server/tserver/src/main/java/org/apache/accumulo/tserver/WriteTracker.java

/*
 * 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.accumulo.tserver;

import java.util.ArrayList;
import java.util.EnumMap;
import java.util.List;
import java.util.Map;
import java.util.Set;
import java.util.TreeSet;
import java.util.concurrent.atomic.AtomicLong;

import org.apache.accumulo.core.clientImpl.TabletType;
import org.apache.accumulo.core.dataImpl.KeyExtent;
import org.apache.accumulo.tserver.tablet.Tablet;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

/**
 * This little class keeps track of writes in progress and allows readers to wait for writes that
 * started before the read. It assumes that the operation ids are monotonically increasing.
 *
 */
class WriteTracker {
  private static final Logger log = LoggerFactory.getLogger(WriteTracker.class);

  private static final AtomicLong operationCounter = new AtomicLong(1);
  private final Map<TabletType,TreeSet<Long>> inProgressWrites = new EnumMap<>(TabletType.class);

  WriteTracker() {
    for (TabletType ttype : TabletType.values()) {
      inProgressWrites.put(ttype, new TreeSet<>());
    }
  }

  synchronized long startWrite(TabletType ttype) {
    long operationId = operationCounter.getAndIncrement();
    inProgressWrites.get(ttype).add(operationId);
    return operationId;
  }

  synchronized void finishWrite(long operationId) {
    if (operationId == -1)
      return;

    boolean removed = false;

    for (TabletType ttype : TabletType.values()) {
      removed = inProgressWrites.get(ttype).remove(operationId);
      if (removed)
        break;
    }

    if (!removed) {
      throw new IllegalArgumentException(
          "Attempted to finish write not in progress,  operationId " + operationId);
    }

    this.notifyAll();
  }

  synchronized void waitForWrites(TabletType ttype) {
    long operationId = operationCounter.getAndIncrement();
    while (inProgressWrites.get(ttype).floor(operationId) != null) {
      try {
        this.wait();
      } catch (InterruptedException e) {
        log.error("{}", e.getMessage(), e);
      }
    }
  }

  public long startWrite(Set<Tablet> keySet) {
    if (keySet.isEmpty())
      return -1;

    List<KeyExtent> extents = new ArrayList<>(keySet.size());

    for (Tablet tablet : keySet)
      extents.add(tablet.getExtent());

    return startWrite(TabletType.type(extents));
  }
}