PoolChunk.java — netty Source File

Source Code

/*
 * 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.CleanableDirectBuffer;
import io.netty.util.internal.LongLongHashMap;
import io.netty.util.internal.SystemPropertyUtil;

import java.nio.ByteBuffer;
import java.util.ArrayDeque;
import java.util.Deque;
import java.util.PriorityQueue;
import java.util.concurrent.atomic.LongAdder;
import java.util.concurrent.locks.ReentrantLock;

/**
 * Description of algorithm for PageRun/PoolSubpage allocation from PoolChunk
 *
 * Notation: The following terms are important to understand the code
 * > page  - a page is the smallest unit of memory chunk that can be allocated
 * > run   - a run is a collection of pages
 * > chunk - a chunk is a collection of runs
 * > in this code chunkSize = maxPages * pageSize
 *
 * To begin we allocate a byte array of size = chunkSize
 * Whenever a ByteBuf of given size needs to be created we search for the first position
 * in the byte array that has enough empty space to accommodate the requested size and
 * return a (long) handle that encodes this offset information, (this memory segment is then
 * marked as reserved so it is always used by exactly one ByteBuf and no more)
 *
 * For simplicity all sizes are normalized according to {@link PoolArena#sizeClass#size2SizeIdx(int)} method.
 * This ensures that when we request for memory segments of size > pageSize the normalizedCapacity
 * equals the next nearest size in {@link SizeClasses}.
 *
 *
 *  A chunk has the following layout:
 *
 *     /-----------------\
 *     | run             |
 *     |                 |
 *     |                 |
 *     |-----------------|
 *     | run             |
 *     |                 |
 *     |-----------------|
 *     | unalloctated    |
 *     | (freed)         |
// ... (680 more lines)