线程互斥锁及条件变量的使用

程序要求：

  在程序当中，创建两个线程，其中一个为生产者，一个为消费者。同时创建一把互斥锁保证两者不能够同时访问结构体当中buffer，可以把它比作是一个“仓库”。必须要等生产完成之后才可以去采用读取。添加条件变量是与锁综合起来的条件判定。

  具体程序如下：

#include <stdio.h>
#include <stdlib.h>
#include <time.h>
#include "pthread.h"

#define BUFFER_SIZE 2

/* Circular buffer of integers. */
struct prodcons
{
  int buffer[BUFFER_SIZE];      /* the actual data */
  pthread_mutex_t lock;         /* mutex ensuring exclusive access to buffer */
  int readpos, writepos;        /* positions for reading and writing */
  pthread_cond_t notempty;      /* signaled when buffer is not empty */
  pthread_cond_t notfull;       /* signaled when buffer is not full */
};

/* Initialize a buffer */
void init(struct prodcons *prod)
{
  pthread_mutex_init(&prod->lock,NULL);
  pthread_cond_init(&prod->notempty,NULL);
  pthread_cond_init(&prod->notfull,NULL);
  prod->readpos = 0;
  prod->writepos = 0;
}
/* Store an integer in the buffer */
void put(struct prodcons * prod, int data)
{
        pthread_mutex_lock(&prod->lock);
        /* Wait until buffer is not full */
        while ((prod->writepos + 1) % BUFFER_SIZE == prod->readpos)
        {
            printf("producer wait for not full\n");
            pthread_cond_wait(&prod->notfull, &prod->lock);
        }
          /* Write the data and advance write pointer */
        prod->buffer[prod->writepos] = data;
        prod->writepos++;
        if (prod->writepos >= BUFFER_SIZE)
            prod->writepos = 0;
          /*Signal that the buffer is now not empty */
        pthread_cond_signal(&prod->notempty);
        pthread_mutex_unlock(&prod->lock);
}
/* Read and remove an integer from the buffer */
int get(struct prodcons *prod)
{
        int data;
        pthread_mutex_lock(&prod->lock);
        /* Wait until buffer is not empty */
        while (prod->writepos == prod->readpos)
        {
            printf("consumer wait for not empty\n");
            pthread_cond_wait(&prod->notempty, &prod->lock);
        }
        /* Read the data and advance read pointer */
        data = prod->buffer[prod->readpos];
        prod->readpos++;
        if (prod->readpos >= BUFFER_SIZE)
            prod->readpos = 0;
        /* Signal that the buffer is now not full */
        pthread_cond_signal(&prod->notfull);
        pthread_mutex_unlock(&prod->lock);
        return data;
}

#define OVER (-1)
struct prodcons buffer;
/*--------------------------------------------------------*/
void * producer(void * data)
{
    int n;
    for (n = 0; n < 5; n++)
    {
        printf("producer sleep 1 second......\n");
        sleep(1);
        printf("put the %d product\n", n);
        put(&buffer, n);
    }
    for(n=5; n<10; n++)
    {
        printf("producer sleep 3 second......\n");
        sleep(3);
        printf("put the %d product\n",n);
        put(&buffer,n);
    }
    put(&buffer, OVER);
    printf("producer stopped!\n");
    return NULL;
}
/*--------------------------------------------------------*/
void * consumer(void * data)
{
    int d=0;
    while (1)
    {
        printf("consumer sleep 2 second......\n");
        sleep(2);
        d=get(&buffer);
        printf("get the %d product\n", d);
//        d = get(&buffer);
        if (d == OVER ) break;
    }
    printf("consumer stopped!\n");
    return NULL;
}
/*--------------------------------------------------------*/
int main(int argc,char *argv[])
{
    pthread_t th_a, th_b;
    void * retval;
    init(&buffer);
    pthread_create(&th_a, NULL, producer, 0);
    pthread_create(&th_b, NULL, consumer, 0);
    /* Wait until producer and consumer finish. */
    pthread_join(th_a, &retval);
    pthread_join(th_b, &retval);
    return 0;
}