/*
* RHQ Management Platform
* Copyright (C) 2005-2008 Red Hat, Inc.
* All rights reserved.
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation version 2 of the License.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software
* Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
*/
package org.rhq.enterprise.communications;
import java.util.concurrent.ConcurrentLinkedQueue;
import java.util.concurrent.Semaphore;
import mazz.i18n.Logger;
import org.rhq.enterprise.communications.command.Command;
import org.rhq.enterprise.communications.command.CommandResponse;
import org.rhq.enterprise.communications.command.client.CommandPreprocessor;
import org.rhq.enterprise.communications.command.server.CommandListener;
import org.rhq.enterprise.communications.i18n.CommI18NFactory;
import org.rhq.enterprise.communications.i18n.CommI18NResourceKeys;
import org.rhq.enterprise.communications.util.ConcurrencyManager.Permit;
import org.rhq.enterprise.communications.util.NotPermittedException;
/**
* This is a listener for commands coming into the {@link ServiceContainer}'s {@link CommandPreprocessor} and will
* immediately drop the command if the global concurrent limit has been exceeded. In other words, if we've received too
* many incoming commands at the same time, we'll start dropping additional incoming commands under the command
* processor can catch up.
*
* @author John Mazzitelli
*/
public class GlobalConcurrencyLimitCommandListener implements CommandListener {
public static final String CONCURRENCY_LIMIT_NAME = "rhq.communications.global-concurrency-limit-semaphore";
private static final Logger LOG = CommI18NFactory.getLogger(GlobalConcurrencyLimitCommandListener.class);
private final ServiceContainer serviceContainer;
private final ConcurrentLinkedQueue<Permit> permitsObtained;
private final Semaphore droppedCommands;
public GlobalConcurrencyLimitCommandListener(ServiceContainer serviceContainer) {
this.serviceContainer = serviceContainer;
this.permitsObtained = new ConcurrentLinkedQueue<Permit>();
this.droppedCommands = new Semaphore(0);
}
/**
* This will be called for every command coming in. We'll check to see if we are permitted to process this command -
* if we've reached the global concurrency limit, this method will throw a {@link NotPermittedException}.
*
* @see CommandListener#receivedCommand(Command)
*/
public void receivedCommand(Command command) {
try {
Permit permit = this.serviceContainer.getConcurrencyManager().getPermit(CONCURRENCY_LIMIT_NAME);
this.permitsObtained.add(permit);
} catch (NotPermittedException npe) {
LOG.debug(CommI18NResourceKeys.COMMAND_NOT_PERMITTED, command, npe.getSleepBeforeRetry());
this.droppedCommands.release(); // adds 1 to the semaphore count so we know we dropped another command
throw npe; // command processor will get this and abort the command
}
}
/**
* This is called for every command that finished which includes all commands that succeeded, failed or was not
* permitted due to {@link #receivedCommand(Command)} throwing a {@link NotPermittedException}.
*
* @see CommandListener#processedCommand(Command, CommandResponse)
*/
public void processedCommand(Command command, CommandResponse response) {
// The droppedCommands is a semaphore so we can use it for its thread-safety.
// If there are 1 or more droppedCommand permits, it means we dropped commands
// (number of commands dropped were the number of permits in the droppedCommands semaphore).
// If we can acquire a droppedCommands permit, it means this listener needs to finish processing
// dropped commands and thus we should not release a concurrency manager permit (since
// we only add to permitsObtained when we got a concurrency manager permit).
// If we cannot acquire a droppedCommands permit, it means this listener has no more
// dropped commands to process and we can start releasing concurrency manager permits.
if (!this.droppedCommands.tryAcquire()) {
// Notice that we don't care which permit we release, just get the head of the queue
// and release it. Permits are not directly associated with a command - concurrency
// manager just cares about the number of permits, not which commands go with which permits.
// Note also that if the concurrency manager happened to be swapped out between the time
// we got the permit and now, this release request will be ignored and nothing will break
// since permits are associated with the concurrency manager that granted them and giving a
// permit to a concurrency manager that didn't grant it will simply be a no-op.
this.serviceContainer.getConcurrencyManager().releasePermit(this.permitsObtained.poll());
}
}
}