通过例子学习 Go 和 Rust ---- Mutex 互斥锁

互斥锁是并发编程的时候会用到的东西，它表示一份数据不可以被两个进程同时访问.

Go

// A Mutex is a mutual exclusion lock.
// The zero value for a Mutex is an unlocked mutex.
//
// A Mutex must not be copied after first use.
type Mutex struct {
    state int32
    sema  uint32
}

// Lock locks m.
// If the lock is already in use, the calling goroutine
// blocks until the mutex is available.
func (m *Mutex) Lock() {
    // Fast path: grab unlocked mutex.
    if atomic.CompareAndSwapInt32(&m.state, 0, mutexLocked) {
        if race.Enabled {
            race.Acquire(unsafe.Pointer(m))
        }
        return
    }
    // Slow path (outlined so that the fast path can be inlined)
    m.lockSlow()
}

举个栗子

import (
    "sync"
)

const (
    N = 10
)

func main() {
    data := 0
    var lock sync.Mutex
    done := make(chan bool)
    for i := 0; i < N; i++ {
        go func() {
            lock.Lock()
            data += 1
            if data == N {
                done <- true
            }
            lock.Unlock()
        }()
    }
    <- done
}

Rust

pub struct Mutex<T: ?Sized> {
    // Note that this mutex is in a *box*, not inlined into the struct itself.
    // Once a native mutex has been used once, its address can never change (it
    // can't be moved). This mutex type can be safely moved at any time, so to
    // ensure that the native mutex is used correctly we box the inner mutex to
    // give it a constant address.
    inner: Box<sys::Mutex>,
    poison: poison::Flag,
    data: UnsafeCell<T>,
}

impl<T: ?Sized> Mutex<T> {
    pub fn lock(&self) -> LockResult<MutexGuard<'_, T>> {
        unsafe {
            self.inner.raw_lock();
            MutexGuard::new(self)
        }
    }
}

pub struct MutexGuard<'a, T: ?Sized + 'a> {
    lock: &'a Mutex<T>,
    poison: poison::Guard,
}

impl<T: ?Sized> Drop for MutexGuard<'_, T> {
    #[inline]
    fn drop(&mut self) {
        unsafe {
            self.lock.poison.done(&self.poison);
            self.lock.inner.raw_unlock();
        }
    }
}

又举个栗子

use std::sync::{Arc, Mutex};
use std::thread;
use std::sync::mpsc::channel;

fn main() {
    const N: usize = 10;

    let data = Arc::new(Mutex::new(0));

    let (tx, rx) = channel();
    for _ in 0..N {
        let (data, tx) = (Arc::clone(&data), tx.clone());
        thread::spawn(move || {
            let mut data = data.lock().unwrap();
            *data += 1;
            if *data == N {
                tx.send(()).unwrap();
            }
        });
    }

    println!("{:?}", rx.recv().unwrap());
    
}