IllegalStateException when attempting to transfer MemorySegment thread ownership

[Ty Young]

When attempting to transfer thread ownership of a MappedMemorySegment, 
an IllegalStateException is thrown:


java.lang.IllegalStateException: Attempted access outside owning thread


with the following code:


MappedMemorySegment segment;

System.out.println("Owner: " + this.address.segment().ownerThread());
System.out.println("Current: " + Thread.currentThread());

if(this.address.segment().ownerThread().equals(Thread.currentThread()))
     segment = (MappedMemorySegment)this.getAddress().segment();

else
     segment = 
(MappedMemorySegment)this.getAddress().segment().withOwnerThread(Thread.currentThread());


This error happens when closing my JavaFX application via its close 
handler on the above else branch. The application calls a static method 
which eventually creates the MappedMemorySegment on the main thread but 
the close handler works on the JavaFX thread as shown from the print output:


Owner: Thread[main,5,main]
Current: Thread[JavaFX Application Thread,5,main]


I tried using unsafe MemorySegment.ofNativeRestricted to make the 
segment thread independent, but it doesn't work out due to 
MemorySegment.ofNativeRestricted always returning a pure 
MemorySegmentImpl implementation instead of the 
**Mapped**MemorySegmentImpl. I'm guessing this is a bug?