linux - 为什么这个 C++11 程序不会死锁？

Question

#include <iostream>
#include <mutex>

using namespace std;

int main()
{
    mutex m;
    m.lock();
    cout << "locked once\n";

    m.lock();
    cout << "locked twice\n";

    return 0;
}

输出:

./a.out 
locked once
locked twice

程序是否需要在第二次锁定时死锁，即互斥体被同一个线程锁定两次？

Answer 1

If lock is called by a thread that already owns the mutex, the behavior is undefined: the program may deadlock, or, if the implementation can detect the deadlock, a resource_deadlock_would_occur error condition may be thrown.

http://en.cppreference.com/w/cpp/thread/mutex/lock