线程

Rust 线程的运作方式与其他语言中的线程类似：

use std::thread;
use std::time::Duration;

fn main() {
    thread::spawn(|| {
        for i in 1..10 {
            println!("Count in thread: {i}!");
            thread::sleep(Duration::from_millis(5));
        }
    });

    for i in 1..5 {
        println!("Main thread: {i}");
        thread::sleep(Duration::from_millis(5));
    }
}
  • 线程均为守护程序线程，主线程不会等待这些线程。
  • 线程紧急警报 (panic) 是彼此独立的。
    • 紧急警报可以携带载荷，并可以使用 downcast_ref 对载荷进行解压缩。

  • Rust thread APIs look not too different from e.g. C++ ones.

  • Run the example.

    • 5ms timing is loose enough that main and spawned threads stay mostly in lockstep.
    • Notice that the program ends before the spawned thread reaches 10!
    • This is because main ends the program and spawned threads do not make it persist.
      • Compare to pthreads/C++ std::thread/boost::thread if desired.

  • How do we wait around for the spawned thread to complete?

  • thread::spawn returns a JoinHandle. Look at the docs.

    • JoinHandle has a .join() method that blocks.

  • Use let handle = thread::spawn(...) and later handle.join() to wait for the thread to finish and have the program count all the way to 10.

  • Now what if we want to return a value?

  • Look at docs again:

  • Use the Result return value from handle.join() to get access to the returned value.

  • Ok, what about the other case?

    • Trigger a panic in the thread. Note that this doesn't panic main.
    • Access the panic payload. This is a good time to talk about Any.

  • Now we can return values from threads! What about taking inputs?

    • Capture something by reference in the thread closure.
    • An error message indicates we must move it.
    • Move it in, see we can compute and then return a derived value.

  • If we want to borrow?

    • Main kills child threads when it returns, but another function would just return and leave them running.
    • That would be stack use-after-return, which violates memory safety!
    • How do we avoid this? see next slide.