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Diffstat (limited to 'src/libcore/future/future.rs')
| -rw-r--r-- | src/libcore/future/future.rs | 122 |
1 files changed, 0 insertions, 122 deletions
diff --git a/src/libcore/future/future.rs b/src/libcore/future/future.rs deleted file mode 100644 index 733ebdc0e97..00000000000 --- a/src/libcore/future/future.rs +++ /dev/null @@ -1,122 +0,0 @@ -#![stable(feature = "futures_api", since = "1.36.0")] - -use crate::marker::Unpin; -use crate::ops; -use crate::pin::Pin; -use crate::task::{Context, Poll}; - -/// A future represents an asynchronous computation. -/// -/// A future is a value that may not have finished computing yet. This kind of -/// "asynchronous value" makes it possible for a thread to continue doing useful -/// work while it waits for the value to become available. -/// -/// # The `poll` method -/// -/// The core method of future, `poll`, *attempts* to resolve the future into a -/// final value. This method does not block if the value is not ready. Instead, -/// the current task is scheduled to be woken up when it's possible to make -/// further progress by `poll`ing again. The `context` passed to the `poll` -/// method can provide a [`Waker`], which is a handle for waking up the current -/// task. -/// -/// When using a future, you generally won't call `poll` directly, but instead -/// `.await` the value. -/// -/// [`Waker`]: ../task/struct.Waker.html -#[doc(spotlight)] -#[must_use = "futures do nothing unless you `.await` or poll them"] -#[stable(feature = "futures_api", since = "1.36.0")] -#[lang = "future_trait"] -#[rustc_on_unimplemented(label = "`{Self}` is not a future", message = "`{Self}` is not a future")] -pub trait Future { - /// The type of value produced on completion. - #[stable(feature = "futures_api", since = "1.36.0")] - type Output; - - /// Attempt to resolve the future to a final value, registering - /// the current task for wakeup if the value is not yet available. - /// - /// # Return value - /// - /// This function returns: - /// - /// - [`Poll::Pending`] if the future is not ready yet - /// - [`Poll::Ready(val)`] with the result `val` of this future if it - /// finished successfully. - /// - /// Once a future has finished, clients should not `poll` it again. - /// - /// When a future is not ready yet, `poll` returns `Poll::Pending` and - /// stores a clone of the [`Waker`] copied from the current [`Context`]. - /// This [`Waker`] is then woken once the future can make progress. - /// For example, a future waiting for a socket to become - /// readable would call `.clone()` on the [`Waker`] and store it. - /// When a signal arrives elsewhere indicating that the socket is readable, - /// [`Waker::wake`] is called and the socket future's task is awoken. - /// Once a task has been woken up, it should attempt to `poll` the future - /// again, which may or may not produce a final value. - /// - /// Note that on multiple calls to `poll`, only the [`Waker`] from the - /// [`Context`] passed to the most recent call should be scheduled to - /// receive a wakeup. - /// - /// # Runtime characteristics - /// - /// Futures alone are *inert*; they must be *actively* `poll`ed to make - /// progress, meaning that each time the current task is woken up, it should - /// actively re-`poll` pending futures that it still has an interest in. - /// - /// The `poll` function is not called repeatedly in a tight loop -- instead, - /// it should only be called when the future indicates that it is ready to - /// make progress (by calling `wake()`). If you're familiar with the - /// `poll(2)` or `select(2)` syscalls on Unix it's worth noting that futures - /// typically do *not* suffer the same problems of "all wakeups must poll - /// all events"; they are more like `epoll(4)`. - /// - /// An implementation of `poll` should strive to return quickly, and should - /// not block. Returning quickly prevents unnecessarily clogging up - /// threads or event loops. If it is known ahead of time that a call to - /// `poll` may end up taking awhile, the work should be offloaded to a - /// thread pool (or something similar) to ensure that `poll` can return - /// quickly. - /// - /// # Panics - /// - /// Once a future has completed (returned `Ready` from `poll`), calling its - /// `poll` method again may panic, block forever, or cause other kinds of - /// problems; the `Future` trait places no requirements on the effects of - /// such a call. However, as the `poll` method is not marked `unsafe`, - /// Rust's usual rules apply: calls must never cause undefined behavior - /// (memory corruption, incorrect use of `unsafe` functions, or the like), - /// regardless of the future's state. - /// - /// [`Poll::Pending`]: ../task/enum.Poll.html#variant.Pending - /// [`Poll::Ready(val)`]: ../task/enum.Poll.html#variant.Ready - /// [`Context`]: ../task/struct.Context.html - /// [`Waker`]: ../task/struct.Waker.html - /// [`Waker::wake`]: ../task/struct.Waker.html#method.wake - #[stable(feature = "futures_api", since = "1.36.0")] - fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output>; -} - -#[stable(feature = "futures_api", since = "1.36.0")] -impl<F: ?Sized + Future + Unpin> Future for &mut F { - type Output = F::Output; - - fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> { - F::poll(Pin::new(&mut **self), cx) - } -} - -#[stable(feature = "futures_api", since = "1.36.0")] -impl<P> Future for Pin<P> -where - P: Unpin + ops::DerefMut<Target: Future>, -{ - type Output = <<P as ops::Deref>::Target as Future>::Output; - - fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> { - Pin::get_mut(self).as_mut().poll(cx) - } -} |