How to function dispatch_group? - objective-c

Question

I am using dispatch_group in my code, but it's functionality not cleared to me.
I have used below code:
1.dispatch_group_t group = dispatch_group_create();
2.dispatch_group_enter(group);
3.[self exportVideoAsset:avAsset withRange:CMTimeRangeMake(start1, duration1) inGCDGroup:group];
4.dispatch_group_enter(group);
5.[self exportVideoAsset:avAsset withRange:CMTimeRangeMake(start2, duration2) inGCDGroup:group];
Here 2 and 4 line execute first and then execute exportVideoAsset function in line 3 and 5. But here in 3 and 5 line, function exportVideoAsset is execute without no sequential order. But I want exportVideoAsset function in line 3 will always execute first, then execute line 5.

Answer 1

You can try this it always call block1 first then after call block2.
Working fine on Xcode 11, iOS13
dispatch_group_t group = dispatch_group_create();
dispatch_group_async(group,dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^ {
// block1
NSLog(#"Block1");
});
[NSThread sleepForTimeInterval:1.0];
dispatch_group_async(group,dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^ {
// block2
NSLog(#"Block2");
});
or
dispatch_group_t group = dispatch_group_create();
dispatch_group_enter(group);
// Task is completed, so signal that it has finished
NSLog(#"Block1");
dispatch_group_leave(group);
// Make the second task wait until group1 has completed before running
dispatch_group_enter(group);
// Task is completed, so signal that it has finished
NSLog(#"Block2");
dispatch_group_leave(group);