C ++ pthreads和struct的损坏数据

Question

I'm new to pthreads and having a hard time creating a thread with a struct and keeping it's data intact while re-casting it from a void pointer.

I've spent days searching around trying to find a reason for this and haven't had much luck. Out of my two structures (using two different threads) one re-casts correctly in the thread, but for whatever reason, the second doesn't.

Structs:

struct Arguments {
    List linkedList;
    Node node;
    Arguments(){}
    Arguments (List *newList, Node *newNode){
        linkedList = *newList;
        pcb = *newPCB;
    }
};

struct ClockControl {
    int counter = 0;
    pthread_mutex_t lock;
};

Threads:

void *schedule(void *args){

    //Arguments *newArgs = static_cast<Arguments*>(args); <-- Tried this, doesn't work either.
    arguments *newArgs = (arguments *) args;
    List tempList = (newArgs ->linkedList);  //DATA HERE IS CORRUPTED/WRONG
    Node tempNode = (newArgs ->node);  //DATA HERE IS CORRUPTED/WRONG

    cout << "Flagged" << Lendl;

    return NULL;
}

void *clockTime(void *clock){
    //This thread works fine

    clockControl *newClock = (clockControl*) clock;
    int localVariable = 0;

    localVariable = (newClock -> counter);

    pthread_mutex_lock(&(newClock -> lock));
    localVariable++;
    newClock->counter = localVariable;
    pthread_mutex_unlock(&(newClock -> lock));

    return NULL;
}

Main:

int main(int argc, char** argv)
{  
    pthread_t threads[NUM_THREADS];  //Defined as 5

    clockControl clock;
    clock.counter = 0;
    pthread_mutex_init(&clock.lock, NULL);

    //Lists are initialized with variables.    
    List pendingList = initializeList();
    List readyList = initializeList();


    Arguments *args = new Arguments(&readyList, &pendingList.head->info);

    while (clock.counter < 6000){
        pthread_create(&threads[1], NULL, clockTime, (void*) &clock);

        if (clock.counter == pendingList.head->info.timeCreated){

            pthread_create(&threads[0], NULL, schedule, (void*) &args);
                          //INSPECTING args HERE HAS ACCURATE DATA

    }

        //Clean up threads
        for (int i = 0; i < 2; i++){
            pthread_join(threads[i],NULL);
        }
    }
}

Like I said, I've searched around and pretty much spinning my wheels at this point. I have a suspicion it might be that the memory is being freed or cleaned up prior to the thread getting executed, but I can't find a way around it.

Any help would be appreciated.

Answer 1

You are passing the address of the pointer to args to your schedule function. When you use &args , args is already an Arguments* so you are passing an Arguments** . To solve this you can simply pass args by itself to the function.

Also just so you know, reinterpret_cast<Arguments*> is probably more appropriate than static_cast in this circumstance.

Answer 2

These two lines of code should be swapped

localVariable = (newClock -> counter);

pthread_mutex_lock(&(newClock -> lock)); z

ie

pthread_mutex_lock(&(newClock -> lock));
localVariable = (newClock -> counter);

So that localVariable will be the right value when more that one thread is reading the counter and updating it