use crate::runtime::{blocking, context, io, time, Spawner};
use std::{error, fmt};
cfg_rt_core! {
use crate::task::JoinHandle;
use std::future::Future;
}
/// Handle to the runtime
#[derive(Debug, Clone)]
pub struct Handle {
pub(super) spawner: Spawner,
/// Handles to the I/O drivers
pub(super) io_handle: io::Handle,
/// Handles to the time drivers
pub(super) time_handle: time::Handle,
/// Source of `Instant::now()`
pub(super) clock: time::Clock,
/// Blocking pool spawner
pub(super) blocking_spawner: blocking::Spawner,
}
impl Handle {
/// Enter the runtime context
pub fn enter<F, R>(&self, f: F) -> R
where
F: FnOnce() -> R,
{
context::enter(self.clone(), f)
}
/// Returns a Handle view over the currently running Runtime
///
/// # Panic
///
/// A Runtime must have been started or this will panic
///
/// # Examples
///
/// This allows for the current handle to be gotten when running in a `#`
///
/// ```
/// # use tokio::runtime::Runtime;
///
/// # fn dox() {
/// # let rt = Runtime::new().unwrap();
/// # rt.spawn(async {
/// use tokio::runtime::Handle;
///
/// let handle = Handle::current();
/// handle.spawn(async {
/// println!("now running in the existing Runtime");
/// })
/// # });
/// # }
/// ```
pub fn current() -> Self {
context::current().expect("not currently running on the Tokio runtime.")
}
/// 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::current().ok_or(TryCurrentError(()))
}
}
cfg_rt_core! {
impl Handle {
/// Spawn 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.
///
/// 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();
/// let handle = rt.handle();
///
/// // Spawn a future onto the runtime
/// handle.spawn(async {
/// println!("now running on a worker thread");
/// });
/// # }
/// ```
///
/// # Panics
///
/// This function panics if the spawn fails. Failure occurs if the executor
/// is currently at capacity and is unable to spawn a new future.
pub fn spawn<F>(&self, future: F) -> JoinHandle<F::Output>
where
F: Future + Send + 'static,
F::Output: Send + 'static,
{
self.spawner.spawn(future)
}
}
}
/// Error returned by `try_current` when no Runtime has been started
pub struct TryCurrentError(());
impl fmt::Debug for TryCurrentError {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
f.debug_struct("TryCurrentError").finish()
}
}
impl fmt::Display for TryCurrentError {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
f.write_str("no tokio Runtime has been initialized")
}
}
impl error::Error for TryCurrentError {}