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diff --git a/java/com/google/gerrit/metrics/MetricMaker.java b/java/com/google/gerrit/metrics/MetricMaker.java
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+++ b/java/com/google/gerrit/metrics/MetricMaker.java
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+// Copyright (C) 2015 The Android Open Source Project
+//
+// Licensed 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 com.google.gerrit.metrics;
+
+import com.google.common.base.Supplier;
+import com.google.common.collect.ImmutableSet;
+import com.google.gerrit.extensions.registration.RegistrationHandle;
+import java.util.Set;
+
+/** Factory to create metrics for monitoring. */
+public abstract class MetricMaker {
+  /**
+   * Metric whose value increments during the life of the process.
+   *
+   * @param name field name
+   * @param desc field description
+   * @return counter
+   */
+  public abstract Counter0 newCounter(String name, Description desc);
+
+  public abstract <F1> Counter1<F1> newCounter(String name, Description desc, Field<F1> field1);
+
+  public abstract <F1, F2> Counter2<F1, F2> newCounter(
+      String name, Description desc, Field<F1> field1, Field<F2> field2);
+
+  public abstract <F1, F2, F3> Counter3<F1, F2, F3> newCounter(
+      String name, Description desc, Field<F1> field1, Field<F2> field2, Field<F3> field3);
+
+  /**
+   * Metric recording time spent on an operation.
+   *
+   * @param name field name
+   * @param desc field description
+   * @return timer
+   */
+  public abstract Timer0 newTimer(String name, Description desc);
+
+  public abstract <F1> Timer1<F1> newTimer(String name, Description desc, Field<F1> field1);
+
+  public abstract <F1, F2> Timer2<F1, F2> newTimer(
+      String name, Description desc, Field<F1> field1, Field<F2> field2);
+
+  public abstract <F1, F2, F3> Timer3<F1, F2, F3> newTimer(
+      String name, Description desc, Field<F1> field1, Field<F2> field2, Field<F3> field3);
+
+  /**
+   * Metric recording statistical distribution of values.
+   *
+   * @param name field name
+   * @param desc field description
+   * @return histogram
+   */
+  public abstract Histogram0 newHistogram(String name, Description desc);
+
+  public abstract <F1> Histogram1<F1> newHistogram(String name, Description desc, Field<F1> field1);
+
+  public abstract <F1, F2> Histogram2<F1, F2> newHistogram(
+      String name, Description desc, Field<F1> field1, Field<F2> field2);
+
+  public abstract <F1, F2, F3> Histogram3<F1, F2, F3> newHistogram(
+      String name, Description desc, Field<F1> field1, Field<F2> field2, Field<F3> field3);
+
+  /**
+   * Constant value that does not change.
+   *
+   * @param name unique name of the metric.
+   * @param value only value of the metric.
+   * @param desc description of the metric.
+   */
+  public <V> void newConstantMetric(String name, V value, Description desc) {
+    desc.setConstant();
+
+    @SuppressWarnings("unchecked")
+    Class<V> type = (Class<V>) value.getClass();
+    CallbackMetric0<V> metric = newCallbackMetric(name, type, desc);
+    newTrigger(metric, () -> metric.set(value));
+  }
+
+  /**
+   * Instantaneous reading of a value.
+   *
+   * <pre>
+   * metricMaker.newCallbackMetric(&quot;memory&quot;,
+   *     new Description(&quot;Total bytes of memory used&quot;)
+   *        .setGauge()
+   *        .setUnit(Units.BYTES),
+   *     new Supplier&lt;Long&gt;() {
+   *       public Long get() {
+   *         return Runtime.getRuntime().totalMemory();
+   *       }
+   *     });
+   * </pre>
+   *
+   * @param name unique name of the metric.
+   * @param valueClass type of value recorded by the metric.
+   * @param desc description of the metric.
+   * @param trigger function to compute the value of the metric.
+   */
+  public <V> void newCallbackMetric(
+      String name, Class<V> valueClass, Description desc, Supplier<V> trigger) {
+    CallbackMetric0<V> metric = newCallbackMetric(name, valueClass, desc);
+    newTrigger(metric, () -> metric.set(trigger.get()));
+  }
+
+  /**
+   * Instantaneous reading of a single value.
+   *
+   * @param name field name
+   * @param valueClass field type
+   * @param desc field description
+   * @return callback
+   */
+  public abstract <V> CallbackMetric0<V> newCallbackMetric(
+      String name, Class<V> valueClass, Description desc);
+
+  public abstract <F1, V> CallbackMetric1<F1, V> newCallbackMetric(
+      String name, Class<V> valueClass, Description desc, Field<F1> field1);
+
+  /**
+   * Connect logic to populate a previously created {@link CallbackMetric}.
+   *
+   * @param metric1 previously created callback
+   * @param trigger trigger to connect
+   * @return registration handle
+   */
+  public RegistrationHandle newTrigger(CallbackMetric<?> metric1, Runnable trigger) {
+    return newTrigger(ImmutableSet.<CallbackMetric<?>>of(metric1), trigger);
+  }
+
+  public RegistrationHandle newTrigger(
+      CallbackMetric<?> metric1, CallbackMetric<?> metric2, Runnable trigger) {
+    return newTrigger(ImmutableSet.of(metric1, metric2), trigger);
+  }
+
+  public RegistrationHandle newTrigger(
+      CallbackMetric<?> metric1,
+      CallbackMetric<?> metric2,
+      CallbackMetric<?> metric3,
+      Runnable trigger) {
+    return newTrigger(ImmutableSet.of(metric1, metric2, metric3), trigger);
+  }
+
+  public abstract RegistrationHandle newTrigger(Set<CallbackMetric<?>> metrics, Runnable trigger);
+
+  /**
+   * Sanitize the given metric name.
+   *
+   * @param name the name to sanitize.
+   * @return sanitized version of the name.
+   */
+  public String sanitizeMetricName(String name) {
+    return name;
+  }
+}