rx.internal.util.unsafe.SpmcArrayQueue 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.
*
* Original License: https://github.com/JCTools/JCTools/blob/master/LICENSE
* Original location: https://github.com/JCTools/JCTools/blob/master/jctools-core/src/main/java/org/jctools/queues/SpmcArrayQueue.java
*/
package rx.internal.util.unsafe;
abstract class SpmcArrayQueueL1Pad extends ConcurrentCircularArrayQueue {
long p10, p11, p12, p13, p14, p15, p16;
long p30, p31, p32, p33, p34, p35, p36, p37;
public SpmcArrayQueueL1Pad(int capacity) {
super(capacity);
}
}
abstract class SpmcArrayQueueProducerField extends SpmcArrayQueueL1Pad {
protected final static long P_INDEX_OFFSET;
static {
try {
P_INDEX_OFFSET =
UnsafeAccess.UNSAFE.objectFieldOffset(SpmcArrayQueueProducerField.class.getDeclaredField("producerIndex"));
} catch (NoSuchFieldException e) {
throw new RuntimeException(e);
}
}
private volatile long producerIndex;
protected final long lvProducerIndex() {
return producerIndex;
}
protected final void soTail(long v) {
UnsafeAccess.UNSAFE.putOrderedLong(this, P_INDEX_OFFSET, v);
}
public SpmcArrayQueueProducerField(int capacity) {
super(capacity);
}
}
abstract class SpmcArrayQueueL2Pad extends SpmcArrayQueueProducerField {
long p20, p21, p22, p23, p24, p25, p26;
long p30, p31, p32, p33, p34, p35, p36, p37;
public SpmcArrayQueueL2Pad(int capacity) {
super(capacity);
}
}
abstract class SpmcArrayQueueConsumerField extends SpmcArrayQueueL2Pad {
protected final static long C_INDEX_OFFSET;
static {
try {
C_INDEX_OFFSET =
UnsafeAccess.UNSAFE.objectFieldOffset(SpmcArrayQueueConsumerField.class.getDeclaredField("consumerIndex"));
} catch (NoSuchFieldException e) {
throw new RuntimeException(e);
}
}
private volatile long consumerIndex;
public SpmcArrayQueueConsumerField(int capacity) {
super(capacity);
}
protected final long lvConsumerIndex() {
return consumerIndex;
}
protected final boolean casHead(long expect, long newValue) {
return UnsafeAccess.UNSAFE.compareAndSwapLong(this, C_INDEX_OFFSET, expect, newValue);
}
}
abstract class SpmcArrayQueueMidPad extends SpmcArrayQueueConsumerField {
long p20, p21, p22, p23, p24, p25, p26;
long p30, p31, p32, p33, p34, p35, p36, p37;
public SpmcArrayQueueMidPad(int capacity) {
super(capacity);
}
}
abstract class SpmcArrayQueueProducerIndexCacheField extends SpmcArrayQueueMidPad {
// This is separated from the consumerIndex which will be highly contended in the hope that this value spends most
// of it's time in a cache line that is Shared(and rarely invalidated)
private volatile long producerIndexCache;
public SpmcArrayQueueProducerIndexCacheField(int capacity) {
super(capacity);
}
protected final long lvProducerIndexCache() {
return producerIndexCache;
}
protected final void svProducerIndexCache(long v) {
producerIndexCache = v;
}
}
abstract class SpmcArrayQueueL3Pad extends SpmcArrayQueueProducerIndexCacheField {
long p40, p41, p42, p43, p44, p45, p46;
long p30, p31, p32, p33, p34, p35, p36, p37;
public SpmcArrayQueueL3Pad(int capacity) {
super(capacity);
}
}
public final class SpmcArrayQueue extends SpmcArrayQueueL3Pad {
public SpmcArrayQueue(final int capacity) {
super(capacity);
}
@Override
public boolean offer(final E e) {
if (null == e) {
throw new NullPointerException("Null is not a valid element");
}
final E[] lb = buffer;
final long currProducerIndex = lvProducerIndex();
final long offset = calcElementOffset(currProducerIndex);
if (null != lvElement(lb, offset)) {
// strict check as per https://github.com/JCTools/JCTools/issues/21#issuecomment-50204120
int size = (int) (currProducerIndex - lvConsumerIndex());
if (size == capacity) {
return false;
}
else {
// spin wait for slot to clear, buggers wait freedom
while (null != lvElement(lb, offset));
}
}
spElement(lb, offset, e);
// single producer, so store ordered is valid. It is also required to correctly publish the element
// and for the consumers to pick up the tail value.
soTail(currProducerIndex + 1);
return true;
}
/**
* {@inheritDoc}
*
* Note that we are not doing the the whole poll/tryPoll thing here like we do in MPMC/MPSC, that is because the
* problem we try to solve there is caused by having multiple producers making progress concurrently which can
* create 'bubbles' of claimed but not fully visible elements in the queue. For a single producer the problem
* doesn't exist.
*/
@Override
public E poll() {
long currentConsumerIndex;
final long currProducerIndexCache = lvProducerIndexCache();
do {
currentConsumerIndex = lvConsumerIndex();
if (currentConsumerIndex >= currProducerIndexCache) {
long currProducerIndex = lvProducerIndex();
if (currentConsumerIndex >= currProducerIndex) {
return null;
} else {
svProducerIndexCache(currProducerIndex);
}
}
} while (!casHead(currentConsumerIndex, currentConsumerIndex + 1));
// consumers are gated on latest visible tail, and so can't see a null value in the queue or overtake
// and wrap to hit same location.
final long offset = calcElementOffset(currentConsumerIndex);
final E[] lb = buffer;
// load plain, element happens before it's index becomes visible
final E e = lpElement(lb, offset);
// store ordered, make sure nulling out is visible. Producer is waiting for this value.
soElement(lb, offset, null);
return e;
}
@Override
public E peek() {
return lvElement(calcElementOffset(lvConsumerIndex()));
}
@Override
public int size() {
/*
* 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();
while (true) {
final long before = after;
final long currentProducerIndex = lvProducerIndex();
after = lvConsumerIndex();
if (before == after) {
return (int) (currentProducerIndex - after);
}
}
}
@Override
public boolean isEmpty() {
// Order matters!
// Loading consumer before producer allows for producer increments after consumer index is read.
// This ensures the correctness of this method at least for the consumer thread. Other threads POV is not really
// something we can fix here.
return (lvConsumerIndex() == lvProducerIndex());
}
}