Question

There is a rule to find out, for sure, all objects that could possibly have concurrent access in a Java program? My intention is use such rule, if it exists, to find out which Java classes could possibly have concurrent access and then guarantee that they are thread-safe. This rule could be very useful when inspecting a large Java project. I’ve thought to look for static methods, but I’m not sure if this is the only way an object can be accessible to multiple threads.

Answer 1

It seems very, very unlikely that such a thing exists as a single rule. Imagine the following:

public void maybeAccessConcurrently(Program x) {
    if(halts(x)) {
        accessConcurrentObject();
    } else {
        // don't.
    }
}

I don’t know about you, but I can’t really contrive a rule that isn’t equivalent to deciding the halting problem here, especially not by simple inspection of types or declarations. I think you may find that like other static analysis techniques, there are a set of properties that you can check within reason. The Bandera project appears to be an effort to use various model-checking techniques to verify properties of concurrent Java code. There may be other similar efforts (all of which are most likely to involve model checking, given the presence of concurrency).