profiles: add abstractions to assist dictionary table assembly.

Author: jhalliday

exporters/otlp/profiles/src/main/java/io/opentelemetry/exporter/otlp/profiles/DictionaryTable.java

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+/*
+ * Copyright The OpenTelemetry Authors
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+package io.opentelemetry.exporter.otlp.profiles;
+
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+
+/**
+ * This data structure is effectively an indexed Set.
+ *
+ * <p>It stores each offered element without duplication (like a Set, not a List), but supports
+ * reference to elements by their position (like a List index).
+ *
+ * <p>This class is not threadsafe and must be externally synchronized.
+ *
+ * <p>For a given Object o, after i = putIfAbsent(o), then getTable().get(i).equals(o);
+ *
+ * <p>This class is internal and is hence not for public use. Its APIs are unstable and can change
+ * at any time.
+ *
+ * @param <T> the type of elements maintained by this table. The type should implement equals and
+ *     hashCode in a manner consistent with Set/Map key expectations.
+ */
+public class DictionaryTable<T> {
+
+  // Whilst it's possible to compute either from the other, we keep two views on the data,
+  // prioritising access efficiency over memory footprint.
+  private final List<T> table = new ArrayList<>();
+  private final Map<T, Integer> map = new HashMap<>();
+
+  /**
+   * Stores the provided element if an equivalent is not already present, and returns its index.
+   *
+   * <p>Note that whilst the update semantics of this method are consistent with Map.putIfAbsent,
+   * the return value is always the index, i.e. reflects the post-update state, not the prior state,
+   * and therefore does not allow for determining if the method had an effect or not.
+   *
+   * @param value an element to store.
+   * @return the index of the added or existing element.
+   */
+  public Integer putIfAbsent(T value) {
+    Integer index = map.computeIfAbsent(value, k -> map.size());
+    if (map.size() != table.size()) {
+      table.add(value);
+    }
+    return index;
+  }
+
+  /**
+   * Provides a view of the Table in List form.
+   *
+   * @return an immutable List containing the table entries in index position.
+   */
+  public List<T> getTable() {
+    return Collections.unmodifiableList(table);
+  }
+}

exporters/otlp/profiles/src/main/java/io/opentelemetry/exporter/otlp/profiles/ProfileDictionaryCompositor.java

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+/*
+ * Copyright The OpenTelemetry Authors
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+package io.opentelemetry.exporter.otlp.profiles;
+
+import io.opentelemetry.api.common.Value;
+import io.opentelemetry.exporter.otlp.internal.data.ImmutableFunctionData;
+import io.opentelemetry.exporter.otlp.internal.data.ImmutableKeyValueAndUnitData;
+import io.opentelemetry.exporter.otlp.internal.data.ImmutableLinkData;
+import io.opentelemetry.exporter.otlp.internal.data.ImmutableLocationData;
+import io.opentelemetry.exporter.otlp.internal.data.ImmutableMappingData;
+import io.opentelemetry.exporter.otlp.internal.data.ImmutableProfileDictionaryData;
+import io.opentelemetry.exporter.otlp.internal.data.ImmutableStackData;
+import java.util.Collections;
+
+/**
+ * This class allows for the assembly of the reference tables which form a ProfileDictionaryData.
+ *
+ * <p>It's effectively a builder, though without the fluent API. Instead, mutation methods return
+ * the index of the offered element, this information being required to construct any element that
+ * references into the tables.
+ *
+ * <p>Note this class does not enforce referential integrity, i.e. will accept an element which
+ * references a non-existing element.
+ *
+ * <p>This class is not threadsafe and must be externally synchronized.
+ *
+ * <p>This class is internal and is hence not for public use. Its APIs are unstable and can change
+ * at any time.
+ */
+public class ProfileDictionaryCompositor {
+
+  // This implementation relies on the *Data interface impls having equals/hashCode that works.
+  // The provided AutoValue_* ones do, but it's potentially fragile if used externally.
+
+  private final DictionaryTable<MappingData> mappingTable = new DictionaryTable<>();
+  private final DictionaryTable<LocationData> locationTable = new DictionaryTable<>();
+  private final DictionaryTable<FunctionData> functionTable = new DictionaryTable<>();
+  private final DictionaryTable<LinkData> linkTable = new DictionaryTable<>();
+  private final DictionaryTable<String> stringTable = new DictionaryTable<>();
+  private final DictionaryTable<KeyValueAndUnitData> attributeTable = new DictionaryTable<>();
+  private final DictionaryTable<StackData> stackTable = new DictionaryTable<>();
+
+  public ProfileDictionaryCompositor() {
+
+    // The [0] element of each table should be a 'null' element, such that a 0 value pointer can be
+    // used to indicate null / not set, in preference to requiring an 'optional' modifier on the
+    // pointer declarations. The value of this placeholder element is one with all default field
+    // values, such that it encodes to the minimal number of bytes.
+    // These values are inlined here, as there is no other point of use.
+    // They could be public static constants on this class or the corresponding Immutable*Data
+    // classes if other use cases require them.
+
+    mappingTable.putIfAbsent(ImmutableMappingData.create(0, 0, 0, 0, Collections.emptyList()));
+    locationTable.putIfAbsent(
+        ImmutableLocationData.create(0, 0, Collections.emptyList(), Collections.emptyList()));
+    functionTable.putIfAbsent(ImmutableFunctionData.create(0, 0, 0, 0));
+    linkTable.putIfAbsent(ImmutableLinkData.create("", ""));
+    stringTable.putIfAbsent("");
+    attributeTable.putIfAbsent(
+        ImmutableKeyValueAndUnitData.create(0, Value.of(""), 0)); // TODO api spec
+    stackTable.putIfAbsent(ImmutableStackData.create(Collections.emptyList()));
+  }
+
+  /**
+   * Provides the contents of the dictionary tables as a ProfileDictionaryData.
+   *
+   * <p>The return value is a view, not a copy. No further elements should be inserted after this is
+   * called as it would compromise the intended immutability of the result.
+   *
+   * @return a ProfileDictionaryData with the contents of the tables.
+   */
+  public ProfileDictionaryData getProfileDictionaryData() {
+    return ImmutableProfileDictionaryData.create(
+        mappingTable.getTable(),
+        locationTable.getTable(),
+        functionTable.getTable(),
+        linkTable.getTable(),
+        stringTable.getTable(),
+        attributeTable.getTable(),
+        stackTable.getTable());
+  }
+
+  /**
+   * Stores the provided element if an equivalent is not already present, and returns its index.
+   *
+   * @param mappingData an element to store.
+   * @return the index of the added or existing element.
+   */
+  public int putIfAbsent(MappingData mappingData) {
+    return mappingTable.putIfAbsent(mappingData);
+  }
+
+  /**
+   * Stores the provided element if an equivalent is not already present, and returns its index.
+   *
+   * @param locationData an element to store.
+   * @return the index of the added or existing element.
+   */
+  public int putIfAbsent(LocationData locationData) {
+    return locationTable.putIfAbsent(locationData);
+  }
+
+  /**
+   * Stores the provided element if an equivalent is not already present, and returns its index.
+   *
+   * @param functionData an element to store.
+   * @return the index of the added or existing element.
+   */
+  public int putIfAbsent(FunctionData functionData) {
+    return functionTable.putIfAbsent(functionData);
+  }
+
+  /**
+   * Stores the provided element if an equivalent is not already present, and returns its index.
+   *
+   * @param linkData an element to store.
+   * @return the index of the added or existing element.
+   */
+  public int putIfAbsent(LinkData linkData) {
+    return linkTable.putIfAbsent(linkData);
+  }
+
+  /**
+   * Stores the provided element if an equivalent is not already present, and returns its index.
+   *
+   * @param string an element to store.
+   * @return the index of the added or existing element.
+   */
+  public int putIfAbsent(String string) {
+    return stringTable.putIfAbsent(string);
+  }
+
+  /**
+   * Stores the provided element if an equivalent is not already present, and returns its index.
+   *
+   * @param keyValueAndUnitData an element to store.
+   * @return the index of the added or existing element.
+   */
+  public int putIfAbsent(KeyValueAndUnitData keyValueAndUnitData) {
+    return attributeTable.putIfAbsent(keyValueAndUnitData);
+  }
+
+  /**
+   * Stores the provided element if an equivalent is not already present, and returns its index.
+   *
+   * @param stackData an element to store.
+   * @return the index of the added or existing element.
+   */
+  public int putIfAbsent(StackData stackData) {
+    return stackTable.putIfAbsent(stackData);
+  }
+}

exporters/otlp/profiles/src/test/java/io/opentelemetry/exporter/otlp/profiles/DictionaryTableTest.java

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+/*
+ * Copyright The OpenTelemetry Authors
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+package io.opentelemetry.exporter.otlp.profiles;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+
+class DictionaryTableTest {
+
+  DictionaryTable<String> table;
+
+  @BeforeEach
+  void setUp() {
+    table = new DictionaryTable<>();
+  }
+
+  @Test
+  void isInitiallyEmpty() {
+    assertThat(table.getTable()).isEmpty();
+  }
+
+  @Test
+  void isDeduplicating() {
+    assertThat(table.putIfAbsent("foo")).isEqualTo(0);
+    assertThat(table.putIfAbsent("foo")).isEqualTo(0);
+    assertThat(table.getTable()).size().isEqualTo(1);
+  }
+
+  @Test
+  void isSequencing() {
+    assertThat(table.putIfAbsent("foo")).isEqualTo(0);
+    assertThat(table.putIfAbsent("bar")).isEqualTo(1);
+    assertThat(table.getTable()).size().isEqualTo(2);
+    assertThat(table.getTable().get(0)).isEqualTo("foo");
+    assertThat(table.getTable().get(1)).isEqualTo("bar");
+  }
+}