信号量的互斥同步都是通过PV原语来操作的，我们可以通过注册两个信号量，让它们在互斥的问题上互动，从而达到同步。通过下面实例就可以很容易理解：
#include <stdlib.h> #include <stdio.h> #include <unistd.h> #include <pthread.h> #include <semaphore.h> #include <errno.h> #define return_if_fail(p) if((p) == 0){printf ("[%s]:func error!/n", __func__);return;} typedef struct _PrivInfo { sem_t s1; sem_t s2; time_t end_time; }PrivInfo; static void info_init (PrivInfo* thiz); static void info_destroy (PrivInfo* thiz); static void* pthread_func_1 (PrivInfo* thiz); static void* pthread_func_2 (PrivInfo* thiz); int main (int argc, char** argv) { pthread_t pt_1 = 0; pthread_t pt_2 = 0; int ret = 0; PrivInfo* thiz = NULL; thiz = (PrivInfo* )malloc (sizeof (PrivInfo)); if (thiz == NULL) { printf ("[%s]: Failed to malloc priv.\n"); return -1; } info_init (thiz); ret = pthread_create (&pt_1, NULL, (void*)pthread_func_1, thiz); if (ret != 0) { perror ("pthread_1_create:"); } ret = pthread_create (&pt_2, NULL, (void*)pthread_func_2, thiz); if (ret != 0) { perror ("pthread_2_create:"); } pthread_join (pt_1, NULL); pthread_join (pt_2, NULL); info_destroy (thiz); return 0; } static void info_init (PrivInfo* thiz) { return_if_fail (thiz != NULL); thiz->end_time = time(NULL) + 10; sem_init (&thiz->s1, 0, 1); sem_init (&thiz->s2, 0, 0); return; } static void info_destroy (PrivInfo* thiz) { return_if_fail (thiz != NULL); sem_destroy (&thiz->s1); sem_destroy (&thiz->s2); free (thiz); thiz = NULL; return; } static void* pthread_func_1 (PrivInfo* thiz) { return_if_fail (thiz != NULL); while (time(NULL) < thiz->end_time) { sem_wait (&thiz->s2); printf ("pthread1: pthread1 get the lock.\n"); sem_post (&thiz->s1); printf ("pthread1: pthread1 unlock\n"); sleep (1); } return; } static void* pthread_func_2 (PrivInfo* thiz) { return_if_fail (thiz != NULL); while (time (NULL) < thiz->end_time) { sem_wait (&thiz->s1); printf ("pthread2: pthread2 get the unlock.\n"); sem_post (&thiz->s2); printf ("pthread2: pthread2 unlock.\n"); sleep (1); } return; }
pthread2: pthread2 get the unlock.pthread2: pthread2 unlock.pthread1: pthread1 get the lock.pthread1: pthread1 unlockpthread2: pthread2 get the unlock.pthread2: pthread2 unlock.pthread1: pthread1 get the lock.pthread1: pthread1 unlockpthread2: pthread2 get the unlock.pthread2: pthread2 unlock.pthread1: pthread1 get the lock.pthread1: pthread1 unlockpthread2: pthread2 get the unlock.pthread2: pthread2 unlock.pthread1: pthread1 get the lock.pthread1: pthread1 unlockpthread2: pthread2 get the unlock.pthread2: pthread2 unlock.pthread1: pthread1 get the lock.pthread1: pthread1 unlockpthread2: pthread2 get the unlock.pthread2: pthread2 unlock.pthread1: pthread1 get the lock.pthread1: pthread1 unlockpthread2: pthread2 get the unlock.pthread2: pthread2 unlock.pthread1: pthread1 get the lock.pthread1: pthread1 unlockpthread2: pthread2 get the unlock.pthread2: pthread2 unlock.pthread1: pthread1 get the lock.pthread1: pthread1 unlockpthread2: pthread2 get the unlock.pthread2: pthread2 unlock.pthread1: pthread1 get the lock.pthread1: pthread1 unlockpthread2: pthread2 get the unlock.pthread2: pthread2 unlock.pthread1: pthread1 get the lock.pthread1: pthread1 unlock
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风景如何，其实并不重要。重要的是，你在我的身边。
