How can I share memory between two JVM instances?

Question

I build a huge graph in JVM (Scala) which I want to use repeatedly, tweaking algorithms. I'd rather not reload it each time from disk. Is there a way to have it sit in one JVM while connecting from another, where the algorithms are being developed?

Answer 1

Save your graph to disk, then map it into memory with MappedByteBuffer. Both processes should use the same memory, which will be shared with the page cache.

Answer 2

Two JVMs sounds more complicated than it needs to be. Have you considered doing a kind of "hot deploy" setup, where your main program loads up the graph, displays the UI, and then asks for (or automatically looks for) a jar/class file to load that contains your actual algorithm code? That way your algorithm code would be running in the same jvm as your graph, but you wouldn't have to reload the graph just to reload a new algorithm implementation.

UPDATE to address OP's question in comment:

Here's how you could structure your code so that your algorithms would be swappable. It doesn't matter what the various algorithms do, so long as they are operating on the same input data. Just define an interface like the following, and have your graph algorithms implement it.

public interface GraphAlgorithm {
  public void doStuff(Map<whatever> myBigGraph)
}

If your algorithms are displaying results to some kind of widget, you could pass that in as well, or have doStuff() return some kind of results object.