JavaSymbolResolver used in parallel

[corradomio]

In this moment, it is not possible to use JavaSymbolResolver in parallel.
The problem is in JavaParserFacade, in the static method get:

public static JavaParserFacade get(TypeSolver typeSolver) {
    return instances.computeIfAbsent(typeSolver, JavaParserFacade::new);
}

instances is a WeakHashMap but this class is not thread-safe.
It can be enough to convert this method in a "synchronized" method:

public static **synchronized** JavaParserFacade get(TypeSolver typeSolver) {
    return instances.computeIfAbsent(typeSolver, JavaParserFacade::new);
}

[MysterAitch]

Just wanted to flag up these really helpful / thoughtful comments from @migliorabile in a separate issue, to give some more context:

#2671 (comment)

#2671 (comment)

At the moment, "JavaParserFacade.get()" IS ""the problem""because

1. it is a GLOBAL/STATIC method

2. it caches ALL type solvers

3. it is used in several places inside the library

4. it is NOT synchronized

I tried to remove it, but I have not implemented this part.
The current ""possible"" solution is

1. to create a JavaParserFacadeFactory that contains the map typesolver -> JavaParserFacade (the current static part of JavaParserFacade  inserted in a separated class)

2. to extend TypeSolver with a method "getFactory" that return a JavaParserFacadeFactory >

The call (repeat, used in the library implementation)

JavaParserFacade.get(typeSolver)

it will converted in

public static JavaParserFacade get(TypeSolver typeSolver) {
    return typesolver.getRoot().getFactory().get(typeSolver)
}

In this way, the root typeSolver contains the ""thread-local"" cache of type solvers, and with a minimum impact on the current code. The problem is to change the current typeSolver interface.

But I am not sure.