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use crate::runtime::{blocking, context, io, time, Spawner}; use std::{error, fmt}; cfg_blocking! { use crate::runtime::task; use crate::runtime::blocking::task::BlockingTask; } cfg_rt_core! { use crate::task::JoinHandle; use std::future::Future; } /// Handle to the runtime. /// /// The handle is internally reference-counted and can be freely cloned. A handle can be /// obtained using the [`Runtime::handle`] method. /// /// [`Runtime::handle`]: crate::runtime::Runtime::handle() #[derive(Debug, Clone)] pub struct Handle { pub(super) spawner: Spawner, /// Handles to the I/O drivers pub(super) io_handle: io::Handle, /// Handles to the time drivers pub(super) time_handle: time::Handle, /// Source of `Instant::now()` pub(super) clock: time::Clock, /// Blocking pool spawner pub(super) blocking_spawner: blocking::Spawner, } impl Handle { /// Enter the runtime context. This allows you to construct types that must /// have an executor available on creation such as [`Delay`] or [`TcpStream`]. /// It will also allow you to call methods such as [`tokio::spawn`]. /// /// This function is also available as [`Runtime::enter`]. /// /// [`Delay`]: struct@crate::time::Delay /// [`TcpStream`]: struct@crate::net::TcpStream /// [`Runtime::enter`]: fn@crate::runtime::Runtime::enter /// [`tokio::spawn`]: fn@crate::spawn /// /// # Example /// /// ``` /// use tokio::runtime::Runtime; /// /// fn function_that_spawns(msg: String) { /// // Had we not used `handle.enter` below, this would panic. /// tokio::spawn(async move { /// println!("{}", msg); /// }); /// } /// /// fn main() { /// let rt = Runtime::new().unwrap(); /// let handle = rt.handle().clone(); /// /// let s = "Hello World!".to_string(); /// /// // By entering the context, we tie `tokio::spawn` to this executor. /// handle.enter(|| function_that_spawns(s)); /// } /// ``` pub fn enter<F, R>(&self, f: F) -> R where F: FnOnce() -> R, { context::enter(self.clone(), f) } /// Returns a `Handle` view over the currently running `Runtime` /// /// # Panic /// /// This will panic if called outside the context of a Tokio runtime. That means that you must /// call this on one of the threads **being run by the runtime**. Calling this from within a /// thread created by `std::thread::spawn` (for example) will cause a panic. /// /// # Examples /// /// This can be used to obtain the handle of the surrounding runtime from an async /// block or function running on that runtime. /// /// ``` /// # use std::thread; /// # use tokio::runtime::Runtime; /// # fn dox() { /// # let rt = Runtime::new().unwrap(); /// # rt.spawn(async { /// use tokio::runtime::Handle; /// /// // Inside an async block or function. /// let handle = Handle::current(); /// handle.spawn(async { /// println!("now running in the existing Runtime"); /// }); /// /// # let handle = /// thread::spawn(move || { /// // Notice that the handle is created outside of this thread and then moved in /// handle.block_on(async { /* ... */ }) /// // This next line would cause a panic /// // let handle2 = Handle::current(); /// }); /// # handle.join().unwrap(); /// # }); /// # } /// ``` pub fn current() -> Self { context::current().expect("not currently running on the Tokio runtime.") } /// Returns a Handle view over the currently running Runtime /// /// Returns an error if no Runtime has been started /// /// Contrary to `current`, this never panics pub fn try_current() -> Result<Self, TryCurrentError> { context::current().ok_or(TryCurrentError(())) } } cfg_rt_core! { impl Handle { /// Spawns a future onto the Tokio runtime. /// /// This spawns the given future onto the runtime's executor, usually a /// thread pool. The thread pool is then responsible for polling the future /// until it completes. /// /// See [module level][mod] documentation for more details. /// /// [mod]: index.html /// /// # Examples /// /// ``` /// use tokio::runtime::Runtime; /// /// # fn dox() { /// // Create the runtime /// let rt = Runtime::new().unwrap(); /// let handle = rt.handle(); /// /// // Spawn a future onto the runtime /// handle.spawn(async { /// println!("now running on a worker thread"); /// }); /// # } /// ``` /// /// # Panics /// /// This function will not panic unless task execution is disabled on the /// executor. This can only happen if the runtime was built using /// [`Builder`] without picking either [`basic_scheduler`] or /// [`threaded_scheduler`]. /// /// [`Builder`]: struct@crate::runtime::Builder /// [`threaded_scheduler`]: fn@crate::runtime::Builder::threaded_scheduler /// [`basic_scheduler`]: fn@crate::runtime::Builder::basic_scheduler pub fn spawn<F>(&self, future: F) -> JoinHandle<F::Output> where F: Future + Send + 'static, F::Output: Send + 'static, { self.spawner.spawn(future) } /// Run a future to completion on the Tokio runtime from a synchronous /// context. /// /// This runs the given future on the runtime, blocking until it is /// complete, and yielding its resolved result. Any tasks or timers which /// the future spawns internally will be executed on the runtime. /// /// If the provided executor currently has no active core thread, this /// function might hang until a core thread is added. This is not a /// concern when using the [threaded scheduler], as it always has active /// core threads, but if you use the [basic scheduler], some other /// thread must currently be inside a call to [`Runtime::block_on`]. /// See also [the module level documentation][1], which has a section on /// scheduler types. /// /// This method may not be called from an asynchronous context. /// /// [threaded scheduler]: fn@crate::runtime::Builder::threaded_scheduler /// [basic scheduler]: fn@crate::runtime::Builder::basic_scheduler /// [`Runtime::block_on`]: fn@crate::runtime::Runtime::block_on /// [1]: index.html#runtime-configurations /// /// # Panics /// /// This function panics if the provided future panics, or if called /// within an asynchronous execution context. /// /// # Examples /// /// Using `block_on` with the [threaded scheduler]. /// /// ``` /// use tokio::runtime::Runtime; /// use std::thread; /// /// // Create the runtime. /// // /// // If the rt-threaded feature is enabled, this creates a threaded /// // scheduler by default. /// let rt = Runtime::new().unwrap(); /// let handle = rt.handle().clone(); /// /// // Use the runtime from another thread. /// let th = thread::spawn(move || { /// // Execute the future, blocking the current thread until completion. /// // /// // This example uses the threaded scheduler, so no concurrent call to /// // `rt.block_on` is required. /// handle.block_on(async { /// println!("hello"); /// }); /// }); /// /// th.join().unwrap(); /// ``` /// /// Using the [basic scheduler] requires a concurrent call to /// [`Runtime::block_on`]: /// /// [threaded scheduler]: fn@crate::runtime::Builder::threaded_scheduler /// [basic scheduler]: fn@crate::runtime::Builder::basic_scheduler /// [`Runtime::block_on`]: fn@crate::runtime::Runtime::block_on /// /// ``` /// use tokio::runtime::Builder; /// use tokio::sync::oneshot; /// use std::thread; /// /// // Create the runtime. /// let mut rt = Builder::new() /// .enable_all() /// .basic_scheduler() /// .build() /// .unwrap(); /// /// let handle = rt.handle().clone(); /// /// // Signal main thread when task has finished. /// let (send, recv) = oneshot::channel(); /// /// // Use the runtime from another thread. /// let th = thread::spawn(move || { /// // Execute the future, blocking the current thread until completion. /// handle.block_on(async { /// send.send("done").unwrap(); /// }); /// }); /// /// // The basic scheduler is used, so the thread above might hang if we /// // didn't call block_on on the rt too. /// rt.block_on(async { /// assert_eq!(recv.await.unwrap(), "done"); /// }); /// # th.join().unwrap(); /// ``` /// pub fn block_on<F: Future>(&self, future: F) -> F::Output { self.enter(|| { let mut enter = crate::runtime::enter(true); enter.block_on(future).expect("failed to park thread") }) } } } cfg_blocking! { impl Handle { /// Runs the provided closure on a thread where blocking is acceptable. /// /// In general, issuing a blocking call or performing a lot of compute in a /// future without yielding is not okay, as it may prevent the executor from /// driving other futures forward. This function runs the provided closure /// on a thread dedicated to blocking operations. See the [CPU-bound tasks /// and blocking code][blocking] section for more information. /// /// Tokio will spawn more blocking threads when they are requested through /// this function until the upper limit configured on the [`Builder`] is /// reached. This limit is very large by default, because `spawn_blocking` is /// often used for various kinds of IO operations that cannot be performed /// asynchronously. When you run CPU-bound code using `spawn_blocking`, you /// should keep this large upper limit in mind; to run your CPU-bound /// computations on only a few threads, you should use a separate thread /// pool such as [rayon] rather than configuring the number of blocking /// threads. /// /// This function is intended for non-async operations that eventually /// finish on their own. If you want to spawn an ordinary thread, you should /// use [`thread::spawn`] instead. /// /// Closures spawned using `spawn_blocking` cannot be cancelled. When you /// shut down the executor, it will wait indefinitely for all blocking /// operations to finish. You can use [`shutdown_timeout`] to stop waiting /// for them after a certain timeout. Be aware that this will still not /// cancel the tasks — they are simply allowed to keep running after the /// method returns. /// /// Note that if you are using the [basic scheduler], this function will /// still spawn additional threads for blocking operations. The basic /// scheduler's single thread is only used for asynchronous code. /// /// [`Builder`]: struct@crate::runtime::Builder /// [blocking]: ../index.html#cpu-bound-tasks-and-blocking-code /// [rayon]: https://docs.rs/rayon /// [basic scheduler]: fn@crate::runtime::Builder::basic_scheduler /// [`thread::spawn`]: fn@std::thread::spawn /// [`shutdown_timeout`]: fn@crate::runtime::Runtime::shutdown_timeout /// /// # Examples /// /// ``` /// use tokio::runtime::Runtime; /// /// # async fn docs() -> Result<(), Box<dyn std::error::Error>>{ /// // Create the runtime /// let rt = Runtime::new().unwrap(); /// let handle = rt.handle(); /// /// let res = handle.spawn_blocking(move || { /// // do some compute-heavy work or call synchronous code /// "done computing" /// }).await?; /// /// assert_eq!(res, "done computing"); /// # Ok(()) /// # } /// ``` pub fn spawn_blocking<F, R>(&self, f: F) -> JoinHandle<R> where F: FnOnce() -> R + Send + 'static, R: Send + 'static, { let (task, handle) = task::joinable(BlockingTask::new(f)); let _ = self.blocking_spawner.spawn(task, self); handle } } } /// Error returned by `try_current` when no Runtime has been started pub struct TryCurrentError(()); impl fmt::Debug for TryCurrentError { fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { f.debug_struct("TryCurrentError").finish() } } impl fmt::Display for TryCurrentError { fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { f.write_str("no tokio Runtime has been initialized") } } impl error::Error for TryCurrentError {}