Synchronous dispatch without deadlocking

admin — Mon, 04 Mar 2013 03:59:52 +0000

Dispatches synchronously without deadlocking if the target thread is the current thread.


static inline void dispatch_sync2(dispatch_queue_t queue, dispatch_block_t block) {
 if (dispatch_get_current_queue() == queue) {
 block();
 } else {
 dispatch_sync(queue, block);
 }
}

Running code on the UI thread

admin — Tue, 26 Feb 2013 13:10:48 +0000

As an iOS developer you’ll get to see this all the time, since you have to be enormously careful when running code that does any UI processing; such code must always run in the main (UI) thread, so when running on a different thread it’s necessary to pass a block of code to be executed by the main thread:

dispatch_async(dispatch_get_main_queue(), ^{

// ... code to execute in main thread ...

});

dispatch_async() will run that code right away, asynchronously – ie, it will not wait to queue the code into the main queue. Use dispatch_sync() if you want to wait until it’s done – but be careful! If you target the current queue, it will result in a deadlock. More information in the official documentation.

A2 Apps » GCD

Synchronous dispatch without deadlocking

Running code on the UI thread