C/C++多线程

一、pthread_once使相关代码只执行一次

这个函数使用初值为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。

#include <pthread.h>
int pthread_once(pthread_once_t *once_control, void (*init_routine) (void))

#include <iostream>
#include <pthread.h>
#include <unistd.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<<"main thread enter"<<endl;
    pthread_create(&tid1,NULL,child1,NULL);
    pthread_create(&tid2,NULL,child2,NULL);
    sleep(10);
    cout<<"main thread exit"<<endl;
    return 0;

}

/*
main thread enter
thread 4144080640 enter
once_run in thread 4144080640
thread 139667890611968 return
thread 4152473344 enter
thread 139667899004672 return
main thread exit

*/

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