"iOS Development-multithreading" using GCD to create multithreading (iOS common technology)

GCD

Full name is Grand Central Dispatch

Characteristics:

1. Multi-core technology for automatic CPU utilization
2. Automatically manage the life cycle of threads

Use steps

1. customizing tasks
2. Add a task to a queue

Features of various types of queues

Two modes of execution for synchronous and asynchronous

   /**     *  同步方式执行任务，不管是什么队列，都不会再开一个线程     */    dispatch_sync(<#dispatch_queue_t queue#>, ^{        <#code#>    })    /**     *  异步方式执行任务，除了主队列都会开启一个新线程     */    dispatch_async(<#dispatch_queue_t queue#>, ^{        <#code#>    })

Create a queue global concurrent queue

//获得全局的并发队列,第一个参数是优先级，一般都是0，第二个参数是预留的，也为0  dispatch_get_global_queue(<#long identifier#>, <#unsigned long flags#>)

Use

   dispatch_queue_t queue =  dispatch_get_global_queue(00);    /**     *  同步方式执行任务     */    dispatch_sync(queue, ^{        NSLog(@"%@", NSThread.currentThread);//{number = 1, name = main}    });    /**     *  异步方式执行任务     */    dispatch_async(queue, ^{         NSLog(@"%@", NSThread.currentThread);//{number = 2, name = (null)}    });

Serial queue

//第一个参数是队列的名字，第二个参数为nildispatch_queue_create(<#constchar *label#>, <#dispatch_queue_attr_t attr#>)

dispatch_queue_t queue = dispatch_queue_create("ttf", nil);    /**     *  同步方式执行任务     */    dispatch_sync(queue, ^{        NSLog(@"%@", NSThread.currentThread);    });    /**     *  异步方式执行任务     */    dispatch_async(queue, ^{         NSLog(@"%@", NSThread.currentThread);    });

Using the primary queue

The primary queue cannot be used in conjunction with synchronous execution, or it will deadlock
To use the asynchronous execution mode

dispatch_queue_t queue = dispatch_get_main_queue();

    dispatch_queue_t queue = dispatch_get_main_queue();    /**     *  同步方式执行任务     *///    dispatch_sync(queue, ^{//        NSLog(@"%@", NSThread.currentThread);//    });    /**     *  异步方式执行任务     */    dispatch_async(queue, ^{         NSLog(@"%@", NSThread.currentThread);    });

Communication between threads

dispatch_async(dispatch_get_global_queue(00), ^{    // 执行耗时的异步操作...   dispatch_async(dispatch_get_main_queue(), ^{     // 回到主线程，执行UI刷新操作   });});

Download Images asynchronously

    Uiimageview*imageview = [[UiimageviewALLOC] init]; ImageView. Frame= CGRectMake ( -, -, -, -); ImageView. BackgroundColor= [UicolorRedcolor]; [ Self. ViewAddsubview:imageview];dispatch_queue_tQueue = Dispatch_get_global_queue (0,0);Dispatch_async(Queue, ^{Nsurl*url = [Nsurlurlwithstring:@"Http://img6.cache.netease.com/cnews/2015/5/13/20150513153022b6a55.jpg"]; NSData *data = [NSData Datawithcontentsofurl:url];//This guild is time consuming        UIImage*image = [UIImageImagewithdata:data];Dispatch_async(Dispatch_get_main_queue (), ^{ImageView. Image= Image;    }); });

Disposable code

Code the entire program is executed only once

staticdispatch_once_t onceToken;dispatch_once(&onceToken, ^{    // 只执行1次的代码(这里面默认是线程安全的)});

Queue Group

Can be a few lines preempted into the queue group inside, waiting for the thread in this group to complete the execution, and then do other things

dispatch_group_t group =  0), ^{    // 执行10), ^{    // 执行1个耗时的异步操作});dispatch_group_notify(group, dispatch_get_main_queue(), ^{    // 等前面的异步操作都执行完毕后，回到主线程...});

"iOS Development-multithreading" using GCD to create multithreading (iOS common technology)