linux多线程学习(六)——信号量实现同步。

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 unlock
pthread2: pthread2 get the unlock.
pthread2: pthread2 unlock.
pthread1: pthread1 get the lock.
pthread1: pthread1 unlock
pthread2: pthread2 get the unlock.
pthread2: pthread2 unlock.
pthread1: pthread1 get the lock.
pthread1: pthread1 unlock
pthread2: pthread2 get the unlock.
pthread2: pthread2 unlock.
pthread1: pthread1 get the lock.
pthread1: pthread1 unlock
pthread2: pthread2 get the unlock.
pthread2: pthread2 unlock.
pthread1: pthread1 get the lock.
pthread1: pthread1 unlock
pthread2: pthread2 get the unlock.
pthread2: pthread2 unlock.
pthread1: pthread1 get the lock.
pthread1: pthread1 unlock
pthread2: pthread2 get the unlock.
pthread2: pthread2 unlock.
pthread1: pthread1 get the lock.
pthread1: pthread1 unlock
pthread2: pthread2 get the unlock.
pthread2: pthread2 unlock.
pthread1: pthread1 get the lock.
pthread1: pthread1 unlock
pthread2: pthread2 get the unlock.
pthread2: pthread2 unlock.
pthread1: pthread1 get the lock.
pthread1: pthread1 unlock
pthread2: pthread2 get the unlock.
pthread2: pthread2 unlock.
pthread1: pthread1 get the lock.
pthread1: pthread1 unlock

通过执行结果后，可以看出，会先执行线程二的函数，然后再执行线程一的函数。它们两就实现了同步。在上大学的时候，虽然对这些概念知道，可都没有实践过，所以有时候时间一久就会模糊甚至忘记，到了工作如果还保持这么一种状态，那就太可怕了。虽然现在外面的技术在不断的变化更新，可是不管怎么变，其核心技术还是依旧的，所以我们必须要打好自己的基础，再学习其他新的知识，那时候再学新的知识也会觉得比较简单的。闲话多说了两句，在下一篇文章中，我们将会实现一个经典的实例回顾这段时间对多线程的学习，那就是消费者和生产者。

~~END~~

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