Heinous merge from HEAD. Seems to basically work. Be on guard however.

git-svn-id: https://svn.alfresco.com/repos/alfresco-enterprise/alfresco/BRANCHES/WCM-DEV2/root@4137 c4b6b30b-aa2e-2d43-bbcb-ca4b014f7261

source/java/org/alfresco/repo/transaction/DummyTransactionService.java

@@ -45,6 +45,10 @@ public class DummyTransactionService implements TransactionService
         return false;
     }
 
+    public void setReadOnly(boolean readOnly)
+    {
+    }
+
     public UserTransaction getUserTransaction()
     {
         return txn;

source/java/org/alfresco/repo/transaction/TransactionAwareSingleton.java

@@ -0,0 +1,143 @@
+/*
+ * Copyright (C) 2006 Alfresco, Inc.
+ *
+ * Licensed under the Mozilla Public License version 1.1 
+ * with a permitted attribution clause. You may obtain a
+ * copy of the License at
+ *
+ *   http://www.alfresco.org/legal/license.txt
+ *
+ * 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.alfresco.repo.transaction;
+
+import java.util.concurrent.locks.ReentrantReadWriteLock;
+import java.util.concurrent.locks.ReentrantReadWriteLock.ReadLock;
+import java.util.concurrent.locks.ReentrantReadWriteLock.WriteLock;
+
+/**
+ * A transactionally-safe storage class for singleton objects.  Changes to the singleton
+ * are only visibly promoted when the transaction is committed.
+ * <p>
+ * <code>
+ *    private static final TransactionAwareSingleton<Integer> MY_SINGLETON = new TransactionAwareSingleton<Integer>();
+ * </code>
+ * <p>
+ * All modifications to the singleton via {@link #get()} and {@link #put(T)} are made in a 
+ * transaction-local manner and promoted to the shared value in a thread-safe manner upon
+ * transacton completion.  Transaction-local changes take precedence over the shared value.
+ * 
+ * @see org.alfresco.repo.transaction.AlfrescoTransactionSupport
+ * 
+ * @author Derek Hulley
+ */
+public class TransactionAwareSingleton<T> extends TransactionListenerAdapter
+{
+    private static final String TRANSACTION_KEY = "TransactionAwareSingleton.storage";
+    
+    private final ReadLock singletonReadLock;
+    private final WriteLock singletonWriteLock;
+    private Object singletonValue;
+    
+    public TransactionAwareSingleton()
+    {
+        ReentrantReadWriteLock serverReadWriteLock = new ReentrantReadWriteLock();
+        singletonReadLock = serverReadWriteLock.readLock();
+        singletonWriteLock = serverReadWriteLock.writeLock();
+    }
+    
+    private void setValue(Object value)
+    {
+        // get a write lock
+        singletonWriteLock.lock();
+        try
+        {
+            singletonValue = value;
+        }
+        finally
+        {
+            singletonWriteLock.unlock();
+        }
+    }
+    
+    private Object getValue()
+    {
+        // get a read lock
+        singletonReadLock.lock();
+        try
+        {
+            return singletonValue;
+        }
+        finally
+        {
+            singletonReadLock.unlock();
+        }
+    }
+
+    /**
+     * @return Returns the transaction- and thread-safe wrapped instance
+     */
+    @SuppressWarnings("unchecked")
+    public T get()
+    {
+        // an in-transaction value overrides the singleton
+        TransactionStorage storage = (TransactionStorage) AlfrescoTransactionSupport.getResource(TRANSACTION_KEY);
+        if (storage != null)
+        {
+            return (T) storage.newValue;
+        }
+        else
+        {
+            return (T) getValue();
+        }
+    }
+    
+    /**
+     * Store the value in a transaction- and thread-safe manner.  It will only be persisted
+     * at the end of the transaction but will be visible to the current transaction from
+     * this call onwards.
+     * 
+     * @param value the value to store
+     */
+    public void put(T value)
+    {
+        // the value is changing
+        TransactionStorage storage = (TransactionStorage) AlfrescoTransactionSupport.getResource(TRANSACTION_KEY);
+        if (storage == null)
+        {
+            // it has not changed before
+            storage = new TransactionStorage();
+            AlfrescoTransactionSupport.bindResource(TRANSACTION_KEY, storage);
+            // listen to the transaction
+            AlfrescoTransactionSupport.bindListener(this);
+        }
+        storage.newValue = value;
+    }
+    
+    /**
+     * Promotes the storage value to the single value, if required
+     */
+    public void afterCommit()
+    {
+        TransactionStorage storage = (TransactionStorage) AlfrescoTransactionSupport.getResource(TRANSACTION_KEY);
+        if (storage != null)
+        {
+            // the value was overridden
+            setValue(storage.newValue);
+        }
+    }
+    
+    /**
+     * In-transaction storage of the altered value
+     * @author Derek Hulley
+     */
+    private static class TransactionStorage
+    {
+        public Object newValue;
+    }
+}

source/java/org/alfresco/repo/transaction/TransactionAwareSingletonTest.java

@@ -0,0 +1,224 @@
+/*
+ * Copyright (C) 2006 Alfresco, Inc.
+ *
+ * Licensed under the Mozilla Public License version 1.1 
+ * with a permitted attribution clause. You may obtain a
+ * copy of the License at
+ *
+ *   http://www.alfresco.org/legal/license.txt
+ *
+ * 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.alfresco.repo.transaction;
+
+import java.util.Random;
+
+import javax.transaction.UserTransaction;
+
+import junit.framework.TestCase;
+
+import org.alfresco.repo.transaction.TransactionUtil.TransactionWork;
+import org.alfresco.service.transaction.TransactionService;
+import org.alfresco.util.ApplicationContextHelper;
+import org.springframework.context.ApplicationContext;
+
+/**
+ * @see org.alfresco.repo.transaction.TransactionAwareSingleton
+ * 
+ * @author Derek Hulley
+ */
+public class TransactionAwareSingletonTest extends TestCase
+{
+    private static ApplicationContext ctx = ApplicationContextHelper.getApplicationContext();
+    private static Random rand = new Random();
+    
+    /** the instance to test */
+    private TransactionAwareSingleton<Integer> singleton = new TransactionAwareSingleton<Integer>();
+    private static final Integer INTEGER_ONE = new Integer(1);
+    private static final Integer INTEGER_TWO = new Integer(2);
+    
+    private TransactionService transactionService;
+    
+    public void setUp() throws Exception
+    {
+        transactionService = (TransactionService) ctx.getBean("transactionComponent");
+    }
+    
+    public void testCommit() throws Throwable
+    {
+        UserTransaction txn = transactionService.getUserTransaction();
+        try
+        {
+            txn.begin();
+            
+            singleton.put(INTEGER_ONE);
+            check(INTEGER_ONE, true);
+            check(null, false);
+            
+            // commit
+            txn.commit();
+        }
+        catch (Throwable e)
+        {
+            try { txn.rollback(); } catch (Throwable ee) {}
+            throw e;
+        }
+        check(INTEGER_ONE, true);
+        check(INTEGER_ONE, false);
+    }
+    
+    public void testRollback() throws Throwable
+    {
+        UserTransaction txn = transactionService.getUserTransaction();
+        try
+        {
+            txn.begin();
+            
+            singleton.put(INTEGER_TWO);
+            check(INTEGER_TWO, true);
+            check(null, false);
+            
+            // rollback
+            txn.rollback();
+        }
+        catch (Throwable e)
+        {
+            try { txn.rollback(); } catch (Throwable ee) {}
+            throw e;
+        }
+        check(null, true);
+        check(null, false);
+    }
+    
+    private static final int THREAD_COUNT = 20;
+    public void testThreadsCommit() throws Throwable
+    {
+        TestThread[] threads = new TestThread[THREAD_COUNT];
+        for (int i = 0; i < THREAD_COUNT; i++)
+        {
+            TestThread thread = new TestThread(true);
+            thread.start();
+            threads[i] = thread;
+        }
+        // wait for them to complete
+        for (int i = 0; i < THREAD_COUNT; i++)
+        {
+            while (threads[i].finished == false)
+            {
+                synchronized(this)
+                {
+                    try { wait(20); } catch (Throwable e) {}
+                }
+            }
+            if (threads[i].error != null)
+            {
+                throw threads[i].error;
+            }
+        }
+    }
+    public void testThreadsRollback() throws Throwable
+    {
+        TestThread[] threads = new TestThread[THREAD_COUNT];
+        for (int i = 0; i < THREAD_COUNT; i++)
+        {
+            TestThread thread = new TestThread(false);
+            thread.start();
+            threads[i] = thread;
+        }
+    }
+    
+    /**
+     * Dumps random values into 
+     * @author Derek Hulley
+     */
+    private class TestThread extends Thread
+    {
+        private boolean finished = false;
+        private Throwable error;
+        private boolean commit;
+        private Integer value = new Integer((int)System.nanoTime());
+        
+        public TestThread(boolean commit)
+        {
+            this.commit = commit;
+        }
+        @Override
+        public synchronized void run()
+        {
+            UserTransaction txn = transactionService.getUserTransaction();
+            try
+            {
+                txn.begin();
+                
+                singleton.put(value);
+                
+                // wait for some random time
+                try
+                {
+                    wait((long)(rand.nextDouble() * 1000.0));   // wait up to a second
+                }
+                catch (InterruptedException e)
+                {
+                    // ignore
+                }
+
+                // check
+                check(value, true);
+                
+                if (commit)
+                {
+                    txn.commit();
+                }
+                else
+                {
+                    // rollback
+                    txn.rollback();
+                }
+            }
+            catch (Throwable e)
+            {
+                try { txn.rollback(); } catch (Throwable ee) {}
+                this.error = e;
+            }
+            if (!commit)
+            {
+                try
+                {
+                    // no thread changes
+                    check(null, false);
+                }
+                catch (Throwable e)
+                {
+                    error = e;
+                }
+            }
+            finished = true;
+        }
+    }
+    
+    private void check(final Integer expected, boolean inTransaction)
+    {
+        TransactionWork<Object> checkWork = new TransactionWork<Object>()
+        {
+            public Object doWork() throws Exception
+            {
+                Integer actual = singleton.get();
+                assertTrue("Values don't match: " + expected + " != " + actual, actual == expected);
+                return null;
+            }
+        };
+        if (inTransaction)
+        {
+            TransactionUtil.executeInUserTransaction(transactionService, checkWork);
+        }
+        else
+        {
+            TransactionUtil.executeInNonPropagatingUserTransaction(transactionService, checkWork);
+        }
+    }
+}