C++11多线程学习（3）条件变量

C++11中的条件变量支持把判断条件写到参数里。配合lamda表达式让程序代码更加清晰。第一个参数只支持unique_lock他和lock_guard的区别在于可以在作用域内加锁再解锁，而lock_gurad只能在构造和析构的时候加锁和解锁。

下面是对cv的小应用，轮流打印AB

#include <thread>
#include <iostream>
#include <mutex>
#include <condition_variable>
 using namespace std;
mutex m;
condition_variable cv;
bool flag = true;
 
void printA()
{
    while(1)
    {
		unique_lock<mutex>ul(m);
		cv.wait(ul,[]{return flag;});	
		cout<<"A"<<endl;
		flag=false;
		cv.notify_one();
    }
}
 
void printB()
{
    while(1)
    {
       unique_lock<mutex>ul(m);
	   cv.wait(ul,[]{return !flag;});
	   cout<<"B"<<endl;
	   flag=true;
	   cv.notify_one();
    }
}
 
int main()
{
    std::thread tA(printA);
    std::thread tB(printB);
    tA.join();
    tB.join();
    return 0;
}

再附一个简单的线程安全队列模型

#include <thread>
#include <iostream>
#include <mutex>
#include <condition_variable>
#include <queue>
 using namespace std;
 struct Task
 {
	 Task(thread::id p,int i):pro(p),index(i)
	 { }
	 thread::id pro;
	 int index;
 };
 class Safequeue
 {
 private:
	 mutex _m;
	 condition_variable _cv;
	 queue<Task>_q;
 public:
	 void insert(Task x)
	 {
		 unique_lock<mutex>ul(_m);
		 _q.push(x);
		 _cv.notify_one();
	 }
	 Task take()
	 {
		 unique_lock<mutex>ul(_m);
		 _cv.wait(ul,[this]{return !_q.empty();});
		 Task task=_q.front();
		 _q.pop();
		 return task;
	 }
 };

 Safequeue taskqueue;
 
 void troublemaker()
 {
	 int c=0;
	 while(1)
	 {
		 _sleep(1000);
		 taskqueue.insert(Task(this_thread::get_id(),c++));
	 }
 }
 void worker()
 {
	 while(1)
	 {
		 Task task=taskqueue.take();
		 cout<<this_thread::get_id()<<" get "<<task.index<<" from "<<task.pro<<endl;
	 }
 }
int main()
{
	thread t1(troublemaker);
	thread t2(troublemaker);
	thread w1(worker);
	thread w2(worker);
	t1.join();
	t2.join();
	w1.join();
	w2.join();
}