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：

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#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; 
}
David++