bundles/org.simantics.db.common/src/org/simantics/db/common/procedure/guarded/GuardedAsyncProcedureWrapper.java

   1 /*******************************************************************************
   2  * Copyright (c) 2007, 2010 Association for Decentralized Information Management
   3  * in Industry THTH ry.
   4  * All rights reserved. This program and the accompanying materials
   5  * are made available under the terms of the Eclipse Public License v1.0
   6  * which accompanies this distribution, and is available at
   7  * http://www.eclipse.org/legal/epl-v10.html
   8  *
   9  * Contributors:
  10  *     VTT Technical Research Centre of Finland - initial API and implementation
  11  *******************************************************************************/
  12 package org.simantics.db.common.procedure.guarded;
  13
  14 import java.util.concurrent.atomic.AtomicBoolean;
  15 import java.util.concurrent.atomic.AtomicInteger;
  16
  17 import org.simantics.db.AsyncReadGraph;
  18 import org.simantics.db.common.procedure.adapter.AsyncProcedureAdapter;
  19 import org.simantics.db.procedure.AsyncProcedure;
  20 import org.simantics.db.procedure.Procedure;
  21
  22 /**
  23  * An asynchronous database callback procedure that is guarded against multiple
  24  * invocations to {@link Procedure#execute(Object)} and
  25  * {@link Procedure#exception(Throwable)}. Only the first invocation of is
  26  * delegated or the Nth invocation to {@link Procedure#execute(Object)} where
  27  * Nth is <code>expectedResults</code>.
  28  *
  29  * @author Tuukka Lehtonen
  30  *
  31  * @param <T>
  32  */
  33 public class GuardedAsyncProcedureWrapper<T> extends AsyncProcedureAdapter<T> {
  34
  35     private final AsyncProcedure<T> procedure;
  36     private final AtomicBoolean     onceGuard = new AtomicBoolean(false);
  37     private final AtomicInteger     resultCounter;
  38
  39     public GuardedAsyncProcedureWrapper(AsyncProcedure<T> procedure, int expectedResults) {
  40         this.procedure = procedure;
  41         this.resultCounter = new AtomicInteger(expectedResults);
  42     }
  43
  44     @Override
  45     public void exception(AsyncReadGraph graph, Throwable t) {
  46         if (onceGuard.compareAndSet(false, true)) {
  47             procedure.exception(graph, t);
  48         }
  49     }
  50
  51     @Override
  52     public void execute(AsyncReadGraph graph, T result) {
  53         int count = resultCounter.decrementAndGet();
  54         if (count == 0) {
  55             if (onceGuard.compareAndSet(false, true)) {
  56                 procedure.execute(graph, result);
  57             }
  58         } else if (count < 0) {
  59             System.out.println(this + ": execute invoked more than expected (count=" + count + ", procedure=" + procedure + ")");
  60         }
  61     }
  62
  63 }