io.netty.buffer.PoolSubpage Maven / Gradle / Ivy
/*
* 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.buffer.PoolChunk.RUN_OFFSET_SHIFT;
import static io.netty.buffer.PoolChunk.SIZE_SHIFT;
import static io.netty.buffer.PoolChunk.IS_USED_SHIFT;
import static io.netty.buffer.PoolChunk.IS_SUBPAGE_SHIFT;
import static io.netty.buffer.SizeClasses.LOG2_QUANTUM;
final class PoolSubpage implements PoolSubpageMetric {
final PoolChunk chunk;
final int elemSize;
private final int pageShifts;
private final int runOffset;
private final int runSize;
private final long[] bitmap;
PoolSubpage prev;
PoolSubpage next;
boolean doNotDestroy;
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() {
chunk = null;
pageShifts = -1;
runOffset = -1;
elemSize = -1;
runSize = -1;
bitmap = null;
}
PoolSubpage(PoolSubpage head, PoolChunk chunk, int pageShifts, int runOffset, int runSize, int elemSize) {
this.chunk = chunk;
this.pageShifts = pageShifts;
this.runOffset = runOffset;
this.runSize = runSize;
this.elemSize = elemSize;
bitmap = new long[runSize >>> 6 + LOG2_QUANTUM]; // runSize / 64 / QUANTUM
doNotDestroy = true;
if (elemSize != 0) {
maxNumElems = numAvail = runSize / elemSize;
nextAvail = 0;
bitmapLength = maxNumElems >>> 6;
if ((maxNumElems & 63) != 0) {
bitmapLength ++;
}
for (int i = 0; i < bitmapLength; i ++) {
bitmap[i] = 0;
}
}
addToPool(head);
}
/**
* Returns the bitmap index of the subpage allocation.
*/
long allocate() {
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(PoolSubpage head, int bitmapIdx) {
if (elemSize == 0) {
return true;
}
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);
/* When maxNumElems == 1, the maximum numAvail is also 1.
* Each of these PoolSubpages will go in here when they do free operation.
* If they return true directly from here, then the rest of the code will be unreachable
* and they will not actually be recycled. So return true only on maxNumElems > 1. */
if (maxNumElems > 1) {
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) {
int pages = runSize >> pageShifts;
return (long) runOffset << RUN_OFFSET_SHIFT
| (long) pages << SIZE_SHIFT
| 1L << IS_USED_SHIFT
| 1L << IS_SUBPAGE_SHIFT
| bitmapIdx;
}
@Override
public String toString() {
final boolean doNotDestroy;
final int maxNumElems;
final int numAvail;
final int elemSize;
if (chunk == null) {
// This is the head so there is no need to synchronize at all as these never change.
doNotDestroy = true;
maxNumElems = 0;
numAvail = 0;
elemSize = -1;
} else {
synchronized (chunk.arena) {
if (!this.doNotDestroy) {
doNotDestroy = false;
// Not used for creating the String.
maxNumElems = numAvail = elemSize = -1;
} else {
doNotDestroy = true;
maxNumElems = this.maxNumElems;
numAvail = this.numAvail;
elemSize = this.elemSize;
}
}
}
if (!doNotDestroy) {
return "(" + runOffset + ": not in use)";
}
return "(" + runOffset + ": " + (maxNumElems - numAvail) + '/' + maxNumElems +
", offset: " + runOffset + ", length: " + runSize + ", elemSize: " + elemSize + ')';
}
@Override
public int maxNumElements() {
if (chunk == null) {
// It's the head.
return 0;
}
synchronized (chunk.arena) {
return maxNumElems;
}
}
@Override
public int numAvailable() {
if (chunk == null) {
// It's the head.
return 0;
}
synchronized (chunk.arena) {
return numAvail;
}
}
@Override
public int elementSize() {
if (chunk == null) {
// It's the head.
return -1;
}
synchronized (chunk.arena) {
return elemSize;
}
}
@Override
public int pageSize() {
return 1 << pageShifts;
}
void destroy() {
if (chunk != null) {
chunk.destroy();
}
}
}
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