线程的同步与互斥

抢票的例子

竞争过程

进程A被切走

进程B被切走

结论：

互斥

int pthread_mutex_init(pthread_mutex_t *mutex, const pthread_mutexattr_t *attr);

• mutex: 指向要初始化的互斥锁的指针。
• attr: 用于设置互斥锁属性的指针，通常可以传入 NULL 以使用默认属性。

锁的本质

加锁

解锁

线程安全与重入

死锁

线程同步

生产消费模型

例子

条件变量

demo

#include<iostream>
#include<string>
#include<pthread.h>
#include<unistd.h>int tickets=1000;
pthread_mutex_t mutex=PTHREAD_MUTEX_INITIALIZER;
pthread_cond_t cond=PTHREAD_COND_INITIALIZER;void *start_routine(void* args){std::string name=static_cast<const char*>(args);while(true){pthread_mutex_lock(&mutex);pthread_cond_wait(&cond,&mutex);std::cout<<name<<"->"<<tickets<<std::endl;tickets--;pthread_mutex_unlock(&mutex);}return nullptr;
}int main(){const int num=5;pthread_t tid[num]{};for(int i=0;i<num;i++){char *name=new char[64];snprintf(name,sizeof(name),"thread %d",i+1);pthread_create(tid+i,nullptr,start_routine,name);}while(true){std::cout<<"main thread weak up"<<std::endl;pthread_cond_signal(&cond);sleep(1);}for(int i=0;i<num;i++){pthread_join(tid[i],nullptr);}return 0;}

信号量

常用函数

环形队列

环形队列代码

#include"RingQueue.hpp"
#include<unistd.h>
#include<pthread.h>
#include<random>
#include<iostream>void *ProductorRoutine(void* rq){RingQueue<int> *ringqueue=static_cast<RingQueue<int>*>(rq);while(true){int data=rand()%10+1;ringqueue->Push(data);std::cout<<"生产完成 生产的数据是："<<data<<std::endl;sleep(1);}
}void *ConsumerRoutine(void *rq){RingQueue<int> *ringqueue=static_cast<RingQueue<int>*>(rq);while(true){int data;ringqueue->Pop(data);std::cout<<"消费完成 消费数据是："<<data<<std::endl;sleep(1);}
}int main(){srand((unsigned int)time(nullptr)^getpid()^pthread_self());RingQueue<int> *rq=new RingQueue<int>();pthread_t p,c;pthread_create(&p,nullptr,ProductorRoutine,rq);pthread_create(&c,nullptr,ConsumerRoutine,rq);pthread_join(p,nullptr);pthread_join(c,nullptr);}

#include<semaphore.h>
#include<vector>
#include<cassert>
#include<ctime>
#include<sys/types.h>static const int gcap=5;template<class T>
class RingQueue{
public:void P(sem_t &sem){int n=sem_wait(&sem);assert(n==0);(void)n;}void V(sem_t &sem){int n=sem_post(&sem);assert(n==0);(void)n;}public:RingQueue(const int &cap=gcap):_q(cap),_cap(cap){int n=sem_init(&_spaceSem,0,_cap);assert(n==0);n=sem_init(&_dataSem,0,0);assert(n==0);productorStep=ConsumerStep=0;}void Push(const T &in){P(_spaceSem);_q[productorStep++]=in;productorStep%=_cap;V(_dataSem);}void Pop(T &out){P(_dataSem);out=_q[ConsumerStep++];ConsumerStep%=_cap;V(_spaceSem);}~RingQueue(){sem_destroy(&_spaceSem);sem_destroy(&_dataSem);}private:std::vector<T> _q;int _cap;sem_t _spaceSem;  //生产者 空间资源sem_t _dataSem;   //消费者 数据资源int productorStep;int ConsumerStep;
};