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.bookkeeper.common.util;
  
  import java.util.concurrent.atomic.AtomicLong;
  import java.util.concurrent.locks.Condition;
  import java.util.concurrent.locks.ReentrantLock;
  
  /**
   * Controller for tracking the amount of memory used for some task.
   */
  public class MemoryLimitController {
  
      private final long memoryLimit;
      private final AtomicLong currentUsage = new AtomicLong();
      private final ReentrantLock mutex = new ReentrantLock(false);
      private final Condition condition = mutex.newCondition();
  
      public MemoryLimitController(long memoryLimitBytes) {
          this.memoryLimit = memoryLimitBytes;
      }
  
      public boolean tryReserveMemory(long size) {
          while (true) {
              long current = currentUsage.get();
              long newUsage = current + size;
  
              // We allow one request to go over the limit, to make the notification
              // path simpler and more efficient
              if (current > memoryLimit && memoryLimit > 0) {
                  return false;
              }
  
              if (currentUsage.compareAndSet(current, newUsage)) {
                  return true;
              }
          }
      }
  
      public void reserveMemory(long size) throws InterruptedException {
          if (!tryReserveMemory(size)) {
              mutex.lock();
  
              try {
                  while (!tryReserveMemory(size)) {
                      condition.await();
                  }
              } finally {
                  mutex.unlock();
              }
          }
      }
  
      public void releaseMemory(long size) {
          long newUsage = currentUsage.addAndGet(-size);
          if (newUsage + size > memoryLimit && newUsage <= memoryLimit) {
              // We just crossed the limit. Now we have more space
              mutex.lock();
              try {
                  condition.signalAll();
              } finally {
                  mutex.unlock();
              }
          }
      }
  
      public long currentUsage() {
          return currentUsage.get();
      }
  }