JobLockService implementation

- Provides transaction-aware locking
 - Post-transaction cleanup is automatically done
 - Retrying for lock acquisition is handled internally as well
 - Downgraded the lock concurrency tests for the build machine (maybe 50 threads was too much)
 - Deadlock tests added for the high-level locking


git-svn-id: https://svn.alfresco.com/repos/alfresco-enterprise/alfresco/HEAD/root@13968 c4b6b30b-aa2e-2d43-bbcb-ca4b014f7261

source/java/org/alfresco/repo/lock/JobLockService.java

@@ -0,0 +1,87 @@
+/*
+ * Copyright (C) 2005-2009 Alfresco Software Limited.
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version 2
+ * of the License, or (at your option) any later version.
+
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
+
+ * As a special exception to the terms and conditions of version 2.0 of 
+ * the GPL, you may redistribute this Program in connection with Free/Libre 
+ * and Open Source Software ("FLOSS") applications as described in Alfresco's 
+ * FLOSS exception.  You should have recieved a copy of the text describing 
+ * the FLOSS exception, and it is also available here: 
+ * http://www.alfresco.com/legal/licensing"
+ */
+package org.alfresco.repo.lock;
+
+import org.alfresco.service.namespace.QName;
+
+/**
+ * Service interface for managing job locks.
+ * <p>
+ * Locks are identified by a fully qualified name ({@link QName}) and follow a hierarchical
+ * naming convention i.e. locks higher up a hierarchy can be shared but will prevent explicit
+ * (exclusive) locks from being taken.  For example:  If exclusive lock <b>a.a.a</b> has been
+ * taken, then <b>a.a</b> and <b>a</b> are all implicitly taken as shared locks.  Exclusive lock
+ * <b>a.a.b</b> can be taken by another process and will share locks <b>a.a</b> and <b>a</b>
+ * with the first process.  It will not be possible for a third process to take a lock on
+ * <b>a.a</b>, however.
+ * <p>
+ * <b><u>LOCK ORDERING</u>:</b><br>
+ * The transactional locks will be applied in strict alphabetical order.  A very basic deadlock
+ * prevention system (at least) must be in place when applying or reapplying locks and be biased
+ * against locks applied non-alphabetically.
+ * 
+ * @author Derek Hulley
+ * @since 3.2
+ */
+public interface JobLockService
+{
+    /**
+     * Take a transactionally-managed lock.  This method can be called repeatedly to both
+     * initially acquire the lock as well as to maintain the lock.  This method should
+     * either be called again before the lock expires or the transaction should end before
+     * the lock expires.
+     * <p>
+     * The following rules apply to taking and releasing locks:<br>
+     *  - Expired locks can be taken by any process<br>
+     *  - Lock expiration does not prevent a lock from being refreshed or released<br>
+     *  - Only locks that were manipulated using another token will cause failure
+     * <p>
+     * The locks are automatically released when the transaction is terminated.
+     * <p>
+     * Any failure to acquire the lock (after retries), refresh the lock or subsequently
+     * release the owned locks will invalidate the transaction and cause rollback.
+     * 
+     * @param lockQName             the name of the lock to acquire
+     * @param timeToLive            the time (in milliseconds) for the lock to remain valid
+     * @throws LockAcquisitionException if the lock could not be acquired
+     * @throws IllegalStateException if a transaction is not active
+     */
+    void getTransacionalLock(QName lockQName, long timeToLive);
+    
+    /**
+     * {@inheritDoc JobLockService#getTransacionalLock(QName, long)}
+     * <p>
+     * If the lock cannot be immediately acquired, the process will wait and retry.  Note
+     * that second and subsequent attempts to get the lock during a transaction cannot
+     * make use of retrying; the lock is actually being refreshed and will therefore never
+     * become valid if it doesn't refresh directly.
+     * 
+     * @param retryWait             the time (in milliseconds) to wait before trying again
+     * @param retryCount            the maximum number of times to attempt the lock acquisition
+     * @throws LockAcquisitionException if the lock could not be acquired
+     * @throws IllegalStateException if a transaction is not active
+     */
+    void getTransacionalLock(QName lockQName, long timeToLive, long retryWait, int retryCount);
+}