Expand description
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 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. While not meant as a ‘try/catch’ mechanism, panics
in Rust can nonetheless be caught (unless compiling with panic=abort
) with
catch_unwind
and recovered
from, or alternatively be resumed with
resume_unwind
. If the panic
is not caught the thread will exit, but the panic may optionally be
detected from a different thread with join
. If the main thread panics
without the panic being caught, 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 thread (i.e., join).
§Spawning a thread
A new thread can be spawned using the thread::spawn
function:
use std::thread;
thread::spawn(move || {
// some work here
});
RunIn this example, the spawned thread is “detached,” which means that there is no way for the program to learn when the spawned thread completes or otherwise terminates.
To learn when a thread completes, it is necessary to capture the JoinHandle
object that is returned by the call to spawn
, which provides
a join
method that allows the caller to wait for the completion of the
spawned thread:
use std::thread;
let thread_join_handle = thread::spawn(move || {
// some work here
});
// some work here
let res = thread_join_handle.join();
RunThe join
method returns a thread::Result
containing Ok
of the final
value produced by the spawned thread, or Err
of the value given to
a call to panic!
if the thread panicked.
Note that there is no parent/child relationship between a thread that spawns a new thread and the thread being spawned. In particular, the spawned thread may or may not outlive the spawning thread, unless the spawning thread is the main thread.
§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 thread:
use std::thread;
thread::Builder::new().name("thread1".to_string()).spawn(move || {
println!("Hello, world!");
});
Run§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
function, and callingthread
on theJoinHandle
. - 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.
§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.
§Naming threads
Threads are able to have associated names for identification purposes. By default, spawned
threads are unnamed. To specify a name for a thread, build the thread with Builder
and pass
the desired thread name to Builder::name
. To retrieve the thread name from within the
thread, use Thread::name
. A couple of examples where the name of a thread gets used:
- If a panic occurs in a named thread, the thread name will be printed in the panic message.
- The thread name is provided to the OS where applicable (e.g.,
pthread_setname_np
in unix-like platforms).
§Stack size
The default stack size is platform-dependent and subject to change. Currently, it is 2 MiB on all Tier-1 platforms.
There are two ways to manually specify the stack size for spawned threads:
- Build the thread with
Builder
and pass the desired stack size toBuilder::stack_size
. - Set the
RUST_MIN_STACK
environment variable to an integer representing the desired stack size (in bytes). Note that settingBuilder::stack_size
will override this. Be aware that changes toRUST_MIN_STACK
may be ignored after program start.
Note that the stack size of the main thread is not determined by Rust.
Structs§
- An error returned by
LocalKey::try_with
. - Thread factory, which can be used in order to configure the properties of a new thread.
- An owned permission to join on a thread (block on its termination).
- A thread local storage key which owns its contents.
- A scope to spawn scoped threads in.
- An owned permission to join on a scoped thread (block on its termination).
- A handle to a thread.
- A unique identifier for a running thread.
Functions§
- Returns an estimate of the default amount of parallelism a program should use.
- Gets a handle to the thread that invokes it.
- Determines whether the current thread is unwinding because of panic.
- Blocks unless or until the current thread’s token is made available.
- Blocks unless or until the current thread’s token is made available or the specified duration has been reached (may wake spuriously).
- park_timeout_msDeprecatedUse
park_timeout
. - Create a scope for spawning scoped threads.
- Puts the current thread to sleep for at least the specified amount of time.
- sleep_msDeprecatedUse
sleep
. - Spawns a new thread, returning a
JoinHandle
for it. - Cooperatively gives up a timeslice to the OS scheduler.
- sleep_untilExperimentalPuts the current thread to sleep until the specified deadline has passed.
Type Aliases§
- A specialized
Result
type for threads.