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// Unless explicitly stated otherwise all files in this repository are licensed under the
// MIT/Apache-2.0 License, at your convenience
//
// This product includes software developed at Datadog (https://www.datadoghq.com/). Copyright 2020 Datadog, Inc.
//
//! Task abstraction for building executors.
//!
//! # Spawning
//!
//! To spawn a future onto the Glommio executor, we first need to allocate it on the heap and keep some
//! state alongside it. The state indicates whether the future is ready for polling, waiting to be
//! woken up, or completed. Such a future is called a *task*.
//!
//! When a task is run, its future gets polled. If polling does not complete the task, that means
//! it's waiting for another future and needs to go to sleep. When woken up, its schedule function
//! will be invoked, pushing it back into the queue so that it can be run again.
//!
//! Paired with a task there usually is a [`JoinHandle`] that can be used to wait for the task's
//! completion.
//!
//! # Cancellation
//!
//! Both [`Task`] and [`JoinHandle`] have methods that cancel the task. When canceled, the task's
//! future will not be polled again and will get dropped instead.
//!
//! If canceled by the [`Task`] instance, the task is destroyed immediately. If canceled by the
//! [`JoinHandle`] instance, it will be scheduled one more time and the next attempt to run it will
//! simply destroy it.
//!
//! The `JoinHandle` future will then evaluate to `None`, but only after the task's future is
//! dropped.
//!
//! # Performance
//!
//! Task construction incurs a single allocation that holds its state, the schedule function, and
//! the future or the result of the future if completed.
//!
//! The layout of a task is equivalent to 4 `usize`s followed by the schedule function, and then by
//! a union of the future and its output.
//!
//! # Waking
//!
//! The handy [`waker_fn`] constructor converts any function into a [`Waker`]. Every time it is
//! woken, the function gets called:
//!
//! ```
//! let waker = glommio::task::waker_fn(|| println!("Wake!"));
//!
//! // Prints "Wake!" twice.
//! waker.wake_by_ref();
//! waker.wake_by_ref();
//! ```
//!
//! [`spawn_local`]: fn.spawn_local.html
//! [`waker_fn`]: fn.waker_fn.html
//! [`Task`]: struct.Task.html
//! [`JoinHandle`]: struct.JoinHandle.html
//! [`Waker`]: https://doc.rust-lang.org/std/task/struct.Waker.html

#![warn(missing_docs, missing_debug_implementations)]
#![doc(test(attr(deny(rust_2018_idioms, warnings))))]
#![doc(test(attr(allow(unused_extern_crates, unused_variables))))]

pub(crate) mod header;
pub(crate) mod join_handle;
pub(crate) mod raw;
pub(crate) mod state;
pub(crate) mod task_impl;
pub(crate) mod utils;
pub(crate) mod waker_fn;

pub use crate::task::join_handle::JoinHandle;
pub use crate::task::task_impl::Task;
pub use crate::task::waker_fn::waker_fn;