C++ 11 多线程学习笔记3 -- 死锁

小灰灰 2023-07-05 11:51 14阅读 0赞

[**https://www.bilibili.com/video/av39161756?p=4**][https_www.bilibili.com_video_av39161756_p_4]

**1.拥有一些资源，同时请求一些资源**

#include <iostream>
    #include <thread>
    #include <future>
    #include <mutex>
    #include <string>
    #include <fstream>
    
    
    using namespace std;
    
    class LofFile { 
    public:
    	LofFile() { 
    		f.open("log.txt");
    	}
    
    	void share_print(string id, int val) { 
    		lock_guard<mutex> locker(m_mutex);
    		lock_guard<mutex> locker2(m_mutex2);
    		cout << "from " << id << ":" << val << endl;
    	}
    	void share_print2(string id, int val) { 
    		lock_guard<mutex> locker2(m_mutex2);
    		lock_guard<mutex> locker(m_mutex);
    		cout << "from " << id << ":" << val << endl;
    	}
    protected:
    private:
    	mutex m_mutex;
    	mutex m_mutex2;
    	ofstream f;
    };
    
    void fountion1(LofFile & log) { 
    	for (int i = 0; i > -1000; i--) { 
    		log.share_print( "from t1: ", i);
    	}
    }
    
    
    int main()
    { 
    	LofFile log;
    	thread t1(fountion1,ref(log));
    
    	for (int i = 0; i < 1000; i++) { 
    		log.share_print2("from main: ",i);
    	}
    	//如果上面的代码抛出异常，t在join之前就会被销毁，这个时候代码就报错了
    	t1.join();
    
    	return 0;
    }

**2.std::lock控制锁的顺序**

#include <iostream>
    #include <thread>
    #include <future>
    #include <mutex>
    #include <string>
    #include <fstream>
    
    
    
    using namespace std;
    
    class LofFile { 
    public:
    	LofFile() { 
    		f.open("log.txt");
    	}
    
    	void share_print(string id, int val) { 
    		std::lock(m_mutex, m_mutex2);
    		lock_guard<mutex> locker(m_mutex,std::adopt_lock);
    		lock_guard<mutex> locker2(m_mutex2, std::adopt_lock);
    		cout << "from " << id << ":" << val << endl;
    	}
    	void share_print2(string id, int val) { 
    		std::lock(m_mutex, m_mutex2);
    		lock_guard<mutex> locker2(m_mutex2,std::adopt_lock);
    		lock_guard<mutex> locker(m_mutex, std::adopt_lock);
    		cout << "from " << id << ":" << val << endl;
    	}
    protected:
    private:
    	mutex m_mutex;
    	mutex m_mutex2;
    	ofstream f;
    };
    
    void fountion1(LofFile & log) { 
    	for (int i = 0; i > -100; i--) { 
    		log.share_print( "from t1: ", i);
    	}
    }
    
    
    int main()
    { 
    	LofFile log;
    	thread t1(fountion1,ref(log));
    
    	for (int i = 0; i < 100; i++) { 
    		log.share_print2("from main: ",i);
    	}
    	//如果上面的代码抛出异常，t在join之前就会被销毁，这个时候代码就报错了
    	t1.join();
    
    	return 0;
    }

**用std::lock给锁加一个顺序，就可以避免死锁**  
**lock参数个数不固定**

--------------------

**使用尽量少的锁  
在使用了一个锁之后，调用其他不熟悉的函数需要小心，因为其他函数可能包含其他的锁**

[https_www.bilibili.com_video_av39161756_p_4]: https://www.bilibili.com/video/av39161756?p=4