前言

聊天列表的刷新,消息收取的处理,都是大量数据的本地或者内存的处理.都可以考虑用dispatch_source_t来优化性能.

• 当同一时间，一个事件的的触发频率很高，那么Dispatch Source会将这些响应以ADD的方式进行累积，然后等系统空闲时最终处理，如果触发频率比较零散，那么Dispatch Source会将这些事件分别响应。

@implementation YHRefreshViewController {
    dispatch_source_t _eventUnion;
}


- (void)viewDidLoad {
    [super viewDidLoad];
    _eventUnion = dispatch_source_create(DISPATCH_SOURCE_TYPE_DATA_ADD, 0, 0, dispatch_get_main_queue());
    dispatch_source_set_event_handler(_eventUnion, ^{
        NSLog(@"event Union"); //执行
    });
    dispatch_resume(_eventUnion);
}

- (void)touchesBegan:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event{
    for (int i = 0; i < 10; i++) {
        dispatch_source_merge_data(_eventUnion, 1);
    }
}


@end

• 上面代码只会打印一次
  +下面我们来看下DISPATCH_SOURCE_TYPE_DATA_ADD的所有类型

dispatch_source_merge_data()触发
1.
/*!
 * @const DISPATCH_SOURCE_TYPE_DATA_ADD
 * @discussion A dispatch source that coalesces data obtained via calls to
 * dispatch_source_merge_data(). An ADD is used to coalesce the data.
 */
#define DISPATCH_SOURCE_TYPE_DATA_ADD
 联合频率比较高的事件,传递数据会相加

2.
/*!
 * @const DISPATCH_SOURCE_TYPE_DATA_OR
 * @discussion A dispatch source that coalesces data obtained via calls to
 * dispatch_source_merge_data(). A bitwise OR is used to coalesce the data.
 */
#define DISPATCH_SOURCE_TYPE_DATA_OR
 联合频率比较高的事件,传递数据会按位或

3.
/*!
 * @const DISPATCH_SOURCE_TYPE_WRITE
 * @discussion A dispatch source that monitors a file descriptor for available
 * buffer space to write bytes.
 */
#define DISPATCH_SOURCE_TYPE_WRITE

可以作为定时器,需要dispatch_source_set_timer();