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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 org.jctools.queues;
import org.jctools.util.Pow2;
import org.jctools.util.RangeUtil;
import org.jctools.util.SpscLookAheadUtil;
import static org.jctools.queues.LinkedArrayQueueUtil.length;
import static org.jctools.util.UnsafeRefArrayAccess.*;
/**
* An SPSC array queue which starts at initialCapacity and grows to maxCapacity in linked chunks,
* doubling theirs size every time until the full blown backing array is used.
* The queue grows only when the current chunk is full and elements are not copied on
* resize, instead a link to the new chunk is stored in the old chunk for the consumer to follow.
*
* @param
*/
public class SpscGrowableArrayQueue extends BaseSpscLinkedArrayQueue
{
private final int maxQueueCapacity;
private long lookAheadStep;
public SpscGrowableArrayQueue(final int capacity)
{
this(Math.max(8, Pow2.roundToPowerOfTwo(capacity / 8)), capacity);
}
public SpscGrowableArrayQueue(final int chunkSize, final int capacity)
{
RangeUtil.checkGreaterThanOrEqual(capacity, 16, "capacity");
// minimal chunk size of eight makes sure minimal lookahead step is 2
RangeUtil.checkGreaterThanOrEqual(chunkSize, 8, "chunkSize");
maxQueueCapacity = Pow2.roundToPowerOfTwo(capacity);
int chunkCapacity = Pow2.roundToPowerOfTwo(chunkSize);
RangeUtil.checkLessThan(chunkCapacity, maxQueueCapacity, "chunkCapacity");
long mask = chunkCapacity - 1;
// need extra element to point at next array
E[] buffer = allocateRefArray(chunkCapacity + 1);
producerBuffer = buffer;
producerMask = mask;
consumerBuffer = buffer;
consumerMask = mask;
producerBufferLimit = mask - 1; // we know it's all empty to start with
adjustLookAheadStep(chunkCapacity);
}
@Override
final boolean offerColdPath(
final E[] buffer,
final long mask,
final long index,
final long offset,
final E v,
final Supplier s)
{
final long lookAheadStep = this.lookAheadStep;
// normal case, go around the buffer or resize if full (unless we hit max capacity)
if (lookAheadStep > 0)
{
long lookAheadElementOffset = calcCircularRefElementOffset(index + lookAheadStep, mask);
// Try and look ahead a number of elements so we don't have to do this all the time
if (null == lvRefElement(buffer, lookAheadElementOffset))
{
producerBufferLimit = index + lookAheadStep - 1; // joy, there's plenty of room
writeToQueue(buffer, v == null ? s.get() : v, index, offset);
return true;
}
// we're at max capacity, can use up last element
final int maxCapacity = maxQueueCapacity;
if (mask + 1 == maxCapacity)
{
if (null == lvRefElement(buffer, offset))
{
writeToQueue(buffer, v == null ? s.get() : v, index, offset);
return true;
}
// we're full and can't grow
return false;
}
// not at max capacity, so must allow extra slot for next buffer pointer
if (null == lvRefElement(buffer, calcCircularRefElementOffset(index + 1, mask)))
{ // buffer is not full
writeToQueue(buffer, v == null ? s.get() : v, index, offset);
}
else
{
// allocate new buffer of same length
final E[] newBuffer = allocateRefArray((int) (2 * (mask + 1) + 1));
producerBuffer = newBuffer;
producerMask = length(newBuffer) - 2;
final long offsetInNew = calcCircularRefElementOffset(index, producerMask);
linkOldToNew(index, buffer, offset, newBuffer, offsetInNew, v == null ? s.get() : v);
int newCapacity = (int) (producerMask + 1);
if (newCapacity == maxCapacity)
{
long currConsumerIndex = lvConsumerIndex();
// use lookAheadStep to store the consumer distance from final buffer
this.lookAheadStep = -(index - currConsumerIndex);
producerBufferLimit = currConsumerIndex + maxCapacity;
}
else
{
producerBufferLimit = index + producerMask - 1;
adjustLookAheadStep(newCapacity);
}
}
return true;
}
// the step is negative (or zero) in the period between allocating the max sized buffer and the
// consumer starting on it
else
{
final long prevElementsInOtherBuffers = -lookAheadStep;
// until the consumer starts using the current buffer we need to check consumer index to
// verify size
long currConsumerIndex = lvConsumerIndex();
int size = (int) (index - currConsumerIndex);
int maxCapacity = (int) mask + 1; // we're on max capacity or we wouldn't be here
if (size == maxCapacity)
{
// consumer index has not changed since adjusting the lookAhead index, we're full
return false;
}
// if consumerIndex progressed enough so that current size indicates it is on same buffer
long firstIndexInCurrentBuffer = producerBufferLimit - maxCapacity + prevElementsInOtherBuffers;
if (currConsumerIndex >= firstIndexInCurrentBuffer)
{
// job done, we've now settled into our final state
adjustLookAheadStep(maxCapacity);
}
// consumer is still on some other buffer
else
{
// how many elements out of buffer?
this.lookAheadStep = (int) (currConsumerIndex - firstIndexInCurrentBuffer);
}
producerBufferLimit = currConsumerIndex + maxCapacity;
writeToQueue(buffer, v == null ? s.get() : v, index, offset);
return true;
}
}
private void adjustLookAheadStep(int capacity)
{
lookAheadStep = SpscLookAheadUtil.computeLookAheadStep(capacity);
}
@Override
public int capacity()
{
return maxQueueCapacity;
}
}
