| use crate::task::JoinHandle; |
| |
| use std::future::Future; |
| |
| cfg_rt! { |
| /// Spawns a new asynchronous task, returning a |
| /// [`JoinHandle`](super::JoinHandle) for it. |
| /// |
| /// The provided future will start running in the background immediately |
| /// when `spawn` is called, even if you don't await the returned |
| /// `JoinHandle`. |
| /// |
| /// Spawning a task enables the task to execute concurrently to other tasks. The |
| /// spawned task may execute on the current thread, or it may be sent to a |
| /// different thread to be executed. The specifics depend on the current |
| /// [`Runtime`](crate::runtime::Runtime) configuration. |
| /// |
| /// It is guaranteed that spawn will not synchronously poll the task being spawned. |
| /// This means that calling spawn while holding a lock does not pose a risk of |
| /// deadlocking with the spawned task. |
| /// |
| /// There is no guarantee that a spawned task will execute to completion. |
| /// When a runtime is shutdown, all outstanding tasks are dropped, |
| /// regardless of the lifecycle of that task. |
| /// |
| /// This function must be called from the context of a Tokio runtime. Tasks running on |
| /// the Tokio runtime are always inside its context, but you can also enter the context |
| /// using the [`Runtime::enter`](crate::runtime::Runtime::enter()) method. |
| /// |
| /// # Examples |
| /// |
| /// In this example, a server is started and `spawn` is used to start a new task |
| /// that processes each received connection. |
| /// |
| /// ```no_run |
| /// use tokio::net::{TcpListener, TcpStream}; |
| /// |
| /// use std::io; |
| /// |
| /// async fn process(socket: TcpStream) { |
| /// // ... |
| /// # drop(socket); |
| /// } |
| /// |
| /// #[tokio::main] |
| /// async fn main() -> io::Result<()> { |
| /// let listener = TcpListener::bind("127.0.0.1:8080").await?; |
| /// |
| /// loop { |
| /// let (socket, _) = listener.accept().await?; |
| /// |
| /// tokio::spawn(async move { |
| /// // Process each socket concurrently. |
| /// process(socket).await |
| /// }); |
| /// } |
| /// } |
| /// ``` |
| /// |
| /// To run multiple tasks in parallel and receive their results, join |
| /// handles can be stored in a vector. |
| /// ``` |
| /// # #[tokio::main(flavor = "current_thread")] async fn main() { |
| /// async fn my_background_op(id: i32) -> String { |
| /// let s = format!("Starting background task {}.", id); |
| /// println!("{}", s); |
| /// s |
| /// } |
| /// |
| /// let ops = vec![1, 2, 3]; |
| /// let mut tasks = Vec::with_capacity(ops.len()); |
| /// for op in ops { |
| /// // This call will make them start running in the background |
| /// // immediately. |
| /// tasks.push(tokio::spawn(my_background_op(op))); |
| /// } |
| /// |
| /// let mut outputs = Vec::with_capacity(tasks.len()); |
| /// for task in tasks { |
| /// outputs.push(task.await.unwrap()); |
| /// } |
| /// println!("{:?}", outputs); |
| /// # } |
| /// ``` |
| /// This example pushes the tasks to `outputs` in the order they were |
| /// started in. If you do not care about the ordering of the outputs, then |
| /// you can also use a [`JoinSet`]. |
| /// |
| /// [`JoinSet`]: struct@crate::task::JoinSet |
| /// |
| /// # Panics |
| /// |
| /// Panics if called from **outside** of the Tokio runtime. |
| /// |
| /// # Using `!Send` values from a task |
| /// |
| /// The task supplied to `spawn` must implement `Send`. However, it is |
| /// possible to **use** `!Send` values from the task as long as they only |
| /// exist between calls to `.await`. |
| /// |
| /// For example, this will work: |
| /// |
| /// ``` |
| /// use tokio::task; |
| /// |
| /// use std::rc::Rc; |
| /// |
| /// fn use_rc(rc: Rc<()>) { |
| /// // Do stuff w/ rc |
| /// # drop(rc); |
| /// } |
| /// |
| /// #[tokio::main] |
| /// async fn main() { |
| /// tokio::spawn(async { |
| /// // Force the `Rc` to stay in a scope with no `.await` |
| /// { |
| /// let rc = Rc::new(()); |
| /// use_rc(rc.clone()); |
| /// } |
| /// |
| /// task::yield_now().await; |
| /// }).await.unwrap(); |
| /// } |
| /// ``` |
| /// |
| /// This will **not** work: |
| /// |
| /// ```compile_fail |
| /// use tokio::task; |
| /// |
| /// use std::rc::Rc; |
| /// |
| /// fn use_rc(rc: Rc<()>) { |
| /// // Do stuff w/ rc |
| /// # drop(rc); |
| /// } |
| /// |
| /// #[tokio::main] |
| /// async fn main() { |
| /// tokio::spawn(async { |
| /// let rc = Rc::new(()); |
| /// |
| /// task::yield_now().await; |
| /// |
| /// use_rc(rc.clone()); |
| /// }).await.unwrap(); |
| /// } |
| /// ``` |
| /// |
| /// Holding on to a `!Send` value across calls to `.await` will result in |
| /// an unfriendly compile error message similar to: |
| /// |
| /// ```text |
| /// `[... some type ...]` cannot be sent between threads safely |
| /// ``` |
| /// |
| /// or: |
| /// |
| /// ```text |
| /// error[E0391]: cycle detected when processing `main` |
| /// ``` |
| #[track_caller] |
| pub fn spawn<F>(future: F) -> JoinHandle<F::Output> |
| where |
| F: Future + Send + 'static, |
| F::Output: Send + 'static, |
| { |
| // preventing stack overflows on debug mode, by quickly sending the |
| // task to the heap. |
| if cfg!(debug_assertions) && std::mem::size_of::<F>() > 2048 { |
| spawn_inner(Box::pin(future), None) |
| } else { |
| spawn_inner(future, None) |
| } |
| } |
| |
| #[track_caller] |
| pub(super) fn spawn_inner<T>(future: T, name: Option<&str>) -> JoinHandle<T::Output> |
| where |
| T: Future + Send + 'static, |
| T::Output: Send + 'static, |
| { |
| use crate::runtime::{context, task}; |
| |
| #[cfg(all( |
| tokio_unstable, |
| tokio_taskdump, |
| feature = "rt", |
| target_os = "linux", |
| any( |
| target_arch = "aarch64", |
| target_arch = "x86", |
| target_arch = "x86_64" |
| ) |
| ))] |
| let future = task::trace::Trace::root(future); |
| let id = task::Id::next(); |
| let task = crate::util::trace::task(future, "task", name, id.as_u64()); |
| |
| match context::with_current(|handle| handle.spawn(task, id)) { |
| Ok(join_handle) => join_handle, |
| Err(e) => panic!("{}", e), |
| } |
| } |
| } |