/*
    * Copyright 2024 The Netty Project
    *
    * The Netty Project 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:
    *
    *   https://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 io.netty.buffer;
  
  import io.netty.util.internal.PlatformDependent;
  import io.netty.util.internal.SystemPropertyUtil;
  import io.netty.util.internal.UnstableApi;
  import io.netty.util.internal.logging.InternalLogger;
  import io.netty.util.internal.logging.InternalLoggerFactory;
  
  import static io.netty.util.internal.PlatformDependent.javaVersion;
  
  /**
   * An auto-tuning pooling {@link ByteBufAllocator}, that follows an anti-generational hypothesis.
   * <p>
   * <strong>Note:</strong> this allocator is <strong>experimental</strong>. It is recommended to roll out usage slowly,
   * and to carefully monitor application performance in the process.
   * <p>
   * See the {@link AdaptivePoolingAllocator} class documentation for implementation details.
   */
  @UnstableApi
  public final class AdaptiveByteBufAllocator extends AbstractByteBufAllocator
          implements ByteBufAllocatorMetricProvider, ByteBufAllocatorMetric {
      private static final InternalLogger logger = InternalLoggerFactory.getInstance(AdaptiveByteBufAllocator.class);
      private static final boolean DEFAULT_USE_CACHED_MAGAZINES_FOR_NON_EVENT_LOOP_THREADS;
  
      static {
          DEFAULT_USE_CACHED_MAGAZINES_FOR_NON_EVENT_LOOP_THREADS = SystemPropertyUtil.getBoolean(
                  "io.netty.allocator.useCachedMagazinesForNonEventLoopThreads", false);
          logger.debug("-Dio.netty.allocator.useCachedMagazinesForNonEventLoopThreads: {}",
                       DEFAULT_USE_CACHED_MAGAZINES_FOR_NON_EVENT_LOOP_THREADS);
      }
  
      private final AdaptiveAllocatorApi direct;
      private final AdaptiveAllocatorApi heap;
  
      public AdaptiveByteBufAllocator() {
          this(!PlatformDependent.isExplicitNoPreferDirect());
      }
  
      public AdaptiveByteBufAllocator(boolean preferDirect) {
          this(preferDirect, DEFAULT_USE_CACHED_MAGAZINES_FOR_NON_EVENT_LOOP_THREADS);
      }
  
      public AdaptiveByteBufAllocator(boolean preferDirect, boolean useCacheForNonEventLoopThreads) {
          super(preferDirect);
          if (javaVersion() < 8) {
              // The implementation uses StampedLock, which was introduced in Java 8.
              throw new IllegalStateException("This allocator require Java 8 or newer.");
          }
          direct = new AdaptivePoolingAllocator(new DirectChunkAllocator(this), useCacheForNonEventLoopThreads);
          heap = new AdaptivePoolingAllocator(new HeapChunkAllocator(this), useCacheForNonEventLoopThreads);
      }
  
      @Override
      protected ByteBuf newHeapBuffer(int initialCapacity, int maxCapacity) {
          return toLeakAwareBuffer(heap.allocate(initialCapacity, maxCapacity));
      }
  
      @Override
      protected ByteBuf newDirectBuffer(int initialCapacity, int maxCapacity) {
          return toLeakAwareBuffer(direct.allocate(initialCapacity, maxCapacity));
      }
  
      @Override
      public boolean isDirectBufferPooled() {
          return true;
      }
  
      @Override
      public long usedHeapMemory() {
          return heap.usedMemory();
      }
  
      @Override
      public long usedDirectMemory() {
          return direct.usedMemory();
      }
  
      @Override
      public ByteBufAllocatorMetric metric() {
          return this;
      }
  
      interface AdaptiveAllocatorApi {
          ByteBuf allocate(int initialCapacity, int maxCapacity);
         long usedMemory();
     }
 
     private static final class HeapChunkAllocator implements AdaptivePoolingAllocator.ChunkAllocator {
         private final ByteBufAllocator allocator;
 
         private HeapChunkAllocator(ByteBufAllocator allocator) {
             this.allocator = allocator;
         }
 
         @Override
         public AbstractByteBuf allocate(int initialCapacity, int maxCapacity) {
             return PlatformDependent.hasUnsafe() ?
                     new UnpooledUnsafeHeapByteBuf(allocator, initialCapacity, maxCapacity) :
                     new UnpooledHeapByteBuf(allocator, initialCapacity, maxCapacity);
         }
     }
 
     private static final class DirectChunkAllocator implements AdaptivePoolingAllocator.ChunkAllocator {
         private final ByteBufAllocator allocator;
 
         private DirectChunkAllocator(ByteBufAllocator allocator) {
             this.allocator = allocator;
         }
 
         @Override
         public AbstractByteBuf allocate(int initialCapacity, int maxCapacity) {
             return PlatformDependent.hasUnsafe() ?
                     UnsafeByteBufUtil.newUnsafeDirectByteBuf(allocator, initialCapacity, maxCapacity) :
                     new UnpooledDirectByteBuf(allocator, initialCapacity, maxCapacity);
         }
     }
 }