10.7 GCD 串行列队, 并行列队

GCD

主要学习的知识点有：串行列队，并行列队，死锁，group，栅栏

·串行列队：A执行完，执行B，B执行完再执行C 排队执行 SERIAL
·并行列队：无序执行 CONCURRENT

·死锁没事少用同步方法，很容易造成主线程死锁

·栅栏：AB可以无序执行，CD也可以无序执行，但是我们要AB执行完再执行CD，这样我们就不好设置依赖关系了
·栅栏就可以挡在AB和CD的中间，等AB执行完了再执行CD

#import "ViewController.h"

@interface ViewController ()

@end

@implementation ViewController

- (void)viewDidLoad {

    [super viewDidLoad];

#if 0

//    主线程
    dispatch_queue_t mainQueue = dispatch_get_main_queue();

//    子线程  异步执行
    dispatch_queue_t subQueue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);
    
    dispatch_async(subQueue, ^{
        
        NSLog(@"task");
    });
    
    NSLog(@"hello");

#endif
    
    
#if 0

    //异步执行
    dispatch_queue_t globalQueue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);

    for (NSInteger i = 0; i<100; i++) {
        
        dispatch_async(globalQueue, ^{
            
           
            NSLog(@"i = %ld",i);

        });
    }

#endif
    
    //自己创建一个新的线程

    dispatch_queue_t customQueue = dispatch_queue_create("apple.queue",DISPATCH_QUEUE_CONCURRENT);
   
#if 0

    dispatch_sync(customQueue, ^{
        
        NSLog(@"task");
    });

    NSLog(@"hello");

#endif

   
#if 0

    // 串联列队 有序执行打印 i = 0, i = 1, i = 2....    DISPATCH_QUEUE_SERIAL

    customQueue = dispatch_queue_create("apple.queue2", DISPATCH_QUEUE_SERIAL);
    
    customQueue = dispatch_get_main_queue();
    
    for (NSInteger i = 0; i<100; i++) {
    
        dispatch_async(customQueue, ^{
            
            NSLog(@"i = %ld",i);
        });
    }
    
    NSLog(@"hello world");

#endif
    
#if 0
    
    NSLog(@"hello world");
    //典型的死锁    dispatch等待main打印"welcome"，而打印这个方法是在主线程，造成死锁
    //主线程执行dispatch，dispatch又要用到主线程，进入一个死循环中，死锁
    dispatch_sync(dispatch_get_main_queue(), ^{

        NSLog(@"welcome");
        
    });

    NSLog(@"======");
#endif 
   
#if 0

    //并联列队     无序执行，我们并不知道哪个先执行完                DISPATCH_QUEUE_CONCURRENT
    dispatch_queue_t queue = dispatch_queue_create("apple.queu3", DISPATCH_QUEUE_CONCURRENT);

   dispatch_async(queue, ^{
      
       NSLog(@"1");
   });
   
    dispatch_async(queue, ^{
        
        NSLog(@"2");
    });

    dispatch_async(queue, ^{
        
        NSLog(@"3");
    });

    NSLog(@"done");
    
#endif
    
#if 0
    
    dispatch_group_t group = dispatch_group_create();

    dispatch_queue_t queue = dispatch_queue_create("apple.queu3", DISPATCH_QUEUE_CONCURRENT);

    dispatch_group_async(group, queue, ^{
        
        NSLog(@"1");
    });
    
    //group_notify不能放在最上面，group里为空时就会执行，放在group最上面的话就为空，其他group_async方法还没有调用它就会先执行
    //所有异步方法执行完后，打印"done"
    dispatch_group_notify(group, queue, ^{
       
        NSLog(@"done");
    });

    //异步方法中又有异步方法，比如网络请求，group有可能不知道什么时候才执行notify
    dispatch_group_async(group, queue, ^{
        
        //所以我们设置一个标记，在开始这个异步方法前enter
        dispatch_group_enter(group);
        dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
            
            NSLog(@"2");
            //执行完后leave
            dispatch_group_leave(group);
        });
    });

    dispatch_group_async(group, queue, ^{
        
        NSLog(@"3");
        
    });

    dispatch_group_async(group, queue, ^{
        
        NSLog(@"4");
        
    });

    dispatch_group_async(group, queue, ^{
        
        NSLog(@"5");
        
    });

#endif
   
    dispatch_queue_t queue = dispatch_queue_create("apple.queu3",DISPATCH_QUEUE_CONCURRENT);

#if 0

    //一个异步方法，比如说网络下载
    dispatch_async(queue, ^{

        //下载data...
        NSData *data;//....
        
        //当我们要显示时一定要在主线程里面执行
        dispatch_async(dispatch_get_main_queue(), ^{
            //主线程中显示图片
            UIImage *image = [UIImage imageWithData:data];
            
        });
    });

#endif
    
#if 0
    //1、2可以无序执行，3、4也可以无序执行，但是我们要1、2执行完再执行3、4.  这样我们就不好设置依赖关系了

    dispatch_async(queue, ^{
        
        NSLog(@"1");
    });   
    
    dispatch_async(queue, ^{
        
        NSLog(@"2");
    });

    //栅栏就可以挡在1、2和3、4的中间，等1、2执行完了再执行3、4

    dispatch_barrier_async(queue, ^{
        
        NSLog(@"barrier");
    });
    
    dispatch_async(queue, ^{
        
        NSLog(@"3");
    });

    dispatch_async(queue, ^{
        
        NSLog(@"4");
    });

#endif

}

@end