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/*
* Copyright 2013 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 io.netty.util;
import io.netty.util.concurrent.FastThreadLocal;
import io.netty.util.internal.SystemPropertyUtil;
import io.netty.util.internal.logging.InternalLogger;
import io.netty.util.internal.logging.InternalLoggerFactory;
import java.lang.ref.WeakReference;
import java.util.Arrays;
import java.util.Map;
import java.util.WeakHashMap;
import java.util.concurrent.atomic.AtomicInteger;
import static io.netty.util.internal.MathUtil.safeFindNextPositivePowerOfTwo;
import static java.lang.Math.max;
import static java.lang.Math.min;
/**
* Light-weight object pool based on a thread-local stack.
*
* @param the type of the pooled object
*/
public abstract class Recycler {
private static final InternalLogger logger = InternalLoggerFactory.getInstance(Recycler.class);
@SuppressWarnings("rawtypes")
private static final Handle NOOP_HANDLE = new Handle() {
@Override
public void recycle(Object object) {
// NOOP
}
};
private static final AtomicInteger ID_GENERATOR = new AtomicInteger(Integer.MIN_VALUE);
private static final int OWN_THREAD_ID = ID_GENERATOR.getAndIncrement();
private static final int DEFAULT_INITIAL_MAX_CAPACITY_PER_THREAD = 4 * 1024; // Use 4k instances as default.
private static final int DEFAULT_MAX_CAPACITY_PER_THREAD;
private static final int INITIAL_CAPACITY;
private static final int MAX_SHARED_CAPACITY_FACTOR;
private static final int MAX_DELAYED_QUEUES_PER_THREAD;
private static final int LINK_CAPACITY;
private static final int RATIO;
static {
// In the future, we might have different maxCapacity for different object types.
// e.g. io.netty.recycler.maxCapacity.writeTask
// io.netty.recycler.maxCapacity.outboundBuffer
int maxCapacityPerThread = SystemPropertyUtil.getInt("io.netty.recycler.maxCapacityPerThread",
SystemPropertyUtil.getInt("io.netty.recycler.maxCapacity", DEFAULT_INITIAL_MAX_CAPACITY_PER_THREAD));
if (maxCapacityPerThread < 0) {
maxCapacityPerThread = DEFAULT_INITIAL_MAX_CAPACITY_PER_THREAD;
}
DEFAULT_MAX_CAPACITY_PER_THREAD = maxCapacityPerThread;
MAX_SHARED_CAPACITY_FACTOR = max(2,
SystemPropertyUtil.getInt("io.netty.recycler.maxSharedCapacityFactor",
2));
MAX_DELAYED_QUEUES_PER_THREAD = max(0,
SystemPropertyUtil.getInt("io.netty.recycler.maxDelayedQueuesPerThread",
// We use the same value as default EventLoop number
NettyRuntime.availableProcessors() * 2));
LINK_CAPACITY = safeFindNextPositivePowerOfTwo(
max(SystemPropertyUtil.getInt("io.netty.recycler.linkCapacity", 16), 16));
// By default we allow one push to a Recycler for each 8th try on handles that were never recycled before.
// This should help to slowly increase the capacity of the recycler while not be too sensitive to allocation
// bursts.
RATIO = safeFindNextPositivePowerOfTwo(SystemPropertyUtil.getInt("io.netty.recycler.ratio", 8));
if (logger.isDebugEnabled()) {
if (DEFAULT_MAX_CAPACITY_PER_THREAD == 0) {
logger.debug("-Dio.netty.recycler.maxCapacityPerThread: disabled");
logger.debug("-Dio.netty.recycler.maxSharedCapacityFactor: disabled");
logger.debug("-Dio.netty.recycler.linkCapacity: disabled");
logger.debug("-Dio.netty.recycler.ratio: disabled");
} else {
logger.debug("-Dio.netty.recycler.maxCapacityPerThread: {}", DEFAULT_MAX_CAPACITY_PER_THREAD);
logger.debug("-Dio.netty.recycler.maxSharedCapacityFactor: {}", MAX_SHARED_CAPACITY_FACTOR);
logger.debug("-Dio.netty.recycler.linkCapacity: {}", LINK_CAPACITY);
logger.debug("-Dio.netty.recycler.ratio: {}", RATIO);
}
}
INITIAL_CAPACITY = min(DEFAULT_MAX_CAPACITY_PER_THREAD, 256);
}
private final int maxCapacityPerThread;
private final int maxSharedCapacityFactor;
private final int ratioMask;
private final int maxDelayedQueuesPerThread;
private final FastThreadLocal> threadLocal = new FastThreadLocal>() {
@Override
protected Stack initialValue() {
return new Stack(Recycler.this, Thread.currentThread(), maxCapacityPerThread, maxSharedCapacityFactor,
ratioMask, maxDelayedQueuesPerThread);
}
@Override
protected void onRemoval(Stack value) {
// Let us remove the WeakOrderQueue from the WeakHashMap directly if its safe to remove some overhead
if (value.threadRef.get() == Thread.currentThread()) {
if (DELAYED_RECYCLED.isSet()) {
DELAYED_RECYCLED.get().remove(value);
}
}
}
};
protected Recycler() {
this(DEFAULT_MAX_CAPACITY_PER_THREAD);
}
protected Recycler(int maxCapacityPerThread) {
this(maxCapacityPerThread, MAX_SHARED_CAPACITY_FACTOR);
}
protected Recycler(int maxCapacityPerThread, int maxSharedCapacityFactor) {
this(maxCapacityPerThread, maxSharedCapacityFactor, RATIO, MAX_DELAYED_QUEUES_PER_THREAD);
}
protected Recycler(int maxCapacityPerThread, int maxSharedCapacityFactor,
int ratio, int maxDelayedQueuesPerThread) {
ratioMask = safeFindNextPositivePowerOfTwo(ratio) - 1;
if (maxCapacityPerThread <= 0) {
this.maxCapacityPerThread = 0;
this.maxSharedCapacityFactor = 1;
this.maxDelayedQueuesPerThread = 0;
} else {
this.maxCapacityPerThread = maxCapacityPerThread;
this.maxSharedCapacityFactor = max(1, maxSharedCapacityFactor);
this.maxDelayedQueuesPerThread = max(0, maxDelayedQueuesPerThread);
}
}
@SuppressWarnings("unchecked")
public final T get() {
if (maxCapacityPerThread == 0) {
return newObject((Handle) NOOP_HANDLE);
}
Stack stack = threadLocal.get();
DefaultHandle handle = stack.pop();
if (handle == null) {
handle = stack.newHandle();
handle.value = newObject(handle);
}
return (T) handle.value;
}
/**
* @deprecated use {@link Handle#recycle(Object)}.
*/
@Deprecated
public final boolean recycle(T o, Handle handle) {
if (handle == NOOP_HANDLE) {
return false;
}
DefaultHandle h = (DefaultHandle) handle;
if (h.stack.parent != this) {
return false;
}
h.recycle(o);
return true;
}
final int threadLocalCapacity() {
return threadLocal.get().elements.length;
}
final int threadLocalSize() {
return threadLocal.get().size;
}
protected abstract T newObject(Handle handle);
public interface Handle {
void recycle(T object);
}
static final class DefaultHandle implements Handle {
private int lastRecycledId;
private int recycleId;
boolean hasBeenRecycled;
private Stack stack;
private Object value;
DefaultHandle(Stack stack) {
this.stack = stack;
}
@Override
public void recycle(Object object) {
if (object != value) {
throw new IllegalArgumentException("object does not belong to handle");
}
Stack stack = this.stack;
if (lastRecycledId != recycleId || stack == null) {
throw new IllegalStateException("recycled already");
}
stack.push(this);
}
}
private static final FastThreadLocal, WeakOrderQueue>> DELAYED_RECYCLED =
new FastThreadLocal, WeakOrderQueue>>() {
@Override
protected Map, WeakOrderQueue> initialValue() {
return new WeakHashMap, WeakOrderQueue>();
}
};
// a queue that makes only moderate guarantees about visibility: items are seen in the correct order,
// but we aren't absolutely guaranteed to ever see anything at all, thereby keeping the queue cheap to maintain
private static final class WeakOrderQueue {
static final WeakOrderQueue DUMMY = new WeakOrderQueue();
// Let Link extend AtomicInteger for intrinsics. The Link itself will be used as writerIndex.
@SuppressWarnings("serial")
static final class Link extends AtomicInteger {
private final DefaultHandle[] elements = new DefaultHandle[LINK_CAPACITY];
private int readIndex;
Link next;
}
// This act as a place holder for the head Link but also will reclaim space once finalized.
// Its important this does not hold any reference to either Stack or WeakOrderQueue.
static final class Head {
private final AtomicInteger availableSharedCapacity;
Link link;
Head(AtomicInteger availableSharedCapacity) {
this.availableSharedCapacity = availableSharedCapacity;
}
/// TODO: In the future when we move to Java9+ we should use java.lang.ref.Cleaner.
@Override
protected void finalize() throws Throwable {
try {
super.finalize();
} finally {
Link head = link;
link = null;
while (head != null) {
reclaimSpace(LINK_CAPACITY);
Link next = head.next;
// Unlink to help GC and guard against GC nepotism.
head.next = null;
head = next;
}
}
}
void reclaimSpace(int space) {
assert space >= 0;
availableSharedCapacity.addAndGet(space);
}
boolean reserveSpace(int space) {
return reserveSpace(availableSharedCapacity, space);
}
static boolean reserveSpace(AtomicInteger availableSharedCapacity, int space) {
assert space >= 0;
for (;;) {
int available = availableSharedCapacity.get();
if (available < space) {
return false;
}
if (availableSharedCapacity.compareAndSet(available, available - space)) {
return true;
}
}
}
}
// chain of data items
private final Head head;
private Link tail;
// pointer to another queue of delayed items for the same stack
private WeakOrderQueue next;
private final WeakReference owner;
private final int id = ID_GENERATOR.getAndIncrement();
private WeakOrderQueue() {
owner = null;
head = new Head(null);
}
private WeakOrderQueue(Stack stack, Thread thread) {
tail = new Link();
// Its important that we not store the Stack itself in the WeakOrderQueue as the Stack also is used in
// the WeakHashMap as key. So just store the enclosed AtomicInteger which should allow to have the
// Stack itself GCed.
head = new Head(stack.availableSharedCapacity);
head.link = tail;
owner = new WeakReference(thread);
}
static WeakOrderQueue newQueue(Stack stack, Thread thread) {
final WeakOrderQueue queue = new WeakOrderQueue(stack, thread);
// Done outside of the constructor to ensure WeakOrderQueue.this does not escape the constructor and so
// may be accessed while its still constructed.
stack.setHead(queue);
return queue;
}
private void setNext(WeakOrderQueue next) {
assert next != this;
this.next = next;
}
/**
* Allocate a new {@link WeakOrderQueue} or return {@code null} if not possible.
*/
static WeakOrderQueue allocate(Stack stack, Thread thread) {
// We allocated a Link so reserve the space
return Head.reserveSpace(stack.availableSharedCapacity, LINK_CAPACITY)
? newQueue(stack, thread) : null;
}
void add(DefaultHandle handle) {
handle.lastRecycledId = id;
Link tail = this.tail;
int writeIndex;
if ((writeIndex = tail.get()) == LINK_CAPACITY) {
if (!head.reserveSpace(LINK_CAPACITY)) {
// Drop it.
return;
}
// We allocate a Link so reserve the space
this.tail = tail = tail.next = new Link();
writeIndex = tail.get();
}
tail.elements[writeIndex] = handle;
handle.stack = null;
// we lazy set to ensure that setting stack to null appears before we unnull it in the owning thread;
// this also means we guarantee visibility of an element in the queue if we see the index updated
tail.lazySet(writeIndex + 1);
}
boolean hasFinalData() {
return tail.readIndex != tail.get();
}
// transfer as many items as we can from this queue to the stack, returning true if any were transferred
@SuppressWarnings("rawtypes")
boolean transfer(Stack dst) {
Link head = this.head.link;
if (head == null) {
return false;
}
if (head.readIndex == LINK_CAPACITY) {
if (head.next == null) {
return false;
}
this.head.link = head = head.next;
this.head.reclaimSpace(LINK_CAPACITY);
}
final int srcStart = head.readIndex;
int srcEnd = head.get();
final int srcSize = srcEnd - srcStart;
if (srcSize == 0) {
return false;
}
final int dstSize = dst.size;
final int expectedCapacity = dstSize + srcSize;
if (expectedCapacity > dst.elements.length) {
final int actualCapacity = dst.increaseCapacity(expectedCapacity);
srcEnd = min(srcStart + actualCapacity - dstSize, srcEnd);
}
if (srcStart != srcEnd) {
final DefaultHandle[] srcElems = head.elements;
final DefaultHandle[] dstElems = dst.elements;
int newDstSize = dstSize;
for (int i = srcStart; i < srcEnd; i++) {
DefaultHandle element = srcElems[i];
if (element.recycleId == 0) {
element.recycleId = element.lastRecycledId;
} else if (element.recycleId != element.lastRecycledId) {
throw new IllegalStateException("recycled already");
}
srcElems[i] = null;
if (dst.dropHandle(element)) {
// Drop the object.
continue;
}
element.stack = dst;
dstElems[newDstSize ++] = element;
}
if (srcEnd == LINK_CAPACITY && head.next != null) {
// Add capacity back as the Link is GCed.
this.head.reclaimSpace(LINK_CAPACITY);
this.head.link = head.next;
}
head.readIndex = srcEnd;
if (dst.size == newDstSize) {
return false;
}
dst.size = newDstSize;
return true;
} else {
// The destination stack is full already.
return false;
}
}
}
static final class Stack {
// we keep a queue of per-thread queues, which is appended to once only, each time a new thread other
// than the stack owner recycles: when we run out of items in our stack we iterate this collection
// to scavenge those that can be reused. this permits us to incur minimal thread synchronisation whilst
// still recycling all items.
final Recycler parent;
// We store the Thread in a WeakReference as otherwise we may be the only ones that still hold a strong
// Reference to the Thread itself after it died because DefaultHandle will hold a reference to the Stack.
//
// The biggest issue is if we do not use a WeakReference the Thread may not be able to be collected at all if
// the user will store a reference to the DefaultHandle somewhere and never clear this reference (or not clear
// it in a timely manner).
final WeakReference threadRef;
final AtomicInteger availableSharedCapacity;
final int maxDelayedQueues;
private final int maxCapacity;
private final int ratioMask;
private DefaultHandle[] elements;
private int size;
private int handleRecycleCount = -1; // Start with -1 so the first one will be recycled.
private WeakOrderQueue cursor, prev;
private volatile WeakOrderQueue head;
Stack(Recycler parent, Thread thread, int maxCapacity, int maxSharedCapacityFactor,
int ratioMask, int maxDelayedQueues) {
this.parent = parent;
threadRef = new WeakReference(thread);
this.maxCapacity = maxCapacity;
availableSharedCapacity = new AtomicInteger(max(maxCapacity / maxSharedCapacityFactor, LINK_CAPACITY));
elements = new DefaultHandle[min(INITIAL_CAPACITY, maxCapacity)];
this.ratioMask = ratioMask;
this.maxDelayedQueues = maxDelayedQueues;
}
// Marked as synchronized to ensure this is serialized.
synchronized void setHead(WeakOrderQueue queue) {
queue.setNext(head);
head = queue;
}
int increaseCapacity(int expectedCapacity) {
int newCapacity = elements.length;
int maxCapacity = this.maxCapacity;
do {
newCapacity <<= 1;
} while (newCapacity < expectedCapacity && newCapacity < maxCapacity);
newCapacity = min(newCapacity, maxCapacity);
if (newCapacity != elements.length) {
elements = Arrays.copyOf(elements, newCapacity);
}
return newCapacity;
}
@SuppressWarnings({ "unchecked", "rawtypes" })
DefaultHandle pop() {
int size = this.size;
if (size == 0) {
if (!scavenge()) {
return null;
}
size = this.size;
}
size --;
DefaultHandle ret = elements[size];
elements[size] = null;
if (ret.lastRecycledId != ret.recycleId) {
throw new IllegalStateException("recycled multiple times");
}
ret.recycleId = 0;
ret.lastRecycledId = 0;
this.size = size;
return ret;
}
boolean scavenge() {
// continue an existing scavenge, if any
if (scavengeSome()) {
return true;
}
// reset our scavenge cursor
prev = null;
cursor = head;
return false;
}
boolean scavengeSome() {
WeakOrderQueue prev;
WeakOrderQueue cursor = this.cursor;
if (cursor == null) {
prev = null;
cursor = head;
if (cursor == null) {
return false;
}
} else {
prev = this.prev;
}
boolean success = false;
do {
if (cursor.transfer(this)) {
success = true;
break;
}
WeakOrderQueue next = cursor.next;
if (cursor.owner.get() == null) {
// If the thread associated with the queue is gone, unlink it, after
// performing a volatile read to confirm there is no data left to collect.
// We never unlink the first queue, as we don't want to synchronize on updating the head.
if (cursor.hasFinalData()) {
for (;;) {
if (cursor.transfer(this)) {
success = true;
} else {
break;
}
}
}
if (prev != null) {
prev.setNext(next);
}
} else {
prev = cursor;
}
cursor = next;
} while (cursor != null && !success);
this.prev = prev;
this.cursor = cursor;
return success;
}
void push(DefaultHandle item) {
Thread currentThread = Thread.currentThread();
if (threadRef.get() == currentThread) {
// The current Thread is the thread that belongs to the Stack, we can try to push the object now.
pushNow(item);
} else {
// The current Thread is not the one that belongs to the Stack
// (or the Thread that belonged to the Stack was collected already), we need to signal that the push
// happens later.
pushLater(item, currentThread);
}
}
private void pushNow(DefaultHandle item) {
if ((item.recycleId | item.lastRecycledId) != 0) {
throw new IllegalStateException("recycled already");
}
item.recycleId = item.lastRecycledId = OWN_THREAD_ID;
int size = this.size;
if (size >= maxCapacity || dropHandle(item)) {
// Hit the maximum capacity or should drop - drop the possibly youngest object.
return;
}
if (size == elements.length) {
elements = Arrays.copyOf(elements, min(size << 1, maxCapacity));
}
elements[size] = item;
this.size = size + 1;
}
private void pushLater(DefaultHandle item, Thread thread) {
// we don't want to have a ref to the queue as the value in our weak map
// so we null it out; to ensure there are no races with restoring it later
// we impose a memory ordering here (no-op on x86)
Map, WeakOrderQueue> delayedRecycled = DELAYED_RECYCLED.get();
WeakOrderQueue queue = delayedRecycled.get(this);
if (queue == null) {
if (delayedRecycled.size() >= maxDelayedQueues) {
// Add a dummy queue so we know we should drop the object
delayedRecycled.put(this, WeakOrderQueue.DUMMY);
return;
}
// Check if we already reached the maximum number of delayed queues and if we can allocate at all.
if ((queue = WeakOrderQueue.allocate(this, thread)) == null) {
// drop object
return;
}
delayedRecycled.put(this, queue);
} else if (queue == WeakOrderQueue.DUMMY) {
// drop object
return;
}
queue.add(item);
}
boolean dropHandle(DefaultHandle handle) {
if (!handle.hasBeenRecycled) {
if ((++handleRecycleCount & ratioMask) != 0) {
// Drop the object.
return true;
}
handle.hasBeenRecycled = true;
}
return false;
}
DefaultHandle newHandle() {
return new DefaultHandle(this);
}
}
}
