io.rsocket.internal.jctools.queues.BaseMpscLinkedArrayQueue Maven / Gradle / Ivy
/*
* 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 io.rsocket.internal.jctools.queues;
import static io.rsocket.internal.jctools.queues.CircularArrayOffsetCalculator.allocate;
import static io.rsocket.internal.jctools.queues.LinkedArrayQueueUtil.length;
import static io.rsocket.internal.jctools.queues.LinkedArrayQueueUtil.modifiedCalcElementOffset;
import static io.rsocket.internal.jctools.util.UnsafeAccess.UNSAFE;
import static io.rsocket.internal.jctools.util.UnsafeAccess.fieldOffset;
import static io.rsocket.internal.jctools.util.UnsafeRefArrayAccess.calcElementOffset;
import static io.rsocket.internal.jctools.util.UnsafeRefArrayAccess.lvElement;
import static io.rsocket.internal.jctools.util.UnsafeRefArrayAccess.soElement;
import io.rsocket.internal.jctools.queues.IndexedQueueSizeUtil.IndexedQueue;
import io.rsocket.internal.jctools.util.PortableJvmInfo;
import io.rsocket.internal.jctools.util.Pow2;
import io.rsocket.internal.jctools.util.RangeUtil;
import java.util.AbstractQueue;
import java.util.Iterator;
abstract class BaseMpscLinkedArrayQueuePad1 extends AbstractQueue implements IndexedQueue {
long p01, p02, p03, p04, p05, p06, p07;
long p10, p11, p12, p13, p14, p15, p16, p17;
}
// $gen:ordered-fields
abstract class BaseMpscLinkedArrayQueueProducerFields extends BaseMpscLinkedArrayQueuePad1 {
private static final long P_INDEX_OFFSET =
fieldOffset(BaseMpscLinkedArrayQueueProducerFields.class, "producerIndex");
private volatile long producerIndex;
@Override
public final long lvProducerIndex() {
return producerIndex;
}
final void soProducerIndex(long newValue) {
UNSAFE.putOrderedLong(this, P_INDEX_OFFSET, newValue);
}
final boolean casProducerIndex(long expect, long newValue) {
return UNSAFE.compareAndSwapLong(this, P_INDEX_OFFSET, expect, newValue);
}
}
abstract class BaseMpscLinkedArrayQueuePad2 extends BaseMpscLinkedArrayQueueProducerFields {
long p01, p02, p03, p04, p05, p06, p07;
long p10, p11, p12, p13, p14, p15, p16, p17;
}
// $gen:ordered-fields
abstract class BaseMpscLinkedArrayQueueConsumerFields extends BaseMpscLinkedArrayQueuePad2 {
private static final long C_INDEX_OFFSET =
fieldOffset(BaseMpscLinkedArrayQueueConsumerFields.class, "consumerIndex");
private volatile long consumerIndex;
protected long consumerMask;
protected E[] consumerBuffer;
@Override
public final long lvConsumerIndex() {
return consumerIndex;
}
final long lpConsumerIndex() {
return UNSAFE.getLong(this, C_INDEX_OFFSET);
}
final void soConsumerIndex(long newValue) {
UNSAFE.putOrderedLong(this, C_INDEX_OFFSET, newValue);
}
}
abstract class BaseMpscLinkedArrayQueuePad3 extends BaseMpscLinkedArrayQueueConsumerFields {
long p0, p1, p2, p3, p4, p5, p6, p7;
long p10, p11, p12, p13, p14, p15, p16, p17;
}
// $gen:ordered-fields
abstract class BaseMpscLinkedArrayQueueColdProducerFields
extends BaseMpscLinkedArrayQueuePad3 {
private static final long P_LIMIT_OFFSET =
fieldOffset(BaseMpscLinkedArrayQueueColdProducerFields.class, "producerLimit");
private volatile long producerLimit;
protected long producerMask;
protected E[] producerBuffer;
final long lvProducerLimit() {
return producerLimit;
}
final boolean casProducerLimit(long expect, long newValue) {
return UNSAFE.compareAndSwapLong(this, P_LIMIT_OFFSET, expect, newValue);
}
final void soProducerLimit(long newValue) {
UNSAFE.putOrderedLong(this, P_LIMIT_OFFSET, newValue);
}
}
/**
* 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.
*
* @param
*/
public abstract class BaseMpscLinkedArrayQueue
extends BaseMpscLinkedArrayQueueColdProducerFields
implements MessagePassingQueue, QueueProgressIndicators {
// No post padding here, subclasses must add
private static final Object JUMP = new Object();
private static final Object BUFFER_CONSUMED = new Object();
private static final int CONTINUE_TO_P_INDEX_CAS = 0;
private static final int RETRY = 1;
private static final int QUEUE_FULL = 2;
private static final int QUEUE_RESIZE = 3;
/**
* @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) {
RangeUtil.checkGreaterThanOrEqual(initialCapacity, 2, "initialCapacity");
int p2capacity = Pow2.roundToPowerOfTwo(initialCapacity);
// leave lower bit of mask clear
long mask = (p2capacity - 1) << 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 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());
}
@Override
public String toString() {
return this.getClass().getName();
}
@Override
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 CONTINUE_TO_P_INDEX_CAS:
break;
case RETRY:
continue;
case QUEUE_FULL:
return false;
case QUEUE_RESIZE:
resize(mask, buffer, pIndex, e, null);
return true;
}
}
if (casProducerIndex(pIndex, pIndex + 2)) {
break;
}
}
// INDEX visible before ELEMENT
final long offset = modifiedCalcElementOffset(pIndex, mask);
soElement(buffer, offset, e); // release element e
return true;
}
/**
* {@inheritDoc}
*
* This implementation is correct for single consumer thread use only.
*/
@SuppressWarnings("unchecked")
@Override
public E poll() {
final E[] buffer = consumerBuffer;
final long index = lpConsumerIndex();
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 = nextBuffer(buffer, mask);
return newBufferPoll(nextBuffer, index);
}
soElement(buffer, offset, null); // release element null
soConsumerIndex(index + 2); // release cIndex
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 = lpConsumerIndex();
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.
do {
e = lvElement(buffer, offset);
} while (e == null);
}
if (e == JUMP) {
return newBufferPeek(nextBuffer(buffer, mask), index);
}
return (E) e;
}
/** We do not inline resize into this method because we do not resize on fill. */
private int offerSlowPath(long mask, long pIndex, long producerLimit) {
final long cIndex = lvConsumerIndex();
long bufferCapacity = getCurrentBufferCapacity(mask);
if (cIndex + bufferCapacity > pIndex) {
if (!casProducerLimit(producerLimit, cIndex + bufferCapacity)) {
// retry from top
return RETRY;
} else {
// continue to pIndex CAS
return CONTINUE_TO_P_INDEX_CAS;
}
}
// full and cannot grow
else if (availableInQueue(pIndex, cIndex) <= 0) {
// offer should return false;
return QUEUE_FULL;
}
// grab index for resize -> set lower bit
else if (casProducerIndex(pIndex, pIndex + 1)) {
// trigger a resize
return QUEUE_RESIZE;
} else {
// failed resize attempt, retry from top
return RETRY;
}
}
/** @return available elements in queue * 2 */
protected abstract long availableInQueue(long pIndex, long cIndex);
@SuppressWarnings("unchecked")
private E[] nextBuffer(final E[] buffer, final long mask) {
final long offset = nextArrayOffset(mask);
final E[] nextBuffer = (E[]) lvElement(buffer, offset);
consumerBuffer = nextBuffer;
consumerMask = (length(nextBuffer) - 2) << 1;
soElement(buffer, offset, BUFFER_CONSUMED);
return nextBuffer;
}
private long nextArrayOffset(long mask) {
return modifiedCalcElementOffset(mask + 2, Long.MAX_VALUE);
}
private E newBufferPoll(E[] nextBuffer, long index) {
final long offset = modifiedCalcElementOffset(index, consumerMask);
final E n = lvElement(nextBuffer, offset); // LoadLoad
if (n == null) {
throw new IllegalStateException("new buffer must have at least one element");
}
soElement(nextBuffer, offset, null); // StoreStore
soConsumerIndex(index + 2);
return n;
}
private E newBufferPeek(E[] nextBuffer, long index) {
final long offset = modifiedCalcElementOffset(index, consumerMask);
final E n = lvElement(nextBuffer, offset); // LoadLoad
if (null == n) {
throw new IllegalStateException("new buffer must have at least one element");
}
return n;
}
@Override
public long currentProducerIndex() {
return lvProducerIndex() / 2;
}
@Override
public long currentConsumerIndex() {
return lvConsumerIndex() / 2;
}
@Override
public abstract int capacity();
@Override
public boolean relaxedOffer(E e) {
return offer(e);
}
@SuppressWarnings("unchecked")
@Override
public E relaxedPoll() {
final E[] buffer = consumerBuffer;
final long index = lpConsumerIndex();
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 = nextBuffer(buffer, mask);
return newBufferPoll(nextBuffer, index);
}
soElement(buffer, offset, null);
soConsumerIndex(index + 2);
return (E) e;
}
@SuppressWarnings("unchecked")
@Override
public E relaxedPeek() {
final E[] buffer = consumerBuffer;
final long index = lpConsumerIndex();
final long mask = consumerMask;
final long offset = modifiedCalcElementOffset(index, mask);
Object e = lvElement(buffer, offset); // LoadLoad
if (e == JUMP) {
return newBufferPeek(nextBuffer(buffer, mask), index);
}
return (E) e;
}
@Override
public int fill(Supplier s) {
long result =
0; // result is a long because we want to have a safepoint check at regular intervals
final int capacity = capacity();
do {
final int filled = fill(s, PortableJvmInfo.RECOMENDED_OFFER_BATCH);
if (filled == 0) {
return (int) result;
}
result += filled;
} while (result <= capacity);
return (int) result;
}
@Override
public int fill(Supplier s, int batchSize) {
long mask;
E[] buffer;
long pIndex;
int claimedSlots;
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)
// NOTE: mask/buffer may get changed by resizing -> only use for array access after successful
// CAS.
// Only by virtue offloading them between the lvProducerIndex and a successful
// casProducerIndex are they
// safe to use.
mask = this.producerMask;
buffer = this.producerBuffer;
// a successful CAS ties the ordering, lv(pIndex) -> [mask/buffer] -> cas(pIndex)
// we want 'limit' slots, but will settle for whatever is visible to 'producerLimit'
long batchIndex = Math.min(producerLimit, pIndex + 2 * batchSize);
if (pIndex >= producerLimit || producerLimit < batchIndex) {
int result = offerSlowPath(mask, pIndex, producerLimit);
switch (result) {
case CONTINUE_TO_P_INDEX_CAS:
// offer slow path verifies only one slot ahead, we cannot rely on indication here
case RETRY:
continue;
case QUEUE_FULL:
return 0;
case QUEUE_RESIZE:
resize(mask, buffer, pIndex, null, s);
return 1;
}
}
// claim limit slots at once
if (casProducerIndex(pIndex, batchIndex)) {
claimedSlots = (int) ((batchIndex - pIndex) / 2);
break;
}
}
for (int i = 0; i < claimedSlots; i++) {
final long offset = modifiedCalcElementOffset(pIndex + 2 * i, mask);
soElement(buffer, offset, s.get());
}
return claimedSlots;
}
@Override
public void fill(Supplier s, WaitStrategy w, ExitCondition exit) {
while (exit.keepRunning()) {
if (fill(s, PortableJvmInfo.RECOMENDED_OFFER_BATCH) == 0) {
int idleCounter = 0;
while (exit.keepRunning() && fill(s, PortableJvmInfo.RECOMENDED_OFFER_BATCH) == 0) {
idleCounter = w.idle(idleCounter);
}
}
}
}
@Override
public int drain(Consumer c) {
return drain(c, capacity());
}
@Override
public int drain(final Consumer c, final int limit) {
// Impl note: there are potentially some small gains to be had by manually inlining
// relaxedPoll() and hoisting
// reused fields out to reduce redundant reads.
int i = 0;
E m;
for (; i < limit && (m = relaxedPoll()) != null; i++) {
c.accept(m);
}
return i;
}
@Override
public void drain(Consumer c, WaitStrategy w, ExitCondition exit) {
int idleCounter = 0;
while (exit.keepRunning()) {
E e = relaxedPoll();
if (e == null) {
idleCounter = w.idle(idleCounter);
continue;
}
idleCounter = 0;
c.accept(e);
}
}
/**
* Get an iterator for this queue. This method is thread safe.
*
* The iterator provides a best-effort snapshot of the elements in the queue. The returned
* iterator is not guaranteed to return elements in queue order, and races with the consumer
* thread may cause gaps in the sequence of returned elements. Like {link #relaxedPoll}, the
* iterator may not immediately return newly inserted elements.
*
* @return The iterator.
*/
@Override
public Iterator iterator() {
return new WeakIterator();
}
private final class WeakIterator implements Iterator {
private long nextIndex;
private E nextElement;
private E[] currentBuffer;
private int currentBufferLength;
WeakIterator() {
setBuffer(consumerBuffer);
nextElement = getNext();
}
@Override
public boolean hasNext() {
return nextElement != null;
}
@Override
public E next() {
E e = nextElement;
nextElement = getNext();
return e;
}
private void setBuffer(E[] buffer) {
this.currentBuffer = buffer;
this.currentBufferLength = length(buffer);
this.nextIndex = 0;
}
private E getNext() {
while (true) {
while (nextIndex < currentBufferLength - 1) {
long offset = calcElementOffset(nextIndex++);
E e = lvElement(currentBuffer, offset);
if (e != null && e != JUMP) {
return e;
}
}
long offset = calcElementOffset(currentBufferLength - 1);
Object nextArray = lvElement(currentBuffer, offset);
if (nextArray == BUFFER_CONSUMED) {
// Consumer may have passed us, just jump to the current consumer buffer
setBuffer(consumerBuffer);
} else if (nextArray != null) {
setBuffer((E[]) nextArray);
} else {
return null;
}
}
}
}
private void resize(long oldMask, E[] oldBuffer, long pIndex, E e, Supplier s) {
assert (e != null && s == null) || (e == null || s != null);
int newBufferLength = getNextBufferSize(oldBuffer);
final E[] newBuffer;
try {
newBuffer = allocate(newBufferLength);
} catch (OutOfMemoryError oom) {
assert lvProducerIndex() == pIndex + 1;
soProducerIndex(pIndex);
throw oom;
}
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 == null ? s.get() : e); // element in new array
soElement(oldBuffer, nextArrayOffset(oldMask), newBuffer); // buffer linked
// ASSERT code
final long cIndex = lvConsumerIndex();
final long availableInQueue = availableInQueue(pIndex, cIndex);
RangeUtil.checkPositive(availableInQueue, "availableInQueue");
// 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);
}
/** @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);
}