Can ANTLR4 parsers (in Java) be instrumented to be interruptible? - antlr

Question

I'd like to run my ANTLR parser with an ExecutorService so I can call Future.cancel() on it after a timeout. AIUI, I need the parser to check Thread.isInterrupted(); is there a mechanism in the parser interface for this kind of instrumentation?
In the cases where this is relevant, the parser seems to be deep in PredictionContext recursion.

Answer 1

There is a ParseCancellationException (https://javadoc.io/doc/org.antlr/antlr4-runtime/latest/index.html).
Per the docs: “This exception is thrown to cancel a parsing operation. This exception does not extend RecognitionException, allowing it to bypass the standard error recovery mechanisms. BailErrorStrategy throws this exception in response to a parse error.”
You can attach a Listener that overrides enterEveryRule() to your parser. You could have a method on that listener to set a flag to throw the ParseCancellationException the next time the parser enters a rule (which happens very frequently).
Here's a short example of what the listener might look like:
public class CancelListener extends YourBaseListener {
public boolean cancel = false;
#Override
public void enterEveryRule(ParserRuleContext ctx) {
if (cancel) {
throw new ParseCancellationException("gotta go");
}
super.enterEveryRule(ctx);
}
}
then you can add that listener to your parser:
parser.addParseListener(cancelListener);
And then:
cancelListener.cancel = true