[rules-users] OptaPlanner: Solver.isEveryProblemFactChangeProcessed() return true before the last fact change is processed

[Geoffrey De Smet]

On 30-04-14 12:17, Hagai wrote:
> Using OptaPlanner 6.0.1.Final and following the documentation for real-time
> planning:
> "Alternatively, you can subscribe to the BestSolutionChangedEvent.
> A BestSolutionChangedEvent doesn't guarantee that every ProblemFactChange
> has been
> processed already, so check Solver.isEveryProblemFactChangeProcessed() and
> ignore any
> BestSolutionChangedEvent fired while that method returns false."
>
> However, Solver.isEveryProblemFactChangeProcessed() return true before the
> last fact change is processed.
> This is documented in the code DefaultSolver.java: *// TODO bug: the last
> ProblemFactChange might already been polled, but not processed yet*
>
> I believe this can be fixed using the following code in
> DefaultSolver.checkProblemFactChanges:
>
>              ProblemFactChange problemFactChange =
> problemFactChangeQueue*.peek()*;
>              while (problemFactChange != null) {
>                  score = doProblemFactChange(problemFactChange);
>                  *problemFactChangeQueue.poll();*
>                  count++;
>                  problemFactChange = problemFactChangeQueue*.peek()*;
>              }
>
> This way the queue will not be empty until the fact change is processed.

Thanks for reporting.
This is definitely an issue indeed, if 
isEveryProblemFactChangeProcessed() is called from a different thread 
than then solver thread.
The javadoc clearly promises that isEveryProblemFactChangeProcessed() is 
thread-safe.
I 'll take a look into fixing it with your suggestion.

Note: In practice, you 'll usually call 
isEveryProblemFactChangeProcessed() in the bestSolutionChanged() event, 
which is called in the solver thread,
so it's not an issue in that particular case.
For 6.1.0.Beta4, I 've cleaned up the docs to describe that usage 
pattern better:
https://github.com/droolsjbpm/optaplanner/commit/256fa1fe285392f8ad81b1a40816db641a768bb9


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