/*******************************************************************************
* Copyright (c) 1998, 2008 Oracle. All rights reserved.
* This program and the accompanying materials are made available under the
* terms of the Eclipse Public License v1.0 and Eclipse Distribution License v. 1.0
* which accompanies this distribution.
* The Eclipse Public License is available at http://www.eclipse.org/legal/epl-v10.html
* and the Eclipse Distribution License is available at
* http://www.eclipse.org/org/documents/edl-v10.php.
*
* Contributors:
* Oracle - initial API and implementation from Oracle TopLink
******************************************************************************/
package org.eclipse.persistence.internal.helper;
import java.io.*;
import java.util.*;
import java.util.concurrent.ConcurrentHashMap;
import org.eclipse.persistence.exceptions.*;
import org.eclipse.persistence.internal.localization.*;
import org.eclipse.persistence.internal.identitymaps.CacheKey;
import org.eclipse.persistence.logging.*;
/**
* INTERNAL:
* <p>
* <b>Purpose</b>: To maintain concurrency for a particular task.
* It is a wrappers of a semaphore that allows recursive waits by a single thread.
* <p>
* <b>Responsibilities</b>:
* <ul>
* <li> Keep track of the active thread.
* <li> Wait all other threads until the first thread is done.
* <li> Maintain the depth of the active thread.
* </ul>
*/
public class ConcurrencyManager implements Serializable {
protected int numberOfReaders;
protected int depth;
protected int numberOfWritersWaiting;
protected transient Thread activeThread;
public static Map<Thread, DeferredLockManager> deferredLockManagers = initializeDeferredLockManagers();
protected boolean lockedByMergeManager;
/** Cachekey owner set when ConcurrencyMananger is used within an cachekey on an identity map
* Used to store the owner so that the object involved can be retrieved from the cachekey
*/
protected CacheKey ownerCacheKey;
/**
* Initialize the newly allocated instance of this class.
* Set the depth to zero.
*/
public ConcurrencyManager() {
this.depth = 0;
this.numberOfReaders = 0;
this.numberOfWritersWaiting = 0;
}
/**
* Initialize a new ConcurrencyManger, setting depth to zero and setting the
* owner cacheKey.
*/
public ConcurrencyManager(CacheKey cacheKey) {
this();
this.ownerCacheKey = cacheKey;
}
/**
* Wait for all threads except the active thread.
* If the active thread just increment the depth.
* This should be called before entering a critical section.
*/
public void acquire() throws ConcurrencyException {
this.acquire(false);
}
/**
* Wait for all threads except the active thread.
* If the active thread just increment the depth.
* This should be called before entering a critical section.
* called with true from the merge process, if true then the refresh will not refresh the object
*/
public synchronized void acquire(boolean forMerge) throws ConcurrencyException {
while (((this.activeThread != null) || (this.numberOfReaders > 0)) && (this.activeThread != Thread.currentThread())) {
// This must be in a while as multiple threads may be released, or another thread may rush the acquire after one is released.
try {
this.numberOfWritersWaiting++;
wait();
this.numberOfWritersWaiting--;
} catch (InterruptedException exception) {
throw ConcurrencyException.waitWasInterrupted(exception.getMessage());
}
}
if (this.activeThread == null) {
this.activeThread = Thread.currentThread();
}
this.lockedByMergeManager = forMerge;
this.depth++;
}
/**
* If the lock is not acquired already acquire it and return true.
* If it has been acquired already return false
* Added for CR 2317
*/
public boolean acquireNoWait() throws ConcurrencyException {
return acquireNoWait(false);
}
/**
* If the lock is not acquired already acquire it and return true.
* If it has been acquired already return false
* Added for CR 2317
* called with true from the merge process, if true then the refresh will not refresh the object
*/
public synchronized boolean acquireNoWait(boolean forMerge) throws ConcurrencyException {
if ((this.activeThread == null) || (this.activeThread == Thread.currentThread())) {
//if I own the lock increment depth
acquire(forMerge);
return true;
} else {
return false;
}
}
/**
* If the lock is not acquired already acquire it and return true.
* If it has been acquired already return false
* Added for CR 2317
* called with true from the merge process, if true then the refresh will not refresh the object
*/
public synchronized boolean acquireWithWait(boolean forMerge, int wait) throws ConcurrencyException {
if ((this.activeThread == null) || (this.activeThread == Thread.currentThread())) {
//if I own the lock increment depth
acquire(forMerge);
return true;
} else {
try {
wait(wait);
} catch (InterruptedException e) {
return false;
}
if ((this.activeThread == null) || (this.activeThread == Thread.currentThread())){
acquire(forMerge);
return true;
}
return false;
}
}
/**
* If the activeThread is not set, acquire it and return true.
* If the activeThread is set, it has been acquired already, return false.
* Added for Bug 5840635
* Call with true from the merge process, if true then the refresh will not refresh the object.
*/
public synchronized boolean acquireIfUnownedNoWait(boolean forMerge) throws ConcurrencyException {
// Only acquire lock if active thread is null. Do not check current thread.
if (this.activeThread == null) {
// if lock is unowned increment depth
acquire(forMerge);
return true;
} else {
return false;
}
}
/**
* Add deferred lock into a hashtable to avoid deadlock
*/
public void acquireDeferredLock() throws ConcurrencyException {
Thread currentThread = Thread.currentThread();
DeferredLockManager lockManager = getDeferredLockManager(currentThread);
if (lockManager == null) {
lockManager = new DeferredLockManager();
putDeferredLock(currentThread, lockManager);
}
lockManager.incrementDepth();
synchronized (this) {
while (this.numberOfReaders != 0) {
// There are readers of this object, wait until they are done before determining if
//there are any other writers. If not we will wait on the readers for acquire. If another
//thread is also waiting on the acquire then a deadlock could occur. See bug 3049635
//We could release all active locks before releasing deferred but the object may not be finished building
//we could make the readers get a hard lock, but then we would just build a deferred lock even though
//the object is not being built.
try {
this.numberOfWritersWaiting++;
wait();
this.numberOfWritersWaiting--;
} catch (InterruptedException exception) {
throw ConcurrencyException.waitWasInterrupted(exception.getMessage());
}
}
if ((this.activeThread == currentThread) || (!isAcquired())) {
lockManager.addActiveLock(this);
acquire();
} else {
lockManager.addDeferredLock(this);
if (AbstractSessionLog.getLog().shouldLog(SessionLog.FINER)) {
AbstractSessionLog.getLog().log(SessionLog.FINER, "acquiring_deferred_lock", getOwnerCacheKey().getObject(), currentThread.getName());
}
}
}
}
/**
* Check the lock state, if locked, acquire and release a deferred lock.
* This optimizes out the normal deferred-lock check if not locked.
*/
public void checkDeferredLock() throws ConcurrencyException {
// If it is not locked, then just return.
if (this.activeThread == null) {
return;
}
acquireDeferredLock();
releaseDeferredLock();
}
/**
* Check the lock state, if locked, acquire and release a read lock.
* This optimizes out the normal read-lock check if not locked.
*/
public void checkReadLock() throws ConcurrencyException {
// If it is not locked, then just return.
if (this.activeThread == null) {
return;
}
acquireReadLock();
releaseReadLock();
}
/**
* Wait on any writer.
* Allow concurrent reads.
*/
public synchronized void acquireReadLock() throws ConcurrencyException {
// Cannot check for starving writers as will lead to deadlocks.
while ((this.activeThread != null) && (this.activeThread != Thread.currentThread())) {
try {
wait();
} catch (InterruptedException exception) {
throw ConcurrencyException.waitWasInterrupted(exception.getMessage());
}
}
this.numberOfReaders++;
}
/**
* If this is acquired return false otherwise acquire readlock and return true
*/
public synchronized boolean acquireReadLockNoWait() {
if ((this.activeThread == null) || (this.activeThread == Thread.currentThread())) {
acquireReadLock();
return true;
} else {
return false;
}
}
/**
* Return the active thread.
*/
public Thread getActiveThread() {
return activeThread;
}
/**
* Return the deferred lock manager from the thread
*/
public static DeferredLockManager getDeferredLockManager(Thread thread) {
return getDeferredLockManagers().get(thread);
}
/**
* Return the deferred lock manager hashtable (thread - DeferredLockManager).
*/
protected static Map<Thread, DeferredLockManager> getDeferredLockManagers() {
return deferredLockManagers;
}
/**
* Init the deferred lock managers (thread - DeferredLockManager).
*/
protected static Map initializeDeferredLockManagers() {
return new ConcurrentHashMap();
}
/**
* Return the current depth of the active thread.
*/
public int getDepth() {
return depth;
}
/**
* Number of writer that want the lock.
* This is used to ensure that a writer is not starved.
*/
public int getNumberOfReaders() {
return numberOfReaders;
}
/**
* Number of writers that want the lock.
* This is used to ensure that a writer is not starved.
*/
public int getNumberOfWritersWaiting() {
return numberOfWritersWaiting;
}
/**
* Returns the owner cache key for this concurrency manager
*/
public CacheKey getOwnerCacheKey() {
return this.ownerCacheKey;
}
/**
* Return if a thread has acquire this manager.
*/
public boolean isAcquired() {
return depth > 0;
}
/**
* INTERNAL:
* Used byt the refresh process to determine if this concurrency manager is locked by
* the merge process. If it is then the refresh should not refresh the object
*/
public boolean isLockedByMergeManager() {
return this.lockedByMergeManager;
}
/**
* Check if the deferred locks of a thread are all released
*/
public static boolean isBuildObjectOnThreadComplete(Thread thread, Map recursiveSet) {
if (recursiveSet.containsKey(thread)) {
return true;
}
recursiveSet.put(thread, thread);
DeferredLockManager lockManager = getDeferredLockManager(thread);
if (lockManager == null) {
return true;
}
Vector deferredLocks = lockManager.getDeferredLocks();
for (Enumeration deferredLocksEnum = deferredLocks.elements();
deferredLocksEnum.hasMoreElements();) {
ConcurrencyManager deferedLock = (ConcurrencyManager)deferredLocksEnum.nextElement();
Thread activeThread = null;
if (deferedLock.isAcquired()) {
activeThread = deferedLock.getActiveThread();
// the active thread may be set to null at anypoint
// if added for CR 2330
if (activeThread != null) {
DeferredLockManager currentLockManager = getDeferredLockManager(activeThread);
if (currentLockManager == null) {
return false;
} else if (currentLockManager.isThreadComplete()) {
activeThread = deferedLock.getActiveThread();
// The lock may suddenly finish and no longer have an active thread.
if (activeThread != null) {
if (!isBuildObjectOnThreadComplete(activeThread, recursiveSet)) {
return false;
}
}
} else {
return false;
}
}
}
}
return true;
}
/**
* Return if this manager is within a nested acquire.
*/
public boolean isNested() {
return depth > 1;
}
public void putDeferredLock(Thread thread, DeferredLockManager lockManager) {
getDeferredLockManagers().put(thread, lockManager);
}
/**
* Decrement the depth for the active thread.
* Assume the current thread is the active one.
* Raise an error if the depth become < 0.
* The notify will release the first thread waiting on the object,
* if no threads are waiting it will do nothing.
*/
public synchronized void release() throws ConcurrencyException {
if (this.depth == 0) {
throw ConcurrencyException.signalAttemptedBeforeWait();
} else {
this.depth--;
}
if (this.depth == 0) {
this.activeThread = null;
this.lockedByMergeManager = false;
notifyAll();
}
}
/**
* Release the deferred lock.
* This uses a deadlock detection and resolution algorithm to avoid cache deadlocks.
* The deferred lock manager keeps track of the lock for a thread, so that other
* thread know when a deadlock has occurred and can resolve it.
*/
public void releaseDeferredLock() throws ConcurrencyException {
Thread currentThread = Thread.currentThread();
DeferredLockManager lockManager = getDeferredLockManager(currentThread);
if (lockManager == null) {
return;
}
int depth = lockManager.getThreadDepth();
if (depth > 1) {
lockManager.decrementDepth();
return;
}
// If the set is null or empty, means there is no deferred lock for this thread, return.
if (!lockManager.hasDeferredLock()) {
lockManager.releaseActiveLocksOnThread();
removeDeferredLockManager(currentThread);
return;
}
lockManager.setIsThreadComplete(true);
// Thread have three stages, one where they are doing work (i.e. building objects)
// two where they are done their own work but may be waiting on other threads to finish their work,
// and a third when they and all the threads they are waiting on are done.
// This is essentially a busy wait to determine if all the other threads are done.
while (true) {
// 2612538 - the default size of Map (32) is appropriate
Map recursiveSet = new IdentityHashMap();
if (isBuildObjectOnThreadComplete(currentThread, recursiveSet)) {// Thread job done.
lockManager.releaseActiveLocksOnThread();
removeDeferredLockManager(currentThread);
AbstractSessionLog.getLog().log(SessionLog.FINER, "deferred_locks_released", currentThread.getName());
return;
} else {// Not done yet, wait and check again.
try {
Thread.sleep(1);
} catch (InterruptedException ignoreAndContinue) {
}
}
}
}
/**
* Decrement the number of readers.
* Used to allow concurrent reads.
*/
public synchronized void releaseReadLock() throws ConcurrencyException {
if (this.numberOfReaders == 0) {
throw ConcurrencyException.signalAttemptedBeforeWait();
} else {
this.numberOfReaders--;
}
if (this.numberOfReaders == 0) {
notifyAll();
}
}
/**
* Remove the deferred lock manager for the thread
*/
public static DeferredLockManager removeDeferredLockManager(Thread thread) {
return getDeferredLockManagers().remove(thread);
}
/**
* Set the active thread.
*/
public void setActiveThread(Thread activeThread) {
this.activeThread = activeThread;
}
/**
* Set the current depth of the active thread.
*/
protected void setDepth(int depth) {
this.depth = depth;
}
/**
* INTERNAL:
* Used by the mergemanager to let the read know not to refresh this object as it is being
* loaded by the merge process.
*/
public void setIsLockedByMergeManager(boolean state) {
this.lockedByMergeManager = state;
}
/**
* Track the number of readers.
*/
protected void setNumberOfReaders(int numberOfReaders) {
this.numberOfReaders = numberOfReaders;
}
/**
* Number of writers that want the lock.
* This is used to ensure that a writer is not starved.
*/
protected void setNumberOfWritersWaiting(int numberOfWritersWaiting) {
this.numberOfWritersWaiting = numberOfWritersWaiting;
}
public synchronized void transitionToDeferredLock(){
Thread currentThread = Thread.currentThread();
DeferredLockManager lockManager = getDeferredLockManager(currentThread);
if (lockManager == null) {
lockManager = new DeferredLockManager();
putDeferredLock(currentThread, lockManager);
}
lockManager.incrementDepth();
lockManager.addActiveLock(this);
}
/**
* Print the nested depth.
*/
public String toString() {
Object[] args = { new Integer(getDepth()) };
return Helper.getShortClassName(getClass()) + ToStringLocalization.buildMessage("nest_level", args);
}
}