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What's the best way to lock multiple std::mutex'es?(锁定多个std：：mutex的最佳方式是什么？)

转载 作者：bug小助手 更新时间：2023-10-25 19:33:46 26 4
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Note: This question concerns C++11. The answer to the same question in C++17 (or later revisions) may have changed. For details:

注意：此问题与C++11有关。C++17(或更高版本)中对同一问题的答案可能已更改。有关详情，请访问：







When we want to lock multiple std::mutex'es, we use std::lock(). But std::lock() does not provide RAII feature.

当我们想要锁定多个std：：mutex时，我们使用std：：lock()。但是std：：lock()不提供RAII功能。



When we want to lock a std::mutex in RAII way, we use std::lock_guard. But std::lock_guard cannot lock multiple std::mutex'es safely.

当我们想要以RAII方式锁定std：：mutex时，我们使用std：：lock_Guard。但是std：：lock_Guard不能安全地锁定多个std：：mutex。



Is there any way to take the advantages of both methods, to lock multiple std::mutex'es in RAII way?

有没有办法利用这两种方法的优点，以一种简单的方式锁定多个std：：mutex？


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Yes, you can use a std::unique_lock with std::defer_lock. It tells the unique_lock to not lock the mutex immediately, but to build the RAII wrapper.

可以，您可以将std：：Unique_lock与std：：defer_lock一起使用。它告诉UNIQUE_LOCK不要立即锁定互斥锁，而是构建RAII包装器。



std::unique_lock<std::mutex> lk1(mutex1, std::defer_lock);
std::unique_lock<std::mutex> lk2(mutex2, std::defer_lock);
std::lock(lk1, lk2);


Due to its variadic nature std::lock is not bound to only two arguments but can be used with as many arguments as your compiler has support for.

由于它的可变性质，std：：lock不仅绑定到两个参数，而且可以与编译器支持的任意多个参数一起使用。



Howard Hinnant also pointed out an interesting fact about performance, you can check this link if you are interested. He addresses performance concerns and shows that std::lock can be implemented efficiently, I can also recommend to read all the comments in that post.

霍华德·辛纳特还指出了一个关于性能的有趣事实，如果你感兴趣，可以查看这个链接。他解决了性能问题，并展示了Std：：Lock可以有效地实现，我还可以推荐阅读该帖子中的所有评论。



As you've pointed out, std::lock_guard in itself doesn't provide a deadlock-free way of locking multiple mutexs. Without a safe method, you run into the Dining Philosophers Problem.

正如您所指出的，std：：lock_guard本身并不提供锁定多个互斥锁的无死锁方式。如果没有一个安全的方法，你就会遇到吃饭哲学家问题。


std::lock implements a deadlock-free algorithm which locks multiple Lockable objects.
It can be used with

Lock实现了一种无死锁的算法，该算法锁定多个可锁定对象。它可以与



std::mutex m1, m2;

{   // Option A - lock mutexes first, adopt later
    std::lock(m1, m2);
    std::lock_guard<std::mutex> lock1(m1, std::adopt_lock);
    std::lock_guard<std::mutex> lock2(m2, std::adopt_lock);
    // critical section ...
}

{   // Option B - defer first, lock locks later
    std::unique_lock<std::mutex> lock1(m1, std::defer_lock);
    std::unique_lock<std::mutex> lock2(m2, std::defer_lock);
    std::lock(lock1, lock2);
    // critical section ...
}

{    // Option C - std::scoped_lock (C++17, but provided here for completeness)
    std::scoped_lock lock(m1, m2);
}

If you don't need the extra features that std::unique_lock provides (e.g. transferring ownership of the lock elsewhere), then std::lock_guard should be preferred.

如果您不需要std：：only_lock提供的额外功能(例如，将锁的所有权转移到其他地方)，那么应该首选std：：lock_Guard。



Note: the examples show only two locks, but all methods work with arbitrarily many locks.

注意：示例中只显示了两个锁，但所有方法都可以处理任意多个锁。


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