Common GCD methods and common GCD Methods

Source: Internet
Author: User

Common GCD methods and common GCD Methods

// 1. Create a main thread (Serial)

Dispatch_async (dispatch_get_main_queue (), ^ {

// Refresh the interface code

});

// 2. Create an asynchronous thread (parallel)

Dispatch_async (dispatch_get_global_queue (DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^ {

// Put the time-consuming code here

});

// 3. gcd latency

Double delayInSeconds = 1.0;

Dispatch_time_t popTime = dispatch_time (DISPATCH_TIME_NOW, delayInSeconds * NSEC_PER_SEC );

Dispatch_after (popTime, dispatch_get_main_queue (), ^ (void ){

// Delay code

});

// 4. gcd is executed only once

Static dispatch_once_t onceToken;

Dispatch_once (& onceToken, ^ {

// Execute the Code only once

});

// 5. There are three tasks. The first two tasks need to be executed asynchronously and concurrently. The first two tasks are executed before the third task is executed.

Dispatch_async (dispatch_get_global_queue (DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^ {

// Create a group

Dispatch_group_t group = dispatch_group_create ();

// Associate a task with a group

Dispatch_group_async (group, dispatch_get_global_queue (DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^ {

// Task 1

NSLog (@ "******** execute Task 1 ******");

});

// Associate a task with a group

Dispatch_group_async (group, dispatch_get_global_queue (DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^ {

// Task 2

NSLog (@ "******** execute Task 2 ******");

});

// Wait until the tasks in the group are completed and return to the main thread for block callback.

Dispatch_group_policy (group, dispatch_get_main_queue (), ^ {

// Task 3

NSLog (@ "******* wait for the tasks in the group to be completed, return to the main thread to execute block callback, and execute Task 3 ******");

});

});

 

// 6. When dispatch_barrier_async is used, dispatch_barrier_async is executed only after the previous task is executed, and the subsequent task will be executed only after it is executed.

Dispatch_queue_t queue = dispatch_queue_create ("create_asy_queue", DISPATCH_QUEUE_CONCURRENT );

Dispatch_async (queue, ^ {

NSLog (@ "dispatch_async1 ");

});

Dispatch_async (queue, ^ {

NSLog (@ "dispatch_async2 ");

});

Dispatch_barrier_async (queue, ^ {

NSLog (@ "dispatch_barrier_async ");

Dispatch_async (dispatch_get_main_queue (), ^ {

NSLog (@ "Refresh interface ");

});

});

Dispatch_async (queue, ^ {

[NSThread sleepForTimeInterval: 1];

NSLog (@ "dispatch_async3 ");

});

/* 7. Another use of GCD is to allow programs to run on the background for a long time.

When GCD is not used, when the app is exited by pressing the home key, the app only needs 5 seconds to save or clear resources. However, after using GCD, the app can run for up to 10 minutes in the background for a long time. This time can be used to clear the local cache and send statistics.

The sample code for long-running programs in the background is as follows:

*/

// AppDelegate. h file

@ Property (assign, nonatomic) UIBackgroundTaskIdentifier backgroundUpdateTask;

// AppDelegate. m file

-(Void) applicationDidEnterBackground :( UIApplication *) application

{

[Self beingBackgroundUpdateTask];

// Add the code you need to run for a long time

[Self endBackgroundUpdateTask];

}

-(Void) beingBackgroundUpdateTask

{

Self. backgroundUpdateTask = [[UIApplication sharedApplication] beginBackgroundTaskWithExpirationHandler: ^ {

[Self endBackgroundUpdateTask];

}];

}

-(Void) endBackgroundUpdateTask

{

[[UIApplication sharedApplication] endBackgroundTask: self. backgroundUpdateTask];

Self. backgroundUpdateTask = UIBackgroundTaskInvalid;

}

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