async-std/docs/src/tutorials/integrating-std-thread.md

Exercise: Waiting for std::thread

Parallel processing is usually done via [threads]. In async-std, we have similar concept, called a [task]. These two worlds seem different - and in some regards, they are - though they are easy to connect. In this exercise, you will learn how to connect to concurrent/parallel components easily, by connecting a thread to a task.

Understanding the problem

The standard thread API in Rust is std::thread. Specifically, it contains the [spawn] function, which allows us to start a thread:

std::thread::spawn(|| {
    println!("in child thread");
})
println!("in parent thread");

This creates a thread, immediately [schedules] it to run, and continues. This is crucial: once the thread is spawned, it is independent of its parent thread. If you want to wait for the thread to end, you need to capture its [JoinHandle] and join it with your current thread:

let thread = std::thread::spawn(|| {
    println!("in child thread");
})
thread.join();
println!("in parent thread");

This comes at a cost though: the waiting thread will [block] until the child is done. Wouldn't it be nice if we could just use the .await syntax here and leave the opportunity for another task to be scheduled while waiting?

Backchannels

[threads]: TODO: wikipedia [task]: TODO: docs link [spawn]: TODO: docs link [JoinHandle]: TODO: docs link [schedules]: TODO: Glossary link [block]: TODO: Link to blocking