use crate::runtime::{context, scheduler, RuntimeFlavor};
/// Handle to the runtime.
///
/// The handle is internally reference-counted and can be freely cloned. A handle can be
/// obtained using the [`Runtime::handle`] method.
///
/// [`Runtime::handle`]: crate::runtime::Runtime::handle()
#[derive(Debug, Clone)]
// When the `rt` feature is *not* enabled, this type is still defined, but not
// included in the public API.
pub struct Handle {
pub(crate) inner: scheduler::Handle,
}
use crate::runtime::task::JoinHandle;
use crate::util::error::{CONTEXT_MISSING_ERROR, THREAD_LOCAL_DESTROYED_ERROR};
use std::future::Future;
use std::marker::PhantomData;
use std::{error, fmt};
/// Runtime context guard.
///
/// Returned by [`Runtime::enter`] and [`Handle::enter`], the context guard exits
/// the runtime context on drop.
///
/// [`Runtime::enter`]: fn@crate::runtime::Runtime::enter
#[derive(Debug)]
#[must_use = "Creating and dropping a guard does nothing"]
pub struct EnterGuard<'a> {
_guard: context::SetCurrentGuard,
_handle_lifetime: PhantomData<&'a Handle>,
}
impl Handle {
/// 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`] and [`Handle::current`]
/// without panicking.
///
/// [`Sleep`]: struct@crate::time::Sleep
/// [`TcpStream`]: struct@crate::net::TcpStream
/// [`tokio::spawn`]: fn@crate::spawn
pub fn enter(&self) -> EnterGuard<'_> {
EnterGuard {
_guard: match context::try_set_current(&self.inner) {
Some(guard) => guard,
None => panic!("{}", crate::util::error::THREAD_LOCAL_DESTROYED_ERROR),
},
_handle_lifetime: PhantomData,
}
}
/// Returns a `Handle` view over the currently running `Runtime`.
///
/// # Panics
///
/// This will panic if called outside the context of a Tokio runtime. That means that you must
/// call this on one of the threads **being run by the runtime**, or from a thread with an active
/// `EnterGuard`. Calling this from within a thread created by `std::thread::spawn` (for example)
/// will cause a panic unless that thread has an active `EnterGuard`.
///
/// # Examples
///
/// This can be used to obtain the handle of the surrounding runtime from an async
/// block or function running on that runtime.
///
/// ```
/// # use std::thread;
/// # use tokio::runtime::Runtime;
/// # fn dox() {
/// # let rt = Runtime::new().unwrap();
/// # rt.spawn(async {
/// use tokio::runtime::Handle;
///
/// // Inside an async block or function.
/// let handle = Handle::current();
/// handle.spawn(async {
/// println!("now running in the existing Runtime");
/// });
///
/// # let handle =
/// thread::spawn(move || {
/// // Notice that the handle is created outside of this thread and then moved in
/// handle.spawn(async { /* ... */ });
/// // This next line would cause a panic because we haven't entered the runtime
/// // and created an EnterGuard
/// // let handle2 = Handle::current(); // panic
/// // So we create a guard here with Handle::enter();
/// let _guard = handle.enter();
/// // Now we can call Handle::current();
/// let handle2 = Handle::current();
/// });
/// # handle.join().unwrap();
/// # });
/// # }
/// ```
#[track_caller]
pub fn current() -> Self {
Handle {
inner: scheduler::Handle::current(),
}
}
/// Returns a Handle view over the currently running Runtime
///
/// Returns an error if no Runtime has been started
///
/// Contrary to `current`, this never panics
pub fn try_current() -> Result<Self, TryCurrentError> {
context::try_current().map(|inner| Handle { inner })
}
/// 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][mod] documentation for more details.
///
/// [mod]: index.html
///
/// # Examples
///
/// ```
/// use tokio::runtime::Runtime;
///
/// # fn dox() {
/// // Create the runtime
/// let rt = Runtime::new().unwrap();
/// // Get a handle from this runtime
/// let handle = rt.handle();
///
/// // Spawn a future onto the runtime using the handle
/// handle.spawn(async {
/// println!("now running on a worker thread");
/// });
/// # }
/// ```
#[track_caller]
pub fn spawn<F>(&self, future: F) -> JoinHandle<F::Output>
where
F: Future + Send + 'static,
F::Output: Send + 'static,
{
self.spawn_named(future, None)
}
/// Runs the provided function on an executor dedicated to blocking.
/// operations.
///
/// # Examples
///
/// ```
/// use tokio::runtime::Runtime;
///
/// # fn dox() {
/// // Create the runtime
/// let rt = Runtime::new().unwrap();
/// // Get a handle from this runtime
/// let handle = rt.handle();
///
/// // Spawn a blocking function onto the runtime using the handle
/// handle.spawn_blocking(|| {
/// println!("now running on a worker thread");
/// });
/// # }
#[track_caller]
pub fn spawn_blocking<F, R>(&self, func: F) -> JoinHandle<R>
where
F: FnOnce() -> R + Send + 'static,
R: Send + 'static,
{
self.inner.blocking_spawner().spawn_blocking(self, func)
}
/// Runs a future to completion on this `Handle`'s associated `Runtime`.
///
/// 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.
///
/// When this is used on a `current_thread` runtime, only the
/// [`Runtime::block_on`] method can drive the IO and timer drivers, but the
/// `Handle::block_on` method cannot drive them. This means that, when using
/// this method on a current_thread runtime, anything that relies on IO or
/// timers will not work unless there is another thread currently calling
/// [`Runtime::block_on`] on the same runtime.
///
/// # If the runtime has been shut down
///
/// If the `Handle`'s associated `Runtime` has been shut down (through
/// [`Runtime::shutdown_background`], [`Runtime::shutdown_timeout`], or by
/// dropping it) and `Handle::block_on` is used it might return an error or
/// panic. Specifically IO resources will return an error and timers will
/// panic. Runtime independent futures will run as normal.
///
/// # Panics
///
/// This function panics if the provided future panics, if called within an
/// asynchronous execution context, or if a timer future is executed on a
/// runtime that has been shut down.
///
/// # Examples
///
/// ```
/// use tokio::runtime::Runtime;
///
/// // Create the runtime
/// let rt = Runtime::new().unwrap();
///
/// // Get a handle from this runtime
/// let handle = rt.handle();
///
/// // Execute the future, blocking the current thread until completion
/// handle.block_on(async {
/// println!("hello");
/// });
/// ```
///
/// Or using `Handle::current`:
///
/// ```
/// use tokio::runtime::Handle;
///
/// #[tokio::main]
/// async fn main () {
/// let handle = Handle::current();
/// std::thread::spawn(move || {
/// // Using Handle::block_on to run async code in the new thread.
/// handle.block_on(async {
/// println!("hello");
/// });
/// });
/// }
/// ```
///
/// [`JoinError`]: struct@crate::task::JoinError
/// [`JoinHandle`]: struct@crate::task::JoinHandle
/// [`Runtime::block_on`]: fn@crate::runtime::Runtime::block_on
/// [`Runtime::shutdown_background`]: fn@crate::runtime::Runtime::shutdown_background
/// [`Runtime::shutdown_timeout`]: fn@crate::runtime::Runtime::shutdown_timeout
/// [`spawn_blocking`]: crate::task::spawn_blocking
/// [`tokio::fs`]: crate::fs
/// [`tokio::net`]: crate::net
/// [`tokio::time`]: crate::time
#[track_caller]
pub fn block_on<F: Future>(&self, future: F) -> F::Output {
#[cfg(all(tokio_unstable, feature = "tracing"))]
let future =
crate::util::trace::task(future, "block_on", None, super::task::Id::next().as_u64());
// Enter the runtime context. This sets the current driver handles and
// prevents blocking an existing runtime.
let mut enter = context::enter_runtime(&self.inner, true);
// Block on the future
enter
.blocking
.block_on(future)
.expect("failed to park thread")
}
#[track_caller]
pub(crate) fn spawn_named<F>(&self, future: F, _name: Option<&str>) -> JoinHandle<F::Output>
where
F: Future + Send + 'static,
F::Output: Send + 'static,
{
let id = crate::runtime::task::Id::next();
#[cfg(all(tokio_unstable, feature = "tracing"))]
let future = crate::util::trace::task(future, "task", _name, id.as_u64());
self.inner.spawn(future, id)
}
/// Returns the flavor of the current `Runtime`.
///
/// # Examples
///
/// ```
/// use tokio::runtime::{Handle, RuntimeFlavor};
///
/// #[tokio::main(flavor = "current_thread")]
/// async fn main() {
/// assert_eq!(RuntimeFlavor::CurrentThread, Handle::current().runtime_flavor());
/// }
/// ```
///
/// ```
/// use tokio::runtime::{Handle, RuntimeFlavor};
///
/// #[tokio::main(flavor = "multi_thread", worker_threads = 4)]
/// async fn main() {
/// assert_eq!(RuntimeFlavor::MultiThread, Handle::current().runtime_flavor());
/// }
/// ```
pub fn runtime_flavor(&self) -> RuntimeFlavor {
match self.inner {
scheduler::Handle::CurrentThread(_) => RuntimeFlavor::CurrentThread,
#[cfg(all(feature = "rt-multi-thread", not(tokio_wasi)))]
scheduler::Handle::MultiThread(_) => RuntimeFlavor::MultiThread,
}
}
}
cfg_metrics! {
use crate::runtime::RuntimeMetrics;
impl Handle {
/// Returns a view that lets you get information about how the runtime
/// is performing.
pub fn metrics(&self) -> RuntimeMetrics {
RuntimeMetrics::new(self.clone())
}
}
}
/// Error returned by `try_current` when no Runtime has been started
#[derive(Debug)]
pub struct TryCurrentError {
kind: TryCurrentErrorKind,
}
impl TryCurrentError {
pub(crate) fn new_no_context() -> Self {
Self {
kind: TryCurrentErrorKind::NoContext,
}
}
pub(crate) fn new_thread_local_destroyed() -> Self {
Self {
kind: TryCurrentErrorKind::ThreadLocalDestroyed,
}
}
/// Returns true if the call failed because there is currently no runtime in
/// the Tokio context.
pub fn is_missing_context(&self) -> bool {
matches!(self.kind, TryCurrentErrorKind::NoContext)
}
/// Returns true if the call failed because the Tokio context thread-local
/// had been destroyed. This can usually only happen if in the destructor of
/// other thread-locals.
pub fn is_thread_local_destroyed(&self) -> bool {
matches!(self.kind, TryCurrentErrorKind::ThreadLocalDestroyed)
}
}
enum TryCurrentErrorKind {
NoContext,
ThreadLocalDestroyed,
}
impl fmt::Debug for TryCurrentErrorKind {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
use TryCurrentErrorKind::*;
match self {
NoContext => f.write_str("NoContext"),
ThreadLocalDestroyed => f.write_str("ThreadLocalDestroyed"),
}
}
}
impl fmt::Display for TryCurrentError {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
use TryCurrentErrorKind::*;
match self.kind {
NoContext => f.write_str(CONTEXT_MISSING_ERROR),
ThreadLocalDestroyed => f.write_str(THREAD_LOCAL_DESTROYED_ERROR),
}
}
}
impl error::Error for TryCurrentError {}