [`thread::Builder::spawn`]: struct.Builder.html#method.spawn #[stable(feature = "rust1", since = "1.0.0")] pub struct JoinHandle<T>(JoinInner<T>); impl<T> JoinHandle<T> { /// Extracts a handle to the underlying thread. /// /// # Examples /// /// ``` /// #![feature(thread_id)] /// /// use std::thread; /// /// let builder = thread::Builder::new(); /// /// let join_handle: thread::JoinHandle<_> = builder.spawn(|| { /// // some work here /// }).unwrap(); /// /// let thread = join_handle.thread(); /// println!("thread id: {:?}", thread.id()); /// ``` #[stable(feature = "rust1", since = "1.0.0")] pub fn thread(&self) -> &Thread { &self.0.thread } /// Waits for the associated thread to finish. /// /// If the child thread panics, [`Err`] is returned with the parameter given /// to [`panic`]. /// /// [`Err`]: ../../std/result/enum.Result.html#variant.Err /// [`panic`]: ../../std/macro.panic.html /// /// # Examples /// /// ``` /// use std::thread; /// /// let builder = thread::Builder::new(); /// /// let join_handle: thread::JoinHandle<_> = builder.spawn(|| { /// // some work here /// }).unwrap(); /// join_handle.join().expect("Couldn't join on the associated thread"); /// ``` #[stable(feature = "rust1", since = "1.0.0")] pub fn join(mut self) -> Result<T> { self.0.join() } } impl<T> AsInner<imp::Thread> for JoinHandle<T> { fn as_inner(&self) -> &imp::Thread { self.0.native.as_ref().unwrap() } } impl<T> IntoInner<imp::Thread> for JoinHandle<T> { fn into_inner(self) -> imp::Thread { self.0.native.unwrap() } } #[stable(feature = "std_debug", since = "1.15.0")] impl<T> fmt::Debug for JoinHandle<T> { fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result { f.pad("JoinHandle { .. }") } } fn _assert_sync_and_send() { fn _assert_both<T: Send + Sync>() {} _assert_both::<JoinHandle<()>>(); _assert_both::<Thread>(); } //////////////////////////////////////////////////////////////////////////////// // Tests //////////////////////////////////////////////////////////////////////////////// #[cfg(all(test, not(target_os = "emscripten")))] mod tests { use any::Any; use sync::mpsc::{channel, Sender}; use result; use super::{Builder}; use thread; use time::Duration; use u32; // !!! These tests are dangerous. If something is buggy, they will hang, !!! // !!! instead of exiting cleanly. This might wedge the buildbots. !!! #[test] fn test_unnamed_thread() { thread::spawn(move|| { assert!(thread::current().name().is_none()); }).join().ok().unwrap(); } #[test] fn test_named_thread() { Builder::new().name("ada lovelace".to_string()).spawn(move|| { assert!(thread::current().name().unwrap() == "ada lovelace".to_string()); }).unwrap().join().unwrap(); } #[test] #[should_panic] fn test_invalid_named_thread() { let _ = Builder::new().name("ada l\0velace".to_string()).spawn(|| {}); } #[test] fn test_run_basic() { let (tx, rx) = channel(); thread::spawn(move|| { tx.send(()).unwrap(); }); rx.recv().unwrap(); } #[test] fn test_join_panic() { match thread::spawn(move|| { panic!() }).join() { result::Result::Err(_) => (), result::Result::Ok(()) => panic!() } } #[test] fn test_spawn_sched() { let (tx, rx) = channel(); fn f(i: i32, tx: Sender<()>) { let tx = tx.clone(); thread::spawn(move|| { if i == 0 { tx.send(()).unwrap(); } else { f(i - 1, tx); } }); } f(10, tx); rx.recv().unwrap(); } #[test] fn test_spawn_sched_childs_on_default_sched() { let (tx, rx) = channel(); thread::spawn(move|| { thread::spawn(move|| { tx.send(()).unwrap(); }); }); rx.recv().unwrap(); } fn avoid_copying_the_body<F>(spawnfn: F) where F: FnOnce(Box<Fn() + Send>) { let (tx, rx) = channel(); let x: Box<_> = box 1; let x_in_parent = (&*x) as *const i32 as usize; spawnfn(Box::new(move|| { let x_in_child = (&*x) as *const i32 as usize; tx.send(x_in_child).unwrap(); })); let x_in_child = rx.recv().unwrap(); assert_eq!(x_in_parent, x_in_child); } #[test] fn test_avoid_copying_the_body_spawn() { avoid_copying_the_body(|v| { thread::spawn(move || v()); }); } #[test] fn test_avoid_copying_the_body_thread_spawn() { avoid_copying_the_body(|f| { thread::spawn(move|| { f(); }); }) } #[test] fn test_avoid_copying_the_body_join() { avoid_copying_the_body(|f| { let _ = thread::spawn(move|| { f() }).join(); }) } #[test] fn test_child_doesnt_ref_parent() { // If the child refcounts the parent thread, this will stack overflow when // climbing the thread tree to dereference each ancestor. (See #1789) // (well, it would if the constant were 8000+ - I lowered it to be more // valgrind-friendly. try this at home, instead..!) const GENERATIONS: u32 = 16; fn child_no(x: u32) -> Box<Fn() + Send> { return Box::new(move|| { if x < GENERATIONS { thread::spawn(move|| child_no(x+1)()); } }); } thread::spawn(|| child_no(0)()); } #[test] fn test_simple_newsched_spawn() { thread::spawn(move || {}); } #[test] fn test_try_panic_message_static_str() { match thread::spawn(move|| { panic!("static string"); }).join() { Err(e) => { type T = &'static str; assert!(e.is::<T>()); assert_eq!(*e.downcast::<T>().unwrap(), "static string"); } Ok(()) => panic!() } } #[test] fn test_try_panic_message_owned_str() { match thread::spawn(move|| { panic!("owned string".to_string()); }).join() { Err(e) => { type T = String; assert!(e.is::<T>()); assert_eq!(*e.downcast::<T>().unwrap(), "owned string".to_string()); } Ok(()) => panic!() } } #[test] fn test_try_panic_message_any() { match thread::spawn(move|| { panic!(box 413u16 as Box<Any + Send>); }).join() { Err(e) => { type T = Box<Any + Send>; assert!(e.is::<T>()); let any = e.downcast::<T>().unwrap(); assert!(any.is::<u16>()); assert_eq!(*any.downcast::<u16>().unwrap(), 413); } Ok(()) => panic!() } } #[test] fn test_try_panic_message_unit_struct() { struct Juju; match thread::spawn(move|| { panic!(Juju) }).join() { Err(ref e) if e.is::<Juju>() => {} Err(_) | Ok(()) => panic!() } } #[test] fn test_park_timeout_unpark_before() { for _ in 0..10 { thread::current().unpark(); thread::park_timeout(Duration::from_millis(u32::MAX as u64)); } } #[test] fn test_park_timeout_unpark_not_called() { for _ in 0..10 { thread::park_timeout(Duration::from_millis(10)); } } #[test] fn test_park_timeout_unpark_called_other_thread() { for _ in 0..10 { let th = thread::current(); let _guard = thread::spawn(move || { super::sleep(Duration::from_millis(50)); th.unpark(); }); thread::park_timeout(Duration::from_millis(u32::MAX as u64)); } } #[test] fn sleep_ms_smoke() { thread::sleep(Duration::from_millis(2)); } #[test] fn test_thread_id_equal() { assert!(thread::current().id() == thread::current().id()); } #[test] fn test_thread_id_not_equal() { let spawned_id = thread::spawn(|| thread::current().id()).join().unwrap(); assert!(thread::current().id() != spawned_id); } // NOTE: the corresponding test for stderr is in run-pass/thread-stderr, due // to the test harness apparently interfering with stderr configuration. }