content: /*
   * Licensed to the Apache Software Foundation (ASF) under one or more
   * contributor license agreements. See the NOTICE file distributed with
   * this work for additional information regarding copyright ownership.
   * The ASF licenses this file to You under the Apache License, Version 2.0
   * (the "License"); you may not use this file except in compliance with
   * the License. You may obtain a copy of the License at
   *
   *    http://www.apache.org/licenses/LICENSE-2.0
   *
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS,
   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   * See the License for the specific language governing permissions and
   * limitations under the License.
   */
  
  package org.apache.kafka.server.share.session;
  
  import org.apache.kafka.common.Uuid;
  import org.apache.kafka.common.requests.ShareRequestMetadata;
  import org.apache.kafka.common.utils.ImplicitLinkedHashCollection;
  import org.apache.kafka.server.metrics.KafkaMetricsGroup;
  import org.apache.kafka.server.network.ConnectionDisconnectListener;
  import org.apache.kafka.server.share.CachedSharePartition;
  import org.apache.kafka.server.share.ShareGroupListener;
  
  import com.yammer.metrics.core.Meter;
  
  import java.util.HashMap;
  import java.util.Map;
  import java.util.concurrent.TimeUnit;
  
  /**
   * Caches share sessions.
   * <p>
   * See tryEvict for an explanation of the cache eviction strategy.
   * <p>
   * The ShareSessionCache is thread-safe because all of its methods are synchronized.
   * Note that individual share sessions have their own locks which are separate from the
   * ShareSessionCache lock.  In order to avoid deadlock, the ShareSessionCache lock
   * must never be acquired while an individual ShareSession lock is already held.
   */
  public class ShareSessionCache {
      // Visible for testing.
      static final String SHARE_SESSIONS_COUNT = "ShareSessionsCount";
      // Visible for testing.
      static final String SHARE_PARTITIONS_COUNT = "SharePartitionsCount";
      private static final String SHARE_SESSION_EVICTIONS_PER_SEC = "ShareSessionEvictionsPerSec";
  
      /**
       * Metric for the rate of eviction of share sessions.
       */
      private final Meter evictionsMeter;
      /**
       * The listener for connection disconnect events for the client.
       */
      private final ConnectionDisconnectListener connectionDisconnectListener;
      /**
       * Map of session key to ShareSession.
       */
      private final Map<ShareSessionKey, ShareSession> sessions = new HashMap<>();
      /**
       * Map of groupId to number of members in the group.
       */
      private final Map<String, Integer> numMembersPerGroup = new HashMap<>();
      /**
       * The map to store the client connection id to session key. This is used to remove the session
       * from the cache when the respective client disconnects.
       */
      private final Map<String, ShareSessionKey> connectionIdToSessionMap;
      /**
       * The listener for share group events. This is used to notify the listener when the group members
       * change.
       */
      private ShareGroupListener shareGroupListener;
  
      private final int maxEntries;
      private long numPartitions = 0;
  
      @SuppressWarnings("this-escape")
      public ShareSessionCache(int maxEntries) {
          this.maxEntries = maxEntries;
          // Register metrics for ShareSessionCache.
          KafkaMetricsGroup metricsGroup = new KafkaMetricsGroup("kafka.server", "ShareSessionCache");
          metricsGroup.newGauge(SHARE_SESSIONS_COUNT, this::size);
          metricsGroup.newGauge(SHARE_PARTITIONS_COUNT, this::totalPartitions);
          this.connectionIdToSessionMap = new HashMap<>();
          this.connectionDisconnectListener = new ClientConnectionDisconnectListener();
          this.evictionsMeter = metricsGroup.newMeter(SHARE_SESSION_EVICTIONS_PER_SEC, "evictions", TimeUnit.SECONDS);
      }
  
      /**
       * Get a session by session key.
       *
       * @param key The share session key.
       * @return The session, or None if no such session was found.
       */
      public synchronized ShareSession get(ShareSessionKey key) {
          return sessions.getOrDefault(key, null);
      }
  
      /**
       * Get the number of entries currently in the share session cache.
       */
      public synchronized int size() {
          return sessions.size();
      }
  
      /**
       * Remove all the share sessions from cache.
       */
      public synchronized void removeAllSessions() {
          sessions.clear();
          numMembersPerGroup.clear();
          numPartitions = 0;
      }
  
      public synchronized long totalPartitions() {
          return numPartitions;
      }
  
      public synchronized ShareSession remove(ShareSessionKey key) {
          ShareSession session = get(key);
          if (session != null)
              return remove(session);
          return null;
      }
  
      /**
       * Maybe remove the session and notify listeners. This is called when the connection is disconnected
       * for the client. The session may have already been removed by the client as part of final epoch,
       * hence check if the session is still present in the cache.
       *
       * @param key The share session key.
       */
      public synchronized void maybeRemoveAndNotifyListeners(ShareSessionKey key) {
          ShareSession session = get(key);
          if (session != null) {
              // Notify the share group listener that member has left the group. Notify listener prior
              // removing the session from the cache to ensure that the listener has access to the session
              // while it is still in the cache.
              if (shareGroupListener != null) {
                  shareGroupListener.onMemberLeave(key.groupId(), key.memberId());
              }
              // As session is not null hence it's removed as part of connection disconnect. Hence,
              // update the evictions metric.
              evictionsMeter.mark();
              // Try removing session if not already removed. The listener might have removed the session
              // already.
              remove(session);
          }
          // Notify the share group listener if the group is empty. This should be checked regardless
          // session is evicted by connection disconnect or client's final epoch.
          int numMembers = numMembersPerGroup.getOrDefault(key.groupId(), 0);
          if (numMembers == 0) {
              // Remove the group from the map as it is empty.
              numMembersPerGroup.remove(key.groupId());
              if (shareGroupListener != null) {
                  shareGroupListener.onGroupEmpty(key.groupId());
              }
          }
      }
  
      /**
       * Remove an entry from the session cache.
       *
       * @param session The session.
       * @return The removed session, or None if there was no such session.
       */
      public synchronized ShareSession remove(ShareSession session) {
          ShareSession removeResult = sessions.remove(session.key());
          if (removeResult != null) {
              numPartitions = numPartitions - session.cachedSize();
              numMembersPerGroup.compute(session.key().groupId(), (k, v) -> v != null ? v - 1 : 0);
          }
          return removeResult;
      }
  
      /**
       * Update the size of the cache by updating the total number of share partitions.
       *
       * @param session  The session.
       */
      public synchronized void updateNumPartitions(ShareSession session) {
          numPartitions += session.updateCachedSize();
      }
  
      /**
       * Maybe create a new session and add it to the cache.
       * @param groupId - The group id in the share fetch request.
       * @param memberId - The member id in the share fetch request.
       * @param partitionMap - The topic partitions to be added to the session.
       * @param clientConnectionId - The client connection id.
       * @return - The session key if the session was created, or null if the session was not created.
       */
      public synchronized ShareSessionKey maybeCreateSession(
          String groupId,
          Uuid memberId,
          ImplicitLinkedHashCollection<CachedSharePartition> partitionMap,
          String clientConnectionId
      ) {
          if (sessions.size() < maxEntries) {
              ShareSession session = new ShareSession(new ShareSessionKey(groupId, memberId), partitionMap,
                  ShareRequestMetadata.nextEpoch(ShareRequestMetadata.INITIAL_EPOCH));
              sessions.put(session.key(), session);
              updateNumPartitions(session);
              numMembersPerGroup.compute(session.key().groupId(), (k, v) -> v != null ? v + 1 : 1);
              connectionIdToSessionMap.put(clientConnectionId, session.key());
              return session.key();
          }
          return null;
      }
  
      public ConnectionDisconnectListener connectionDisconnectListener() {
          return connectionDisconnectListener;
      }
  
      public synchronized void registerShareGroupListener(ShareGroupListener shareGroupListener) {
          this.shareGroupListener = shareGroupListener;
      }
  
      // Visible for testing.
      Meter evictionsMeter() {
          return evictionsMeter;
      }
  
      // Visible for testing.
      Integer numMembers(String groupId) {
          return numMembersPerGroup.get(groupId);
      }
  
      private final class ClientConnectionDisconnectListener implements ConnectionDisconnectListener {
  
          // When the client disconnects, the corresponding session should be removed from the cache.
          @Override
          public void onDisconnect(String connectionId) {
              ShareSessionKey shareSessionKey = connectionIdToSessionMap.remove(connectionId);
              if (shareSessionKey != null) {
                  // Try removing session and notify listeners. The session might already be removed
                  // as part of final epoch from client, so we need to check if the session is still
                  // present in the cache.
                  maybeRemoveAndNotifyListeners(shareSessionKey);
              }
          }
      }
  }
  