生产者与消费者问题(Linux 下 C 语言实现)(一)

reader_writer1.c:

#include <stdio.h>
#include <pthread.h>
#include <unistd.h>
#include <semaphore.h>
#include <stdlib.h>
#include <sys/types.h>
#include <signal.h>
#include <errno.h>

#define SIZE 1000        // the size of the buffer
#define SECS 10            // the time to run

pthread_mutex_t mut = PTHREAD_MUTEX_INITIALIZER;
sem_t sem_empty, sem_full;

long buffer[SIZE] = {0};

// record the times to meet lock
int read_lock_times = 0;
int write_lock_times = 0;

// record the times of reading or writing
int read_num = 0;
int write_num = 0;

// signal handler
void sig_handler(int sig_num)
{
    printf("Meet %d read locks\n", read_lock_times);
    printf("Meet %d write locks\n", write_lock_times);
    printf("Read %d numbers\n", read_num);
    printf("Write %d numbers\n", write_num);

    exit(0);
}

void * read_thread(void * args)
{
    while(1)
    {

        sem_wait(&sem_empty);

        if( pthread_mutex_trylock(&mut) == EBUSY)
        {
            ++ read_lock_times;

            pthread_mutex_lock(&mut);
        }

        ++ read_num;

        pthread_mutex_unlock(&mut);

        sem_post(&sem_full);
    }
}

void * write_thread(void * args)
{
    while(1)
    {

        sem_wait(&sem_full);

        if( pthread_mutex_trylock(&mut) == EBUSY)
        {
            ++ write_lock_times;

            pthread_mutex_lock(&mut);
        }

        buffer[write_num%SIZE] = write_num;
        ++write_num;

        pthread_mutex_unlock(&mut);

        sem_post(&sem_empty);
    }
}

int main()
{
    // install the signal handler
    struct sigaction action;
    action.sa_handler = sig_handler;
    sigaction(SIGALRM, &action, NULL);

    alarm(SECS);

    sem_init(&sem_empty, 0, 0);
    sem_init(&sem_full, 0, SIZE);

    pthread_t tid1, tid2;
    pthread_create(&tid1, NULL, read_thread, NULL);
    pthread_create(&tid2, NULL, write_thread, NULL);

    pthread_join(tid1, NULL);
    pthread_join(tid2, NULL);

    sem_destroy(&sem_empty);
    sem_destroy(&sem_full);

    pthread_mutex_destroy(&mut);

    return 0;
}

背景无需多说。

 

上述代码假定缓冲池容量固定，大小由 SIZE 控制。

 

在 SECS 秒后，会输出 读线程、写线程 遇到的锁的个数，以及 读写的数目。

 

以下是上面程序的输出：

 

/home/adamas:~$ time ./read_writer1

 

Meet 1 read locks
Meet 0 write locks
Read 1137205 numbers
Write 1137794 numbers

 

real 0m10.017s
user 0m4.252s
sys 0m5.640s

显然，这里的输出数目与 SIZE 密切相关，并不是越大越好，SIZE 定义为 10,000，反而不如定义为 1,000 快。

 

下一篇中谈谈使用 C++ 中的 vector 来代替本文中的 固定容量数组。