dispatch_sync vs. dispatch_async on main queue

Question

Bear with me, this is going to take some explaining. I have a function that looks like the one below.

Context: \"aProject\" is a Core Data entity named LPProject with an

Answer 1

I think it is more easy to understand with diagram:

For the situation the author described:

|taskQ| ***********start|

|dispatch_1 ***********|---------

|dispatch_2 *************|---------

.

|dispatch_n ***************************|----------

|main queue(sync)|**start to dispatch to main|

*************************|--dispatch_1--|--dispatch_2--|--dispatch3--|*****************************|--dispatch_n|,

which make the sync main queue so busy that finally fail the task.