目录

版本1 双信号量版

 版本二 单信号量版

 版本三 信号量版

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共享资源是100个数字（一个计数器的++  由两个进程争抢完成）

首先访问临界资源（对计数器++操作）是肯定的要加锁的，交替打印肯定要用条件变量来互相唤醒 互相锁死

也可以使用信号量对临界资源做判断

所以使用wait的时候不需要释放锁 

版本1 双信号量版

唤醒对方条件不满足的信号量 

//双条件变量版本
void thread1() {
	while (true) {
		unique_lock<mutex> locker(mut);  //会自动解锁
		if (g_nums % 2 == 1 && g_nums <= num)
		{
			cout << "Thread1:" << g_nums << endl;
			g_nums++;
		}
		cond2.notify_one();
		cond1.wait(locker);
		if (g_nums >= num+1)
				break;
	}
	cout << "1 done"<< endl;
	cond2.notify_one();
}
 void thread2() {
	while (true) {
		unique_lock<mutex> locker(mut);
		if (g_nums % 2 == 0 && g_nums <= num)
		{
			cout << "Thread2:" << g_nums << endl;
			g_nums++;
		}
		cond1.notify_one();
		cond2.wait(locker);
		if (g_nums >= num + 1)
			break;
	}
	cout << "2 done" << endl;
	cond1.notify_one();
}
int main() {
	thread t1(thread1);
	thread t2(thread2);
	t1.join();
	t2.join();
	cout << "done" << endl;
	return 0;
}

 版本二 单信号量版

//单条件变量版本
void thread1()
{
	while (true)
	{
		unique_lock<mutex> lock(mut);
		if (g_nums % 2 == 1 && g_nums <= num)
		{
			cout << "thread 1:" << g_nums ++<< endl;
			
		}
	       cond.notify_one();  //唤醒另一个进程
			cond.wait(lock); //把当前的进程锁住
			if (g_nums >= num+1)
				break;
	}
	cout << "1 done"<< endl;
	cond.notify_one();
}
void thread2() {
	while (1) {
		unique_lock<mutex> locker(mut);
		if (g_nums % 2 == 0 && g_nums <= num)
		{
			cout << "Thread2:" << g_nums << endl;
			g_nums++;
		}
		cond.notify_one();
		cond.wait(locker);
      if (g_nums >= num+1)
				break;
	}
	cout << "2 done" << endl;
	cond.notify_one();
}
int main() {
	thread t1(thread1);
	thread t2(thread2);
	t1.join();
	t2.join();
	cout << "done" << endl;
	return 0;
}

 版本三 信号量版

C++在语言级别并没有支持semaphore

我们自己实现一个

#pragma once

#include <iostream>
#include <mutex>
#include <condition_variable>

using namespace std;

class semaphore {
public:
	semaphore(int num=0)
		:count(num)
	{
	}
	~semaphore()
	{}
	void single() //V
	{
		unique_lock<mutex> lock(mtx);
		if (++count <= 0)
			cond.notify_one();
	}
	void wait() //p
	{
		unique_lock<mutex> lock(mtx);
		if (--count < 0)
			cond.wait(lock);
	}


private:
	int count;
	mutex mtx;
	condition_variable cond;

};

 然后可以正常使用

 //信号量版本
void thread1()
{
	while (true)
	{
		if (g_nums % 2 == 1 && g_nums <= num)
		{
			cout << "thread 1:" << g_nums++ << endl;
			smp1.single();
		}
		smp2.wait();
		//cond.notify_one();  //唤醒另一个进程
		//cond.wait(lock); //把当前的进程锁住
		if (g_nums >= num + 1)
			break;
	}
	cout << "1 done" << endl;
	smp1.single();
}


void thread2() {
	while (true) {
		if (g_nums % 2 == 0 && g_nums <= num)
		{
			cout << "Thread2:" << g_nums ++<< endl;
			smp2.single();
		}
		smp1.wait();
			if (g_nums >= num+1)
				break;
	}
	cout << "2 done" << endl;
	smp2.single();
}


int main() 
{
	thread t1(thread1);
	thread t2(thread2);
	t1.join();
	t2.join();
	cout << "done" << endl;
	return 0;
}