深入Pthread(四)：一次初始化-pthread_once_t

深入Pthread(四)：一次初始化-pthread_once_t

 

用到的API：

pthread_once_t once_control = PTHREAD_ONCE_INIT;

int pthread_once(pthread_once_t* once_control, void (*init_routine)(void));

    

    有些事需要一次且僅需要一次執行。通常當初始化應用程序時，可以比較容易地將其放在main函數中。但當你寫一個庫時，就不能在main裏面初始化了，你可以用靜態初始化，但使用一次初始化（pthread_once_t）會比較容易些。

 

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; 

}