c - C 中使用信号量的多线程生产者和消费者

Question

我在项目运行时遇到问题，希望有人能够提供帮助。指导原则如下:

您将使用pthread 包创建 4 个生产者线程和 4 个消费者线程。每个生产者线程插入将字符“X”放入大小为 10,000,000 个字符的缓冲区中。每个消费者线程都会删除最近插入的来自缓冲区的字符。然后每个线程重复该过程

到目前为止，我的代码如下所示:

#include <stdlib.h>
#include <stdio.h>
#include <unistd.h>
#include <sys/ipc.h>
#include <sys/sem.h>
#include <semaphore.h>
#include <pthread.h>

#define N 10000000

sem_t mutex;
sem_t full;
sem_t empty;

typedef struct
{
    char const* buf[N];
    char in;
    char out;

} bufferItems;

bufferItems sharedBuffer;


void *producer(void *arg) {

    while(1) {
        sem_wait(&empty);
        sem_wait(&mutex);
        sharedBuffer.buf[sharedBuffer.in] = "X";
        sharedBuffer.in = (sharedBuffer.in+1)%N;
        printf("Producer\n");
        sem_post(&mutex);
        sem_post(&full);


    }

}

void *consumer(void *arg){

    while(1){
        sem_wait(&full);
        sem_wait(&mutex);
        sharedBuffer.buf[sharedBuffer.out] = NULL;
        sharedBuffer.out = (sharedBuffer.out+1)%N;
        printf("Consumer\n");
        sem_post(&mutex);
        sem_post(&empty);

    }

}


int main(void) {

    sem_init(&mutex, 0, 0);
    sem_init(&full, 0, 0);
    sem_init(&empty, 0, N);

    pthread_t p;
    pthread_t c;


    // create four producer threads
    for(int t=0; t<4; t++){
        printf("In main: creating producer thread %d\n", t);
        int err = pthread_create(&p,NULL,producer,NULL);
        if (err){
            printf("ERROR from pthread_create() on producer thread %d\n", err);
            exit(-1);
        }
    }


    // create four consumer threads
    for(int t=0; t<4; t++){
        printf("In main: creating consumer thread %d\n", t);
        int err = pthread_create(&c,NULL,consumer,NULL);
        if (err){
            printf("ERROR; from pthread_create() on consumer thread %d\n", err);
            exit(-1);
        }
    }
}

但是我运行它时得到的输出是这样的:

In main: creating producer thread 0
In main: creating producer thread 1
In main: creating producer thread 2
In main: creating producer thread 3
In main: creating consumer thread 0
In main: creating consumer thread 1
In main: creating consumer thread 2
In main: creating consumer thread 3

似乎子线程没有执行，或者信号量没有正常工作，因此出现死锁。任何有关如何使我的代码更好或正常工作的建议将不胜感激。

Answer 1

您需要调用pthread_join创建所有子线程后在主线程中。 pthread_join 等待指定线程终止。否则主线程将退出并过早取出所有子线程。