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/*******************************************************************************
* Copyright (c) 2009 IBM Corporation and others.
* All rights reserved. This program and the accompanying materials
* are made available under the terms of the Eclipse Public License v1.0
* which accompanies this distribution, and is available at
* http://www.eclipse.org/legal/epl-v10.html
*
* Contributors:
* IBM Corporation - initial API and implementation
*******************************************************************************/
package org.eclipse.e4.core.internal.contexts;
import java.util.Set;
import org.eclipse.e4.core.contexts.IContextFunction;
import org.eclipse.e4.core.contexts.IEclipseContext;
import org.eclipse.e4.core.internal.contexts.EclipseContext.Scheduled;
public class ValueComputation extends Computation {
final static private Object NotAValue = new Object();
private Object cachedValue = NotAValue;
private IContextFunction function;
private EclipseContext originatingContext;
private boolean computing; // cycle detection
private String name;
public ValueComputation(String name, IEclipseContext originatingContext, IContextFunction computedValue) {
this.originatingContext = (EclipseContext) originatingContext;
this.function = computedValue;
this.name = name;
}
public void handleInvalid(ContextChangeEvent event, Set<Scheduled> scheduled) {
cachedValue = NotAValue;
if (name.equals(event.getName()))
invalidateComputation();
int eventType = event.getEventType();
originatingContext.invalidate(name, eventType == ContextChangeEvent.DISPOSE ? ContextChangeEvent.REMOVED : eventType, event.getOldValue(), scheduled);
}
public Object get() {
if (!isValid())
throw new IllegalArgumentException("Reusing invalidated computation"); //$NON-NLS-1$
if (cachedValue != NotAValue)
return cachedValue;
if (this.computing)
throw new RuntimeException("Cycle while computing value" + this.toString()); //$NON-NLS-1$
originatingContext.pushComputation(this);
computing = true;
try {
cachedValue = function.compute(originatingContext);
validComputation = true;
} finally {
computing = false;
originatingContext.popComputation(this);
}
return cachedValue;
}
public String toString() {
if (function == null)
return super.toString();
return function.toString();
}
}
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