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# SetHandler

Sets the handler block to run when the timer fires.

```
virtual kern_return_t SetHandler(OSAction *action);
```

## Parameters

`action`

The [`OSAction`](/documentation/DriverKit/OSAction) object that contains your custom callback method. The dispatch source object retains your action object until you call this method again or cancel the dispatch source.

## Return Value

[`kIOReturnSuccess`](/documentation/DriverKit/kIOReturnSuccess) on success, or another value if an error occurs. See [Error Codes](/documentation/DriverKit/error-codes).

---

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