/*
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* CDDL HEADER START
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*
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* The contents of this file are subject to the terms of the
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* Common Development and Distribution License, Version 1.0 only
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* (the "License"). You may not use this file except in compliance
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* with the License.
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*
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* You can obtain a copy of the license at
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* trunk/opends/resource/legal-notices/OpenDS.LICENSE
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* or https://OpenDS.dev.java.net/OpenDS.LICENSE.
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* See the License for the specific language governing permissions
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* and limitations under the License.
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*
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* When distributing Covered Code, include this CDDL HEADER in each
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* file and include the License file at
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* trunk/opends/resource/legal-notices/OpenDS.LICENSE. If applicable,
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* add the following below this CDDL HEADER, with the fields enclosed
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* by brackets "[]" replaced with your own identifying information:
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* Portions Copyright [yyyy] [name of copyright owner]
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*
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* CDDL HEADER END
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*
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*
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* Portions Copyright 2006-2007 Sun Microsystems, Inc.
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*/
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package org.opends.server.api;
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import java.util.List;
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import java.util.concurrent.locks.Lock;
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import org.opends.server.core.DirectoryServer;
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import org.opends.server.config.ConfigException;
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import org.opends.server.types.DN;
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import org.opends.server.types.Entry;
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import org.opends.server.types.InitializationException;
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import org.opends.server.types.LockType;
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import org.opends.server.types.LockManager;
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import org.opends.server.types.DebugLogLevel;
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import org.opends.server.admin.std.server.EntryCacheCfg;
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import org.opends.server.loggers.debug.DebugTracer;
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import static org.opends.server.loggers.debug.DebugLogger.*;
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/**
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* This class defines the set of methods that must be implemented by a
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* Directory Server entry cache. Note that components accessing the
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* entry cache must not depend on any particular behavior. For
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* example, if a call is made to <CODE>putEntry</CODE> to store an
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* entry in the cache, there is no guarantee that immediately calling
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* <CODE>getEntry</CODE> will be able to retrieve it. There are
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* several potential reasons for this, including:
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* <UL>
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* <LI>The entry may have been deleted or replaced by another thread
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* between the <CODE>putEntry</CODE> and <CODE>getEntry</CODE>
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* calls.</LI>
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* <LI>The entry cache may implement a purging mechanism and the
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* entry added may have been purged between the
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* <CODE>putEntry</CODE> and <CODE>getEntry</CODE> calls.</LI>
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* <LI>The entry cache may implement some kind of filtering
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* mechanism to determine which entries to store, and entries
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* not matching the appropriate criteria may not be stored.</LI>
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* <LI>The entry cache may not actually store any entries (this is
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* the behavior of the default cache that will be used if none
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* is configured).</LI>
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* </UL>
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*
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* @param <T> The type of configuration handled by this entry
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* cache.
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*/
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public abstract class EntryCache
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<T extends EntryCacheCfg>
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implements BackendInitializationListener
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{
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/**
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* Default constructor which is implicitly called from all entry
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* cache implementations.
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*/
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public EntryCache()
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{
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// Register with backend initialization listener to clear cache
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// entries belonging to given backend that about to go offline.
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DirectoryServer.registerBackendInitializationListener(this);
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}
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/**
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* The tracer object for the debug logger.
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*/
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private static final DebugTracer TRACER = getTracer();
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/**
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* The maximum length of time to try to obtain a lock
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* before giving up.
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*/
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protected long lockTimeout;
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/**
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* Initializes this entry cache implementation so that it will be
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* available for storing and retrieving entries.
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*
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* @param configuration The configuration to use to initialize
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* the entry cache.
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*
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* @throws ConfigException If there is a problem with the provided
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* configuration entry that would prevent
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* this entry cache from being used.
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*
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* @throws InitializationException If a problem occurs during the
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* initialization process that is
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* not related to the
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* configuration.
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*/
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public abstract void initializeEntryCache(T configuration)
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throws ConfigException, InitializationException;
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/**
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* Indicates whether the provided configuration is acceptable for
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* this entry cache. It should be possible to call this method on
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* an uninitialized entry cache instance in order to determine
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* whether the entry cache would be able to use the provided
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* configuration.
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* <BR><BR>
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* Note that implementations which use a subclass of the provided
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* configuration class will likely need to cast the configuration
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* to the appropriate subclass type.
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*
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* @param configuration The entry cache configuration for
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* which to make the determination.
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* @param unacceptableReasons A list that may be used to hold the
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* reasons that the provided
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* configuration is not acceptable.
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*
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* @return {@code true} if the provided configuration is acceptable
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* for this entry cache, or {@code false} if not.
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*/
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public boolean isConfigurationAcceptable(
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EntryCacheCfg configuration,
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List<String> unacceptableReasons)
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{
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// This default implementation does not perform any special
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// validation. It should be overridden by entry cache
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// implementations that wish to perform more detailed validation.
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return true;
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}
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/**
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* Performs any necessary cleanup work (e.g., flushing all cached
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* entries and releasing any other held resources) that should be
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* performed when the server is to be shut down or the entry cache
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* destroyed or replaced.
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*/
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public abstract void finalizeEntryCache();
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/**
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* Indicates whether the entry cache currently contains the entry
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* with the specified DN. This method may be called without holding
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* any locks if a point-in-time check is all that is required.
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* Note that this method is called from @see #getEntry(DN entryDN,
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* LockType lockType, List lockList)
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*
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* @param entryDN The DN for which to make the determination.
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*
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* @return <CODE>true</CODE> if the entry cache currently contains
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* the entry with the specified DN, or <CODE>false</CODE>
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* if not.
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*/
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public abstract boolean containsEntry(DN entryDN);
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/**
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* Retrieves the entry with the specified DN from the cache. The
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* caller should have already acquired a read or write lock for the
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* entry if such protection is needed.
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* Note that this method is called from @see #getEntry(DN entryDN,
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* LockType lockType, List lockList)
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*
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* @param entryDN The DN of the entry to retrieve.
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*
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* @return The requested entry if it is present in the cache, or
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* <CODE>null</CODE> if it is not present.
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*/
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public abstract Entry getEntry(DN entryDN);
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/**
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* Retrieves the entry with the specified DN from the cache,
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* obtaining a lock on the entry before it is returned. If the
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* entry is present in the cache, then a lock will be obtained for
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* that entry and appended to the provided list before the entry is
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* returned. If the entry is not present, then no lock will be
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* obtained. Note that although this method is declared non-final
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* it is not recommended for subclasses to implement this method.
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*
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* @param entryDN The DN of the entry to retrieve.
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* @param lockType The type of lock to obtain (it may be
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* <CODE>NONE</CODE>).
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* @param lockList The list to which the obtained lock will be
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* added (note that no lock will be added if the
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* lock type was <CODE>NONE</CODE>).
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*
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* @return The requested entry if it is present in the cache, or
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* <CODE>null</CODE> if it is not present.
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*/
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public Entry getEntry(DN entryDN,
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LockType lockType,
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List<Lock> lockList) {
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if (!containsEntry(entryDN)) {
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return null;
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}
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// Obtain a lock for the entry before actually retrieving the
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// entry itself thus preventing any stale entries being returned,
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// see Issue #1589 for more details. If an error occurs, then
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// make sure no lock is held and return null. Otherwise, return
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// the entry.
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switch (lockType)
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{
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case READ:
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// Try to obtain a read lock for the entry.
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Lock readLock = LockManager.lockRead(entryDN, lockTimeout);
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if (readLock == null)
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{
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// We couldn't get the lock, so we have to return null.
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return null;
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}
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else
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{
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try
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{
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lockList.add(readLock);
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// and load.
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Entry entry = getEntry(entryDN);
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if (entry == null)
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{
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lockList.remove(readLock);
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LockManager.unlock(entryDN, readLock);
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return null;
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}
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return entry;
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}
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catch (Exception e)
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{
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if (debugEnabled())
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{
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TRACER.debugCaught(DebugLogLevel.ERROR, e);
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}
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// The attempt to add the lock to the list failed,
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// so we need to release the lock and return null.
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try
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{
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LockManager.unlock(entryDN, readLock);
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}
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catch (Exception e2)
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{
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if (debugEnabled())
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{
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TRACER.debugCaught(DebugLogLevel.ERROR, e2);
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}
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}
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return null;
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}
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}
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case WRITE:
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// Try to obtain a write lock for the entry.
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Lock writeLock = LockManager.lockWrite(entryDN, lockTimeout);
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if (writeLock == null)
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{
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// We couldn't get the lock, so we have to return null.
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return null;
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}
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else
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{
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try
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{
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lockList.add(writeLock);
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// and load.
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Entry entry = getEntry(entryDN);
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if (entry == null)
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{
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lockList.remove(writeLock);
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LockManager.unlock(entryDN, writeLock);
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return null;
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}
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return entry;
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}
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catch (Exception e)
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{
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if (debugEnabled())
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{
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TRACER.debugCaught(DebugLogLevel.ERROR, e);
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}
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// The attempt to add the lock to the list failed,
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// so we need to release the lock and return null.
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try
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{
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LockManager.unlock(entryDN, writeLock);
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}
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catch (Exception e2)
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{
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if (debugEnabled())
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{
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TRACER.debugCaught(DebugLogLevel.ERROR, e2);
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}
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}
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return null;
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}
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}
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case NONE:
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// We don't need to obtain a lock, so just return the entry.
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Entry entry = getEntry(entryDN);
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if (entry == null)
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{
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return null;
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}
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return entry;
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default:
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// This is an unknown type of lock, so we'll return null.
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return null;
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}
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}
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/**
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* Retrieves the requested entry if it is present in the cache,
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* obtaining a lock on the entry before it is returned. If the
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* entry is present in the cache, then a lock will be obtained for
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* that entry and appended to the provided list before the entry is
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* returned. If the entry is not present, then no lock will be
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* obtained. Note that although this method is declared non-final
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* it is not recommended for subclasses to implement this method.
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*
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* @param backend The backend associated with the entry to
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* retrieve.
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* @param entryID The entry ID within the provided backend for
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* the specified entry.
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* @param lockType The type of lock to obtain (it may be
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* <CODE>NONE</CODE>).
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* @param lockList The list to which the obtained lock will be
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* added (note that no lock will be added if the
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* lock type was <CODE>NONE</CODE>).
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*
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* @return The requested entry if it is present in the cache, or
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* <CODE>null</CODE> if it is not present.
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*/
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public Entry getEntry(Backend backend, long entryID,
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LockType lockType,
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List<Lock> lockList) {
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// Translate given backend/entryID pair to entryDN.
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DN entryDN = getEntryDN(backend, entryID);
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if (entryDN == null) {
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return null;
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}
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// Delegate to by DN lock and load method.
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return getEntry(entryDN, lockType, lockList);
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}
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/**
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* Retrieves the entry ID for the entry with the specified DN from
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* the cache. The caller should have already acquired a read or
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* write lock for the entry if such protection is needed.
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*
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* @param entryDN The DN of the entry for which to retrieve the
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* entry ID.
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*
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* @return The entry ID for the requested entry, or -1 if it is
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* not present in the cache.
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*/
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public abstract long getEntryID(DN entryDN);
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/**
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* Retrieves the entry DN for the entry with the specified ID on
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* the specific backend from the cache. The caller should have
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* already acquired a read or write lock for the entry if such
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* protection is needed.
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* Note that this method is called from @see #getEntry(Backend
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* backend, long entryID, LockType lockType, List lockList)
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*
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* @param backend The backend associated with the entry for
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* which to retrieve the entry DN.
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* @param entryID The entry ID within the provided backend
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* for which to retrieve the entry DN.
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*
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* @return The entry DN for the requested entry, or
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* <CODE>null</CODE> if it is not present in the cache.
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*/
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protected abstract DN getEntryDN(Backend backend, long entryID);
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/**
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* Stores the provided entry in the cache. Note that the mechanism
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* that it uses to achieve this is implementation-dependent, and it
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* is acceptable for the entry to not actually be stored in any
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* cache.
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*
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* @param entry The entry to store in the cache.
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* @param backend The backend with which the entry is associated.
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* @param entryID The entry ID within the provided backend that
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* uniquely identifies the specified entry.
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*/
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public abstract void putEntry(Entry entry, Backend backend,
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long entryID);
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/**
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* Stores the provided entry in the cache only if it does not
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* conflict with an entry that already exists. Note that the
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* mechanism that it uses to achieve this is
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* implementation-dependent, and it is acceptable for the entry to
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* not actually be stored in any cache. However, this method must
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* not overwrite an existing version of the entry.
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*
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* @param entry The entry to store in the cache.
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* @param backend The backend with which the entry is associated.
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* @param entryID The entry ID within the provided backend that
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* uniquely identifies the specified entry.
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*
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* @return <CODE>false</CODE> if an existing entry or some other
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* problem prevented the method from completing
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* successfully, or <CODE>true</CODE> if there was no
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* conflict and the entry was either stored or the cache
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* determined that this entry should never be cached for
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* some reason.
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*/
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public abstract boolean putEntryIfAbsent(Entry entry,
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Backend backend,
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long entryID);
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/**
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* Removes the specified entry from the cache.
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*
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* @param entryDN The DN of the entry to remove from the cache.
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*/
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public abstract void removeEntry(DN entryDN);
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/**
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* Removes all entries from the cache. The cache should still be
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* available for future use.
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*/
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public abstract void clear();
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/**
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* Removes all entries from the cache that are associated with the
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* provided backend.
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*
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* @param backend The backend for which to flush the associated
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* entries.
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*/
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public abstract void clearBackend(Backend backend);
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/**
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* Removes all entries from the cache that are below the provided
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* DN.
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*
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* @param baseDN The base DN below which all entries should be
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* flushed.
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*/
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public abstract void clearSubtree(DN baseDN);
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/**
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* Attempts to react to a scenario in which it is determined that
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* the system is running low on available memory. In this case, the
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* entry cache should attempt to free some memory if possible to try
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* to avoid out of memory errors.
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*/
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public abstract void handleLowMemory();
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/**
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* {@inheritDoc}
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*/
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public void performBackendInitializationProcessing(Backend backend)
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{
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// Do nothing.
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}
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/**
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* {@inheritDoc}
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*/
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public void performBackendFinalizationProcessing(Backend backend)
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{
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// Do not clear any backends if the server is shutting down.
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if ( !(DirectoryServer.getInstance().isShuttingDown()) ) {
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clearBackend(backend);
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}
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}
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}
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