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/*******************************************************************************
* Copyright (c) 2008 Wind River Systems, Inc. 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:
* Wind River Systems - initial API and implementation
*******************************************************************************/
package org.eclipse.tm.tcf.util;
import java.util.HashSet;
import org.eclipse.tm.tcf.protocol.IChannel;
import org.eclipse.tm.tcf.protocol.IToken;
import org.eclipse.tm.tcf.protocol.Protocol;
/**
* Objects of this class are used cache TCF remote data.
* The cache is asynchronous state machine. The states are:
* 1. Valid - cache is in sync with remote data, use getError() and getData() to get cached data;
* 2. Invalid - cache is out out of sync, start data retrieval by calling validate();
* 3. Pending - cache is waiting result of a command that was sent to remote peer.
* @param <V> - type of data to be stored in the cache.
*/
public abstract class TCFDataCache<V> implements Runnable {
private Throwable error;
private boolean valid;
private V data;
protected final IChannel channel;
protected IToken command;
private final HashSet<Runnable> waiting_list = new HashSet<Runnable>();
public TCFDataCache(IChannel channel) {
assert channel != null;
this.channel = channel;
}
/**
* @return true if cache contains up-to-date data (or data retrieval error).
*/
public boolean isValid() {
return valid;
}
/**
* @return true if data retrieval is in progress.
*/
public boolean isPending() {
return command != null;
}
/**
* @return error object if data retrieval ended with an error, or null if retrieval was successful.
* Note: It is prohibited to call this method when cache is not valid.
*/
public Throwable getError() {
assert valid;
return error;
}
/**
* @return cached data object.
* Note: It is prohibited to call this method when cache is not valid.
*/
public V getData() {
assert valid;
return data;
}
/**
* Notify waiting clients about cache state change and remove them from wait list.
* It is responsibility of clients to check if the state change was one they are waiting for.
*/
public void run() {
if (waiting_list.isEmpty()) return;
Runnable[] arr = waiting_list.toArray(new Runnable[waiting_list.size()]);
waiting_list.clear();
for (Runnable r : arr) r.run();
}
/**
* Add a client call-back to cache wait list.
* @param req
*/
public void wait(Runnable cb) {
assert !valid;
if (cb != null) waiting_list.add(cb);
}
/**
* Initiate data retrieval if the cache is not valid.
* @return true if the cache is already valid
*/
public boolean validate() {
assert Protocol.isDispatchThread();
if (channel.getState() != IChannel.STATE_OPEN) {
error = null;
command = null;
valid = true;
data = null;
}
else {
if (command != null) return false;
if (!valid && !startDataRetrieval()) return false;
}
assert valid;
assert command == null;
run();
return true;
}
/**
* End cache pending state.
* @param token - pending command handle.
* @param error - data retrieval error or null
* @param data - up-to-date data object
*/
public void set(IToken token, Throwable error, V data) {
assert Protocol.isDispatchThread();
if (command != token) return;
command = null;
if (channel.getState() != IChannel.STATE_OPEN) data = null;
this.error = error;
this.data = data;
valid = true;
run();
}
/**
* Force cache to become valid, cancel pending data retrieval if any.
* @param data - up-to-date data object
*/
public void reset(V data) {
if (command != null) {
command.cancel();
command = null;
}
this.data = data;
error = null;
valid = true;
run();
}
/**
* Invalidate the cache. If retrieval is in progress - let it continue.
*/
public void reset() {
error = null;
valid = false;
data = null;
run();
}
/**
* Force cache to invalid state, cancel pending data retrieval if any.
*/
public void cancel() {
if (command != null) {
command.cancel();
command = null;
}
error = null;
valid = false;
data = null;
run();
}
/**
* Sub-classes should override this method to implement actual data retrieval logic.
* @return true is all done, false if retrieval is in progress.
*/
protected abstract boolean startDataRetrieval();
}
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