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https://github.com/eclipse-cdt/cdt
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[302628] Moved to a non-API package.
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Pawel Piech
parent
845bf5a063
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package org.eclipse.cdt.dsf.concurrent;
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/*******************************************************************************
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* Copyright (c) 2008 Wind River Systems, Inc. and others.
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* All rights reserved. This program and the accompanying materials
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* are made available under the terms of the Eclipse Public License v1.0
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* which accompanies this distribution, and is available at
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* http://www.eclipse.org/legal/epl-v10.html
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*
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* Contributors:
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* Wind River Systems - initial API and implementation
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*******************************************************************************/
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import java.util.LinkedList;
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import java.util.List;
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import java.util.concurrent.Executor;
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import org.eclipse.cdt.dsf.internal.DsfPlugin;
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import org.eclipse.core.runtime.IStatus;
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import org.eclipse.core.runtime.Status;
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/**
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* A general purpose cache, which caches the result of a single request.
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* Sub classes need to implement {@link #retrieve(DataRequestMonitor)} to fetch
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* data from the data source. Clients are responsible for calling
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* {@link #disable()} and {@link #reset()} to manage the state of the cache in
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* response to events from the data source.
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* <p>
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* This cache requires an executor to use. The executor is used to synchronize
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* access to the cache state and data.
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* </p>
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* @since 2.1
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*/
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@ConfinedToDsfExecutor("fExecutor")
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public abstract class DataCache<V> {
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final private Executor fExecutor;
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private boolean fValid;
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protected DataRequestMonitor<V> fRm;
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private V fData;
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private IStatus fStatus;
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private List<DataRequestMonitor<V>> fWaitingList = new LinkedList<DataRequestMonitor<V>>();
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public DataCache(Executor executor) {
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fExecutor = executor;
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}
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/**
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* Sub-classes should override this method to retrieve the cache data
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* from its source.
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*
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* @param rm Request monitor for completion of data retrieval.
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*/
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protected abstract void retrieve(DataRequestMonitor<V> rm);
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/**
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* Returns <code>true</code> if the cache is currently valid. I.e.
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* whether the cache can return a value immediately without first
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* retrieving it from the data source.
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*/
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public boolean isValid() {
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return fValid;
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}
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/**
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* Returns <code>true</code> if the cache is currently waiting for data
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* from the data source.
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*/
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public boolean isPending() {
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return fRm != null;
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}
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/**
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* Returns the current data value held by this cache. Clients should first
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* call isValid() to determine if the data is up to date.
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*/
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public V getData() {
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return fData;
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}
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/**
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* Returns the status of the source request held by this cache. Clients
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* should first call isValid() to determine if the data is up to date.
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*/
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public IStatus getStatus() {
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return fStatus;
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}
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/**
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* Request data from the cache. The cache is valid, it will complete the
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* request immediately, otherwise data will first be retrieved from the
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* source.
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* @param req
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*/
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public void request(final DataRequestMonitor<V> rm) {
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if (!fValid) {
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boolean first = fWaitingList.isEmpty();
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fWaitingList.add(rm);
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if(first) {
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fRm = new DataRequestMonitor<V>(fExecutor, null) {
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@Override
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protected void handleCompleted() {
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if (!isCanceled()) {
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fValid = true;
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fRm = null;
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set(getData(), getStatus());
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}
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}
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};
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retrieve(fRm);
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}
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} else {
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rm.setData(fData);
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rm.setStatus(fStatus);
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rm.done();
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}
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}
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private void set(V data, IStatus status) {
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fData = data;
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fStatus = status;
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List<DataRequestMonitor<V>> waitingList = fWaitingList;
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fWaitingList = new LinkedList<DataRequestMonitor<V>>();
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for (DataRequestMonitor<V> rm : waitingList) {
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rm.setData(data);
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rm.setStatus(status);
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rm.done();
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}
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}
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/**
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* Resets the cache with a data value <code>null</code> and an error
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* status with code {@link IDsfStatusConstants#INVALID_STATE}.
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*
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* @see #reset(Object, IStatus)
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*/
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public void reset() {
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reset(null, new Status(IStatus.ERROR, DsfPlugin.PLUGIN_ID, IDsfStatusConstants.INVALID_STATE, "Cache reset", null)); //$NON-NLS-1$
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}
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/**
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* Resets the cache with given data and status. Resetting the cache
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* forces the cache to be invalid and cancels any current pending requests
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* from data source.
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* <p>
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* This method should be called when the data source has issued an event
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* indicating that the source data has changed but data may still be
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* retrieved. Clients may need to re-request data following cache reset.
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* </p>
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* @param data The data that should be returned to any clients currently
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* waiting for cache data.
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* @status The status that should be returned to any clients currently
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* waiting for cache data.
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*/
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public void reset(V data, IStatus status) {
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fValid = false;
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if (fRm != null) {
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fRm.cancel();
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fRm = null;
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}
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set(data, status);
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}
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/**
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* Disables the cache with a data value <code>null</code> and an error
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* status with code {@link IDsfStatusConstants#INVALID_STATE}.
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*
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* @see #disable(Object, IStatus)
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*/
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public void disable() {
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disable(null, new Status(IStatus.ERROR, DsfPlugin.PLUGIN_ID, IDsfStatusConstants.INVALID_STATE, "Cache disable", null)); //$NON-NLS-1$
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}
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/**
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* Resets the cache then disables it. When a cache is disabled it means
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* that it is valid and requests to the data source will not be sent.
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* <p>
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* This method should be called when the data source has issued an event
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* indicating that the source data has changed and future requests for
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* data will return the given data and status. Once the source data
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* becomes available again, clients should call {@link #reset()}.
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* </p>
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* @param data The data that should be returned to any clients waiting for
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* cache data and for clients requesting data until the cache is reset again.
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* @status The status that should be returned to any clients waiting for
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* cache data and for clients requesting data until the cache is reset again.
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*
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* @see #reset(Object, IStatus)
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*/
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public void disable(V data, IStatus status) {
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reset(data, status);
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fValid = true;
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}
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}
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