/* * %W% %E% * * Copyright 1990-2006 Sun Microsystems, Inc. All Rights Reserved. * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER * * This program is free software; you can redistribute it and/or * modify it under the terms of the GNU General Public License version * 2 only, as published by the Free Software Foundation. * * 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 version 2 for more details (a copy is * included at /legal/license.txt). * * You should have received a copy of the GNU General Public License * version 2 along with this work; if not, write to the Free Software * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA * 02110-1301 USA * * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa * Clara, CA 95054 or visit www.sun.com if you need additional * information or have any questions. */ package com.sun.jump.module.contentstore; import com.sun.jump.module.JUMPModule; /** * JUMPContentStore provides a base class for all content stores * in the JUMP system. Concrete content stores extend this class and provides * an instance of the JUMPStore to be used for this * content store. * * This also implements the JUMPModule to indicate that all * the subclasses of this class is a JUMP module. */ public abstract class JUMPContentStore implements JUMPModule { private static int exclusiveAccess = 0; private static int readAccess = 0; private static Object lock = new Object(); /** * Creates a new instance of JUMPContentStore */ protected JUMPContentStore() { } /** * Returns a JUMPStore instance to be used by the * content store. Typically this method is called from the * JUMPContentStore.openStore(boolean) when creating the StoreHandle. * The subclass of JUMPContentStore can choose to either work with a single * instance of JUMPStore, which this getStore() returns, * or use multiple instances. */ protected abstract JUMPStore getStore(); /** * Open the store for read-only or exclusive access. In exclsuive * access mutable operations can be performed on the store, whereas * in read-only mode, only immutable operations can be performed. This * method ensures that there can only be a single component that can * be in exclusuive mode. The caller blocks till the store is accessible * with the requested access. */ protected JUMPStoreHandle openStore(boolean accessExclusive) { if (accessExclusive) { synchronized (lock) { while (exclusiveAccess > 0 || readAccess > 0) { try { // Wait until closeStore is called... lock.wait(); } catch (InterruptedException e) {} } exclusiveAccess++; return new JUMPStoreHandle(getStore(), accessExclusive); } } else { // read-only synchronized(lock) { while (exclusiveAccess > 0) { try { // Wait until closeStore is called... lock.wait(); } catch (InterruptedException e) {} } readAccess++; return new JUMPStoreHandle(getStore(), accessExclusive); } } } /** * Called to indicate that the content store does not access the store * anymore. */ protected void closeStore(JUMPStoreHandle storeHandle) { synchronized (lock) { if (storeHandle.isExclusive()) { exclusiveAccess--; } else { readAccess--; } lock.notifyAll(); // Notify all threads waiting at openStore() } } }
