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.cassandra.service.paxos.cleanup;
  
  import java.util.ArrayDeque;
  import java.util.Map;
  import java.util.concurrent.ConcurrentHashMap;
  import java.util.concurrent.TimeUnit;
  import java.util.function.Consumer;
  import java.util.function.Predicate;
  
  import com.google.common.annotations.VisibleForTesting;
  import com.google.common.base.Preconditions;
  
  import org.slf4j.Logger;
  import org.slf4j.LoggerFactory;
  
  import org.apache.cassandra.db.ConsistencyLevel;
  import org.apache.cassandra.db.DecoratedKey;
  import org.apache.cassandra.schema.TableMetadata;
  import org.apache.cassandra.service.paxos.AbstractPaxosRepair;
  import org.apache.cassandra.service.paxos.Ballot;
  import org.apache.cassandra.service.paxos.PaxosRepair;
  import org.apache.cassandra.utils.NoSpamLogger;
  
  import static org.apache.cassandra.service.paxos.Commit.isAfter;
  
  /**
   * Coordinates repairs on a given key to prevent multiple repairs being scheduled for a single key
   */
  public class PaxosTableRepairs implements AbstractPaxosRepair.Listener
  {
      private static final Logger logger = LoggerFactory.getLogger(PaxosTableRepairs.class);
  
      static class KeyRepair
      {
          private final DecoratedKey key;
  
          private final ArrayDeque<AbstractPaxosRepair> queued = new ArrayDeque<>();
  
          private KeyRepair(DecoratedKey key)
          {
              this.key = key;
          }
  
          void onFirst(Predicate<AbstractPaxosRepair> predicate, Consumer<AbstractPaxosRepair> consumer, boolean removeBeforeAction)
          {
              while (!queued.isEmpty())
              {
                  AbstractPaxosRepair repair = queued.peek();
                  if (repair.isComplete())
                  {
                      queued.remove();
                      continue;
                  }
  
                  if (predicate.test(repair))
                  {
                      if (removeBeforeAction)
                          queued.remove();
                      consumer.accept(repair);
                  }
                  return;
              }
          }
  
          void clear()
          {
              while (!queued.isEmpty())
                  queued.remove().cancelUnexceptionally();
          }
  
          AbstractPaxosRepair startOrGetOrQueue(PaxosTableRepairs tableRepairs, DecoratedKey key, Ballot incompleteBallot, ConsistencyLevel consistency, TableMetadata table, Consumer<PaxosRepair.Result> onComplete)
          {
              Preconditions.checkArgument(this.key.equals(key));
  
              if (!queued.isEmpty() && !isAfter(incompleteBallot, queued.peekLast().incompleteBallot()))
              {
                  queued.peekLast().addListener(onComplete);
                  return queued.peekLast();
              }
  
              AbstractPaxosRepair repair = tableRepairs.createRepair(key, incompleteBallot, consistency, table);
  
              repair.addListener(tableRepairs);
              repair.addListener(onComplete);
  
              queued.add(repair);
              maybeScheduleNext();
              return repair;
          }
  
          @VisibleForTesting
          AbstractPaxosRepair activeRepair()
          {
              return queued.peek();
          }
  
          @VisibleForTesting
          boolean queueContains(AbstractPaxosRepair repair)
          {
              return queued.contains(repair);
          }
  
          void maybeScheduleNext()
          {
              onFirst(repair -> !repair.isStarted(), AbstractPaxosRepair::start, false);
          }
  
          void complete(AbstractPaxosRepair repair)
          {
              queued.remove(repair);
              maybeScheduleNext();
          }
  
          int pending()
          {
              return queued.size();
          }
  
          boolean isEmpty()
          {
              return queued.isEmpty();
          }
      }
  
      private final Map<DecoratedKey, KeyRepair> keyRepairs = new ConcurrentHashMap<>();
  
      @VisibleForTesting
      KeyRepair getKeyRepairUnsafe(DecoratedKey key)
      {
          return keyRepairs.get(key);
      }
  
      synchronized AbstractPaxosRepair startOrGetOrQueue(DecoratedKey key, Ballot incompleteBallot, ConsistencyLevel consistency, TableMetadata table, Consumer<PaxosRepair.Result> onComplete)
      {
          KeyRepair keyRepair = keyRepairs.computeIfAbsent(key, KeyRepair::new);
          return keyRepair.startOrGetOrQueue(this, key, incompleteBallot, consistency, table, onComplete);
      }
  
      public synchronized void onComplete(AbstractPaxosRepair repair, AbstractPaxosRepair.Result result)
      {
          KeyRepair keyRepair = keyRepairs.get(repair.partitionKey());
          if (keyRepair == null)
          {
              NoSpamLogger.log(logger, NoSpamLogger.Level.WARN, 1, TimeUnit.MINUTES,
                               "onComplete callback fired for nonexistant KeyRepair");
              return;
          }
  
          keyRepair.complete(repair);
          if (keyRepair.queueContains(repair))
              NoSpamLogger.log(logger, NoSpamLogger.Level.WARN, 1, TimeUnit.MINUTES,
                               "repair not removed after call to onComplete");
  
          if (keyRepair.isEmpty())
              keyRepairs.remove(repair.partitionKey());
      }
  
      synchronized void evictHungRepairs(long activeSinceNanos)
      {
          Predicate<AbstractPaxosRepair> timeoutPredicate = repair -> repair.startedNanos() - activeSinceNanos < 0;
          for (KeyRepair repair : keyRepairs.values())
          {
              if (repair.isEmpty())
                  NoSpamLogger.log(logger, NoSpamLogger.Level.WARN, 1, TimeUnit.MINUTES,
                                   "inactive KeyRepair found, this means post-repair cleanup/schedule isn't working properly");
              repair.onFirst(timeoutPredicate, r -> {
                  logger.warn("cancelling timed out paxos repair: {}", r);
                  r.cancelUnexceptionally();
              }, true);
              repair.maybeScheduleNext();
              if (repair.isEmpty())
                  keyRepairs.remove(repair.key);
          }
      }
  
      synchronized void clear()
      {
          for (KeyRepair repair : keyRepairs.values())
              repair.clear();
          keyRepairs.clear();
      }
  
      @VisibleForTesting
      synchronized boolean hasActiveRepairs(DecoratedKey key)
      {
          return keyRepairs.containsKey(key);
      }
  
      AbstractPaxosRepair createRepair(DecoratedKey key, Ballot incompleteBallot, ConsistencyLevel consistency, TableMetadata table)
      {
          return PaxosRepair.create(consistency, key, incompleteBallot, table);
      }
  }
  