Refactor ConcurrentHashMap creation code to a helper method

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=132352263

java/google/registry/monitoring/metrics/Counter.java

@@ -15,6 +15,8 @@
 package google.registry.monitoring.metrics;
 
 import static com.google.common.base.Preconditions.checkArgument;
+import static google.registry.monitoring.metrics.MetricsUtils.DEFAULT_CONCURRENCY_LEVEL;
+import static google.registry.monitoring.metrics.MetricsUtils.newConcurrentHashMap;
 
 import com.google.common.annotations.VisibleForTesting;
 import com.google.common.collect.ImmutableList;
@@ -40,15 +42,6 @@ import org.joda.time.Instant;
 public final class Counter extends AbstractMetric<Long>
     implements SettableMetric<Long>, IncrementableMetric {
 
-  /**
-   * The below constants replicate the default initial capacity, load factor, and concurrency level
-   * for {@link ConcurrentHashMap} as of Java SE 7. They are hardcoded here so that the concurrency
-   * level in {@code valueLocks} below can be set identically.
-   */
-  private static final int HASHMAP_INITIAL_CAPACITY = 16;
-  private static final float HASHMAP_LOAD_FACTOR = 0.75f;
-  private static final int HASHMAP_CONCURRENCY_LEVEL = 16;
-
   /**
    * A map of the {@link Counter} values, with a list of label values as the keys.
    *
@@ -63,8 +56,7 @@ public final class Counter extends AbstractMetric<Long>
    * implementations of {@link MetricWriter} to encode resets of monotonic counters.
    */
   private final ConcurrentHashMap<ImmutableList<String>, Instant> valueStartTimestamps =
-      new ConcurrentHashMap<>(
+      newConcurrentHashMap(DEFAULT_CONCURRENCY_LEVEL);
-          HASHMAP_INITIAL_CAPACITY, HASHMAP_LOAD_FACTOR, HASHMAP_CONCURRENCY_LEVEL);
 
   /**
    * A fine-grained lock to ensure that {@code values} and {@code valueStartTimestamps} are modified
@@ -73,7 +65,7 @@ public final class Counter extends AbstractMetric<Long>
    *
    * @see Striped
    */
-  private final Striped<Lock> valueLocks = Striped.lock(HASHMAP_CONCURRENCY_LEVEL);
+  private final Striped<Lock> valueLocks = Striped.lock(DEFAULT_CONCURRENCY_LEVEL);
 
   Counter(
       String name,

java/google/registry/monitoring/metrics/EventMetric.java

@@ -14,6 +14,9 @@
 
 package google.registry.monitoring.metrics;
 
+import static google.registry.monitoring.metrics.MetricsUtils.DEFAULT_CONCURRENCY_LEVEL;
+import static google.registry.monitoring.metrics.MetricsUtils.newConcurrentHashMap;
+
 import com.google.common.annotations.VisibleForTesting;
 import com.google.common.collect.ImmutableList;
 import com.google.common.collect.ImmutableSet;
@@ -38,22 +41,10 @@ import org.joda.time.Instant;
  */
 public final class EventMetric extends AbstractMetric<Distribution> {
 
-  /**
-   * The below constants replicate the default initial capacity, load factor, and concurrency level
-   * for {@link ConcurrentHashMap} as of Java SE 7. They are hardcoded here so that the concurrency
-   * level in {@code valueLocks} below can be set identically.
-   */
-  private static final int HASHMAP_INITIAL_CAPACITY = 16;
-
-  private static final float HASHMAP_LOAD_FACTOR = 0.75f;
-  private static final int HASHMAP_CONCURRENCY_LEVEL = 16;
-
   private final ConcurrentHashMap<ImmutableList<String>, Instant> valueStartTimestamps =
-      new ConcurrentHashMap<>(
+      newConcurrentHashMap(DEFAULT_CONCURRENCY_LEVEL);
-          HASHMAP_INITIAL_CAPACITY, HASHMAP_LOAD_FACTOR, HASHMAP_CONCURRENCY_LEVEL);
   private final ConcurrentHashMap<ImmutableList<String>, MutableDistribution> values =
-      new ConcurrentHashMap<>(
+      newConcurrentHashMap(DEFAULT_CONCURRENCY_LEVEL);
-          HASHMAP_INITIAL_CAPACITY, HASHMAP_LOAD_FACTOR, HASHMAP_CONCURRENCY_LEVEL);
 
   private final DistributionFitter distributionFitter;
 
@@ -64,7 +55,7 @@ public final class EventMetric extends AbstractMetric<Distribution> {
    *
    * @see Striped
    */
-  private final Striped<Lock> valueLocks = Striped.lock(HASHMAP_CONCURRENCY_LEVEL);
+  private final Striped<Lock> valueLocks = Striped.lock(DEFAULT_CONCURRENCY_LEVEL);
 
   EventMetric(
       String name,

java/google/registry/monitoring/metrics/MetricsUtils.java

@@ -17,6 +17,7 @@ package google.registry.monitoring.metrics;
 import static com.google.common.base.Preconditions.checkArgument;
 
 import com.google.common.collect.ImmutableList;
+import java.util.concurrent.ConcurrentHashMap;
 
 /** Static helper methods for the Metrics library. */
 final class MetricsUtils {
@@ -25,6 +26,16 @@ final class MetricsUtils {
   private static final String LABEL_SIZE_ERROR =
       "The count of labelValues must be equal to the underlying Metric's count of labels.";
 
+  /**
+   * The below constants replicate the default initial capacity, load factor, and concurrency level
+   * for {@link ConcurrentHashMap} as of Java SE 7. They are recorded here so that a {@link
+   * com.google.common.util.concurrent.Striped} object can be constructed with a concurrency level
+   * matching the default concurrency level of a {@link ConcurrentHashMap}.
+   */
+  private static final int HASHMAP_INITIAL_CAPACITY = 16;
+  private static final float HASHMAP_LOAD_FACTOR = 0.75f;
+  static final int DEFAULT_CONCURRENCY_LEVEL = 16;
+
   private MetricsUtils() {}
 
   /**
@@ -53,4 +64,8 @@ final class MetricsUtils {
         !Double.isInfinite(value) && !Double.isNaN(value) && !NEGATIVE_ZERO.equals(value),
         "value must be finite, not NaN, and not -0.0");
   }
+
+  static <K, V> ConcurrentHashMap<K, V> newConcurrentHashMap(int concurrencyLevel) {
+    return new ConcurrentHashMap<>(HASHMAP_INITIAL_CAPACITY, HASHMAP_LOAD_FACTOR, concurrencyLevel);
+  }
 }