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# CFRunLoopWakeUp(_:)

Wakes a waiting CFRunLoop object.

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

## Parameters

`rl`

The run loop to wake up.

## 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(_:)`](/documentation/CoreFoundation/CFRunLoopWakeUp(_:)) to cause the run loop to wake up after setting a source to be signaled, if they want the source handled immediately.

---

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