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#![doc(html_root_url = "https://docs.rs/tokio-current-thread/0.1.6")] #![deny(warnings, missing_docs, missing_debug_implementations)] //! A single-threaded executor which executes tasks on the same thread from which //! they are spawned. //! //! //! The crate provides: //! //! * [`CurrentThread`] is the main type of this crate. It executes tasks on the current thread. //! The easiest way to start a new [`CurrentThread`] executor is to call //! [`block_on_all`] with an initial task to seed the executor. //! All tasks that are being managed by a [`CurrentThread`] executor are able to //! spawn additional tasks by calling [`spawn`]. //! //! //! Application authors will not use this crate directly. Instead, they will use the //! `tokio` crate. Library authors should only depend on `tokio-current-thread` if they //! are building a custom task executor. //! //! For more details, see [executor module] documentation in the Tokio crate. //! //! [`CurrentThread`]: struct.CurrentThread.html //! [`spawn`]: fn.spawn.html //! [`block_on_all`]: fn.block_on_all.html //! [executor module]: https://docs.rs/tokio/0.1/tokio/executor/index.html extern crate futures; extern crate tokio_executor; mod scheduler; use self::scheduler::Scheduler; use tokio_executor::park::{Park, ParkThread, Unpark}; use tokio_executor::{Enter, SpawnError}; use futures::future::{ExecuteError, ExecuteErrorKind, Executor}; use futures::{executor, Async, Future}; use std::cell::Cell; use std::error::Error; use std::fmt; use std::rc::Rc; use std::sync::{atomic, mpsc, Arc}; use std::thread; use std::time::{Duration, Instant}; /// Executes tasks on the current thread pub struct CurrentThread<P: Park = ParkThread> { /// Execute futures and receive unpark notifications. scheduler: Scheduler<P::Unpark>, /// Current number of futures being executed. /// /// The LSB is used to indicate that the runtime is preparing to shut down. /// Thus, to get the actual number of pending futures, `>>1`. num_futures: Arc<atomic::AtomicUsize>, /// Thread park handle park: P, /// Handle for spawning new futures from other threads spawn_handle: Handle, /// Receiver for futures spawned from other threads spawn_receiver: mpsc::Receiver<Box<Future<Item = (), Error = ()> + Send + 'static>>, /// The thread-local ID assigned to this executor. id: u64, } /// Executes futures on the current thread. /// /// All futures executed using this executor will be executed on the current /// thread. As such, `run` will wait for these futures to complete before /// returning. /// /// For more details, see the [module level](index.html) documentation. #[derive(Debug, Clone)] pub struct TaskExecutor { // Prevent the handle from moving across threads. _p: ::std::marker::PhantomData<Rc<()>>, } /// Returned by the `turn` function. #[derive(Debug)] pub struct Turn { polled: bool, } impl Turn { /// `true` if any futures were polled at all and `false` otherwise. pub fn has_polled(&self) -> bool { self.polled } } /// A `CurrentThread` instance bound to a supplied execution context. pub struct Entered<'a, P: Park + 'a> { executor: &'a mut CurrentThread<P>, enter: &'a mut Enter, } /// Error returned by the `run` function. #[derive(Debug)] pub struct RunError { _p: (), } impl fmt::Display for RunError { fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result { write!(fmt, "{}", self.description()) } } impl Error for RunError { fn description(&self) -> &str { "Run error" } } /// Error returned by the `run_timeout` function. #[derive(Debug)] pub struct RunTimeoutError { timeout: bool, } impl fmt::Display for RunTimeoutError { fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result { write!(fmt, "{}", self.description()) } } impl Error for RunTimeoutError { fn description(&self) -> &str { if self.timeout { "Run timeout error (timeout)" } else { "Run timeout error (not timeout)" } } } /// Error returned by the `turn` function. #[derive(Debug)] pub struct TurnError { _p: (), } impl fmt::Display for TurnError { fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result { write!(fmt, "{}", self.description()) } } impl Error for TurnError { fn description(&self) -> &str { "Turn error" } } /// Error returned by the `block_on` function. #[derive(Debug)] pub struct BlockError<T> { inner: Option<T>, } impl<T> fmt::Display for BlockError<T> { fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result { write!(fmt, "Block error") } } impl<T: fmt::Debug> Error for BlockError<T> { fn description(&self) -> &str { "Block error" } } /// This is mostly split out to make the borrow checker happy. struct Borrow<'a, U: 'a> { id: u64, scheduler: &'a mut Scheduler<U>, num_futures: &'a atomic::AtomicUsize, } trait SpawnLocal { fn spawn_local(&mut self, future: Box<Future<Item = (), Error = ()>>, already_counted: bool); } struct CurrentRunner { spawn: Cell<Option<*mut SpawnLocal>>, id: Cell<Option<u64>>, } thread_local! { /// Current thread's task runner. This is set in `TaskRunner::with` static CURRENT: CurrentRunner = CurrentRunner { spawn: Cell::new(None), id: Cell::new(None), } } thread_local! { /// Unique ID to assign to each new executor launched on this thread. /// /// The unique ID is used to determine if the currently running executor matches the one /// referred to by a `Handle` so that direct task dispatch can be used. static EXECUTOR_ID: Cell<u64> = Cell::new(0) } /// Run the executor bootstrapping the execution with the provided future. /// /// This creates a new [`CurrentThread`] executor, spawns the provided future, /// and blocks the current thread until the provided future and **all** /// subsequently spawned futures complete. In other words: /// /// * If the provided bootstrap future does **not** spawn any additional tasks, /// `block_on_all` returns once `future` completes. /// * If the provided bootstrap future **does** spawn additional tasks, then /// `block_on_all` returns once **all** spawned futures complete. /// /// See [module level][mod] documentation for more details. /// /// [`CurrentThread`]: struct.CurrentThread.html /// [mod]: index.html pub fn block_on_all<F>(future: F) -> Result<F::Item, F::Error> where F: Future, { let mut current_thread = CurrentThread::new(); let ret = current_thread.block_on(future); current_thread.run().unwrap(); ret.map_err(|e| e.into_inner().expect("unexpected execution error")) } /// Executes a future on the current thread. /// /// The provided future must complete or be canceled before `run` will return. /// /// Unlike [`tokio::spawn`], this function will always spawn on a /// `CurrentThread` executor and is able to spawn futures that are not `Send`. /// /// # Panics /// /// This function can only be invoked from the context of a `run` call; any /// other use will result in a panic. /// /// [`tokio::spawn`]: ../fn.spawn.html pub fn spawn<F>(future: F) where F: Future<Item = (), Error = ()> + 'static, { TaskExecutor::current() .spawn_local(Box::new(future)) .unwrap(); } // ===== impl CurrentThread ===== impl CurrentThread<ParkThread> { /// Create a new instance of `CurrentThread`. pub fn new() -> Self { CurrentThread::new_with_park(ParkThread::new()) } } impl<P: Park> CurrentThread<P> { /// Create a new instance of `CurrentThread` backed by the given park /// handle. pub fn new_with_park(park: P) -> Self { let unpark = park.unpark(); let (spawn_sender, spawn_receiver) = mpsc::channel(); let thread = thread::current().id(); let id = EXECUTOR_ID.with(|idc| { let id = idc.get(); idc.set(id + 1); id }); let scheduler = Scheduler::new(unpark); let notify = scheduler.notify(); let num_futures = Arc::new(atomic::AtomicUsize::new(0)); CurrentThread { scheduler: scheduler, num_futures: num_futures.clone(), park, id, spawn_handle: Handle { sender: spawn_sender, num_futures: num_futures, notify: notify, shut_down: Cell::new(false), thread: thread, id, }, spawn_receiver: spawn_receiver, } } /// Returns `true` if the executor is currently idle. /// /// An idle executor is defined by not currently having any spawned tasks. /// /// Note that this method is inherently racy -- if a future is spawned from a remote `Handle`, /// this method may return `true` even though there are more futures to be executed. pub fn is_idle(&self) -> bool { self.num_futures.load(atomic::Ordering::SeqCst) <= 1 } /// Spawn the future on the executor. /// /// This internally queues the future to be executed once `run` is called. pub fn spawn<F>(&mut self, future: F) -> &mut Self where F: Future<Item = (), Error = ()> + 'static, { self.borrow().spawn_local(Box::new(future), false); self } /// Synchronously waits for the provided `future` to complete. /// /// This function can be used to synchronously block the current thread /// until the provided `future` has resolved either successfully or with an /// error. The result of the future is then returned from this function /// call. /// /// Note that this function will **also** execute any spawned futures on the /// current thread, but will **not** block until these other spawned futures /// have completed. /// /// The caller is responsible for ensuring that other spawned futures /// complete execution. pub fn block_on<F>(&mut self, future: F) -> Result<F::Item, BlockError<F::Error>> where F: Future, { let mut enter = tokio_executor::enter().expect("failed to start `current_thread::Runtime`"); self.enter(&mut enter).block_on(future) } /// Run the executor to completion, blocking the thread until **all** /// spawned futures have completed. pub fn run(&mut self) -> Result<(), RunError> { let mut enter = tokio_executor::enter().expect("failed to start `current_thread::Runtime`"); self.enter(&mut enter).run() } /// Run the executor to completion, blocking the thread until all /// spawned futures have completed **or** `duration` time has elapsed. pub fn run_timeout(&mut self, duration: Duration) -> Result<(), RunTimeoutError> { let mut enter = tokio_executor::enter().expect("failed to start `current_thread::Runtime`"); self.enter(&mut enter).run_timeout(duration) } /// Perform a single iteration of the event loop. /// /// This function blocks the current thread even if the executor is idle. pub fn turn(&mut self, duration: Option<Duration>) -> Result<Turn, TurnError> { let mut enter = tokio_executor::enter().expect("failed to start `current_thread::Runtime`"); self.enter(&mut enter).turn(duration) } /// Bind `CurrentThread` instance with an execution context. pub fn enter<'a>(&'a mut self, enter: &'a mut Enter) -> Entered<'a, P> { Entered { executor: self, enter, } } /// Returns a reference to the underlying `Park` instance. pub fn get_park(&self) -> &P { &self.park } /// Returns a mutable reference to the underlying `Park` instance. pub fn get_park_mut(&mut self) -> &mut P { &mut self.park } fn borrow(&mut self) -> Borrow<P::Unpark> { Borrow { id: self.id, scheduler: &mut self.scheduler, num_futures: &*self.num_futures, } } /// Get a new handle to spawn futures on the executor /// /// Different to the executor itself, the handle can be sent to different /// threads and can be used to spawn futures on the executor. pub fn handle(&self) -> Handle { self.spawn_handle.clone() } } impl<P: Park> Drop for CurrentThread<P> { fn drop(&mut self) { // Signal to Handles that no more futures can be spawned by setting LSB. // // NOTE: this isn't technically necessary since the send on the mpsc will fail once the // receiver is dropped, but it's useful to illustrate how clean shutdown will be // implemented (e.g., by setting the LSB). let pending = self.num_futures.fetch_add(1, atomic::Ordering::SeqCst); // TODO: We currently ignore any pending futures at the time we shut down. // // The "proper" fix for this is to have an explicit shutdown phase (`shutdown_on_idle`) // which sets LSB (as above) do make Handle::spawn stop working, and then runs until // num_futures.load() == 1. let _ = pending; } } impl tokio_executor::Executor for CurrentThread { fn spawn( &mut self, future: Box<Future<Item = (), Error = ()> + Send>, ) -> Result<(), SpawnError> { self.borrow().spawn_local(future, false); Ok(()) } } impl<T> tokio_executor::TypedExecutor<T> for CurrentThread where T: Future<Item = (), Error = ()> + 'static, { fn spawn(&mut self, future: T) -> Result<(), SpawnError> { self.borrow().spawn_local(Box::new(future), false); Ok(()) } } impl<P: Park> fmt::Debug for CurrentThread<P> { fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result { fmt.debug_struct("CurrentThread") .field("scheduler", &self.scheduler) .field( "num_futures", &self.num_futures.load(atomic::Ordering::SeqCst), ) .finish() } } // ===== impl Entered ===== impl<'a, P: Park> Entered<'a, P> { /// Spawn the future on the executor. /// /// This internally queues the future to be executed once `run` is called. pub fn spawn<F>(&mut self, future: F) -> &mut Self where F: Future<Item = (), Error = ()> + 'static, { self.executor.borrow().spawn_local(Box::new(future), false); self } /// Synchronously waits for the provided `future` to complete. /// /// This function can be used to synchronously block the current thread /// until the provided `future` has resolved either successfully or with an /// error. The result of the future is then returned from this function /// call. /// /// Note that this function will **also** execute any spawned futures on the /// current thread, but will **not** block until these other spawned futures /// have completed. /// /// The caller is responsible for ensuring that other spawned futures /// complete execution. pub fn block_on<F>(&mut self, future: F) -> Result<F::Item, BlockError<F::Error>> where F: Future, { let mut future = executor::spawn(future); let notify = self.executor.scheduler.notify(); loop { let res = self .executor .borrow() .enter(self.enter, || future.poll_future_notify(¬ify, 0)); match res { Ok(Async::Ready(e)) => return Ok(e), Err(e) => return Err(BlockError { inner: Some(e) }), Ok(Async::NotReady) => {} } self.tick(); if let Err(_) = self.executor.park.park() { return Err(BlockError { inner: None }); } } } /// Run the executor to completion, blocking the thread until **all** /// spawned futures have completed. pub fn run(&mut self) -> Result<(), RunError> { self.run_timeout2(None).map_err(|_| RunError { _p: () }) } /// Run the executor to completion, blocking the thread until all /// spawned futures have completed **or** `duration` time has elapsed. pub fn run_timeout(&mut self, duration: Duration) -> Result<(), RunTimeoutError> { self.run_timeout2(Some(duration)) } /// Perform a single iteration of the event loop. /// /// This function blocks the current thread even if the executor is idle. pub fn turn(&mut self, duration: Option<Duration>) -> Result<Turn, TurnError> { let res = if self.executor.scheduler.has_pending_futures() { self.executor.park.park_timeout(Duration::from_millis(0)) } else { match duration { Some(duration) => self.executor.park.park_timeout(duration), None => self.executor.park.park(), } }; if res.is_err() { return Err(TurnError { _p: () }); } let polled = self.tick(); Ok(Turn { polled }) } /// Returns a reference to the underlying `Park` instance. pub fn get_park(&self) -> &P { &self.executor.park } /// Returns a mutable reference to the underlying `Park` instance. pub fn get_park_mut(&mut self) -> &mut P { &mut self.executor.park } fn run_timeout2(&mut self, dur: Option<Duration>) -> Result<(), RunTimeoutError> { if self.executor.is_idle() { // Nothing to do return Ok(()); } let mut time = dur.map(|dur| (Instant::now() + dur, dur)); loop { self.tick(); if self.executor.is_idle() { return Ok(()); } match time { Some((until, rem)) => { if let Err(_) = self.executor.park.park_timeout(rem) { return Err(RunTimeoutError::new(false)); } let now = Instant::now(); if now >= until { return Err(RunTimeoutError::new(true)); } time = Some((until, until - now)); } None => { if let Err(_) = self.executor.park.park() { return Err(RunTimeoutError::new(false)); } } } } } /// Returns `true` if any futures were processed fn tick(&mut self) -> bool { // Spawn any futures that were spawned from other threads by manually // looping over the receiver stream // FIXME: Slightly ugly but needed to make the borrow checker happy let (mut borrow, spawn_receiver) = ( Borrow { id: self.executor.id, scheduler: &mut self.executor.scheduler, num_futures: &*self.executor.num_futures, }, &mut self.executor.spawn_receiver, ); while let Ok(future) = spawn_receiver.try_recv() { borrow.spawn_local(future, true); } // After any pending futures were scheduled, do the actual tick borrow .scheduler .tick(borrow.id, &mut *self.enter, borrow.num_futures) } } impl<'a, P: Park> fmt::Debug for Entered<'a, P> { fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result { fmt.debug_struct("Entered") .field("executor", &self.executor) .field("enter", &self.enter) .finish() } } // ===== impl Handle ===== /// Handle to spawn a future on the corresponding `CurrentThread` instance #[derive(Clone)] pub struct Handle { sender: mpsc::Sender<Box<Future<Item = (), Error = ()> + Send + 'static>>, num_futures: Arc<atomic::AtomicUsize>, shut_down: Cell<bool>, notify: executor::NotifyHandle, thread: thread::ThreadId, /// The thread-local ID assigned to this Handle's executor. id: u64, } // Manual implementation because the Sender does not implement Debug impl fmt::Debug for Handle { fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result { fmt.debug_struct("Handle") .field("shut_down", &self.shut_down.get()) .finish() } } impl Handle { /// Spawn a future onto the `CurrentThread` instance corresponding to this handle /// /// # Panics /// /// This function panics if the spawn fails. Failure occurs if the `CurrentThread` /// instance of the `Handle` does not exist anymore. pub fn spawn<F>(&self, future: F) -> Result<(), SpawnError> where F: Future<Item = (), Error = ()> + Send + 'static, { if thread::current().id() == self.thread { let mut e = TaskExecutor::current(); if e.id() == Some(self.id) { return e.spawn_local(Box::new(future)); } } if self.shut_down.get() { return Err(SpawnError::shutdown()); } // NOTE: += 2 since LSB is the shutdown bit let pending = self.num_futures.fetch_add(2, atomic::Ordering::SeqCst); if pending % 2 == 1 { // Bring the count back so we still know when the Runtime is idle. self.num_futures.fetch_sub(2, atomic::Ordering::SeqCst); // Once the Runtime is shutting down, we know it won't come back. self.shut_down.set(true); return Err(SpawnError::shutdown()); } self.sender .send(Box::new(future)) .expect("CurrentThread does not exist anymore"); // use 0 for the id, CurrentThread does not make use of it self.notify.notify(0); Ok(()) } /// Provides a best effort **hint** to whether or not `spawn` will succeed. /// /// This function may return both false positives **and** false negatives. /// If `status` returns `Ok`, then a call to `spawn` will *probably* /// succeed, but may fail. If `status` returns `Err`, a call to `spawn` will /// *probably* fail, but may succeed. /// /// This allows a caller to avoid creating the task if the call to `spawn` /// has a high likelihood of failing. pub fn status(&self) -> Result<(), SpawnError> { if self.shut_down.get() { return Err(SpawnError::shutdown()); } Ok(()) } } // ===== impl TaskExecutor ===== impl TaskExecutor { /// Returns an executor that executes futures on the current thread. /// /// The user of `TaskExecutor` must ensure that when a future is submitted, /// that it is done within the context of a call to `run`. /// /// For more details, see the [module level](index.html) documentation. pub fn current() -> TaskExecutor { TaskExecutor { _p: ::std::marker::PhantomData, } } /// Get the current executor's thread-local ID. fn id(&self) -> Option<u64> { CURRENT.with(|current| current.id.get()) } /// Spawn a future onto the current `CurrentThread` instance. pub fn spawn_local( &mut self, future: Box<Future<Item = (), Error = ()>>, ) -> Result<(), SpawnError> { CURRENT.with(|current| match current.spawn.get() { Some(spawn) => { unsafe { (*spawn).spawn_local(future, false) }; Ok(()) } None => Err(SpawnError::shutdown()), }) } } impl tokio_executor::Executor for TaskExecutor { fn spawn( &mut self, future: Box<Future<Item = (), Error = ()> + Send>, ) -> Result<(), SpawnError> { self.spawn_local(future) } } impl<F> tokio_executor::TypedExecutor<F> for TaskExecutor where F: Future<Item = (), Error = ()> + 'static, { fn spawn(&mut self, future: F) -> Result<(), SpawnError> { self.spawn_local(Box::new(future)) } } impl<F> Executor<F> for TaskExecutor where F: Future<Item = (), Error = ()> + 'static, { fn execute(&self, future: F) -> Result<(), ExecuteError<F>> { CURRENT.with(|current| match current.spawn.get() { Some(spawn) => { unsafe { (*spawn).spawn_local(Box::new(future), false) }; Ok(()) } None => Err(ExecuteError::new(ExecuteErrorKind::Shutdown, future)), }) } } // ===== impl Borrow ===== impl<'a, U: Unpark> Borrow<'a, U> { fn enter<F, R>(&mut self, _: &mut Enter, f: F) -> R where F: FnOnce() -> R, { CURRENT.with(|current| { current.id.set(Some(self.id)); current.set_spawn(self, || f()) }) } } impl<'a, U: Unpark> SpawnLocal for Borrow<'a, U> { fn spawn_local(&mut self, future: Box<Future<Item = (), Error = ()>>, already_counted: bool) { if !already_counted { // NOTE: we have a borrow of the Runtime, so we know that it isn't shut down. // NOTE: += 2 since LSB is the shutdown bit self.num_futures.fetch_add(2, atomic::Ordering::SeqCst); } self.scheduler.schedule(future); } } // ===== impl CurrentRunner ===== impl CurrentRunner { fn set_spawn<F, R>(&self, spawn: &mut SpawnLocal, f: F) -> R where F: FnOnce() -> R, { struct Reset<'a>(&'a CurrentRunner); impl<'a> Drop for Reset<'a> { fn drop(&mut self) { self.0.spawn.set(None); self.0.id.set(None); } } let _reset = Reset(self); let spawn = unsafe { hide_lt(spawn as *mut SpawnLocal) }; self.spawn.set(Some(spawn)); f() } } unsafe fn hide_lt<'a>(p: *mut (SpawnLocal + 'a)) -> *mut (SpawnLocal + 'static) { use std::mem; mem::transmute(p) } // ===== impl RunTimeoutError ===== impl RunTimeoutError { fn new(timeout: bool) -> Self { RunTimeoutError { timeout } } /// Returns `true` if the error was caused by the operation timing out. pub fn is_timeout(&self) -> bool { self.timeout } } impl From<tokio_executor::EnterError> for RunTimeoutError { fn from(_: tokio_executor::EnterError) -> Self { RunTimeoutError::new(false) } } // ===== impl BlockError ===== impl<T> BlockError<T> { /// Returns the error yielded by the future being blocked on pub fn into_inner(self) -> Option<T> { self.inner } } impl<T> From<tokio_executor::EnterError> for BlockError<T> { fn from(_: tokio_executor::EnterError) -> Self { BlockError { inner: None } } }