---
title: cancel()
framework: dispatch
role: symbol
role_heading: Instance Method
path: dispatch/dispatchsourceprotocol/cancel()
---

# cancel()

Asynchronously cancels the dispatch source, preventing any further invocation of its event handler block.

## Declaration

```swift
func cancel()
```

## Discussion

Discussion Cancellation prevents any further invocation of the event handler block for the dispatch source, but does not interrupt any work that is already in progress. If a cancellation handler was set before cancellation, it is sub mitted to the target queue once any in-progress event handler work is finished. Once the cancellation handler is submitted, it is safe to close the source’s handle (file descriptor or mach port). It is invalid to close a file descriptor or deallocate a mach port that is currently being tracked by a dispatch source object before the cancellation handler is invoked.

## See Also

### Canceling a Dispatch Source

- [isCancelled](dispatch/dispatchsourceprotocol/iscancelled.md)
- [setCancelHandler(handler:)](dispatch/dispatchsourceprotocol/setcancelhandler(handler:).md)
- [setCancelHandler(qos:flags:handler:)](dispatch/dispatchsourceprotocol/setcancelhandler(qos:flags:handler:).md)