poolthreadcache源码阅读

package io.netty.buffer;


import io.netty.buffer.PoolArena.SizeClass;
import io.netty.util.Recycler;
import io.netty.util.Recycler.Handle;
import io.netty.util.internal.MathUtil;
import io.netty.util.internal.PlatformDependent;
import io.netty.util.internal.logging.InternalLogger;
import io.netty.util.internal.logging.InternalLoggerFactory;

import java.nio.ByteBuffer;
import java.util.Queue;

/**
* Acts a Thread cache for allocations. This implementation is moduled after
* <a href="http://people.freebsd.org/~jasone/jemalloc/bsdcan2006/jemalloc.pdf">jemalloc</a> and the descripted
* technics of
* <a href="https://www.facebook.com/notes/facebook-engineering/scalable-memory-allocation-using-jemalloc/480222803919">
* Scalable memory allocation using jemalloc</a>.
*/
final class PoolThreadCache {

private static final InternalLogger logger = InternalLoggerFactory.getInstance(PoolThreadCache.class);

final PoolArena<byte[]> heapArena;
final PoolArena<ByteBuffer> directArena;

// Hold the caches for the different size classes, which are tiny, small and normal.
private final MemoryRegionCache<byte[]>[] tinySubPageHeapCaches;
private final MemoryRegionCache<byte[]>[] smallSubPageHeapCaches;
private final MemoryRegionCache<ByteBuffer>[] tinySubPageDirectCaches;
private final MemoryRegionCache<ByteBuffer>[] smallSubPageDirectCaches;
private final MemoryRegionCache<byte[]>[] normalHeapCaches;
private final MemoryRegionCache<ByteBuffer>[] normalDirectCaches;

// Used for bitshifting when calculate the index of normal caches later
private final int numShiftsNormalDirect;
private final int numShiftsNormalHeap;
private final int freeSweepAllocationThreshold;

private int allocations;

// TODO: Test if adding padding helps under contention
//private long pad0, pad1, pad2, pad3, pad4, pad5, pad6, pad7;

/**
* tinyCacheSize 的默认值为 512
* smallCacheSize 的默认值为 256
* normalCacheSize 的默认值为 64
*/
PoolThreadCache(PoolArena<byte[]> heapArena, PoolArena<ByteBuffer> directArena,
int tinyCacheSize, int smallCacheSize, int normalCacheSize,
int maxCachedBufferCapacity, int freeSweepAllocationThreshold) {
if (maxCachedBufferCapacity < 0) {
throw new IllegalArgumentException("maxCachedBufferCapacity: "
+ maxCachedBufferCapacity + " (expected: >= 0)");
}
this.freeSweepAllocationThreshold = freeSweepAllocationThreshold;
this.heapArena = heapArena;
this.directArena = directArena;
if (directArena != null) {
tinySubPageDirectCaches = createSubPageCaches(
tinyCacheSize, PoolArena.numTinySubpagePools, SizeClass.Tiny);
smallSubPageDirectCaches = createSubPageCaches(
smallCacheSize, directArena.numSmallSubpagePools, SizeClass.Small);

numShiftsNormalDirect = log2(directArena.pageSize);
normalDirectCaches = createNormalCaches(
normalCacheSize, maxCachedBufferCapacity, directArena);

directArena.numThreadCaches.getAndIncrement();
} else {
// No directArea is configured so just null out all caches
tinySubPageDirectCaches = null;
smallSubPageDirectCaches = null;
normalDirectCaches = null;
numShiftsNormalDirect = -1;
}
if (heapArena != null) {
// Create the caches for the heap allocations
tinySubPageHeapCaches = createSubPageCaches(
tinyCacheSize, PoolArena.numTinySubpagePools, SizeClass.Tiny);
smallSubPageHeapCaches = createSubPageCaches(
smallCacheSize, heapArena.numSmallSubpagePools, SizeClass.Small);

numShiftsNormalHeap = log2(heapArena.pageSize);
normalHeapCaches = createNormalCaches(
normalCacheSize, maxCachedBufferCapacity, heapArena);

heapArena.numThreadCaches.getAndIncrement();
} else {
// No heapArea is configured so just null out all caches
tinySubPageHeapCaches = null;
smallSubPageHeapCaches = null;
normalHeapCaches = null;
numShiftsNormalHeap = -1;
}

// Only check if there are caches in use.
if ((tinySubPageDirectCaches != null || smallSubPageDirectCaches != null || normalDirectCaches != null
|| tinySubPageHeapCaches != null || smallSubPageHeapCaches != null || normalHeapCaches != null)
&& freeSweepAllocationThreshold < 1) {
throw new IllegalArgumentException("freeSweepAllocationThreshold: "
+ freeSweepAllocationThreshold + " (expected: > 0)");
}
}

private static <T> MemoryRegionCache<T>[] createSubPageCaches(
int cacheSize, int numCaches, SizeClass sizeClass) {
if (cacheSize > 0 && numCaches > 0) {
@SuppressWarnings("unchecked")
MemoryRegionCache<T>[] cache = new MemoryRegionCache[numCaches];
for (int i = 0; i < cache.length; i++) {
// TODO: maybe use cacheSize / cache.length
cache[i] = new SubPageMemoryRegionCache<T>(cacheSize, sizeClass);
}
return cache;
} else {
return null;
}
}

private static <T> MemoryRegionCache<T>[] createNormalCaches(
int cacheSize, int maxCachedBufferCapacity, PoolArena<T> area) {
if (cacheSize > 0 && maxCachedBufferCapacity > 0) {
int max = Math.min(area.chunkSize, maxCachedBufferCapacity);
int arraySize = Math.max(1, log2(max / area.pageSize) + 1);

@SuppressWarnings("unchecked")
MemoryRegionCache<T>[] cache = new MemoryRegionCache[arraySize];
for (int i = 0; i < cache.length; i++) {
cache[i] = new NormalMemoryRegionCache<T>(cacheSize);
}
return cache;
} else {
return null;
}
}

private static int log2(int val) {
int res = 0;
while (val > 1) {
val >>= 1;
res++;
}
return res;
}

/**
* Try to allocate a tiny buffer out of the cache. Returns {@code true} if successful {@code false} otherwise
*/
boolean allocateTiny(PoolArena<?> area, PooledByteBuf<?> buf, int reqCapacity, int normCapacity) {
return allocate(cacheForTiny(area, normCapacity), buf, reqCapacity);
}

/**
* Try to allocate a small buffer out of the cache. Returns {@code true} if successful {@code false} otherwise
*/
boolean allocateSmall(PoolArena<?> area, PooledByteBuf<?> buf, int reqCapacity, int normCapacity) {
return allocate(cacheForSmall(area, normCapacity), buf, reqCapacity);
}

/**
* Try to allocate a small buffer out of the cache. Returns {@code true} if successful {@code false} otherwise
*/
boolean allocateNormal(PoolArena<?> area, PooledByteBuf<?> buf, int reqCapacity, int normCapacity) {
return allocate(cacheForNormal(area, normCapacity), buf, reqCapacity);
}

@SuppressWarnings({ "unchecked", "rawtypes" })
private boolean allocate(MemoryRegionCache<?> cache, PooledByteBuf buf, int reqCapacity) {
if (cache == null) {
// no cache found so just return false here
return false;
}
boolean allocated = cache.allocate(buf, reqCapacity);
if (++ allocations >= freeSweepAllocationThreshold) {
allocations = 0;
trim();
}
return allocated;
}

/**
* Add {@link PoolChunk} and {@code handle} to the cache if there is enough room.
* Returns {@code true} if it fit into the cache {@code false} otherwise.
*/
@SuppressWarnings({ "unchecked", "rawtypes" })
boolean add(PoolArena<?> area, PoolChunk chunk, long handle, int normCapacity, SizeClass sizeClass) {
MemoryRegionCache<?> cache = cache(area, normCapacity, sizeClass);
if (cache == null) {
return false;
}
return cache.add(chunk, handle);
}

private MemoryRegionCache<?> cache(PoolArena<?> area, int normCapacity, SizeClass sizeClass) {
switch (sizeClass) {
case Normal:
return cacheForNormal(area, normCapacity);
case Small:
return cacheForSmall(area, normCapacity);
case Tiny:
return cacheForTiny(area, normCapacity);
default:
throw new Error();
}
}

/**
* Should be called if the Thread that uses this cache is about to exist to release resources out of the cache
*/
void free() {
int numFreed = free(tinySubPageDirectCaches) +
free(smallSubPageDirectCaches) +
free(normalDirectCaches) +
free(tinySubPageHeapCaches) +
free(smallSubPageHeapCaches) +
free(normalHeapCaches);

if (numFreed > 0 && logger.isDebugEnabled()) {
logger.debug("Freed {} thread-local buffer(s) from thread: {}", numFreed, Thread.currentThread().getName());
}

if (directArena != null) {
directArena.numThreadCaches.getAndDecrement();
}

if (heapArena != null) {
heapArena.numThreadCaches.getAndDecrement();
}
}

private static int free(MemoryRegionCache<?>[] caches) {
if (caches == null) {
return 0;
}

int numFreed = 0;
for (MemoryRegionCache<?> c: caches) {
numFreed += free(c);
}
return numFreed;
}

private static int free(MemoryRegionCache<?> cache) {
if (cache == null) {
return 0;
}
return cache.free();
}

void trim() {
trim(tinySubPageDirectCaches);
trim(smallSubPageDirectCaches);
trim(normalDirectCaches);
trim(tinySubPageHeapCaches);
trim(smallSubPageHeapCaches);
trim(normalHeapCaches);
}

private static void trim(MemoryRegionCache<?>[] caches) {
if (caches == null) {
return;
}
for (MemoryRegionCache<?> c: caches) {
trim(c);
}
}

private static void trim(MemoryRegionCache<?> cache) {
if (cache == null) {
return;
}
cache.trim();
}

private MemoryRegionCache<?> cacheForTiny(PoolArena<?> area, int normCapacity) {
int idx = PoolArena.tinyIdx(normCapacity);
if (area.isDirect()) {
return cache(tinySubPageDirectCaches, idx);
}
return cache(tinySubPageHeapCaches, idx);
}

private MemoryRegionCache<?> cacheForSmall(PoolArena<?> area, int normCapacity) {
int idx = PoolArena.smallIdx(normCapacity);
if (area.isDirect()) {
return cache(smallSubPageDirectCaches, idx);
}
return cache(smallSubPageHeapCaches, idx);
}

private MemoryRegionCache<?> cacheForNormal(PoolArena<?> area, int normCapacity) {
if (area.isDirect()) {
int idx = log2(normCapacity >> numShiftsNormalDirect);
return cache(normalDirectCaches, idx);
}
int idx = log2(normCapacity >> numShiftsNormalHeap);
return cache(normalHeapCaches, idx);
}

private static <T> MemoryRegionCache<T> cache(MemoryRegionCache<T>[] cache, int idx) {
if (cache == null || idx > cache.length - 1) {
return null;
}
return cache[idx];
}

/**
* Cache used for buffers which are backed by TINY or SMALL size.
*/
private static final class SubPageMemoryRegionCache<T> extends MemoryRegionCache<T> {
SubPageMemoryRegionCache(int size, SizeClass sizeClass) {
super(size, sizeClass);
}

@Override
protected void initBuf(
PoolChunk<T> chunk, long handle, PooledByteBuf<T> buf, int reqCapacity) {
chunk.initBufWithSubpage(buf, handle, reqCapacity);
}
}

/**
* Cache used for buffers which are backed by NORMAL size.
*/
private static final class NormalMemoryRegionCache<T> extends MemoryRegionCache<T> {
NormalMemoryRegionCache(int size) {
super(size, SizeClass.Normal);
}

@Override
protected void initBuf(
PoolChunk<T> chunk, long handle, PooledByteBuf<T> buf, int reqCapacity) {
chunk.initBuf(buf, handle, reqCapacity);
}
}

private abstract static class MemoryRegionCache<T> {
private final int size;
private final Queue<Entry<T>> queue;
private final SizeClass sizeClass;
private int allocations;

MemoryRegionCache(int size, SizeClass sizeClass) {
this.size = MathUtil.safeFindNextPositivePowerOfTwo(size);
queue = PlatformDependent.newFixedMpscQueue(this.size);
this.sizeClass = sizeClass;
}

/**
* Init the {@link PooledByteBuf} using the provided chunk and handle with the capacity restrictions.
*/
protected abstract void initBuf(PoolChunk<T> chunk, long handle,
PooledByteBuf<T> buf, int reqCapacity);

/**
* Add to cache if not already full.
*/
@SuppressWarnings("unchecked")
public final boolean add(PoolChunk<T> chunk, long handle) {
Entry<T> entry = newEntry(chunk, handle);
boolean queued = queue.offer(entry);
if (!queued) {
// If it was not possible to cache the chunk, immediately recycle the entry
entry.recycle();
}

return queued;
}

/**
* Allocate something out of the cache if possible and remove the entry from the cache.
*/
public final boolean allocate(PooledByteBuf<T> buf, int reqCapacity) {
Entry<T> entry = queue.poll();
if (entry == null) {
return false;
}
initBuf(entry.chunk, entry.handle, buf, reqCapacity);
entry.recycle();

// allocations is not thread-safe which is fine as this is only called from the same thread all time.
++ allocations;
return true;
}

/**
* Clear out this cache and free up all previous cached {@link PoolChunk}s and {@code handle}s.
*/
public final int free() {
return free(Integer.MAX_VALUE);
}

private int free(int max) {
int numFreed = 0;
for (; numFreed < max; numFreed++) {
Entry<T> entry = queue.poll();
if (entry != null) {
freeEntry(entry);
} else {
// all cleared
return numFreed;
}
}
return numFreed;
}

/**
* Free up cached {@link PoolChunk}s if not allocated frequently enough.
*/
public final void trim() {
int free = size - allocations;
allocations = 0;

// We not even allocated all the number that are
if (free > 0) {
free(free);
}
}

@SuppressWarnings({ "unchecked", "rawtypes" })
private void freeEntry(Entry entry) {
PoolChunk chunk = entry.chunk;
long handle = entry.handle;

// recycle now so PoolChunk can be GC'ed.
entry.recycle();

chunk.arena.freeChunk(chunk, handle, sizeClass);
}

static final class Entry<T> {
final Handle<Entry<?>> recyclerHandle;
PoolChunk<T> chunk;
long handle = -1;

Entry(Handle<Entry<?>> recyclerHandle) {
this.recyclerHandle = recyclerHandle;
}

void recycle() {
chunk = null;
handle = -1;
recyclerHandle.recycle(this);
}
}

@SuppressWarnings("rawtypes")
private static Entry newEntry(PoolChunk<?> chunk, long handle) {
Entry entry = RECYCLER.get();
entry.chunk = chunk;
entry.handle = handle;
return entry;
}

@SuppressWarnings("rawtypes")
private static final Recycler<Entry> RECYCLER = new Recycler<Entry>() {
@SuppressWarnings("unchecked")
@Override
protected Entry newObject(Handle<Entry> handle) {
return new Entry(handle);
}
};
}
}