StripeIndex.java
- /*
- * #%L
- * wcm.io
- * %%
- * Copyright (C) 2023 wcm.io
- * %%
- * 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.
- * #L%
- */
- package io.wcm.handler.mediasource.dam.impl.metadata.concurrency;
- /**
- * Maps keys to a striped index set. Each key is mapped to a index within the max stripe count.
- *
- * <p>
- * The logic is extracted from <a href=
- * "https://github.com/google/guava/blob/master/guava/src/com/google/common/util/concurrent/Striped.java">Striped</a>,
- * initially written by Dimitris Andreou from the Guava team (Apache 2.0 license).
- * </p>
- */
- final class StripeIndex {
- // Capacity (power of two) minus one, for fast mod evaluation
- private final int mask;
- private final int size;
- // A bit mask were all bits are set.
- private static final int ALL_SET = ~0;
- // The largest power of two that can be represented as an {@code int}.
- private static final int MAX_POWER_OF_TWO = 1 << (Integer.SIZE - 2);
- /**
- * @param stripes the minimum number of stripes required
- */
- StripeIndex(int stripes) {
- if (stripes <= 0) {
- throw new IllegalArgumentException("Invalid number of stripes: " + stripes);
- }
- this.mask = stripes > MAX_POWER_OF_TWO ? ALL_SET : ceilToPowerOfTwo(stripes) - 1;
- this.size = (mask == ALL_SET) ? Integer.MAX_VALUE : mask + 1;
- }
- /** Returns the total number of stripes in this instance. */
- int size() {
- return size;
- }
- /**
- * Returns the index to which the given key is mapped, so that getAt(indexFor(key)) == get(key).
- */
- int indexFor(Object key) {
- int hash = smear(key.hashCode());
- return hash & mask;
- }
- private static int smear(int hashCode) {
- int newHashCode = hashCode;
- newHashCode ^= (newHashCode >>> 20) ^ (newHashCode >>> 12);
- return newHashCode ^ (newHashCode >>> 7) ^ (newHashCode >>> 4);
- }
- private static int ceilToPowerOfTwo(int x) {
- return 1 << log2RoundCeiling(x);
- }
- private static int log2RoundCeiling(int x) {
- return Integer.SIZE - Integer.numberOfLeadingZeros(x - 1);
- }
- }