futures/lib.rs
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//! Abstractions for asynchronous programming.
//!
//! This crate provides a number of core abstractions for writing asynchronous code:
//!
//! - [Futures](::Future) (sometimes called promises), which represent a single
//! asychronous computation that may result in a final value or an error.
//!
//! - [Streams](::Stream), which represent a series of values or errors produced asynchronously.
//!
//! - [Sinks](::Sink), which support asynchronous writing of data.
//!
//! - [Executors](::executor), which are responsible for running asynchronous tasks.
//!
//! The crate also contains abstractions for [asynchronous I/O](::io) and
//! [cross-task communication](::channel).
//!
//! Underlying all of this is the *task system*, which is a form of lightweight
//! threading. Large asynchronous computations are built up using futures,
//! streams and sinks, and then spawned as independent tasks that are run to
//! completion, but *do not block* the thread running them.
#![no_std]
#![doc(html_root_url = "https://docs.rs/futures/0.2.2")]
#![cfg_attr(feature = "nightly", feature(cfg_target_has_atomic))]
#![cfg_attr(feature = "nightly", feature(use_extern_macros))]
extern crate futures_async_runtime;
extern crate futures_core;
extern crate futures_channel;
extern crate futures_executor;
extern crate futures_io;
extern crate futures_sink;
extern crate futures_stable;
extern crate futures_util;
#[cfg(feature = "nightly")] extern crate futures_macro_async;
#[cfg(feature = "nightly")] extern crate futures_macro_await;
pub use futures_core::future::{Future, IntoFuture};
pub use futures_util::future::FutureExt;
pub use futures_core::stream::Stream;
pub use futures_util::stream::StreamExt;
pub use futures_sink::Sink;
pub use futures_util::sink::SinkExt;
// Macros redefined here because macro re-exports are unstable.
/// A macro for extracting the successful type of a `Poll<T, E>`.
///
/// This macro bakes in propagation of both errors and `Pending` signals by
/// returning early.
#[macro_export]
macro_rules! try_ready {
($e:expr) => (match $e {
Ok($crate::prelude::Async::Ready(t)) => t,
Ok($crate::prelude::Async::Pending) => return Ok($crate::prelude::Async::Pending),
Err(e) => return Err(From::from(e)),
})
}
/// A macro to create a `static` of type `LocalKey`.
///
/// This macro is intentionally similar to the `thread_local!`, and creates a
/// `static` which has a `get_mut` method to access the data on a task.
///
/// The data associated with each task local is per-task, so different tasks
/// will contain different values.
#[macro_export]
macro_rules! task_local {
(static $NAME:ident: $t:ty = $e:expr) => (
static $NAME: $crate::task::LocalKey<$t> = {
fn __init() -> $t { $e }
fn __key() -> ::std::any::TypeId {
struct __A;
::std::any::TypeId::of::<__A>()
}
$crate::task::LocalKey {
__init: __init,
__key: __key,
}
};
)
}
pub use futures_core::{Async, Poll, Never};
#[cfg(feature = "std")]
pub mod channel {
//! Cross-task communication.
//!
//! Like threads, concurrent tasks sometimes need to communicate with each
//! other. This module contains two basic abstractions for doing so:
//!
//! - [oneshot](::channel::oneshot), a way of sending a single value from
//! one task to another.
//!
//! - [mpsc](::channel::mpsc), a multi-producer, single-consumer channel for
//! sending values between tasks, analogous to the similarly-named structure
//! in the standard library.
pub use futures_channel::{oneshot, mpsc};
}
#[cfg(feature = "std")]
pub mod executor {
//! Task execution.
//!
//! All asynchronous computation occurs within an executor, which is
//! capable of spawning futures as tasks. This module provides several
//! built-in executors, as well as tools for building your own.
//!
//! # Using a thread pool (M:N task scheduling)
//!
//! Most of the time tasks should be executed on a [thread
//! pool](::executor::ThreadPool). A small set of worker threads can handle
//! a very large set of spawned tasks (which are much lighter weight than
//! threads).
//!
//! The simplest way to use a thread pool is to
//! [`run`](::executor::ThreadPool::run) an initial task on it, which can
//! then spawn further tasks back onto the pool to complete its work:
//!
//! ```
//! use futures::executor::ThreadPool;
//! # use futures::future::{Future, lazy};
//! # let my_app: Box<Future<Item = (), Error = ()>> = Box::new(lazy(|_| Ok(())));
//!
//! // assuming `my_app: Future`
//! ThreadPool::new().expect("Failed to create threadpool").run(my_app);
//! ```
//!
//! The call to [`run`](::executor::ThreadPool::run) will block the current
//! thread until the future defined by `my_app` completes, and will return
//! the result of that future.
//!
//! # Spawning additional tasks
//!
//! There are two ways to spawn a task:
//!
//! - Spawn onto a "default" executor by calling the top-level
//! [`spawn`](::executor::spawn) function or [pulling the executor from the
//! task context](::task::Context::executor).
//!
//! - Spawn onto a specific executor by calling its
//! [`spawn`](::executor::Executor::spawn) method directly.
//!
//! Every task always has an associated default executor, which is usually
//! the executor on which the task is running.
//!
//! # Single-threaded execution
//!
//! In addition to thread pools, it's possible to run a task (and the tasks
//! it spawns) entirely within a single thread via the
//! [`LocalPool`](::executor::LocalPool) executor. Aside from cutting down
//! on synchronization costs, this executor also makes it possible to
//! execute non-`Send` tasks, via
//! [`spawn_local`](::executor::LocalExecutor::spawn_local). The `LocalPool`
//! is best suited for running I/O-bound tasks that do relatively little
//! work between I/O operations.
//!
//! There is also a convenience function,
//! [`block_on`](::executor::block_on), for simply running a future to
//! completion on the current thread, while routing any spawned tasks
//! to a global thread pool.
// TODO: add docs (or link to apr) for implementing an executor
pub use futures_executor::{
BlockingStream,
Enter, EnterError,
LocalExecutor, LocalPool,
Spawn, SpawnWithHandle,
ThreadPool, ThreadPoolBuilder, JoinHandle,
block_on, block_on_stream, enter, spawn, spawn_with_handle
};
pub use futures_core::executor::{SpawnError, Executor};
}
pub mod future {
//! Asynchronous values.
//!
//! This module contains:
//!
//! - The [`Future` trait](::Future).
//!
//! - The [`FutureExt`](::future::FutureExt) trait, which provides adapters
//! for chaining and composing futures.
//!
//! - Top-level future combinators like [`lazy`](::future::lazy) which
//! creates a future from a closure that defines its return value, and
//! [`result`](::future::result), which constructs a future with an
//! immediate defined value.
pub use futures_core::future::{
FutureOption, FutureResult, Future, IntoFuture, err, ok, result
};
pub use futures_util::future::{
AndThen, Empty, Flatten, FlattenStream, ErrInto, Fuse,
Inspect, IntoStream, Join, Join3, Join4, Join5, Lazy, LoopFn,
Map, MapErr, OrElse, PollFn, Select, Then, Either, Loop, FutureExt, empty,
lazy, loop_fn, poll_fn
};
#[cfg(feature = "std")]
pub use futures_util::future::{
CatchUnwind, JoinAll, SelectAll, SelectOk, Shared, SharedError, SharedItem,
join_all, select_all, select_ok
};
}
#[cfg(feature = "std")]
pub mod io {
//! Asynchronous I/O.
//!
//! This module is the asynchronous version of `std::io`. It defines two
//! traits, [`AsyncRead`](::io::AsyncRead) and
//! [`AsyncWrite`](::io::AsyncWrite), which mirror the `Read` and `Write`
//! traits of the standard library. However, these traits integrate with the
//! asynchronous task system, so that if an I/O object isn't ready for
//! reading (or writing), the thread is not blocked, and instead the current
//! task is queued to be woken when I/O is ready.
//!
//! In addition, the [`AsyncReadExt`](::io::AsyncReadExt) and
//! [`AsyncWriteExt`](::io::AsyncWriteExt) extension traits offer a variety
//! of useful combinators for operating with asynchronous I/O objects,
//! including ways to work with them using futures, streams and sinks.
pub use futures_io::{
Error, Initializer, IoVec, ErrorKind, AsyncRead, AsyncWrite, Result
};
pub use futures_util::io::{
AsyncReadExt, AsyncWriteExt, AllowStdIo, Close, CopyInto, Flush,
Read, ReadExact, ReadHalf, ReadToEnd, Window, WriteAll, WriteHalf,
};
}
#[cfg(feature = "std")]
pub mod never {
//! This module contains the `Never` type.
//!
//! Values of this type can never be created and will never exist.
pub use futures_core::never::*;
}
pub mod prelude {
//! A "prelude" for crates using the `futures` crate.
//!
//! This prelude is similar to the standard library's prelude in that you'll
//! almost always want to import its entire contents, but unlike the standard
//! library's prelude you'll have to do so manually:
//!
//! ```
//! use futures::prelude::*;
//! ```
//!
//! The prelude may grow over time as additional items see ubiquitous use.
pub use futures_core::{
Future,
IntoFuture,
Stream,
Async,
Poll,
Never,
task,
};
#[cfg(feature = "std")]
pub use futures_core::executor::Executor;
#[cfg(feature = "nightly")]
pub use futures_stable::{
StableFuture,
StableStream
};
#[cfg(all(feature = "nightly", feature = "std"))]
pub use futures_stable::StableExecutor;
pub use futures_sink::Sink;
#[cfg(feature = "std")]
pub use futures_io::{
AsyncRead,
AsyncWrite,
};
pub use futures_util::{
FutureExt,
StreamExt,
SinkExt,
};
#[cfg(feature = "std")]
pub use futures_util::{
AsyncReadExt,
AsyncWriteExt,
};
#[cfg(feature = "nightly")]
pub use futures_macro_async::{
async,
async_stream,
async_block,
async_stream_block,
};
#[cfg(feature = "nightly")]
pub use futures_macro_await::{
await,
stream_yield,
await_item
};
}
pub mod sink {
//! Asynchronous sinks.
//!
//! This module contains:
//!
//! - The [`Sink` trait](::Sink), which allows you to asynchronously write data.
//!
//! - The [`SinkExt`](::sink::SinkExt) trait, which provides adapters
//! for chaining and composing sinks.
pub use futures_sink::Sink;
pub use futures_util::sink::{
Close, Fanout, Flush, Send, SendAll, SinkErrInto, SinkMapErr, With,
WithFlatMap, SinkExt,
};
#[cfg(feature = "std")]
pub use futures_util::sink::Buffer;
}
pub mod stream {
//! Asynchronous streams.
//!
//! This module contains:
//!
//! - The [`Stream` trait](::Stream), for objects that can asynchronously
//! produce a sequence of values.
//!
//! - The [`StreamExt`](::StreamExt) trait, which provides adapters
//! for chaining and composing streams.
//!
//! - Top-level stream contructors like [`iter_ok`](::stream::iter_ok) which
//! creates a stream from an iterator, and
//! [`futures_unordered`](::stream::futures_unordered()), which constructs a
//! stream from a collection of futures.
pub use futures_core::stream::Stream;
pub use futures_util::stream::{
AndThen, Chain, Concat, Empty, Filter, FilterMap, Flatten, Fold,
ForEach, Forward, ErrInto, Fuse, Inspect, InspectErr, IterOk,
IterResult, Map, MapErr, Once, OrElse, Peekable, PollFn, Repeat, Select,
Skip, SkipWhile, StreamFuture, Take, TakeWhile, Then, Unfold, Zip,
StreamExt, empty, iter_ok, iter_result, once, poll_fn, repeat, unfold,
};
#[cfg(feature = "std")]
pub use futures_util::stream::{
futures_unordered, select_all, BufferUnordered, Buffered, CatchUnwind, Chunks, Collect,
FuturesUnordered, FuturesOrdered, ReuniteError, SelectAll, SplitSink, SplitStream,
futures_ordered,
};
}
pub mod task {
//! Tools for working with tasks.
//!
//! This module contains:
//!
//! - [`Context`](::task::Context), which provides contextual data present
//! for every task, including a handle for waking up the task.
//!
//! - [`Waker`](::task::Waker), a handle for waking up a task.
//!
//! - [`LocalKey`](::task::LocalKey), a key for task-local data; you should
//! use the [`task_local` macro](../macro.task_local.html) to set up such keys.
//!
//! Tasks themselves are generally created by spawning a future onto [an
//! executor](::executor). However, you can manually construct a task by
//! creating your own `Context` instance, and polling a future with it.
//!
//! The remaining types and traits in the module are used for implementing
//! executors or dealing with synchronization issues around task wakeup.
pub use futures_core::task::{
Context, LocalMap, Waker, UnsafeWake,
};
#[cfg_attr(feature = "nightly", cfg(target_has_atomic = "ptr"))]
pub use futures_core::task::AtomicWaker;
#[cfg(feature = "std")]
pub use futures_core::task::{LocalKey, Wake};
}
#[cfg(feature = "nightly")]
pub mod stable {
//! `async/await` futures which can be pinned to a particular location.
//!
//! This module contains:
//!
//! - The [`StableFuture`](::StableFuture) and [`StableStream`](::StableStream)
//! traits which allow for immovable, self-referential `Future`s and `Streams`.
//!
//! - The [`StableExecutor`](::StableExecutor) trait for `Executor`s which
//! take [`PinBox`](::std::boxed:PinBox)ed `Future`s.
//!
//! - A [`block_on_stable`](::block_on_stable) function for blocking on
//! `StableFuture`s.
//!
//! These immovable future types are most commonly used with the async/await
//! macros, which are included in the prelude. These macros can be used to
//! write asynchronous code in an ergonomic blocking style:
//!
//! ```rust
//! /// A simple async function which returns immediately once polled:
//! #[async]
//! fn foo() -> Result<i32, i32> {
//! Ok(1)
//! }
//!
//! /// Async functions can `await!` the result of other async functions:
//! #[async]
//! fn bar() -> Result<i32, i32> {
//! let foo_num = await!(foo())?;
//! Ok(foo_num + 5)
//! }
//!
//! /// Async functions can also choose to return a `Box`ed `Future` type.
//! /// To opt into `Send`able futures, use `#[async(boxed, send)]`.
//! #[async(boxed)]
//! fn boxed(x: i32) -> Result<i32, i32> {
//! Ok(
//! await!(foo())? + await!(bar()) + x
//! )
//! }
//!
//! /// Async expressions can also be written in `async_block!`s:
//! fn async_block() -> impl StableFuture<Item = i32, Error = i32> {
//! println!("Runs before the future is returned");
//! async_block! {
//! println!("Runs the first time the future is polled");
//! Ok(5)
//! }
//! }
//!
//! /// The futures that result from async functions can be pinned and used
//! /// with other `Future` combinators:
//! #[async]
//! fn join_two_futures() -> Result<(i32, i32), i32> {
//! let joined = foo().pin().join(bar().pin());
//! await!(joined)
//! }
//!
//! /// Streams can also be written in this style using the
//! /// `#[async_stream(item = ItemType)]` macro. The `stream_yield!`
//! /// macro is used to yield elements, and the `async_stream_block!`
//! /// macro can be used to write async streams inside other functions:
//! #[async_stream(boxed, send, item = u64)]
//! fn stream_boxed() -> Result<(), i32> {
//! let foo_result = await!(foo())?;
//! stream_yield!(foo_result as u64);
//! stream_yield!(22);
//! Ok(())
//! }
//!
//! /// Finally #[async] can be used on `for` loops to loop over the results
//! /// of a stream:
//! #[async]
//! fn async_for() -> Result<(), i32> {
//! #[async]
//! for i in stream_boxed() {
//! println!("yielded {}", i);
//! }
//! Ok(())
//! }
//! ```
pub use futures_stable::{StableFuture, StableStream};
#[cfg(feature = "std")]
pub use futures_stable::{StableExecutor, block_on_stable};
}
#[cfg(feature = "nightly")]
#[doc(hidden)]
pub mod __rt {
#[cfg(feature = "std")]
pub extern crate std;
pub use futures_async_runtime::*;
}