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.connect.runtime.distributed;
  
  import org.apache.kafka.common.utils.CircularIterator;
  import org.apache.kafka.common.utils.LogContext;
  import org.apache.kafka.connect.storage.ClusterConfigState;
  import org.apache.kafka.connect.util.ConnectorTaskId;
  
  import org.slf4j.Logger;
  
  import java.nio.ByteBuffer;
  import java.util.ArrayList;
  import java.util.Collection;
  import java.util.Collections;
  import java.util.HashMap;
  import java.util.List;
  import java.util.Map;
  
  import static org.apache.kafka.common.message.JoinGroupResponseData.JoinGroupResponseMember;
  import static org.apache.kafka.connect.runtime.distributed.ConnectProtocol.Assignment;
  import static org.apache.kafka.connect.runtime.distributed.WorkerCoordinator.LeaderState;
  
  
  /**
   * An assignor that computes a unweighted round-robin distribution of connectors and tasks. The
   * connectors are assigned to the workers first, followed by the tasks. This is to avoid
   * load imbalance when several 1-task connectors are running, given that a connector is usually
   * more lightweight than a task.
   * <p>
   * Note that this class is NOT thread-safe.
   */
  public class EagerAssignor implements ConnectAssignor {
      private final Logger log;
  
      public EagerAssignor(LogContext logContext) {
          this.log = logContext.logger(EagerAssignor.class);
      }
  
      @Override
      public Map<String, ByteBuffer> performAssignment(String leaderId, String protocol,
                                                       List<JoinGroupResponseMember> allMemberMetadata,
                                                       WorkerCoordinator coordinator) {
          log.debug("Performing task assignment");
          Map<String, ExtendedWorkerState> memberConfigs = new HashMap<>();
          for (JoinGroupResponseMember member : allMemberMetadata)
              memberConfigs.put(member.memberId(), IncrementalCooperativeConnectProtocol.deserializeMetadata(ByteBuffer.wrap(member.metadata())));
  
          long maxOffset = findMaxMemberConfigOffset(memberConfigs, coordinator);
          Long leaderOffset = ensureLeaderConfig(maxOffset, coordinator);
          if (leaderOffset == null)
              return fillAssignmentsAndSerialize(memberConfigs.keySet(), Assignment.CONFIG_MISMATCH,
                      leaderId, memberConfigs.get(leaderId).url(), maxOffset,
                      new HashMap<>(), new HashMap<>());
          return performTaskAssignment(leaderId, leaderOffset, memberConfigs, coordinator);
      }
  
      private Long ensureLeaderConfig(long maxOffset, WorkerCoordinator coordinator) {
          // If this leader is behind some other members, we can't do assignment
          if (coordinator.configSnapshot().offset() < maxOffset) {
              // We might be able to take a new snapshot to catch up immediately and avoid another round of syncing here.
              // Alternatively, if this node has already passed the maximum reported by any other member of the group, it
              // is also safe to use this newer state.
              ClusterConfigState updatedSnapshot = coordinator.configFreshSnapshot();
              if (updatedSnapshot.offset() < maxOffset) {
                  log.info("Was selected to perform assignments, but do not have latest config found in sync request. " +
                          "Returning an empty configuration to trigger re-sync.");
                  return null;
              } else {
                  coordinator.configSnapshot(updatedSnapshot);
                  return updatedSnapshot.offset();
              }
          }
          return maxOffset;
      }
  
      private Map<String, ByteBuffer> performTaskAssignment(String leaderId, long maxOffset,
                                                            Map<String, ExtendedWorkerState> memberConfigs,
                                                            WorkerCoordinator coordinator) {
          Map<String, Collection<String>> connectorAssignments = new HashMap<>();
          Map<String, Collection<ConnectorTaskId>> taskAssignments = new HashMap<>();
  
          // Perform round-robin task assignment. Assign all connectors and then all tasks because assigning both the
          // connector and its tasks can lead to very uneven distribution of work in some common cases (e.g. for connectors
          // that generate only 1 task each; in a cluster of 2 or an even # of nodes, only even nodes will be assigned
          // connectors and only odd nodes will be assigned tasks, but tasks are, on average, actually more resource
          // intensive than connectors).
          List<String> connectorsSorted = sorted(coordinator.configSnapshot().connectors());
          CircularIterator<String> memberIt = new CircularIterator<>(sorted(memberConfigs.keySet()));
          for (String connectorId : connectorsSorted) {
              String connectorAssignedTo = memberIt.next();
              log.trace("Assigning connector {} to {}", connectorId, connectorAssignedTo);
              Collection<String> memberConnectors = connectorAssignments.computeIfAbsent(connectorAssignedTo, k -> new ArrayList<>());
              memberConnectors.add(connectorId);
          }
          for (String connectorId : connectorsSorted) {
              for (ConnectorTaskId taskId : sorted(coordinator.configSnapshot().tasks(connectorId))) {
                  String taskAssignedTo = memberIt.next();
                  log.trace("Assigning task {} to {}", taskId, taskAssignedTo);
                  Collection<ConnectorTaskId> memberTasks = taskAssignments.computeIfAbsent(taskAssignedTo, k -> new ArrayList<>());
                  memberTasks.add(taskId);
              }
          }
  
          coordinator.leaderState(new LeaderState(memberConfigs, connectorAssignments, taskAssignments));
  
          return fillAssignmentsAndSerialize(memberConfigs.keySet(), Assignment.NO_ERROR,
                  leaderId, memberConfigs.get(leaderId).url(), maxOffset, connectorAssignments, taskAssignments);
      }
  
      private Map<String, ByteBuffer> fillAssignmentsAndSerialize(Collection<String> members,
                                                                  short error,
                                                                  String leaderId,
                                                                  String leaderUrl,
                                                                  long maxOffset,
                                                                  Map<String, Collection<String>> connectorAssignments,
                                                                  Map<String, Collection<ConnectorTaskId>> taskAssignments) {
  
          Map<String, ByteBuffer> groupAssignment = new HashMap<>();
          for (String member : members) {
              Collection<String> connectors = connectorAssignments.get(member);
              if (connectors == null) {
                  connectors = Collections.emptyList();
              }
              Collection<ConnectorTaskId> tasks = taskAssignments.get(member);
              if (tasks == null) {
                  tasks = Collections.emptyList();
              }
              Assignment assignment = new Assignment(error, leaderId, leaderUrl, maxOffset, connectors, tasks);
              log.debug("Assignment: {} -> {}", member, assignment);
              groupAssignment.put(member, ConnectProtocol.serializeAssignment(assignment));
          }
          log.debug("Finished assignment");
          return groupAssignment;
      }
  
      private long findMaxMemberConfigOffset(Map<String, ExtendedWorkerState> memberConfigs,
                                             WorkerCoordinator coordinator) {
          // The new config offset is the maximum seen by any member. We always perform assignment using this offset,
          // even if some members have fallen behind. The config offset used to generate the assignment is included in
          // the response so members that have fallen behind will not use the assignment until they have caught up.
          Long maxOffset = null;
          for (Map.Entry<String, ExtendedWorkerState> stateEntry : memberConfigs.entrySet()) {
              long memberRootOffset = stateEntry.getValue().offset();
              if (maxOffset == null)
                  maxOffset = memberRootOffset;
              else
                  maxOffset = Math.max(maxOffset, memberRootOffset);
          }
  
          log.debug("Max config offset root: {}, local snapshot config offsets root: {}",
                    maxOffset, coordinator.configSnapshot().offset());
          return maxOffset;
      }
  
      private static <T extends Comparable<T>> List<T> sorted(Collection<T> members) {
          List<T> res = new ArrayList<>(members);
          Collections.sort(res);
          return res;
      }
  
  }
  