/*
* 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_voltpatches.util;
import static org.jctools_voltpatches.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.
* <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>
*/
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);
}
private UnsafeRefArrayAccess() {
}
/**
* 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 <E> 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 <E> 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> 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> 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);
}
}