All Downloads are FREE. Search and download functionalities are using the official Maven repository.

com.alibaba.rocketmq.shade.io.netty.util.internal.ConcurrentCircularArrayQueue Maven / Gradle / Ivy

/*
 * Copyright 2015 The Netty Project
 *
 * The Netty Project licenses this file to you 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.
 */
/*
 * 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;


import java.util.AbstractQueue;
import java.util.Iterator;

/**
 * Forked from JCTools.
 *
 * 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. *

* * @param */ abstract class ConcurrentCircularArrayQueue extends ConcurrentCircularArrayQueueL0Pad { protected static final int REF_BUFFER_PAD; private static final long REF_ARRAY_BASE; private static final int REF_ELEMENT_SHIFT; static { final int scale = PlatformDependent0.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"); } // 2 cache lines pad // TODO: replace 64 with the value we can detect REF_BUFFER_PAD = (64 * 2) / scale; // Including the buffer pad in the array base offset REF_ARRAY_BASE = PlatformDependent0.UNSAFE.arrayBaseOffset(Object[].class) + (REF_BUFFER_PAD * scale); } protected final long mask; // @Stable :( protected final E[] buffer; @SuppressWarnings("unchecked") public ConcurrentCircularArrayQueue(int capacity) { int actualCapacity = roundToPowerOfTwo(capacity); mask = actualCapacity - 1; // pad data on either end with some empty slots. buffer = (E[]) new Object[actualCapacity + REF_BUFFER_PAD * 2]; } private static int roundToPowerOfTwo(final int value) { return 1 << (32 - Integer.numberOfLeadingZeros(value - 1)); } /** * @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 static 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 static final void spElement(E[] buffer, long offset, E e) { PlatformDependent0.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 static final void soElement(E[] buffer, long offset, E e) { PlatformDependent0.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 static final E lpElement(E[] buffer, long offset) { return (E) PlatformDependent0.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 static final E lvElement(E[] buffer, long offset) { return (E) PlatformDependent0.UNSAFE.getObjectVolatile(buffer, offset); } @Override public Iterator iterator() { throw new UnsupportedOperationException(); } @Override public void clear() { while (poll() != null || !isEmpty()) { // looping } } public int capacity() { return (int) (mask + 1); } } abstract class ConcurrentCircularArrayQueueL0Pad extends AbstractQueue { long p00, p01, p02, p03, p04, p05, p06, p07; long p30, p31, p32, p33, p34, p35, p36, p37; }





© 2015 - 2024 Weber Informatics LLC | Privacy Policy