fe/src/main/java/org/apache/impala/util/ExecutorMembershipSnapshot.java

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//   http://www.apache.org/licenses/LICENSE-2.0
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package org.apache.impala.util;

import java.util.Set;
import java.util.concurrent.atomic.AtomicReference;

import org.apache.impala.thrift.TNetworkAddress;
import org.apache.impala.thrift.TUpdateExecutorMembershipRequest;
import com.google.common.collect.Sets;

/**
 * Singleton class that represents a snapshot of the Impalad executor membership. Host
 * membership is determined by both IP address and hostname (to mimic the backend's
 * Scheduler). A new snapshot is created whenever the cluster membership changes
 * so that clients don't need to hold a lock while examining a snapshot.
 */
public class ExecutorMembershipSnapshot {
  // The latest instance of the ExecutorMembershipSnapshot.
  private static AtomicReference<ExecutorMembershipSnapshot> cluster_ =
      new AtomicReference<ExecutorMembershipSnapshot>(new ExecutorMembershipSnapshot());

  // The set of hosts that are members of the cluster given by hostname.
  private final Set<String> hostnames_;

  // The set of hosts that are members of the cluster given by IP address.
  private final Set<String> ipAddresses_;

  // The number of executor nodes of the cluster.  Normally, this will be equal to
  // hostnames_.size(), except in the test minicluster where there are multiple
  // impalad's running on a single host.
  private final int numExecutors_;

  // Used only to construct the initial ExecutorMembershipSnapshot. Before we get the
  // first snapshot, assume one node (the localhost) to mimic Scheduler.
  private ExecutorMembershipSnapshot() {
    hostnames_ = Sets.newHashSet();
    ipAddresses_ = Sets.newHashSet();
    numExecutors_ = 1;
  }

  // Construct a new snapshot based on the TUpdateExecutorMembershipRequest.
  private ExecutorMembershipSnapshot(TUpdateExecutorMembershipRequest request) {
    hostnames_ = request.getHostnames();
    ipAddresses_ = request.getIp_addresses();
    numExecutors_ = request.getNum_executors();
  }

  // Determine whether a host, given either by IP address or hostname, is a member of
  // this snapshot.  Returns true if it is, false otherwise.
  public boolean contains(TNetworkAddress address) {
    String host = address.getHostname();
    return ipAddresses_.contains(host) || hostnames_.contains(host);
  }

  // The number of nodes in this snapshot.
  public int numExecutors() { return numExecutors_; }

  // Atomically update the singleton snapshot instance.  After the update completes,
  // all calls to getCluster() will return the new snapshot.
  public static void update(TUpdateExecutorMembershipRequest request) {
    cluster_.set(new ExecutorMembershipSnapshot(request));
  }

  // Return the current singleton snapshot instance.
  public static ExecutorMembershipSnapshot getCluster() { return cluster_.get(); }
}