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# CMTimebaseSetTimerDispatchSourceToFireImmediately(_:timerSource:)

Sets the timer dispatch source to fire immediately once, overriding any previous timer call.

```
func CMTimebaseSetTimerDispatchSourceToFireImmediately(_ timebase: CMTimebase, timerSource: dispatch_source_t) -> OSStatus
```

## Discussion

The timer source you specify must be on the list of timers the timebase manages. This is equivalent to calling `dispatch_source_set_timer(timerSource, DISPATCH_TIME_NOW, 0, 0 )`; except that the timebase gets to know that it shouldn’t interfere.

---

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