Memory Mapped file segment (file is empty)

[Paul Sandoz]

Hi Johannes,

This is the correct list. Feedback on the API and its usability is very important, as well as whether the implementation works as expected.

This was fixed in https://bugs.openjdk.java.net/browse/JDK-8246095 <https://bugs.openjdk.java.net/browse/JDK-8246095>

https://github.com/openjdk/panama-foreign/blob/foreign-memaccess/src/jdk.incubator.foreign/share/classes/jdk/internal/foreign/MappedMemorySegmentImpl.java#L102 <https://github.com/openjdk/panama-foreign/blob/foreign-memaccess/src/jdk.incubator.foreign/share/classes/jdk/internal/foreign/MappedMemorySegmentImpl.java#L102>

What JDK build are you using?

Paul.

> On Jun 24, 2020, at 3:48 PM, Johannes Lichtenberger <lichtenberger.johannes at gmail.com> wrote:
> 
> Hi,
> 
> I guess that's not the right mailinglist to ask for help with the API, but
> maybe you can point me at least somewhere.
> 
> Currently I face the problem, that I can't get a memory segment on an empty
> file when I want to memory map a file. However, a writer would write to the
> memory mapped file.
> 
> I want to be able to swap a rather old RandomAccessFile based
> implementation with a memory mapped file implementation. The two classes
> (actually three, but only the FileReader and FileWriter matters) are rather
> simple.
> 
> The old package:
> 
> https://github.com/sirixdb/sirix/tree/master/bundles/sirix-core/src/main/java/org/sirix/io/file
> 
> 
> and the new package
> 
> https://github.com/sirixdb/sirix/tree/master/bundles/sirix-core/src/main/java/org/sirix/io/memorymapped
> 
> This line fails if the underlying file size is 0:
> 
> https://github.com/sirixdb/sirix/blob/7bdbd5d17a034f02902f8f7dd0ef7012d89c81fb/bundles/sirix-core/src/main/java/org/sirix/io/memorymapped/MemoryMappedFileWriter.java#L83
> 
> Stacktrace  (Precondition fails, so I'm not using the API in the intended
> way):
> 
> java.lang.IllegalArgumentException: Requested bytes size must be > 0.
> 
> at
> jdk.incubator.foreign/jdk.internal.foreign.Utils.makeMappedSegment(Utils.java:140)
> at
> jdk.incubator.foreign/jdk.incubator.foreign.MemorySegment.mapFromPath(MemorySegment.java:398)
> at
> org.sirix.io.memorymapped.MemoryMappedFileWriter.<init>(MemoryMappedFileWriter.java:83)
> 
> 
> So, it might be easiest to write a more or less direct conversion to the
> Foreign Memory API. Maybe someone can help or point me to a helpful
> Mailinglist/Forum/whatever.
> 
> Kind regards
> Johannes