Advanced usage of IOS thread GCD

A previous article on the thread of the blog has introduced the simple use of gcd and examples, today, because the project has a special application GCD examples, for everyone to introduce two special needs of the use of GCD method.

Objective: to accomplish one thing, and then do the next, to ensure the function execution cycle.

Solution: The following 2 solutions are available

1. Create barrier waiting thread

Dispatch_async (Dispatch_get_main_queue (), ^{
    
[self actionfirst];
   
});

Dispatch_barrier_async (Dispatch_get_main_queue (), ^{
   
[self actionnext];
   
});

2. Create group thread groups (that is, queue queues)

dispatch_group_t group = Dispatch_group_create ();

Dispatch_group_async (Group, Dispatch_get_main_queue (), ^{

[self actionfirst];

});

Dispatch_group_notify (Group, Dispatch_get_main_queue (), ^{

[self actionnext];

});


The code for the problem appears as follows:

-(void) Example

{
[Self actionfirst];

[Self actionnext];
}

cause : When calling the example function, because the Actionfirst function executes longer, Actionfirst may not have finished executing when the Actionnext function finishes executing, Causes a crash when executing actionnext.

Advanced usage of IOS thread GCD