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/**
* Licensed to the Apache Software Foundation (ASF) under one
* or more contributor license agreements. See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership. The ASF licenses this file
* to you under the Apache License, Version 2.0 (the
* "License"); you may not use this file except in compliance
* with the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing,
* software distributed under the License is distributed on an
* "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
* KIND, either express or implied. See the License for the
* specific language governing permissions and limitations
* under the License.
*/
package org.apache.curator.framework.recipes.locks;
import com.google.common.collect.Maps;
import com.google.common.util.concurrent.MoreExecutors;
import org.apache.curator.framework.CuratorFramework;
import java.io.IOException;
import java.util.Collection;
import java.util.concurrent.ConcurrentMap;
import java.util.concurrent.Executor;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.atomic.AtomicInteger;
import org.apache.curator.utils.PathUtils;
/**
* A re-entrant mutex that works across JVMs. Uses Zookeeper to hold the lock. All processes in all JVMs that
* use the same lock path will achieve an inter-process critical section. Further, this mutex is
* "fair" - each user will get the mutex in the order requested (from ZK's point of view)
*/
public class InterProcessMutex implements InterProcessLock, Revocable
{
private final LockInternals internals;
private final String basePath;
private final ConcurrentMap threadData = Maps.newConcurrentMap();
private static class LockData
{
final Thread owningThread;
final String lockPath;
final AtomicInteger lockCount = new AtomicInteger(1);
private LockData(Thread owningThread, String lockPath)
{
this.owningThread = owningThread;
this.lockPath = lockPath;
}
}
private static final String LOCK_NAME = "lock-";
/**
* @param client client
* @param path the path to lock
*/
public InterProcessMutex(CuratorFramework client, String path)
{
this(client, path, new StandardLockInternalsDriver());
}
/**
* @param client client
* @param path the path to lock
* @param driver lock driver
*/
public InterProcessMutex(CuratorFramework client, String path, LockInternalsDriver driver)
{
this(client, path, LOCK_NAME, 1, driver);
}
/**
* Acquire the mutex - blocking until it's available. Note: the same thread
* can call acquire re-entrantly. Each call to acquire must be balanced by a call
* to {@link #release()}
*
* @throws Exception ZK errors, connection interruptions
*/
@Override
public void acquire() throws Exception
{
if ( !internalLock(-1, null) )
{
throw new IOException("Lost connection while trying to acquire lock: " + basePath);
}
}
/**
* Acquire the mutex - blocks until it's available or the given time expires. Note: the same thread
* can call acquire re-entrantly. Each call to acquire that returns true must be balanced by a call
* to {@link #release()}
*
* @param time time to wait
* @param unit time unit
* @return true if the mutex was acquired, false if not
* @throws Exception ZK errors, connection interruptions
*/
@Override
public boolean acquire(long time, TimeUnit unit) throws Exception
{
return internalLock(time, unit);
}
/**
* Returns true if the mutex is acquired by a thread in this JVM
*
* @return true/false
*/
@Override
public boolean isAcquiredInThisProcess()
{
return (threadData.size() > 0);
}
/**
* Perform one release of the mutex if the calling thread is the same thread that acquired it. If the
* thread had made multiple calls to acquire, the mutex will still be held when this method returns.
*
* @throws Exception ZK errors, interruptions, current thread does not own the lock
*/
@Override
public void release() throws Exception
{
/*
Note on concurrency: a given lockData instance
can be only acted on by a single thread so locking isn't necessary
*/
Thread currentThread = Thread.currentThread();
LockData lockData = threadData.get(currentThread);
if ( lockData == null )
{
throw new IllegalMonitorStateException("You do not own the lock: " + basePath);
}
int newLockCount = lockData.lockCount.decrementAndGet();
if ( newLockCount > 0 )
{
return;
}
if ( newLockCount < 0 )
{
throw new IllegalMonitorStateException("Lock count has gone negative for lock: " + basePath);
}
try
{
internals.releaseLock(lockData.lockPath);
}
finally
{
threadData.remove(currentThread);
}
}
/**
* Return a sorted list of all current nodes participating in the lock
*
* @return list of nodes
* @throws Exception ZK errors, interruptions, etc.
*/
public Collection getParticipantNodes() throws Exception
{
return LockInternals.getParticipantNodes(internals.getClient(), basePath, internals.getLockName(), internals.getDriver());
}
@Override
public void makeRevocable(RevocationListener listener)
{
makeRevocable(listener, MoreExecutors.sameThreadExecutor());
}
@Override
public void makeRevocable(final RevocationListener listener, Executor executor)
{
internals.makeRevocable(new RevocationSpec(executor, new Runnable()
{
@Override
public void run()
{
listener.revocationRequested(InterProcessMutex.this);
}
}));
}
InterProcessMutex(CuratorFramework client, String path, String lockName, int maxLeases, LockInternalsDriver driver)
{
basePath = PathUtils.validatePath(path);
internals = new LockInternals(client, driver, path, lockName, maxLeases);
}
boolean isOwnedByCurrentThread()
{
LockData lockData = threadData.get(Thread.currentThread());
return (lockData != null) && (lockData.lockCount.get() > 0);
}
protected byte[] getLockNodeBytes()
{
return null;
}
protected String getLockPath()
{
LockData lockData = threadData.get(Thread.currentThread());
return lockData != null ? lockData.lockPath : null;
}
private boolean internalLock(long time, TimeUnit unit) throws Exception
{
/*
Note on concurrency: a given lockData instance
can be only acted on by a single thread so locking isn't necessary
*/
Thread currentThread = Thread.currentThread();
LockData lockData = threadData.get(currentThread);
if ( lockData != null )
{
// re-entering
lockData.lockCount.incrementAndGet();
return true;
}
String lockPath = internals.attemptLock(time, unit, getLockNodeBytes());
if ( lockPath != null )
{
LockData newLockData = new LockData(currentThread, lockPath);
threadData.put(currentThread, newLockData);
return true;
}
return false;
}
}