rx.internal.util.unsafe.ConcurrentCircularArrayQueue 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/ConcurrentCircularArrayQueue.java
*/
package rx.internal.util.unsafe;
import static rx.internal.util.unsafe.UnsafeAccess.UNSAFE;
import java.util.AbstractQueue;
import java.util.Iterator;
abstract class ConcurrentCircularArrayQueueL0Pad extends AbstractQueue implements MessagePassingQueue {
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 prvention. It is expected theat subclasses handle post
* padding.
*
* Offset calculation is separate from access to enable the reuse of a give compute offset.
*
* Load/Store methods using a buffer parameter are provided to allow the prevention of final field reload after a
* LoadLoad barrier.
*
*
* @author nitsanw
*
* @param
*/
public abstract class ConcurrentCircularArrayQueue extends ConcurrentCircularArrayQueueL0Pad {
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
* @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 iterator() {
throw new UnsupportedOperationException();
}
@Override
public void clear() {
// we have to test isEmpty because of the weaker poll() guarantee
while (poll() != null || !isEmpty())
;
}
}