co.elastic.apm.agent.shaded.jctools.queues.MpscArrayQueue 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 co.elastic.apm.agent.shaded.jctools.queues;
import co.elastic.apm.agent.shaded.jctools.util.PortableJvmInfo;
import static co.elastic.apm.agent.shaded.jctools.util.UnsafeAccess.UNSAFE;
import static co.elastic.apm.agent.shaded.jctools.util.UnsafeAccess.fieldOffset;
import static co.elastic.apm.agent.shaded.jctools.util.UnsafeRefArrayAccess.*;
abstract class MpscArrayQueueL1Pad extends ConcurrentCircularArrayQueue
{
long p00, p01, p02, p03, p04, p05, p06, p07;
long p10, p11, p12, p13, p14, p15, p16;
MpscArrayQueueL1Pad(int capacity)
{
super(capacity);
}
}
//$gen:ordered-fields
abstract class MpscArrayQueueProducerIndexField extends MpscArrayQueueL1Pad
{
private final static long P_INDEX_OFFSET = fieldOffset(MpscArrayQueueProducerIndexField.class, "producerIndex");
private volatile long producerIndex;
MpscArrayQueueProducerIndexField(int capacity)
{
super(capacity);
}
@Override
public final long lvProducerIndex()
{
return producerIndex;
}
protected final boolean casProducerIndex(long expect, long newValue)
{
return UNSAFE.compareAndSwapLong(this, P_INDEX_OFFSET, expect, newValue);
}
}
abstract class MpscArrayQueueMidPad extends MpscArrayQueueProducerIndexField
{
long p01, p02, p03, p04, p05, p06, p07;
long p10, p11, p12, p13, p14, p15, p16, p17;
MpscArrayQueueMidPad(int capacity)
{
super(capacity);
}
}
//$gen:ordered-fields
abstract class MpscArrayQueueProducerLimitField extends MpscArrayQueueMidPad
{
private final static long P_LIMIT_OFFSET = fieldOffset(MpscArrayQueueProducerLimitField.class, "producerLimit");
// First unavailable index the producer may claim up to before rereading the consumer index
private volatile long producerLimit;
MpscArrayQueueProducerLimitField(int capacity)
{
super(capacity);
this.producerLimit = capacity;
}
protected final long lvProducerLimit()
{
return producerLimit;
}
protected final void soProducerLimit(long newValue)
{
UNSAFE.putOrderedLong(this, P_LIMIT_OFFSET, newValue);
}
}
abstract class MpscArrayQueueL2Pad extends MpscArrayQueueProducerLimitField
{
long p00, p01, p02, p03, p04, p05, p06, p07;
long p10, p11, p12, p13, p14, p15, p16;
MpscArrayQueueL2Pad(int capacity)
{
super(capacity);
}
}
//$gen:ordered-fields
abstract class MpscArrayQueueConsumerIndexField extends MpscArrayQueueL2Pad
{
private final static long C_INDEX_OFFSET = fieldOffset(MpscArrayQueueConsumerIndexField.class, "consumerIndex");
protected long consumerIndex;
MpscArrayQueueConsumerIndexField(int capacity)
{
super(capacity);
}
protected final long lpConsumerIndex()
{
return consumerIndex;
}
@Override
public final long lvConsumerIndex()
{
return UNSAFE.getLongVolatile(this, C_INDEX_OFFSET);
}
protected void soConsumerIndex(long newValue)
{
UNSAFE.putOrderedLong(this, C_INDEX_OFFSET, newValue);
}
}
abstract class MpscArrayQueueL3Pad extends MpscArrayQueueConsumerIndexField
{
long p01, p02, p03, p04, p05, p06, p07;
long p10, p11, p12, p13, p14, p15, p16, p17;
MpscArrayQueueL3Pad(int capacity)
{
super(capacity);
}
}
/**
* A Multi-Producer-Single-Consumer queue based on a {@link co.elastic.apm.agent.shaded.jctools.queues.ConcurrentCircularArrayQueue}. This
* implies that any thread may call the offer method, but only a single thread may call poll/peek for correctness to
* maintained.
* This implementation follows patterns documented on the package level for False Sharing protection.
* This implementation is using the Fast Flow
* method for polling from the queue (with minor change to correctly publish the index) and an extension of
* the Leslie Lamport concurrent queue algorithm (originated by Martin Thompson) on the producer side.
*
* @param
* @author nitsanw
*/
public class MpscArrayQueue extends MpscArrayQueueL3Pad
{
public MpscArrayQueue(final int capacity)
{
super(capacity);
}
/**
* {@link #offer}} if {@link #size()} is less than threshold.
*
* @param e the object to offer onto the queue, not null
* @param threshold the maximum allowable size
* @return true if the offer is successful, false if queue size exceeds threshold
* @since 1.0.1
*/
public boolean offerIfBelowThreshold(final E e, int threshold)
{
if (null == e)
{
throw new NullPointerException();
}
final long mask = this.mask;
final long capacity = mask + 1;
long producerLimit = lvProducerLimit(); // LoadLoad
long pIndex;
do
{
pIndex = lvProducerIndex(); // LoadLoad
long available = producerLimit - pIndex;
long size = capacity - available;
if (size >= threshold)
{
final long cIndex = lvConsumerIndex(); // LoadLoad
size = pIndex - cIndex;
if (size >= threshold)
{
return false; // the size exceeds threshold
}
else
{
// update producer limit to the next index that we must recheck the consumer index
producerLimit = cIndex + capacity;
// this is racy, but the race is benign
soProducerLimit(producerLimit);
}
}
}
while (!casProducerIndex(pIndex, pIndex + 1));
/*
* NOTE: the new producer index value is made visible BEFORE the element in the array. If we relied on
* the index visibility to poll() we would need to handle the case where the element is not visible.
*/
// Won CAS, move on to storing
final long offset = calcElementOffset(pIndex, mask);
soElement(buffer, offset, e); // StoreStore
return true; // AWESOME :)
}
/**
* {@inheritDoc}
*
* IMPLEMENTATION NOTES:
* Lock free offer using a single CAS. As class name suggests access is permitted to many threads
* concurrently.
*
* @see java.util.Queue#offer
* @see co.elastic.apm.agent.shaded.jctools.queues.MessagePassingQueue#offer
*/
@Override
public boolean offer(final E e)
{
if (null == e)
{
throw new NullPointerException();
}
// use a cached view on consumer index (potentially updated in loop)
final long mask = this.mask;
long producerLimit = lvProducerLimit(); // LoadLoad
long pIndex;
do
{
pIndex = lvProducerIndex(); // LoadLoad
if (pIndex >= producerLimit)
{
final long cIndex = lvConsumerIndex(); // LoadLoad
producerLimit = cIndex + mask + 1;
if (pIndex >= producerLimit)
{
return false; // FULL :(
}
else
{
// update producer limit to the next index that we must recheck the consumer index
// this is racy, but the race is benign
soProducerLimit(producerLimit);
}
}
}
while (!casProducerIndex(pIndex, pIndex + 1));
/*
* NOTE: the new producer index value is made visible BEFORE the element in the array. If we relied on
* the index visibility to poll() we would need to handle the case where the element is not visible.
*/
// Won CAS, move on to storing
final long offset = calcElementOffset(pIndex, mask);
soElement(buffer, offset, e); // StoreStore
return true; // AWESOME :)
}
/**
* A wait free alternative to offer which fails on CAS failure.
*
* @param e new element, not null
* @return 1 if next element cannot be filled, -1 if CAS failed, 0 if successful
*/
public final int failFastOffer(final E e)
{
if (null == e)
{
throw new NullPointerException();
}
final long mask = this.mask;
final long capacity = mask + 1;
final long pIndex = lvProducerIndex(); // LoadLoad
long producerLimit = lvProducerLimit(); // LoadLoad
if (pIndex >= producerLimit)
{
final long cIndex = lvConsumerIndex(); // LoadLoad
producerLimit = cIndex + capacity;
if (pIndex >= producerLimit)
{
return 1; // FULL :(
}
else
{
// update producer limit to the next index that we must recheck the consumer index
soProducerLimit(producerLimit); // StoreLoad
}
}
// look Ma, no loop!
if (!casProducerIndex(pIndex, pIndex + 1))
{
return -1; // CAS FAIL :(
}
// Won CAS, move on to storing
final long offset = calcElementOffset(pIndex, mask);
soElement(buffer, offset, e);
return 0; // AWESOME :)
}
/**
* {@inheritDoc}
*
* IMPLEMENTATION NOTES:
* Lock free poll using ordered loads/stores. As class name suggests access is limited to a single thread.
*
* @see java.util.Queue#poll
* @see co.elastic.apm.agent.shaded.jctools.queues.MessagePassingQueue#poll
*/
@Override
public E poll()
{
final long cIndex = lpConsumerIndex();
final long offset = calcElementOffset(cIndex);
// Copy field to avoid re-reading after volatile load
final E[] buffer = this.buffer;
// If we can't see the next available element we can't poll
E e = lvElement(buffer, offset); // LoadLoad
if (null == e)
{
/*
* NOTE: Queue may not actually be empty in the case of a producer (P1) being interrupted after
* winning the CAS on offer but before storing the element in the queue. Other producers may go on
* to fill up the queue after this element.
*/
if (cIndex != lvProducerIndex())
{
do
{
e = lvElement(buffer, offset);
}
while (e == null);
}
else
{
return null;
}
}
spElement(buffer, offset, null);
soConsumerIndex(cIndex + 1); // StoreStore
return e;
}
/**
* {@inheritDoc}
*
* IMPLEMENTATION NOTES:
* Lock free peek using ordered loads. As class name suggests access is limited to a single thread.
*
* @see java.util.Queue#poll
* @see co.elastic.apm.agent.shaded.jctools.queues.MessagePassingQueue#poll
*/
@Override
public E peek()
{
// Copy field to avoid re-reading after volatile load
final E[] buffer = this.buffer;
final long cIndex = lpConsumerIndex(); // LoadLoad
final long offset = calcElementOffset(cIndex);
E e = lvElement(buffer, offset);
if (null == e)
{
/*
* NOTE: Queue may not actually be empty in the case of a producer (P1) being interrupted after
* winning the CAS on offer but before storing the element in the queue. Other producers may go on
* to fill up the queue after this element.
*/
if (cIndex != lvProducerIndex())
{
do
{
e = lvElement(buffer, offset);
}
while (e == null);
}
else
{
return null;
}
}
return e;
}
@Override
public boolean relaxedOffer(E e)
{
return offer(e);
}
@Override
public E relaxedPoll()
{
final E[] buffer = this.buffer;
final long cIndex = lpConsumerIndex();
final long offset = calcElementOffset(cIndex);
// If we can't see the next available element we can't poll
E e = lvElement(buffer, offset); // LoadLoad
if (null == e)
{
return null;
}
spElement(buffer, offset, null);
soConsumerIndex(cIndex + 1); // StoreStore
return e;
}
@Override
public E relaxedPeek()
{
final E[] buffer = this.buffer;
final long mask = this.mask;
final long cIndex = lpConsumerIndex();
return lvElement(buffer, calcElementOffset(cIndex, mask));
}
@Override
public int drain(Consumer c)
{
return drain(c, capacity());
}
@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(final Consumer c, final int limit)
{
final E[] buffer = this.buffer;
final long mask = this.mask;
final long cIndex = lpConsumerIndex();
for (int i = 0; i < limit; i++)
{
final long index = cIndex + i;
final long offset = calcElementOffset(index, mask);
final E e = lvElement(buffer, offset);// LoadLoad
if (null == e)
{
return i;
}
spElement(buffer, offset, null);
soConsumerIndex(index + 1); // ordered store -> atomic and ordered for size()
c.accept(e);
}
return limit;
}
@Override
public int fill(Supplier s, int limit)
{
final long mask = this.mask;
final long capacity = mask + 1;
long producerLimit = lvProducerLimit(); // LoadLoad
long pIndex;
int actualLimit = 0;
do
{
pIndex = lvProducerIndex(); // LoadLoad
long available = producerLimit - pIndex;
if (available <= 0)
{
final long cIndex = lvConsumerIndex(); // LoadLoad
producerLimit = cIndex + capacity;
available = producerLimit - pIndex;
if (available <= 0)
{
return 0; // FULL :(
}
else
{
// update producer limit to the next index that we must recheck the consumer index
soProducerLimit(producerLimit); // StoreLoad
}
}
actualLimit = Math.min((int) available, limit);
}
while (!casProducerIndex(pIndex, pIndex + actualLimit));
// right, now we claimed a few slots and can fill them with goodness
final E[] buffer = this.buffer;
for (int i = 0; i < actualLimit; i++)
{
// Won CAS, move on to storing
final long offset = calcElementOffset(pIndex + i, mask);
soElement(buffer, offset, s.get());
}
return actualLimit;
}
@Override
public void drain(Consumer c, WaitStrategy w, ExitCondition exit)
{
final E[] buffer = this.buffer;
final long mask = this.mask;
long cIndex = lpConsumerIndex();
int counter = 0;
while (exit.keepRunning())
{
for (int i = 0; i < 4096; i++)
{
final long offset = calcElementOffset(cIndex, mask);
final E e = lvElement(buffer, offset);// LoadLoad
if (null == e)
{
counter = w.idle(counter);
continue;
}
cIndex++;
counter = 0;
spElement(buffer, offset, null);
soConsumerIndex(cIndex); // ordered store -> atomic and ordered for size()
c.accept(e);
}
}
}
@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;
}
}
}