boost::scoped_lock 似乎没有锁定 std::cout

Question

我正在使用boost 1.54.0和Visual Studio 2010。对于代码：

#include <iostream>
#include "boost/thread/thread.hpp"
#include "boost/thread/mutex.hpp"
boost::mutex mx1;
void func1()
{
    {
        boost::mutex::scoped_lock(mx1);
        std::cout << "Thread " << boost::this_thread::get_id() << " starting work." << std::endl;
    }
    int x = 0;
    for (int i=0; i<100; i++)
        x++;
    {
        boost::mutex::scoped_lock(mx1);
        std::cout << "Thread " << boost::this_thread::get_id() << " finished." << std::endl;
    }
}
int main(void)
{
    boost::thread thread1(&func1);
    boost::thread thread2(&func1);
    thread1.join();
    thread2.join();
    return 0;
}

大约一半的时间我得到以下内容（显然，线程 ID 和执行顺序不同）：

Thread Thread 15b0 starting work.
1a18 starting work.
Thread 15b0 finished.
Thread 1a18 finished.

。而不是这个（这是我所期望的）：

Thread 15b0 starting work.
Thread 1a18 starting work.
Thread 15b0 finished.
Thread 1a18 finished.

但是，使用

mx1.lock();
std::cout << "Thread " << boost::this_thread::get_id() << " starting work." << std::endl;
mx1.unlock();

。似乎没有问题。

输出似乎始终遵循相同的模式。 我是否错误地使用了互斥锁，或者它与 std：：cout 有关？

Answer 1

替换

    boost::mutex::scoped_lock(mx1);

跟

    boost::mutex::scoped_lock lock(mx1);

您成为作用域锁最常出现的拼写错误的受害者：-）