深入Pthread(四)：一次初始化-pthread_once_t

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用到的API：
pthread_once_t once_control = PTHREAD_ONCE_INIT;
int pthread_once(pthread_once_t* once_control, void (*init_routine)(void));

    有些事需要一次且仅需要一次执行。通常当初始化应用程序时，可以比较容易地将其放在main函数中。但当你写一个库时，就不能在main里面初始化了，你可以用静态初始化，但使用一次初始化（pthread_once_t）会比较容易些。

例程：
#include <pthread.h>
#include "errors.h"

pthread_once_t once_block = PTHREAD_ONCE_INIT;
pthread_mutex_t mutex;

/*This is the one-time initialization routine. It will be
* called exactly once, no matter how many calls to pthread_once
* with the same control structure are made during the course of
* the program.
*/

void once init routine (void)
{
    int status;

status = pthread_mutex_init (&mutex, NULL);

if (status != 0)

err_abort (status, "Init Mutex");

}

/* Thread start routine that calls pthread_once.
*/
void *thread routine (void *arg)
{
    int status;
    status = pthread_once (&once_block, once_init_routine);
    if (status != 0)
        err_abort (status, "Once init");
    status = pthread_mutex_lock (&mutex);
    if (status != 0)
        err_abort (status, "Lock mutex");
    printf ("thread routine has locked the mutex./n");

    status = pthread_mutex_unlock (&mutex);
    if (status ! = 0)
        err_abort (status, "Unlock mutex");
    return NULL;

}

int main (int argc, char *argv[])
{
    pthread_t thread_id;
    char *input, buffer[64];
    int status;
    status = pthread_create (&thread_id, NULL, thread_routine, NULL);
    if (status != 0)
        err_abort (status, "Create thread");
    status = pthread_once (&once_block, once_init_routine);
    if (status != 0)
        err_abort (status, "Once init");
    status = pthread_mutex_lock (&mutex);
    if (status != 0)
        err_abort (status, "Lock mutex");
    printf ("Main has locked the mutex./n");
    status = pthread_mutex_unlock (&mutex);
    if (status != 0)
        err_abort (status, "Unlock mutex");
    status = pthread_join (thread_id, NULL);
    if (status != 0)
        err_abort (status, "Join thread");
    return 0;

}

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