diff --git a/src/stream/mod.rs b/src/stream/mod.rs index c41ceb6..7e8939b 100644 --- a/src/stream/mod.rs +++ b/src/stream/mod.rs @@ -1,4 +1,4 @@ -//! Asynchronous iteration. +//! Composable asynchronous iteration. //! //! This module is an async version of [`std::iter`]. //! diff --git a/src/task/mod.rs b/src/task/mod.rs index fc702df..069aa3a 100644 --- a/src/task/mod.rs +++ b/src/task/mod.rs @@ -1,26 +1,122 @@ -//! Asynchronous tasks. +//! Types and Traits for working with asynchronous tasks.. //! //! This module is similar to [`std::thread`], except it uses asynchronous tasks in place of //! threads. //! -//! [`std::thread`]: https://doc.rust-lang.org/std/thread/index.html +//! [`std::thread`]: https://doc.rust-lang.org/std/thread //! -//! # Examples +//! ## The task model //! -//! Spawn a task and await its result: +//! An executing asynchronous Rust program consists of a collection of native OS threads, on top of +//! which multiple stackless coroutines are multiplexed. We refer to these as "tasks". Tasks can +//! be named, and provide some built-in support for synchronization. //! +//! Communication between tasks can be done through channels, Rust's message-passing types, along +//! with [other forms of tasks synchronization](../sync/index.html) and shared-memory data +//! structures. In particular, types that are guaranteed to be threadsafe are easily shared between +//! tasks using the atomically-reference-counted container, [`Arc`]. +//! +//! Fatal logic errors in Rust cause *thread panic*, during which a thread will unwind the stack, +//! running destructors and freeing owned resources. If a panic occurs inside a task, there is no +//! meaningful way of recovering, so the panic will propagate through any thread boundaries all the +//! way to the root task. This is also known as a "panic = abort" model. +//! +//! ## Spawning a task +//! +//! A new task can be spawned using the [`task::spawn`][`spawn`] function: +//! +//! ```no_run +//! use async_std::task; +//! +//! task::spawn(async { +//! // some work here +//! }); //! ``` +//! +//! In this example, the spawned task is "detached" from the current task. This means that it can +//! outlive its parent (the task that spawned it), unless this parent is the root task. +//! +//! The root task can also wait on the completion of the child task; a call to [`spawn`] produces a +//! [`JoinHandle`], which provides implements `Future` and can be `await`ed: +//! +//! ``` +//! use async_std::task; +//! //! # async_std::task::block_on(async { //! # +//! let child = task::spawn(async { +//! // some work here +//! }); +//! // some work here +//! let res = child.await; +//! # +//! # }) +//! ``` +//! +//! The `await` operator returns the final value produced by the child task. +//! +//! ## Configuring tasks +//! +//! A new task can be configured before it is spawned via the [`Builder`] type, +//! which currently allows you to set the name and stack size for the child task: +//! +//! ``` +//! # #![allow(unused_must_use)] //! use async_std::task; //! -//! let handle = task::spawn(async { -//! 1 + 2 +//! # async_std::task::block_on(async { +//! # +//! task::Builder::new().name("child1".to_string()).spawn(async { +//! println!("Hello, world!"); //! }); -//! assert_eq!(handle.await, 3); //! # //! # }) //! ``` +//! +//! ## The `Task` type +//! +//! Tasks are represented via the [`Task`] type, which you can get in one of +//! two ways: +//! +//! * By spawning a new task, e.g., using the [`task::spawn`][`spawn`] +//! function, and calling [`task`][`JoinHandle::task`] on the [`JoinHandle`]. +//! * By requesting the current task, using the [`task::current`] function. +//! +//! ## Task-local storage +//! +//! This module also provides an implementation of task-local storage for Rust +//! programs. Task-local storage is a method of storing data into a global +//! variable that each task in the program will have its own copy of. +//! Tasks do not share this data, so accesses do not need to be synchronized. +//! +//! A task-local key owns the value it contains and will destroy the value when the +//! task exits. It is created with the [`task_local!`] macro and can contain any +//! value that is `'static` (no borrowed pointers). It provides an accessor function, +//! [`with`], that yields a shared reference to the value to the specified +//! closure. Task-local keys allow only shared access to values, as there would be no +//! way to guarantee uniqueness if mutable borrows were allowed. +//! +//! ## Naming tasks +//! +//! Tasks are able to have associated names for identification purposes. By default, spawned +//! tasks are unnamed. To specify a name for a task, build the task with [`Builder`] and pass +//! the desired task name to [`Builder::name`]. To retrieve the task name from within the +//! task, use [`Task::name`]. +//! +//! [`Arc`]: ../gsync/struct.Arc.html +//! [`spawn`]: fn.spawn.html +//! [`JoinHandle`]: struct.JoinHandle.html +//! [`JoinHandle::task`]: struct.JoinHandle.html#method.task +//! [`join`]: struct.JoinHandle.html#method.join +//! [`panic!`]: https://doc.rust-lang.org/std/macro.panic.html +//! [`Builder`]: struct.Builder.html +//! [`Builder::stack_size`]: struct.Builder.html#method.stack_size +//! [`Builder::name`]: struct.Builder.html#method.name +//! [`task::current`]: fn.current.html +//! [`Task`]: struct.Thread.html +//! [`Task::name`]: struct.Task.html#method.name +//! [`task_local!`]: ../macro.task_local.html +//! [`with`]: struct.LocalKey.html#method.with #[doc(inline)] pub use std::task::{Context, Poll, Waker};