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| 1 | +package datadog.context; |
| 2 | + |
| 3 | +import static java.lang.Math.max; |
| 4 | +import static java.util.Arrays.copyOfRange; |
| 5 | +import static java.util.Objects.requireNonNull; |
| 6 | + |
| 7 | +import java.util.ArrayList; |
| 8 | +import java.util.List; |
| 9 | +import java.util.function.BinaryOperator; |
| 10 | + |
| 11 | +/** |
| 12 | + * Static helpers to manipulate context collections. |
| 13 | + * |
| 14 | + * <p>Typical usages include: |
| 15 | + * |
| 16 | + * <pre>{@code |
| 17 | + * // Finding a context value from multiple sources: |
| 18 | + * Span span = findFirst(spanKey, message, request, CURRENT) |
| 19 | + * // Find all context values from different sources: |
| 20 | + * List<Error> errors = findAll(errorKey, message, request, CURRENT) |
| 21 | + * // Capture multiple contexts in a single one: |
| 22 | + * Context aggregate = combine(message, request, CURRENT) |
| 23 | + * // Combine multiple contexts into a single one using custom merge rules: |
| 24 | + * Context combined = combine( |
| 25 | + * (current, next) -> { |
| 26 | + * var metric = current.get(metricKey); |
| 27 | + * var nextMetric = next.get(metricKey); |
| 28 | + * return current.with(metricKey, metric.add(nextMetric)); |
| 29 | + * }, message, request, CURRENT); |
| 30 | + * }</pre> |
| 31 | + * |
| 32 | + * where {@link #CURRENT} denotes a carrier with the current context. |
| 33 | + */ |
| 34 | +public final class ContextHelpers { |
| 35 | + /** A helper object carrying the {@link Context#current()} context. */ |
| 36 | + public static final Object CURRENT = new Object(); |
| 37 | + |
| 38 | + private ContextHelpers() {} |
| 39 | + |
| 40 | + /** |
| 41 | + * Find the first context value from given context carriers. |
| 42 | + * |
| 43 | + * @param key The key used to store the value. |
| 44 | + * @param carriers The carrier to get context and value from. |
| 45 | + * @param <T> The type of the value to look for. |
| 46 | + * @return The first context value found, {@code null} if not found. |
| 47 | + */ |
| 48 | + public static <T> T findFirst(ContextKey<T> key, Object... carriers) { |
| 49 | + requireNonNull(key, "key cannot be null"); |
| 50 | + for (Object carrier : carriers) { |
| 51 | + requireNonNull(carrier, "carrier cannot be null"); |
| 52 | + Context context = carrier == CURRENT ? Context.current() : Context.from(carrier); |
| 53 | + T value = context.get(key); |
| 54 | + if (value != null) { |
| 55 | + return value; |
| 56 | + } |
| 57 | + } |
| 58 | + return null; |
| 59 | + } |
| 60 | + |
| 61 | + /** |
| 62 | + * Find all the context values from the given context carriers. |
| 63 | + * |
| 64 | + * @param key The key used to store the value. |
| 65 | + * @param carriers The carriers to get context and value from. |
| 66 | + * @param <T> The type of the values to look for. |
| 67 | + * @return A list of all values found, in context order. |
| 68 | + */ |
| 69 | + public static <T> List<T> findAll(ContextKey<T> key, Object... carriers) { |
| 70 | + requireNonNull(key, "key cannot be null"); |
| 71 | + List<T> values = new ArrayList<>(carriers.length); |
| 72 | + for (Object carrier : carriers) { |
| 73 | + requireNonNull(carrier, "carrier cannot be null"); |
| 74 | + Context context = carrier == CURRENT ? Context.current() : Context.from(carrier); |
| 75 | + T value = context.get(key); |
| 76 | + if (value != null) { |
| 77 | + values.add(value); |
| 78 | + } |
| 79 | + } |
| 80 | + return values; |
| 81 | + } |
| 82 | + |
| 83 | + /** |
| 84 | + * Combine contexts and their values, keeping the first founds. |
| 85 | + * |
| 86 | + * @param contexts The contexts to combine. |
| 87 | + * @return A context containing all the values from all the given context, keeping the first value |
| 88 | + * found for a given key. |
| 89 | + */ |
| 90 | + public static Context combine(Context... contexts) { |
| 91 | + return combine(ContextHelpers::combineKeepingFirst, contexts); |
| 92 | + } |
| 93 | + |
| 94 | + /** |
| 95 | + * Combine multiple contexts into a single one. |
| 96 | + * |
| 97 | + * @param combiner The context combiner, taking already combined context as first parameter, any |
| 98 | + * following one as second parameter, and returning the combined context. |
| 99 | + * @param contexts The contexts to combine. |
| 100 | + * @return The combined context. |
| 101 | + */ |
| 102 | + public static Context combine(BinaryOperator<Context> combiner, Context... contexts) { |
| 103 | + requireNonNull(combiner, "combiner cannot be null"); |
| 104 | + Context result = new IndexedContext(new Object[0]); |
| 105 | + for (Context context : contexts) { |
| 106 | + requireNonNull(context, "context cannot be null"); |
| 107 | + result = combiner.apply(result, context); |
| 108 | + } |
| 109 | + return result; |
| 110 | + } |
| 111 | + |
| 112 | + private static Context combineKeepingFirst(Context current, Context next) { |
| 113 | + if (!(current instanceof IndexedContext)) { |
| 114 | + throw new IllegalStateException("Left context is supposed to be an IndexedContext"); |
| 115 | + } |
| 116 | + IndexedContext currentIndexed = (IndexedContext) current; |
| 117 | + if (next instanceof EmptyContext) { |
| 118 | + return current; |
| 119 | + } else if (next instanceof SingletonContext) { |
| 120 | + SingletonContext nextSingleton = (SingletonContext) next; |
| 121 | + // Check if the single next value is already define in current so next context can be skipped |
| 122 | + if (nextSingleton.index < currentIndexed.store.length |
| 123 | + && currentIndexed.store[nextSingleton.index] != null) { |
| 124 | + return current; |
| 125 | + } |
| 126 | + // Always store next value otherwise |
| 127 | + Object[] store = |
| 128 | + copyOfRange( |
| 129 | + currentIndexed.store, 0, max(currentIndexed.store.length, nextSingleton.index + 1)); |
| 130 | + store[nextSingleton.index] = nextSingleton.value; |
| 131 | + return new IndexedContext(store); |
| 132 | + } else if (next instanceof IndexedContext) { |
| 133 | + IndexedContext nextIndexed = (IndexedContext) next; |
| 134 | + // Don't prematurely allocate store. Only allocate if: |
| 135 | + // * nextIndexed has more values that currentIndexed, |
| 136 | + // so the additional values will always be kept |
| 137 | + // * nextIndexed has values that currentIndexed do not have |
| 138 | + Object[] store = null; |
| 139 | + // Allocate store if nextIndexed has more elements than currentIndexed |
| 140 | + if (nextIndexed.store.length > currentIndexed.store.length) { |
| 141 | + store = copyOfRange(currentIndexed.store, 0, nextIndexed.store.length); |
| 142 | + } |
| 143 | + // Apply nextIndexed values if not set in currentIndexed |
| 144 | + for (int i = 0; i < currentIndexed.store.length; i++) { |
| 145 | + Object nextValue = nextIndexed.store[i]; |
| 146 | + if (nextValue != null && currentIndexed.store[i] == null) { |
| 147 | + if (store == null) { |
| 148 | + store = copyOfRange(currentIndexed.store, 0, currentIndexed.store.length); |
| 149 | + } |
| 150 | + store[i] = nextValue; |
| 151 | + } |
| 152 | + } |
| 153 | + // Apply any additional values from nextIndexed if any |
| 154 | + for (int i = currentIndexed.store.length; i < nextIndexed.store.length; i++) { |
| 155 | + Object nextValue = nextIndexed.store[i]; |
| 156 | + if (nextValue != null) { |
| 157 | + store[i] = nextValue; |
| 158 | + } |
| 159 | + } |
| 160 | + // If store was not allocated, no value from nextIndexed was taken |
| 161 | + return store == null ? current : new IndexedContext(store); |
| 162 | + } |
| 163 | + throw new IllegalStateException("Unsupported context type: " + next.getClass().getName()); |
| 164 | + } |
| 165 | +} |
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