c - C 中的生产者消费者程序 - 段错误(核心转储)

Question

嗨，我对 C 编程有点陌生。面临生产者消费者问题。当我尝试运行下面的代码时，我会遇到段错误(核心转储)。请建议我哪里出错了。但这段代码适用于一个消费者，但对于多个消费者，它会抛出错误。

代码:

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

#define MAXNITEMS       20
#define MAXNTHREADS     5
void *produce(void *arg);
void *consume(void *arg);
/* globals shared by threads */
int     nitems=MAXNITEMS;     /* read-only by producer and consumer */
int     buff[MAXNITEMS];
int     Nsignals;

struct {
    pthread_mutex_t       mutex;
    int buff[MAXNITEMS];
    int       nput;   /* next index to store */
    int       nval;   /* next value to store */
} put = { PTHREAD_MUTEX_INITIALIZER }; 
/** struct put is used by producer only ***/
struct{
    pthread_mutex_t    mutex;
    pthread_cond_t     cond;
    int                 nready;  /* number ready for consumer */
} nready = {PTHREAD_MUTEX_INITIALIZER,PTHREAD_COND_INITIALIZER,0};

int main(int argc, char **argv)
{
    int       i, prod, con;
    pthread_t tid_produce[MAXNTHREADS],  tid_consume[MAXNTHREADS];
    printf("Enter the number of producers : \n");
    scanf("%d",&prod);
    printf("Enter the number of consumers: \n");
    scanf("%d",&con);
    /* create all producers and consumers */
    for (i = 0; i < prod; i++) 
    {
        printf("1 %d\n", i);
        pthread_create(&tid_produce[i], NULL,produce, NULL);
    }
    for (i = 0; i < con; i++) {
        printf("2 %d\n", i);
        pthread_create(&tid_consume[i], NULL, consume, NULL);
    }
    for (i = 0; i < prod; i++) {
        printf("3 %d\n", i);
        pthread_join(tid_produce[i], NULL);
    }
    for (i = 0; i < con; i++) {
        printf("4 %d\n", i);
        pthread_join(tid_consume[i], NULL);
    }
    exit(0);
}

void *produce(void *arg)
{
    for ( ; ; ) 
    {
        pthread_mutex_lock(&put.mutex);
        if (put.nput >= nitems) {
            pthread_mutex_unlock(&put.mutex);
            return(NULL); /* array is full, we're done */
        }
        put.buff[put.nput] = put.nval;
        printf ("producer %lu produced :%d \n",pthread_self(), put.buff[put.nput]);
        put.nput++;
        put.nval++;
        printf("outside producer lock\n");
        pthread_mutex_unlock(&put.mutex);
        *((int *) arg) += 1;
    }
}

void *consume(void *arg)
{
    int       i;
    for (i = 0; i < nitems; i++) {
        pthread_mutex_lock(&nready.mutex);
        while (nready.nready == 0){
            pthread_cond_wait(&nready.cond,&nready.mutex);
        }
        printf ("consumer %lu consumed %d \n", pthread_self(),nready.nready);
        nready.nready--;
        pthread_mutex_unlock(&nready.mutex);

        if (buff[i] != i)
            printf("buff[%d] = %d\n", i, buff[i]);
    }
    return(NULL);
}

Answer 1

product(...) 内的

*((int *) arg) += 1 会导致段错误。因为 pthread_create(&tid_ Produce[i], NULL,product, NULL); 将 NULL 作为 arg 传递。

所以我们需要为arg分配一些内存。

// main
int i, prod, con;
pthread_t tid_produce[MAXNTHREADS],  tid_consume[MAXNTHREADS];
int p_arg[MAXNTHREADS]; // <======
// ...
for (i = 0; i < prod; i++)
{
    pthread_create(&tid_produce[i], NULL,produce, p_arg+i); // <====
}