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A module that is everything required to understands Druid Segments

There is a newer version: 31.0.0

/*
 * 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.druid.frame.channel;

import com.google.common.base.Preconditions;
import com.google.errorprone.annotations.concurrent.GuardedBy;
import org.apache.druid.java.util.common.StringUtils;
import org.apache.druid.query.ResourceLimitExceededException;

/**
 * Tracks the byte usage with an upper bound bytes limit. Reservation of bytes beyond limit throws
 * {@link ResourceLimitExceededException}.
 */
public class ByteTracker
{
  private final long maxBytes;

  @GuardedBy("this")
  private long currentBytes;

  public ByteTracker(long maxBytes)
  {
    this.maxBytes = maxBytes;
  }

  public synchronized void reserve(long byteCount) throws ResourceLimitExceededException
  {
    Preconditions.checkState(byteCount >= 0, "Can't reserve negative bytes");

    if (Math.addExact(currentBytes, byteCount) > maxBytes) {
      throw new ResourceLimitExceededException(
          StringUtils.format(
              "Can't allocate any more bytes. maxBytes = %d, currentBytes = %d, requestedBytes = %d",
              maxBytes,
              currentBytes,
              byteCount
          )
      );
    }
    currentBytes = Math.addExact(currentBytes, byteCount);
  }

  public synchronized void release(long byteCount)
  {
    Preconditions.checkState(byteCount >= 0, "Can't release negative bytes");
    Preconditions.checkState(
        currentBytes >= byteCount,
        StringUtils.format(
            "Can't release more than used bytes. currentBytes : %d, releasingBytes : %d",
            currentBytes,
            byteCount
        )
    );
    currentBytes = Math.subtractExact(currentBytes, byteCount);
  }

  public static ByteTracker unboundedTracker()
  {
    return new ByteTracker(Long.MAX_VALUE);
  }
}