c++11多线程学习笔记之二 mutex使用

最新推荐文章于 2023-11-04 13:52:26 发布

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最新推荐文章于 2023-11-04 13:52:26 发布

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原文链接：http://www.cnblogs.com/itdef/p/4559146.html

本文通过一个C++多线程示例程序，演示了std::mutex中try_lock()与lock()的区别。try_lock()用于尝试获取锁而不阻塞，若锁已被占用，则返回失败；而lock()则会等待锁可用。示例程序展示了当多个线程尝试增加全局计数器时，这两种锁机制的行为差异。

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// 1111111.cpp : 定义控制台应用程序的入口点。
//

#include "stdafx.h"
#include <iostream>
#include <thread>
#include <mutex>         

int gcounter = 0;
std::mutex gmtx;    
std::mutex gmtxOutput;

void Increases() {
	for (int i = 0; i<10000; ++i) {
		if (gmtx.try_lock()) {   // only increase if currently not locked:
			++gcounter;
			gmtx.unlock();
		}
		else{
			gmtxOutput.lock();
			std::cout << "try lock failed" << std::endl;
			gmtxOutput.unlock();
		}
	}
}

int _tmain(int argc, _TCHAR* argv[]) {
	std::thread threads[10];
	for (int i = 0; i<10; ++i)
		threads[i] = std::thread(Increases);

	for (auto& th : threads) 
		th.join();
	std::cout << "counter is " << gcounter << std::endl;

	return 0;
}

输出:

try lock failed
try lock failed
try lock failed
try lock failed
try lock failed
try lock failed
try lock failed
try lock failed
try lock failed
try lock failed
try lock failed
try lock failed
try lock failed
try lock failed
try lock failed
try lock failed
try lock failed
counter is 99983
请按任意键继续. . .