Bug: MappedMemorySegmentImpl uses internal FileChannelImpl

[Maurizio Cimadamore]

Note that to be able to map a file we need a file descriptor. The file 
system you provided has support for channels, etc. but note that the 
channels implementation do not support mapping using MappedByteBuffer:

https://github.com/google/jimfs/blob/master/jimfs/src/main/java/com/google/common/jimfs/JimfsFileChannel.java#L592

So I don't really see how we could make this work. At the end of the 
day, MemorySegment.mapFromPath has to end up calling `mmap` - and we 
need to be able to retrieve the parameters of the mmap call from somewhere.

Maurizio


On 29/06/2020 16:55, Ty Young wrote:
> Tried using Google's in-memory filesystem:
>
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> https://github.com/google/jimfs
>
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> for storing mmap files but ran into an issue because 
> MappedMemorySegmentImpl uses internal FileChannelImpl method:
>
>
> https://github.com/openjdk/panama-foreign/blob/acc11115db42cc0e17efdf361d58c65f4e922f39/src/jdk.incubator.foreign/share/classes/jdk/internal/foreign/MappedMemorySegmentImpl.java#L105 
>
>
>
> which causes a class casting exception when using Google's in-memory 
> Java filesystem and probably other implementations as well.
>
>
>