Function tokio::task::block_in_place
source · [−]pub fn block_in_place<F, R>(f: F) -> R where
F: FnOnce() -> R,
Expand description
Runs the provided blocking function on the current thread without blocking the executor.
In general, issuing a blocking call or performing a lot of compute in a future without yielding is problematic, as it may prevent the executor from driving other tasks forward. Calling this function informs the executor that the currently executing task is about to block the thread, so the executor is able to hand off any other tasks it has to a new worker thread before that happens. See the CPU-bound tasks and blocking code section for more information.
Be aware that although this function avoids starving other independently
spawned tasks, any other code running concurrently in the same task will
be suspended during the call to block_in_place
. This can happen e.g.
when using the join!
macro. To avoid this issue, use
spawn_blocking
instead of block_in_place
.
Note that this function cannot be used within a current_thread
runtime
because in this case there are no other worker threads to hand off tasks
to. On the other hand, calling the function outside a runtime is
allowed. In this case, block_in_place
just calls the provided closure
normally.
Code running behind block_in_place
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.
Examples
use tokio::task;
task::block_in_place(move || {
// do some compute-heavy work or call synchronous code
});
Code running inside block_in_place
may use block_on
to reenter the
async context.
use tokio::task;
use tokio::runtime::Handle;
task::block_in_place(move || {
Handle::current().block_on(async move {
// do something async
});
});
Panics
This function panics if called from a current_thread
runtime.