/*
    * Copyright 2022 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.ByteProcessor;
  import io.netty.util.IllegalReferenceCountException;
  import io.netty.util.NettyRuntime;
  import io.netty.util.Recycler;
  import io.netty.util.ReferenceCounted;
  import io.netty.util.concurrent.FastThreadLocal;
  import io.netty.util.concurrent.FastThreadLocalThread;
  import io.netty.util.internal.ObjectPool;
  import io.netty.util.internal.ObjectUtil;
  import io.netty.util.internal.PlatformDependent;
  import io.netty.util.internal.ReferenceCountUpdater;
  import io.netty.util.internal.SystemPropertyUtil;
  import io.netty.util.internal.ThreadExecutorMap;
  import io.netty.util.internal.UnstableApi;
  
  import java.io.IOException;
  import java.io.InputStream;
  import java.io.OutputStream;
  import java.nio.ByteBuffer;
  import java.nio.ByteOrder;
  import java.nio.channels.ClosedChannelException;
  import java.nio.channels.FileChannel;
  import java.nio.channels.GatheringByteChannel;
  import java.nio.channels.ScatteringByteChannel;
  import java.util.Arrays;
  import java.util.Queue;
  import java.util.Set;
  import java.util.concurrent.ConcurrentLinkedQueue;
  import java.util.concurrent.CopyOnWriteArraySet;
  import java.util.concurrent.atomic.AtomicIntegerFieldUpdater;
  import java.util.concurrent.atomic.AtomicLong;
  import java.util.concurrent.atomic.AtomicReferenceFieldUpdater;
  import java.util.concurrent.locks.StampedLock;
  
  /**
   * An auto-tuning pooling allocator, that follows an anti-generational hypothesis.
   * <p>
   * The allocator is organized into a list of Magazines, and each magazine has a chunk-buffer that they allocate buffers
   * from.
   * <p>
   * The magazines hold the mutexes that ensure the thread-safety of the allocator, and each thread picks a magazine
   * based on the id of the thread. This spreads the contention of multi-threaded access across the magazines.
   * If contention is detected above a certain threshold, the number of magazines are increased in response to the
   * contention.
   * <p>
   * The magazines maintain histograms of the sizes of the allocations they do. The histograms are used to compute the
   * preferred chunk size. The preferred chunk size is one that is big enough to service 10 allocations of the
   * 99-percentile size. This way, the chunk size is adapted to the allocation patterns.
   * <p>
   * Computing the preferred chunk size is a somewhat expensive operation. Therefore, the frequency with which this is
   * done, is also adapted to the allocation pattern. If a newly computed preferred chunk is the same as the previous
   * preferred chunk size, then the frequency is reduced. Otherwise, the frequency is increased.
   * <p>
   * This allows the allocator to quickly respond to changes in the application workload,
   * without suffering undue overhead from maintaining its statistics.
   * <p>
   * Since magazines are "relatively thread-local", the allocator has a central queue that allow excess chunks from any
   * magazine, to be shared with other magazines.
   * The {@link #createSharedChunkQueue()} method can be overridden to customize this queue.
   */
  @UnstableApi
  final class AdaptivePoolingAllocator {
  
      enum MagazineCaching {
          EventLoopThreads,
          FastThreadLocalThreads,
          None
      }
  
      private static final int EXPANSION_ATTEMPTS = 3;
      private static final int INITIAL_MAGAZINES = 4;
      private static final int RETIRE_CAPACITY = 4 * 1024;
      private static final int MIN_CHUNK_SIZE = 128 * 1024;
      private static final int MAX_STRIPES = NettyRuntime.availableProcessors() * 2;
      private static final int BUFS_PER_CHUNK = 10; // For large buffers, aim to have about this many buffers per chunk.
  
      /**
       * The maximum size of a pooled chunk, in bytes. Allocations bigger than this will never be pooled.
       * <p>
       * This number is 10 MiB, and is derived from the limitations of internal histograms.
       */
      private static final int MAX_CHUNK_SIZE =
             BUFS_PER_CHUNK * (1 << AllocationStatistics.HISTO_MAX_BUCKET_SHIFT); // 10 MiB.
 
     /**
      * The capacity if the central queue that allow chunks to be shared across magazines.
      * The default size is {@link NettyRuntime#availableProcessors()},
      * and the maximum number of magazines is twice this.
      * <p>
      * This means the maximum amount of memory that we can have allocated-but-not-in-use is
      * 5 * {@link NettyRuntime#availableProcessors()} * {@link #MAX_CHUNK_SIZE} bytes.
      */
     private static final int CENTRAL_QUEUE_CAPACITY = SystemPropertyUtil.getInt(
             "io.netty.allocator.centralQueueCapacity", NettyRuntime.availableProcessors());
 
     private static final Object NO_MAGAZINE = Boolean.TRUE;
 
     private final ChunkAllocator chunkAllocator;
     private final Queue<Chunk> centralQueue;
     private final StampedLock magazineExpandLock;
     private volatile Magazine[] magazines;
     private final FastThreadLocal<Object> threadLocalMagazine;
     private final Set<Magazine> liveCachedMagazines;
     private volatile boolean freed;
 
     AdaptivePoolingAllocator(ChunkAllocator chunkAllocator, MagazineCaching magazineCaching) {
         ObjectUtil.checkNotNull(chunkAllocator, "chunkAllocator");
         ObjectUtil.checkNotNull(magazineCaching, "magazineCaching");
         this.chunkAllocator = chunkAllocator;
         centralQueue = ObjectUtil.checkNotNull(createSharedChunkQueue(), "centralQueue");
         magazineExpandLock = new StampedLock();
         if (magazineCaching != MagazineCaching.None) {
             assert magazineCaching == MagazineCaching.EventLoopThreads ||
                    magazineCaching == MagazineCaching.FastThreadLocalThreads;
             final boolean cachedMagazinesNonEventLoopThreads =
                     magazineCaching == MagazineCaching.FastThreadLocalThreads;
             final Set<Magazine> liveMagazines = new CopyOnWriteArraySet<Magazine>();
             threadLocalMagazine = new FastThreadLocal<Object>() {
                 @Override
                 protected Object initialValue() {
                     if (cachedMagazinesNonEventLoopThreads || ThreadExecutorMap.currentExecutor() != null) {
                         Magazine mag = new Magazine(AdaptivePoolingAllocator.this, false);
 
                         if (FastThreadLocalThread.willCleanupFastThreadLocals(Thread.currentThread())) {
                             // Only add it to the liveMagazines if we can guarantee that onRemoval(...) is called,
                             // as otherwise we might end up holding the reference forever.
                             liveMagazines.add(mag);
                         }
                         return mag;
                     }
                     return NO_MAGAZINE;
                 }
 
                 @Override
                 protected void onRemoval(final Object value) throws Exception {
                     if (value != NO_MAGAZINE) {
                         liveMagazines.remove(value);
                     }
                 }
             };
             liveCachedMagazines = liveMagazines;
         } else {
             threadLocalMagazine = null;
             liveCachedMagazines = null;
         }
         Magazine[] mags = new Magazine[INITIAL_MAGAZINES];
         for (int i = 0; i < mags.length; i++) {
             mags[i] = new Magazine(this);
         }
         magazines = mags;
     }
 
     /**
      * Create a thread-safe multi-producer, multi-consumer queue to hold chunks that spill over from the
      * internal Magazines.
      * <p>
      * Each Magazine can only hold two chunks at any one time: the chunk it currently allocates from,
      * and the next-in-line chunk which will be used for allocation once the current one has been used up.
      * This queue will be used by magazines to share any excess chunks they allocate, so that they don't need to
      * allocate new chunks when their current and next-in-line chunks have both been used up.
      * <p>
      * The simplest implementation of this method is to return a new {@link ConcurrentLinkedQueue}.
      * However, the {@code CLQ} is unbounded, and this means there's no limit to how many chunks can be cached in this
      * queue.
      * <p>
      * Each chunk in this queue can be up to {@link #MAX_CHUNK_SIZE} in size, so it is recommended to use a bounded
      * queue to limit the maximum memory usage.
      * <p>
      * The default implementation will create a bounded queue with a capacity of {@link #CENTRAL_QUEUE_CAPACITY}.
      *
      * @return A new multi-producer, multi-consumer queue.
      */
     private static Queue<Chunk> createSharedChunkQueue() {
         return PlatformDependent.newFixedMpmcQueue(CENTRAL_QUEUE_CAPACITY);
     }
 
     ByteBuf allocate(int size, int maxCapacity) {
         if (size <= MAX_CHUNK_SIZE) {
             Thread currentThread = Thread.currentThread();
             boolean willCleanupFastThreadLocals = FastThreadLocalThread.willCleanupFastThreadLocals(currentThread);
             AdaptiveByteBuf buf = AdaptiveByteBuf.newInstance(willCleanupFastThreadLocals);
             try {
                 if (allocate(size, maxCapacity, currentThread, buf)) {
                     // Allocation did work, the ownership will is transferred to the caller.
                     AdaptiveByteBuf result = buf;
                     buf = null;
                     return result;
                 }
             } finally {
                 if (buf != null) {
                     // We didn't handover ownership of the buf, release it now so we don't leak.
                     buf.release();
                 }
             }
         }
         // The magazines failed us, or the buffer is too big to be pooled.
         return chunkAllocator.allocate(size, maxCapacity);
     }
 
     private boolean allocate(int size, int maxCapacity, Thread currentThread, AdaptiveByteBuf buf) {
         int sizeBucket = AllocationStatistics.sizeBucket(size); // Compute outside of Magazine lock for better ILP.
         FastThreadLocal<Object> threadLocalMagazine = this.threadLocalMagazine;
         if (threadLocalMagazine != null && currentThread instanceof FastThreadLocalThread) {
             Object mag = threadLocalMagazine.get();
             if (mag != NO_MAGAZINE) {
                 boolean allocated = ((Magazine) mag).tryAllocate(size, sizeBucket, maxCapacity, buf);
                 assert allocated : "Allocation of threadLocalMagazine must always succeed";
                 return true;
             }
         }
         long threadId = currentThread.getId();
         Magazine[] mags;
         int expansions = 0;
         do {
             mags = magazines;
             int mask = mags.length - 1;
             int index = (int) (threadId & mask);
             for (int i = 0, m = Integer.numberOfTrailingZeros(~mask); i < m; i++) {
                 Magazine mag = mags[index + i & mask];
                 if (mag.tryAllocate(size, sizeBucket, maxCapacity, buf)) {
                     // Was able to allocate.
                     return true;
                 }
             }
             expansions++;
         } while (expansions <= EXPANSION_ATTEMPTS && tryExpandMagazines(mags.length));
         return false;
     }
 
     /**
      * Allocate into the given buffer. Used by {@link AdaptiveByteBuf#capacity(int)}.
      */
     void allocate(int size, int maxCapacity, AdaptiveByteBuf into) {
         Magazine magazine = into.chunk.magazine;
         if (!allocate(size, maxCapacity, Thread.currentThread(), into)) {
             // Create a one-off chunk for this allocation as the previous allocate call did not work out.
             AbstractByteBuf innerChunk = chunkAllocator.allocate(size, maxCapacity);
             Chunk chunk = new Chunk(innerChunk, magazine, false);
             try {
                 chunk.readInitInto(into, size, maxCapacity);
             } finally {
                 // As the chunk is an one-off we need to always call release explicitly as readInitInto(...)
                 // will take care of retain once when successful. Once The AdaptiveByteBuf is released it will
                 // completely release the Chunk and so the contained innerChunk.
                 chunk.release();
             }
         }
     }
 
     long usedMemory() {
         long sum = 0;
         for (Chunk chunk : centralQueue) {
             sum += chunk.capacity();
         }
         for (Magazine magazine : magazines) {
             sum += magazine.usedMemory.get();
         }
         if (liveCachedMagazines != null) {
             for (Magazine magazine : liveCachedMagazines) {
                 sum += magazine.usedMemory.get();
             }
         }
         return sum;
     }
 
     private boolean tryExpandMagazines(int currentLength) {
         if (currentLength >= MAX_STRIPES) {
             return true;
         }
         long writeLock = magazineExpandLock.tryWriteLock();
         if (writeLock != 0) {
             try {
                 Magazine[] mags = magazines;
                 if (mags.length >= MAX_STRIPES || mags.length > currentLength || freed) {
                     return true;
                 }
                 int preferredChunkSize = mags[0].sharedPrefChunkSize;
                 Magazine[] expanded = new Magazine[mags.length * 2];
                 for (int i = 0, l = expanded.length; i < l; i++) {
                     Magazine m = new Magazine(this);
                     m.localPrefChunkSize = preferredChunkSize;
                     m.sharedPrefChunkSize = preferredChunkSize;
                     expanded[i] = m;
                 }
                 magazines = expanded;
                 for (Magazine magazine : mags) {
                     magazine.free();
                 }
             } finally {
                 magazineExpandLock.unlockWrite(writeLock);
             }
         }
         return true;
     }
 
     private boolean offerToQueue(Chunk buffer) {
         if (freed) {
             return false;
         }
         return centralQueue.offer(buffer);
     }
 
     // Ensure that we release all previous pooled resources when this object is finalized. This is needed as otherwise
     // we might end up with leaks. While these leaks are usually harmless in reality it would still at least be
     // very confusing for users.
     @Override
     protected void finalize() throws Throwable {
         try {
             super.finalize();
         } finally {
             free();
         }
     }
 
     private void free() {
         freed = true;
         long stamp = magazineExpandLock.writeLock();
         try {
             Magazine[] mags = magazines;
             for (Magazine magazine : mags) {
                 magazine.free();
             }
         } finally {
             magazineExpandLock.unlockWrite(stamp);
         }
         for (;;) {
             Chunk chunk = centralQueue.poll();
             if (chunk == null) {
                 break;
             }
             chunk.release();
         }
     }
 
     static int sizeBucket(int size) {
         return AllocationStatistics.sizeBucket(size);
     }
 
     @SuppressWarnings("checkstyle:finalclass") // Checkstyle mistakenly believes this class should be final.
     private static class AllocationStatistics {
         private static final int MIN_DATUM_TARGET = 1024;
         private static final int MAX_DATUM_TARGET = 65534;
         private static final int INIT_DATUM_TARGET = 9;
         private static final int HISTO_MIN_BUCKET_SHIFT = 13; // Smallest bucket is 1 << 13 = 8192 bytes in size.
         private static final int HISTO_MAX_BUCKET_SHIFT = 20; // Biggest bucket is 1 << 20 = 1 MiB bytes in size.
         private static final int HISTO_BUCKET_COUNT = 1 + HISTO_MAX_BUCKET_SHIFT - HISTO_MIN_BUCKET_SHIFT; // 8 buckets.
         private static final int HISTO_MAX_BUCKET_MASK = HISTO_BUCKET_COUNT - 1;
         private static final int SIZE_MAX_MASK = MAX_CHUNK_SIZE - 1;
 
         protected final AdaptivePoolingAllocator parent;
         private final boolean shareable;
         private final short[][] histos = {
                 new short[HISTO_BUCKET_COUNT], new short[HISTO_BUCKET_COUNT],
                 new short[HISTO_BUCKET_COUNT], new short[HISTO_BUCKET_COUNT],
         };
         private short[] histo = histos[0];
         private final int[] sums = new int[HISTO_BUCKET_COUNT];
 
         private int histoIndex;
         private int datumCount;
         private int datumTarget = INIT_DATUM_TARGET;
         protected volatile int sharedPrefChunkSize = MIN_CHUNK_SIZE;
         protected volatile int localPrefChunkSize = MIN_CHUNK_SIZE;
 
         private AllocationStatistics(AdaptivePoolingAllocator parent, boolean shareable) {
             this.parent = parent;
             this.shareable = shareable;
         }
 
         protected void recordAllocationSize(int bucket) {
             histo[bucket]++;
             if (datumCount++ == datumTarget) {
                 rotateHistograms();
             }
         }
 
         static int sizeBucket(int size) {
             if (size == 0) {
                 return 0;
             }
             // Minimum chunk size is 128 KiB. We'll only make bigger chunks if the 99-percentile is 16 KiB or greater,
             // so we truncate and roll up the bottom part of the histogram to 8 KiB.
             // The upper size band is 1 MiB, and that gives us exactly 8 size buckets,
             // which is a magical number for JIT optimisations.
             int normalizedSize = size - 1 >> HISTO_MIN_BUCKET_SHIFT & SIZE_MAX_MASK;
             return Math.min(Integer.SIZE - Integer.numberOfLeadingZeros(normalizedSize), HISTO_MAX_BUCKET_MASK);
         }
 
         private void rotateHistograms() {
             short[][] hs = histos;
             for (int i = 0; i < HISTO_BUCKET_COUNT; i++) {
                 sums[i] = (hs[0][i] & 0xFFFF) + (hs[1][i] & 0xFFFF) + (hs[2][i] & 0xFFFF) + (hs[3][i] & 0xFFFF);
             }
             int sum = 0;
             for (int count : sums) {
                 sum  += count;
             }
             int targetPercentile = (int) (sum * 0.99);
             int sizeBucket = 0;
             for (; sizeBucket < sums.length; sizeBucket++) {
                 if (sums[sizeBucket] > targetPercentile) {
                     break;
                 }
                 targetPercentile -= sums[sizeBucket];
             }
             int percentileSize = 1 << sizeBucket + HISTO_MIN_BUCKET_SHIFT;
             int prefChunkSize = Math.max(percentileSize * BUFS_PER_CHUNK, MIN_CHUNK_SIZE);
             localPrefChunkSize = prefChunkSize;
             if (shareable) {
                 for (Magazine mag : parent.magazines) {
                     prefChunkSize = Math.max(prefChunkSize, mag.localPrefChunkSize);
                 }
             }
             if (sharedPrefChunkSize != prefChunkSize) {
                 // Preferred chunk size changed. Increase check frequency.
                 datumTarget = Math.max(datumTarget >> 1, MIN_DATUM_TARGET);
                 sharedPrefChunkSize = prefChunkSize;
             } else {
                 // Preferred chunk size did not change. Check less often.
                 datumTarget = Math.min(datumTarget << 1, MAX_DATUM_TARGET);
             }
 
             histoIndex = histoIndex + 1 & 3;
             histo = histos[histoIndex];
             datumCount = 0;
             Arrays.fill(histo, (short) 0);
         }
 
         /**
          * Get the preferred chunk size, based on statistics from the {@linkplain #recordAllocationSize(int) recorded}
          * allocation sizes.
          * <p>
          * This method must be thread-safe.
          *
          * @return The currently preferred chunk allocation size.
          */
         protected int preferredChunkSize() {
             return sharedPrefChunkSize;
         }
     }
 
     private static final class Magazine extends AllocationStatistics {
         private static final AtomicReferenceFieldUpdater<Magazine, Chunk> NEXT_IN_LINE;
         static {
             NEXT_IN_LINE = AtomicReferenceFieldUpdater.newUpdater(Magazine.class, Chunk.class, "nextInLine");
         }
         private static final Chunk MAGAZINE_FREED = new Chunk();
 
         private Chunk current;
         @SuppressWarnings("unused") // updated via NEXT_IN_LINE
         private volatile Chunk nextInLine;
         private final AtomicLong usedMemory;
         private final StampedLock allocationLock;
 
         Magazine(AdaptivePoolingAllocator parent) {
             this(parent, true);
         }
 
         Magazine(AdaptivePoolingAllocator parent, boolean shareable) {
             super(parent, shareable);
 
             // We only need the StampedLock if this Magazine will be shared across threads.
             if (shareable) {
                 allocationLock = new StampedLock();
             } else {
                 allocationLock = null;
             }
             usedMemory = new AtomicLong();
         }
 
         public boolean tryAllocate(int size, int sizeBucket, int maxCapacity, AdaptiveByteBuf buf) {
             if (allocationLock == null) {
                 // This magazine is not shared across threads, just allocate directly.
                 return allocate(size, sizeBucket, maxCapacity, buf);
             }
 
             // Try to retrieve the lock and if successful allocate.
             long writeLock = allocationLock.tryWriteLock();
             if (writeLock != 0) {
                 try {
                     return allocate(size, sizeBucket, maxCapacity, buf);
                 } finally {
                     allocationLock.unlockWrite(writeLock);
                 }
             }
             return false;
         }
 
         private boolean allocate(int size, int sizeBucket, int maxCapacity, AdaptiveByteBuf buf) {
             recordAllocationSize(sizeBucket);
             Chunk curr = current;
             if (curr != null) {
                 if (curr.remainingCapacity() > size) {
                     curr.readInitInto(buf, size, maxCapacity);
                     // We still have some bytes left that we can use for the next allocation, just early return.
                     return true;
                 }
 
                 // At this point we know that this will be the last time current will be used, so directly set it to
                 // null and release it once we are done.
                 current = null;
                 if (curr.remainingCapacity() == size) {
                     try {
                         curr.readInitInto(buf, size, maxCapacity);
                         return true;
                     } finally {
                         curr.release();
                     }
                 }
             }
             Chunk last = curr;
             assert current == null;
             // The fast-path for allocations did not work.
             //
             // Try to fetch the next "Magazine local" Chunk first, if this this fails as we don't have
             // one setup we will poll our centralQueue. If this fails as well we will just allocate a new Chunk.
             //
             // In any case we will store the Chunk as the current so it will be used again for the next allocation and
             // so be "reserved" by this Magazine for exclusive usage.
             if (nextInLine != null) {
                 curr = NEXT_IN_LINE.getAndSet(this, null);
                 if (curr == MAGAZINE_FREED) {
                     // Allocation raced with a stripe-resize that freed this magazine.
                     restoreMagazineFreed();
                     return false;
                 }
             } else {
                 curr = parent.centralQueue.poll();
                 if (curr == null) {
                     curr = newChunkAllocation(size);
                 }
             }
             current = curr;
             assert current != null;
             if (last != null) {
                 if (last.remainingCapacity() < RETIRE_CAPACITY) {
                     last.release();
                 } else {
                     transferChunk(last);
                 }
             }
             if (curr.remainingCapacity() > size) {
                 curr.readInitInto(buf, size, maxCapacity);
             } else if (curr.remainingCapacity() == size) {
                 try {
                     curr.readInitInto(buf, size, maxCapacity);
                 } finally {
                     // Release in a finally block so even if readInitInto(...) would throw we would still correctly
                     // release the current chunk before null it out.
                     curr.release();
                     current = null;
                 }
             } else {
                 Chunk newChunk = newChunkAllocation(size);
                 try {
                     newChunk.readInitInto(buf, size, maxCapacity);
                     if (curr.remainingCapacity() < RETIRE_CAPACITY) {
                         curr.release();
                         current = newChunk;
                     } else {
                         transferChunk(newChunk);
                     }
                     newChunk = null;
                 } finally {
                     if (newChunk != null) {
                         assert current == null;
                         // Something went wrong, let's ensure we not leak the newChunk.
                         newChunk.release();
                     }
                 }
             }
             return true;
         }
 
         private void restoreMagazineFreed() {
             Chunk next = NEXT_IN_LINE.getAndSet(this, MAGAZINE_FREED);
             if (next != null && next != MAGAZINE_FREED) {
                 next.release(); // A chunk snuck in through a race. Release it after restoring MAGAZINE_FREED state.
             }
         }
 
         private void transferChunk(Chunk current) {
             if (NEXT_IN_LINE.compareAndSet(this, null, current)
                     || parent.offerToQueue(current)) {
                 return;
             }
             Chunk nextChunk = NEXT_IN_LINE.get(this);
             if (nextChunk != null && current.remainingCapacity() > nextChunk.remainingCapacity()) {
                 if (NEXT_IN_LINE.compareAndSet(this, nextChunk, current)) {
                     if (nextChunk != MAGAZINE_FREED) {
                         nextChunk.release();
                     }
                     return;
                 }
             }
             // Next-in-line is occupied AND the central queue is full.
             // Rare that we should get here, but we'll only do one allocation out of this chunk, then.
             current.release();
         }
 
         private Chunk newChunkAllocation(int promptingSize) {
             int size = Math.max(promptingSize * BUFS_PER_CHUNK, preferredChunkSize());
             ChunkAllocator chunkAllocator = parent.chunkAllocator;
             return new Chunk(chunkAllocator.allocate(size, size), this, true);
         }
 
         boolean trySetNextInLine(Chunk chunk) {
             return NEXT_IN_LINE.compareAndSet(this, null, chunk);
         }
 
         void free() {
             // Release the current Chunk and the next that was stored for later usage.
             restoreMagazineFreed();
             long stamp = allocationLock.writeLock();
             try {
                 if (current != null) {
                     current.release();
                     current = null;
                 }
             } finally {
                 allocationLock.unlockWrite(stamp);
             }
         }
     }
 
     private static final class Chunk implements ReferenceCounted {
 
         private final AbstractByteBuf delegate;
         private final Magazine magazine;
         private final int capacity;
         private final boolean pooled;
         private int allocatedBytes;
         private static final long REFCNT_FIELD_OFFSET =
                 ReferenceCountUpdater.getUnsafeOffset(Chunk.class, "refCnt");
         private static final AtomicIntegerFieldUpdater<Chunk> AIF_UPDATER =
                 AtomicIntegerFieldUpdater.newUpdater(Chunk.class, "refCnt");
 
         private static final ReferenceCountUpdater<Chunk> updater =
                 new ReferenceCountUpdater<Chunk>() {
                     @Override
                     protected AtomicIntegerFieldUpdater<Chunk> updater() {
                         return AIF_UPDATER;
                     }
                     @Override
                     protected long unsafeOffset() {
                         return REFCNT_FIELD_OFFSET;
                     }
                 };
 
         // Value might not equal "real" reference count, all access should be via the updater
         @SuppressWarnings({"unused", "FieldMayBeFinal"})
         private volatile int refCnt;
 
         Chunk() {
             // Constructor only used by the MAGAZINE_FREED sentinel.
             delegate = null;
             magazine = null;
             capacity = 0;
             pooled = false;
         }
 
         Chunk(AbstractByteBuf delegate, Magazine magazine, boolean pooled) {
             this.delegate = delegate;
             this.magazine = magazine;
             this.pooled = pooled;
             capacity = delegate.capacity();
             magazine.usedMemory.getAndAdd(capacity);
             updater.setInitialValue(this);
         }
 
         @Override
         public Chunk touch(Object hint) {
             return this;
         }
 
         @Override
         public int refCnt() {
             return updater.refCnt(this);
         }
 
         @Override
         public Chunk retain() {
             return updater.retain(this);
         }
 
         @Override
         public Chunk retain(int increment) {
             return updater.retain(this, increment);
         }
 
         @Override
         public Chunk touch() {
             return this;
         }
 
         @Override
         public boolean release() {
             if (updater.release(this)) {
                 deallocate();
                 return true;
             }
             return false;
         }
 
         @Override
         public boolean release(int decrement) {
             if (updater.release(this, decrement)) {
                 deallocate();
                 return true;
             }
             return false;
         }
 
         private void deallocate() {
             Magazine mag = magazine;
             AdaptivePoolingAllocator parent = mag.parent;
             int chunkSize = mag.preferredChunkSize();
             int memSize = delegate.capacity();
             if (!pooled || memSize < chunkSize || memSize > chunkSize + (chunkSize >> 1)) {
                 // Drop the chunk if the parent allocator is closed, or if the chunk is smaller than the
                 // preferred chunk size, or over 50% larger than the preferred chunk size.
                 mag.usedMemory.getAndAdd(-capacity());
                 delegate.release();
             } else {
                 updater.resetRefCnt(this);
                 delegate.setIndex(0, 0);
                 allocatedBytes = 0;
                 if (!mag.trySetNextInLine(this)) {
                     if (!parent.offerToQueue(this)) {
                         // The central queue is full. Ensure we release again as we previously did use resetRefCnt()
                         // which did increase the reference count by 1.
                         boolean released = updater.release(this);
                         delegate.release();
                         assert released;
                     }
                 }
             }
         }
 
         public void readInitInto(AdaptiveByteBuf buf, int size, int maxCapacity) {
             int startIndex = allocatedBytes;
             allocatedBytes = startIndex + size;
             Chunk chunk = this;
             chunk.retain();
             try {
                 buf.init(delegate, chunk, 0, 0, startIndex, size, maxCapacity);
                 chunk = null;
             } finally {
                 if (chunk != null) {
                     // If chunk is not null we know that buf.init(...) failed and so we need to manually release
                     // the chunk again as we retained it before calling buf.init(...).
                     chunk.release();
                 }
             }
         }
 
         public int remainingCapacity() {
             return capacity - allocatedBytes;
         }
 
         public int capacity() {
             return capacity;
         }
     }
 
     static final class AdaptiveByteBuf extends AbstractReferenceCountedByteBuf {
         static final ObjectPool<AdaptiveByteBuf> RECYCLER = ObjectPool.newPool(
                 new ObjectPool.ObjectCreator<AdaptiveByteBuf>() {
                     @Override
                     public AdaptiveByteBuf newObject(ObjectPool.Handle<AdaptiveByteBuf> handle) {
                         return new AdaptiveByteBuf(handle);
                     }
                 });
 
         static AdaptiveByteBuf newInstance(boolean useThreadLocal) {
             if (useThreadLocal) {
                 AdaptiveByteBuf buf = RECYCLER.get();
                 buf.resetRefCnt();
                 buf.discardMarks();
                 return buf;
             }
             return new AdaptiveByteBuf(null);
         }
 
         private final ObjectPool.Handle<AdaptiveByteBuf> handle;
 
         private int adjustment;
         private AbstractByteBuf rootParent;
         private Chunk chunk;
         private int length;
         private ByteBuffer tmpNioBuf;
         private boolean hasArray;
         private boolean hasMemoryAddress;
 
         AdaptiveByteBuf(ObjectPool.Handle<AdaptiveByteBuf> recyclerHandle) {
             super(0);
             handle = recyclerHandle;
         }
 
         void init(AbstractByteBuf unwrapped, Chunk wrapped, int readerIndex, int writerIndex,
                   int adjustment, int capacity, int maxCapacity) {
             this.adjustment = adjustment;
             chunk = wrapped;
             length = capacity;
             maxCapacity(maxCapacity);
             setIndex0(readerIndex, writerIndex);
             hasArray = unwrapped.hasArray();
             hasMemoryAddress = unwrapped.hasMemoryAddress();
             rootParent = unwrapped;
             tmpNioBuf = unwrapped.internalNioBuffer(adjustment, capacity).slice();
         }
 
         private AbstractByteBuf rootParent() {
             final AbstractByteBuf rootParent = this.rootParent;
             if (rootParent != null) {
                 return rootParent;
             }
             throw new IllegalReferenceCountException();
         }
 
         @Override
         public ByteBuf retainedSlice() {
             if (handle == null) {
                 return super.retainedSlice();
             }
             // If the handle is not null we can use the Pooled variants that use a Recycler.
             ensureAccessible();
             return PooledSlicedByteBuf.newInstance(this, this, readerIndex(), readableBytes());
         }
 
         @Override
         public ByteBuf retainedSlice(int index, int length) {
             if (handle == null) {
                 return super.retainedSlice(index, length);
             }
             // If the handle is not null we can use the Pooled variants that use a Recycler.
             ensureAccessible();
             return PooledSlicedByteBuf.newInstance(this, this, index, length);
         }
 
         @Override
         public ByteBuf retainedDuplicate() {
             if (handle == null) {
                 return super.retainedDuplicate();
             }
             // If the handle is not null we can use the Pooled variants that use a Recycler.
             ensureAccessible();
             return PooledDuplicatedByteBuf.newInstance(this, this, readerIndex(), writerIndex());
         }
 
         @Override
         public int capacity() {
             return length;
         }
 
         @Override
         public ByteBuf capacity(int newCapacity) {
             if (newCapacity == capacity()) {
                 ensureAccessible();
                 return this;
             }
             checkNewCapacity(newCapacity);
             if (newCapacity < capacity()) {
                 length = newCapacity;
                 setIndex0(Math.min(readerIndex(), newCapacity), Math.min(writerIndex(), newCapacity));
                 return this;
             }
 
             // Reallocation required.
             ByteBuffer data = tmpNioBuf;
             data.clear();
             tmpNioBuf = null;
             Chunk chunk = this.chunk;
             Magazine magazine = chunk.magazine;
             AdaptivePoolingAllocator allocator = magazine.parent;
             int readerIndex = this.readerIndex;
             int writerIndex = this.writerIndex;
             allocator.allocate(newCapacity, maxCapacity(), this);
             tmpNioBuf.put(data);
             tmpNioBuf.clear();
             chunk.release();
             this.readerIndex = readerIndex;
             this.writerIndex = writerIndex;
             return this;
         }
 
         @Override
         public ByteBufAllocator alloc() {
             return rootParent().alloc();
         }
 
         @Override
         public ByteOrder order() {
             return rootParent().order();
         }
 
         @Override
         public ByteBuf unwrap() {
             return null;
         }
 
         @Override
         public boolean isDirect() {
             return rootParent().isDirect();
         }
 
         @Override
         public int arrayOffset() {
             return idx(rootParent().arrayOffset());
         }
 
         @Override
         public boolean hasMemoryAddress() {
             return hasMemoryAddress;
         }
 
         @Override
         public long memoryAddress() {
             ensureAccessible();
             return rootParent().memoryAddress() + adjustment;
         }
 
         @Override
         public ByteBuffer nioBuffer(int index, int length) {
             checkIndex(index, length);
             return rootParent().nioBuffer(idx(index), length);
         }
 
         @Override
         public ByteBuffer internalNioBuffer(int index, int length) {
             checkIndex(index, length);
             return (ByteBuffer) internalNioBuffer().position(index).limit(index + length);
         }
 
         private ByteBuffer internalNioBuffer() {
             return (ByteBuffer) tmpNioBuf.clear();
         }
 
         @Override
         public ByteBuffer[] nioBuffers(int index, int length) {
             checkIndex(index, length);
             return rootParent().nioBuffers(idx(index), length);
         }
 
         @Override
         public boolean hasArray() {
             return hasArray;
         }
 
         @Override
         public byte[] array() {
             ensureAccessible();
             return rootParent().array();
         }
 
         @Override
         public ByteBuf copy(int index, int length) {
             checkIndex(index, length);
             return rootParent().copy(idx(index), length);
         }
 
         @Override
         public int nioBufferCount() {
             return rootParent().nioBufferCount();
         }
 
         @Override
         protected byte _getByte(int index) {
             return rootParent()._getByte(idx(index));
         }
 
         @Override
         protected short _getShort(int index) {
             return rootParent()._getShort(idx(index));
         }
 
         @Override
         protected short _getShortLE(int index) {
             return rootParent()._getShortLE(idx(index));
         }
 
         @Override
         protected int _getUnsignedMedium(int index) {
             return rootParent()._getUnsignedMedium(idx(index));
         }
 
         @Override
         protected int _getUnsignedMediumLE(int index) {
             return rootParent()._getUnsignedMediumLE(idx(index));
         }
 
         @Override
         protected int _getInt(int index) {
             return rootParent()._getInt(idx(index));
         }
 
         @Override
         protected int _getIntLE(int index) {
             return rootParent()._getIntLE(idx(index));
         }
 
         @Override
         protected long _getLong(int index) {
             return rootParent()._getLong(idx(index));
         }
 
         @Override
         protected long _getLongLE(int index) {
             return rootParent()._getLongLE(idx(index));
         }
 
         @Override
         public ByteBuf getBytes(int index, ByteBuf dst, int dstIndex, int length) {
             checkIndex(index, length);
             rootParent().getBytes(idx(index), dst, dstIndex, length);
             return this;
         }
 
         @Override
         public ByteBuf getBytes(int index, byte[] dst, int dstIndex, int length) {
             checkIndex(index, length);
             rootParent().getBytes(idx(index), dst, dstIndex, length);
             return this;
         }
 
         @Override
         public ByteBuf getBytes(int index, ByteBuffer dst) {
             checkIndex(index, dst.remaining());
             rootParent().getBytes(idx(index), dst);
             return this;
         }
 
         @Override
         protected void _setByte(int index, int value) {
             rootParent()._setByte(idx(index), value);
         }
 
         @Override
         protected void _setShort(int index, int value) {
             rootParent()._setShort(idx(index), value);
         }
 
         @Override
         protected void _setShortLE(int index, int value) {
             rootParent()._setShortLE(idx(index), value);
         }
 
         @Override
         protected void _setMedium(int index, int value) {
             rootParent()._setMedium(idx(index), value);
         }
 
         @Override
         protected void _setMediumLE(int index, int value) {
             rootParent()._setMediumLE(idx(index), value);
         }
 
         @Override
         protected void _setInt(int index, int value) {
             rootParent()._setInt(idx(index), value);
         }
 
         @Override
         protected void _setIntLE(int index, int value) {
             rootParent()._setIntLE(idx(index), value);
         }
 
         @Override
         protected void _setLong(int index, long value) {
             rootParent()._setLong(idx(index), value);
         }
 
         @Override
         protected void _setLongLE(int index, long value) {
             rootParent().setLongLE(idx(index), value);
         }
 
         @Override
         public ByteBuf setBytes(int index, byte[] src, int srcIndex, int length) {
             checkIndex(index, length);
             rootParent().setBytes(idx(index), src, srcIndex, length);
             return this;
         }
 
         @Override
         public ByteBuf setBytes(int index, ByteBuf src, int srcIndex, int length) {
             checkIndex(index, length);
             rootParent().setBytes(idx(index), src, srcIndex, length);
             return this;
         }
 
         @Override
         public ByteBuf setBytes(int index, ByteBuffer src) {
             checkIndex(index, src.remaining());
             rootParent().setBytes(idx(index), src);
             return this;
         }
 
         @Override
         public ByteBuf getBytes(int index, OutputStream out, int length)
                 throws IOException {
             checkIndex(index, length);
             if (length != 0) {
                 ByteBufUtil.readBytes(alloc(), internalNioBuffer().duplicate(), index, length, out);
             }
             return this;
         }
 
         @Override
         public int getBytes(int index, GatheringByteChannel out, int length)
                 throws IOException {
             return out.write(internalNioBuffer(index, length).duplicate());
         }
 
         @Override
         public int getBytes(int index, FileChannel out, long position, int length)
                 throws IOException {
             return out.write(internalNioBuffer(index, length).duplicate(), position);
         }
 
         @Override
         public int setBytes(int index, InputStream in, int length)
                 throws IOException {
             checkIndex(index, length);
             final AbstractByteBuf rootParent = rootParent();
             if (rootParent.hasArray()) {
                 return rootParent.setBytes(idx(index), in, length);
             }
             byte[] tmp = ByteBufUtil.threadLocalTempArray(length);
             int readBytes = in.read(tmp, 0, length);
             if (readBytes <= 0) {
                 return readBytes;
             }
             setBytes(index, tmp, 0, readBytes);
             return readBytes;
         }
 
         @Override
         public int setBytes(int index, ScatteringByteChannel in, int length)
                 throws IOException {
             try {
                 return in.read(internalNioBuffer(index, length).duplicate());
             } catch (ClosedChannelException ignored) {
                 return -1;
             }
         }
 
         @Override
         public int setBytes(int index, FileChannel in, long position, int length)
                 throws IOException {
             try {
                 return in.read(internalNioBuffer(index, length).duplicate(), position);
             } catch (ClosedChannelException ignored) {
                 return -1;
             }
         }
 
         @Override
         public int forEachByte(int index, int length, ByteProcessor processor) {
             checkIndex(index, length);
             int ret = rootParent().forEachByte(idx(index), length, processor);
             return forEachResult(ret);
         }
 
         @Override
         public int forEachByteDesc(int index, int length, ByteProcessor processor) {
             checkIndex(index, length);
             int ret = rootParent().forEachByteDesc(idx(index), length, processor);
             return forEachResult(ret);
         }
 
         private int forEachResult(int ret) {
             if (ret < adjustment) {
                 return -1;
             }
             return ret - adjustment;
         }
 
         @Override
         public boolean isContiguous() {
             return rootParent().isContiguous();
         }
 
         private int idx(int index) {
             return index + adjustment;
         }
 
         @Override
         protected void deallocate() {
             if (chunk != null) {
                 chunk.release();
             }
             tmpNioBuf = null;
             chunk = null;
             rootParent = null;
             if (handle instanceof Recycler.EnhancedHandle) {
                 ((Recycler.EnhancedHandle<?>) handle).unguardedRecycle(this);
             } else if (handle != null) {
                 handle.recycle(this);
             }
         }
     }
 
     /**
      * The strategy for how {@link AdaptivePoolingAllocator} should allocate chunk buffers.
      */
     interface ChunkAllocator {
         /**
          * Allocate a buffer for a chunk. This can be any kind of {@link AbstractByteBuf} implementation.
          * @param initialCapacity The initial capacity of the returned {@link AbstractByteBuf}.
          * @param maxCapacity The maximum capacity of the returned {@link AbstractByteBuf}.
          * @return The buffer that represents the chunk memory.
          */
         AbstractByteBuf allocate(int initialCapacity, int maxCapacity);
     }
 }