Java C++ without JNI

Question

My app is written in Java. There is a C++ library I need to utilize. I don't want to use JNI.

60 times a second, the C++ app needs to send the Java app 10MB of data; and the Java app needs to send the C++ app 10 MB of data.

Both apps are running on the same machine; the OS is either Linux or Mac OS X.

What is the most efficient way to do this? (At the moment, I'm considering TCPIP ports; but in C++, I can do memory mapping -- can I do something similar in Java?)

Thanks!

Answer 1

Yes, Java has memory-mapped files with the NIO framework.

If you're trying to avoid JNI because you didn't want to write stubs, you can also interface with C++ code (at least ones that are extern "C") using JNA. For best performance, use direct mapping (concrete classes with native methods, not a mapped interface)---see documentation for more details. :-)

Answer 2

Using mapped files is a way of hand-rolling a highly optimized rpc. You might consider starting with a web service talking over local sockets, using MTOM for attaching the data, or just dropping it into a file. Then you could measure the performance. If the data was a problem, you could then use mapping.

Note that there are some odd restrictions on this that make your code sensitive to whether it is running on Windows or not. On Windows, you can't delete something that is open.

I should point out that I have done exactly what you are proposing here. It has a control channel on a socket, and the data is shared via a file that is mmapped in C++ (or the Windows equivalent) and NIO mapped in Java. It works. I've never measured maximum throughput, though.