75 lines
2.8 KiB
Java
75 lines
2.8 KiB
Java
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package supervision;
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import akka.actor.*;
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import akka.japi.pf.DeciderBuilder;
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import akka.japi.pf.ReceiveBuilder;
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import scala.PartialFunction;
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import scala.runtime.BoxedUnit;
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import java.util.HashMap;
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import java.util.Map;
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import static supervision.FlakyExpressionCalculator.FlakinessException;
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import static supervision.FlakyExpressionCalculator.Result;
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import static supervision.FlakyExpressionCalculator.Position.Left;
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// A very simple service that accepts arithmetic expressions and tries to
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// evaluate them. Since the calculation is dangerous (at least for the sake
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// of this example) it is delegated to a worker actor of type
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// FlakyExpressionCalculator.
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class ArithmeticService extends AbstractLoggingActor {
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// Map of workers to the original actors requesting the calculation
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Map<ActorRef, ActorRef> pendingWorkers = new HashMap<>();
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private SupervisorStrategy strategy = new OneForOneStrategy(false, DeciderBuilder.
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match(FlakinessException.class, e -> {
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log().warning("Evaluation of a top level expression failed, restarting.");
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return SupervisorStrategy.restart();
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}).
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match(ArithmeticException.class, e -> {
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log().error("Evaluation failed because of: {}", e.getMessage());
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notifyConsumerFailure(sender(), e);
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return SupervisorStrategy.stop();
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}).
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match(Throwable.class, e -> {
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log().error("Unexpected failure: {}", e.getMessage());
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notifyConsumerFailure(sender(), e);
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return SupervisorStrategy.stop();
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}).build());
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@Override
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public SupervisorStrategy supervisorStrategy() {
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return strategy;
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}
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private void notifyConsumerFailure(ActorRef worker, Throwable failure) {
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// Status.Failure is a message type provided by the Akka library. The
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// reason why it is used is because it is recognized by the "ask" pattern
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// and the Future returned by ask will fail with the provided exception.
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ActorRef pending = pendingWorkers.get(worker);
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if (pending != null) {
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pending.tell(new Status.Failure(failure), self());
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pendingWorkers.remove(worker);
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}
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}
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private void notifyConsumerSuccess(ActorRef worker, Integer result) {
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ActorRef pending = pendingWorkers.get(worker);
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if (pending != null) {
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pending.tell(result, self());
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pendingWorkers.remove(worker);
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}
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}
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@Override
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public PartialFunction<Object, BoxedUnit> receive() {
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return ReceiveBuilder.
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match(Expression.class, expr -> {
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// We delegate the dangerous task of calculation to a worker, passing the
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// expression as a constructor argument to the actor.
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ActorRef worker = context().actorOf(FlakyExpressionCalculator.props(expr, Left));
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pendingWorkers.put(worker, sender());
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}).
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match(Result.class, r -> notifyConsumerSuccess(sender(), r.getValue())).build();
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}
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}
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