iOS 多线程（NSThread、GCD、NSOperation）

　　ios中得多线程技术主要使用3种：NSThread、NSOperation和GCD

　　一、NSThread: 最轻量级方法，但是不安全需要手动加锁，需要自己管理生命周期

　　　　NSThread的使用方法有2种：　　　

// 第一种，需要start
1 NSThread *th1 = [[NSThread alloc] initWithTarget:self selector:@selector(btnClick) object:nil];
     [th1 setName:@"线程1"];
     [th1 start];

// 第二种
1 [NSThread detachNewThreadSelector:@selector(btnClick) toTarget:self withObject:nil];

　　因为NSThread使用不安全，我们需要给它加锁(主要的实现代码)：

 @property (nonatomic,assign) NSInteger fruits;
 @property (nonatomic,strong) NSLock *lock;
 - (void)viewDidLoad
 {
     [super viewDidLoad];

     _lock = [[NSLock alloc] init];
     _fruits = ;
 }

 - (void)btnClick
 {
     @synchronized(_lock){ // 加锁

         while (_fruits > ) {

             NSLog(@"当前线程为:%@ , 剩余票数为:%d",[NSThread currentThread], _fruits);

             _fruits--;
         }
     }
 }

　　二、GCD:（Grand Central Dispatch）是一种多核编码技术，用纯C语言编写。

　　异步：具备开启线程的功能

　　同步：不具备开启线程的功能

　　并行队列：多个任务可以同时执行

　　串行队列：执行完一个任务后再执行下一个任务

　　下面来进行用代码说明：

 // 自定义异步方法
 - (void)async:(dispatch_queue_t)queue
 {
     // 异步执行
     dispatch_async(queue, ^{

         NSLog(@"im1-%@",[NSThread currentThread]);
     });
     dispatch_async(queue, ^{

         NSLog(@"im2-%@",[NSThread currentThread]);
     });
     dispatch_async(queue, ^{

         NSLog(@"im3-%@",[NSThread currentThread]);
     });
     dispatch_async(queue, ^{

         NSLog(@"im4-%@",[NSThread currentThread]);
     });

 }

 // 自定义同步方法
 - (void)sync:(dispatch_queue_t)queue
 {
     // 同步执行
     dispatch_sync(queue, ^{

         NSLog(@"im1-%@",[NSThread currentThread]);
     });
     dispatch_sync(queue, ^{

         NSLog(@"im2-%@",[NSThread currentThread]);
     });
     dispatch_sync(queue, ^{

         NSLog(@"im3-%@",[NSThread currentThread]);
     });
     dispatch_sync(queue, ^{

         NSLog(@"im4-%@",[NSThread currentThread]);
     });

 }

调用异步执行方法：

 // 创建一个全局并行队列
     dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, );

     // 异步执行
     [self async:queue];

最终的结果为：开启了四个线程,并且执行顺序是不定

 -- ::20.438 GCD[:1f07] im3-<NSThread: 0x7177ee0>{name = (null), num = }
 -- ::20.432 GCD[:] im1-<NSThread: 0x7177d70>{name = (null), num = }
 -- ::20.440 GCD[:] im4-<NSThread: 0x7178490>{name = (null), num = }
 -- ::20.432 GCD[:1a03] im2-<NSThread: 0x75429f0>{name = (null), num = }

 // 创建一个全局串行队列
     dispatch_queue_t queue = dispatch_queue_create("wys", NULL);

     // 异步执行
     [self async:queue];

最终的结果为：开启了一个线程,执行顺序为从上往下依次执行

 -- ::19.415 GCD[:] im1-<NSThread: 0x71631a0>{name = (null), num = }
 -- ::19.428 GCD[:] im2-<NSThread: 0x71631a0>{name = (null), num = }
 -- ::19.437 GCD[:] im3-<NSThread: 0x71631a0>{name = (null), num = }
 -- ::19.450 GCD[:] im4-<NSThread: 0x71631a0>{name = (null), num = }

调用主队列执行方法：

 // 创建主队列
     dispatch_queue_t queue = dispatch_get_main_queue();

     // 异步执行
     [self async:queue];

最红的结果为：顺序执行并且不开启线程，在主线程中执行

 -- ::45.320 GCD[:c07] im1-<NSThread: 0x71560c0>{name = (null), num = }
 -- ::45.333 GCD[:c07] im2-<NSThread: 0x71560c0>{name = (null), num = }
 -- ::45.339 GCD[:c07] im3-<NSThread: 0x71560c0>{name = (null), num = }
 -- ::45.347 GCD[:c07] im4-<NSThread: 0x71560c0>{name = (null), num = }

 // 创建主队列
     dispatch_queue_t queue = dispatch_get_main_queue();

     NSLog(@"start");

     // 同步执行
     [self sync:queue];

     NSLog(@"end");

最终的结果为：执行到start就卡住了，不能往下执行

 -- ::12.856 GCD[:c07] start

调用同步执行方法：

 // 创建全局并行队列
     dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, );

     // 同步执行
     [self sync:queue];

最终的结果为：不开启线程，并且顺序执行，直接主线程执行

 -- ::27.448 GCD[:c07] im1-<NSThread: 0x71133c0>{name = (null), num = }
 -- ::27.458 GCD[:c07] im2-<NSThread: 0x71133c0>{name = (null), num = }
 -- ::27.468 GCD[:c07] im3-<NSThread: 0x71133c0>{name = (null), num = }
 -- ::27.472 GCD[:c07] im4-<NSThread: 0x71133c0>{name = (null), num = }

 // 创建串行队列
     dispatch_queue_t queue = dispatch_queue_create("wys", NULL);

     // 同步执行
     [self sync:queue];

最终的结果为：不开启线程，并且顺序执行，直接主线程执行

 -- ::40.609 GCD[:c07] im1-<NSThread: 0x713e570>{name = (null), num = }
 -- ::40.621 GCD[:c07] im2-<NSThread: 0x713e570>{name = (null), num = }
 -- ::40.626 GCD[:c07] im3-<NSThread: 0x713e570>{name = (null), num = }
 -- ::40.634 GCD[:c07] im4-<NSThread: 0x713e570>{name = (null), num = }

多线程之间的通信：UI界面的更新一定要在主线程中执行

 dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, ), ^{ // 全局并行队列异步执行

         NSLog(@"全局并行队列异步执行 - %@",[NSThread currentThread]);

         // 获取网络图片数据
         NSString *str = @"https://ss0.bdstatic.com/70cFv8Sh_Q1YnxGkpoWK1HF6hhy/it/u=3384245408,2851245305&fm=21&gp=0.jpg";
         NSURL *url = [NSURL URLWithString:str];

         NSData *data = [NSData dataWithContentsOfURL:url];

         UIImage *image = [UIImage imageWithData:data];

         dispatch_async(dispatch_get_main_queue(), ^{ // 主线程异步执行

             NSLog(@"主线程异步执行 - %@",[NSThread currentThread]);

             // 更新界面
             [_im1 setImage:image];
         });

     });

最终的结果为：

-- ::08.513 GCD[:] 全局并行队列异步执行 -<NSThread: 0x754c530>{name = (null), num = }
-- ::10.657 GCD[:c07] 主线程异步执行 -<NSThread: 0x7132c80>{name = (null), num = }

利用多线程来实现延时执行：

1、利用GCD

 double delayInSeconds = 2.0; // 延时时长
         dispatch_time_t popTime = dispatch_time(DISPATCH_TIME_NOW, (int64_t)(delayInSeconds * NSEC_PER_SEC));
         dispatch_after(popTime, dispatch_get_main_queue(), ^(void){ // 在主线程中执行

             NSLog(@"%@",[NSThread currentThread]);

             // 更新界面
             [_im1 setImage:image];

         });

2、利用此方法，performSelector为你要调用的方法，withObject为你要传得值，afterDelay为延时时长

 [self performSelector:@selector(downLoad) withObject:nil afterDelay:0.5f];

队列组：

 dispatch_group_t group = dispatch_group_create();
     dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, );

     dispatch_group_async(group, queue, ^{

         // 代码1
     });

     dispatch_group_async(group, queue, ^{

         // 代码2
     });

     dispatch_group_notify(group, queue, ^{

         // 执行完代码1和代码2后，再执行此方法
     });

　　

　　三、NSOperation:基于GCD，能控制最大并发线程数，主要有2个类：NSInvocationOperation和NSBlockOperation

　　其步骤为: 创建队列、添加操作、将操作添加到队列

　　A、NSInvocationOperation:

 - (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event
 {
     NSOperationQueue *queue = [[NSOperationQueue alloc] init];

     NSInvocationOperation *invo = [[NSInvocationOperation alloc] initWithTarget:self selector:@selector(buy) object:nil];

     [queue addOperation:invo];

 }

 - (void)buy
 {
     NSLog(@"%@",[NSThread currentThread]);
 }

最后的结果为：开启了一个线程

 -- ::54.060 op1[:1e07] <NSThread: 0x71a6de0>{name = (null), num = }

　　

　　B、NSBlockOperation

 NSOperationQueue *queue = [[NSOperationQueue alloc] init];

     NSBlockOperation *b1 = [NSBlockOperation blockOperationWithBlock:^{

         NSLog(@"111--%@",[NSThread currentThread]);
     }];
     NSBlockOperation *b2 = [NSBlockOperation blockOperationWithBlock:^{

         NSLog(@"222--%@",[NSThread currentThread]);
     }];
     NSBlockOperation *b3 = [NSBlockOperation blockOperationWithBlock:^{

         NSLog(@"333--%@",[NSThread currentThread]);
     }];

     [queue addOperation:b1];
     [queue addOperation:b2];
     [queue addOperation:b3];

最后的结果为：开启了三个线程，自动异步执行

 -- ::59.897 op1[:1a03] --<NSThread: 0x7544fa0>{name = (null), num = }
 -- ::59.901 op1[:] --<NSThread: 0x71506f0>{name = (null), num = }
 -- ::59.902 op1[:] --<NSThread: 0x7545e60>{name = (null), num = }

设置依赖：

 // 设置依赖 ,b2依赖b1,b3依赖b2，所以执行顺序为,b1->b2->b3
     [b2 addDependency:b1];
     [b3 addDependency:b2];

设置队列的最大并发数量

 // 设置最大并发(最多同时并发执行3个任务)
     queue.maxConcurrentOperationCount = ;

　　C、主队列

 NSOperationQueue *queue = [[NSOperationQueue alloc] init];

     [queue addOperationWithBlock:^{

           NSLog(@"-------%@",[NSThread currentThread]);

                // 获取网络图片数据
                  NSString *str = @"https://ss0.bdstatic.com/70cFv8Sh_Q1YnxGkpoWK1HF6hhy/it/u=3384245408,2851245305&fm=21&gp=0.jpg";
                  NSURL *url = [NSURL URLWithString:str];

                  NSData *data = [NSData dataWithContentsOfURL:url];

                  UIImage *image = [UIImage imageWithData:data];

         [[NSOperationQueue mainQueue] addOperationWithBlock:^{ // 主队列

                  NSLog(@"******%@",[NSThread currentThread]);

                  // 更新界面
                  [_im1 setImage:image];
             }];
     }];

最后的结果为:

 -- ::16.077 op1[:1c03] -------<NSThread: 0x71613e0>{name = (null), num = }
 -- ::17.593 op1[:c07] ******<NSThread: 0x7134fa0>{name = (null), num = } // 主队列