Question

I noticed that they don’t return pointers when created, but actual objects. So to get a pointer, I’m trying to declare it like this:

dispatch_queue_t* queue;
*queue = dispatch_queue_create("double_buffer_protection_queue", DISPATCH_QUEUE_SERIAL);

The C++ programmer in me says that should work, but it gives a BAD_ACCESS error, so I’m guessing I’m approaching this the wrong way.

If I want a serial queue that can be accessed by any object in my program, how do I do it? The code I showed above was meant to go in the AppDelegate class.

Answer 1

In Grand Central Dispatch, using actual objects is proper way. For instance,

class Manager
{
    Manager()
    {
        m_queue = dispatch_queue_create("double_buffer_protection_queue", DISPATCH_QUEUE_SERIAL);

        m_worker = new Worker(m_queue);
    }

    ~Manager()
    {
        dispatch_release(m_queue);
        delete m_worker;
    }

    dispatch_queue_t m_queue;
    Worker *m_worker;
}

And then the another owner of the queue must retain and release it by itself like Objective-C objects.

class Worker
{
    Worker(dispatch_queue_t queue)
    // Worker(dispatch_queue_t &queue) /* reference might be ok. */
    {
        m_queue = queue;
        dispatch_retain(m_queue);
    }

    ~Worker()
    {
        dispatch_release(m_queue);
    }

    dispatch_queue_t m_queue;
}