线程高级编程

一次性初始化

pthread_once_t once_control = PTHREAD_ONCE_INIT;//控制参数，用来确定是否已调用相关的初始化例程。
int pthread_once(pthread_once_t *once_control,void (*init_routine)(void));
//使用初值为PTHREAD_ONCE_INIT的once_control变量保证init_routine()函数在本进程执行序列中仅执行一次。

　　如果once_control的初值不是PTHREAD_ONCE_INIT（Linux Threads定义为0），pthread_once() 的行为就会不正常。

#include<iostream>  
#include<pthread.h>  
using namespace std;  
  
pthread_once_t once = PTHREAD_ONCE_INIT;  
  
void once_run(void)  
{  
        cout<<"once_run in thread "<<(unsigned int )pthread_self()<<endl;  
}  
  
void * child1(void * arg)  
{  
        pthread_t tid =pthread_self();  
        cout<<"thread "<<(unsigned int )tid<<" enter"<<endl;  
        pthread_once(&once,once_run);  
        cout<<"thread "<<tid<<" return"<<endl;  
}  
  
  
void * child2(void * arg)  
{  
        pthread_t tid =pthread_self();  
        cout<<"thread "<<(unsigned int )tid<<" enter"<<endl;  
        pthread_once(&once,once_run);  
        cout<<"thread "<<tid<<" return"<<endl;  
}  
  
int main(void)  
{  
        pthread_t tid1,tid2;  
        cout<<"hello"<<endl;  
        pthread_create(&tid1,NULL,child1,NULL);  
        pthread_create(&tid2,NULL,child2,NULL);  
        sleep(10);  
        cout<<"main thread exit"<<endl;  
        return 0;  
  
}

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