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# CFRunLoopSourceSignal(_:)

Signals a CFRunLoopSource object, marking it as ready to fire.

```
func CFRunLoopSourceSignal(_ source: CFRunLoopSource!)
```

## Parameters

`source`

The run loop source to signal.

## Discussion

This function has no effect on version 1 sources, which are automatically handled when Mach messages arrive for them. After signaling a version 0 source, you need to call [`CFRunLoopWakeUp(_:)`](/documentation/CoreFoundation/CFRunLoopWakeUp(_:)) on one of the run loops in which the source is registered to get the source handled immediately.

---

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