Question regarding implementation about promises

[shoumikhin]

Hi Michael,

There's a section in the docs on how the dispatch group can help with testing. And you can use any dispatch queue, including a concurrent one to run the work block. E.g. see how one is set as a default. Afaik, the dispatch_async API guarantees it always completes before the block argument gets control.

Thanks.

[MikePendo]

Hi @shoumikhin ,
Thanks a lot for your help.
I am not sure what you meant by
Afaik, the dispatch_async API guarantees it always completes before the block argument gets control.

My point was, assuming u have a lot of nested then: following the async:, how u guarantee the work inside the async: wont start its execution before the nested then: have all bee finished and all the promises are ready to run their observers code? (Am I making my question clear? I mean is my concern legit).

Another point (out of curiosity ) u r always using dispatch with groups, what was the the benefit to use groups over just dispatch_async? I mean I dont see see and wait or notify for those groups later on

[MikePendo]

@shoumikhin
Sorry too bothering you but for instance if I have the following test:

- (void)testAsyncDifferentQueues {
    
    dispatch_queue_attr_t attributesPromise = dispatch_queue_attr_make_with_qos_class(DISPATCH_QUEUE_SERIAL,QOS_CLASS_USER_INITIATED,0);
    dispatch_queue_attr_t attributesRunFrom = dispatch_queue_attr_make_with_qos_class(DISPATCH_QUEUE_SERIAL,QOS_CLASS_BACKGROUND,0);
    dispatch_queue_t serialForPromise = dispatch_queue_create("serial.promise", attributesPromise);
    dispatch_queue_t serialRunFrom = dispatch_queue_create("serial.runFrom", attributesRunFrom);
    [FBLPromise setDefaultDispatchQueue:serialForPromise];
    
    dispatch_async(serialRunFrom, ^{
        [[FBLPromise async:^(FBLPromiseFulfillBlock fulfill, FBLPromiseRejectBlock __unused _) {
                  fulfill(@42);
        }] then:^id (id value) {
            NSLog(@"do I come here");
            return nil;
        }];
        NSLog(@"Should finish before then");
    });   
    [[NSRunLoop mainRunLoop] runUntilDate:[NSDate dateWithTimeIntervalSinceNow:1]];
}

What guarantee that "Should finish before then" will be done before "do I come here".
it indeed what happens but I am not sure what guarantee that. dispatch_group_async?