linux多线程学习（七）——实现“生产者和消费者”

在上一篇文章中，利用信号量实现了线程间的互斥，这一篇将要利用信号量的互斥同步机制来实现一个经典实例，就是“生产者和消费者”。

1、简单描述生产者和消费者的问题。

有一个缓冲区和两个线程：生产者和消费者。生产者把产品放入缓冲区，而消费者从缓冲区中拿走。当缓冲区满时，生产者必须等待；另外，当缓冲区空时，消费者必须等待，并且缓冲区不能同时进行生产者和消费者的操作。

#include
#include
#include
#include
#include
#include
#include

#define FIFO "my_fifo"
#define N    10
#define return_if_fail(p) if((p) == 0){printf ("[%s]:func error!/n", __func__);return;}

typedef struct _PrivInfo
{
  sem_t avail;
  sem_t full;
  sem_t mutex;
  char  buf_r[255];
  time_t end_time;
  int fd;
}PrivInfo;

static void info_init (PrivInfo* thiz);
static void info_destroy (PrivInfo* thiz);
static void* productor (PrivInfo* thiz);
static void* consumer (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 PrivInfo./n", __func__);
    return -1;
  }

  info_init (thiz);

  ret = pthread_create (&pt_1, NULL, (void*)productor, thiz);
  if (ret != 0)
  {
    perror ("pthread_1_create:");
  }

  ret = pthread_create (&pt_2, NULL, (void*)consumer, thiz);
  if (ret != 0)
  {
    perror ("pthread_2_func:");
  }

  pthread_join (pt_1, NULL);
  pthread_join (pt_2, NULL);

  info_destroy (thiz);
  thiz = NULL;

  return 0;
}

static void info_init (PrivInfo* thiz)
{
  return_if_fail (thiz != NULL);

  thiz->end_time = time(NULL) + 10;

  sem_init (&thiz->avail, 0, N);
  sem_init (&thiz->full, 0, 0);
  sem_init (&thiz->mutex, 0, 1);

  if (mkfifo (FIFO, O_CREAT|O_EXCL) && (errno != EEXIST))
  {
    printf ("cannot create fifo server./n");
  }

  printf ("Prepareing for reading bytes.../n");

  memset (thiz->buf_r, 0, sizeof (thiz->buf_r));

  thiz->fd = open (FIFO, O_RDWR|O_NONBLOCK, 0777);
  if (thiz->fd == -1)
  {
    perror ("open FIFO:");
    info_destroy (thiz);
    exit (1);
  }

  return ;
}

static void info_destroy (PrivInfo* thiz)
{
  return_if_fail (thiz != NULL);

  sem_destroy (&thiz->avail);
  sem_destroy (&thiz->full);
  sem_destroy (&thiz->mutex);

  free (thiz);
  thiz = NULL;

  return;
}

static void* productor (PrivInfo* thiz)
{
  return_if_fail (thiz != NULL);

 int ret = 0;

  while (time (NULL) < thiz->end_time)
  {
    sem_wait (&thiz->avail);
    sem_wait (&thiz->mutex);

    if ((ret = write (thiz->fd, "hello", 5)) == -1)
    {
       if (errno == EAGAIN)
       {
           printf ("The FIFO has not been read, Please try later again./n");
       }
       else
       {
           printf ("write hello to the FIFO./n");
       }
    }

    sem_post (&thiz->full);
    sem_post (&thiz->mutex);

    sleep (1);
  }

  return;
}

static void* consumer (PrivInfo* thiz)
{
   return_if_fail (thiz != NULL);

   int ret = 0;

   while (time (NULL) < thiz->end_time)
  {
     sem_wait (&thiz->full);
     sem_wait (&thiz->mutex);

     if ((ret = read(thiz->fd, thiz->buf_r, 255)) > 0)
     {

        printf ("read %s frm FIFO./n", thiz->buf_r);
      }
      else
      {
        if (errno == EAGAIN)
        {
           printf ("no data yet./n");
        }
      }

      sem_post (&thiz->avail);
      sem_post (&thiz->mutex);

      sleep(1);
  }

  return;
}

从上面的经典例子中，结合了多线程的同时性编程问题。学习线程算是告了一段落，在以后的编程应用中，希望能落实到实践中去，大家一起加油~~