| /* PersistentHasthable.java -- Persistent hash table. |
| Copyright (C) 2006 Free Software Foundation, Inc. |
| |
| This file is part of GNU Classpath. |
| |
| GNU Classpath 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, or (at your option) |
| any later version. |
| |
| GNU Classpath 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 GNU Classpath; see the file COPYING. If not, write to the |
| Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA |
| 02110-1301 USA. |
| |
| Linking this library statically or dynamically with other modules is |
| making a combined work based on this library. Thus, the terms and |
| conditions of the GNU General Public License cover the whole |
| combination. |
| |
| As a special exception, the copyright holders of this library give you |
| permission to link this library with independent modules to produce an |
| executable, regardless of the license terms of these independent |
| modules, and to copy and distribute the resulting executable under |
| terms of your choice, provided that you also meet, for each linked |
| independent module, the terms and conditions of the license of that |
| module. An independent module is a module which is not derived from |
| or based on this library. If you modify this library, you may extend |
| this exception to your version of the library, but you are not |
| obligated to do so. If you do not wish to do so, delete this |
| exception statement from your version. */ |
| |
| package gnu.classpath.tools.rmi; |
| |
| import java.io.BufferedInputStream; |
| import java.io.BufferedOutputStream; |
| import java.io.File; |
| import java.io.FileInputStream; |
| import java.io.FileOutputStream; |
| import java.io.ObjectInputStream; |
| import java.io.ObjectOutputStream; |
| import java.io.Serializable; |
| import java.util.Hashtable; |
| import java.util.Map; |
| import java.util.TimerTask; |
| |
| /** |
| * The persistent hash table. The changes are written to dist after |
| * SAVE_AT_MOST_AFTER time from the latest database change or at most after |
| * ALWAYS_UPDATE, if the database is updated very frequently. To ensure that no |
| * information is lost, the shutdown method must be called before exit. |
| * |
| * @author Audrius Meskauskas (audriusa@bioinformatics.org) |
| */ |
| public class PersistentHashTable |
| extends Hashtable |
| implements Serializable, Persistent |
| { |
| |
| /** |
| * Use serialVersionUID for interoperability |
| */ |
| private static final long serialVersionUID = 1; |
| |
| class WriteToDiskTask extends TimerTask |
| { |
| /** |
| * Save the database. |
| */ |
| public void run() |
| { |
| writeContent(); |
| sheduled = null; |
| } |
| } |
| |
| /** |
| * The database file. |
| */ |
| File database; |
| |
| /** |
| * The currently sheduled write to disk task, null if none. |
| */ |
| WriteToDiskTask sheduled = null; |
| |
| /** |
| * The time, when the disk database was last updated. |
| */ |
| long lastUpdated; |
| |
| /** |
| * Setting to false prevents the automated disk update. |
| * The initial value is true to prevent writing while reading and is set |
| * to false in createInstance. |
| */ |
| transient boolean ready; |
| |
| /** |
| * Use static method to obtain the instance. |
| */ |
| private PersistentHashTable(File file) |
| { |
| if (file == null) |
| throw new NullPointerException("Null file provided"); |
| database = file; |
| } |
| |
| /** |
| * Create a new persistent table that stores its information into the given |
| * file. |
| * |
| * @param file |
| * the file, where the table stores its information. |
| * @param coldStart |
| * if true, the existing file with this name will be erased and |
| * ignored. Otherwise, it will be assumed that the file contains the |
| * persistent table information. |
| */ |
| public static Map createInstance(File file, boolean coldStart) |
| { |
| try |
| { |
| PersistentHashTable k2v; |
| if (file.exists()) |
| { |
| if (coldStart) |
| { |
| file.delete(); |
| k2v = new PersistentHashTable(file); |
| } |
| else |
| { |
| FileInputStream fi = new FileInputStream(file); |
| BufferedInputStream b = new BufferedInputStream(fi); |
| ObjectInputStream oin = new ObjectInputStream(b); |
| |
| k2v = (PersistentHashTable) oin.readObject(); |
| oin.close(); |
| } |
| } |
| else |
| k2v = new PersistentHashTable(file); |
| |
| k2v.ready = true; |
| return k2v; |
| } |
| catch (Exception ioex) |
| { |
| InternalError ierr = new InternalError("Unable to intialize with file " |
| + file); |
| ierr.initCause(ioex); |
| throw ierr; |
| } |
| } |
| |
| |
| /** |
| * Write the database content to the disk. |
| */ |
| public synchronized void writeContent() |
| { |
| try |
| { |
| FileOutputStream fou = new FileOutputStream(database); |
| BufferedOutputStream b = new BufferedOutputStream(fou); |
| ObjectOutputStream oout = new ObjectOutputStream(b); |
| oout.writeObject(this); |
| oout.close(); |
| } |
| catch (Exception ioex) |
| { |
| InternalError ierr = new InternalError( |
| "Failed to write database to disk: "+ database); |
| ierr.initCause(ioex); |
| throw ierr; |
| } |
| } |
| |
| /** |
| * Mark the modified database as modified. The database will be written after |
| * several seconds, unless another modification occurs. |
| */ |
| public void markDirty() |
| { |
| if (System.currentTimeMillis() - lastUpdated > ALWAYS_UPDATE) |
| { |
| // Force storing to disk under intensive operation. |
| writeContent(); |
| lastUpdated = System.currentTimeMillis(); |
| if (sheduled != null) |
| { |
| sheduled.cancel(); |
| sheduled = null; |
| } |
| } |
| else |
| { |
| // Otherwise coalesce the disk database copy update events. |
| if (sheduled != null) |
| sheduled.cancel(); |
| sheduled = new WriteToDiskTask(); |
| timer.schedule(sheduled, SAVE_AT_MOST_AFTER); |
| } |
| } |
| |
| /** |
| * Save the current database state to the disk before exit. |
| */ |
| public void shutdown() |
| { |
| if (sheduled != null) |
| { |
| writeContent(); |
| sheduled = null; |
| } |
| } |
| |
| /** |
| * Update the memory maps and mark as should be written to the disk. |
| */ |
| public Object put(Object key, Object value) |
| { |
| super.put(key, value); |
| if (ready) |
| markDirty(); |
| return value; |
| } |
| |
| /** |
| * Update the memory maps and mark as should be written to the disk. |
| */ |
| public Object remove(Object key) |
| { |
| Object removed = super.remove(key); |
| if (ready) |
| markDirty(); |
| return removed; |
| } |
| |
| } |