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   /*
    * 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 io.netty.util.internal.StringUtil;
  
  import java.util.ArrayList;
  import java.util.Collections;
  import java.util.Iterator;
  import java.util.List;
  
  import static java.lang.Math.*;
  
  import java.nio.ByteBuffer;
  
  final class PoolChunkList<T> implements PoolChunkListMetric {
      private static final Iterator<PoolChunkMetric> EMPTY_METRICS = Collections.<PoolChunkMetric>emptyList().iterator();
      private final PoolArena<T> arena;
      private final PoolChunkList<T> nextList;
      private final int minUsage;
      private final int maxUsage;
      private final int maxCapacity;
      private PoolChunk<T> head;
      private final int freeMinThreshold;
      private final int freeMaxThreshold;
  
      // This is only update once when create the linked like list of PoolChunkList in PoolArena constructor.
      private PoolChunkList<T> prevList;
  
      // TODO: Test if adding padding helps under contention
      //private long pad0, pad1, pad2, pad3, pad4, pad5, pad6, pad7;
  
      PoolChunkList(PoolArena<T> arena, PoolChunkList<T> nextList, int minUsage, int maxUsage, int chunkSize) {
          assert minUsage <= maxUsage;
          this.arena = arena;
          this.nextList = nextList;
          this.minUsage = minUsage;
          this.maxUsage = maxUsage;
          maxCapacity = calculateMaxCapacity(minUsage, chunkSize);
  
          // the thresholds are aligned with PoolChunk.usage() logic:
          // 1) basic logic: usage() = 100 - freeBytes * 100L / chunkSize
          //    so, for example: (usage() >= maxUsage) condition can be transformed in the following way:
          //      100 - freeBytes * 100L / chunkSize >= maxUsage
          //      freeBytes <= chunkSize * (100 - maxUsage) / 100
          //      let freeMinThreshold = chunkSize * (100 - maxUsage) / 100, then freeBytes <= freeMinThreshold
          //
          //  2) usage() returns an int value and has a floor rounding during a calculation,
          //     to be aligned absolute thresholds should be shifted for "the rounding step":
          //       freeBytes * 100 / chunkSize < 1
          //       the condition can be converted to: freeBytes < 1 * chunkSize / 100
          //     this is why we have + 0.99999999 shifts. A example why just +1 shift cannot be used:
          //       freeBytes = 16777216 == freeMaxThreshold: 16777216, usage = 0 < minUsage: 1, chunkSize: 16777216
          //     At the same time we want to have zero thresholds in case of (maxUsage == 100) and (minUsage == 100).
          //
          freeMinThreshold = (maxUsage == 100) ? 0 : (int) (chunkSize * (100.0 - maxUsage + 0.99999999) / 100L);
          freeMaxThreshold = (minUsage == 100) ? 0 : (int) (chunkSize * (100.0 - minUsage + 0.99999999) / 100L);
      }
  
      /**
       * Calculates the maximum capacity of a buffer that will ever be possible to allocate out of the {@link PoolChunk}s
       * that belong to the {@link PoolChunkList} with the given {@code minUsage} and {@code maxUsage} settings.
       */
      private static int calculateMaxCapacity(int minUsage, int chunkSize) {
          minUsage = minUsage0(minUsage);
  
          if (minUsage == 100) {
              // If the minUsage is 100 we can not allocate anything out of this list.
              return 0;
          }
  
          // Calculate the maximum amount of bytes that can be allocated from a PoolChunk in this PoolChunkList.
          //
          // As an example:
          // - If a PoolChunkList has minUsage == 25 we are allowed to allocate at most 75% of the chunkSize because
          //   this is the maximum amount available in any PoolChunk in this PoolChunkList.
          return  (int) (chunkSize * (100L - minUsage) / 100L);
      }
  
      void prevList(PoolChunkList<T> prevList) {
          assert this.prevList == null;
          this.prevList = prevList;
      }
  
      boolean allocate(PooledByteBuf<T> buf, int reqCapacity, int sizeIdx, PoolThreadCache threadCache) {
         int normCapacity = arena.sizeClass.sizeIdx2size(sizeIdx);
         if (normCapacity > maxCapacity) {
             // Either this PoolChunkList is empty or the requested capacity is larger then the capacity which can
             // be handled by the PoolChunks that are contained in this PoolChunkList.
             return false;
         }
 
         for (PoolChunk<T> cur = head; cur != null; cur = cur.next) {
             if (cur.allocate(buf, reqCapacity, sizeIdx, threadCache)) {
                 if (cur.freeBytes <= freeMinThreshold) {
                     remove(cur);
                     nextList.add(cur);
                 }
                 return true;
             }
         }
         return false;
     }
 
     boolean free(PoolChunk<T> chunk, long handle, int normCapacity, ByteBuffer nioBuffer) {
         chunk.free(handle, normCapacity, nioBuffer);
         if (chunk.freeBytes > freeMaxThreshold) {
             remove(chunk);
             // Move the PoolChunk down the PoolChunkList linked-list.
             return move0(chunk);
         }
         return true;
     }
 
     private boolean move(PoolChunk<T> chunk) {
         assert chunk.usage() < maxUsage;
 
         if (chunk.freeBytes > freeMaxThreshold) {
             // Move the PoolChunk down the PoolChunkList linked-list.
             return move0(chunk);
         }
 
         // PoolChunk fits into this PoolChunkList, adding it here.
         add0(chunk);
         return true;
     }
 
     /**
      * Moves the {@link PoolChunk} down the {@link PoolChunkList} linked-list so it will end up in the right
      * {@link PoolChunkList} that has the correct minUsage / maxUsage in respect to {@link PoolChunk#usage()}.
      */
     private boolean move0(PoolChunk<T> chunk) {
         if (prevList == null) {
             // There is no previous PoolChunkList so return false which result in having the PoolChunk destroyed and
             // all memory associated with the PoolChunk will be released.
             assert chunk.usage() == 0;
             return false;
         }
         return prevList.move(chunk);
     }
 
     void add(PoolChunk<T> chunk) {
         if (chunk.freeBytes <= freeMinThreshold) {
             nextList.add(chunk);
             return;
         }
         add0(chunk);
     }
 
     /**
      * Adds the {@link PoolChunk} to this {@link PoolChunkList}.
      */
     void add0(PoolChunk<T> chunk) {
         chunk.parent = this;
         if (head == null) {
             head = chunk;
             chunk.prev = null;
             chunk.next = null;
         } else {
             chunk.prev = null;
             chunk.next = head;
             head.prev = chunk;
             head = chunk;
         }
     }
 
     private void remove(PoolChunk<T> cur) {
         if (cur == head) {
             head = cur.next;
             if (head != null) {
                 head.prev = null;
             }
         } else {
             PoolChunk<T> next = cur.next;
             cur.prev.next = next;
             if (next != null) {
                 next.prev = cur.prev;
             }
         }
     }
 
     @Override
     public int minUsage() {
         return minUsage0(minUsage);
     }
 
     @Override
     public int maxUsage() {
         return min(maxUsage, 100);
     }
 
     private static int minUsage0(int value) {
         return max(1, value);
     }
 
     @Override
     public Iterator<PoolChunkMetric> iterator() {
         arena.lock();
         try {
             if (head == null) {
                 return EMPTY_METRICS;
             }
             List<PoolChunkMetric> metrics = new ArrayList<PoolChunkMetric>();
             for (PoolChunk<T> cur = head;;) {
                 metrics.add(cur);
                 cur = cur.next;
                 if (cur == null) {
                     break;
                 }
             }
             return metrics.iterator();
         } finally {
             arena.unlock();
         }
     }
 
     @Override
     public String toString() {
         StringBuilder buf = new StringBuilder();
         arena.lock();
         try {
             if (head == null) {
                 return "none";
             }
 
             for (PoolChunk<T> cur = head;;) {
                 buf.append(cur);
                 cur = cur.next;
                 if (cur == null) {
                     break;
                 }
                 buf.append(StringUtil.NEWLINE);
             }
         } finally {
             arena.unlock();
         }
         return buf.toString();
     }
 
     void destroy(PoolArena<T> arena) {
         PoolChunk<T> chunk = head;
         while (chunk != null) {
             arena.destroyChunk(chunk);
             chunk = chunk.next;
         }
         head = null;
     }
 }