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//! Abstractions for asynchronous programming.
//! This crate provides a number of core abstractions for writing asynchronous
//! code:
//! - [Futures](crate::future::Future) are single eventual values produced by
//! asychronous computations. Some programming languages (e.g. JavaScript)
//! call this concept "promise".
//! - [Streams](crate::stream::Stream) represent a series of values
//! produced asynchronously.
//! - [Sinks](crate::sink::Sink) provide support for asynchronous writing of
//! data.
//! - [Executors](crate::executor) are responsible for running asynchronous
//! tasks.
//! The crate also contains abstractions for [asynchronous I/O](crate::io) and
//! [cross-task communication](crate::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.
#![feature(pin, arbitrary_self_types, futures_api)]
#![warn(missing_docs, missing_debug_implementations)]
#![doc(html_root_url = "")]
#![cfg_attr(feature = "nightly", feature(cfg_target_has_atomic))]
#[doc(hidden)] pub use futures_util::core_reexport;
#[doc(hidden)] pub use futures_core::future::Future;
#[doc(hidden)] pub use futures_core::future::TryFuture;
#[doc(hidden)] pub use futures_util::future::FutureExt;
#[doc(hidden)] pub use futures_util::try_future::TryFutureExt;
#[doc(hidden)] pub use futures_core::stream::Stream;
#[doc(hidden)] pub use futures_core::stream::TryStream;
#[doc(hidden)] pub use futures_util::stream::StreamExt;
#[doc(hidden)] pub use futures_util::try_stream::TryStreamExt;
#[doc(hidden)] pub use futures_sink::Sink;
#[doc(hidden)] pub use futures_util::sink::SinkExt;
#[doc(hidden)] pub use futures_core::task::Poll;
// Macro reexports
pub use futures_util::{
// Error/readiness propagation
try_ready, try_poll, ready,
#[cfg(feature = "std")]
pub use futures_util::{
// Async-await
join, try_join, select, pending, poll, spawn, spawn_with_handle,
#[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](crate::channel::oneshot), a way of sending a single value
//! from one task to another.
//! - [mpsc](crate::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 = "compat")]
pub mod compat {
//! Interop between `futures` 0.1 and 0.3.
pub use futures_util::compat::{
#[cfg(feature = "tokio-compat")]
pub use futures_util::compat::TokioDefaultSpawn;
#[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](crate::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`](crate::executor::ThreadPool::run) an initial task on it, which
//! can then spawn further tasks back onto the pool to complete its work:
//! ```
//! #![feature(pin, arbitrary_self_types, futures_api)]
//! use futures::executor::ThreadPool;
//! # use futures::future::{Future, lazy};
//! # let my_app = lazy(|_| 42);
//! // assumping `my_app: Future`
//! ThreadPool::new().expect("Failed to create threadpool").run(my_app);
//! ```
//! The call to [`run`](crate::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" spawner by calling the top-level
//! [`spawn`](crate::executor::spawn) function or [pulling the spawner
//! from the task context](crate::task::Context::spawner).
//! - Spawn onto a specific spawner by calling its
//! [`spawn_obj`](crate::executor::Spawn::spawn_obj) method directly.
//! Every task always has an associated default spawner, 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`](crate::executor::LocalPool) executor. Aside from cutting
//! down on synchronization costs, this executor also makes it possible to
//! spawn non-`Send` tasks, via
//! [`spawn_local_obj`](crate::executor::LocalSpawn::spawn_local_obj).
//! 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`](crate::executor::block_on), for simply running a future to
//! completion on the current thread, while routing any spawned tasks
//! to a global thread pool.
pub use futures_executor::{
Enter, EnterError,
LocalSpawn, LocalPool,
ThreadPool, ThreadPoolBuilder,
block_on, block_on_stream, enter,
pub mod future {
//! Asynchronous values.
//! This module contains:
//! - The [`Future` trait](crate::future::Future).
//! - The [`FutureExt`](crate::future::FutureExt) trait, which provides
//! adapters for chaining and composing futures.
//! - Top-level future combinators like [`lazy`](crate::future::lazy) which
//! creates a future from a closure that defines its return value, and
//! [`ready`](crate::future::ready), which constructs a future with an
//! immediate defined value.
pub use futures_core::future::{
Future, TryFuture,
FutureObj, LocalFutureObj, UnsafeFutureObj,
pub use futures_util::future::{
empty, Empty,
lazy, Lazy,
maybe_done, MaybeDone,
poll_fn, PollFn,
ready, Ready,
FlattenStream, Flatten, Fuse, Inspect, IntoStream, Join, Join3, Join4,
Join5, Map, Then, WithSpawner,
#[cfg(feature = "std")]
pub use futures_util::future::{
abortable, Abortable, AbortHandle, AbortRegistration, Aborted,
// For FutureExt:
CatchUnwind, Shared
// ToDo: JoinAll, SelectAll, SelectOk, join_all, select_all, select_ok
pub use futures_util::try_future::{
AndThen, ErrInto, FlattenSink, IntoFuture, MapErr, MapOk, OrElse,
TryJoin, TryJoin3, TryJoin4, TryJoin5,
#[cfg(feature = "std")]
pub mod io {
//! Asynchronous I/O.
//! This module is the asynchronous version of `std::io`. It defines two
//! traits, [`AsyncRead`](crate::io::AsyncRead) and
//! [`AsyncWrite`](crate::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`](crate::io::AsyncReadExt) and
//! [`AsyncWriteExt`](crate::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,
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 crate::future::{self, Future, TryFuture, FutureExt, TryFutureExt};
pub use crate::stream::{self, Stream, TryStream, StreamExt, TryStreamExt};
pub use crate::task::{self, Poll, SpawnExt};
pub use crate::sink::{self, Sink, SinkExt};
#[cfg(feature = "std")]
pub use crate::io::{ AsyncRead, AsyncWrite, AsyncReadExt, AsyncWriteExt };
pub mod sink {
//! Asynchronous sinks.
//! This module contains:
//! - The [`Sink` trait](crate::sink::Sink), which allows you to
//! asynchronously write data.
//! - The [`SinkExt`](crate::sink::SinkExt) trait, which provides adapters
//! for chaining and composing sinks.
pub use futures_sink::Sink;
pub use futures_util::sink::{
Close, Flush, Send, SendAll, SinkErrInto, SinkMapErr, With,
SinkExt, Fanout, Drain, DrainError, drain,
// WithFlatMap,
#[cfg(feature = "std")]
pub use futures_util::sink::Buffer;
pub mod stream {
//! Asynchronous streams.
//! This module contains:
//! - The [`Stream` trait](crate::stream::Stream), for objects that can
//! asynchronously produce a sequence of values.
//! - The [`StreamExt`](crate::stream::StreamExt) trait, which provides
//! adapters for chaining and composing streams.
//! - Top-level stream contructors like [`iter_ok`](crate::stream::iter)
//! which creates a stream from an iterator, and
//! [`futures_unordered`](crate::stream::futures_unordered()), which
//! constructs a stream from a collection of futures.
pub use futures_core::stream::{Stream, TryStream};
pub use futures_util::stream::{
iter, Iter,
repeat, Repeat,
empty, Empty,
once, Once,
poll_fn, PollFn,
unfold, Unfold,
Chain, Concat, Filter, FilterMap, Flatten, Fold, Forward, ForEach, Fuse,
StreamFuture, Inspect, Map, Next, Peekable, Select, Skip, SkipWhile,
Take, TakeWhile, Then, Zip
#[cfg(feature = "std")]
pub use futures_util::stream::{
futures_ordered, FuturesOrdered,
futures_unordered, FuturesUnordered,
// For StreamExt:
BufferUnordered, Buffered, CatchUnwind, Chunks, Collect, SplitStream,
SplitSink, ReuniteError,
// ToDo: select_all, SelectAll,
pub use futures_util::try_stream::{
TryNext, TryForEach, ErrInto,
TryFold, TrySkipWhile,
// ToDo: AndThen, ErrInto, InspectErr, MapErr, OrElse
#[cfg(feature = "std")]
pub use futures_util::try_stream::{
// For TryStreamExt:
TryCollect, TryBufferUnordered,
// ToDo: AndThen, InspectErr, MapErr, OrElse
pub mod task {
//! Tools for working with tasks.
//! This module contains:
//! - [`Context`](crate::task::Context), which provides contextual data
//! present for every task, including a handle for waking up the task.
//! - [`Waker`](crate::task::Waker), a handle for waking up a task.
//! Tasks themselves are generally created by spawning a future onto [an
//! executor](crate::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, Poll, Spawn,
Waker, LocalWaker, UnsafeWake,
SpawnErrorKind, SpawnObjError, SpawnLocalObjError,
#[cfg(feature = "std")]
pub use futures_core::task::{
Wake, local_waker, local_waker_from_nonlocal
pub use futures_util::task::{SpawnExt, SpawnError};
#[cfg(feature = "std")]
pub use futures_util::task::{
LocalWakerRef, local_waker_ref, local_waker_ref_from_nonlocal, JoinHandle
feature = "nightly",
cfg(all(target_has_atomic = "cas", target_has_atomic = "ptr"))
pub use futures_util::task::AtomicWaker;