c - 缓慢的 pthread 消费者

Question

我使用 pthreads 和信号量在 C 中实现了生产者/消费者问题的解决方案。

我的主线程是生产者，我启动 N 个消费者线程。

我的代码是:

typedef struct
{
    int buf[BUFSIZE];     /* shared var */
    int in;               /* buf[in%BUFSIZE] is the first empty slot */
    int out;              /* buf[out%BUFSIZE] is the first full slot */
    sem_t full;           /* keep track of the number of full spots */
    sem_t empty;          /* keep track of the number of empty spots */
    pthread_mutex_t mutex;          /* enforce mutual exclusion to shared data */
} CONSUMER_STRUCT;

CONSUMER_STRUCT shared;

这是我的每个消费者线程的代码:

void *Consumer(void *arg)
{
    int fd, workerID, i, hit=0;

    workerID = *(int *)arg;

    for (;;) {
        sem_wait(&shared.full);
        pthread_mutex_lock(&shared.mutex);
        fd = shared.buf[shared.out];
        printf("\n[C%d] Consumed. I got  %d ...Valor do buffer: %d na posição %d\n\n\n", workerID, fd, shared.buf[shared.out], shared.out);
        ftp(fd, hit);
        shared.buf[shared.out] = 0;
        shared.out = (shared.out+1)%BUFSIZE;
        fflush(stdout);
        printf("\n\n\n\nEstado do buffer:\n\n\n\n");
        for (i = 0; i < BUFSIZE; i++) {
            //printf("%d ", shared.buf[i]);
        }
        /* Release the buffer */
        pthread_mutex_unlock(&shared.mutex);
        /* Increment the number of full slots */
        sem_post(&shared.empty);
        hit++;
    }
    return NULL;
}

这是我的生产者线程的代码:

item = socketfd;

sem_wait(&shared.empty);
pthread_mutex_lock(&shared.mutex);

shared.buf[shared.in] = item;

shared.in = (shared.in + 1) % BUFSIZE;
fflush(stdout);

pthread_mutex_unlock(&shared.mutex);
sem_post(&shared.full);

一切正常，但提供 22 个文件大约需要 20 秒，而每个请求创建一个线程大约需要 2 秒!这似乎一次执行一个线程，我想“同时”执行所有线程。

我的实现方法是否做错了什么？

Answer 1

对于那些可能遇到类似问题的人，这里是解决方法。

感谢@Martin James 和@EOF。

void *Consumer(void *arg)
{
    int fd, workerID, i, hit=0;

    workerID = *(int *)arg;

    for (;;) {
        sem_wait(&shared.full);
        pthread_mutex_lock(&shared.mutex);
        fd = shared.buf[shared.out];
        shared.buf[shared.out] = 0;
        shared.out = (shared.out+1)%BUFSIZE;
        pthread_mutex_unlock(&shared.mutex);
        printf("\n[C%d] Consumed. I got  %d ...Valor do buffer: %d na posição %d\n\n\n", workerID, fd, shared.buf[shared.out], shared.out);
        ftp(fd, hit);
        fflush(stdout);
        printf("\n\n\n\nEstado do buffer:\n\n\n\n");
        for (i = 0; i < BUFSIZE; i++) {
            //printf("%d ", shared.buf[i]);
        }
        /* Release the buffer */
        /* Increment the number of full slots */
        sem_post(&shared.empty);
        hit++;
    }
    return NULL;
}

问题是我锁定了互斥锁，执行了一个函数，然后解锁了互斥锁。这就是导致执行延迟如此之多的原因。