GCD group,

GCD group,

Asynchronous intra-group requests compete for resources with events executed in an out-group order.

1) create a group

Dispatch_group_t group = dispatch_group_create ();

 

2) in-group asynchronous ST1, DISPATCH_QUEUE_PRIORITY_DEFAULT is the default priority.

Dispatch_group_async (group, dispatch_get_global_queue (DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^ {// do something 1 });

 

3) in-group asynchronous ST2, DISPATCH_QUEUE_PRIORITY_DEFAULT is the default priority.

Dispatch_group_async (group, dispatch_get_global_queue (DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^ {// do something 2 });

 

4) group notifications to obtain the main thread. This is the end of all asynchronous operations in the group.

Dispatch_group_policy (group, dispatch_get_main_queue (), ^ {// do something} after all groups are completed });

 

 

5) ST3 outside the group

// Do something 3