io.netty.util.internal.shaded.org.jctools.queues.MpmcArrayQueue 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.netty.util.internal.shaded.org.jctools.queues;
import io.netty.util.internal.shaded.org.jctools.util.PortableJvmInfo;
import io.netty.util.internal.shaded.org.jctools.util.RangeUtil;
import static io.netty.util.internal.shaded.org.jctools.util.UnsafeAccess.UNSAFE;
import static io.netty.util.internal.shaded.org.jctools.util.UnsafeRefArrayAccess.lpElement;
import static io.netty.util.internal.shaded.org.jctools.util.UnsafeRefArrayAccess.soElement;
abstract class MpmcArrayQueueL1Pad extends ConcurrentSequencedCircularArrayQueue
{
long p00, p01, p02, p03, p04, p05, p06, p07;
long p10, p11, p12, p13, p14, p15, p16;
public MpmcArrayQueueL1Pad(int capacity)
{
super(capacity);
}
}
//$gen:ordered-fields
abstract class MpmcArrayQueueProducerIndexField extends MpmcArrayQueueL1Pad
{
private final static long P_INDEX_OFFSET;
static
{
try
{
P_INDEX_OFFSET = UNSAFE.objectFieldOffset(MpmcArrayQueueProducerIndexField.class
.getDeclaredField("producerIndex"));
}
catch (NoSuchFieldException e)
{
throw new RuntimeException(e);
}
}
private volatile long producerIndex;
public MpmcArrayQueueProducerIndexField(int capacity)
{
super(capacity);
}
@Override
public final long lvProducerIndex()
{
return producerIndex;
}
protected final boolean casProducerIndex(long expect, long newValue)
{
return UNSAFE.compareAndSwapLong(this, P_INDEX_OFFSET, expect, newValue);
}
}
abstract class MpmcArrayQueueL2Pad extends MpmcArrayQueueProducerIndexField
{
long p01, p02, p03, p04, p05, p06, p07;
long p10, p11, p12, p13, p14, p15, p16, p17;
public MpmcArrayQueueL2Pad(int capacity)
{
super(capacity);
}
}
//$gen:ordered-fields
abstract class MpmcArrayQueueConsumerIndexField extends MpmcArrayQueueL2Pad
{
private final static long C_INDEX_OFFSET;
static
{
try
{
C_INDEX_OFFSET = UNSAFE.objectFieldOffset(MpmcArrayQueueConsumerIndexField.class
.getDeclaredField("consumerIndex"));
}
catch (NoSuchFieldException e)
{
throw new RuntimeException(e);
}
}
private volatile long consumerIndex;
public MpmcArrayQueueConsumerIndexField(int capacity)
{
super(capacity);
}
@Override
public final long lvConsumerIndex()
{
return consumerIndex;
}
protected final boolean casConsumerIndex(long expect, long newValue)
{
return UNSAFE.compareAndSwapLong(this, C_INDEX_OFFSET, expect, newValue);
}
}
abstract class MpmcArrayQueueL3Pad extends MpmcArrayQueueConsumerIndexField
{
long p01, p02, p03, p04, p05, p06, p07;
long p10, p11, p12, p13, p14, p15, p16, p17;
public MpmcArrayQueueL3Pad(int capacity)
{
super(capacity);
}
}
/**
* A Multi-Producer-Multi-Consumer queue based on a {@link io.netty.util.internal.shaded.org.jctools.queues.ConcurrentCircularArrayQueue}. This
* implies that any and all threads may call the offer/poll/peek methods and correctness is maintained.
* This implementation follows patterns documented on the package level for False Sharing protection.
* The algorithm for offer/poll is an adaptation of the one put forward by D. Vyukov (See here). The original
* algorithm uses an array of structs which should offer nice locality properties but is sadly not possible in
* Java (waiting on Value Types or similar). The alternative explored here utilizes 2 arrays, one for each
* field of the struct. There is a further alternative in the experimental project which uses iteration phase
* markers to achieve the same algo and is closer structurally to the original, but sadly does not perform as
* well as this implementation.
*
* Tradeoffs to keep in mind:
*
* - Padding for false sharing: counter fields and queue fields are all padded as well as either side of
* both arrays. We are trading memory to avoid false sharing(active and passive).
*
- 2 arrays instead of one: The algorithm requires an extra array of longs matching the size of the
* elements array. This is doubling/tripling the memory allocated for the buffer.
*
- Power of 2 capacity: Actual elements buffer (and sequence buffer) is the closest power of 2 larger or
* equal to the requested capacity.
*
*
* @param type of the element stored in the {@link java.util.Queue}
*/
public class MpmcArrayQueue extends MpmcArrayQueueL3Pad
{
public MpmcArrayQueue(final int capacity)
{
super(RangeUtil.checkGreaterThanOrEqual(capacity, 2, "capacity"));
}
@Override
public boolean offer(final E e)
{
if (null == e)
{
throw new NullPointerException();
}
final long mask = this.mask;
final long capacity = mask + 1;
final long[] sBuffer = sequenceBuffer;
long pIndex;
long seqOffset;
long seq;
long cIndex = Long.MIN_VALUE;// start with bogus value, hope we don't need it
do
{
pIndex = lvProducerIndex();
seqOffset = calcSequenceOffset(pIndex, mask);
seq = lvSequence(sBuffer, seqOffset);
// consumer has not moved this seq forward, it's as last producer left
if (seq < pIndex)
{
// Extra check required to ensure [Queue.offer == false iff queue is full]
if (pIndex - capacity >= cIndex && // test against cached cIndex
pIndex - capacity >= (cIndex = lvConsumerIndex()))
{ // test against latest cIndex
return false;
}
else
{
seq = pIndex + 1; // (+) hack to make it go around again without CAS
}
}
}
while (seq > pIndex || // another producer has moved the sequence(or +)
!casProducerIndex(pIndex, pIndex + 1)); // failed to increment
soElement(buffer, calcElementOffset(pIndex, mask), e);
soSequence(sBuffer, seqOffset, pIndex + 1); // seq++;
return true;
}
/**
* {@inheritDoc}
*
* Because return null indicates queue is empty we cannot simply rely on next element visibility for poll
* and must test producer index when next element is not visible.
*/
@Override
public E poll()
{
// local load of field to avoid repeated loads after volatile reads
final long[] sBuffer = sequenceBuffer;
final long mask = this.mask;
long cIndex;
long seq;
long seqOffset;
long expectedSeq;
long pIndex = -1; // start with bogus value, hope we don't need it
do
{
cIndex = lvConsumerIndex();
seqOffset = calcSequenceOffset(cIndex, mask);
seq = lvSequence(sBuffer, seqOffset);
expectedSeq = cIndex + 1;
if (seq < expectedSeq)
{ // slot has not been moved by producer
if (cIndex >= pIndex && // test against cached pIndex
cIndex == (pIndex = lvProducerIndex()))
{ // update pIndex if we must
// strict empty check, this ensures [Queue.poll() == null iff isEmpty()]
return null;
}
else
{
seq = expectedSeq + 1; // trip another go around
}
}
}
while (seq > expectedSeq || // another consumer beat us to it
!casConsumerIndex(cIndex, cIndex + 1)); // failed the CAS
final long offset = calcElementOffset(cIndex, mask);
final E e = lpElement(buffer, offset);
soElement(buffer, offset, null);
soSequence(sBuffer, seqOffset, cIndex + mask + 1);// i.e. seq += capacity
return e;
}
@Override
public E peek()
{
long cIndex;
E e;
do
{
cIndex = lvConsumerIndex();
// other consumers may have grabbed the element, or queue might be empty
e = lpElement(buffer, calcElementOffset(cIndex));
// only return null if queue is empty
}
while (e == null && cIndex != lvProducerIndex());
return e;
}
@Override
public boolean relaxedOffer(E e)
{
if (null == e)
{
throw new NullPointerException();
}
final long mask = this.mask;
final long[] sBuffer = sequenceBuffer;
long pIndex;
long seqOffset;
long seq;
do
{
pIndex = lvProducerIndex();
seqOffset = calcSequenceOffset(pIndex, mask);
seq = lvSequence(sBuffer, seqOffset);
if (seq < pIndex)
{ // slot not cleared by consumer yet
return false;
}
}
while (seq > pIndex || // another producer has moved the sequence
!casProducerIndex(pIndex, pIndex + 1)); // failed to increment
soElement(buffer, calcElementOffset(pIndex, mask), e);
soSequence(sBuffer, seqOffset, pIndex + 1);
return true;
}
@Override
public E relaxedPoll()
{
final long[] sBuffer = sequenceBuffer;
final long mask = this.mask;
long cIndex;
long seqOffset;
long seq;
long expectedSeq;
do
{
cIndex = lvConsumerIndex();
seqOffset = calcSequenceOffset(cIndex, mask);
seq = lvSequence(sBuffer, seqOffset);
expectedSeq = cIndex + 1;
if (seq < expectedSeq)
{
return null;
}
}
while (seq > expectedSeq || // another consumer beat us to it
!casConsumerIndex(cIndex, cIndex + 1)); // failed the CAS
final long offset = calcElementOffset(cIndex, mask);
final E e = lpElement(buffer, offset);
soElement(buffer, offset, null);
soSequence(sBuffer, seqOffset, cIndex + mask + 1);
return e;
}
@Override
public E relaxedPeek()
{
long currConsumerIndex = lvConsumerIndex();
return lpElement(buffer, calcElementOffset(currConsumerIndex));
}
@Override
public int drain(Consumer c)
{
final int capacity = capacity();
int sum = 0;
while (sum < capacity)
{
int drained = 0;
if ((drained = drain(c, PortableJvmInfo.RECOMENDED_POLL_BATCH)) == 0)
{
break;
}
sum += drained;
}
return sum;
}
@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 drain(Consumer c, int limit)
{
final long[] sBuffer = sequenceBuffer;
final long mask = this.mask;
final E[] buffer = this.buffer;
long cIndex;
long seqOffset;
long seq;
long expectedSeq;
for (int i = 0; i < limit; i++)
{
do
{
cIndex = lvConsumerIndex();
seqOffset = calcSequenceOffset(cIndex, mask);
seq = lvSequence(sBuffer, seqOffset);
expectedSeq = cIndex + 1;
if (seq < expectedSeq)
{
return i;
}
}
while (seq > expectedSeq || // another consumer beat us to it
!casConsumerIndex(cIndex, cIndex + 1)); // failed the CAS
final long offset = calcElementOffset(cIndex, mask);
final E e = lpElement(buffer, offset);
soElement(buffer, offset, null);
soSequence(sBuffer, seqOffset, cIndex + mask + 1);
c.accept(e);
}
return limit;
}
@Override
public int fill(Supplier s, int limit)
{
final long[] sBuffer = sequenceBuffer;
final long mask = this.mask;
final E[] buffer = this.buffer;
long pIndex;
long seqOffset;
long seq;
for (int i = 0; i < limit; i++)
{
do
{
pIndex = lvProducerIndex();
seqOffset = calcSequenceOffset(pIndex, mask);
seq = lvSequence(sBuffer, seqOffset);
if (seq < pIndex)
{ // slot not cleared by consumer yet
return i;
}
}
while (seq > pIndex || // another producer has moved the sequence
!casProducerIndex(pIndex, pIndex + 1)); // failed to increment
soElement(buffer, calcElementOffset(pIndex, mask), s.get());
soSequence(sBuffer, seqOffset, pIndex + 1);
}
return limit;
}
@Override
public void drain(
Consumer c,
WaitStrategy w,
ExitCondition exit)
{
int idleCounter = 0;
while (exit.keepRunning())
{
if (drain(c, PortableJvmInfo.RECOMENDED_POLL_BATCH) == 0)
{
idleCounter = w.idle(idleCounter);
continue;
}
idleCounter = 0;
}
}
@Override
public void fill(
Supplier s,
WaitStrategy w,
ExitCondition exit)
{
int idleCounter = 0;
while (exit.keepRunning())
{
if (fill(s, PortableJvmInfo.RECOMENDED_OFFER_BATCH) == 0)
{
idleCounter = w.idle(idleCounter);
continue;
}
idleCounter = 0;
}
}
}