iOS Development multithreading-technical Solutions

<span id="Label3"></p>Pthread Implementing multithreaded Operations<p><p>Code implementation:</p></p><pre><pre><code>void * run(void *param){    for (NSInteger i = 0; i < 1000; i++) {        NSLog(@"---buttonclick---%zd---%@", i, [NSThread currentThread]);    }    return NULL;}@implementation ViewController- (IBAction)clickButton:(id)sender {    // 定义一个线程    pthread_t thread;    // 创建一个线程  (参1)pthread_t *restrict:创建线程的指针，(参2)const pthread_attr_t *restrict:线程属性  (参3)void *(*)(void *):线程执行的函数的指针，(参4)void *restrict:null    pthread_create(&thread, NULL, run, NULL);    // 何时回收线程不需要你考虑    pthread_t thread2;    pthread_create(&thread2, NULL, run, NULL);}</code></pre></pre>Nsthread Implementing multithreading<p><p>A Nsthread object represents a thread</p></p>Multiple ways to create threads <ul class=" list-paddingleft-2"> <li><li><p>The first way: create a restart thread first</p><pre><code>  // 创建线程  NSThread *thread = [[NSThread alloc] initWithTarget:self selector:@selector(run:) object:@"jack"];  // 线程启动了，事情做完了才会死， 一个NSThread对象就代表一条线程  [thread start];</code></pre></li></li> <li><li><p>Second type: Create and start a thread directly</p><pre><code>  // 直接创建并启动线程  [NSThread detachNewThreadSelector:@selector(run:) toTarget:self withObject:@"jack"];</code></pre></li></li> <li><li><p>The third type:</p><pre><code>  // 直接创建并启动线程  [self performSelectorInBackground:@selector(run:) withObject:@"jack"];  // 使线程进入阻塞状态  [NSThread sleepForTimeInterval:2.0];  #pragma mark - 执行run方法  - (void)run:(NSString *)param  {      // 当前线程是否是主线程      for (NSInteger i = 0; i < 100; i++) {          NSLog(@"---%@---%zd---%d", [NSThread currentThread], i,  [NSThread isMainThread]);      }  }</code></pre></li></li> <li><li><p>Advantages of Method 2 and method 3: The advantages of shortcut method 1: you can easily get the thread</p></li></li> </ul>Inter-thread Communication <ul class=" list-paddingleft-2"> <ul class=" list-paddingleft-2"> <li><p>The embodiment of inter-thread communication</p></li> </ul> </ul><p><p>1 Threads pass data to another 1 threads</p></p><p><p>After performing a specific task in 1 threads, go to another 1 thread to continue the task</p></p><p><p>Common methods of Inter-thread communication: Small program image download</p></p><pre><pre><code>- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event {    // 获取图片的url    NSURL *url = [NSURL URLWithString:@"http://7xjanq.com1.z0.glb.clouddn.com/6478.jpg"];// 另开1条线程 object用于数据的传递    NSThread *thread = [[NSThread alloc] initWithTarget:self selector:@selector(downLoadWithURL:) object:url];    // 由于下面下载图片的耗时太长，应领开启线程来完成    [thread start];}// 下载图片- (void)downLoadWithURL:(NSURL *)url{    NSLog(@"%@", [NSThread currentThread]);    // 下载图片    NSData *data = [NSData dataWithContentsOfURL:url];    // 生成图片    UIImage *image = [UIImage imageWithData:data];    // 返回主线程显示图片    [self.imageView performSelectorOnMainThread:@selector(setImage:) withObject:image waitUntilDone:YES];}</code></pre></pre><p><p>The above two ways of using threads are obsolete, and most of our operating threads in development use GCD and nsoperation for multithreaded Operations.</p></p><p><p>The following I will give you a systematic introduction of how GCD is the implementation of multi-threaded</p></p>GCD Implementing Multithreading GCD Introduction<p><p>The GCD full name is Grand Central Dispatch, which translates to "super-powerful hub scheduler", GCD is a solution for multi-core parallel computing by apple, GCD automatically uses more CPU cores (such as dual-core, quad-core) to enable thread execution, GCD Automatically manages the life cycle of threads (creating threads, scheduling tasks, destroying Threads) without requiring our programmers to manually manage Memory.</p></p>Tasks and queues<p><p>Tasks: executing in synchronous functions and asynchronous functions</p></p><p><p>Queue: used to hold tasks (concurrent Serial)</p></p><p><p>The GCD automatically takes the task out of the queue and places it on the corresponding thread, and the Task's removal follows the fifo, which is the abbreviation for first-in, first-out queues, and Initial-Input-Output. The first entry task is completed and finished, followed by the next Task.</p></p>Synchronization functions and asynchronous functions, concurrent queues and serial queues <ul class=" list-paddingleft-2"> <ul class=" list-paddingleft-2"> <li><p>Perform tasks synchronously: tasks can be performed immediately in the current thread without the ability to open threads</p></li> <li><p>Perform a task asynchronously: perform a task at the end of the current thread, with the ability to open a new thread</p></li> <li><p>Concurrent queues: allow multiple tasks to execute concurrently</p></li> <li><p>Serial queue: Once a task is completed, the next task is executed</p></li> </ul> </ul><p><p>To create a concurrent/serial queue code:</p></p><pre><pre><code>// 创建并发队列 // 参1:const char *label 队列名称 // 参2:dispatch_queue_attr_t attr 队列类型dispatch_queue_t queueConcurrent = dispatch_queue_create("520it.com", DISPATCH_QUEUE_CONCURRENT);// 创建串行队列  serial 串行  concurrent并发dispatch_queue_t queueSerial = dispatch_queue_create("520it.com", DISPATCH_QUEUE_SERIAL);// 获取全局队列 全局队列是并发队列 // 参1:队列的优先级 // 参2:0(以后可能用到的参数)dispatch_queue_t queueGlobal = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);// 全局并发队列的优先级#define DISPATCH_QUEUE_PRIORITY_HIGH 2 // 高#define DISPATCH_QUEUE_PRIORITY_DEFAULT 0 // 默认（中）#define DISPATCH_QUEUE_PRIORITY_LOW (-2) // 低#define DISPATCH_QUEUE_PRIORITY_BACKGROUND INT16_MIN // 后台// 获取主队列  在主队列中的任务都会在主线程中执行。dispatch_queue_t queueMain = dispatch_get_main_queue();</code></pre></pre><p><p>The Synchronous/asynchronous function code represents:</p></p><pre><code>GCD synchronous function Serial queue (immediate execution, current thread)//1:dispatch_queue_t queue//parameter 2: task Dispatch_sync (queueserial, ^{   for (nsinte Ger i = 0; I < 10; I++) {       nslog (@ "~~~%@", [nsthread currentthread]),  }});//synchronous function Parallel queue (immediate execution, current Thread) Dispatch_ Sync (queueconcurrent, ^{   for (nsinteger i = 0; i < i++) {       nslog (@ "~~~%@", [ Nsthread currentthread]);    });//asynchronous function Serial queue (another thread, multiple tasks executed sequentially) dispatch_async (queueserial, ^{   dispatch_async (queueserial, ^{       for (nsinteger i = 0; i < ten i++) {           nslog (@ "~ ~ ~ %@ ", [nsthread currentthread]);        }    });    dispatch_async (queueserial, ^{       for (nsinteger i = 0; i <; i++) {  &nbs P        nslog (@ "~~~%@", [nsthread currentthread]);        }    });    dispatch_async (queueserial, ^{       for (nsinteger i = 0; i < ten; i++) {           n SLog (@ "~~~%@", [nsthread currentthread]);        }    }); /async function Parallel Queue (another thread, multiple tasks executed together) dispatch_async (queueconcurrent, ^{   dispatch_async (queueserial, ^{           for (nsinteger i = 0; i < ten; i++) {                NSLog (@ "~~~%@", [nsthread currentthread]);            }    });    dispatch_async (queueserial, ^{       for (nsinteger i = 0; i <; i++) {  &nbs P        nslog (@ "~~~%@", [nsthread currentthread]);        }    });    dispatch_async (queueserial, ^{       for (nsinteger i = 0; i <; i++) {  &nbs P        nslog (@ "~~~%@", [nsthread currentthread]);       }    }); /home column: (any Task will be added to the main Thread's queue as long as it is in the primary Queue)</code></pre> <blockquote> <blockquote> <p>Note: Adding a task to the current serial queue with the sync function (sync Function) will get stuck in the current serial queue</p> </blockquote> </blockquote><p><p>Explanation: Use the synchronization function to add task A to the serial queue, stating that the code after task A will be executed immediately after task a finishes executing the current serial Queue. however, the current queue is a serial queue, which means that task a must wait until the task B in the current serial queue is completed before it can be executed, so you must perform the task immediately in task a, and you must wait until task B finishes executing to perform the next task, so it will Die. You wait for me, I wait for you, no one can Execute.</p></p>GCD Implementing thread Communication<p><p>Small item: Download picture</p></p><p><p>The code is as Follows:</p></p><pre><pre><code>// 获取图片的urlNSURL *url = [NSURL URLWithString:@"http://7xjanq.com1.z0.glb.clouddn.com/6478.jpg"];// 开启线程下载图片dispatch_queue_t queue = dispatch_queue_create("111", DISPATCH_QUEUE_CONCURRENT);dispatch_async(queue, ^{    NSData *data = [NSData dataWithContentsOfURL:url];    UIImage *image = [UIImage imageWithData:data];    // 下载完成后返回主线程显示图片    dispatch_async(dispatch_get_main_queue(), ^{        self.imageView.image = image;    });});</code></pre></pre>GCD Other common functions dispatch_barrier fence<pre><pre><code>// 1.barrier : 在barrier前面的先执行，然后再执行barrier，然后再执行barrier后面的 barrier的queue不能是全局的并发队列dispatch_queue_t queue = dispatch_queue_create("11", DISPATCH_QUEUE_CONCURRENT);dispatch_async(queue, ^{    for (int i = 0;  i < 100; i++) {        NSLog(@"%@--1", [NSThread currentThread]);    }});dispatch_async(queue, ^{    for (int i = 0;  i < 100; i++) {        NSLog(@"%@--2", [NSThread currentThread]);    }});dispatch_barrier_async(queue, ^{    for (int i = 0;  i < 100; i++) {        NSLog(@"%@--3", [NSThread currentThread]);    }});dispatch_async(queue, ^{    for (int i = 0;  i < 100; i++) {        NSLog(@"%@--4", [NSThread currentThread]);    }});</code></pre></pre><p><p>Dispatch_after deferred execution</p></p><pre><pre><code>// 延迟执行// 方法1[self performSelector:@selector(run:) withObject:@"参数" afterDelay:2.0];// 方法2dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(2.0 * NSEC_PER_SEC)), dispatch_get_main_queue(), ^{    for (NSInteger i = 0; i < 100; i++) {        NSLog(@"%@", [NSThread currentThread]);    }});// 方法3[NSTimer scheduledTimerWithTimeInterval:2.0 target:self selector:@selector(run) userInfo:nil repeats:NO];</code></pre></pre><p><p>Dispatch_once execution of the entire program in one run</p></p><pre><pre><code>// 整个程序中只执行一次static dispatch_once_t onceToken;dispatch_once(&onceToken, ^{    // 一次性代码});</code></pre></pre><p><p>Function: implement a Single-grain object of a class</p></p><p><p>Singleton mode: share a single resource throughout the application (this resource only needs to be created initialized 1 times)</p></p><pre><pre><code>static id _person;+ (instancetype)sharePerson{    static dispatch_once_t onceToken;    dispatch_once(&onceToken, ^{        _person = [[super alloc] init];    });    return _person;}+ (instancetype)allocWithZone:(struct _NSZone *)zone{    static dispatch_once_t onceToken;    dispatch_once(&onceToken, ^{        _person = [super allocWithZone:zone];    });    return _person;}- (id)copy{    return _person;}</code></pre></pre><p><p>In the development of general custom macro, more convenient, a line of code to FIX.</p></p>Dispatch_apply Fast Iteration<p><p>Sample Applet: cut a picture in one folder to another folder</p></p><pre><pre><code>// 将图片剪切到另一个文件夹里NSString *from = @"/Users/Ammar/Pictures/壁纸";NSString *to = @"/Users/Ammar/Pictures/to";NSFileManager *manager = [NSFileManager defaultManager];NSArray *subPaths = [manager subpathsAtPath:from];// 快速迭代dispatch_apply(subPaths.count, dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^(size_t index) {   NSLog(@"%@ - %zd", [NSThread currentThread], index);    NSString *subPath = subPaths[index];    NSString *fromPath = [from stringByAppendingPathComponent:subPath];    NSString *toPath = [to stringByAppendingPathComponent:subPath];    // 剪切    [manager moveItemAtPath:fromPath toPath:toPath error:nil];    NSLog(@"%@---%zd", [NSThread currentThread], index);});</code></pre></pre><p><p>Dispatch_group Queue Group</p></p><p><p>Sample Applet: requirements Download image 1 Download Picture 2 Add a new picture to picture 1 and picture 2</p></p><p><p>//create Queue <br>    dispatch_queue_t queue = Dispatch_get_global_queue (dispatch_queue_priority_default, 0); </p> </p><pre><code>Create groups dispatch_group_t group = dispatch_group_create ();//use Group queue to download pictures 1dispatch_group_async (group, queue, ^{    NSData *data = [nsdata datawithcontentsofurl:[nsurl urlwithstring:@ "http://7xjanq.com1.z0.glb.clouddn.com/6478.jpg" ]];    self.image1 = [UIImage imagewithdata:data];    nslog (@ "1%@", [nsthread currentthread]); /use group queue to download pictures 2dispatch_group_async (group, queue, ^{   nsdata *data = [nsdata Datawithcontentsofurl:[nsurl urlwithstring:@ "http://7xjanq.com1.z0.glb.clouddn.com/6478.jpg"];    self.image2 = [UIImage imagewithdata:data];    nslog (@ "2%@", [nsthread currentthread]); /add picture 1 and Picture 2 to a picture dispatch_group_notify (group, queue, ^{   cgfloat Imagew = self.imageView.bounds.size.width;    cgfloat Imageh = self.imageView.bounds.size.height;    //open Bitmap context    uigraphicsbeginimagecontext (self.imageView.bounds.size);    //drawing    [self.image1 drawinrect:cgrectmake (0, 0, imaGeW * 0.5, imageh)];    [self.image2 drawinrect:cgrectmake (imagew * 0.5, 0, Imagew * 0.5, imageh)];    //the picture out    uiimage *image = Uigraphicsgetimagefromcurrentimagecontext ();    //close The graphics context    uigraphicsendimagecontext ();    //display pictures on the main thread    dispatch_async (dispatch_get_main_queue (), ^{        Self.imageView.image = image;    });    nslog (@ "3%@", [nsthread currentthread]);});</code></pre>GCD Timer<p><p>GCD timers are not affected by mode and are therefore more accurate than nstimer</p></p><pre><code>static int count = 0;dispatch_after (dispatch_time (dispatch_time_now, (int64_t) (2.0 * nsec_per_sec)), dispatch_get_main _queue (), ^{   //the Meaning of this sentence is now very understood});//gcd timer dispatch_queue_t queue = Dispatch_get_global_queue (dispatch_queue _priority_default, 0);//1. Create a timer source//parameter 1: type timer//parameter 2: handle//parameter 3:mask 0//parameter 4: queue   (note: dispatch_source_t essence is oc object, representing Source) Self.timer = dispatch_source_create (dispatch_source_type_timer, 0, 0, queue);//rigorous, time interval needs to use unit int64_t, do multiplication after the unit changed// The following code indicates how much the callback function interval is int64_t interval = (int64_t) (2.0 * nsec_per_sec); How to set the start time CGD gave us a way to set the time  //1:dispatch_time_t when to pass a time, delta is the increment dispatch_time_t start = Dispatch_time ( dispatch_time_now, (int64_t) (3.0 * nsec_per_sec)); Starting from now 3 seconds//2. set the various properties of the Timer//parameter 1:timer//parameter 2: start time//parameter 3: time Interval//parameter 4: Pass 0 does not need   Dispatch_time_now indicates that GCD time is now expressed in NS Dispa Tch_source_set_timer (self.timer, start, interval, 0);//3. Set the callback (that is, what to do at each Interval) Dispatch_source_set_event_handler ( self.timer, ^{   nslog (@ "----------------%@", [nsthreadcurrentthread]);    //if you want to do it 5 times, stop    count++;    if (count = = 5) {       dispatch_cancel (self.timer),        self.tim ER = nil;    });//4. Start timer   (restore) Dispatch_resume (self.timer);</code></pre><p><p>Finish speaking GCD should talk about nsoperation, it is GCD object-oriented package, It is more convenient to use,</p></p>Nsoperation Implementing multithreading<p><p>Nsoperation is an abstract class and does not have the ability to encapsulate operations, it must use its subclasses</p></p><pre><pre><code>NSInvocationOperationNSBlockOperation自定义子类继承NSOperation，实现内部相应的方法</code></pre></pre><p><p>To implement multithreaded steps with Nsoperation:</p></p><pre><pre><code>创建任务 NSOperation 对象创建 NSOperationQueue 队列将任务 NSOperation 对象 add 到 NSOperationQueue 队列中去</code></pre></pre><p><p>Nsinvocationoperation</p></p><p><p>The code is as Follows:</p></p><pre><pre><code>NSInvocationOperation *op = [[NSInvocationOperation alloc] initWithTarget:self selector:@selector(run) object:nil];[op start];</code></pre></pre><p><p>Note: by default, Calling the Start method does not open a new thread to execute, but instead executes the operation synchronously in the current thread, and the operation is performed asynchronously only if the nsoperation is placed in a nsoperationqueue</p></p>Nsblockoperation<pre><pre><code>NSBlockOperation *op = [NSBlockOperation blockOperationWithBlock:^{    // 在主线程      NSLog(@"下载1------%@", [NSThread currentThread]);}];// 添加额外的任务(在子线程执行)，封装数大于1才会异步执行[op addExecutionBlock:^{    NSLog(@"下载2------%@", [NSThread currentThread]);}];</code></pre></pre><p><p>Custom operation: need to implement-(void) the main method, what needs to be done in the Mian method</p></p>Nsoperationqueue<p><p>Create a queue using Nsoperationqueue: primary and global queues</p></p><pre><pre><code>// 创建一个其他队列(包括串行队列和并发队列) 放到这个队列中的NSOperation对象会自动放到子线程中执行NSOperationQueue *queue = [[NSOperationQueue alloc] init];// 创建一个主队列，放到这个队列中的NSOperation对象会自动放到子线程中执行NSOperationQueue *mainQueue = [NSOperationQueue mainQueue];// 表示并发数量：即同时执行任务的最大数。queue.maxConcurrentOperationCount = 1;</code></pre></pre>cancellation, pause, and recovery of a queue:<pre><pre><code>// NSOpertion的 - cancel 方法也可以停止单个操作- (void)cancelAllOperations; // YES代表暂停队列，NO代表恢复队列- (void)setSuspended:(BOOL)b;</code></pre></pre>Add dependency<pre><pre><code>NSOperationQueue *queue = [[NSOperationQueue alloc] init];NSBlockOperation *block1 = [NSBlockOperation blockOperationWithBlock:^{    NSLog(@"download1 -------------- %@", [NSThread currentThread]);}];NSBlockOperation *block2 = [NSBlockOperation blockOperationWithBlock:^{    NSLog(@"download2 -------------- %@", [NSThread currentThread]);}];NSBlockOperation *block3 = [NSBlockOperation blockOperationWithBlock:^{    NSLog(@"download3 -------------- %@", [NSThread currentThread]);}];// 添加依赖: block1 和 block2执行完后 再执行 block3  block3依赖于block1和block2// 给block3添加依赖 让block3在block1和block2之后执行[block3 addDependency:block1];[block3 addDependency:block2];[queue addOperation:block1];[queue addOperation:block2];[queue addOperation:block3];</code></pre></pre><p><p>Note: you cannot loop dependencies, but you can cross-queue dependencies regardless of which queue the Nsoperation object is IN. As long as two nsoperation objects can be relied upon</p></p>Inter-thread Communication<p><p>example: Download a picture</p></p><pre><pre><code>// 下载图片 operation实现线程间通信[[[NSOperationQueue alloc] init] addOperation:[NSBlockOperation blockOperationWithBlock:^{    UIImage *image = [UIImage imageWithData:[NSData dataWithContentsOfURL:[NSURL URLWithString:@"http://7xjanq.com1.z0.glb.clouddn.com/6478.jpg"]]];    // 返回主线程    [[NSOperationQueue mainQueue] addOperation:[NSBlockOperation blockOperationWithBlock:^{        self.imageView.image = image;    }]];}]];</code></pre></pre><p><p>example: download picture 1 and Picture 2 and synthesize the picture</p></p><pre><code>Nsoperationqueue *queue = [[nsoperationqueue alloc] init];//download picture 1__block UIImage *image1 = nil; Nsblockoperation *block1 = [nsblockoperation blockoperationwithblock:^{   image1 = [UIImage imageWithData:[ NSData Datawithcontentsofurl:[nsurl urlwithstring:@ "http://7xjanq.com1.z0.glb.clouddn.com/6478.jpg"]]];}];/ /download image 2__block UIImage *image2 = nil; Nsblockoperation *block2 = [nsblockoperation blockoperationwithblock:^{   image2 = [UIImage imageWithData:[ NSData Datawithcontentsofurl:[nsurl urlwithstring:@ "http://7xjanq.com1.z0.glb.clouddn.com/6478.jpg"] [];}]; CGFloat Imagew = self.imageView.bounds.size.width; CGFloat Imageh = self.imageview.bounds.size.height;//synthetic picture Nsblockoperation *block3 = [nsblockoperation blockoperationwithblock:^{   uigraphicsbeginimagecontext (cgsizemake (imagew, imageH));    [ Image1 drawinrect:cgrectmake (0, 0, imagew * 0.5, imageh)];    [image2 drawinrect:cgrectmake (0.5 * imagew, 0, 0.5 * imagew, imageh)];   &NBSP UIImage *image3 = Uigraphicsgetimagefromcurrentimagecontext ();    uigraphicsendimagecontext ();    //switch back to the main thread display picture    [[nsoperationqueue mainqueue] addoperation:[nsblockoperation blockoperationwithblock:^{       self.imageview.image = image3;    }]];}];/ /set Dependency [block3 adddependency:block1]; [block3 adddependency:block2];//add task to queue [addoperation:block1]; [queue addoperation:block2]; [queue addoperation:block3];</code></pre>Application<p><p>Application: Sdwebimage framework of the underlying main function implementation is based on multi-threading, using multi-threading, we can achieve a small picture of the multi-image Download. The logic here is actually quite complicated.</p></p><p><p>To achieve a small picture of multi-image download ideas:</p></p><p><p></p></p><p><p>The code implementation is shown in the Code.</p></p><p><p>See this code: multithreading</p></p><pre><pre><code>https://github.com/lizhaoLoveIT/Multithreading</code></pre></pre><p><p>iOS Development multithreading-technical Solutions</p></p></span>