pub struct Runtime { /* private fields */ }
Expand description
The Tokio runtime.
The runtime provides an I/O driver, task scheduler, timer, and blocking pool, necessary for running asynchronous tasks.
Instances of Runtime
can be created using new
, or Builder
.
However, most users will use the #[tokio::main]
annotation on their
entry point instead.
See module level documentation for more details.
Shutdown
Shutting down the runtime is done by dropping the value, or calling
Runtime::shutdown_background
or Runtime::shutdown_timeout
.
Tasks spawned through Runtime::spawn
keep running until they yield.
Then they are dropped. They are not guaranteed to run to completion, but
might do so if they do not yield until completion.
Blocking functions spawned through Runtime::spawn_blocking
keep running
until they return.
The thread initiating the shutdown blocks until all spawned work has been
stopped. This can take an indefinite amount of time. The Drop
implementation waits forever for this.
shutdown_background
and shutdown_timeout
can be used if waiting forever
is undesired. When the timeout is reached, spawned work that did not stop
in time and threads running it are leaked. The work continues to run until
one of the stopping conditions is fulfilled, but the thread initiating the
shutdown is unblocked.
Once the runtime has been dropped, any outstanding I/O resources bound to it will no longer function. Calling any method on them will result in an error.
Sharing
The Tokio runtime implements Sync
and Send
to allow you to wrap it
in a Arc
. Most fn take &self
to allow you to call them concurrently
across multiple threads.
Calls to shutdown
and shutdown_timeout
require exclusive ownership of
the runtime type and this can be achieved via Arc::try_unwrap
when only
one strong count reference is left over.
Implementations§
source§impl Runtime
impl Runtime
sourcepub fn handle(&self) -> &Handle
pub fn handle(&self) -> &Handle
Returns a handle to the runtime’s spawner.
The returned handle can be used to spawn tasks that run on this runtime, and can
be cloned to allow moving the Handle
to other threads.
Calling Handle::block_on
on a handle to a current_thread
runtime is error-prone.
Refer to the documentation of Handle::block_on
for more.
Examples
use tokio::runtime::Runtime;
let rt = Runtime::new()
.unwrap();
let handle = rt.handle();
// Use the handle...
sourcepub fn spawn<F>(&self, future: F) -> JoinHandle<F::Output> ⓘwhere
F: Future + Send + 'static,
F::Output: Send + 'static,
pub fn spawn<F>(&self, future: F) -> JoinHandle<F::Output> ⓘwhere
F: Future + Send + 'static,
F::Output: Send + 'static,
Spawns a future onto the Tokio runtime.
This spawns the given future onto the runtime’s executor, usually a thread pool. The thread pool is then responsible for polling the future until it completes.
The provided future will start running in the background immediately
when spawn
is called, even if you don’t await the returned
JoinHandle
.
See module level documentation for more details.
Examples
use tokio::runtime::Runtime;
// Create the runtime
let rt = Runtime::new().unwrap();
// Spawn a future onto the runtime
rt.spawn(async {
println!("now running on a worker thread");
});
sourcepub fn spawn_blocking<F, R>(&self, func: F) -> JoinHandle<R> ⓘwhere
F: FnOnce() -> R + Send + 'static,
R: Send + 'static,
pub fn spawn_blocking<F, R>(&self, func: F) -> JoinHandle<R> ⓘwhere
F: FnOnce() -> R + Send + 'static,
R: Send + 'static,
Runs the provided function on an executor dedicated to blocking operations.
Examples
use tokio::runtime::Runtime;
// Create the runtime
let rt = Runtime::new().unwrap();
// Spawn a blocking function onto the runtime
rt.spawn_blocking(|| {
println!("now running on a worker thread");
});
sourcepub fn block_on<F: Future>(&self, future: F) -> F::Output
pub fn block_on<F: Future>(&self, future: F) -> F::Output
Runs a future to completion on the Tokio runtime. This is the runtime’s entry point.
This runs the given future on the current thread, blocking until it is complete, and yielding its resolved result. Any tasks or timers which the future spawns internally will be executed on the runtime.
Non-worker future
Note that the future required by this function does not run as a worker. The expectation is that other tasks are spawned by the future here. Awaiting on other futures from the future provided here will not perform as fast as those spawned as workers.
Multi thread scheduler
When the multi thread scheduler is used this will allow futures to run within the io driver and timer context of the overall runtime.
Any spawned tasks will continue running after block_on
returns.
Current thread scheduler
When the current thread scheduler is enabled block_on
can be called concurrently from multiple threads. The first call
will take ownership of the io and timer drivers. This means
other threads which do not own the drivers will hook into that one.
When the first block_on
completes, other threads will be able to
“steal” the driver to allow continued execution of their futures.
Any spawned tasks will be suspended after block_on
returns. Calling
block_on
again will resume previously spawned tasks.
Panics
This function panics if the provided future panics, or if called within an asynchronous execution context.
Examples
use tokio::runtime::Runtime;
// Create the runtime
let rt = Runtime::new().unwrap();
// Execute the future, blocking the current thread until completion
rt.block_on(async {
println!("hello");
});
sourcepub fn enter(&self) -> EnterGuard<'_>
pub fn enter(&self) -> EnterGuard<'_>
Enters the runtime context.
This allows you to construct types that must have an executor
available on creation such as Sleep
or TcpStream
. It will
also allow you to call methods such as tokio::spawn
.
Example
use tokio::runtime::Runtime;
fn function_that_spawns(msg: String) {
// Had we not used `rt.enter` below, this would panic.
tokio::spawn(async move {
println!("{}", msg);
});
}
fn main() {
let rt = Runtime::new().unwrap();
let s = "Hello World!".to_string();
// By entering the context, we tie `tokio::spawn` to this executor.
let _guard = rt.enter();
function_that_spawns(s);
}
sourcepub fn shutdown_timeout(self, duration: Duration)
pub fn shutdown_timeout(self, duration: Duration)
Shuts down the runtime, waiting for at most duration
for all spawned
work to stop.
See the struct level documentation for more details.
Examples
use tokio::runtime::Runtime;
use tokio::task;
use std::thread;
use std::time::Duration;
fn main() {
let runtime = Runtime::new().unwrap();
runtime.block_on(async move {
task::spawn_blocking(move || {
thread::sleep(Duration::from_secs(10_000));
});
});
runtime.shutdown_timeout(Duration::from_millis(100));
}
sourcepub fn shutdown_background(self)
pub fn shutdown_background(self)
Shuts down the runtime, without waiting for any spawned work to stop.
This can be useful if you want to drop a runtime from within another runtime.
Normally, dropping a runtime will block indefinitely for spawned blocking tasks
to complete, which would normally not be permitted within an asynchronous context.
By calling shutdown_background()
, you can drop the runtime from such a context.
Note however, that because we do not wait for any blocking tasks to complete, this may result in a resource leak (in that any blocking tasks are still running until they return.
See the struct level documentation for more details.
This function is equivalent to calling shutdown_timeout(Duration::from_nanos(0))
.
use tokio::runtime::Runtime;
fn main() {
let runtime = Runtime::new().unwrap();
runtime.block_on(async move {
let inner_runtime = Runtime::new().unwrap();
// ...
inner_runtime.shutdown_background();
});
}