Get current dispatch queue?

Question

I have a method which should support being called from any queue, and should expect to.

It runs some code in a background thread itself, and then uses dispatch

Answer 1

There is actually still a way to compare the queue.

When you set up your queue, make sure that you add the label. For my purposes, I have a shared queue that is used for accessing a database to prevent database locking. In my DB.m file I have defined the shared queue function like:

const char *kTransactionQueueLabel = "DB_TRANSACTION_DISPATCH_QUEUE";

+ (dispatch_queue_t)sharedDBTransactionQueue {
    static dispatch_queue_t sharedDBQueue = nil;
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        sharedDBQueue = dispatch_queue_create(kTransactionQueueLabel, DISPATCH_QUEUE_SERIAL);
    });

    return sharedDBQueue;
}

The shared db transaction queue is used locally in the file to dispatch all executions to the database. However, there is also a public accessor on this to allow dispatching entire transactions to the database. So internally, if a DB access method is called from within the transaction queue, we need to dispatch internally on a different queue (all synchronous dispatches). So internally, I always dispatch on the proper queue by using the below getter.

/**
 * @description Decide which queue to use - if we are already in a transaction, use the internal access queue, otherwise use the shared transaction queue.
 */
- (dispatch_queue_t)getProperQueueForExecution {
    const char *currentLabel = dispatch_queue_get_label(DISPATCH_CURRENT_QUEUE_LABEL);
    dispatch_queue_t sharedAccessQueue = [DB sharedDBTransactionQueue];
    if (strcmp(currentLabel, kTransactionQueueLabel) == 0) {
        sharedAccessQueue = [DB sharedInternalDBAccessQueue];
    }

    return sharedAccessQueue;
}

Hopefully this helps. Sorry for the long example. The Gist of it is that you can use

const char *currentLabel = dispatch_queue_get_label(DISPATCH_CURRENT_QUEUE_LABEL);

to get the label of the current queue and compare to a defined label.