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/*
* Copyright 2006 Amazon Technologies, Inc. or its affiliates.
* Amazon, Amazon.com and Carbonado are trademarks or registered trademarks
* of Amazon Technologies, Inc. or its affiliates. All rights reserved.
*
* Licensed 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 com.amazon.carbonado.spi;
import java.util.Map;
import java.util.concurrent.TimeUnit;
import org.cojen.util.WeakIdentityMap;
import com.amazon.carbonado.IsolationLevel;
import com.amazon.carbonado.PersistException;
import com.amazon.carbonado.RepositoryException;
import com.amazon.carbonado.Transaction;
/**
* Generic transaction manager for repositories.
*
* @param <Txn> Transaction type
* @author Brian S O'Neill
*/
public abstract class TransactionManager<Txn> {
private static final int NOT_CLOSED = 0, CLOSED = 1, SUSPENDED = 2;
private final ThreadLocal<TransactionScope<Txn>> mCurrentScope;
private final Map<TransactionScope<Txn>, ?> mAllScopes;
private int mClosedState;
public TransactionManager() {
mCurrentScope = new ThreadLocal<TransactionScope<Txn>>();
mAllScopes = new WeakIdentityMap();
}
/**
* Returns the thread-local TransactionScope, creating it if needed.
*/
public TransactionScope<Txn> localTransactionScope() {
TransactionScope<Txn> scope = mCurrentScope.get();
if (scope == null) {
int closedState;
synchronized (this) {
closedState = mClosedState;
scope = new TransactionScope<Txn>(this, closedState != NOT_CLOSED);
mAllScopes.put(scope, null);
}
mCurrentScope.set(scope);
if (closedState == SUSPENDED) {
// Immediately suspend new scope.
scope.getLock().lock();
}
}
return scope;
}
/**
* Closes all transaction scopes. Should be called only when repository is
* closed.
*
* @param suspend when true, indefinitely suspend all threads interacting
* with transactions
*/
public synchronized void close(boolean suspend) throws RepositoryException {
if (mClosedState == SUSPENDED) {
// If suspended, attempting to close again will likely deadlock.
return;
}
if (suspend) {
for (TransactionScope<?> scope : mAllScopes.keySet()) {
// Lock scope but don't release it. This prevents other threads
// from beginning work during shutdown, which will likely fail
// along the way.
scope.getLock().lock();
}
}
mClosedState = suspend ? SUSPENDED : CLOSED;
for (TransactionScope<?> scope : mAllScopes.keySet()) {
scope.close();
}
}
/**
* Returns supported isolation level, which may be higher. If isolation
* level cannot go higher (or lower than parent) then return null.
*
* @param parent optional parent transaction
* @param level desired isolation level (may be null)
*/
protected abstract IsolationLevel selectIsolationLevel(Transaction parent,
IsolationLevel level);
/**
* Return true if transactions support "for update" mode.
*
* @since 1.2
*/
protected abstract boolean supportsForUpdate();
/**
* Creates an internal transaction representation, with the optional parent
* transaction. If parent is not null and real nested transactions are not
* supported, simply return parent transaction for supporting fake nested
* transactions.
*
* @param parent optional parent transaction
* @param level required isolation level
* @return new transaction, parent transaction, or possibly null if required
* isolation level is none
*/
protected abstract Txn createTxn(Txn parent, IsolationLevel level) throws Exception;
/**
* Creates an internal transaction representation, with the optional parent
* transaction. If parent is not null and real nested transactions are not
* supported, simply return parent transaction for supporting fake nested
* transactions.
*
* <p>The default implementation of this method just calls the regular
* createTxn method, ignoring the timeout parameter.
*
* @param parent optional parent transaction
* @param level required isolation level
* @param timeout desired timeout for lock acquisition, never negative
* @param unit timeout unit, never null
* @return new transaction, parent transaction, or possibly null if required
* isolation level is none
*/
protected Txn createTxn(Txn parent, IsolationLevel level,
int timeout, TimeUnit unit)
throws Exception
{
return createTxn(parent, level);
}
/**
* Called when a transaction is about to be reused. The default
* implementation of this method does nothing. Override if any preparation
* is required to ready a transaction for reuse.
*
* @param txn transaction to reuse, never null
* @since 1.1.3
*/
protected void reuseTxn(Txn txn) throws Exception {
}
/**
* Commits and closes the given internal transaction.
*
* @return true if transaction object is still valid
*/
protected abstract boolean commitTxn(Txn txn) throws PersistException;
/**
* Aborts and closes the given internal transaction.
*/
protected abstract void abortTxn(Txn txn) throws PersistException;
}
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