---
title: "CFMachPortSetInvalidationCallBack(_:_:)"
framework: corefoundation
role: symbol
role_heading: Function
path: "corefoundation/cfmachportsetinvalidationcallback(_:_:)"
---

# CFMachPortSetInvalidationCallBack(_:_:)

Sets the callback function invoked when a CFMachPort object is invalidated.

## Declaration

```swift
func CFMachPortSetInvalidationCallBack(_ port: CFMachPort!, _ callout: CFMachPortInvalidationCallBack!)
```

## Parameters

- `port`: The CFMachPort object to modify.
- `callout`: The callback function to invoke when port is invalidated. Pass NULL to remove a callback.

## Discussion

Discussion If port is already invalid, callout is invoked immediately.

## See Also

### Configuring a CFMachPort Object

- [CFMachPortInvalidate(_:)](corefoundation/cfmachportinvalidate(_:).md)
- [CFMachPortCreateRunLoopSource(_:_:_:)](corefoundation/cfmachportcreaterunloopsource(_:_:_:).md)