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    #![allow(
        clippy::cognitive_complexity,
        clippy::large_enum_variant,
        clippy::needless_doctest_main
    )]
    #![warn(
        missing_debug_implementations,
        missing_docs,
        rust_2018_idioms,
        unreachable_pub
    )]
    #![cfg_attr(docsrs, deny(broken_intra_doc_links))]
    #![doc(test(
        no_crate_inject,
        attr(deny(warnings, rust_2018_idioms), allow(dead_code, unused_variables))
    ))]
    #![cfg_attr(docsrs, feature(doc_cfg))]

    //! A runtime for writing reliable network applications without compromising speed.
    //!
    //! Tokio is an event-driven, non-blocking I/O platform for writing asynchronous
    //! applications with the Rust programming language. At a high level, it
    //! provides a few major components:
    //!
    //! * Tools for [working with asynchronous tasks][tasks], including
    //!   [synchronization primitives and channels][sync] and [timeouts, sleeps, and
    //!   intervals][time].
    //! * APIs for [performing asynchronous I/O][io], including [TCP and UDP][net] sockets,
    //!   [filesystem][fs] operations, and [process] and [signal] management.
    //! * A [runtime] for executing asynchronous code, including a task scheduler,
    //!   an I/O driver backed by the operating system's event queue (epoll, kqueue,
    //!   IOCP, etc...), and a high performance timer.
    //!
    //! Guide level documentation is found on the [website].
    //!
    //! [tasks]: #working-with-tasks
    //! [sync]: crate::sync
    //! [time]: crate::time
    //! [io]: #asynchronous-io
    //! [net]: crate::net
    //! [fs]: crate::fs
    //! [process]: crate::process
    //! [signal]: crate::signal
    //! [fs]: crate::fs
    //! [runtime]: crate::runtime
    //! [website]: https://tokio.rs/tokio/tutorial
    //!
    //! # A Tour of Tokio
    //!
    //! Tokio consists of a number of modules that provide a range of functionality
    //! essential for implementing asynchronous applications in Rust. In this
    //! section, we will take a brief tour of Tokio, summarizing the major APIs and
    //! their uses.
    //!
    //! The easiest way to get started is to enable all features. Do this by
    //! enabling the `full` feature flag:
    //!
    //! ```toml
    //! tokio = { version = "1", features = ["full"] }
    //! ```
    //!
    //! ### Authoring applications
    //!
    //! Tokio is great for writing applications and most users in this case shouldn't
    //! worry too much about what features they should pick. If you're unsure, we suggest
    //! going with `full` to ensure that you don't run into any road blocks while you're
    //! building your application.
    //!
    //! #### Example
    //!
    //! This example shows the quickest way to get started with Tokio.
    //!
    //! ```toml
    //! tokio = { version = "1", features = ["full"] }
    //! ```
    //!
    //! ### Authoring libraries
    //!
    //! As a library author your goal should be to provide the lighest weight crate
    //! that is based on Tokio. To achieve this you should ensure that you only enable
    //! the features you need. This allows users to pick up your crate without having
    //! to enable unnecessary features.
    //!
    //! #### Example
    //!
    //! This example shows how you may want to import features for a library that just
    //! needs to `tokio::spawn` and use a `TcpStream`.
    //!
    //! ```toml
    //! tokio = { version = "1", features = ["rt", "net"] }
    //! ```
    //!
    //! ## Working With Tasks
    //!
    //! Asynchronous programs in Rust are based around lightweight, non-blocking
    //! units of execution called [_tasks_][tasks]. The [`tokio::task`] module provides
    //! important tools for working with tasks:
    //!
    //! * The [`spawn`] function and [`JoinHandle`] type, for scheduling a new task
    //!   on the Tokio runtime and awaiting the output of a spawned task, respectively,
    //! * Functions for [running blocking operations][blocking] in an asynchronous
    //!   task context.
    //!
    //! The [`tokio::task`] module is present only when the "rt" feature flag
    //! is enabled.
    //!
    //! [tasks]: task/index.html#what-are-tasks
    //! [`tokio::task`]: crate::task
    //! [`spawn`]: crate::task::spawn()
    //! [`JoinHandle`]: crate::task::JoinHandle
    //! [blocking]: task/index.html#blocking-and-yielding
    //!
    //! The [`tokio::sync`] module contains synchronization primitives to use when
    //! needing to communicate or share data. These include:
    //!
    //! * channels ([`oneshot`], [`mpsc`], and [`watch`]), for sending values
    //!   between tasks,
    //! * a non-blocking [`Mutex`], for controlling access to a shared, mutable
    //!   value,
    //! * an asynchronous [`Barrier`] type, for multiple tasks to synchronize before
    //!   beginning a computation.
    //!
    //! The `tokio::sync` module is present only when the "sync" feature flag is
    //! enabled.
    //!
    //! [`tokio::sync`]: crate::sync
    //! [`Mutex`]: crate::sync::Mutex
    //! [`Barrier`]: crate::sync::Barrier
    //! [`oneshot`]: crate::sync::oneshot
    //! [`mpsc`]: crate::sync::mpsc
    //! [`watch`]: crate::sync::watch
    //!
    //! The [`tokio::time`] module provides utilities for tracking time and
    //! scheduling work. This includes functions for setting [timeouts][timeout] for
    //! tasks, [sleeping][sleep] work to run in the future, or [repeating an operation at an
    //! interval][interval].
    //!
    //! In order to use `tokio::time`, the "time" feature flag must be enabled.
    //!
    //! [`tokio::time`]: crate::time
    //! [sleep]: crate::time::sleep()
    //! [interval]: crate::time::interval()
    //! [timeout]: crate::time::timeout()
    //!
    //! Finally, Tokio provides a _runtime_ for executing asynchronous tasks. Most
    //! applications can use the [`#[tokio::main]`][main] macro to run their code on the
    //! Tokio runtime. However, this macro provides only basic configuration options. As
    //! an alternative, the [`tokio::runtime`] module provides more powerful APIs for configuring
    //! and managing runtimes. You should use that module if the `#[tokio::main]` macro doesn't
    //! provide the functionality you need.
    //!
    //! Using the runtime requires the "rt" or "rt-multi-thread" feature flags, to
    //! enable the basic [single-threaded scheduler][rt] and the [thread-pool
    //! scheduler][rt-multi-thread], respectively. See the [`runtime` module
    //! documentation][rt-features] for details. In addition, the "macros" feature
    //! flag enables the `#[tokio::main]` and `#[tokio::test]` attributes.
    //!
    //! [main]: attr.main.html
    //! [`tokio::runtime`]: crate::runtime
    //! [`Builder`]: crate::runtime::Builder
    //! [`Runtime`]: crate::runtime::Runtime
    //! [rt]: runtime/index.html#basic-scheduler
    //! [rt-multi-thread]: runtime/index.html#threaded-scheduler
    //! [rt-features]: runtime/index.html#runtime-scheduler
    //!
    //! ## CPU-bound tasks and blocking code
    //!
    //! Tokio is able to concurrently run many tasks on a few threads by repeatedly
    //! swapping the currently running task on each thread. However, this kind of
    //! swapping can only happen at `.await` points, so code that spends a long time
    //! without reaching an `.await` will prevent other tasks from running. To
    //! combat this, Tokio provides two kinds of threads: Core threads and blocking
    //! threads. The core threads are where all asynchronous code runs, and Tokio
    //! will by default spawn one for each CPU core. The blocking threads are
    //! spawned on demand, can be used to run blocking code that would otherwise
    //! block other tasks from running and are kept alive when not used for a certain
    //! amount of time which can be configured with [`thread_keep_alive`].
    //! Since it is not possible for Tokio to swap out blocking tasks, like it
    //! can do with asynchronous code, the upper limit on the number of blocking
    //! threads is very large. These limits can be configured on the [`Builder`].
    //!
    //! To spawn a blocking task, you should use the [`spawn_blocking`] function.
    //!
    //! [`Builder`]: crate::runtime::Builder
    //! [`spawn_blocking`]: crate::task::spawn_blocking()
    //! [`thread_keep_alive`]: crate::runtime::Builder::thread_keep_alive()
    //!
    //! ```
    //! #[tokio::main]
    //! async fn main() {
    //!     // This is running on a core thread.
    //!
    //!     let blocking_task = tokio::task::spawn_blocking(|| {
    //!         // This is running on a blocking thread.
    //!         // Blocking here is ok.
    //!     });
    //!
    //!     // We can wait for the blocking task like this:
    //!     // If the blocking task panics, the unwrap below will propagate the
    //!     // panic.
    //!     blocking_task.await.unwrap();
    //! }
    //! ```
    //!
    //! If your code is CPU-bound and you wish to limit the number of threads used
    //! to run it, you should run it on another thread pool such as [rayon]. You
    //! can use an [`oneshot`] channel to send the result back to Tokio when the
    //! rayon task finishes.
    //!
    //! [rayon]: https://docs.rs/rayon
    //! [`oneshot`]: crate::sync::oneshot
    //!
    //! ## Asynchronous IO
    //!
    //! As well as scheduling and running tasks, Tokio provides everything you need
    //! to perform input and output asynchronously.
    //!
    //! The [`tokio::io`] module provides Tokio's asynchronous core I/O primitives,
    //! the [`AsyncRead`], [`AsyncWrite`], and [`AsyncBufRead`] traits. In addition,
    //! when the "io-util" feature flag is enabled, it also provides combinators and
    //! functions for working with these traits, forming as an asynchronous
    //! counterpart to [`std::io`].
    //!
    //! Tokio also includes APIs for performing various kinds of I/O and interacting
    //! with the operating system asynchronously. These include:
    //!
    //! * [`tokio::net`], which contains non-blocking versions of [TCP], [UDP], and
    //!   [Unix Domain Sockets][UDS] (enabled by the "net" feature flag),
    //! * [`tokio::fs`], similar to [`std::fs`] but for performing filesystem I/O
    //!   asynchronously (enabled by the "fs" feature flag),
    //! * [`tokio::signal`], for asynchronously handling Unix and Windows OS signals
    //!   (enabled by the "signal" feature flag),
    //! * [`tokio::process`], for spawning and managing child processes (enabled by
    //!   the "process" feature flag).
    //!
    //! [`tokio::io`]: crate::io
    //! [`AsyncRead`]: crate::io::AsyncRead
    //! [`AsyncWrite`]: crate::io::AsyncWrite
    //! [`AsyncBufRead`]: crate::io::AsyncBufRead
    //! [`std::io`]: std::io
    //! [`tokio::net`]: crate::net
    //! [TCP]: crate::net::tcp
    //! [UDP]: crate::net::UdpSocket
    //! [UDS]: crate::net::unix
    //! [`tokio::fs`]: crate::fs
    //! [`std::fs`]: std::fs
    //! [`tokio::signal`]: crate::signal
    //! [`tokio::process`]: crate::process
    //!
    //! # Examples
    //!
    //! A simple TCP echo server:
    //!
    //! ```no_run
    //! use tokio::net::TcpListener;
    //! use tokio::io::{AsyncReadExt, AsyncWriteExt};
    //!
    //! #[tokio::main]
    //! async fn main() -> Result<(), Box<dyn std::error::Error>> {
    //!     let listener = TcpListener::bind("127.0.0.1:8080").await?;
    //!
    //!     loop {
    //!         let (mut socket, _) = listener.accept().await?;
    //!
    //!         tokio::spawn(async move {
    //!             let mut buf = [0; 1024];
    //!
    //!             // In a loop, read data from the socket and write the data back.
    //!             loop {
    //!                 let n = match socket.read(&mut buf).await {
    //!                     // socket closed
    //!                     Ok(n) if n == 0 => return,
    //!                     Ok(n) => n,
    //!                     Err(e) => {
    //!                         eprintln!("failed to read from socket; err = {:?}", e);
    //!                         return;
    //!                     }
    //!                 };
    //!
    //!                 // Write the data back
    //!                 if let Err(e) = socket.write_all(&buf[0..n]).await {
    //!                     eprintln!("failed to write to socket; err = {:?}", e);
    //!                     return;
    //!                 }
    //!             }
    //!         });
    //!     }
    //! }
    //! ```
    //!
    //! ## Feature flags
    //!
    //! Tokio uses a set of [feature flags] to reduce the amount of compiled code. It
    //! is possible to just enable certain features over others. By default, Tokio
    //! does not enable any features but allows one to enable a subset for their use
    //! case. Below is a list of the available feature flags. You may also notice
    //! above each function, struct and trait there is listed one or more feature flags
    //! that are required for that item to be used. If you are new to Tokio it is
    //! recommended that you use the `full` feature flag which will enable all public APIs.
    //! Beware though that this will pull in many extra dependencies that you may not
    //! need.
    //!
    //! - `full`: Enables all Tokio public API features listed below except `test-util`.
    //! - `rt`: Enables `tokio::spawn`, the basic (current thread) scheduler,
    //!         and non-scheduler utilities.
    //! - `rt-multi-thread`: Enables the heavier, multi-threaded, work-stealing scheduler.
    //! - `io-util`: Enables the IO based `Ext` traits.
    //! - `io-std`: Enable `Stdout`, `Stdin` and `Stderr` types.
    //! - `net`: Enables `tokio::net` types such as `TcpStream`, `UnixStream` and `UdpSocket`,
    //!          as well as (on Unix-like systems) `AsyncFd`
    //! - `time`: Enables `tokio::time` types and allows the schedulers to enable
    //!           the built in timer.
    //! - `process`: Enables `tokio::process` types.
    //! - `macros`: Enables `#[tokio::main]` and `#[tokio::test]` macros.
    //! - `sync`: Enables all `tokio::sync` types.
    //! - `signal`: Enables all `tokio::signal` types.
    //! - `fs`: Enables `tokio::fs` types.
    //! - `test-util`: Enables testing based infrastructure for the Tokio runtime.
    //!
    //! _Note: `AsyncRead` and `AsyncWrite` traits do not require any features and are
    //! always available._
    //!
    //! ### Internal features
    //!
    //! These features do not expose any new API, but influence internal
    //! implementation aspects of Tokio, and can pull in additional
    //! dependencies.
    //!
    //! - `parking_lot`: As a potential optimization, use the _parking_lot_ crate's
    //! synchronization primitives internally. MSRV may increase according to the
    //! _parking_lot_ release in use.
    //!
    //! ### Unstable features
    //!
    //! These feature flags enable **unstable** features. The public API may break in 1.x
    //! releases. To enable these features, the `--cfg tokio_unstable` must be passed to
    //! `rustc` when compiling. This is easiest done using the `RUSTFLAGS` env variable:
    //! `RUSTFLAGS="--cfg tokio_unstable"`.
    //!
    //! - `tracing`: Enables tracing events.
    //!
    //! [feature flags]: https://doc.rust-lang.org/cargo/reference/manifest.html#the-features-section

    // Includes re-exports used by macros.
    //
    // This module is not intended to be part of the public API. In general, any
    // `doc(hidden)` code is not part of Tokio's public and stable API.
    #[macro_use]
    #[doc(hidden)]
    pub mod macros;

    cfg_fs! {
        pub mod fs;
    }

    mod future;

    pub mod io;
    pub mod net;

    mod loom;
    mod park;

    cfg_process! {
        pub mod process;
    }

    #[cfg(any(feature = "net", feature = "fs", feature = "io-std"))]
    mod blocking;

    cfg_rt! {
        pub mod runtime;
    }

    pub(crate) mod coop;

    cfg_signal! {
        pub mod signal;
    }

    cfg_signal_internal! {
        #[cfg(not(feature = "signal"))]
        #[allow(dead_code)]
        #[allow(unreachable_pub)]
        pub(crate) mod signal;
    }

    cfg_sync! {
        pub mod sync;
    }
    cfg_not_sync! {
        mod sync;
    }

    pub mod task;
    cfg_rt! {
        pub use task::spawn;
    }

    cfg_time! {
        pub mod time;
    }

    mod util;

    /// Due to the `Stream` trait's inclusion in `std` landing later than Tokio's 1.0
    /// release, most of the Tokio stream utilities have been moved into the [`tokio-stream`]
    /// crate.
    ///
    /// # Why was `Stream` not included in Tokio 1.0?
    ///
    /// Originally, we had planned to ship Tokio 1.0 with a stable `Stream` type
    /// but unfortunetly the [RFC] had not been merged in time for `Stream` to
    /// reach `std` on a stable compiler in time for the 1.0 release of Tokio. For
    /// this reason, the team has decided to move all `Stream` based utilities to
    /// the [`tokio-stream`] crate. While this is not ideal, once `Stream` has made
    /// it into the standard library and the MSRV period has passed, we will implement
    /// stream for our different types.
    ///
    /// While this may seem unfortunate, not all is lost as you can get much of the
    /// `Stream` support with `async/await` and `while let` loops. It is also possible
    /// to create a `impl Stream` from `async fn` using the [`async-stream`] crate.
    ///
    /// [`tokio-stream`]: https://docs.rs/tokio-stream
    /// [`async-stream`]: https://docs.rs/async-stream
    /// [RFC]: https://github.com/rust-lang/rfcs/pull/2996
    ///
    /// # Example
    ///
    /// Convert a [`sync::mpsc::Receiver`] to an `impl Stream`.
    ///
    /// ```rust,no_run
    /// use tokio::sync::mpsc;
    ///
    /// let (tx, mut rx) = mpsc::channel::<usize>(16);
    ///
    /// let stream = async_stream::stream! {
    ///     while let Some(item) = rx.recv().await {
    ///         yield item;
    ///     }
    /// };
    /// ```
    pub mod stream {}

    cfg_macros! {
        /// Implementation detail of the `select!` macro. This macro is **not**
        /// intended to be used as part of the public API and is permitted to
        /// change.
        #[doc(hidden)]
        pub use tokio_macros::select_priv_declare_output_enum;

        cfg_rt! {
            #[cfg(feature = "rt-multi-thread")]
            #[cfg(not(test))] // Work around for rust-lang/rust#62127
            #[cfg_attr(docsrs, doc(cfg(feature = "macros")))]
            pub use tokio_macros::main;

            #[cfg(feature = "rt-multi-thread")]
            #[cfg_attr(docsrs, doc(cfg(feature = "macros")))]
            pub use tokio_macros::test;

            cfg_not_rt_multi_thread! {
                #[cfg(not(test))] // Work around for rust-lang/rust#62127
                pub use tokio_macros::main_rt as main;
                pub use tokio_macros::test_rt as test;
            }
        }

        // Always fail if rt is not enabled.
        cfg_not_rt! {
            #[cfg(not(test))]
            pub use tokio_macros::main_fail as main;
            pub use tokio_macros::test_fail as test;
        }
    }

    // TODO: rm
    #[cfg(feature = "io-util")]
    #[cfg(test)]
    fn is_unpin<T: Unpin>() {}