c，创建线程和线程function

Question

I created dispatch_queue_thread_t struct in the headerfile.
This code assign the thread, task and queue to the dThread struct

dispatch_queue_thread_t *dThread;
dThread = (dispatch_queue_thread_t *) malloc(sizeof(dispatch_queue_thread_t));

pthread_t dispatcher_thread;

if(pthread_create(&dispatcher_thread, NULL, dispatcher_threadloop, (void *)dispatch_queue)){
        perror("ERROR creating thread."); exit(EXIT_FAILURE);
}

dThread->task=NULL;
dThread->queue=dispatch_queue;
dThread->thread=dispatcher_thread;

This code is the thread functions for dispatcher_thread.
I need to use thread in dThread to check if there is any task is assigned to it and if not need to assign the task to it.
How do I do that? Is my code correct?

  void *dispatcher_threadloop(void * queue){

//thread loop of the dispatch thread- pass the tast to one of worker thread
dispatch_queue_t *dQueue;
dQueue=queue;

//can I do this?
dispatch_queue_thread_t *dThread;

printf("message-boss1");
dQueue = (dispatch_queue_t *)queue;
if (dQueue->HEAD!=NULL){
    for(;;){
        sem_wait(dQueue->queue_task_semaphore);
        dThread->task = dQueue->HEAD;
        dQueue->HEAD =  dQueue->HEAD->next;
        dQueue->HEAD->prev = NULL;
        sem_post(dQueue->queue_task_semaphore);

        //TODO
    }
}

printf("message-boss2");

}

Answer 1

No. The dThread variable in dispatcher_threadloop() isn't initialised, so it's an error to dereference it.

It seems like you should be passing dThread to the thread function instead of dispatchQueue , as the thread function can obtain the latter from the former. Something like this (note that casting to and from void * is unnecessary):

dispatch_queue_thread_t *dThread;
dThread = malloc(sizeof *dThread);

dThread->task = NULL;
dThread->queue = dispatch_queue;

if (pthread_create(&dThread->thread, NULL, dispatcher_threadloop, dThread)) {
    perror("ERROR creating thread.");
    exit(EXIT_FAILURE);
}

then in the thread function:

void *dispatcher_threadloop(void *arg)
{
    dispatch_queue_thread_t *dThread = arg;
    dispatch_queue_t *dQueue = dThread->queue;

    /* ... */