[seam-commits] Seam SVN: r8642 - trunk/examples/wiki/src/main/org/jboss/seam/wiki/core/nestedset/listener.

Author: christian.bauer(a)jboss.com Date: 2008-08-08 13:26:13 -0400 (Fri, 08 Aug 2008) New Revision: 8642 Added: trunk/examples/wiki/src/main/org/jboss/seam/wiki/core/nestedset/listener/NestedSetMonitor.java Modified: trunk/examples/wiki/src/main/org/jboss/seam/wiki/core/nestedset/listener/NestedSetOperation.java trunk/examples/wiki/src/main/org/jboss/seam/wiki/core/nestedset/listener/NestedSetPostDeleteEventListener.java trunk/examples/wiki/src/main/org/jboss/seam/wiki/core/nestedset/listener/NestedSetPostInsertEventListener.java Log: Nested set modifications require some form of locking, serializing in-memory for now Added: trunk/examples/wiki/src/main/org/jboss/seam/wiki/core/nestedset/listener/NestedSetMonitor.java =================================================================== --- trunk/examples/wiki/src/main/org/jboss/seam/wiki/core/nestedset/listener/NestedSetMonitor.java (rev 0) +++ trunk/examples/wiki/src/main/org/jboss/seam/wiki/core/nestedset/listener/NestedSetMonitor.java 2008-08-08 17:26:13 UTC (rev 8642) @@ -0,0 +1,49 @@ +package org.jboss.seam.wiki.core.nestedset.listener; + +import org.hibernate.event.EventSource; + +import java.util.concurrent.locks.ReentrantLock; +import java.util.concurrent.locks.Lock; +import java.util.concurrent.TimeUnit; + +/** + * An alternative to table locking, we serialize nested set insert/updates in memory. + * + * <p> + * Any nested set tree modification potentially updates all rows in a database table. This + * requires several <tt>UPDATE</tt> statements, and also <tt>INSERT</tt> and <tt>DELETE</tt>. + * Any concurrent commit to the rows betwen <tt>UPDATE</tt> statements would be fatal and + * corrupt the tree information. The usual solution is to lock the whole table(s). Because + * MySQL has a compleltey unusable locking system (locking a table commits the current transaction, you + * need to lock all tables you are going to use from that point on, etc.), and because portability is + * a concern of this Nested Set implementation, we work around the problem with an in-memory exclusive lock. + * </p> + * <p> + * <b>NOTE:</b> This does NOT work if several applications modify the nested set + * tree in the same tables! + * </p> + * + * @author Christian Bauer + */ +public class NestedSetMonitor { + + private static final int LOCK_TIMEOUT_SECONDS = 10; + + private static final Lock lock = new ReentrantLock(true); + + public static void executeOperation(NestedSetOperation operation, EventSource session) { + try { + if (lock.tryLock(LOCK_TIMEOUT_SECONDS, TimeUnit.SECONDS)) { + try { + operation.execute(session); + } finally { + lock.unlock(); + } + } else { + throw new RuntimeException("Could not aquire lock to update nested set tree"); + } + } catch (InterruptedException ex) { + throw new RuntimeException("Current thread could not aquire lock, has been interrupted"); + } + } +} Modified: trunk/examples/wiki/src/main/org/jboss/seam/wiki/core/nestedset/listener/NestedSetOperation.java =================================================================== --- trunk/examples/wiki/src/main/org/jboss/seam/wiki/core/nestedset/listener/NestedSetOperation.java 2008-08-08 16:02:46 UTC (rev 8641) +++ trunk/examples/wiki/src/main/org/jboss/seam/wiki/core/nestedset/listener/NestedSetOperation.java 2008-08-08 17:26:13 UTC (rev 8642) @@ -43,7 +43,7 @@ * for the deprecated <tt>Session#connection()</tt> method. * </p> * - * TODO: We should lock the tables! + * TODO: We should lock the tables! Instead we are using the NestedSetMonitor as a workaround... * * @author Christian Bauer */ Modified: trunk/examples/wiki/src/main/org/jboss/seam/wiki/core/nestedset/listener/NestedSetPostDeleteEventListener.java =================================================================== --- trunk/examples/wiki/src/main/org/jboss/seam/wiki/core/nestedset/listener/NestedSetPostDeleteEventListener.java 2008-08-08 16:02:46 UTC (rev 8641) +++ trunk/examples/wiki/src/main/org/jboss/seam/wiki/core/nestedset/listener/NestedSetPostDeleteEventListener.java 2008-08-08 17:26:13 UTC (rev 8642) @@ -26,7 +26,10 @@ if ( NestedSetNode.class.isAssignableFrom(event.getEntity().getClass())) { log.debug("executing nested set delete operation, recalculating the tree"); - new DeleteNestedSetOperation( (NestedSetNode)event.getEntity() ).execute(event.getSession()); + NestedSetMonitor.executeOperation( + new DeleteNestedSetOperation( (NestedSetNode)event.getEntity() ), + event.getSession() + ); } } Modified: trunk/examples/wiki/src/main/org/jboss/seam/wiki/core/nestedset/listener/NestedSetPostInsertEventListener.java =================================================================== --- trunk/examples/wiki/src/main/org/jboss/seam/wiki/core/nestedset/listener/NestedSetPostInsertEventListener.java 2008-08-08 16:02:46 UTC (rev 8641) +++ trunk/examples/wiki/src/main/org/jboss/seam/wiki/core/nestedset/listener/NestedSetPostInsertEventListener.java 2008-08-08 17:26:13 UTC (rev 8642) @@ -26,7 +26,10 @@ if ( NestedSetNode.class.isAssignableFrom(event.getEntity().getClass())) { log.debug("executing nested set insert operation, recalculating the tree"); - new InsertNestedSetOperation( (NestedSetNode)event.getEntity() ).execute(event.getSession()); + NestedSetMonitor.executeOperation( + new InsertNestedSetOperation((NestedSetNode)event.getEntity()), + event.getSession() + ); } }