iOS 多线程

下面是多线程的一些基本方法

- (IBAction)GcdButton:(UIButton*)sender {
   
    //GCD多线程分两种方式:1.串行队列2.并行队列
    //串行队列特点:任务是一个一个的执行,当一个任务执行完毕再执行另一个,多个任务不是同时进行,而是一个一个的执行.
    //并行队列:多个任务可以同时执行,谁先完成任务不一定,提高任务的执行效率,是工作中很常用的一种方式
   
    //串行队列的使用:
    //1.创建主线程队列
    /*
    dispatch_queue_t mainQueue = dispatch_get_main_queue();
   
    //将任务放在队列中执行
    dispatch_async(mainQueue, ^{
       
        NSLog(@"是否是主线程1 = %d",[NSThread isMainThread]);
       
    });
    dispatch_async(mainQueue, ^{
       
        NSLog(@"是否是主线程2 = %d",[NSThread isMainThread]);
       
    });
    dispatch_async(mainQueue, ^{
       
        NSLog(@"是否是主线程3 = %d",[NSThread isMainThread]);
       
    });
    dispatch_async(mainQueue, ^{
       
        NSLog(@"是否是主线程4 = %d",[NSThread isMainThread]);
       
    });
    */
   
    //自定义串行队列
    //参数1.队列标识符,通常以公司逆向域名形式命名
    //参数2.队列类型DISPATCH_QUEUE_SERIAL是串行队列类型
    /*
    dispatch_queue_t serialQueue = dispatch_queue_create("com.lanou3g.GCD.Serial", DISPATCH_QUEUE_SERIAL);
   
    dispatch_async(serialQueue, ^{
       
        NSLog(@"是否是主线程1 = %d",[NSThread isMainThread]);
       
    });
    dispatch_async(serialQueue, ^{
       
        NSLog(@"是否是主线程2= %d",[NSThread isMainThread]);
       
    });
    dispatch_async(serialQueue, ^{
       
        NSLog(@"是否是主线程3 = %d",[NSThread isMainThread]);
       
    });
    dispatch_async(serialQueue, ^{
       
        NSLog(@"是否是主线程4 = %d",[NSThread isMainThread]);
       
    });
    */
   
    //系统的并行队列
    //参数1.并行队列执行优先级
    //参数2.备用参数设置为0
    /*
    dispatch_queue_t golBalQueue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);
    dispatch_async(golBalQueue, ^{
       
        NSLog(@"是否是主线程1 = %d",[NSThread isMainThread]);
       
    });
    dispatch_async(golBalQueue, ^{
       
        NSLog(@"是否是主线程2= %d",[NSThread isMainThread]);
       
    });
    dispatch_async(golBalQueue, ^{
       
        NSLog(@"是否是主线程3 = %d",[NSThread isMainThread]);
       
    });
    dispatch_async(golBalQueue, ^{
       
        NSLog(@"是否是主线程4 = %d",[NSThread isMainThread]);
       
    });
    */
   
    //自定义并行队列
    //参数1.队列标识符
    //参数2.队列类型
    /*
    dispatch_queue_t conCurrentQueue = dispatch_queue_create("com.lanou3g.GCD.ConCurrent", DISPATCH_QUEUE_CONCURRENT);
    //执行队列
    dispatch_async(conCurrentQueue, ^{
       
        dispatch_async(conCurrentQueue, ^{
           
            NSLog(@"是否是主线程1 = %d",[NSThread isMainThread]);
           
        });
        dispatch_async(conCurrentQueue, ^{
           
            NSLog(@"是否是主线程2= %d",[NSThread isMainThread]);
           
        });
        dispatch_async(conCurrentQueue, ^{
           
            NSLog(@"是否是主线程3 = %d",[NSThread isMainThread]);
           
        });
        dispatch_async(conCurrentQueue, ^{
           
            NSLog(@"是否是主线程4 = %d",[NSThread isMainThread]);
           
        });
    });
    */
   
    //http://img4.duitang.com/uploads/item/201207/28/20120728105310_jvAjW.thumb.600_0.jpeg
   
    //创建子线程异步并行,回到主线程,刷新数据
    /*
    dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
      
        NSURL *url = [NSURL URLWithString:@"http://img4.duitang.com/uploads/item/201207/28/20120728105310_jvAjW.thumb.600_0.jpeg"];
        NSData *data = [NSData dataWithContentsOfURL:url];
        dispatch_async(dispatch_get_main_queue(), ^{
           //回到主线程,刷新数据
            self.MyimageView.image = [UIImage imageWithData:data];
           
        });
    });
    */
   
    //延迟多少秒执行队列里的任务(上拉下拉偏移量的延迟)
    dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(3* NSEC_PER_SEC)), dispatch_get_main_queue(), ^{
       
       
        NSLog(@"延迟三秒我才被打印");
    });
   
    //只执行一次(单例)
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
       
        NSLog(@"我只被打印一次");
       
    });
   
}

@end

单例最新的写法

+(instancetype)ShareSingleModel{
   
    //不同的子线程可能同时走 会创建多个单例对象
    //也可以采用枷锁或解锁()
    static SingleModel *singleModel =nil;
   
    //不管有多少个线程都只走一次(以后的写法)
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
       
        singleModel = [[SingleModelalloc]init];
       
    });
   
    return singleModel;
    /*
     以前的写法
    if (singleModel == nil) {
        singleModel = [[SingleModel alloc] init];
    }
    return singleModel;
     */
}

//解决其他多线程方法(除了GCD)的多线程问题
//对线程进行加锁/解锁,会占用很大的系统资源
+(instancetype)shareSingleM{
    static SingleModel *singleM =nil;
   
    @synchronized(self){
        if (singleM == nil) {
            singleM = [[[selfclass]alloc]init];
        }
    }
   
    return singleM;

}