dispatch_source_t計時器小記

查看FBKVOController時，看到 dispatch_source_t 創建的定時器，然後就網路上查閱資料了解了一下,大致步驟是：
1.創建調度源 dispatch_source_create(dispatch_source_type_t type, uintptr_t handle, unsigned long mask, dispatch_queue_t _Nullable queue);

2. 設置計時器 dispatch_source_set_timer(dispatch_source_t source, dispatch_time_t start, uint64_t interval, uint64_t leeway);

3.設置給調度源 事件處理程序塊 dispatch_source_set_event_handler(dispatch_source_t source, dispatch_block_t _Nullable handler);
4.恢復啟用 dispatch_resume(dispatch_object_t object);

5.設置掛起計時器或者 取消調度源dispatch_source_cancel(dispatch_source_t source); or dispatch_suspend(dispatch_object_t object);

注意：suspend狀態如果將計時器置為nil將會報錯，suspend後需要resume後方可 置為nil, 或者直接cancel,再將計時器置為nil

下方為示例代碼：

    dispatch_queue_t queue = dispatch_get_global_queue(0, 0);
    _timer = dispatch_source_create(DISPATCH_SOURCE_TYPE_TIMER, 0, 0, queue);
    dispatch_source_set_timer(_timer, dispatch_time(DISPATCH_TIME_NOW, 0 *NSEC_PER_SEC), 1.0 * NSEC_PER_SEC, 0);
    __block NSInteger i = 0;
    __weak typeof(self) weakSelf = self;
    dispatch_source_set_event_handler(_timer, ^{
        i ++;
        NSLog(@"次數 ： %ld", (long)i);
        if (i == 10) {
            [weakSelf cancel];
        }
    });
    
    dispatch_resume(_timer);
}

- (void)cancel {
    dispatch_source_cancel(_timer);
    _timer = nil;
    NSLog(@"計時器銷毀");
}

以上是個人學習記錄，如果錯誤還請指正，謝謝。