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.arrow.memory;
  
  /**
   * An allocation listener being notified for allocation/deallocation
   *
   * <p>It might be called from multiple threads if the allocator hierarchy shares a listener, in
   * which case, the provider should take care of making the implementation thread-safe.
   */
  public interface AllocationListener {
  
    AllocationListener NOOP = new AllocationListener() {};
  
    /**
     * Called each time a new buffer has been requested.
     *
     * <p>An exception can be safely thrown by this method to terminate the allocation.
     *
     * @param size the buffer size being allocated
     */
    default void onPreAllocation(long size) {}
  
    /**
     * Called each time a new buffer has been allocated.
     *
     * <p>An exception cannot be thrown by this method.
     *
     * @param size the buffer size being allocated
     */
    default void onAllocation(long size) {}
  
    /**
     * Informed each time a buffer is released from allocation.
     *
     * <p>An exception cannot be thrown by this method.
     *
     * @param size The size of the buffer being released.
     */
    default void onRelease(long size) {}
  
    /**
     * Called whenever an allocation failed, giving the caller a chance to create some space in the
     * allocator (either by freeing some resource, or by changing the limit), and, if successful,
     * allowing the allocator to retry the allocation.
     *
     * @param size the buffer size that was being allocated
     * @param outcome the outcome of the failed allocation. Carries information of what failed
     * @return true, if the allocation can be retried; false if the allocation should fail
     */
    default boolean onFailedAllocation(long size, AllocationOutcome outcome) {
      return false;
    }
  
    /**
     * Called immediately after a child allocator was added to the parent allocator.
     *
     * @param parentAllocator The parent allocator to which a child was added
     * @param childAllocator The child allocator that was just added
     */
    default void onChildAdded(BufferAllocator parentAllocator, BufferAllocator childAllocator) {}
  
    /**
     * Called immediately after a child allocator was removed from the parent allocator.
     *
     * @param parentAllocator The parent allocator from which a child was removed
     * @param childAllocator The child allocator that was just removed
     */
    default void onChildRemoved(BufferAllocator parentAllocator, BufferAllocator childAllocator) {}
  }
  