[英]Segmentation fault in reader-writer appilication using posix semaphore in c
在此代碼中,寫入器遞增數據變量,而讀取器打印此數據變量。 任何時候只有一個寫入器可以寫入,但是當寫入器不在數據上寫入時,所有讀取器都可以打印數據。
附加的代碼有時會成功運行,但有時會給出分段錯誤錯誤。
#include<stdio.h>
#include<pthread.h>
#include<semaphore.h>
#include<stdlib.h>
#include<unistd.h>
int reader_count;
int data = 10; /* data on which writer write update & reader read */
/* sem_write: to isolate reader & writer thread */
sem_t sem_write;
/* sem_read: to increment reader counter & sem_write */
sem_t sem_read;
void *writer(void *arg);
void *reader(void *arg);
int main(void)
{
pthread_t t[10];
int i = 10;
if (sem_init(&sem_read, 0, 1))
exit(1);
if (sem_init(&sem_write, 0, 1))
exit(1);
/* 5 writer create */
while (i != 5)
pthread_create(&t[i--], NULL, writer, NULL);
/* 5 reader create */
while (i)
pthread_create(&t[i--], NULL, reader, NULL);
/* wait for all threads to completed */
while (i != 10)
pthread_join(t[i++], NULL);
sem_destroy(&sem_read);
sem_destroy(&sem_write);
return 0;
}
void *writer(void *arg)
{
sem_wait(&sem_write);
sleep(1); /* writing work */
data++;
sem_post(&sem_write);
pthread_exit(NULL);
}
void *reader(void *arg)
{
sem_wait(&sem_read);
reader_count++;
if (reader_count == 1)
sem_wait(&sem_write);
sem_post(&sem_read);
sleep(1); /* reading work */
printf("Data: %d\n", data);
sem_wait(&sem_read);
reader_count--;
if (!reader_count)
sem_post(&sem_write);
sem_post(&sem_read);
pthread_exit(NULL);
}
您訪問t[10]
越界
int i = 10;
....
while (i != 5)
pthread_create(&t[i--], NULL, writer, NULL);
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