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| 1 | +/* |
| 2 | + * Copyright (c) 2016-present, RxJava Contributors. |
| 3 | + * |
| 4 | + * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in |
| 5 | + * compliance with the License. You may obtain a copy of the License at |
| 6 | + * |
| 7 | + * http://www.apache.org/licenses/LICENSE-2.0 |
| 8 | + * |
| 9 | + * Unless required by applicable law or agreed to in writing, software distributed under the License is |
| 10 | + * distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See |
| 11 | + * the License for the specific language governing permissions and limitations under the License. |
| 12 | + */ |
| 13 | + |
| 14 | +package org.openidentityplatform.rxjava3.internal.util; |
| 15 | + |
| 16 | +import java.util.concurrent.atomic.AtomicLong; |
| 17 | + |
| 18 | +import io.reactivex.rxjava3.annotations.NonNull; |
| 19 | +import io.reactivex.rxjava3.plugins.RxJavaPlugins; |
| 20 | + |
| 21 | +/** |
| 22 | + * Utility class to help with backpressure-related operations such as request aggregation. |
| 23 | + */ |
| 24 | +public final class BackpressureHelper { |
| 25 | + /** Utility class. */ |
| 26 | + private BackpressureHelper() { |
| 27 | + throw new IllegalStateException("No instances!"); |
| 28 | + } |
| 29 | + |
| 30 | + /** |
| 31 | + * Adds two long values and caps the sum at {@link Long#MAX_VALUE}. |
| 32 | + * @param a the first value |
| 33 | + * @param b the second value |
| 34 | + * @return the sum capped at {@link Long#MAX_VALUE} |
| 35 | + */ |
| 36 | + public static long addCap(long a, long b) { |
| 37 | + long u = a + b; |
| 38 | + if (u < 0L) { |
| 39 | + return Long.MAX_VALUE; |
| 40 | + } |
| 41 | + return u; |
| 42 | + } |
| 43 | + |
| 44 | + /** |
| 45 | + * Multiplies two long values and caps the product at {@link Long#MAX_VALUE}. |
| 46 | + * @param a the first value |
| 47 | + * @param b the second value |
| 48 | + * @return the product capped at {@link Long#MAX_VALUE} |
| 49 | + */ |
| 50 | + public static long multiplyCap(long a, long b) { |
| 51 | + long u = a * b; |
| 52 | + if (((a | b) >>> 31) != 0) { |
| 53 | + if (u / a != b) { |
| 54 | + return Long.MAX_VALUE; |
| 55 | + } |
| 56 | + } |
| 57 | + return u; |
| 58 | + } |
| 59 | + |
| 60 | + /** |
| 61 | + * Atomically adds the positive value n to the requested value in the {@link AtomicLong} and |
| 62 | + * caps the result at {@link Long#MAX_VALUE} and returns the previous value. |
| 63 | + * @param requested the {@code AtomicLong} holding the current requested value |
| 64 | + * @param n the value to add, must be positive (not verified) |
| 65 | + * @return the original value before the add |
| 66 | + */ |
| 67 | + public static long add(@NonNull AtomicLong requested, long n) { |
| 68 | + for (;;) { |
| 69 | + long r = requested.get(); |
| 70 | + if (r == Long.MAX_VALUE) { |
| 71 | + return Long.MAX_VALUE; |
| 72 | + } |
| 73 | + long u = addCap(r, n); |
| 74 | + if (requested.compareAndSet(r, u)) { |
| 75 | + return r; |
| 76 | + } |
| 77 | + } |
| 78 | + } |
| 79 | + |
| 80 | + /** |
| 81 | + * Atomically adds the positive value n to the requested value in the {@link AtomicLong} and |
| 82 | + * caps the result at {@link Long#MAX_VALUE} and returns the previous value and |
| 83 | + * considers {@link Long#MIN_VALUE} as a cancel indication (no addition then). |
| 84 | + * @param requested the {@code AtomicLong} holding the current requested value |
| 85 | + * @param n the value to add, must be positive (not verified) |
| 86 | + * @return the original value before the add |
| 87 | + */ |
| 88 | + public static long addCancel(@NonNull AtomicLong requested, long n) { |
| 89 | + for (;;) { |
| 90 | + long r = requested.get(); |
| 91 | + if (r == Long.MIN_VALUE) { |
| 92 | + return Long.MIN_VALUE; |
| 93 | + } |
| 94 | + if (r == Long.MAX_VALUE) { |
| 95 | + return Long.MAX_VALUE; |
| 96 | + } |
| 97 | + long u = addCap(r, n); |
| 98 | + if (requested.compareAndSet(r, u)) { |
| 99 | + return r; |
| 100 | + } |
| 101 | + } |
| 102 | + } |
| 103 | + |
| 104 | + /** |
| 105 | + * Atomically subtract the given number (positive, not validated) from the target field unless it contains {@link Long#MAX_VALUE}. |
| 106 | + * @param requested the target field holding the current requested amount |
| 107 | + * @param n the produced element count, positive (not validated) |
| 108 | + * @return the new amount |
| 109 | + */ |
| 110 | + public static long produced(@NonNull AtomicLong requested, long n) { |
| 111 | + for (;;) { |
| 112 | + long current = requested.get(); |
| 113 | + if (current == Long.MAX_VALUE) { |
| 114 | + return Long.MAX_VALUE; |
| 115 | + } |
| 116 | + long update = current - n; |
| 117 | + if (update < 0L) { |
| 118 | + RxJavaPlugins.onError(new IllegalStateException("More produced than requested: " + update)); |
| 119 | + update = 0L; |
| 120 | + } |
| 121 | + if (requested.compareAndSet(current, update)) { |
| 122 | + return update; |
| 123 | + } |
| 124 | + } |
| 125 | + } |
| 126 | + |
| 127 | + /** |
| 128 | + * Atomically subtract the given number (positive, not validated) from the target field if |
| 129 | + * it doesn't contain {@link Long#MIN_VALUE} (indicating some cancelled state) or {@link Long#MAX_VALUE} (unbounded mode). |
| 130 | + * @param requested the target field holding the current requested amount |
| 131 | + * @param n the produced element count, positive (not validated) |
| 132 | + * @return the new amount |
| 133 | + */ |
| 134 | + public static long producedCancel(@NonNull AtomicLong requested, long n) { |
| 135 | + for (;;) { |
| 136 | + long current = requested.get(); |
| 137 | + if (current == Long.MIN_VALUE) { |
| 138 | + return Long.MIN_VALUE; |
| 139 | + } |
| 140 | + if (current == Long.MAX_VALUE) { |
| 141 | + return Long.MAX_VALUE; |
| 142 | + } |
| 143 | + long update = current - n; |
| 144 | + if (update < 0L) { |
| 145 | + RxJavaPlugins.onError(new IllegalStateException("More produced than requested: " + update)); |
| 146 | + update = 0L; |
| 147 | + } |
| 148 | + if (requested.compareAndSet(current, update)) { |
| 149 | + return update; |
| 150 | + } |
| 151 | + } |
| 152 | + } |
| 153 | +} |
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