Linux相互排斥与同步应用（三）：posix线程实现单个生产者和单个消费者模型

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在第一节说到了生产者消费者问题，这一节我们来实现这样一个稍作改动的模型： 初始时缓冲区为空。生产者向缓冲区写入数据。消费者在缓冲区为空的情况下睡眠，当生产者写满缓冲区一半之后后通知消费者能够開始消费。生产者開始睡眠。直到消费者消费完缓冲区一半后通知生产者能够開始生产为止，当中生产者和消费者对缓冲区的訪问时相互排斥的。

以下来看一下实现：

#include <stdio.h>
#include <pthread.h>
#include <unistd.h>

#define MAX_BUFFER 6

int buffer = 0;

pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER;
pthread_cond_t cond_consumer = PTHREAD_COND_INITIALIZER;
pthread_cond_t cond_productor = PTHREAD_COND_INITIALIZER;

void *consumer_th(void *arg)
{

    for (;;) {
        pthread_mutex_lock(&mutex);

        if (buffer <= 0) {
            printf("=%s->%d=====consumer wait productor to product, start sleep..., buffer=%d\n", __func__, __LINE__, buffer);
            pthread_cond_wait(&cond_consumer, &mutex);//当消费者发现缓冲区为空时開始睡眠
        }

        buffer--; //消费者消耗一个缓冲区
        printf("=%s->%d====consumer consume a buffer, buffer=%d\n", __func__, __LINE__, buffer);
        if (buffer < MAX_BUFFER/2) {
            pthread_cond_signal(&cond_productor); //当消费者发现缓冲区不足一半时通知生产者開始生产
            printf("=%s->%d====Notify productor...,, buffer: %d\n", __func__, __LINE__, buffer);
        }

        pthread_mutex_unlock(&mutex);

        sleep(3);
    }

    return NULL;
}

void *productor_th(void *arg)
{

    for (;;) {
        sleep(1);

        pthread_mutex_lock(&mutex);

        if (buffer >= MAX_BUFFER) {
            printf("=%s->%d=====productor wait consumer to consume, start sleep..., buffer=%d\n", __func__, __LINE__, buffer);
            pthread_cond_wait(&cond_productor, &mutex);//当缓冲区满时。暂停生产
        }

        buffer++;//生产者添加一个缓冲区
        printf("=%s->%d====Product add a buffer..., buffer: %d\n", __func__, __LINE__, buffer);

        if (buffer > MAX_BUFFER/2) {
            pthread_cond_signal(&cond_consumer);//当缓冲区添加到一半时，通知消费者能够開始消费
            printf("=%s->%d====Notify consumer...,, buffer: %d\n", __func__, __LINE__, buffer);
        }

        pthread_mutex_unlock(&mutex);
    }
    return NULL;
}

int main(int argc, const char *argv[])
{
    pthread_t tid_productor, tid_consumer;

    if (0 != pthread_create(&tid_consumer, NULL, consumer_th, NULL)) {
        printf("pthread_create failed!\n");
        return -1;
    }

    if (0 != pthread_create(&tid_productor, NULL, productor_th, NULL)) {
        printf("pthread_create failed!\n");
        return -1;
    }

    pthread_join(tid_productor, NULL);
    pthread_join(tid_consumer, NULL);

    return 0;
}

以下是程序执行输出结果：

=consumer_th->20=====consumer wait productor to product, start sleep..., buffer=0//消费者開始睡眠等待生产者唤醒
=productor_th->54====Product add a buffer..., buffer: 1
=productor_th->54====Product add a buffer..., buffer: 2
=productor_th->54====Product add a buffer..., buffer: 3
=productor_th->54====Product add a buffer..., buffer: 4//生产者開始写缓冲区，当写到第4（超过一半）个通知消费者
=productor_th->58====Notify consumer...,, buffer: 4
=consumer_th->25====consumer consume a buffer, buffer=3//消费者一边消费缓冲区
=productor_th->54====Product add a buffer..., buffer: 4//生产者一边生产缓冲区
=productor_th->58====Notify consumer...,, buffer: 4
=productor_th->54====Product add a buffer..., buffer: 5
=productor_th->58====Notify consumer...,, buffer: 5
=consumer_th->25====consumer consume a buffer, buffer=4
=productor_th->54====Product add a buffer..., buffer: 5
=productor_th->58====Notify consumer...,, buffer: 5
=productor_th->54====Product add a buffer..., buffer: 6
=productor_th->58====Notify consumer...,, buffer: 6
=productor_th->49=====productor wait consumer to consume, start sleep..., buffer=6//当生产者生产缓冲区满时，開始睡眠
=consumer_th->25====consumer consume a buffer, buffer=5
=consumer_th->25====consumer consume a buffer, buffer=4
=consumer_th->25====consumer consume a buffer, buffer=3
=consumer_th->25====consumer consume a buffer, buffer=2//当消费者消费缓冲区到不足一半时。唤醒生产者開始生产
=consumer_th->28====Notify productor...,, buffer: 2
=productor_th->54====Product add a buffer..., buffer: 3
=productor_th->54====Product add a buffer..., buffer: 4
=productor_th->58====Notify consumer...,, buffer: 4
=productor_th->54====Product add a buffer..., buffer: 5
=productor_th->58====Notify consumer...,, buffer: 5
=consumer_th->25====consumer consume a buffer, buffer=4
=productor_th->54====Product add a buffer..., buffer: 5
=productor_th->58====Notify consumer...,, buffer: 5
=productor_th->54====Product add a buffer..., buffer: 6
=productor_th->58====Notify consumer...,, buffer: 6
=productor_th->49=====productor wait consumer to consume, start sleep..., buffer=6

本节源代码下载：

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