Add timer for batching reports. (envoyproxy#73)

* Add periodic timer.

* change timer class.

* rename Reset to Start.

mixerclient/BUILD

@@ -42,6 +42,7 @@ cc_library(
         "include/attribute.h",
         "include/client.h",
         "include/options.h",
+        "include/timer.h",
     ],
     visibility = ["//visibility:public"],
     deps = [

mixerclient/include/client.h

@@ -20,6 +20,7 @@
 #include "google/protobuf/stubs/status.h"
 #include "mixer/v1/service.pb.h"
 #include "options.h"
+#include "timer.h"
 
 namespace istio {
 namespace mixer_client {
@@ -64,6 +65,9 @@ struct MixerClientOptions {
   TransportCheckFunc check_transport;
   TransportReportFunc report_transport;
   TransportQuotaFunc quota_transport;
+
+  // Timer create function.
+  TimerCreateFunc timer_create_func;
 };
 
 class MixerClient {

mixerclient/include/timer.h

@@ -0,0 +1,47 @@
+/* Copyright 2017 Istio Authors. All Rights Reserved.
+ *
+ * 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.
+ */
+
+#ifndef MIXERCLIENT_TIMER_H
+#define MIXERCLIENT_TIMER_H
+
+#include <memory>
+
+namespace istio {
+namespace mixer_client {
+
+// Represent a timer created by caller's environment.
+class Timer {
+ public:
+  // Delete the timer, stopping it first if needed.
+  virtual ~Timer() {}
+
+  // Stop a pending timeout without destroying the underlying timer.
+  virtual void Stop() = 0;
+
+  // Start a pending timeout. If a timeout is already pending,
+  // it will be reset to the new timeout.
+  virtual void Start(int interval_ms) = 0;
+};
+
+// Defines a function to create a timer calling the function
+// with desired interval. The returned object can be used to stop
+// the timer.
+using TimerCreateFunc =
+    std::function<std::unique_ptr<Timer>(std::function<void()> timer_func)>;
+
+}  // namespace mixer_client
+}  // namespace istio
+
+#endif  // MIXERCLIENT_TIMER_H