com.gemstone.org.jgroups.blocks.DistributedLockManager Maven / Gradle / Ivy
Show all versions of gemfire-jgroups Show documentation
/** Notice of modification as required by the LGPL
* This file was modified by Gemstone Systems Inc. on
* $Date$
**/
package com.gemstone.org.jgroups.blocks;
import com.gemstone.org.jgroups.util.GemFireTracer;
import com.gemstone.org.jgroups.ChannelException;
import com.gemstone.org.jgroups.blocks.VotingAdapter.FailureVoteResult;
import com.gemstone.org.jgroups.blocks.VotingAdapter.VoteResult;
import com.gemstone.org.jgroups.util.ExternalStrings;
import com.gemstone.org.jgroups.util.Rsp;
import com.gemstone.org.jgroups.util.RspList;
import java.io.Serializable;
import java.util.HashMap;
/**
* Distributed lock manager is responsible for maintaining the lock information
* consistent on all participating nodes.
*
* @author Roman Rokytskyy ([email protected])
* @author Robert Schaffar-Taurok ([email protected])
* @version $Id: DistributedLockManager.java,v 1.6 2005/06/08 15:56:54 publicnmi Exp $
*/
public class DistributedLockManager implements TwoPhaseVotingListener, LockManager, VoteResponseProcessor {
/**
* Definitions for the implementation of the VoteResponseProcessor
*/
private static final int PROCESS_CONTINUE = 0;
private static final int PROCESS_SKIP = 1;
private static final int PROCESS_BREAK = 2;
/**
* This parameter means that lock acquisition expires after 5 seconds.
* If there were no "commit" operation on prepared lock, then it
* is treated as expired and is removed from the prepared locks table.
*/
private static final long ACQUIRE_EXPIRATION = 5000;
/**
* This parameter is used during lock releasing. If group fails to release
* the lock during the specified period of time, unlocking fails.
*/
private static final long VOTE_TIMEOUT = 10000;
// list of all prepared locks
private final HashMap preparedLocks = new HashMap();
// list of all prepared releases
private final HashMap preparedReleases = new HashMap();
// list of locks on the node
private final HashMap heldLocks = new HashMap();
private final TwoPhaseVotingAdapter votingAdapter;
private final Object id;
protected final GemFireTracer log=GemFireTracer.getLog(getClass());
// @todo check if the node with the same id is already in the group.
/**
* Create instance of this class.
*
* @param voteChannel instance of {@link VotingAdapter} that will be used
* for voting purposes on the lock decrees. voteChannel() will
* be wrapped by the instance of the {@link TwoPhaseVotingAdapter}.
*
* @param id the unique identifier of this lock manager.
*/
public DistributedLockManager(VotingAdapter voteChannel, Object id) {
this(new TwoPhaseVotingAdapter(voteChannel), id);
}
// @todo check if the node with the same id is already in the group.
/**
* Constructor for the DistributedLockManager_cl object.
*
* @param channel instance of {@link TwoPhaseVotingAdapter}
* that will be used for voting purposes on the lock decrees.
*
* @param id the unique identifier of this lock manager.
*/
public DistributedLockManager(TwoPhaseVotingAdapter channel, Object id) {
this.id = id;
this.votingAdapter = channel;
this.votingAdapter.addListener(this);
}
/**
* Performs local lock. This method also performs the clean-up of the lock
* table, all expired locks are removed.
*/
private boolean localLock(LockDecree lockDecree) {
// remove expired locks
removeExpired(lockDecree);
LockDecree localLock =
(LockDecree) heldLocks.get(lockDecree.getKey());
if (localLock == null) {
// promote lock into commited state
lockDecree.commit();
// no lock exist, perform local lock, note:
// we do not store locks that were requested by other manager.
if (lockDecree.managerId.equals(id))
heldLocks.put(lockDecree.getKey(), lockDecree);
// everything is fine :)
return true;
} else
if (localLock.requester.equals(lockDecree.requester))
// requester already owns the lock
return true;
else
// lock does not belong to requester
return false;
}
/**
* Returns true if the requested lock can be granted by the
* current node.
*
* @param decree instance of LockDecree containing information
* about the lock.
*/
private boolean canLock(LockDecree decree) {
// clean expired locks
removeExpired(decree);
LockDecree lock = (LockDecree)heldLocks.get(decree.getKey());
if (lock == null)
return true;
else
return lock.requester.equals(decree.requester);
}
/**
* Returns true if the requested lock can be released by the
* current node.
*
* @param decree instance of {@link LockDecree} containing information
* about the lock.
*/
private boolean canRelease(LockDecree decree) {
// clean expired locks
removeExpired(decree);
// we need to check only hold locks, because
// prepared locks cannot contain the lock
LockDecree lock = (LockDecree)heldLocks.get(decree.getKey());
if (lock == null)
// check if this holds...
return true;
else
return lock.requester.equals(decree.requester);
}
/**
* Removes expired locks.
*
* @param decree instance of {@link LockDecree} describing the lock.
*/
private void removeExpired(LockDecree decree) {
// remove the invalid (expired) lock
LockDecree localLock = (LockDecree)heldLocks.get(decree.getKey());
if (localLock != null && !localLock.isValid())
heldLocks.remove(localLock.getKey());
}
/**
* Releases lock locally.
*
* @param lockDecree instance of {@link LockDecree} describing the lock.
*/
private boolean localRelease(LockDecree lockDecree) {
// remove expired locks
removeExpired(lockDecree);
LockDecree localLock=
(LockDecree) heldLocks.get(lockDecree.getKey());
if(localLock == null) {
// no lock exist
return true;
}
else if(localLock.requester.equals(lockDecree.requester)) {
// requester owns the lock, release the lock
heldLocks.remove(lockDecree.getKey());
return true;
}
else
// lock does not belong to requester
return false;
}
/**
* Locks an object with lockId on behalf of the specified
* owner.
*
* @param lockId Object representing the object to be locked.
* @param owner object that requests the lock.
* @param timeout time during which group members should decide
* whether to grant a lock or not.
*
* @throws LockNotGrantedException when the lock cannot be granted.
*
* @throws ClassCastException if lockId or owner are not serializable.
*
* @throws ChannelException if something bad happened to underlying channel.
*/
public void lock(Object lockId, Object owner, int timeout)
throws LockNotGrantedException, ChannelException
{
if (!(lockId instanceof Serializable) || !(owner instanceof Serializable))
throw new ClassCastException("DistributedLockManager " +
"works only with serializable objects.");
boolean acquired = votingAdapter.vote(
new AcquireLockDecree(lockId, owner, id), timeout);
if (!acquired)
throw new LockNotGrantedException("Lock cannot be granted.");
}
/**
* Unlocks an object with lockId on behalf of the specified
* owner.
*
* since 2.2.9 this method is only a wrapper for
* unlock(Object lockId, Object owner, boolean releaseMultiLocked).
* Use that with releaseMultiLocked set to true if you want to be able to
* release multiple locked locks (for example after a merge)
*
* @param lockId long representing the object to be unlocked.
* @param owner object that releases the lock.
*
* @throws LockNotReleasedException when the lock cannot be released.
* @throws ClassCastException if lockId or owner are not serializable.
*
*/
public void unlock(Object lockId, Object owner)
throws LockNotReleasedException, ChannelException
{
try {
unlock(lockId, owner, false);
} catch (LockMultiLockedException e) {
// This should never happen when releaseMultiLocked is false
log.error(ExternalStrings.DistributedLockManager_CAUGHT_MULTILOCKEDEXCEPTION_BUT_RELEASEMULTILOCKED_IS_FALSE, e);
}
}
/**
* Unlocks an object with lockId on behalf of the specified
* owner.
* @param lockId long representing the object to be unlocked.
* @param owner object that releases the lock.
* @param releaseMultiLocked releases also multiple locked locks. (eg. locks that are locked by another DLM after a merge)
*
* @throws LockNotReleasedException when the lock cannot be released.
* @throws ClassCastException if lockId or owner are not serializable.
* @throws LockMultiLockedException if releaseMultiLocked is true and a multiple locked lock has been released.
*/
public void unlock(Object lockId, Object owner, boolean releaseMultiLocked)
throws LockNotReleasedException, ChannelException, LockMultiLockedException
{
if (!(lockId instanceof Serializable) || !(owner instanceof Serializable))
throw new ClassCastException("DistributedLockManager " +
"works only with serializable objects.");
ReleaseLockDecree releaseLockDecree = new ReleaseLockDecree(lockId, owner, id);
boolean released = false;
if (releaseMultiLocked) {
released = votingAdapter.vote(releaseLockDecree, VOTE_TIMEOUT, this);
if (releaseLockDecree.isMultipleLocked()) {
throw new LockMultiLockedException("Lock was also locked by other DistributedLockManager(s)");
}
} else {
released = votingAdapter.vote(releaseLockDecree, VOTE_TIMEOUT);
}
if (!released)
throw new LockNotReleasedException("Lock cannot be unlocked.");
}
/**
* Checks the list of prepared locks/unlocks to determine if we are in the
* middle of the two-phase commit process for the lock acqusition/release.
* Here we do not tolerate if the request comes from the same node on behalf
* of the same owner.
*
* @param preparedContainer either preparedLocks or
* preparedReleases depending on the situation.
*
* @param requestedDecree instance of LockDecree representing
* the lock.
*/
private boolean checkPrepared(HashMap preparedContainer,
LockDecree requestedDecree)
{
LockDecree preparedDecree =
(LockDecree)preparedContainer.get(requestedDecree.getKey());
// if prepared lock is not valid, remove it from the list
if ((preparedDecree != null) && !preparedDecree.isValid()) {
preparedContainer.remove(preparedDecree.getKey());
preparedDecree = null;
}
if (preparedDecree != null) {
if (requestedDecree.requester.equals(preparedDecree.requester))
return true;
else
return false;
} else
// it was not prepared... sorry...
return true;
}
/**
* Prepare phase for the lock acquisition or release.
*
* @param decree should be an instance LockDecree, if not,
* we throw VoteException to be ignored by the
* VoteChannel.
*
* @return true when preparing the lock operation succeeds.
*
* @throws VoteException if we should be ignored during voting.
*/
public synchronized boolean prepare(Object decree) throws VoteException {
if (!(decree instanceof LockDecree))
throw new VoteException("Uknown decree type. Ignore me.");
if (decree instanceof AcquireLockDecree) {
AcquireLockDecree acquireDecree = (AcquireLockDecree)decree;
if(log.isDebugEnabled()) log.debug("Preparing to acquire decree " + acquireDecree.lockId);
if (!checkPrepared(preparedLocks, acquireDecree))
// there is a prepared lock owned by third party
return false;
if (canLock(acquireDecree)) {
preparedLocks.put(acquireDecree.getKey(), acquireDecree);
return true;
} else
// we are unable to aquire local lock
return false;
} else
if (decree instanceof ReleaseLockDecree) {
ReleaseLockDecree releaseDecree = (ReleaseLockDecree)decree;
if(log.isDebugEnabled()) log.debug("Preparing to release decree " + releaseDecree.lockId);
if (!checkPrepared(preparedReleases, releaseDecree))
// there is a prepared release owned by third party
return false;
if (canRelease(releaseDecree)) {
preparedReleases.put(releaseDecree.getKey(), releaseDecree);
// we have local lock and the prepared lock
return true;
} else
// we were unable to aquire local lock
return false;
} else
if (decree instanceof MultiLockDecree) {
// Here we abuse the voting mechanism for notifying the other lockManagers of multiple locked objects.
MultiLockDecree multiLockDecree = (MultiLockDecree)decree;
if(log.isDebugEnabled()) {
log.debug("Marking " + multiLockDecree.getKey() + " as multilocked");
}
LockDecree lockDecree = (LockDecree)heldLocks.get(multiLockDecree.getKey());
if (lockDecree != null) {
lockDecree.setMultipleLocked(true);
}
return true;
}
// we should not be here
return false;
}
/**
* Commit phase for the lock acquisition or release.
*
* @param decree should be an instance LockDecree, if not,
* we throw VoteException to be ignored by the
* VoteChannel.
*
* @return true when commiting the lock operation succeeds.
*
* @throws VoteException if we should be ignored during voting.
*/
public synchronized boolean commit(Object decree) throws VoteException {
if (!(decree instanceof LockDecree))
throw new VoteException("Uknown decree type. Ignore me.");
if (decree instanceof AcquireLockDecree) {
if(log.isDebugEnabled()) log.debug("Committing decree acquisition " + ((LockDecree)decree).lockId);
if (!checkPrepared(preparedLocks, (LockDecree)decree))
// there is a prepared lock owned by third party
return false;
if (localLock((LockDecree)decree)) {
preparedLocks.remove(((LockDecree)decree).getKey());
return true;
} else
return false;
} else
if (decree instanceof ReleaseLockDecree) {
if(log.isDebugEnabled()) log.debug("Committing decree release " + ((LockDecree)decree).lockId);
if (!checkPrepared(preparedReleases, (LockDecree)decree))
// there is a prepared release owned by third party
return false;
if (localRelease((LockDecree)decree)) {
preparedReleases.remove(((LockDecree)decree).getKey());
return true;
} else
return false;
} else
if (decree instanceof MultiLockDecree) {
return true;
}
// we should not be here
return false;
}
/**
* Abort phase for the lock acquisition or release.
*
* @param decree should be an instance LockDecree, if not,
* we throw VoteException to be ignored by the
* VoteChannel.
*
* @throws VoteException if we should be ignored during voting.
*/
public synchronized void abort(Object decree) throws VoteException {
if (!(decree instanceof LockDecree))
throw new VoteException("Uknown decree type. Ignore me.");
if (decree instanceof AcquireLockDecree) {
if(log.isDebugEnabled()) log.debug("Aborting decree acquisition " + ((LockDecree)decree).lockId);
if (!checkPrepared(preparedLocks, (LockDecree)decree))
// there is a prepared lock owned by third party
return;
preparedLocks.remove(((LockDecree)decree).getKey());
} else
if (decree instanceof ReleaseLockDecree) {
if(log.isDebugEnabled()) log.debug("Aborting decree release " + ((LockDecree)decree).lockId);
if (!checkPrepared(preparedReleases, (LockDecree)decree))
// there is a prepared release owned by third party
return;
preparedReleases.remove(((LockDecree)decree).getKey());
}
}
/**
* Processes the response list and votes like the default processResponses method with the consensusType VOTE_ALL
* If the result of the voting is false, but this DistributedLockManager owns the lock, the result is changed to
* true and the lock is released, but marked as multiple locked. (only in the prepare state to reduce traffic)
*
* Note: we do not support voting in case of Byzantine failures, i.e.
* when the node responds with the fault message.
*/
public boolean processResponses(RspList responses, int consensusType, Object decree) throws ChannelException {
if (responses == null) {
return false;
}
int totalPositiveVotes = 0;
int totalNegativeVotes = 0;
for (int i = 0; i < responses.size(); i++) {
Rsp response = (Rsp) responses.elementAt(i);
switch (checkResponse(response)) {
case PROCESS_SKIP:
continue;
case PROCESS_BREAK:
return false;
}
VoteResult result = (VoteResult) response.getValue();
totalPositiveVotes += result.getPositiveVotes();
totalNegativeVotes += result.getNegativeVotes();
}
boolean voteResult = (totalNegativeVotes == 0 && totalPositiveVotes > 0);
if (decree instanceof TwoPhaseVotingAdapter.TwoPhaseWrapper) {
TwoPhaseVotingAdapter.TwoPhaseWrapper wrappedDecree = (TwoPhaseVotingAdapter.TwoPhaseWrapper)decree;
if (wrappedDecree.isPrepare()) {
Object unwrappedDecree = wrappedDecree.getDecree();
if (unwrappedDecree instanceof ReleaseLockDecree) {
ReleaseLockDecree releaseLockDecree = (ReleaseLockDecree)unwrappedDecree;
LockDecree lock = null;
if ((lock = (LockDecree)heldLocks.get(releaseLockDecree.getKey())) != null) {
// If there is a local lock...
if (!voteResult) {
// ... and another DLM voted negatively, but this DLM owns the lock
// we inform the other node, that it's lock is multiple locked
if (informLockingNodes(releaseLockDecree)) {
// we set the local lock to multiple locked
lock.setMultipleLocked(true);
voteResult = true;
}
}
if (lock.isMultipleLocked()) {
//... and the local lock is marked as multilocked
// we mark the releaseLockDecree als multiple locked for evaluation when unlock returns
releaseLockDecree.setMultipleLocked(true);
}
}
}
}
}
return voteResult;
}
/**
* This method checks the response and says the processResponses() method
* what to do.
* @return PROCESS_CONTINUE to continue calculating votes,
* PROCESS_BREAK to stop calculating votes from the nodes,
* PROCESS_SKIP to skip current response.
* @throws ChannelException when the response is fatal to the
* current voting process.
*/
private int checkResponse(Rsp response) throws ChannelException {
if (!response.wasReceived()) {
if (log.isDebugEnabled())
log.debug("Response from node " + response.getSender() + " was not received.");
throw new ChannelException("Node " + response.getSender() + " failed to respond.");
}
if (response.wasSuspected()) {
if (log.isDebugEnabled())
log.debug("Node " + response.getSender() + " was suspected.");
return PROCESS_SKIP;
}
Object object = response.getValue();
// we received exception/error, something went wrong
// on one of the nodes... and we do not handle such faults
if (object instanceof Throwable) {
throw new ChannelException("Node " + response.getSender() + " is faulty.");
}
if (object == null) {
return PROCESS_SKIP;
}
// it is always interesting to know the class that caused failure...
if (!(object instanceof VoteResult)) {
String faultClass = object.getClass().getName();
// ...but we do not handle byzantine faults
throw new ChannelException("Node " + response.getSender() + " generated fault (class " + faultClass + ')');
}
// what if we received the response from faulty node?
if (object instanceof FailureVoteResult) {
if (log.isErrorEnabled())
log.error(ExternalStrings.DistributedLockManager_0, ((FailureVoteResult) object).getReason());
return PROCESS_BREAK;
}
// everything is fine :)
return PROCESS_CONTINUE;
}
private boolean informLockingNodes(ReleaseLockDecree releaseLockDecree) throws ChannelException {
return votingAdapter.vote(new MultiLockDecree(releaseLockDecree), VOTE_TIMEOUT);
}
/**
* This class represents the lock
*/
public static class LockDecree implements Serializable {
private static final long serialVersionUID = -7422058144576778340L;
protected final Object lockId;
protected final Object requester;
protected final Object managerId;
protected boolean commited;
private boolean multipleLocked = false;
protected LockDecree(Object lockId, Object requester, Object managerId) {
this.lockId = lockId;
this.requester = requester;
this.managerId = managerId;
}
/**
* Returns the key that should be used for Map lookup.
*/
public Object getKey() { return lockId; }
/**
* This is a place-holder for future lock expiration code.
*/
public boolean isValid() { return true; }
public void commit() { this.commited = true; }
/**
* @return Returns the multipleLocked.
*/
public boolean isMultipleLocked() {
return multipleLocked;
}
/**
* @param multipleLocked The multipleLocked to set.
*/
public void setMultipleLocked(boolean multipleLocked) {
this.multipleLocked = multipleLocked;
}
/**
* This is hashcode from the java.lang.Long class.
*/
@Override // GemStoneAddition
public int hashCode() {
return lockId.hashCode();
}
@Override // GemStoneAddition
public boolean equals(Object other) {
if (other instanceof LockDecree) {
return ((LockDecree)other).lockId.equals(this.lockId);
} else {
return false;
}
}
}
/**
* This class represents the lock to be released.
*/
public static class AcquireLockDecree extends LockDecree {
private static final long serialVersionUID = 7608853900623293300L;
private final long creationTime;
protected AcquireLockDecree(Object lockId, Object requester, Object managerId) {
super(lockId, requester, managerId);
this.creationTime = System.currentTimeMillis();
}
@Override
public boolean equals(Object o) { // GemStoneAddition for findbugs
return super.equals(o);
}
@Override
public int hashCode() { // GemStoneAddition for findbugs
return super.hashCode();
}
/**
* Lock aquire decree is valid for a ACQUIRE_EXPIRATION
* time after creation and if the lock is still valid (in the
* future locks will be leased for a predefined period of time).
*/
@Override // GemStoneAddition
public boolean isValid() {
boolean result = super.isValid();
if (!commited && result)
result = ((creationTime + ACQUIRE_EXPIRATION) > System.currentTimeMillis());
return result;
}
}
/**
* This class represents the lock to be released.
*/
public static class ReleaseLockDecree extends LockDecree {
private static final long serialVersionUID = -159320406385342426L;
ReleaseLockDecree(Object lockId, Object requester, Object managerId) {
super(lockId, requester, managerId);
}
}
/**
* This class represents the lock that has to be marked as multilocked
*/
public static class MultiLockDecree extends LockDecree {
private static final long serialVersionUID = -8775726661815938941L;
MultiLockDecree(Object lockId, Object requester, Object managerId) {
super(lockId, requester, managerId);
}
MultiLockDecree(ReleaseLockDecree releaseLockDecree) {
super(releaseLockDecree.lockId, releaseLockDecree.requester, releaseLockDecree.managerId);
}
}
}