1 files changed, 68 insertions, 0 deletions
diff --git a/java/com/google/gerrit/metrics/dropwizard/CallbackGroup.java b/java/com/google/gerrit/metrics/dropwizard/CallbackGroup.java
new file mode 100644
index 0000000000..f153e7e613
--- /dev/null
+++ b/java/com/google/gerrit/metrics/dropwizard/CallbackGroup.java
@@ -0,0 +1,68 @@
+// 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.dropwizard;
+
+import com.google.common.collect.ImmutableSet;
+import java.util.concurrent.TimeUnit;
+import java.util.concurrent.atomic.AtomicLong;
+
+/**
+ * Run a user specified trigger only once every 2 seconds.
+ *
+ * <p>This allows the same Runnable trigger to be applied to several metrics. When a recorder is
+ * sampling the related metrics only the first access will perform recomputation. Reading other
+ * related metrics will rely on the already set values for the next several seconds.
+ */
+class CallbackGroup implements Runnable {
+  private static final long PERIOD = TimeUnit.SECONDS.toNanos(2);
+
+  private final AtomicLong reloadAt;
+  private final Runnable trigger;
+  private final ImmutableSet<CallbackMetricGlue> metrics;
+  private final Object reloadLock = new Object();
+
+  CallbackGroup(Runnable trigger, ImmutableSet<CallbackMetricGlue> metrics) {
+    this.reloadAt = new AtomicLong(0);
+    this.trigger = trigger;
+    this.metrics = metrics;
+  }
+
+  @Override
+  public void run() {
+    if (reload()) {
+      synchronized (reloadLock) {
+        for (CallbackMetricGlue m : metrics) {
+          m.beginSet();
+        }
+        trigger.run();
+        for (CallbackMetricGlue m : metrics) {
+          m.endSet();
+        }
+      }
+    }
+  }
+
+  private boolean reload() {
+    for (; ; ) {
+      long now = System.nanoTime();
+      long next = reloadAt.get();
+      if (next > now) {
+        return false;
+      } else if (reloadAt.compareAndSet(next, now + PERIOD)) {
+        return true;
+      }
+    }
+  }
+}