GCD各种情况整理

01 异步函数+并发队列：开启多条线程，并发执行任务
02 异步函数+串行队列：开启一条线程，串行执行任务
03 同步函数+并发队列：不开线程，串行执行任务
04 同步函数+串行队列：不开线程，串行执行任务
05 异步函数+主队列：不开线程，在主线程中串行执行任务
06 同步函数+主队列：不开线程，串行执行任务（注意死锁发生）
07 注意同步函数和异步函数在执行顺序上面的差异

//同步函数+主队列:死锁
-(void)syncMain
{
    NSLog(@"----");
    //1.获得主队列
    dispatch_queue_t queue =  dispatch_get_main_queue();
    
    //2.同步函数
    dispatch_sync(queue, ^{
        NSLog(@"---download1---%@",[NSThread currentThread]);
    });
    
    dispatch_sync(queue, ^{
        NSLog(@"---download2---%@",[NSThread currentThread]);
    });
    
    dispatch_sync(queue, ^{
        NSLog(@"---download3---%@",[NSThread currentThread]);
    });
    dispatch_sync(queue, ^{
        NSLog(@"---download4---%@",[NSThread currentThread]);
    });
    
}

//异步函数+主队列:不会开线程,任务串行执行
-(void)asyncMain
{
    //1.获得主队列
    dispatch_queue_t queue =  dispatch_get_main_queue();
    
    //2.异步函数
    dispatch_async(queue, ^{
        NSLog(@"---download1---%@",[NSThread currentThread]);
    });
    
    dispatch_async(queue, ^{
        NSLog(@"---download2---%@",[NSThread currentThread]);
    });
    
    dispatch_async(queue, ^{
        NSLog(@"---download3---%@",[NSThread currentThread]);
    });
    dispatch_async(queue, ^{
        NSLog(@"---download4---%@",[NSThread currentThread]);
    });

}

//同步函数+串行队列:不会开线程,任务串行执行
-(void)syncSerial
{
    
    //创建串行队列
    /*
     第一个参数:C语言字符串,标签
     第二个参数:
     DISPATCH_QUEUE_CONCURRENT:并发队列
     DISPATCH_QUEUE_SERIAL:串行队列
     */
    dispatch_queue_t queue =  dispatch_queue_create("com.520it.download", DISPATCH_QUEUE_SERIAL);
    
    dispatch_sync(queue, ^{
        NSLog(@"---download1---%@",[NSThread currentThread]);
    });
    
    dispatch_sync(queue, ^{
        NSLog(@"---download2---%@",[NSThread currentThread]);
    });
    
    dispatch_sync(queue, ^{
        NSLog(@"---download3---%@",[NSThread currentThread]);
    });
    dispatch_sync(queue, ^{
        NSLog(@"---download4---%@",[NSThread currentThread]);
    });
}
//同步函数+并发队列:不会开线程,任务串行执行
-(void)syncConcurrent
{
    dispatch_queue_t queue = dispatch_get_global_queue(0, 0);
    
    NSLog(@"--syncConcurrent--start-");
    
    dispatch_sync(queue, ^{
        NSLog(@"---download1---%@",[NSThread currentThread]);
    });
    
    dispatch_sync(queue, ^{
        NSLog(@"---download2---%@",[NSThread currentThread]);
    });
    
    dispatch_sync(queue, ^{
        NSLog(@"---download3---%@",[NSThread currentThread]);
    });
    dispatch_sync(queue, ^{
        NSLog(@"---download4---%@",[NSThread currentThread]);
    });
    
      NSLog(@"--syncConcurrent--end-");
}
//异步函数+串行队列:会开启一条线程,任务串行执行
-(void)asyncSerial
{
    //创建串行队列
    /*
     第一个参数:C语言字符串,标签
     第二个参数:
     DISPATCH_QUEUE_CONCURRENT:并发队列
     DISPATCH_QUEUE_SERIAL:串行队列
     */
    dispatch_queue_t queue =  dispatch_queue_create("com.520it.download", DISPATCH_QUEUE_SERIAL);
    
    dispatch_async(queue, ^{
        NSLog(@"---download1---%@",[NSThread currentThread]);
    });
    
    dispatch_async(queue, ^{
        NSLog(@"---download2---%@",[NSThread currentThread]);
    });
    
    dispatch_async(queue, ^{
        NSLog(@"---download3---%@",[NSThread currentThread]);
    });
    dispatch_async(queue, ^{
        NSLog(@"---download4---%@",[NSThread currentThread]);
    });
}
//异步函数+并发队列:会开启新的线程,并发执行
-(void)asyncCONCURRENT
{
    //创建并发队列
    /*
     第一个参数:C语言字符串,标签
     第二个参数:
     DISPATCH_QUEUE_CONCURRENT:并发队列
     DISPATCH_QUEUE_SERIAL:串行队列
     */
//    dispatch_queue_t queue =  dispatch_queue_create("com.520it.download", DISPATCH_QUEUE_CONCURRENT);
    NSLog(@"--asyncCONCURRENT--start-");
    //获得全局并发队列
    /*
     第一个参数:队列的优先级DISPATCH_QUEUE_PRIORITY_DEFAULT
     第二个参数:永远传0
     */
    dispatch_queue_t queue = dispatch_get_global_queue(0, 0);
    //异步函数
    /*
     第一个参数:队列
     第二个参数:block,在里面封装任务
     */
    dispatch_async(queue, ^{
        NSLog(@"---download1---%@",[NSThread currentThread]);
    });
    
    dispatch_async(queue, ^{
        NSLog(@"---download2---%@",[NSThread currentThread]);
    });
    
    dispatch_async(queue, ^{
        NSLog(@"---download3---%@",[NSThread currentThread]);
    });
    dispatch_async(queue, ^{
        NSLog(@"---download4---%@",[NSThread currentThread]);
    });
    
      NSLog(@"--asyncCONCURRENT--end-");
}