/*
* 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/ConcurrentCircularArrayQueue.java
*/
package rx.internal.util.unsafe;
import static rx.internal.util.unsafe.
UnsafeAccess.
UNSAFE;
import java.util.*;
import rx.internal.util.
SuppressAnimalSniffer;
abstract class
ConcurrentCircularArrayQueueL0Pad<E> extends
AbstractQueue<E> implements
MessagePassingQueue<E> {
long
p00,
p01,
p02,
p03,
p04,
p05,
p06,
p07;
long
p30,
p31,
p32,
p33,
p34,
p35,
p36,
p37;
}
/**
* A concurrent access enabling class used by circular array based queues this class exposes an offset computation
* method along with differently memory fenced load/store methods into the underlying array. The class is pre-padded and
* the array is padded on either side to help with False sharing prevention. It is expected that subclasses handle post
* padding.
* <p>
* Offset calculation is separate from access to enable the reuse of a give compute offset.
* <p>
* Load/Store methods using a <i>buffer</i> parameter are provided to allow the prevention of final field reload after a
* LoadLoad barrier.
* <p>
*
* @author nitsanw
*
* @param <E> the element type
*/
@
SuppressAnimalSniffer
public abstract class
ConcurrentCircularArrayQueue<E> extends
ConcurrentCircularArrayQueueL0Pad<E> {
protected static final int
SPARSE_SHIFT =
Integer.
getInteger("sparse.shift", 0);
protected static final int
BUFFER_PAD = 32;
private static final long
REF_ARRAY_BASE;
private static final int
REF_ELEMENT_SHIFT;
static {
final int
scale =
UnsafeAccess.
UNSAFE.
arrayIndexScale(
Object[].class);
if (4 ==
scale) {
REF_ELEMENT_SHIFT = 2 +
SPARSE_SHIFT;
} else if (8 ==
scale) {
REF_ELEMENT_SHIFT = 3 +
SPARSE_SHIFT;
} else {
throw new
IllegalStateException("Unknown pointer size");
}
// Including the buffer pad in the array base offset
REF_ARRAY_BASE =
UnsafeAccess.
UNSAFE.
arrayBaseOffset(
Object[].class)
+ (
BUFFER_PAD << (
REF_ELEMENT_SHIFT -
SPARSE_SHIFT));
}
protected final long
mask;
// @Stable :(
protected final E[]
buffer;
@
SuppressWarnings("unchecked")
public
ConcurrentCircularArrayQueue(int
capacity) {
int
actualCapacity =
Pow2.
roundToPowerOfTwo(
capacity);
mask =
actualCapacity - 1;
// pad data on either end with some empty slots.
buffer = (E[]) new
Object[(
actualCapacity <<
SPARSE_SHIFT) +
BUFFER_PAD * 2];
}
/**
* @param index desirable element index
* @return the offset in bytes within the array for a given index.
*/
protected final long
calcElementOffset(long
index) {
return
calcElementOffset(
index,
mask);
}
/**
* @param index desirable element index
* @param mask the binary mask to make the index wrap around
* @return the offset in bytes within the array for a given index.
*/
protected final long
calcElementOffset(long
index, long
mask) {
return
REF_ARRAY_BASE + ((
index &
mask) <<
REF_ELEMENT_SHIFT);
}
/**
* A plain store (no ordering/fences) of an element to a given offset
*
* @param offset computed via {@link ConcurrentCircularArrayQueue#calcElementOffset(long)}
* @param e a kitty
*/
protected final void
spElement(long
offset, E
e) {
spElement(
buffer,
offset,
e);
}
/**
* A plain store (no ordering/fences) of an element to a given offset
*
* @param buffer this.buffer
* @param offset computed via {@link ConcurrentCircularArrayQueue#calcElementOffset(long)}
* @param e an orderly kitty
*/
protected final void
spElement(E[]
buffer, long
offset, E
e) {
UNSAFE.
putObject(
buffer,
offset,
e);
}
/**
* An ordered store(store + StoreStore barrier) of an element to a given offset
*
* @param offset computed via {@link ConcurrentCircularArrayQueue#calcElementOffset(long)}
* @param e an orderly kitty
*/
protected final void
soElement(long
offset, E
e) {
soElement(
buffer,
offset,
e);
}
/**
* An ordered store(store + StoreStore barrier) of an element to a given offset
*
* @param buffer this.buffer
* @param offset computed via {@link ConcurrentCircularArrayQueue#calcElementOffset(long)}
* @param e an orderly kitty
*/
protected final void
soElement(E[]
buffer, long
offset, E
e) {
UNSAFE.
putOrderedObject(
buffer,
offset,
e);
}
/**
* A plain load (no ordering/fences) of an element from a given offset.
*
* @param offset computed via {@link ConcurrentCircularArrayQueue#calcElementOffset(long)}
* @return the element at the offset
*/
protected final E
lpElement(long
offset) {
return
lpElement(
buffer,
offset);
}
/**
* A plain load (no ordering/fences) of an element from a given offset.
*
* @param buffer this.buffer
* @param offset computed via {@link ConcurrentCircularArrayQueue#calcElementOffset(long)}
* @return the element at the offset
*/
@
SuppressWarnings("unchecked")
protected final E
lpElement(E[]
buffer, long
offset) {
return (E)
UNSAFE.
getObject(
buffer,
offset);
}
/**
* A volatile load (load + LoadLoad barrier) of an element from a given offset.
*
* @param offset computed via {@link ConcurrentCircularArrayQueue#calcElementOffset(long)}
* @return the element at the offset
*/
protected final E
lvElement(long
offset) {
return
lvElement(
buffer,
offset);
}
/**
* A volatile load (load + LoadLoad barrier) of an element from a given offset.
*
* @param buffer this.buffer
* @param offset computed via {@link ConcurrentCircularArrayQueue#calcElementOffset(long)}
* @return the element at the offset
*/
@
SuppressWarnings("unchecked")
protected final E
lvElement(E[]
buffer, long
offset) {
return (E)
UNSAFE.
getObjectVolatile(
buffer,
offset);
}
@
Override
public
Iterator<E>
iterator() {
throw new
UnsupportedOperationException();
}
@
Override
public void
clear() {
// we have to test isEmpty because of the weaker poll() guarantee
while (
poll() != null || !
isEmpty()) { } // NOPMD
}
}