Struct JoinHandle

pub struct JoinHandle<T>(/* private fields */);

An owned permission to join on a thread (block on its termination).

A JoinHandle detaches the associated thread when it is dropped, which means that there is no longer any handle to the thread and no way to join on it.

Due to platform restrictions, it is not possible to Clone this handle: the ability to join a 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();

A thread being detached and outliving the thread that spawned it:

use std::thread;
use std::time::Duration;

let original_thread = thread::spawn(|| {
    let _detached_thread = thread::spawn(|| {
        // Here we sleep to make sure that the first thread returns before.
        thread::sleep(Duration::from_millis(10));
        // This will be called, even though the JoinHandle is dropped.
        println!("♫ Still alive ♫");
    });
});

original_thread.join().expect("The thread being joined has panicked");
println!("Original thread is joined.");

// We make sure that the new thread has time to run, before the main
// thread returns.

thread::sleep(Duration::from_millis(1000));

Implementations

impl<T> JoinHandle<T>

pub fn thread(&self) -> &Thread

Extracts a handle to the underlying thread.

Examples

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());

pub fn join(self) -> Result<T, Box<dyn Any + Send>>

Waits for the associated thread to finish.

This function will return immediately if the associated thread has already finished.

In terms of atomic memory orderings, the completion of the associated thread synchronizes with this function returning. In other words, all operations performed by that thread happen before all operations that happen after join returns.

If the associated thread panics, Err is returned with the parameter given to panic! (though see the Notes below).

Panics

This function may panic on some platforms if a thread attempts to join itself or otherwise may create a deadlock with joining threads.

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");

Notes

If a “foreign” unwinding operation (e.g. an exception thrown from C++ code, or a panic! in Rust code compiled or linked with a different runtime) unwinds all the way to the thread root, the process may be aborted; see the Notes on thread::spawn. If the process is not aborted, this function will return a Result::Err containing an opaque type.

pub fn is_finished(&self) -> bool

Checks if the associated thread has finished running its main function.

is_finished supports implementing a non-blocking join operation, by checking is_finished, and calling join if it returns true. This function does not block. To block while waiting on the thread to finish, use join.

This might return true for a brief moment after the thread’s main function has returned, but before the thread itself has stopped running. However, once this returns true, join can be expected to return quickly, without blocking for any significant amount of time.

Trait Implementations

impl<T> Debug for JoinHandle<T>

fn fmt(&self, f: &mut Formatter<'_>) -> Result<(), Error>

Formats the value using the given formatter.

impl<T> JoinHandleExt for JoinHandle<T>

fn as_pthread_t(&self) -> u64

Extracts the raw pthread_t without taking ownership

fn into_pthread_t(self) -> u64

Consumes the thread, returning the raw pthread_t

impl<T> Send for JoinHandle<T>

impl<T> Sync for JoinHandle<T>