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//! This crate provides a thread pool for executing short, I/O-heavy futures efficiently. //! //! The standard `Runtime` provided by `tokio` uses a thread-pool to allow concurrent execution of //! compute-heavy futures. However, its work-stealing makes it so that futures may be executed on //! different threads to where their reactor are running, which results in unnecessary //! synchronization, and thus lowers the achievable throughput. While this trade-off works well for //! many asynchronous applications, since it spreads load more evenly, it is not a great fit for //! high-performance I/O bound applications where the cost of synchronizing threads is high. This //! can happen, for example, if your application performs frequent but small I/O operations. //! //! This crate provides an alternative implementation of a futures-based thread pool. It spawns a //! pool of threads that each runs a `tokio::runtime::current_thread::Runtime` (and thus each have //! an I/O reactor of their own), and spawns futures onto the pool by assigning the future to //! threads round-robin. Once a future has been spawned onto a thread, it, and any child futures it //! may produce through `tokio::spawn`, remain under the control of that same thread. //! //! In general, you should use `tokio-io-pool` only if you perform a lot of very short I/O //! operations on many futures, and find that you are bottlenecked by work-stealing or reactor //! notifications with the regular `tokio` runtime. If you are unsure what to use, start with the //! `tokio` runtime. //! //! Be aware that this pool does *not* support the //! [`blocking`](https://docs.rs/tokio-threadpool/0.1.5/tokio_threadpool/fn.blocking.html) function //! since it is [not supported](https://github.com/tokio-rs/tokio/issues/432) by the underlying //! `current_thread::Runtime`. Hopefully this will be rectified down the line. //! //! There is some discussion around trying to merge this pool into `tokio` proper; that effort is //! tracked in [tokio-rs/tokio#486](https://github.com/tokio-rs/tokio/issues/486). //! //! # Examples //! //! ```no_run //! use tokio::prelude::*; //! use tokio::io::copy; //! use tokio::net::TcpListener; //! //! fn main() { //! // Bind the server's socket. //! let addr = "127.0.0.1:12345".parse().unwrap(); //! let listener = TcpListener::bind(&addr) //! .expect("unable to bind TCP listener"); //! //! // Pull out a stream of sockets for incoming connections //! let server = listener.incoming() //! .map_err(|e| eprintln!("accept failed = {:?}", e)) //! .for_each(|sock| { //! // Split up the reading and writing parts of the //! // socket. //! let (reader, writer) = sock.split(); //! //! // A future that echos the data and returns how //! // many bytes were copied... //! let bytes_copied = copy(reader, writer); //! //! // ... after which we'll print what happened. //! let handle_conn = bytes_copied.map(|amt| { //! println!("wrote {:?} bytes", amt) //! }).map_err(|err| { //! eprintln!("IO error {:?}", err) //! }); //! //! // Spawn the future as a concurrent task. //! tokio::spawn(handle_conn) //! }); //! //! // Start the Tokio runtime //! tokio_io_pool::run(server); //! } //! ``` #![deny(missing_docs)] #![deny(missing_debug_implementations)] #![deny(missing_copy_implementations)] #![deny(unused_extern_crates)] use futures::sync::oneshot; use futures::try_ready; use std::sync::{atomic, mpsc, Arc}; use std::{fmt, io, thread}; use tokio::executor::SpawnError; use tokio::prelude::*; use tokio::runtime::current_thread; /// Builds an I/O-oriented thread pool ([`Runtime`]) with custom configuration values. /// /// Methods can be chained in order to set the configuration values. The thread pool is constructed /// by calling [`Builder::build`]. New instances of `Builder` are obtained via /// [`Builder::default`]. /// /// See function level documentation for details on the various configuration settings. pub struct Builder { nworkers: usize, name_prefix: Option<String>, after_start: Option<Arc<dyn Fn() + Send + Sync>>, before_stop: Option<Arc<dyn Fn() + Send + Sync>>, } impl fmt::Debug for Builder { fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result { fmt.debug_struct("Builder") .field("nworkers", &self.nworkers) .field("name_prefix", &self.name_prefix) .finish() } } impl Default for Builder { fn default() -> Self { Builder { nworkers: num_cpus::get(), name_prefix: None, after_start: None, before_stop: None, } } } impl Builder { /// Set the number of worker threads for the thread pool instance. /// /// This must be a number between 1 and 32,768 though it is advised to keep /// this value on the smaller side. /// /// The default value is the number of cores available to the system. pub fn pool_size(&mut self, val: usize) -> &mut Self { self.nworkers = val; self } /// Set name prefix of threads spawned by the scheduler /// /// Thread name prefix is used for generating thread names. For example, if prefix is /// `my-pool-`, then threads in the pool will get names like `my-pool-1` etc. /// /// If this configuration is not set, then the thread will use the system default naming /// scheme. pub fn name_prefix<S: Into<String>>(&mut self, val: S) -> &mut Self { self.name_prefix = Some(val.into()); self } /// Execute function `f` after each thread is started but before it starts doing work. /// /// This is intended for bookkeeping and monitoring use cases. pub fn after_start<F>(&mut self, f: F) -> &mut Self where F: Fn() + Send + Sync + 'static, { self.after_start = Some(Arc::new(f)); self } /// Execute function `f` before each thread stops. /// /// This is intended for bookkeeping and monitoring use cases. pub fn before_stop<F>(&mut self, f: F) -> &mut Self where F: Fn() + Send + Sync + 'static, { self.before_stop = Some(Arc::new(f)); self } /// Create the configured [`Runtime`]. /// /// The returned [`Runtime`] instance is ready to spawn tasks. pub fn build(&self) -> io::Result<Runtime> { assert!(self.nworkers > 0); let mut handles = Vec::with_capacity(self.nworkers); let mut threads = Vec::with_capacity(self.nworkers); for i in 0..self.nworkers { let (trigger, exit) = oneshot::channel(); let (handle_tx, handle_rx) = mpsc::sync_channel(1); let mut th = thread::Builder::new(); if let Some(ref prefix) = self.name_prefix { th = th.name(format!("{}{}", prefix, i + 1)); } let before = self.after_start.clone(); let after = self.before_stop.clone(); let jh = th.spawn(move || { if let Some(ref f) = before { f(); } let mut rt = current_thread::Runtime::new().unwrap(); handle_tx.send(rt.handle()).unwrap(); let force_exit: bool = rt.block_on(exit).unwrap(); if !force_exit { rt.run().unwrap(); } if let Some(ref f) = after { f(); } })?; threads.push((trigger, jh)); handles.push(handle_rx.recv().unwrap()); } let handle = Handle { workers: handles, rri: Arc::new(atomic::AtomicUsize::new(0)), }; Ok(Runtime { threads, force_exit: true, handle, }) } } /// Execute the given future and spawn any child futures onto a newly created I/O thread pool. /// /// This function is used to bootstrap the execution of a Tokio application. It does the following: /// /// - Start the Tokio I/O pool using a default configuration. /// - Configure Tokio to make any future spawned with `tokio::spawn` spawn on the pool. /// - Run the given future to completion on the current thread. /// - Block the current thread until the pool becomes idle. /// /// Note that the function will not return immediately once future has completed. Instead it waits /// for the entire pool to become idle. Note also that the top-level future will be executed with /// [`Runtime::block_on`], which calls `Future::wait`, and thus does not provide access to timers, /// clocks, or other tokio runtime goodies. /// /// # Examples /// /// ```no_run /// # extern crate tokio_io_pool; /// # extern crate tokio; /// # extern crate futures; /// # use futures::{Future, Stream}; /// # fn process<T>(_: T) -> Box<Future<Item = (), Error = ()> + Send> { /// # unimplemented!(); /// # } /// # let addr = "127.0.0.1:8080".parse().unwrap(); /// use tokio::net::TcpListener; /// /// let listener = TcpListener::bind(&addr).unwrap(); /// /// let server = listener.incoming() /// .map_err(|e| println!("error = {:?}", e)) /// .for_each(|socket| { /// tokio::spawn(process(socket)) /// }); /// /// tokio_io_pool::run(server); /// ``` pub fn run<F>(future: F) where F: Future<Item = (), Error = ()> + Send + 'static, { let mut rt = Runtime::new(); let _ = rt.block_on(future); rt.shutdown_on_idle(); } /// A handle to a [`Runtime`] that allows spawning additional futures from other threads. #[derive(Clone)] pub struct Handle { workers: Vec<current_thread::Handle>, rri: Arc<atomic::AtomicUsize>, } impl fmt::Debug for Handle { fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result { fmt.debug_struct("Handle") .field("nworkers", &self.workers.len()) .field("next", &self.rri.load(atomic::Ordering::Relaxed)) .finish() } } impl tokio::executor::Executor for Handle { fn spawn( &mut self, future: Box<dyn Future<Item = (), Error = ()> + 'static + Send>, ) -> Result<(), SpawnError> { Handle::spawn(self, future).map(|_| ()) } } impl Handle { /// Spawn a future onto a runtime in the pool. /// /// This spawns the given future onto a single thread runtime's executor. That thread is then /// responsible for polling the future until it completes. pub fn spawn<F>(&self, future: F) -> Result<&Self, SpawnError> where F: Future<Item = (), Error = ()> + Send + 'static, { let worker = self.rri.fetch_add(1, atomic::Ordering::Relaxed) % self.workers.len(); self.workers[worker].spawn(future)?; Ok(self) } /// Spawn all futures yielded by a stream onto the pool. /// /// This produces a future that accepts futures from a `Stream` and spawns them all onto the /// pool round-robin. pub fn spawn_all<S>( &self, stream: S, ) -> impl Future<Item = (), Error = StreamSpawnError<<S as Stream>::Error>> where S: Stream, <S as Stream>::Item: Future<Item = (), Error = ()> + Send + 'static, { Spawner { handle: self.clone(), stream, } } } /// An I/O-oriented thread pool for executing futures. /// /// Each thread in the pool has its own I/O reactor, and futures are spawned onto threads /// round-robin. Futures do not (currently) move between threads in the pool once spawned, and any /// new futures spawned (using `tokio::spawn`) inside futures are scheduled on the same worker as /// the original future. pub struct Runtime { handle: Handle, threads: Vec<(oneshot::Sender<bool>, thread::JoinHandle<()>)>, force_exit: bool, } impl fmt::Debug for Runtime { fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result { fmt.debug_struct("Runtime") .field("nworkers", &self.threads.len()) .finish() } } impl Default for Runtime { fn default() -> Self { Self::new() } } impl Runtime { /// Create a new thread pool with parameters from a default [`Builder`] and return a handle to /// it. /// /// # Panics /// /// Panics if enough threads could not be spawned (see [`Builder::build`]). pub fn new() -> Self { Builder::default().build().unwrap() } /// Return a reference to the pool. /// /// The returned handle reference can be cloned in order to get an owned value of the handle. /// This handle can be used to spawn additional futures onto the pool from other threads. pub fn handle(&self) -> &Handle { &self.handle } /// Spawn a future onto a runtime in the pool. /// /// This spawns the given future onto a single thread runtime's executor. That thread is then /// responsible for polling the future until it completes. pub fn spawn<F>(&self, future: F) -> Result<&Self, SpawnError> where F: Future<Item = (), Error = ()> + Send + 'static, { self.handle.spawn(future)?; Ok(self) } /// Spawn all futures yielded by a stream onto the pool. /// /// This produces a future that accepts futures from a `Stream` and spawns them all onto the /// pool round-robin. #[must_use] pub fn spawn_all<S>( &self, stream: S, ) -> impl Future<Item = (), Error = StreamSpawnError<<S as Stream>::Error>> where S: Stream, <S as Stream>::Item: Future<Item = (), Error = ()> + Send + 'static, { self.handle.spawn_all(stream) } /// Run the given future on the current thread, and dispatch any child futures spawned with /// `tokio::spawn` onto the I/O pool. /// /// Note that child futures of futures that are already running on the pool will be executed on /// the same pool thread as their parent. Only the "top-level" calls to `tokio::spawn` are /// scheduled to the thread pool as a whole. /// /// Note that the top-level future is executed using `Future::wait`, and thus does not provide /// access to timers, clocks, or other tokio runtime goodies. pub fn block_on<F, R, E>(&mut self, future: F) -> Result<R, E> where F: Send + 'static + Future<Item = R, Error = E>, R: Send + 'static, E: Send + 'static, { let mut enter = tokio_executor::enter().expect("already running in executor context"); tokio_executor::with_default(&mut self.handle, &mut enter, |_| future.wait()) } /// Shut down the pool as soon as possible. /// /// Note that once this method has been called, attempts to spawn additional futures onto the /// pool through an outstanding `Handle` may fail. Futures that have not yet resolved will be /// dropped. /// /// The pool will only terminate once any currently-running futures return `NotReady`. pub fn shutdown(self) {} /// Shut down the pool once all spawned futures have completed. /// /// Note that once this method has been called, attempts to spawn additional futures onto the /// pool through an outstanding `Handle` may fail. pub fn shutdown_on_idle(mut self) { self.force_exit = false; } } impl Drop for Runtime { fn drop(&mut self) { let mut handles = Vec::with_capacity(self.threads.len()); for (exit, jh) in self.threads.drain(..) { if let Err(e) = exit.send(self.force_exit) { if !thread::panicking() { panic!("oneshot::Sender::Send: {:?}", e); } } handles.push(jh); } for jh in handles { if let Err(e) = jh.join() { if !thread::panicking() { panic!("JoinHandle::join: {:?}", e); } } } } } /// An error that occurred as a result of spawning futures from a stream given to /// [`Runtime::spawn_all`]. #[derive(Debug)] pub enum StreamSpawnError<SE> { /// An error occurred while spawning a future yielded by the stream onto the pool. Spawn(SpawnError), /// An error occurred while polling the stream for another future. Stream(SE), } impl<SE> From<SE> for StreamSpawnError<SE> { fn from(e: SE) -> Self { StreamSpawnError::Stream(e) } } struct Spawner<S> { handle: Handle, stream: S, } impl<S> fmt::Debug for Spawner<S> where S: fmt::Debug, { fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result { fmt.debug_struct("Spawner") .field("stream", &self.stream) .finish() } } impl<S> Future for Spawner<S> where S: Stream, <S as Stream>::Item: Future<Item = (), Error = ()> + Send + 'static, { type Item = (); type Error = StreamSpawnError<<S as Stream>::Error>; fn poll(&mut self) -> Result<Async<Self::Item>, Self::Error> { while let Some(fut) = try_ready!(self.stream.poll()) { self.handle.spawn(fut).map_err(StreamSpawnError::Spawn)?; } Ok(Async::Ready(())) } } #[cfg(test)] mod tests { use super::*; #[test] fn it_works() { use futures::future::lazy; use futures::sync::oneshot; let (tx, rx) = oneshot::channel(); let rt = Runtime::new(); rt.spawn(lazy(move || { tx.send(()).unwrap(); Ok(()) })) .unwrap(); assert_eq!(rx.wait().unwrap(), ()); rt.shutdown_on_idle(); } #[test] fn spawn_all() { let addr = "127.0.0.1:0".parse().unwrap(); let listener = tokio::net::TcpListener::bind(&addr).expect("unable to bind TCP listener"); let addr = listener.local_addr().unwrap(); let rt = Builder::default().pool_size(1).build().unwrap(); let server = listener .incoming() .map_err(|e| unreachable!("{:?}", e)) .map(|sock| { let (reader, writer) = sock.split(); let bytes_copied = tokio::io::copy(reader, writer); bytes_copied .map(|_| ()) .map_err(|err| unreachable!("{:?}", err)) }); // spawn all connections onto the pool let spawner = rt.spawn_all(server); // spawn the spawner onto the pool too // (a "real" server might wait for it instead) rt.spawn(spawner.map_err(|e| unreachable!("{:?}", e))) .unwrap(); let mut client = ::std::net::TcpStream::connect(&addr).unwrap(); client.write_all(b"hello world").unwrap(); client.shutdown(::std::net::Shutdown::Write).unwrap(); let mut bytes = Vec::new(); client.read_to_end(&mut bytes).unwrap(); assert_eq!(&bytes, b"hello world"); let mut client = ::std::net::TcpStream::connect(&addr).unwrap(); client.write_all(b"bye world").unwrap(); client.shutdown(::std::net::Shutdown::Write).unwrap(); let mut bytes = Vec::new(); client.read_to_end(&mut bytes).unwrap(); assert_eq!(&bytes, b"bye world"); } #[test] fn run() { let addr = "127.0.0.1:0".parse().unwrap(); let listener = tokio::net::TcpListener::bind(&addr).expect("unable to bind TCP listener"); let addr = listener.local_addr().unwrap(); thread::spawn(move || { let server = listener .incoming() .map_err(|e| unreachable!("{:?}", e)) .for_each(|sock| { let (reader, writer) = sock.split(); let bytes_copied = tokio::io::copy(reader, writer); tokio::spawn( bytes_copied .map(|_| ()) .map_err(|err| unreachable!("{:?}", err)), ) }); super::run(server); }); let mut client = ::std::net::TcpStream::connect(&addr).unwrap(); client.write_all(b"hello world").unwrap(); client.shutdown(::std::net::Shutdown::Write).unwrap(); let mut bytes = Vec::new(); client.read_to_end(&mut bytes).unwrap(); assert_eq!(&bytes, b"hello world"); let mut client = ::std::net::TcpStream::connect(&addr).unwrap(); client.write_all(b"bye world").unwrap(); client.shutdown(::std::net::Shutdown::Write).unwrap(); let mut bytes = Vec::new(); client.read_to_end(&mut bytes).unwrap(); assert_eq!(&bytes, b"bye world"); } // futures channels can exchange information between different threads #[test] fn interthread_communication() { use futures::sync::oneshot; let (tx0, rx0) = oneshot::channel::<u32>(); let (tx1, rx1) = oneshot::channel::<u32>(); let rt = Builder::default().pool_size(2).build().unwrap(); rt.spawn(future::ok::<(), ()>(tx0.send(42).unwrap())) .unwrap(); rt.spawn(rx0.map(|v| tx1.send(v + 1).unwrap()).map_err(|_| ())) .unwrap(); assert_eq!(rx1.wait().unwrap(), 43); rt.shutdown_on_idle(); } // A Future that isn't Send can't be spawned into the Runtime, but it _can_ be spawned from a // thread onto that same thread #[test] fn spawn_nonsend_futures() { use futures::future::lazy; use futures::sync::oneshot; use std::rc::Rc; let rt = Runtime::new(); rt.spawn(lazy(|| { let (tx, rx) = oneshot::channel::<u32>(); let x = Rc::new(42u32); // Note: Rc is not Send tokio_current_thread::spawn(lazy(move || { tx.send(*x).unwrap(); Ok(()) })); rx.map(|value| assert_eq!(42, value)).map_err(|_| ()) })) .unwrap(); rt.shutdown_on_idle(); } #[test] fn really_lazy() { super::run(future::lazy(|| { tokio::spawn(future::lazy(|| Ok(()))); Ok(()) })); } }