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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:
*
* http://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 org.glowroot.shaded.netty.buffer;
final class PoolSubpage implements PoolSubpageMetric {
final PoolChunk chunk;
private final int memoryMapIdx;
private final int runOffset;
private final int pageSize;
private final long[] bitmap;
PoolSubpage prev;
PoolSubpage next;
boolean doNotDestroy;
int elemSize;
private int maxNumElems;
private int bitmapLength;
private int nextAvail;
private int numAvail;
// TODO: Test if adding padding helps under contention
//private long pad0, pad1, pad2, pad3, pad4, pad5, pad6, pad7;
/** Special constructor that creates a linked list head */
PoolSubpage(int pageSize) {
chunk = null;
memoryMapIdx = -1;
runOffset = -1;
elemSize = -1;
this.pageSize = pageSize;
bitmap = null;
}
PoolSubpage(PoolChunk chunk, int memoryMapIdx, int runOffset, int pageSize, int elemSize) {
this.chunk = chunk;
this.memoryMapIdx = memoryMapIdx;
this.runOffset = runOffset;
this.pageSize = pageSize;
bitmap = new long[pageSize >>> 10]; // pageSize / 16 / 64
init(elemSize);
}
void init(int elemSize) {
doNotDestroy = true;
this.elemSize = elemSize;
if (elemSize != 0) {
maxNumElems = numAvail = pageSize / elemSize;
nextAvail = 0;
bitmapLength = maxNumElems >>> 6;
if ((maxNumElems & 63) != 0) {
bitmapLength ++;
}
for (int i = 0; i < bitmapLength; i ++) {
bitmap[i] = 0;
}
}
PoolSubpage head = chunk.arena.findSubpagePoolHead(elemSize);
synchronized (head) {
addToPool(head);
}
}
/**
* Returns the bitmap index of the subpage allocation.
*/
long allocate() {
if (elemSize == 0) {
return toHandle(0);
}
/**
* Synchronize on the head of the SubpagePool stored in the {@link PoolArena. This is needed as we synchronize
* on it when calling {@link PoolArena#allocate(PoolThreadCache, int, int)} und try to allocate out of the
* {@link PoolSubpage} pool for a given size.
*/
PoolSubpage head = chunk.arena.findSubpagePoolHead(elemSize);
synchronized (head) {
if (numAvail == 0 || !doNotDestroy) {
return -1;
}
final int bitmapIdx = getNextAvail();
int q = bitmapIdx >>> 6;
int r = bitmapIdx & 63;
assert (bitmap[q] >>> r & 1) == 0;
bitmap[q] |= 1L << r;
if (-- numAvail == 0) {
removeFromPool();
}
return toHandle(bitmapIdx);
}
}
/**
* @return {@code true} if this subpage is in use.
* {@code false} if this subpage is not used by its chunk and thus it's OK to be released.
*/
boolean free(int bitmapIdx) {
if (elemSize == 0) {
return true;
}
/**
* Synchronize on the head of the SubpagePool stored in the {@link PoolArena. This is needed as we synchronize
* on it when calling {@link PoolArena#allocate(PoolThreadCache, int, int)} und try to allocate out of the
* {@link PoolSubpage} pool for a given size.
*/
PoolSubpage head = chunk.arena.findSubpagePoolHead(elemSize);
synchronized (head) {
int q = bitmapIdx >>> 6;
int r = bitmapIdx & 63;
assert (bitmap[q] >>> r & 1) != 0;
bitmap[q] ^= 1L << r;
setNextAvail(bitmapIdx);
if (numAvail ++ == 0) {
addToPool(head);
return true;
}
if (numAvail != maxNumElems) {
return true;
} else {
// Subpage not in use (numAvail == maxNumElems)
if (prev == next) {
// Do not remove if this subpage is the only one left in the pool.
return true;
}
// Remove this subpage from the pool if there are other subpages left in the pool.
doNotDestroy = false;
removeFromPool();
return false;
}
}
}
private void addToPool(PoolSubpage head) {
assert prev == null && next == null;
prev = head;
next = head.next;
next.prev = this;
head.next = this;
}
private void removeFromPool() {
assert prev != null && next != null;
prev.next = next;
next.prev = prev;
next = null;
prev = null;
}
private void setNextAvail(int bitmapIdx) {
nextAvail = bitmapIdx;
}
private int getNextAvail() {
int nextAvail = this.nextAvail;
if (nextAvail >= 0) {
this.nextAvail = -1;
return nextAvail;
}
return findNextAvail();
}
private int findNextAvail() {
final long[] bitmap = this.bitmap;
final int bitmapLength = this.bitmapLength;
for (int i = 0; i < bitmapLength; i ++) {
long bits = bitmap[i];
if (~bits != 0) {
return findNextAvail0(i, bits);
}
}
return -1;
}
private int findNextAvail0(int i, long bits) {
final int maxNumElems = this.maxNumElems;
final int baseVal = i << 6;
for (int j = 0; j < 64; j ++) {
if ((bits & 1) == 0) {
int val = baseVal | j;
if (val < maxNumElems) {
return val;
} else {
break;
}
}
bits >>>= 1;
}
return -1;
}
private long toHandle(int bitmapIdx) {
return 0x4000000000000000L | (long) bitmapIdx << 32 | memoryMapIdx;
}
@Override
public String toString() {
if (!doNotDestroy) {
return "(" + memoryMapIdx + ": not in use)";
}
return String.valueOf('(') + memoryMapIdx + ": " + (maxNumElems - numAvail) + '/' + maxNumElems +
", offset: " + runOffset + ", length: " + pageSize + ", elemSize: " + elemSize + ')';
}
@Override
public int maxNumElements() {
return maxNumElems;
}
@Override
public int numAvailable() {
return numAvail;
}
@Override
public int elementSize() {
return elemSize;
}
@Override
public int pageSize() {
return pageSize;
}
}