GCD Common operations

GCD multithreaded Operations

1) The most used operation

Get Global Queue

dispatch_queue_t queue = Dispatch_get_global_queue (Dispatch_queue_priority_default, 0);

Asynchronous execution

Dispatch_async (Queue, ^{

Download image

Dispatch_async (Dispatch_get_main_queue (), ^{

Back to the main thread update UI

});

});

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2) Delay execution 1-call nsobject method [self performselector: @seletor (Run) Withobject:nil afterdelay:2.0];2-gcd (better, without regenerating method)

Dispatch_after (Dispatch_time (Dispatch_time_now, (int64_t) (2.0 * nsec_per_sec)), Dispatch_get_main_queue (), ^{

NSLog (@ "2222");

});

3) Guarantee method is executed only once throughout the program

Static dispatch_once_t Oncetoken;

Dispatch_once (&oncetoken, ^{

});

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4) Group operations, multiple requests, request completion, and operation

Create a group,

dispatch_group_t group = Dispatch_group_create ();

Open a task download image 1

__block UIImage *image1 = nil;

Dispatch_group_async (Group, Dispatch_get_global_queue (Dispatch_queue_priority_default, 0), ^{

Image1 = [];

});

__block UIImage *image2 = nil;

Dispatch_group_async (Group, Dispatch_get_global_queue (Dispatch_queue_priority_default, 0), ^{

Image2 = [];

});

Dispatch_group_notify (Group, Dispatch_get_main_queue (), ^{

Image1

Image2

});

GCD Common operations