When using GCD, we want to wait until two async blocks are executed and done before moving on to the next steps of execution. What is the best way to do that?
We tried the following, but it doesn't seem to work:
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0), ^ {
// block1
});
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0), ^ {
// block2
});
// wait until both the block1 and block2 are done before start block3
// how to do that?
dispatch_sync(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0), ^ {
// block3
});
Best Answer
Use dispatch groups: see here for an example, "Waiting on Groups of Queued Tasks" in the "Dispatch Queues" chapter of Apple's iOS Developer Library's Concurrency Programming Guide
Your example could look something like this:
and could produce output like this: