2012-12-05 22:11:48 +01:00
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/*
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* Copyright 2012 The Netty Project
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*
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* The Netty Project licenses this file to you under the Apache License,
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* version 2.0 (the "License"); you may not use this file except in compliance
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* with the License. You may obtain a copy of the License at:
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
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* WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
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* License for the specific language governing permissions and limitations
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* under the License.
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*/
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package io.netty.buffer;
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final class PoolSubpage<T> {
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final PoolChunk<T> chunk;
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final int memoryMapIdx;
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final int runOffset;
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final int pageSize;
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final long[] bitmap;
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2013-03-05 15:55:41 +01:00
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PoolSubpage<T> prev;
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PoolSubpage<T> next;
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2012-12-05 22:11:48 +01:00
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boolean doNotDestroy;
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int elemSize;
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int maxNumElems;
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int nextAvail;
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int bitmapLength;
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int numAvail;
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// TODO: Test if adding padding helps under contention
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//private long pad0, pad1, pad2, pad3, pad4, pad5, pad6, pad7;
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2013-03-05 15:55:41 +01:00
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/** Special constructor that creates a linked list head */
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PoolSubpage(int pageSize) {
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chunk = null;
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memoryMapIdx = -1;
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runOffset = -1;
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elemSize = -1;
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this.pageSize = pageSize;
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bitmap = null;
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}
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2012-12-05 22:11:48 +01:00
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PoolSubpage(PoolChunk<T> chunk, int memoryMapIdx, int runOffset, int pageSize, int elemSize) {
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this.chunk = chunk;
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this.memoryMapIdx = memoryMapIdx;
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this.runOffset = runOffset;
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this.pageSize = pageSize;
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bitmap = new long[pageSize >>> 10]; // pageSize / 16 / 64
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init(elemSize);
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}
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void init(int elemSize) {
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doNotDestroy = true;
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this.elemSize = elemSize;
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2013-03-05 15:55:41 +01:00
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if (elemSize != 0) {
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maxNumElems = numAvail = pageSize / elemSize;
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nextAvail = 0;
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bitmapLength = maxNumElems >>> 6;
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if ((maxNumElems & 63) != 0) {
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bitmapLength ++;
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}
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for (int i = 0; i < bitmapLength; i ++) {
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bitmap[i] = 0;
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}
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2012-12-05 22:11:48 +01:00
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}
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2013-03-05 15:55:41 +01:00
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addToPool();
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2012-12-05 22:11:48 +01:00
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}
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/**
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* Returns the bitmap index of the subpage allocation.
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*/
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long allocate() {
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if (elemSize == 0) {
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return toHandle(0);
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}
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if (numAvail == 0 || !doNotDestroy) {
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return -1;
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}
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final int bitmapIdx = nextAvail;
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int q = bitmapIdx >>> 6;
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int r = bitmapIdx & 63;
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assert (bitmap[q] >>> r & 1) == 0;
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bitmap[q] |= 1L << r;
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if (-- numAvail == 0) {
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2013-03-05 15:55:41 +01:00
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removeFromPool();
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2012-12-05 22:11:48 +01:00
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nextAvail = -1;
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} else {
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nextAvail = findNextAvailable();
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}
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return toHandle(bitmapIdx);
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}
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/**
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* @return {@code true} if this subpage is in use.
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* {@code false} if this subpage is not used by its chunk and thus it's OK to be released.
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*/
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boolean free(int bitmapIdx) {
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if (elemSize == 0) {
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return true;
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}
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int q = bitmapIdx >>> 6;
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int r = bitmapIdx & 63;
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assert (bitmap[q] >>> r & 1) != 0;
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bitmap[q] ^= 1L << r;
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if (numAvail ++ == 0) {
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nextAvail = bitmapIdx;
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2013-03-05 15:55:41 +01:00
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addToPool();
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2012-12-05 22:11:48 +01:00
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return true;
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}
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if (numAvail < maxNumElems) {
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return true;
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} else {
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doNotDestroy = false;
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2013-03-05 15:55:41 +01:00
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removeFromPool();
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2012-12-05 22:11:48 +01:00
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return false;
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}
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}
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2013-03-05 15:55:41 +01:00
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private void addToPool() {
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PoolSubpage<T> head = chunk.arena.findSubpagePoolHead(elemSize);
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assert prev == null && next == null;
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prev = head;
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next = head.next;
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next.prev = this;
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head.next = this;
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}
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private void removeFromPool() {
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assert prev != null && next != null;
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prev.next = next;
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next.prev = prev;
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next = null;
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prev = null;
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}
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2012-12-05 22:11:48 +01:00
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private int findNextAvailable() {
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int newNextAvail = -1;
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loop:
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for (int i = 0; i < bitmapLength; i ++) {
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long bits = bitmap[i];
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if (~bits != 0) {
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for (int j = 0; j < 64; j ++) {
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if ((bits & 1) == 0) {
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newNextAvail = i << 6 | j;
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break loop;
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}
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bits >>>= 1;
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}
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}
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}
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if (newNextAvail < maxNumElems) {
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return newNextAvail;
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} else {
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return -1;
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}
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}
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private long toHandle(int bitmapIdx) {
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return 0x4000000000000000L | (long) bitmapIdx << 32 | memoryMapIdx;
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}
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public String toString() {
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if (!doNotDestroy) {
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return "(" + memoryMapIdx + ": not in use)";
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}
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return String.valueOf('(') + memoryMapIdx + ": " + (maxNumElems - numAvail) + '/' + maxNumElems +
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", offset: " + runOffset + ", length: " + pageSize + ", elemSize: " + elemSize + ')';
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}
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}
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