Introduce a BoundedTrie metric which is used to efficiently store and aggregate a collection of string sequences (FQNs) with a limited size.

Author: rohitsinha54

runners/core-java/src/main/java/org/apache/beam/runners/core/metrics/BoundedTrieCell.java

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+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF 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.
+ */
+package org.apache.beam.runners.core.metrics;
+
+import java.util.Arrays;
+import java.util.Objects;
+import java.util.concurrent.atomic.AtomicReference;
+import org.apache.beam.sdk.metrics.BoundedTrie;
+import org.apache.beam.sdk.metrics.MetricName;
+import org.apache.beam.sdk.metrics.MetricsContainer;
+import org.checkerframework.checker.nullness.qual.Nullable;
+
+/**
+ * Tracks the current value for a {@link BoundedTrie} metric.
+ *
+ * <p>This class generally shouldn't be used directly. The only exception is within a runner where a
+ * counter is being reported for a specific step (rather than the counter in the current context).
+ * In that case retrieving the underlying cell and reporting directly to it avoids a step of
+ * indirection.
+ */
+public class BoundedTrieCell implements BoundedTrie, MetricCell<BoundedTrieData> {
+
+  private final DirtyState dirty = new DirtyState();
+  private final AtomicReference<BoundedTrieData> setValue =
+      new AtomicReference<>(BoundedTrieData.empty());
+  private final MetricName name;
+
+  /**
+   * Generally, runners should construct instances using the methods in {@link
+   * MetricsContainerImpl}, unless they need to define their own version of {@link
+   * MetricsContainer}. These constructors are *only* public so runners can instantiate.
+   */
+  public BoundedTrieCell(MetricName name) {
+    this.name = name;
+  }
+
+  @Override
+  public void reset() {
+    setValue.set(BoundedTrieData.empty());
+    dirty.reset();
+  }
+
+  void update(BoundedTrieData data) {
+    BoundedTrieData original;
+    do {
+      original = setValue.get();
+    } while (!setValue.compareAndSet(original, original.combine(data)));
+    dirty.afterModification();
+  }
+
+  @Override
+  public DirtyState getDirty() {
+    return dirty;
+  }
+
+  @Override
+  public BoundedTrieData getCumulative() {
+    return setValue.get();
+  }
+
+  @Override
+  public MetricName getName() {
+    return name;
+  }
+
+  @Override
+  public boolean equals(@Nullable Object object) {
+    if (object instanceof BoundedTrieCell) {
+      BoundedTrieCell boundedTrieCell = (BoundedTrieCell) object;
+      return Objects.equals(dirty, boundedTrieCell.dirty)
+          && Objects.equals(setValue.get(), boundedTrieCell.setValue.get())
+          && Objects.equals(name, boundedTrieCell.name);
+    }
+    return false;
+  }
+
+  @Override
+  public int hashCode() {
+    return Objects.hash(dirty, setValue.get(), name);
+  }
+
+  @Override
+  public void add(Iterable<String> values) {
+    BoundedTrieData original;
+    do {
+      original = setValue.get();
+    } while (!setValue.compareAndSet(original, original.add(values)));
+    dirty.afterModification();
+  }
+
+  @Override
+  public void add(String... values) {
+    add(Arrays.asList(values));
+  }
+}