Question

I have a block of code where I am inside a pthread (lets call this thread a), and I wish to spawn a new pthread (lets call this thread b). Thread b needs to be passed a deque and I have the following code:

void* process_thread_b(void* arg)
{              
  deque<string> *ptr = (deque<string>*)arg;
  cout << "Size -" << ptr->size() << endl;

  deque<string>::iterator it;
  for(it = ptr->begin(); it != ptr->end(); it++)
  {
    cout <<(*it) << endl;
  }
}

The above code is thread b's code. It is passed a deque and it prints out the size correctly. The moment I try printing out any of it’s elements, I get:

terminate called after throwing an instance of 'std::bad_alloc'
 what():  std::bad_alloc
Abort (core dumped)

When I am spawning the pthread, I use the below code…

 deque<string> myDeque;

 // Add strings to deque here...

 pthread_t dispatchCommands;
 pthread_create(&dispatchCommands, NULL, &process_thread_b, (void*)&myDeque);

The bottom code takes place in thread a. Why is it when I try to print out an element of the deque, I am getting an error, yet I can get it’s size?

Answer 1

pthread_create will return long before your thread function begins to execute. Your deque will have been destroyed long ago. You need to create it on the heap.