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/*
* Copyright (c) 2020, 2023 Oracle and/or its affiliates. All rights reserved.
*
* This program and the accompanying materials are made available under the
* terms of the Eclipse Public License v. 2.0 which is available at
* http://www.eclipse.org/legal/epl-2.0,
* or the Eclipse Distribution License v. 1.0 which is available at
* http://www.eclipse.org/org/documents/edl-v10.php.
*
* SPDX-License-Identifier: EPL-2.0 OR BSD-3-Clause
*/
package org.eclipse.persistence.internal.helper;
import org.eclipse.persistence.internal.helper.type.ReadLockAcquisitionMetadata;
import java.util.ArrayList;
import java.util.Collections;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.Vector;
public class ReadLockManager {
public static final int FIRST_INDEX_OF_COLLECTION = 0;
/**
* This vector of read locks is essentially a basket of cache keys (classes that extend concurrency manager) that a
* specific thread has acquired for reading. We need to create this additional logic in order to be able to reduce
* the readers count on a cache key whenever
*
*/
private final Vector readLocks = new Vector<>(1);
/**
* We have seen that the read locks vector we have is very insufficient. We keep it for now due to the tracing code
* that is making use of it. But we also want to have a new tracing map with a lot more metadata
*/
private final Map> mapThreadToReadLockAcquisitionMetadata = new HashMap<>();
/**
* This is a field that will never be cleared. It will be getting ADDs if any problem is detected when we try remove
* a read lock from our tracing.
*/
private final List removeReadLockProblemsDetected = new ArrayList<>();
/**
* add a concurrency manager as deferred locks to the DLM
*/
public synchronized void addReadLock(ConcurrencyManager concurrencyManager) {
final Thread currentThread = Thread.currentThread();
final long currentThreadId = currentThread.getId();
ReadLockAcquisitionMetadata readLockAcquisitionMetadata = ConcurrencyUtil.SINGLETON.createReadLockAcquisitionMetadata(concurrencyManager);
this.readLocks.add(FIRST_INDEX_OF_COLLECTION, concurrencyManager);
if(!mapThreadToReadLockAcquisitionMetadata.containsKey(currentThreadId)) {
List newList = Collections.synchronizedList(new ArrayList<>());
mapThreadToReadLockAcquisitionMetadata.put(currentThreadId, newList );
}
List acquiredReadLocksInCurrentTransactionList = mapThreadToReadLockAcquisitionMetadata.get(currentThreadId);
acquiredReadLocksInCurrentTransactionList.add(FIRST_INDEX_OF_COLLECTION, readLockAcquisitionMetadata);
}
/**
* During normal operation of the concurrency manager, each time a cache key is decrement in the number of readers,
* so must the corresponding read lock manager of the thread be told let go of the cache key object acquired for
* reading.
*
* @param concurrencyManager
* the concurrency cache key that is about to be decrement in number of readers.
*/
public synchronized void removeReadLock(ConcurrencyManager concurrencyManager) {
final Thread currentThread = Thread.currentThread();
final long currentThreadId = currentThread.getId();
boolean readLockManagerHasTracingAboutAddedReadLocksForCurrentThread = mapThreadToReadLockAcquisitionMetadata.containsKey(currentThreadId);
if (!readLockManagerHasTracingAboutAddedReadLocksForCurrentThread) {
String errorMessage = ConcurrencyUtil.SINGLETON.readLockManagerProblem02ReadLockManageHasNoEntriesForThread(concurrencyManager, currentThreadId);
removeReadLockProblemsDetected.add(errorMessage);
return;
}
List readLocksAcquiredDuringCurrentThread = mapThreadToReadLockAcquisitionMetadata.get(currentThreadId);
ReadLockAcquisitionMetadata readLockAquisitionMetadataToRemove = null;
for (ReadLockAcquisitionMetadata currentReadLockAcquisitionMetadata : readLocksAcquiredDuringCurrentThread) {
ConcurrencyManager currentCacheKeyObjectToCheck = currentReadLockAcquisitionMetadata.getCacheKeyWhoseNumberOfReadersThreadIsIncrementing();
boolean dtoToRemoveFound = concurrencyManager.getConcurrencyManagerId() == currentCacheKeyObjectToCheck.getConcurrencyManagerId();
if (dtoToRemoveFound) {
readLockAquisitionMetadataToRemove = currentReadLockAcquisitionMetadata;
break;
}
}
if (readLockAquisitionMetadataToRemove == null) {
String errorMessage = ConcurrencyUtil.SINGLETON.readLockManagerProblem03ReadLockManageHasNoEntriesForThread(concurrencyManager, currentThreadId);
removeReadLockProblemsDetected.add(errorMessage);
return;
}
this.readLocks.remove(concurrencyManager);
readLocksAcquiredDuringCurrentThread.remove(readLockAquisitionMetadataToRemove);
if (readLocksAcquiredDuringCurrentThread.isEmpty()) {
mapThreadToReadLockAcquisitionMetadata.remove(currentThreadId);
}
}
/**
* Return a set of the deferred locks
*/
public synchronized List getReadLocks() {
return Collections.unmodifiableList(readLocks);
}
/**
* Allow the concurrency manager to directly pump a message stating that there was a problem while decrementing the
* number of readers.
*
* @param problemDetected
* the detected problem
*/
public synchronized void addRemoveReadLockProblemsDetected(String problemDetected) {
removeReadLockProblemsDetected.add(problemDetected);
}
/** Getter for {@link #mapThreadToReadLockAcquisitionMetadata} */
public Map> getMapThreadToReadLockAcquisitionMetadata() {
return mapThreadToReadLockAcquisitionMetadata;
}
/** Getter for {@link #removeReadLockProblemsDetected} */
public List getRemoveReadLockProblemsDetected() {
return removeReadLockProblemsDetected;
}
/**
* True if the tracing the data on the object has been completely removed. If this is the case it is perfectly fine
* to remove the read lock manager from from the hash map of Thread To tis ReadLockManager Tracing.
*
* @return true if the current read lock manger contains no information about acquired locks that were never
* released or any errors detected while attempting to remove a cache key. If there is any error detected or
* any read lock acquired in the tracing we definitely do not want this object instance to be thrown out
* from our main tracing. It is probably revealing problems in read lock acquisition and released.
*/
public synchronized boolean isEmpty() {
return readLocks.isEmpty() && removeReadLockProblemsDetected.isEmpty();
}
/**
* Create a new instance {@link ReadLockManager} that is in all regards
* equal to the current instance.
*
* USE CASE:
* This method is meant to be used by algorithms
* that want to dump a snapshot of the current state of the system
* or to go about doing
*/
@Override
public synchronized ReadLockManager clone() {
ReadLockManager clone = new ReadLockManager();
clone.readLocks.addAll(this.readLocks);
for (Map.Entry> currentEntry : this.mapThreadToReadLockAcquisitionMetadata.entrySet()) {
Long key = currentEntry.getKey();
List value = currentEntry.getValue();
clone.mapThreadToReadLockAcquisitionMetadata.put(key, new ArrayList<>(value));
}
clone.removeReadLockProblemsDetected.addAll(this.removeReadLockProblemsDetected);
return clone;
}
}