c++11之once_flag

#include <pthread.h>

#include <iostream>
#include <mutex>

using namespace std;


std::once_flag g_flag;

void once_func()
{
    cout << __FUNCTION__ << "\t" << pthread_self() << " this is once call function!" << endl;
};

void* one_func(void*)
{
    cout << __FUNCTION__ << "\t" << "my thread id is " <<  pthread_self() << endl;
    std::call_once(g_flag, once_func);

    return NULL;
};

void* two_func(void*)
{
    cout << __FUNCTION__ << "\t" << "my thread id is " <<  pthread_self() << endl;
    std::call_once(g_flag, once_func);

    return NULL;
};

int main()
{
    pthread_t one,two,three;
    pthread_create(&one, NULL, one_func, NULL);
    usleep(1000);
    pthread_create(&two, NULL, two_func, NULL);
    usleep(1000);
    pthread_create(&three, NULL, one_func, NULL);
    usleep(1000);

    pthread_join(one, NULL);
    pthread_join(two, NULL);
    pthread_join(three, NULL);

    return 0;
}

编译：g++ -g once_flag_test.cpp -std=c++0x -lpthread

gcc版本：gcc 版本 4.6.3 (Ubuntu/Linaro 4.6.3-1ubuntu5) 

因为用到了c++11的东东，所以在编译时需要加入-std=c++0x

对于once_flag和once_call实现的功能等同于linux中的pthread_once_t和pthread_call。

可以将代码中 pthread相关换成c++11中的thread类，这样就不存在平台问题了，不过windows平台上，可能需要vs2010或者vs2012。

运行结果：

one_func my thread id is 139888413087488
once_func 139888413087488 this is once call function!
two_func my thread id is 139888404694784
one_func my thread id is 139888396302080