---
title: "CFRunLoopWakeUp(_:)"
framework: corefoundation
role: symbol
role_heading: Function
path: "corefoundation/cfrunloopwakeup(_:)"
---

# CFRunLoopWakeUp(_:)

Wakes a waiting CFRunLoop object.

## Declaration

```swift
func CFRunLoopWakeUp(_ rl: CFRunLoop!)
```

## Parameters

- `rl`: The run loop to wake up.

## Discussion

Discussion A run loop goes to sleep when it is waiting for a source or timer to become ready to fire. If no source or timer fires, the run loop stays there until it times out or is explicitly woken up. If a run loop is modified, such as a new source added, you need to wake up the run loop to allow it to process the change. Version 0 sources use CFRunLoopWakeUp(_:) to cause the run loop to wake up after setting a source to be signaled, if they want the source handled immediately.

## See Also

### Starting and Stopping a Run Loop

- [CFRunLoopRun()](corefoundation/cfrunlooprun().md)
- [CFRunLoopRunInMode(_:_:_:)](corefoundation/cfrunloopruninmode(_:_:_:).md)
- [CFRunLoopStop(_:)](corefoundation/cfrunloopstop(_:).md)
- [CFRunLoopIsWaiting(_:)](corefoundation/cfrunloopiswaiting(_:).md)