BUG: withOwnerThread closes MappedMemorySegment

[sundararajan.athijegannathan at oracle.com]

Can you access source?

https://github.com/openjdk/panama-foreign/blob/foreign-jextract/src/jdk.incubator.foreign/share/classes/jdk/incubator/foreign/MemorySegment.java

Yes, afaik it is implementation technical reason. (Maurizio will 
clarify). That said, it should be possible to map different file 
segments to *different* memory segments with different owners, right? 
What's the advantage of mapping the whole & slice to own parts by 
different threads?

-Sundar

On 23/09/20 11:02 am, Ty Young wrote:
> Javadoc isn't working for withOwnerThread or withCleanupAction for me 
> on Netbeans:
>
>
> https://imgur.com/a/Q21pZAC
>
>
> Says it's downloading HTTP Javadoc for about 10 seconds then gives up. 
> Javadoc of other older methods work just fine and I didn't think it'd 
> close the segment as other withers(withAccessModes) do not.
>
>
> So I wasn't able to read it, my bad.
>
>
> Question: is this an absolute requirement because of technical 
> restrains? Could this be removed so that, for example, it is possible 
> to make an array segment unbound but have individual array index 
> segments be bound to a specific thread?
>
>
> On 9/23/20 12:00 AM, sundararajan.athijegannathan at oracle.com wrote:
>> javadoc of MemorySegment.withOwnerThread starts as follows:
>>
>> "    * Obtains a new memory segment backed by the same underlying 
>> memory region as this segment,
>>      * but with different owner thread. As a side-effect, this 
>> segment will be marked as <em>not alive</em>,
>>      * and subsequent operations on this segment will result in 
>> runtime errors.
>> "
>>
>> So the behavior seen is as the specification.
>>
>> -Sundar
>>
>> On 23/09/20 7:36 am, Ty Young wrote:
>>> A bug seems to have been introduced wherein using withOwnerThread 
>>> causes a MappedMemorySegment to close:
>>>
>>>
>>>     File file = new File("./test");
>>>
>>>         if(file.exists())
>>>             file.delete();
>>>
>>>         file.createNewFile();
>>>
>>>         MappedMemorySegment nativeFile = 
>>> MemorySegment.mapFromPath(file.toPath(), 0, 4096, 
>>> FileChannel.MapMode.READ_WRITE);
>>>
>>>         System.out.println(nativeFile.isAlive());
>>>
>>>         MappedMemorySegment segment = 
>>> (MappedMemorySegment)nativeFile.asSlice(4);
>>>         segment = (MappedMemorySegment)nativeFile.asSlice(4);
>>>         segment = 
>>> (MappedMemorySegment)nativeFile.asSlice(4).withOwnerThread(null);
>>>
>>>         System.out.println(nativeFile.isAlive());
>>>         System.out.println(segment.isAlive());
>>>
>>>
>>> which prints true, false, and then true. The original 
>>> MappedMemorySegment was never closed, so this is unexpected.
>>>