Function tokio::task::spawn_blocking [−][src]
pub fn spawn_blocking<F, R>(f: F) -> JoinHandle<R>ⓘwhereNotable traits for JoinHandle<T>
impl<T> Future for JoinHandle<T> type Output = Result<T, JoinError>;
F: FnOnce() -> R + Send + 'static,
R: Send + 'static,
Runs the provided closure on a thread where blocking is acceptable.
In general, issuing a blocking call or performing a lot of compute in a future without yielding is not okay, as it may prevent the executor from driving other futures forward. This function runs the provided closure on a thread dedicated to blocking operations. See the CPU-bound tasks and blocking code section for more information.
Tokio will spawn more blocking threads when they are requested through
this function until the upper limit configured on the Builder
is
reached. This limit is very large by default, because spawn_blocking
is
often used for various kinds of IO operations that cannot be performed
asynchronously. When you run CPU-bound code using spawn_blocking
, you
should keep this large upper limit in mind; to run your CPU-bound
computations on only a few threads, you should use a separate thread
pool such as rayon rather than configuring the number of blocking
threads.
This function is intended for non-async operations that eventually
finish on their own. If you want to spawn an ordinary thread, you should
use thread::spawn
instead.
Closures spawned using spawn_blocking
cannot be cancelled. When you
shut down the executor, it will wait indefinitely for all blocking
operations to finish. You can use shutdown_timeout
to stop waiting
for them after a certain timeout. Be aware that this will still not
cancel the tasks — they are simply allowed to keep running after the
method returns.
Note that if you are using the basic scheduler, this function will still spawn additional threads for blocking operations. The basic scheduler’s single thread is only used for asynchronous code.
Examples
use tokio::task; let res = task::spawn_blocking(move || { // do some compute-heavy work or call synchronous code "done computing" }).await?; assert_eq!(res, "done computing");