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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 io.netty.util.internal.shaded.org.jctools.util;

import static io.netty.util.internal.shaded.org.jctools.util.UnsafeAccess.UNSAFE;

/**
 * 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 */ @InternalAPI public final class UnsafeRefArrayAccess { public static final long REF_ARRAY_BASE; public static final int REF_ELEMENT_SHIFT; static { final int scale = UnsafeAccess.UNSAFE.arrayIndexScale(Object[].class); if (4 == scale) { REF_ELEMENT_SHIFT = 2; } else if (8 == scale) { REF_ELEMENT_SHIFT = 3; } else { throw new IllegalStateException("Unknown pointer size"); } REF_ARRAY_BASE = UnsafeAccess.UNSAFE.arrayBaseOffset(Object[].class); } /** * A plain store (no ordering/fences) of an element to a given offset * * @param buffer this.buffer * @param offset computed via {@link UnsafeRefArrayAccess#calcElementOffset(long)} * @param e an orderly kitty */ public static 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 buffer this.buffer * @param offset computed via {@link UnsafeRefArrayAccess#calcElementOffset} * @param e an orderly kitty */ public static 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 buffer this.buffer * @param offset computed via {@link UnsafeRefArrayAccess#calcElementOffset(long)} * @return the element at the offset */ @SuppressWarnings("unchecked") public static 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 buffer this.buffer * @param offset computed via {@link UnsafeRefArrayAccess#calcElementOffset(long)} * @return the element at the offset */ @SuppressWarnings("unchecked") public static E lvElement(E[] buffer, long offset) { return (E) UNSAFE.getObjectVolatile(buffer, offset); } /** * @param index desirable element index * @return the offset in bytes within the array for a given index. */ public static long calcElementOffset(long index) { return REF_ARRAY_BASE + (index << REF_ELEMENT_SHIFT); } }





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