Bug with extensible predicates and parallel executor

[tmoux]

I tried running the "ExecutorExample" program and encountered this exception:

Exception in thread "main" java.lang.IllegalArgumentException: Predicate true is not marked as extensible.
	at edu.harvard.seas.pl.abcdatalog.engine.bottomup.concurrent.ExtensibleBottomUpEvalManager.addFact(ExtensibleBottomUpEvalManager.java:182)
	at edu.harvard.seas.pl.abcdatalog.engine.bottomup.concurrent.ExtensibleBottomUpEvalManager.eval(ExtensibleBottomUpEvalManager.java:123)
	at edu.harvard.seas.pl.abcdatalog.executor.DatalogParallelExecutor.start(DatalogParallelExecutor.java:90)
	at edu.harvard.seas.pl.abcdatalog.executor.ExecutorExample.main(ExecutorExample.java:122)

After some poking around I found there is a fact "true" that always gets added to the list of initial facts:

AbcDatalog/src/main/java/edu/harvard/seas/pl/abcdatalog/ast/validation/DatalogValidator.java

Line 101 in 493d24a

rewrittenClauses.add(new ValidClause(True.getTrueAtom(), Collections.emptyList()));

The example uses the DatalogParallelExecutor, which uses the ExtensibleBottomUpEvalManager.
The exception is thrown here when trying to add the "true" fact:

AbcDatalog/src/main/java/edu/harvard/seas/pl/abcdatalog/engine/bottomup/concurrent/ExtensibleBottomUpEvalManager.java

Lines 179 to 183 in 493d24a

	public void addFact(PositiveAtom fact) {
	if (!this.extensiblePreds.contains(fact.getPred())) {
	throw new IllegalArgumentException(
	"Predicate " + fact.getPred().getSym() + " is not marked as extensible.");
	}

In the example file, the executor is initialized here:

AbcDatalog/src/main/java/edu/harvard/seas/pl/abcdatalog/executor/ExecutorExample.java

Lines 94 to 95 in 493d24a

	DatalogParallelExecutor ex = new DatalogParallelExecutor();
	ex.initialize(ast, Collections.singleton(edge));

However, there doesn't seem to be a way to add the "true" predicate here as it is private.
Thus, it seems this exception will occur whenever the DatalogParallelExecutor is used.

[aaronbembenek]

Thanks for identifying this and diagnosing the problem! I suspect the true fact was added to handle some corner cases with negation and then DatalogParallelExecutor wasn't subsequently tested (since it doesn't support negation). I've created a bunch of issues (#12, #13, #14) to avoid this in the future.