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https://issues.apache.org/jira/browse/ARROW-1163?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16242190#comment-16242190
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Lu Qi commented on ARROW-1163:
-------------------------------
Hi,Philipp Moritz,
I've been working on reading and writing Tensor in Java for several weeks. I've
got Tensor structure like this:
Class Tensor{ private float[] storage; private int[] shape }
I used JNI to leverage plasma C++ client . One good thing is when writing
tensor ,there is
"getPrimitiveArrayCritical" method which gets the address in Java heap (based
on vm impletation),
thus I can construct Tensor in C++ easily without copying, although it stops GC
in this process, but
plasma writing is non blocking. On the other side of the world, when reading
tensor , I need to copy
the share memory into java heap, this will cost time. So, in order to save
reading time , pure Java
client may be a good choice.
As to pure Java client , may be we can use jni to get fd first and construct a
FileDescriptor .
https://stackoverflow.com/questions/4845122/using-a-numbered-file-descriptor-from-java
> [Plasma] Java client for Plasma
> -------------------------------
>
> Key: ARROW-1163
> URL: https://issues.apache.org/jira/browse/ARROW-1163
> Project: Apache Arrow
> Issue Type: New Feature
> Reporter: Philipp Moritz
>
> We should start thinking about how a Java client for plasma would look like.
> Given the focus of arrow to support Python, C++ and Java really well, it is
> the next important target after Python and C++.
> My preliminary thoughts on it are the following ones: We can either go with
> JNI and wrap the C++ client or (in my opinion preferable) write a pure Java
> client. It would communicate with the Plasma store via Java flatbuffers over
> sockets.
> It seems that the only thing blocking a pure Java client at the moment is the
> way we ship file descriptors for the memory mapped files between store and
> client (see the file fling.cc in the Plasma repo). We would need to get rid
> of that because there is no pure Java API that allows transferring file
> descriptors over a process boundary. So the way to transfer memory mapped
> files over process boundaries then is probably to use the file system and
> keep the memory mapped files in the file system instead of unlinking them
> immediately (as we do at the moment), so they can be opened by the client
> process via their path.
> The challenge in this case is how to clean the files up and make sure they
> are not lying around if the plasma store crashes. One option is to store the
> plasma store PID with the file (i.e. as part of the file name) and let the
> plasma store clean them up the next time it is started); maybe there is OS
> level support for temporary files we can reuse.
> I probably won't get to this for a while, so if anybody needs this or has
> free cycles, they should feel free to chime in. Also opinions on the design
> are appreciated!
> -- Philipp.
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