| use crate::{task::JoinHandle, util::error::CONTEXT_MISSING_ERROR}; |
| |
| use std::future::Future; |
| |
| cfg_rt! { |
| /// Spawns a new asynchronous task, returning a |
| /// [`JoinHandle`](super::JoinHandle) for it. |
| /// |
| /// 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. |
| /// |
| /// 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 |
| /// }); |
| /// } |
| /// } |
| /// ``` |
| /// |
| /// # 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` |
| /// ``` |
| #[cfg_attr(tokio_track_caller, track_caller)] |
| pub fn spawn<T>(future: T) -> JoinHandle<T::Output> |
| where |
| T: Future + Send + 'static, |
| T::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::<T>() > 2048 { |
| spawn_inner(Box::pin(future), None) |
| } else { |
| spawn_inner(future, None) |
| } |
| } |
| |
| #[cfg_attr(tokio_track_caller, 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, |
| { |
| let spawn_handle = crate::runtime::context::spawn_handle().expect(CONTEXT_MISSING_ERROR); |
| let task = crate::util::trace::task(future, "task", name); |
| spawn_handle.spawn(task) |
| } |
| } |