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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 static org.jctools.util.UnsafeRefArrayAccess.*;
/**
* An SPSC array queue which starts at initialCapacity and grows to maxCapacity in linked chunks
* of the initial size. 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 SpscChunkedArrayQueue extends BaseSpscLinkedArrayQueue
{
private final int maxQueueCapacity;
private long producerQueueLimit;
public SpscChunkedArrayQueue(int capacity)
{
this(Math.max(8, Pow2.roundToPowerOfTwo(capacity / 8)), capacity);
}
public SpscChunkedArrayQueue(int chunkSize, 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
producerQueueLimit = maxQueueCapacity;
}
@Override
final boolean offerColdPath(E[] buffer, long mask, long pIndex, long offset, E v, Supplier s)
{
// use a fixed lookahead step based on buffer capacity
final long lookAheadStep = (mask + 1) / 4;
long pBufferLimit = pIndex + lookAheadStep;
long pQueueLimit = producerQueueLimit;
if (pIndex >= pQueueLimit)
{
// we tested against a potentially out of date queue limit, refresh it
final long cIndex = lvConsumerIndex();
producerQueueLimit = pQueueLimit = cIndex + maxQueueCapacity;
// if we're full we're full
if (pIndex >= pQueueLimit)
{
return false;
}
}
// if buffer limit is after queue limit we use queue limit. We need to handle overflow so
// cannot use Math.min
if (pBufferLimit - pQueueLimit > 0)
{
pBufferLimit = pQueueLimit;
}
// go around the buffer or add a new buffer
if (pBufferLimit > pIndex + 1 && // there's sufficient room in buffer/queue to use pBufferLimit
null == lvRefElement(buffer, calcCircularRefElementOffset(pBufferLimit, mask)))
{
producerBufferLimit = pBufferLimit - 1; // joy, there's plenty of room
writeToQueue(buffer, v == null ? s.get() : v, pIndex, offset);
}
else if (null == lvRefElement(buffer, calcCircularRefElementOffset(pIndex + 1, mask)))
{ // buffer is not full
writeToQueue(buffer, v == null ? s.get() : v, pIndex, offset);
}
else
{
// we got one slot left to write into, and we are not full. Need to link new buffer.
// allocate new buffer of same length
final E[] newBuffer = allocateRefArray((int) (mask + 2));
producerBuffer = newBuffer;
linkOldToNew(pIndex, buffer, offset, newBuffer, offset, v == null ? s.get() : v);
}
return true;
}
@Override
public int capacity()
{
return maxQueueCapacity;
}
}
