Loading and closing a model sometimes throws an NPE

[qiemem]

It's very sporadic... and could have something to do with GCs. It seemed to happen when I forced a GC... sometimes... Very strange. Also might happen more frequently when the child model is opening a child model.

Here's the stack:

org.nlogo.nvm.EngineException: Extension exception: java.lang.NullPointerException
 at java.util.concurrent.FutureTask$Sync.innerGet(FutureTask.java:222)
 at java.util.concurrent.FutureTask.get(FutureTask.java:83)
 at ChildModel.waitFor(ChildModel.java:308)
 at ChildModel.runUISafely(ChildModel.java:274)
 at GUIChildModel.<init>(GUIChildModel.java:24)
 at LevelsSpace$LoadModel.perform(LevelsSpace.java:180)
 at org.nlogo.prim._extern.perform(_extern.java:54)
 at org.nlogo.nvm.Context.stepConcurrent(Context.java:91)
 at org.nlogo.nvm.ConcurrentJob.step(ConcurrentJob.java:82)
 at org.nlogo.job.JobThread.org$nlogo$job$JobThread$$runPrimaryJobs(JobThread.scala:143)
 at org.nlogo.job.JobThread$$anonfun$run$1.apply$mcV$sp(JobThread.scala:78)
 at org.nlogo.job.JobThread$$anonfun$run$1.apply(JobThread.scala:76)
 at org.nlogo.job.JobThread$$anonfun$run$1.apply(JobThread.scala:76)
 at scala.util.control.Exception$Catch.apply(Exception.scala:88)
 at org.nlogo.util.Exceptions$.handling(Exceptions.scala:41)
 at org.nlogo.job.JobThread.run(JobThread.scala:75)

I don't see anything in innerGet that could cause it.

[mrerrormessage]

Is it possible that the NPE is in the Callable which is being passed into FutureTask? Alternatively, is it possible that innerGet throws an NPE when the callable throws an Exception?

[mrerrormessage]

This was caused by getActiveWindow returning null. The easiest way to reproduce it is to have levelspace open a bunch of GUI windows and (while it is opening them) switch over to another Java application. I have addressed the issue in the Code Tabs PR by defaulting to positioning the widget relative to the App frame if the active window is null.

[arthurhjorth]

Nice catch, @mrerrormessage!