Function spawn

pub fn spawn<F>(future: F) -> JoinHandle<<F as Future>::Output> 
where
    F: Future + Send + 'static,
    <F as Future>::Output: Send + 'static,

Spawns a new asynchronous task, returning a 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 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 method.

Examples

In this example, a server is started and spawn is used to start a new task that processes each received connection.

use tokio::net::{TcpListener, TcpStream};

use std::io;

async fn process(socket: TcpStream) {
    // ...
}

#[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.

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());
}