com.alipay.sofa.jraft.util.Recyclers Maven / Gradle / Ivy
/*
* Copyright 2014 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 com.alipay.sofa.jraft.util;
import java.lang.ref.WeakReference;
import java.util.Arrays;
import java.util.Map;
import java.util.WeakHashMap;
import java.util.concurrent.atomic.AtomicInteger;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
/**
* Light-weight object pool based on a thread-local stack.
*
* Forked from Netty.
*
* @param the type of the pooled object
*/
public abstract class Recyclers {
private static final Logger LOG = LoggerFactory.getLogger(Recyclers.class);
private static final AtomicInteger idGenerator = new AtomicInteger(Integer.MIN_VALUE);
private static final int OWN_THREAD_ID = idGenerator.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;
static {
int maxCapacityPerThread = SystemPropertyUtil.getInt("jraft.recyclers.maxCapacityPerThread", DEFAULT_INITIAL_MAX_CAPACITY_PER_THREAD);
if (maxCapacityPerThread < 0) {
maxCapacityPerThread = DEFAULT_INITIAL_MAX_CAPACITY_PER_THREAD;
}
DEFAULT_MAX_CAPACITY_PER_THREAD = maxCapacityPerThread;
if (LOG.isDebugEnabled()) {
if (DEFAULT_MAX_CAPACITY_PER_THREAD == 0) {
LOG.debug("-Djraft.recyclers.maxCapacityPerThread: disabled");
} else {
LOG.debug("-Djraft.recyclers.maxCapacityPerThread: {}", DEFAULT_MAX_CAPACITY_PER_THREAD);
}
}
INITIAL_CAPACITY = Math.min(DEFAULT_MAX_CAPACITY_PER_THREAD, 256);
}
public static final Handle NOOP_HANDLE = new Handle() {};
private final int maxCapacityPerThread;
private final ThreadLocal> threadLocal = new ThreadLocal>() {
@Override
protected Stack initialValue() {
return new Stack<>(Recyclers.this, Thread.currentThread(), maxCapacityPerThread);
}
};
protected Recyclers() {
this(DEFAULT_MAX_CAPACITY_PER_THREAD);
}
protected Recyclers(int maxCapacityPerThread) {
this.maxCapacityPerThread = Math.max(0, maxCapacityPerThread);
}
@SuppressWarnings("unchecked")
public final T get() {
if (maxCapacityPerThread == 0) {
return newObject(NOOP_HANDLE);
}
Stack stack = threadLocal.get();
DefaultHandle handle = stack.pop();
if (handle == null) {
handle = stack.newHandle();
handle.value = newObject(handle);
}
return (T) handle.value;
}
public final boolean recycle(T o, Handle handle) {
if (handle == NOOP_HANDLE) {
return false;
}
DefaultHandle h = (DefaultHandle) handle;
final Stack stack = h.stack;
if (h.lastRecycledId != h.recycleId || stack == null) {
throw new IllegalStateException("recycled already");
}
if (stack.parent != this) {
return false;
}
if (o != h.value) {
throw new IllegalArgumentException("o does not belong to handle");
}
h.recycle();
return true;
}
protected abstract T newObject(Handle handle);
public final int threadLocalCapacity() {
return threadLocal.get().elements.length;
}
public final int threadLocalSize() {
return threadLocal.get().size;
}
public interface Handle {}
static final class DefaultHandle implements Handle {
private int lastRecycledId;
private int recycleId;
private Stack stack;
private Object value;
DefaultHandle(Stack stack) {
this.stack = stack;
}
public void recycle() {
Thread thread = Thread.currentThread();
final Stack stack = this.stack;
if (lastRecycledId != recycleId || stack == null) {
throw new IllegalStateException("recycled already");
}
if (thread == stack.thread) {
stack.push(this);
return;
}
// 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 = Recyclers.delayedRecycled.get();
WeakOrderQueue queue = delayedRecycled.get(stack);
if (queue == null) {
delayedRecycled.put(stack, queue = new WeakOrderQueue(stack, thread));
}
queue.add(this);
}
}
private static final ThreadLocal, WeakOrderQueue>> delayedRecycled = ThreadLocal.withInitial(WeakHashMap::new);
// 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 {
private static final int LINK_CAPACITY = 16;
// Let Link extend AtomicInteger for intrinsics. The Link itself will be used as writerIndex.
@SuppressWarnings("serial")
private static final class Link extends AtomicInteger {
private final DefaultHandle[] elements = new DefaultHandle[LINK_CAPACITY];
private int readIndex;
private Link next;
}
// chain of data items
private Link head, tail;
// pointer to another queue of delayed items for the same stack
private WeakOrderQueue next;
private final WeakReference owner;
private final int id = idGenerator.getAndIncrement();
WeakOrderQueue(Stack stack, Thread thread) {
head = tail = new Link();
owner = new WeakReference<>(thread);
synchronized (stackLock(stack)) {
next = stack.head;
stack.head = this;
}
}
private Object stackLock(Stack stack) {
return stack;
}
void add(DefaultHandle handle) {
handle.lastRecycledId = id;
Link tail = this.tail;
int writeIndex;
if ((writeIndex = tail.get()) == LINK_CAPACITY) {
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;
if (head == null) {
return false;
}
if (head.readIndex == LINK_CAPACITY) {
if (head.next == null) {
return false;
}
this.head = head = head.next;
}
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 = Math.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");
}
element.stack = dst;
dstElems[newDstSize++] = element;
srcElems[i] = null;
}
dst.size = newDstSize;
if (srcEnd == LINK_CAPACITY && head.next != null) {
this.head = head.next;
}
head.readIndex = srcEnd;
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 Recyclers parent;
final Thread thread;
private DefaultHandle[] elements;
private final int maxCapacity;
private int size;
private volatile WeakOrderQueue head;
private WeakOrderQueue cursor, prev;
Stack(Recyclers parent, Thread thread, int maxCapacity) {
this.parent = parent;
this.thread = thread;
this.maxCapacity = maxCapacity;
elements = new DefaultHandle[Math.min(INITIAL_CAPACITY, maxCapacity)];
}
int increaseCapacity(int expectedCapacity) {
int newCapacity = elements.length;
int maxCapacity = this.maxCapacity;
do {
newCapacity <<= 1;
} while (newCapacity < expectedCapacity && newCapacity < maxCapacity);
newCapacity = Math.min(newCapacity, maxCapacity);
if (newCapacity != elements.length) {
elements = Arrays.copyOf(elements, newCapacity);
}
return newCapacity;
}
DefaultHandle pop() {
int size = this.size;
if (size == 0) {
if (!scavenge()) {
return null;
}
size = this.size;
}
size--;
DefaultHandle ret = elements[size];
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 cursor = this.cursor;
if (cursor == null) {
cursor = head;
if (cursor == null) {
return false;
}
}
boolean success = false;
WeakOrderQueue prev = this.prev;
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.next = next;
}
} else {
prev = cursor;
}
cursor = next;
} while (cursor != null && !success);
this.prev = prev;
this.cursor = cursor;
return success;
}
void push(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) {
// Hit the maximum capacity - drop the possibly youngest object.
return;
}
if (size == elements.length) {
elements = Arrays.copyOf(elements, Math.min(size << 1, maxCapacity));
}
elements[size] = item;
this.size = size + 1;
}
DefaultHandle newHandle() {
return new DefaultHandle(this);
}
}
}
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