1use std::future::Future;
2use std::panic::catch_unwind;
3use std::thread;
4
5use async_executor::{Executor, Task};
6use async_io::block_on;
7use async_lock::OnceCell;
8use futures_lite::future;
9
10/// Spawns a task onto the global executor (single-threaded by default).
11///
12/// There is a global executor that gets lazily initialized on first use. It is included in this
13/// library for convenience when writing unit tests and small programs, but it is otherwise
14/// more advisable to create your own [`Executor`].
15///
16/// By default, the global executor is run by a single background thread, but you can also
17/// configure the number of threads by setting the `SMOL_THREADS` environment variable.
18///
19/// # Examples
20///
21/// ```
22/// let task = smol::spawn(async {
23/// 1 + 2
24/// });
25///
26/// smol::block_on(async {
27/// assert_eq!(task.await, 3);
28/// });
29/// ```
30pub fn spawn<T: Send + 'static>(future: impl Future<Output = T> + Send + 'static) -> Task<T> {
31 static GLOBAL: OnceCell<Executor<'_>> = OnceCell::new();
32
33 fn global() -> &'static Executor<'static> {
34 GLOBAL.get_or_init_blocking(|| {
35 let num_threads = {
36 // Parse SMOL_THREADS or default to 1.
37 std::env::var("SMOL_THREADS")
38 .ok()
39 .and_then(|s| s.parse().ok())
40 .unwrap_or(1)
41 };
42
43 for n in 1..=num_threads {
44 thread::Builder::new()
45 .name(format!("smol-{}", n))
46 .spawn(|| loop {
47 catch_unwind(|| block_on(global().run(future::pending::<()>()))).ok();
48 })
49 .expect("cannot spawn executor thread");
50 }
51
52 // Prevent spawning another thread by running the process driver on this thread.
53 let ex = Executor::new();
54 #[cfg(not(target_os = "espidf"))]
55 ex.spawn(async_process::driver()).detach();
56 ex
57 })
58 }
59
60 global().spawn(future)
61}
62