Fatal Exception: java.util.concurrent.RejectedExecutionException

Nobody has claimed this yet.

Hello, this is a very weird error that happened just once after thousands of tests being done, and cannot replicate, but here is the stacktrace:

```
Fatal Exception: java.util.concurrent.RejectedExecutionException: Task java.util.concurrent.FutureTask@398a2b3[Not completed] rejected from java.util.concurrent.ThreadPoolExecutor@3020070[Terminated, pool size = 0, active threads = 0, queued tasks = 0, completed tasks = 1]
at java.util.concurrent.ThreadPoolExecutor$AbortPolicy.rejectedExecution(ThreadPoolExecutor.java:2072)
at java.util.concurrent.ThreadPoolExecutor.reject(ThreadPoolExecutor.java:834)
at java.util.concurrent.ThreadPoolExecutor.execute(ThreadPoolExecutor.java:1364)
at java.util.concurrent.AbstractExecutorService.submit(AbstractExecutorService.java:118)
at java.util.concurrent.Executors$DelegatedExecutorService.submit(Executors.java:671)
at com.lyft.kronos.internal.ntp.SntpServiceImpl.syncInBackground(SntpService.kt:119)
at com.lyft.kronos.internal.ntp.SntpServiceImpl.currentTime(SntpService.kt:109)
at com.lyft.kronos.internal.KronosClockImpl.getCurrentTime(KronosClockImpl.kt:19)
at com.lyft.kronos.KronosClock$DefaultImpls.getCurrentTimeMs(KronosClock.java:39)
at com.lyft.kronos.internal.KronosClockImpl.getCurrentTimeMs(KronosClockImpl.kt:8)
```

It points directly to SntpService.kt:

```
override fun syncInBackground() {
ensureServiceIsRunning()

if (state.get() != State.SYNCING) {
executor.submit { sync() }
}
}
```

Maybe should try/catch for RejectedExecutionException? Cheers.

Start in SntpService.kt at syncInBackground(), then trace ensureServiceIsRunning() and the executor used by the submit call. Use the stack trace to understand how a terminated ThreadPoolExecutor can be reached, and verify that the resulting behavior no longer produces the reported fatal RejectedExecutionException.

Written by the indexing model from the issue text.