/*
    * Copyright 2012 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 static io.netty.util.internal.ObjectUtil.checkPositiveOrZero;
  
  import io.netty.util.NettyRuntime;
  import io.netty.util.concurrent.EventExecutor;
  import io.netty.util.concurrent.FastThreadLocal;
  import io.netty.util.concurrent.FastThreadLocalThread;
  import io.netty.util.internal.PlatformDependent;
  import io.netty.util.internal.StringUtil;
  import io.netty.util.internal.SystemPropertyUtil;
  import io.netty.util.internal.ThreadExecutorMap;
  import io.netty.util.internal.logging.InternalLogger;
  import io.netty.util.internal.logging.InternalLoggerFactory;
  
  import java.nio.ByteBuffer;
  import java.util.ArrayList;
  import java.util.Collections;
  import java.util.List;
  import java.util.concurrent.TimeUnit;
  
  public class PooledByteBufAllocator extends AbstractByteBufAllocator implements ByteBufAllocatorMetricProvider {
  
      private static final InternalLogger logger = InternalLoggerFactory.getInstance(PooledByteBufAllocator.class);
      private static final int DEFAULT_NUM_HEAP_ARENA;
      private static final int DEFAULT_NUM_DIRECT_ARENA;
  
      private static final int DEFAULT_PAGE_SIZE;
      private static final int DEFAULT_MAX_ORDER; // 8192 << 9 = 4 MiB per chunk
      private static final int DEFAULT_SMALL_CACHE_SIZE;
      private static final int DEFAULT_NORMAL_CACHE_SIZE;
      static final int DEFAULT_MAX_CACHED_BUFFER_CAPACITY;
      private static final int DEFAULT_CACHE_TRIM_INTERVAL;
      private static final long DEFAULT_CACHE_TRIM_INTERVAL_MILLIS;
      private static final boolean DEFAULT_USE_CACHE_FOR_ALL_THREADS;
      private static final int DEFAULT_DIRECT_MEMORY_CACHE_ALIGNMENT;
      static final int DEFAULT_MAX_CACHED_BYTEBUFFERS_PER_CHUNK;
      private static final boolean DEFAULT_DISABLE_CACHE_FINALIZERS_FOR_FAST_THREAD_LOCAL_THREADS;
  
      private static final int MIN_PAGE_SIZE = 4096;
      private static final int MAX_CHUNK_SIZE = (int) (((long) Integer.MAX_VALUE + 1) / 2);
  
      private static final int CACHE_NOT_USED = 0;
  
      private final Runnable trimTask = new Runnable() {
          @Override
          public void run() {
              PooledByteBufAllocator.this.trimCurrentThreadCache();
          }
      };
  
      static {
          int defaultAlignment = SystemPropertyUtil.getInt(
                  "io.netty.allocator.directMemoryCacheAlignment", 0);
          int defaultPageSize = SystemPropertyUtil.getInt("io.netty.allocator.pageSize", 8192);
          Throwable pageSizeFallbackCause = null;
          try {
              validateAndCalculatePageShifts(defaultPageSize, defaultAlignment);
          } catch (Throwable t) {
              pageSizeFallbackCause = t;
              defaultPageSize = 8192;
              defaultAlignment = 0;
          }
          DEFAULT_PAGE_SIZE = defaultPageSize;
          DEFAULT_DIRECT_MEMORY_CACHE_ALIGNMENT = defaultAlignment;
  
          int defaultMaxOrder = SystemPropertyUtil.getInt("io.netty.allocator.maxOrder", 9);
          Throwable maxOrderFallbackCause = null;
          try {
              validateAndCalculateChunkSize(DEFAULT_PAGE_SIZE, defaultMaxOrder);
          } catch (Throwable t) {
              maxOrderFallbackCause = t;
              defaultMaxOrder = 9;
          }
          DEFAULT_MAX_ORDER = defaultMaxOrder;
  
          // Determine reasonable default for nHeapArena and nDirectArena.
          // Assuming each arena has 3 chunks, the pool should not consume more than 50% of max memory.
          final Runtime runtime = Runtime.getRuntime();
  
          /*
           * We use 2 * available processors by default to reduce contention as we use 2 * available processors for the
           * number of EventLoops in NIO and EPOLL as well. If we choose a smaller number we will run into hot spots as
          * allocation and de-allocation needs to be synchronized on the PoolArena.
          *
          * See https://github.com/netty/netty/issues/3888.
          */
         final int defaultMinNumArena = NettyRuntime.availableProcessors() * 2;
         final int defaultChunkSize = DEFAULT_PAGE_SIZE << DEFAULT_MAX_ORDER;
         DEFAULT_NUM_HEAP_ARENA = Math.max(0,
                 SystemPropertyUtil.getInt(
                         "io.netty.allocator.numHeapArenas",
                         (int) Math.min(
                                 defaultMinNumArena,
                                 runtime.maxMemory() / defaultChunkSize / 2 / 3)));
         DEFAULT_NUM_DIRECT_ARENA = Math.max(0,
                 SystemPropertyUtil.getInt(
                         "io.netty.allocator.numDirectArenas",
                         (int) Math.min(
                                 defaultMinNumArena,
                                 PlatformDependent.maxDirectMemory() / defaultChunkSize / 2 / 3)));
 
         // cache sizes
         DEFAULT_SMALL_CACHE_SIZE = SystemPropertyUtil.getInt("io.netty.allocator.smallCacheSize", 256);
         DEFAULT_NORMAL_CACHE_SIZE = SystemPropertyUtil.getInt("io.netty.allocator.normalCacheSize", 64);
 
         // 32 kb is the default maximum capacity of the cached buffer. Similar to what is explained in
         // 'Scalable memory allocation using jemalloc'
         DEFAULT_MAX_CACHED_BUFFER_CAPACITY = SystemPropertyUtil.getInt(
                 "io.netty.allocator.maxCachedBufferCapacity", 32 * 1024);
 
         // the number of threshold of allocations when cached entries will be freed up if not frequently used
         DEFAULT_CACHE_TRIM_INTERVAL = SystemPropertyUtil.getInt(
                 "io.netty.allocator.cacheTrimInterval", 8192);
 
         if (SystemPropertyUtil.contains("io.netty.allocation.cacheTrimIntervalMillis")) {
             logger.warn("-Dio.netty.allocation.cacheTrimIntervalMillis is deprecated," +
                     " use -Dio.netty.allocator.cacheTrimIntervalMillis");
 
             if (SystemPropertyUtil.contains("io.netty.allocator.cacheTrimIntervalMillis")) {
                 // Both system properties are specified. Use the non-deprecated one.
                 DEFAULT_CACHE_TRIM_INTERVAL_MILLIS = SystemPropertyUtil.getLong(
                         "io.netty.allocator.cacheTrimIntervalMillis", 0);
             } else {
                 DEFAULT_CACHE_TRIM_INTERVAL_MILLIS = SystemPropertyUtil.getLong(
                         "io.netty.allocation.cacheTrimIntervalMillis", 0);
             }
         } else {
             DEFAULT_CACHE_TRIM_INTERVAL_MILLIS = SystemPropertyUtil.getLong(
                     "io.netty.allocator.cacheTrimIntervalMillis", 0);
         }
 
         DEFAULT_USE_CACHE_FOR_ALL_THREADS = SystemPropertyUtil.getBoolean(
                 "io.netty.allocator.useCacheForAllThreads", false);
 
         DEFAULT_DISABLE_CACHE_FINALIZERS_FOR_FAST_THREAD_LOCAL_THREADS = SystemPropertyUtil.getBoolean(
                 "io.netty.allocator.disableCacheFinalizersForFastThreadLocalThreads", false);
 
         // Use 1023 by default as we use an ArrayDeque as backing storage which will then allocate an internal array
         // of 1024 elements. Otherwise we would allocate 2048 and only use 1024 which is wasteful.
         DEFAULT_MAX_CACHED_BYTEBUFFERS_PER_CHUNK = SystemPropertyUtil.getInt(
                 "io.netty.allocator.maxCachedByteBuffersPerChunk", 1023);
 
         if (logger.isDebugEnabled()) {
             logger.debug("-Dio.netty.allocator.numHeapArenas: {}", DEFAULT_NUM_HEAP_ARENA);
             logger.debug("-Dio.netty.allocator.numDirectArenas: {}", DEFAULT_NUM_DIRECT_ARENA);
             if (pageSizeFallbackCause == null) {
                 logger.debug("-Dio.netty.allocator.pageSize: {}", DEFAULT_PAGE_SIZE);
             } else {
                 logger.debug("-Dio.netty.allocator.pageSize: {}", DEFAULT_PAGE_SIZE, pageSizeFallbackCause);
             }
             if (maxOrderFallbackCause == null) {
                 logger.debug("-Dio.netty.allocator.maxOrder: {}", DEFAULT_MAX_ORDER);
             } else {
                 logger.debug("-Dio.netty.allocator.maxOrder: {}", DEFAULT_MAX_ORDER, maxOrderFallbackCause);
             }
             logger.debug("-Dio.netty.allocator.chunkSize: {}", DEFAULT_PAGE_SIZE << DEFAULT_MAX_ORDER);
             logger.debug("-Dio.netty.allocator.smallCacheSize: {}", DEFAULT_SMALL_CACHE_SIZE);
             logger.debug("-Dio.netty.allocator.normalCacheSize: {}", DEFAULT_NORMAL_CACHE_SIZE);
             logger.debug("-Dio.netty.allocator.maxCachedBufferCapacity: {}", DEFAULT_MAX_CACHED_BUFFER_CAPACITY);
             logger.debug("-Dio.netty.allocator.cacheTrimInterval: {}", DEFAULT_CACHE_TRIM_INTERVAL);
             logger.debug("-Dio.netty.allocator.cacheTrimIntervalMillis: {}", DEFAULT_CACHE_TRIM_INTERVAL_MILLIS);
             logger.debug("-Dio.netty.allocator.useCacheForAllThreads: {}", DEFAULT_USE_CACHE_FOR_ALL_THREADS);
             logger.debug("-Dio.netty.allocator.maxCachedByteBuffersPerChunk: {}",
                     DEFAULT_MAX_CACHED_BYTEBUFFERS_PER_CHUNK);
             logger.debug("-Dio.netty.allocator.disableCacheFinalizersForFastThreadLocalThreads: {}",
                          DEFAULT_DISABLE_CACHE_FINALIZERS_FOR_FAST_THREAD_LOCAL_THREADS);
         }
     }
 
     public static final PooledByteBufAllocator DEFAULT =
             new PooledByteBufAllocator(PlatformDependent.directBufferPreferred());
 
     private final PoolArena<byte[]>[] heapArenas;
     private final PoolArena<ByteBuffer>[] directArenas;
     private final int smallCacheSize;
     private final int normalCacheSize;
     private final List<PoolArenaMetric> heapArenaMetrics;
     private final List<PoolArenaMetric> directArenaMetrics;
     private final PoolThreadLocalCache threadCache;
     private final int chunkSize;
     private final PooledByteBufAllocatorMetric metric;
 
     public PooledByteBufAllocator() {
         this(false);
     }
 
     @SuppressWarnings("deprecation")
     public PooledByteBufAllocator(boolean preferDirect) {
         this(preferDirect, DEFAULT_NUM_HEAP_ARENA, DEFAULT_NUM_DIRECT_ARENA, DEFAULT_PAGE_SIZE, DEFAULT_MAX_ORDER);
     }
 
     @SuppressWarnings("deprecation")
     public PooledByteBufAllocator(int nHeapArena, int nDirectArena, int pageSize, int maxOrder) {
         this(false, nHeapArena, nDirectArena, pageSize, maxOrder);
     }
 
     /**
      * @deprecated use
      * {@link PooledByteBufAllocator#PooledByteBufAllocator(boolean, int, int, int, int, int, int, boolean)}
      */
     @Deprecated
     public PooledByteBufAllocator(boolean preferDirect, int nHeapArena, int nDirectArena, int pageSize, int maxOrder) {
         this(preferDirect, nHeapArena, nDirectArena, pageSize, maxOrder,
              0, DEFAULT_SMALL_CACHE_SIZE, DEFAULT_NORMAL_CACHE_SIZE);
     }
 
     /**
      * @deprecated use
      * {@link PooledByteBufAllocator#PooledByteBufAllocator(boolean, int, int, int, int, int, int, boolean)}
      */
     @Deprecated
     public PooledByteBufAllocator(boolean preferDirect, int nHeapArena, int nDirectArena, int pageSize, int maxOrder,
                                   int tinyCacheSize, int smallCacheSize, int normalCacheSize) {
         this(preferDirect, nHeapArena, nDirectArena, pageSize, maxOrder, smallCacheSize,
              normalCacheSize, DEFAULT_USE_CACHE_FOR_ALL_THREADS, DEFAULT_DIRECT_MEMORY_CACHE_ALIGNMENT);
     }
 
     /**
      * @deprecated use
      * {@link PooledByteBufAllocator#PooledByteBufAllocator(boolean, int, int, int, int, int, int, boolean)}
      */
     @Deprecated
     public PooledByteBufAllocator(boolean preferDirect, int nHeapArena,
                                   int nDirectArena, int pageSize, int maxOrder, int tinyCacheSize,
                                   int smallCacheSize, int normalCacheSize,
                                   boolean useCacheForAllThreads) {
         this(preferDirect, nHeapArena, nDirectArena, pageSize, maxOrder,
              smallCacheSize, normalCacheSize,
              useCacheForAllThreads);
     }
 
     public PooledByteBufAllocator(boolean preferDirect, int nHeapArena,
                                   int nDirectArena, int pageSize, int maxOrder,
                                   int smallCacheSize, int normalCacheSize,
                                   boolean useCacheForAllThreads) {
         this(preferDirect, nHeapArena, nDirectArena, pageSize, maxOrder,
              smallCacheSize, normalCacheSize,
              useCacheForAllThreads, DEFAULT_DIRECT_MEMORY_CACHE_ALIGNMENT);
     }
 
     /**
      * @deprecated use
      * {@link PooledByteBufAllocator#PooledByteBufAllocator(boolean, int, int, int, int, int, int, boolean, int)}
      */
     @Deprecated
     public PooledByteBufAllocator(boolean preferDirect, int nHeapArena, int nDirectArena, int pageSize, int maxOrder,
                                   int tinyCacheSize, int smallCacheSize, int normalCacheSize,
                                   boolean useCacheForAllThreads, int directMemoryCacheAlignment) {
         this(preferDirect, nHeapArena, nDirectArena, pageSize, maxOrder,
              smallCacheSize, normalCacheSize,
              useCacheForAllThreads, directMemoryCacheAlignment);
     }
 
     public PooledByteBufAllocator(boolean preferDirect, int nHeapArena, int nDirectArena, int pageSize, int maxOrder,
                                   int smallCacheSize, int normalCacheSize,
                                   boolean useCacheForAllThreads, int directMemoryCacheAlignment) {
         super(preferDirect);
         threadCache = new PoolThreadLocalCache(useCacheForAllThreads);
         this.smallCacheSize = smallCacheSize;
         this.normalCacheSize = normalCacheSize;
 
         if (directMemoryCacheAlignment != 0) {
             if (!PlatformDependent.hasAlignDirectByteBuffer()) {
                 throw new UnsupportedOperationException("Buffer alignment is not supported. " +
                         "Either Unsafe or ByteBuffer.alignSlice() must be available.");
             }
 
             // Ensure page size is a whole multiple of the alignment, or bump it to the next whole multiple.
             pageSize = (int) PlatformDependent.align(pageSize, directMemoryCacheAlignment);
         }
 
         chunkSize = validateAndCalculateChunkSize(pageSize, maxOrder);
 
         checkPositiveOrZero(nHeapArena, "nHeapArena");
         checkPositiveOrZero(nDirectArena, "nDirectArena");
 
         checkPositiveOrZero(directMemoryCacheAlignment, "directMemoryCacheAlignment");
         if (directMemoryCacheAlignment > 0 && !isDirectMemoryCacheAlignmentSupported()) {
             throw new IllegalArgumentException("directMemoryCacheAlignment is not supported");
         }
 
         if ((directMemoryCacheAlignment & -directMemoryCacheAlignment) != directMemoryCacheAlignment) {
             throw new IllegalArgumentException("directMemoryCacheAlignment: "
                     + directMemoryCacheAlignment + " (expected: power of two)");
         }
 
         int pageShifts = validateAndCalculatePageShifts(pageSize, directMemoryCacheAlignment);
 
         if (nHeapArena > 0) {
             heapArenas = newArenaArray(nHeapArena);
             List<PoolArenaMetric> metrics = new ArrayList<PoolArenaMetric>(heapArenas.length);
             final SizeClasses sizeClasses = new SizeClasses(pageSize, pageShifts, chunkSize, 0);
             for (int i = 0; i < heapArenas.length; i ++) {
                 PoolArena.HeapArena arena = new PoolArena.HeapArena(this, sizeClasses);
                 heapArenas[i] = arena;
                 metrics.add(arena);
             }
             heapArenaMetrics = Collections.unmodifiableList(metrics);
         } else {
             heapArenas = null;
             heapArenaMetrics = Collections.emptyList();
         }
 
         if (nDirectArena > 0) {
             directArenas = newArenaArray(nDirectArena);
             List<PoolArenaMetric> metrics = new ArrayList<PoolArenaMetric>(directArenas.length);
             final SizeClasses sizeClasses = new SizeClasses(pageSize, pageShifts, chunkSize,
                     directMemoryCacheAlignment);
             for (int i = 0; i < directArenas.length; i ++) {
                 PoolArena.DirectArena arena = new PoolArena.DirectArena(this, sizeClasses);
                 directArenas[i] = arena;
                 metrics.add(arena);
             }
             directArenaMetrics = Collections.unmodifiableList(metrics);
         } else {
             directArenas = null;
             directArenaMetrics = Collections.emptyList();
         }
         metric = new PooledByteBufAllocatorMetric(this);
     }
 
     @SuppressWarnings("unchecked")
     private static <T> PoolArena<T>[] newArenaArray(int size) {
         return new PoolArena[size];
     }
 
     private static int validateAndCalculatePageShifts(int pageSize, int alignment) {
         if (pageSize < MIN_PAGE_SIZE) {
             throw new IllegalArgumentException("pageSize: " + pageSize + " (expected: " + MIN_PAGE_SIZE + ')');
         }
 
         if ((pageSize & pageSize - 1) != 0) {
             throw new IllegalArgumentException("pageSize: " + pageSize + " (expected: power of 2)");
         }
 
         if (pageSize < alignment) {
             throw new IllegalArgumentException("Alignment cannot be greater than page size. " +
                     "Alignment: " + alignment + ", page size: " + pageSize + '.');
         }
 
         // Logarithm base 2. At this point we know that pageSize is a power of two.
         return Integer.SIZE - 1 - Integer.numberOfLeadingZeros(pageSize);
     }
 
     private static int validateAndCalculateChunkSize(int pageSize, int maxOrder) {
         if (maxOrder > 14) {
             throw new IllegalArgumentException("maxOrder: " + maxOrder + " (expected: 0-14)");
         }
 
         // Ensure the resulting chunkSize does not overflow.
         int chunkSize = pageSize;
         for (int i = maxOrder; i > 0; i --) {
             if (chunkSize > MAX_CHUNK_SIZE / 2) {
                 throw new IllegalArgumentException(String.format(
                         "pageSize (%d) << maxOrder (%d) must not exceed %d", pageSize, maxOrder, MAX_CHUNK_SIZE));
             }
             chunkSize <<= 1;
         }
         return chunkSize;
     }
 
     @Override
     protected ByteBuf newHeapBuffer(int initialCapacity, int maxCapacity) {
         PoolThreadCache cache = threadCache.get();
         PoolArena<byte[]> heapArena = cache.heapArena;
 
         final ByteBuf buf;
         if (heapArena != null) {
             buf = heapArena.allocate(cache, initialCapacity, maxCapacity);
         } else {
             buf = PlatformDependent.hasUnsafe() ?
                     new UnpooledUnsafeHeapByteBuf(this, initialCapacity, maxCapacity) :
                     new UnpooledHeapByteBuf(this, initialCapacity, maxCapacity);
         }
 
         return toLeakAwareBuffer(buf);
     }
 
     @Override
     protected ByteBuf newDirectBuffer(int initialCapacity, int maxCapacity) {
         PoolThreadCache cache = threadCache.get();
         PoolArena<ByteBuffer> directArena = cache.directArena;
 
         final ByteBuf buf;
         if (directArena != null) {
             buf = directArena.allocate(cache, initialCapacity, maxCapacity);
         } else {
             buf = PlatformDependent.hasUnsafe() ?
                     UnsafeByteBufUtil.newUnsafeDirectByteBuf(this, initialCapacity, maxCapacity) :
                     new UnpooledDirectByteBuf(this, initialCapacity, maxCapacity);
         }
 
         return toLeakAwareBuffer(buf);
     }
 
     /**
      * Default number of heap arenas - System Property: io.netty.allocator.numHeapArenas - default 2 * cores
      */
     public static int defaultNumHeapArena() {
         return DEFAULT_NUM_HEAP_ARENA;
     }
 
     /**
      * Default number of direct arenas - System Property: io.netty.allocator.numDirectArenas - default 2 * cores
      */
     public static int defaultNumDirectArena() {
         return DEFAULT_NUM_DIRECT_ARENA;
     }
 
     /**
      * Default buffer page size - System Property: io.netty.allocator.pageSize - default 8192
      */
     public static int defaultPageSize() {
         return DEFAULT_PAGE_SIZE;
     }
 
     /**
      * Default maximum order - System Property: io.netty.allocator.maxOrder - default 9
      */
     public static int defaultMaxOrder() {
         return DEFAULT_MAX_ORDER;
     }
 
     /**
      * Default control creation of PoolThreadCache finalizers for FastThreadLocalThreads -
      * System Property: io.netty.allocator.disableCacheFinalizersForFastThreadLocalThreads - default false
      */
     public static boolean defaultDisableCacheFinalizersForFastThreadLocalThreads() {
         return DEFAULT_DISABLE_CACHE_FINALIZERS_FOR_FAST_THREAD_LOCAL_THREADS;
     }
 
     /**
      * Default thread caching behavior - System Property: io.netty.allocator.useCacheForAllThreads - default false
      */
     public static boolean defaultUseCacheForAllThreads() {
         return DEFAULT_USE_CACHE_FOR_ALL_THREADS;
     }
 
     /**
      * Default prefer direct - System Property: io.netty.noPreferDirect - default false
      */
     public static boolean defaultPreferDirect() {
         return PlatformDependent.directBufferPreferred();
     }
 
     /**
      * Default tiny cache size - default 0
      *
      * @deprecated Tiny caches have been merged into small caches.
      */
     @Deprecated
     public static int defaultTinyCacheSize() {
         return 0;
     }
 
     /**
      * Default small cache size - System Property: io.netty.allocator.smallCacheSize - default 256
      */
     public static int defaultSmallCacheSize() {
         return DEFAULT_SMALL_CACHE_SIZE;
     }
 
     /**
      * Default normal cache size - System Property: io.netty.allocator.normalCacheSize - default 64
      */
     public static int defaultNormalCacheSize() {
         return DEFAULT_NORMAL_CACHE_SIZE;
     }
 
     /**
      * Return {@code true} if direct memory cache alignment is supported, {@code false} otherwise.
      */
     public static boolean isDirectMemoryCacheAlignmentSupported() {
         return PlatformDependent.hasUnsafe();
     }
 
     @Override
     public boolean isDirectBufferPooled() {
         return directArenas != null;
     }
 
     /**
      * @deprecated will be removed
      * Returns {@code true} if the calling {@link Thread} has a {@link ThreadLocal} cache for the allocated
      * buffers.
      */
     @Deprecated
     public boolean hasThreadLocalCache() {
         return threadCache.isSet();
     }
 
     /**
      * @deprecated will be removed
      * Free all cached buffers for the calling {@link Thread}.
      */
     @Deprecated
     public void freeThreadLocalCache() {
         threadCache.remove();
     }
 
     private final class PoolThreadLocalCache extends FastThreadLocal<PoolThreadCache> {
         private final boolean useCacheForAllThreads;
 
         PoolThreadLocalCache(boolean useCacheForAllThreads) {
             this.useCacheForAllThreads = useCacheForAllThreads;
         }
 
         @Override
         protected synchronized PoolThreadCache initialValue() {
             final PoolArena<byte[]> heapArena = leastUsedArena(heapArenas);
             final PoolArena<ByteBuffer> directArena = leastUsedArena(directArenas);
 
             final Thread current = Thread.currentThread();
             final EventExecutor executor = ThreadExecutorMap.currentExecutor();
 
             if (useCacheForAllThreads ||
                     // If the current thread is a FastThreadLocalThread we will always use the cache
                     current instanceof FastThreadLocalThread ||
                     // The Thread is used by an EventExecutor, let's use the cache as the chances are good that we
                     // will allocate a lot!
                     executor != null) {
                 final PoolThreadCache cache = new PoolThreadCache(
                         heapArena, directArena, smallCacheSize, normalCacheSize,
                         DEFAULT_MAX_CACHED_BUFFER_CAPACITY, DEFAULT_CACHE_TRIM_INTERVAL, useCacheFinalizers(current));
 
                 if (DEFAULT_CACHE_TRIM_INTERVAL_MILLIS > 0) {
                     if (executor != null) {
                         executor.scheduleAtFixedRate(trimTask, DEFAULT_CACHE_TRIM_INTERVAL_MILLIS,
                                 DEFAULT_CACHE_TRIM_INTERVAL_MILLIS, TimeUnit.MILLISECONDS);
                     }
                 }
                 return cache;
             }
             // No caching so just use 0 as sizes.
             return new PoolThreadCache(heapArena, directArena, 0, 0, 0, 0, false);
         }
 
         @Override
         protected void onRemoval(PoolThreadCache threadCache) {
             threadCache.free(false);
         }
 
         private <T> PoolArena<T> leastUsedArena(PoolArena<T>[] arenas) {
             if (arenas == null || arenas.length == 0) {
                 return null;
             }
 
             PoolArena<T> minArena = arenas[0];
             //optimized
             //If it is the first execution, directly return minarena and reduce the number of for loop comparisons below
             if (minArena.numThreadCaches.get() == CACHE_NOT_USED) {
                 return minArena;
             }
             for (int i = 1; i < arenas.length; i++) {
                 PoolArena<T> arena = arenas[i];
                 if (arena.numThreadCaches.get() < minArena.numThreadCaches.get()) {
                     minArena = arena;
                 }
             }
 
             return minArena;
         }
     }
 
     private static boolean useCacheFinalizers(Thread current) {
         if (!defaultDisableCacheFinalizersForFastThreadLocalThreads()) {
             return true;
         }
         return current instanceof FastThreadLocalThread &&
                ((FastThreadLocalThread) current).willCleanupFastThreadLocals();
     }
 
     @Override
     public PooledByteBufAllocatorMetric metric() {
         return metric;
     }
 
     /**
      * Return the number of heap arenas.
      *
      * @deprecated use {@link PooledByteBufAllocatorMetric#numHeapArenas()}.
      */
     @Deprecated
     public int numHeapArenas() {
         return heapArenaMetrics.size();
     }
 
     /**
      * Return the number of direct arenas.
      *
      * @deprecated use {@link PooledByteBufAllocatorMetric#numDirectArenas()}.
      */
     @Deprecated
     public int numDirectArenas() {
         return directArenaMetrics.size();
     }
 
     /**
      * Return a {@link List} of all heap {@link PoolArenaMetric}s that are provided by this pool.
      *
      * @deprecated use {@link PooledByteBufAllocatorMetric#heapArenas()}.
      */
     @Deprecated
     public List<PoolArenaMetric> heapArenas() {
         return heapArenaMetrics;
     }
 
     /**
      * Return a {@link List} of all direct {@link PoolArenaMetric}s that are provided by this pool.
      *
      * @deprecated use {@link PooledByteBufAllocatorMetric#directArenas()}.
      */
     @Deprecated
     public List<PoolArenaMetric> directArenas() {
         return directArenaMetrics;
     }
 
     /**
      * Return the number of thread local caches used by this {@link PooledByteBufAllocator}.
      *
      * @deprecated use {@link PooledByteBufAllocatorMetric#numThreadLocalCaches()}.
      */
     @Deprecated
     public int numThreadLocalCaches() {
         PoolArena<?>[] arenas = heapArenas != null ? heapArenas : directArenas;
         if (arenas == null) {
             return 0;
         }
 
         int total = 0;
         for (PoolArena<?> arena : arenas) {
             total += arena.numThreadCaches.get();
         }
 
         return total;
     }
 
     /**
      * Return the size of the tiny cache.
      *
      * @deprecated use {@link PooledByteBufAllocatorMetric#tinyCacheSize()}.
      */
     @Deprecated
     public int tinyCacheSize() {
         return 0;
     }
 
     /**
      * Return the size of the small cache.
      *
      * @deprecated use {@link PooledByteBufAllocatorMetric#smallCacheSize()}.
      */
     @Deprecated
     public int smallCacheSize() {
         return smallCacheSize;
     }
 
     /**
      * Return the size of the normal cache.
      *
      * @deprecated use {@link PooledByteBufAllocatorMetric#normalCacheSize()}.
      */
     @Deprecated
     public int normalCacheSize() {
         return normalCacheSize;
     }
 
     /**
      * Return the chunk size for an arena.
      *
      * @deprecated use {@link PooledByteBufAllocatorMetric#chunkSize()}.
      */
     @Deprecated
     public final int chunkSize() {
         return chunkSize;
     }
 
     final long usedHeapMemory() {
         return usedMemory(heapArenas);
     }
 
     final long usedDirectMemory() {
         return usedMemory(directArenas);
     }
 
     private static long usedMemory(PoolArena<?>[] arenas) {
         if (arenas == null) {
             return -1;
         }
         long used = 0;
         for (PoolArena<?> arena : arenas) {
             used += arena.numActiveBytes();
             if (used < 0) {
                 return Long.MAX_VALUE;
             }
         }
         return used;
     }
 
     /**
      * Returns the number of bytes of heap memory that is currently pinned to heap buffers allocated by a
      * {@link ByteBufAllocator}, or {@code -1} if unknown.
      * A buffer can pin more memory than its {@linkplain ByteBuf#capacity() capacity} might indicate,
      * due to implementation details of the allocator.
      */
     public final long pinnedHeapMemory() {
         return pinnedMemory(heapArenas);
     }
 
     /**
      * Returns the number of bytes of direct memory that is currently pinned to direct buffers allocated by a
      * {@link ByteBufAllocator}, or {@code -1} if unknown.
      * A buffer can pin more memory than its {@linkplain ByteBuf#capacity() capacity} might indicate,
      * due to implementation details of the allocator.
      */
     public final long pinnedDirectMemory() {
         return pinnedMemory(directArenas);
     }
 
     private static long pinnedMemory(PoolArena<?>[] arenas) {
         if (arenas == null) {
             return -1;
         }
         long used = 0;
         for (PoolArena<?> arena : arenas) {
             used += arena.numPinnedBytes();
             if (used < 0) {
                 return Long.MAX_VALUE;
             }
         }
         return used;
     }
 
     final PoolThreadCache threadCache() {
         PoolThreadCache cache =  threadCache.get();
         assert cache != null;
         return cache;
     }
 
     /**
      * Trim thread local cache for the current {@link Thread}, which will give back any cached memory that was not
      * allocated frequently since the last trim operation.
      *
      * Returns {@code true} if a cache for the current {@link Thread} exists and so was trimmed, false otherwise.
      */
     public boolean trimCurrentThreadCache() {
         PoolThreadCache cache = threadCache.getIfExists();
         if (cache != null) {
             cache.trim();
             return true;
         }
         return false;
     }
 
     /**
      * Returns the status of the allocator (which contains all metrics) as string. Be aware this may be expensive
      * and so should not called too frequently.
      */
     public String dumpStats() {
         int heapArenasLen = heapArenas == null ? 0 : heapArenas.length;
         StringBuilder buf = new StringBuilder(512)
                 .append(heapArenasLen)
                 .append(" heap arena(s):")
                 .append(StringUtil.NEWLINE);
         if (heapArenasLen > 0) {
             for (PoolArena<byte[]> a: heapArenas) {
                 buf.append(a);
             }
         }
 
         int directArenasLen = directArenas == null ? 0 : directArenas.length;
 
         buf.append(directArenasLen)
            .append(" direct arena(s):")
            .append(StringUtil.NEWLINE);
         if (directArenasLen > 0) {
             for (PoolArena<ByteBuffer> a: directArenas) {
                 buf.append(a);
             }
         }
 
         return buf.toString();
     }
 }