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/*
* Licensed 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.github.benmanes.caffeine.cache;
import static com.github.benmanes.caffeine.base.UnsafeAccess.UNSAFE;
import static com.github.benmanes.caffeine.cache.BoundedLocalCache.ceilingPowerOfTwo;
import static com.github.benmanes.caffeine.cache.UnsafeRefArrayAccess.REF_ARRAY_BASE;
import static com.github.benmanes.caffeine.cache.UnsafeRefArrayAccess.REF_ELEMENT_SHIFT;
import static com.github.benmanes.caffeine.cache.UnsafeRefArrayAccess.lvElement;
import static com.github.benmanes.caffeine.cache.UnsafeRefArrayAccess.soElement;
import java.lang.reflect.Field;
import java.util.AbstractQueue;
import java.util.Iterator;
/**
* An MPSC array queue which starts at initialCapacity and grows to maxCapacity in
* linked chunks of the initial size. The queue grows only when the current buffer is full and
* elements are not copied on resize, instead a link to the new buffer is stored in the old buffer
* for the consumer to follow.
*
* This is a shaded copy of MpscGrowableArrayQueue provided by
* JCTools from version 2.0.
*
* @author [email protected] (Nitsan Wakart)
*/
final class MpscGrowableArrayQueue extends MpscChunkedArrayQueue {
/**
* @param initialCapacity the queue initial capacity. If chunk size is fixed this will be the
* chunk size. Must be 2 or more.
* @param maxCapacity the maximum capacity will be rounded up to the closest power of 2 and will
* be the upper limit of number of elements in this queue. Must be 4 or more and round up
* to a larger power of 2 than initialCapacity.
*/
public MpscGrowableArrayQueue(int initialCapacity, int maxCapacity) {
super(initialCapacity, maxCapacity);
}
@Override
protected int getNextBufferSize(E[] buffer) {
long maxSize = maxQueueCapacity / 2;
if (buffer.length > maxSize) {
throw new IllegalStateException();
}
final int newSize = 2 * (buffer.length - 1);
return newSize + 1;
}
@Override
protected long getCurrentBufferCapacity(long mask) {
return (mask + 2 == maxQueueCapacity) ? maxQueueCapacity : mask;
}
}
@SuppressWarnings("OvershadowingSubclassFields")
abstract class MpscChunkedArrayQueue extends MpscChunkedArrayQueueColdProducerFields {
long p0, p1, p2, p3, p4, p5, p6, p7;
long p10, p11, p12, p13, p14, p15, p16, p17;
public MpscChunkedArrayQueue(int initialCapacity, int maxCapacity) {
super(initialCapacity, maxCapacity);
}
@Override
protected long availableInQueue(long pIndex, long cIndex) {
return maxQueueCapacity - (pIndex - cIndex);
}
@Override
public int capacity() {
return (int) (maxQueueCapacity / 2);
}
@Override
protected int getNextBufferSize(E[] buffer) {
return buffer.length;
}
@Override
protected long getCurrentBufferCapacity(long mask) {
return mask;
}
}
abstract class MpscChunkedArrayQueueColdProducerFields extends BaseMpscLinkedArrayQueue {
protected final long maxQueueCapacity;
public MpscChunkedArrayQueueColdProducerFields(int initialCapacity, int maxCapacity) {
super(initialCapacity);
if (maxCapacity < 4) {
throw new IllegalArgumentException("Max capacity must be 4 or more");
}
if (ceilingPowerOfTwo(initialCapacity) >= ceilingPowerOfTwo(maxCapacity)) {
throw new IllegalArgumentException(
"Initial capacity cannot exceed maximum capacity(both rounded up to a power of 2)");
}
maxQueueCapacity = ((long) ceilingPowerOfTwo(maxCapacity)) << 1;
}
}
abstract class BaseMpscLinkedArrayQueuePad1 extends AbstractQueue {
long p01, p02, p03, p04, p05, p06, p07;
long p10, p11, p12, p13, p14, p15, p16, p17;
}
abstract class BaseMpscLinkedArrayQueueProducerFields extends BaseMpscLinkedArrayQueuePad1 {
protected long producerIndex;
}
@SuppressWarnings("OvershadowingSubclassFields")
abstract class BaseMpscLinkedArrayQueuePad2 extends BaseMpscLinkedArrayQueueProducerFields {
long p01, p02, p03, p04, p05, p06, p07;
long p10, p11, p12, p13, p14, p15, p16, p17;
}
@SuppressWarnings("NullAway")
abstract class BaseMpscLinkedArrayQueueConsumerFields extends BaseMpscLinkedArrayQueuePad2 {
protected long consumerMask;
protected E[] consumerBuffer;
protected long consumerIndex;
}
@SuppressWarnings("OvershadowingSubclassFields")
abstract class BaseMpscLinkedArrayQueuePad3 extends BaseMpscLinkedArrayQueueConsumerFields {
long p0, p1, p2, p3, p4, p5, p6, p7;
long p10, p11, p12, p13, p14, p15, p16, p17;
}
@SuppressWarnings("NullAway")
abstract class BaseMpscLinkedArrayQueueColdProducerFields
extends BaseMpscLinkedArrayQueuePad3 {
protected volatile long producerLimit;
protected long producerMask;
protected E[] producerBuffer;
}
@SuppressWarnings({"PMD", "NullAway", "restriction"})
abstract class BaseMpscLinkedArrayQueue extends BaseMpscLinkedArrayQueueColdProducerFields {
// No post padding here, subclasses must add
private final static long P_INDEX_OFFSET;
private final static long C_INDEX_OFFSET;
private final static long P_LIMIT_OFFSET;
static {
try {
Field iField = BaseMpscLinkedArrayQueueProducerFields.class.getDeclaredField("producerIndex");
P_INDEX_OFFSET = UNSAFE.objectFieldOffset(iField);
} catch (NoSuchFieldException e) {
throw new RuntimeException(e);
}
try {
Field iField = BaseMpscLinkedArrayQueueConsumerFields.class.getDeclaredField("consumerIndex");
C_INDEX_OFFSET = UNSAFE.objectFieldOffset(iField);
} catch (NoSuchFieldException e) {
throw new RuntimeException(e);
}
try {
Field iField =
BaseMpscLinkedArrayQueueColdProducerFields.class.getDeclaredField("producerLimit");
P_LIMIT_OFFSET = UNSAFE.objectFieldOffset(iField);
} catch (NoSuchFieldException e) {
throw new RuntimeException(e);
}
}
private final static Object JUMP = new Object();
/**
* @param initialCapacity the queue initial capacity. If chunk size is fixed this will be the
* chunk size. Must be 2 or more.
*/
public BaseMpscLinkedArrayQueue(final int initialCapacity) {
if (initialCapacity < 2) {
throw new IllegalArgumentException("Initial capacity must be 2 or more");
}
int p2capacity = ceilingPowerOfTwo(initialCapacity);
// leave lower bit of mask clear
long mask = (p2capacity - 1L) << 1;
// need extra element to point at next array
E[] buffer = allocate(p2capacity + 1);
producerBuffer = buffer;
producerMask = mask;
consumerBuffer = buffer;
consumerMask = mask;
soProducerLimit(mask); // we know it's all empty to start with
}
@Override
public final Iterator iterator() {
throw new UnsupportedOperationException();
}
@Override
public String toString() {
return getClass().getName() + "@" + Integer.toHexString(hashCode());
}
@Override
@SuppressWarnings("MissingDefault")
public boolean offer(final E e) {
if (null == e) {
throw new NullPointerException();
}
long mask;
E[] buffer;
long pIndex;
while (true) {
long producerLimit = lvProducerLimit();
pIndex = lvProducerIndex();
// lower bit is indicative of resize, if we see it we spin until it's cleared
if ((pIndex & 1) == 1) {
continue;
}
// pIndex is even (lower bit is 0) -> actual index is (pIndex >> 1)
// mask/buffer may get changed by resizing -> only use for array access after successful CAS.
mask = this.producerMask;
buffer = this.producerBuffer;
// a successful CAS ties the ordering, lv(pIndex)-[mask/buffer]->cas(pIndex)
// assumption behind this optimization is that queue is almost always empty or near empty
if (producerLimit <= pIndex) {
int result = offerSlowPath(mask, pIndex, producerLimit);
switch (result) {
case 0:
break;
case 1:
continue;
case 2:
return false;
case 3:
resize(mask, buffer, pIndex, e);
return true;
}
}
if (casProducerIndex(pIndex, pIndex + 2)) {
break;
}
}
// INDEX visible before ELEMENT, consistent with consumer expectation
final long offset = modifiedCalcElementOffset(pIndex, mask);
soElement(buffer, offset, e);
return true;
}
/**
* We do not inline resize into this method because we do not resize on fill.
*/
private int offerSlowPath(long mask, long pIndex, long producerLimit) {
int result;
final long cIndex = lvConsumerIndex();
long bufferCapacity = getCurrentBufferCapacity(mask);
result = 0;// 0 - goto pIndex CAS
if (cIndex + bufferCapacity > pIndex) {
if (!casProducerLimit(producerLimit, cIndex + bufferCapacity)) {
result = 1;// retry from top
}
}
// full and cannot grow
else if (availableInQueue(pIndex, cIndex) <= 0) {
result = 2;// -> return false;
}
// grab index for resize -> set lower bit
else if (casProducerIndex(pIndex, pIndex + 1)) {
result = 3;// -> resize
} else {
result = 1;// failed resize attempt, retry from top
}
return result;
}
/**
* @return available elements in queue * 2
*/
protected abstract long availableInQueue(long pIndex, final long cIndex);
/**
* This method assumes index is actually (index << 1) because lower bit is used for resize. This
* is compensated for by reducing the element shift. The computation is constant folded, so
* there's no cost.
*/
private static long modifiedCalcElementOffset(long index, long mask) {
return REF_ARRAY_BASE + ((index & mask) << (REF_ELEMENT_SHIFT - 1));
}
/**
* {@inheritDoc}
*
* This implementation is correct for single consumer thread use only.
*/
@Override
@SuppressWarnings("unchecked")
public E poll() {
final E[] buffer = consumerBuffer;
final long index = consumerIndex;
final long mask = consumerMask;
final long offset = modifiedCalcElementOffset(index, mask);
Object e = lvElement(buffer, offset);// LoadLoad
if (e == null) {
if (index != lvProducerIndex()) {
// poll() == null iff queue is empty, null element is not strong enough indicator, so we
// must
// check the producer index. If the queue is indeed not empty we spin until element is
// visible.
do {
e = lvElement(buffer, offset);
} while (e == null);
} else {
return null;
}
}
if (e == JUMP) {
final E[] nextBuffer = getNextBuffer(buffer, mask);
return newBufferPoll(nextBuffer, index);
}
soElement(buffer, offset, null);
soConsumerIndex(index + 2);
return (E) e;
}
/**
* {@inheritDoc}
*
* This implementation is correct for single consumer thread use only.
*/
@SuppressWarnings("unchecked")
@Override
public E peek() {
final E[] buffer = consumerBuffer;
final long index = consumerIndex;
final long mask = consumerMask;
final long offset = modifiedCalcElementOffset(index, mask);
Object e = lvElement(buffer, offset);// LoadLoad
if (e == null && index != lvProducerIndex()) {
// peek() == null iff queue is empty, null element is not strong enough indicator, so we must
// check the producer index. If the queue is indeed not empty we spin until element is
// visible.
while ((e = lvElement(buffer, offset)) == null) {
;
}
}
if (e == JUMP) {
return newBufferPeek(getNextBuffer(buffer, mask), index);
}
return (E) e;
}
@SuppressWarnings("unchecked")
private E[] getNextBuffer(final E[] buffer, final long mask) {
final long nextArrayOffset = nextArrayOffset(mask);
final E[] nextBuffer = (E[]) lvElement(buffer, nextArrayOffset);
soElement(buffer, nextArrayOffset, null);
return nextBuffer;
}
private static long nextArrayOffset(final long mask) {
return modifiedCalcElementOffset(mask + 2, Long.MAX_VALUE);
}
private E newBufferPoll(E[] nextBuffer, final long index) {
final long offsetInNew = newBufferAndOffset(nextBuffer, index);
final E n = lvElement(nextBuffer, offsetInNew);// LoadLoad
if (n == null) {
throw new IllegalStateException("new buffer must have at least one element");
}
soElement(nextBuffer, offsetInNew, null);// StoreStore
soConsumerIndex(index + 2);
return n;
}
private E newBufferPeek(E[] nextBuffer, final long index) {
final long offsetInNew = newBufferAndOffset(nextBuffer, index);
final E n = lvElement(nextBuffer, offsetInNew);// LoadLoad
if (null == n) {
throw new IllegalStateException("new buffer must have at least one element");
}
return n;
}
private long newBufferAndOffset(E[] nextBuffer, final long index) {
consumerBuffer = nextBuffer;
consumerMask = (nextBuffer.length - 2L) << 1;
final long offsetInNew = modifiedCalcElementOffset(index, consumerMask);
return offsetInNew;
}
@Override
public final int size() {
// NOTE: because indices are on even numbers we cannot use the size util.
/*
* It is possible for a thread to be interrupted or reschedule between the read of the producer
* and consumer indices, therefore protection is required to ensure size is within valid range.
* In the event of concurrent polls/offers to this method the size is OVER estimated as we read
* consumer index BEFORE the producer index.
*/
long after = lvConsumerIndex();
long size;
while (true) {
final long before = after;
final long currentProducerIndex = lvProducerIndex();
after = lvConsumerIndex();
if (before == after) {
size = ((currentProducerIndex - after) >> 1);
break;
}
}
// Long overflow is impossible, so size is always positive. Integer overflow is possible for the
// unbounded
// indexed queues.
if (size > Integer.MAX_VALUE) {
return Integer.MAX_VALUE;
} else {
return (int) size;
}
}
@Override
public final boolean isEmpty() {
// Order matters!
// Loading consumer before producer allows for producer increments after consumer index is read.
// This ensures this method is conservative in it's estimate. Note that as this is an MPMC there
// is
// nothing we can do to make this an exact method.
return (this.lvConsumerIndex() == this.lvProducerIndex());
}
private long lvProducerIndex() {
return UNSAFE.getLongVolatile(this, P_INDEX_OFFSET);
}
private long lvConsumerIndex() {
return UNSAFE.getLongVolatile(this, C_INDEX_OFFSET);
}
private void soProducerIndex(long v) {
UNSAFE.putOrderedLong(this, P_INDEX_OFFSET, v);
}
private boolean casProducerIndex(long expect, long newValue) {
return UNSAFE.compareAndSwapLong(this, P_INDEX_OFFSET, expect, newValue);
}
private void soConsumerIndex(long v) {
UNSAFE.putOrderedLong(this, C_INDEX_OFFSET, v);
}
private long lvProducerLimit() {
return producerLimit;
}
private boolean casProducerLimit(long expect, long newValue) {
return UNSAFE.compareAndSwapLong(this, P_LIMIT_OFFSET, expect, newValue);
}
private void soProducerLimit(long v) {
UNSAFE.putOrderedLong(this, P_LIMIT_OFFSET, v);
}
public long currentProducerIndex() {
return lvProducerIndex() / 2;
}
public long currentConsumerIndex() {
return lvConsumerIndex() / 2;
}
public abstract int capacity();
public boolean relaxedOffer(E e) {
return offer(e);
}
@SuppressWarnings("unchecked")
public E relaxedPoll() {
final E[] buffer = consumerBuffer;
final long index = consumerIndex;
final long mask = consumerMask;
final long offset = modifiedCalcElementOffset(index, mask);
Object e = lvElement(buffer, offset);// LoadLoad
if (e == null) {
return null;
}
if (e == JUMP) {
final E[] nextBuffer = getNextBuffer(buffer, mask);
return newBufferPoll(nextBuffer, index);
}
soElement(buffer, offset, null);
soConsumerIndex(index + 2);
return (E) e;
}
@SuppressWarnings("unchecked")
public E relaxedPeek() {
final E[] buffer = consumerBuffer;
final long index = consumerIndex;
final long mask = consumerMask;
final long offset = modifiedCalcElementOffset(index, mask);
Object e = lvElement(buffer, offset);// LoadLoad
if (e == JUMP) {
return newBufferPeek(getNextBuffer(buffer, mask), index);
}
return (E) e;
}
private void resize(long oldMask, E[] oldBuffer, long pIndex, final E e) {
int newBufferLength = getNextBufferSize(oldBuffer);
final E[] newBuffer = allocate(newBufferLength);
producerBuffer = newBuffer;
final int newMask = (newBufferLength - 2) << 1;
producerMask = newMask;
final long offsetInOld = modifiedCalcElementOffset(pIndex, oldMask);
final long offsetInNew = modifiedCalcElementOffset(pIndex, newMask);
soElement(newBuffer, offsetInNew, e);// element in new array
soElement(oldBuffer, nextArrayOffset(oldMask), newBuffer);// buffer linked
// ASSERT code
final long cIndex = lvConsumerIndex();
final long availableInQueue = availableInQueue(pIndex, cIndex);
if (availableInQueue <= 0) {
throw new IllegalStateException();
}
// Invalidate racing CASs
// We never set the limit beyond the bounds of a buffer
soProducerLimit(pIndex + Math.min(newMask, availableInQueue));
// make resize visible to the other producers
soProducerIndex(pIndex + 2);
// INDEX visible before ELEMENT, consistent with consumer expectation
// make resize visible to consumer
soElement(oldBuffer, offsetInOld, JUMP);
}
@SuppressWarnings("unchecked")
public static E[] allocate(int capacity) {
return (E[]) new Object[capacity];
}
/**
* @return next buffer size(inclusive of next array pointer)
*/
protected abstract int getNextBufferSize(E[] buffer);
/**
* @return current buffer capacity for elements (excluding next pointer and jump entry) * 2
*/
protected abstract long getCurrentBufferCapacity(long mask);
}
/**
* A concurrent access enabling class used by circular array based queues this class exposes an
* offset computation method along with differently memory fenced load/store methods into the
* underlying array. The class is pre-padded and the array is padded on either side to help with
* False sharing prvention. It is expected theat subclasses handle post padding.
*
* Offset calculation is separate from access to enable the reuse of a give compute offset.
*
* Load/Store methods using a buffer parameter are provided to allow the prevention of final
* field reload after a LoadLoad barrier.
*
*/
@SuppressWarnings("restriction")
final class UnsafeRefArrayAccess {
public static final long REF_ARRAY_BASE;
public static final int REF_ELEMENT_SHIFT;
static {
final int scale = UNSAFE.arrayIndexScale(Object[].class);
if (4 == scale) {
REF_ELEMENT_SHIFT = 2;
} else if (8 == scale) {
REF_ELEMENT_SHIFT = 3;
} else {
throw new IllegalStateException("Unknown pointer size");
}
REF_ARRAY_BASE = UNSAFE.arrayBaseOffset(Object[].class);
}
private UnsafeRefArrayAccess() {}
/**
* A plain store (no ordering/fences) of an element to a given offset
*
* @param buffer this.buffer
* @param offset computed via {@link UnsafeRefArrayAccess#calcElementOffset(long)}
* @param e an orderly kitty
*/
public static void spElement(E[] buffer, long offset, E e) {
UNSAFE.putObject(buffer, offset, e);
}
/**
* An ordered store(store + StoreStore barrier) of an element to a given offset
*
* @param buffer this.buffer
* @param offset computed via {@link UnsafeRefArrayAccess#calcElementOffset}
* @param e an orderly kitty
*/
public static void soElement(E[] buffer, long offset, E e) {
UNSAFE.putOrderedObject(buffer, offset, e);
}
/**
* A plain load (no ordering/fences) of an element from a given offset.
*
* @param buffer this.buffer
* @param offset computed via {@link UnsafeRefArrayAccess#calcElementOffset(long)}
* @return the element at the offset
*/
@SuppressWarnings("unchecked")
public static E lpElement(E[] buffer, long offset) {
return (E) UNSAFE.getObject(buffer, offset);
}
/**
* A volatile load (load + LoadLoad barrier) of an element from a given offset.
*
* @param buffer this.buffer
* @param offset computed via {@link UnsafeRefArrayAccess#calcElementOffset(long)}
* @return the element at the offset
*/
@SuppressWarnings("unchecked")
public static E lvElement(E[] buffer, long offset) {
return (E) UNSAFE.getObjectVolatile(buffer, offset);
}
/**
* @param index desirable element index
* @return the offset in bytes within the array for a given index.
*/
public static long calcElementOffset(long index) {
return REF_ARRAY_BASE + (index << REF_ELEMENT_SHIFT);
}
}