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Simplify the first trait in extension_trait.

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Nicholas Nethercote 2022-03-11 11:52:44 +11:00
parent ed2fcce557
commit c10d2d3a6f
7 changed files with 7 additions and 364 deletions
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105
src/future/future/mod.rs
View file

@ -21,110 +21,7 @@ cfg_unstable_default! {
}
extension_trait! {
#[doc = r#"
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 [provided methods] do not really exist in the trait itself, but they become
available when [`FutureExt`] from the [prelude] is imported:
```
# #[allow(unused_imports)]
use async_std::prelude::*;
```
# 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
[provided methods]: #provided-methods
[`FutureExt`]: ../prelude/trait.FutureExt.html
[prelude]: ../prelude/index.html
"#]
pub trait Future {
#[doc = r#"
The type of value produced on completion.
"#]
type Output;
#[doc = r#"
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
"#]
fn poll(self: Pin<&mut Self>, cx: &mut Context) -> Poll<Self::Output>;
}
pub trait Future {}
#[doc = r#"
Extension methods for [`Future`].

46
src/io/buf_read/mod.rs
View file

@ -16,51 +16,7 @@ use crate::io;
use crate::task::{Context, Poll};
extension_trait! {
#[doc = r#"
Allows reading from a buffered byte stream.
This trait is a re-export of [`futures::io::AsyncBufRead`] and is an async version of
[`std::io::BufRead`].
The [provided methods] do not really exist in the trait itself, but they become
available when [`BufReadExt`] from the [prelude] is imported:
```
# #[allow(unused_imports)]
use async_std::io::prelude::*;
```
[`std::io::BufRead`]: https://doc.rust-lang.org/std/io/trait.BufRead.html
[`futures::io::AsyncBufRead`]:
https://docs.rs/futures/0.3/futures/io/trait.AsyncBufRead.html
[provided methods]: #provided-methods
[`BufReadExt`]: ../io/prelude/trait.BufReadExt.html
[prelude]: ../prelude/index.html
"#]
pub trait BufRead {
#[doc = r#"
Returns the contents of the internal buffer, filling it with more data from the
inner reader if it is empty.
This function is a lower-level call. It needs to be paired with the [`consume`]
method to function properly. When calling this method, none of the contents will be
"read" in the sense that later calling `read` may return the same contents. As
such, [`consume`] must be called with the number of bytes that are consumed from
this buffer to ensure that the bytes are never returned twice.
[`consume`]: #tymethod.consume
An empty buffer returned indicates that the stream has reached EOF.
"#]
// TODO: write a proper doctest with `consume`
fn poll_fill_buf(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<&[u8]>>;
#[doc = r#"
Tells this buffer that `amt` bytes have been consumed from the buffer, so they
should no longer be returned in calls to `read`.
"#]
fn consume(self: Pin<&mut Self>, amt: usize);
}
pub trait BufRead {}
#[doc = r#"
Extension methods for [`BufRead`].

44
src/io/read/mod.rs
View file

@ -22,49 +22,7 @@ pub use chain::Chain;
pub use take::Take;
extension_trait! {
#[doc = r#"
Allows reading from a byte stream.
This trait is a re-export of [`futures::io::AsyncRead`] and is an async version of
[`std::io::Read`].
Methods other than [`poll_read`] and [`poll_read_vectored`] do not really exist in the
trait itself, but they become available when [`ReadExt`] from the [prelude] is imported:
```
# #[allow(unused_imports)]
use async_std::prelude::*;
```
[`std::io::Read`]: https://doc.rust-lang.org/std/io/trait.Read.html
[`futures::io::AsyncRead`]:
https://docs.rs/futures/0.3/futures/io/trait.AsyncRead.html
[`poll_read`]: #tymethod.poll_read
[`poll_read_vectored`]: #method.poll_read_vectored
[`ReadExt`]: ../io/prelude/trait.ReadExt.html
[prelude]: ../prelude/index.html
"#]
pub trait Read {
#[doc = r#"
Attempt to read from the `AsyncRead` into `buf`.
"#]
fn poll_read(
self: Pin<&mut Self>,
cx: &mut Context<'_>,
buf: &mut [u8],
) -> Poll<io::Result<usize>>;
#[doc = r#"
Attempt to read from the `AsyncRead` into `bufs` using vectored IO operations.
"#]
fn poll_read_vectored(
self: Pin<&mut Self>,
cx: &mut Context<'_>,
bufs: &mut [IoSliceMut<'_>],
) -> Poll<io::Result<usize>> {
unreachable!("this impl only appears in the rendered docs")
}
}
pub trait Read {}
#[doc = r#"
Extension methods for [`Read`].

32
src/io/seek/mod.rs
View file

@ -5,37 +5,7 @@ use seek::SeekFuture;
use crate::io::SeekFrom;
extension_trait! {
#[doc = r#"
Allows seeking through a byte stream.
This trait is a re-export of [`futures::io::AsyncSeek`] and is an async version of
[`std::io::Seek`].
The [provided methods] do not really exist in the trait itself, but they become
available when [`SeekExt`] the [prelude] is imported:
```
# #[allow(unused_imports)]
use async_std::prelude::*;
```
[`std::io::Seek`]: https://doc.rust-lang.org/std/io/trait.Seek.html
[`futures::io::AsyncSeek`]:
https://docs.rs/futures/0.3/futures/io/trait.AsyncSeek.html
[provided methods]: #provided-methods
[`SeekExt`]: ../io/prelude/trait.SeekExt.html
[prelude]: ../prelude/index.html
"#]
pub trait Seek {
#[doc = r#"
Attempt to seek to an offset, in bytes, in a stream.
"#]
fn poll_seek(
self: Pin<&mut Self>,
cx: &mut Context<'_>,
pos: SeekFrom,
) -> Poll<io::Result<u64>>;
}
pub trait Seek {}
#[doc = r#"
Extension methods for [`Seek`].

58
src/io/write/mod.rs
View file

@ -13,63 +13,7 @@ use write_vectored::WriteVectoredFuture;
use crate::io::{self, IoSlice};
extension_trait! {
#[doc = r#"
Allows writing to a byte stream.
This trait is a re-export of [`futures::io::AsyncWrite`] and is an async version of
[`std::io::Write`].
Methods other than [`poll_write`], [`poll_write_vectored`], [`poll_flush`], and
[`poll_close`] do not really exist in the trait itself, but they become available when
[`WriteExt`] from the [prelude] is imported:
```
# #[allow(unused_imports)]
use async_std::prelude::*;
```
[`std::io::Write`]: https://doc.rust-lang.org/std/io/trait.Write.html
[`futures::io::AsyncWrite`]:
https://docs.rs/futures/0.3/futures/io/trait.AsyncWrite.html
[`poll_write`]: #tymethod.poll_write
[`poll_write_vectored`]: #method.poll_write_vectored
[`poll_flush`]: #tymethod.poll_flush
[`poll_close`]: #tymethod.poll_close
[`WriteExt`]: ../io/prelude/trait.WriteExt.html
[prelude]: ../prelude/index.html
"#]
pub trait Write {
#[doc = r#"
Attempt to write bytes from `buf` into the object.
"#]
fn poll_write(
self: Pin<&mut Self>,
cx: &mut Context<'_>,
buf: &[u8],
) -> Poll<io::Result<usize>>;
#[doc = r#"
Attempt to write bytes from `bufs` into the object using vectored IO operations.
"#]
fn poll_write_vectored(
self: Pin<&mut Self>,
cx: &mut Context<'_>,
bufs: &[IoSlice<'_>]
) -> Poll<io::Result<usize>> {
unreachable!("this impl only appears in the rendered docs")
}
#[doc = r#"
Attempt to flush the object, ensuring that any buffered data reach
their destination.
"#]
fn poll_flush(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<()>>;
#[doc = r#"
Attempt to close the object.
"#]
fn poll_close(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<()>>;
}
pub trait Write {}
#[doc = r#"
Extension methods for [`Write`].

81
src/stream/stream/mod.rs
View file

@ -144,86 +144,7 @@ cfg_unstable! {
}
extension_trait! {
#[doc = r#"
An asynchronous stream of values.
This trait is a re-export of [`futures::stream::Stream`] and is an async version of
[`std::iter::Iterator`].
The [provided methods] do not really exist in the trait itself, but they become
available when [`StreamExt`] from the [prelude] is imported:
```
# #[allow(unused_imports)]
use async_std::prelude::*;
```
[`std::iter::Iterator`]: https://doc.rust-lang.org/std/iter/trait.Iterator.html
[`futures::stream::Stream`]:
https://docs.rs/futures/0.3/futures/stream/trait.Stream.html
[provided methods]: #provided-methods
[`StreamExt`]: ../prelude/trait.StreamExt.html
[prelude]: ../prelude/index.html
"#]
pub trait Stream {
#[doc = r#"
The type of items yielded by this stream.
"#]
type Item;
#[doc = r#"
Attempts to receive the next item from the stream.
There are several possible return values:
* `Poll::Pending` means this stream's next value is not ready yet.
* `Poll::Ready(None)` means this stream has been exhausted.
* `Poll::Ready(Some(item))` means `item` was received out of the stream.
# Examples
```
# fn main() { async_std::task::block_on(async {
#
use std::pin::Pin;
use async_std::prelude::*;
use async_std::stream;
use async_std::task::{Context, Poll};
fn increment(
s: impl Stream<Item = i32> + Unpin,
) -> impl Stream<Item = i32> + Unpin {
struct Increment<S>(S);
impl<S: Stream<Item = i32> + Unpin> Stream for Increment<S> {
type Item = S::Item;
fn poll_next(
mut self: Pin<&mut Self>,
cx: &mut Context<'_>,
) -> Poll<Option<Self::Item>> {
match Pin::new(&mut self.0).poll_next(cx) {
Poll::Pending => Poll::Pending,
Poll::Ready(None) => Poll::Ready(None),
Poll::Ready(Some(item)) => Poll::Ready(Some(item + 1)),
}
}
}
Increment(s)
}
let mut s = increment(stream::once(7));
assert_eq!(s.next().await, Some(8));
assert_eq!(s.next().await, None);
#
# }) }
```
"#]
fn poll_next(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<Self::Item>>;
}
pub trait Stream {}
#[doc = r#"
Extension methods for [`Stream`].

5
src/utils.rs
View file

@ -250,10 +250,7 @@ macro_rules! extension_trait {
// - `$name`: trait name that gets rendered in the docs
// - `$ext`: name of the hidden extension trait
// - `$base`: base trait
#[doc = $doc:tt]
pub trait $name:ident {
$($body_base:tt)*
}
pub trait $name:ident {}
#[doc = $doc_ext:tt]
pub trait $ext:ident: $base:path {