dispatch_barrier_sync / dispatch_barrier_async区别学习

dispatch_barrier_sync / dispatch_barrier_async区别

dispatch_barrier_sync

Submits a barrier block object for execution and waits until that block completes.
提交一个栅栏函数在执行中,它会等待栅栏函数执行完

dispatch_barrier_async

Submits a barrier block for asynchronous execution and returns immediately.提交一个栅栏函数在异步执行中,它会立马返回

• dispatch_barrier_sync 需要等待栅栏执行完才会执行栅栏后面的任务
• dispatch_barrier_async 无需等待栅栏执行完,会继续往下走

共同点：

1、都会等待在它前面插入队列的任务（1、2、3）先执行完
2、都会等待他们自己的任务（barrier）执行完再执行后面的任务（4、5、6）

不共同点：

1、dispatch_barrier_sync需要等待自己的任务（barrier）结束之后，才会继续执行写在barrier后面的任务（4、5、6），然后执行后面的任务
2、dispatch_barrier_async将自己的任务（barrier）插入到queue之后，不会等待自己的任务结束，它会继续把后面的任务（4、5、6）插入到queue

参考代码

 - (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event {
    
    dispatch_async(dispatch_queue_create("mmmmmm", DISPATCH_QUEUE_CONCURRENT), ^{
        [self logBarrierOrder];
    }); 
}

- (void)logBarrierOrder {
    NSLog(@"%@ >>>>>  start ", [NSThread currentThread]);
    dispatch_queue_t queue = dispatch_queue_create("test.barrier.queue", DISPATCH_QUEUE_CONCURRENT);
    //异步函数 无序执行
    
    NSLog(@"%@ >>>>>  barrier 前面 1 ", [NSThread currentThread]);
    dispatch_async(queue, ^{
        sleep(5);
        NSLog(@"%@ >>>>> 任务  1 ", [NSThread currentThread]);
    });
    
    NSLog(@"%@ >>>>>  barrier 前面 2 ", [NSThread currentThread]);
    dispatch_async(queue, ^{
        sleep(3);
        NSLog(@"%@ >>>>> 任务  2 ", [NSThread currentThread]);
    });
    
    NSLog(@"%@ >>>>>  barrier 前面 3 ", [NSThread currentThread]);
    dispatch_async(queue, ^{
        sleep(1);
        NSLog(@"%@ >>>>> 任务  3 ", [NSThread currentThread]);
    });
    NSLog(@"%@ >>>>>  barrier 前面 4.1 ", [NSThread currentThread]);
    
    
    dispatch_barrier_sync(queue, ^{
        sleep(7);
        NSLog(@"%@ ++++++  barrier ++++++ ", [NSThread currentThread]);
    });
    
    
    NSLog(@"%@ >>>>>  barrier 后面 4.2 ", [NSThread currentThread]);
    dispatch_async(queue, ^{
        NSLog(@"%@ >>>>> 任务  4 ", [NSThread currentThread]);
    });
    
    NSLog(@"%@ >>>>>  barrier 后面 5 ", [NSThread currentThread]);
    dispatch_async(queue, ^{
        sleep(10);
        NSLog(@"%@ >>>>> 任务  5 ", [NSThread currentThread]);
    });
    
    NSLog(@"%@ >>>>>  barrier 后面 6 ", [NSThread currentThread]);
    dispatch_async(queue, ^{
        NSLog(@"%@ >>>>> 任务  6 ", [NSThread currentThread]);
    });
    
    NSLog(@"%@ >>>>>  end ", [NSThread currentThread]);
}

Test log

dispatch_barrier_sync

dispatch_barrier_sync

dispatch_barrier_async

dispatch_barrier_async

demo

2017年07月22日08:54:33

文件路径 path 与 NSURL 的 path Component appending 区别

NSString or NSURL

    NSURL *url = [NSURL URLWithString:@"http://hunlimao.com/wi"];
    NSString *urlStr = [NSString stringWithFormat:@"%@",url.absoluteString];
    urlStr = [urlStr stringByAppendingPathComponent:[NSString stringWithFormat:@"%d",77]];
    NSLog(@"%@",urlStr);
// result is http:/hunlimao.com/wi/77         http后面少了”/“

    NSURL *url = [NSURL URLWithString:@"http://hunlimao.com/wi"];
    url = [url URLByAppendingPathComponent:[NSString stringWithFormat:@"/%d",77]];

   //加或不加“/” 结果都一样 url = [url URLByAppendingPathComponent:[NSString stringWithFormat:@"%d",77]];

    NSString *urlStr = [NSString stringWithFormat:@"%@",url.absoluteString];
    NSLog(@"%@",urlStr);
// result is http://hunlimao.com/wi/77       是一个正常 url string

• NSString 的 stringByAppendingPathComponent 是用于处理一般文件或文件夹路径，路径字符串内不允许有两个连续的"//“存在；
• NSURL 的URLByAppendingPathComponent 则是明确用于对 request Url 进行 component 拼接的，拼接的 component 中加不加”/“都一样，这个和 string 的 拼接 component 同理
  参考点1