生产者-消费者，使用C++11的版本

前言

multi-threading以及lambda是C++11的重要升级，下面的经典的生产者-消费者的代码，既使用了C++11的multi-threading相关的库, 又使用了lambda。代码中有注释，应该比较详细。

Talk is cheap show me the code

#include <iostream>
#include <queue>
#include <thread>
#include <mutex>
#include <condition_variable>
using namespace std;

mutex mtx;
condition_variable produce, consume;  // 条件变量是一种同步机制，要和mutex以及lock一起使用

queue<int> q;     // shared value by producers and consumers, which is the critical section
int maxSize = 20;

void consumer()
{
while (true)
{
this_thread::sleep_for(chrono::milliseconds(1000));

unique_lock<mutex> lck(mtx);                        // RAII，程序运行到此block的外面（进入下一个while循环之前），资源（内存）自动释放
consume.wait(lck, [] {return q.size() != 0; });     // wait(block) consumer until q.size() != 0 is true

cout << "consumer " << this_thread::get_id() << ": ";
q.pop();
cout << q.size() << '\n';

produce.notify_all();                               // nodity(wake up) producer when q.size() != maxSize is true
}
}

void producer(int id)
{
while (true)
{
this_thread::sleep_for(chrono::milliseconds(900));      // producer is a little faster than consumer

unique_lock<mutex> lck(mtx);
produce.wait(lck, [] {return q.size() != maxSize; });   // wait(block) producer until q.size() != maxSize is true

cout << "-> producer " << this_thread::get_id() << ": ";
q.push(id);
cout << q.size() << '\n';

consume.notify_all();                                   // notify(wake up) consumer when q.size() != 0 is true
}
}

int main()
{
thread consumers[2], producers[2];

// spawn 2 consumers and 2 producers:
for (int i = 0; i < 2; ++i)
{
consumers[i] = thread(consumer);
producers[i] = thread(producer, i + 1);
}

// join them back: (in this program, never join...)
for (int i = 0; i < 2; ++i)
{
producers[i].join();
consumers[i].join();
}

system("pause");
return 0;
}

扩展阅读

生产者-消费者模型扩展

我的GitHub里的一个项目：线程池(使用C++11)

为什么条件变量和互斥锁要在一起使用。这篇博客使用类Unix操作系统的POSIX multithreading，来讲解条件变量（condition variable） 为什么，以及怎么和互斥锁（mutex and lock）一起配套使用。

Last update: 2017/7/27