---
title: "CFMachPortGetInvalidationCallBack(_:)"
framework: corefoundation
role: symbol
role_heading: Function
path: "corefoundation/cfmachportgetinvalidationcallback(_:)"
---

# CFMachPortGetInvalidationCallBack(_:)

Returns the invalidation callback function for a CFMachPort object.

## Declaration

```swift
func CFMachPortGetInvalidationCallBack(_ port: CFMachPort!) -> CFMachPortInvalidationCallBack!
```

## Parameters

- `port`: The CFMachPort object to examine.

## Return Value

Return Value The callback function invoked when port is invalidated. NULL if no callback has been set with CFMachPortSetInvalidationCallBack(_:_:).

## See Also

### Examining a CFMachPort Object

- [CFMachPortGetContext(_:_:)](corefoundation/cfmachportgetcontext(_:_:).md)
- [CFMachPortGetPort(_:)](corefoundation/cfmachportgetport(_:).md)
- [CFMachPortIsValid(_:)](corefoundation/cfmachportisvalid(_:).md)