[英]Thread don't terminate their job
I am writing a concurrent C program where I want to wait for all threads to finish in the main()
. 我正在编写一个并发的C程序,我想在其中等待
main()
中的所有线程完成。
Based on this solution , I wrote the following code in main()
: 基于此解决方案 ,我在
main()
编写了以下代码:
// Create threads
pthread_t cid[num_mappers];
int t_iter;
for (t_iter = 0; t_iter < num_mappers; t_iter++){
pthread_create(&(cid[t_iter]), NULL, &map_consumer, NULL);
}
// Wait for all threads to finish
for (t_iter = 0; t_iter < num_mappers; t_iter++){
printf("Joining %d\n", t_iter);
int result = pthread_join(cid[t_iter], NULL);
}
printf("Done mapping.\n");
The function passed into threads is defined as: 传递给线程的函数定义为:
// Consumer function for mapping phase
void *map_consumer(void *arg){
while (1){
pthread_mutex_lock(&g_lock);
if (g_cur >= g_numfull){
// No works to do, just quit
return NULL;
}
// Get the file name
char *filename = g_job_queue[g_cur];
g_cur++;
pthread_mutex_unlock(&g_lock);
// Do the mapping
printf("%s\n", filename);
g_map(filename);
}
}
The threads are all successfully created and executed, but the join loop will never finish if num_mappers
>= 2. 所有线程均已成功创建和执行,但是如果
num_mappers
> = 2,则连接循环将永远不会结束。
You return without unlocking the mutex: 您返回时未解锁互斥锁:
pthread_mutex_lock(&g_lock);
if (g_cur >= g_numfull){
// No works to do, just quit
return NULL; <-- mutex is still locked here
}
// Get the file name
char *filename = g_job_queue[g_cur];
g_cur++;
pthread_mutex_unlock(&g_lock);
So only one thread ever returns and ends - the first one, but since it never unlocks the mutex, the other threads remain blocked. 因此,只有一个线程返回并结束-第一个线程,但是由于它从未解锁互斥锁,因此其他线程仍然处于阻塞状态。
You need something more like 您需要更多类似的东西
pthread_mutex_lock(&g_lock);
if (g_cur >= g_numfull){
// No works to do, just quit
pthread_mutex_unlock(&g_lock);
return NULL;
}
// Get the file name
char *filename = g_job_queue[g_cur];
g_cur++;
pthread_mutex_unlock(&g_lock);
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