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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.
 *
 * 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 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 prevention. It is expected that 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 the element type */ @SuppressAnimalSniffer 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 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 iterator() { throw new UnsupportedOperationException(); } @Override public void clear() { // we have to test isEmpty because of the weaker poll() guarantee while (poll() != null || !isEmpty()) { } // NOPMD } }





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