Make stats export interval configurable at runtime. (#422)

Fixes #412.

opencensus/stats/internal/stats_exporter.cc

@@ -37,6 +37,16 @@ StatsExporterImpl* StatsExporterImpl::Get() {
   return global_stats_exporter_impl;
 }
 
+void StatsExporterImpl::SetInterval(absl::Duration interval) {
+  absl::MutexLock l(&mu_);
+  export_interval_ = interval;
+}
+
+absl::Time StatsExporterImpl::GetNextExportTime() const {
+  absl::MutexLock l(&mu_);
+  return absl::Now() + export_interval_;
+}
+
 void StatsExporterImpl::AddView(const ViewDescriptor& view) {
   absl::MutexLock l(&mu_);
   views_[view.name()] = absl::make_unique<opencensus::stats::View>(view);
@@ -90,31 +100,44 @@ void StatsExporterImpl::StartExportThread() EXCLUSIVE_LOCKS_REQUIRED(mu_) {
 }
 
 void StatsExporterImpl::RunWorkerLoop() {
-  absl::Time next_export_time = absl::Now() + export_interval_;
+  absl::Time next_export_time = GetNextExportTime();
   while (true) {
     // SleepFor() returns immediately when given a negative duration.
     absl::SleepFor(next_export_time - absl::Now());
     // In case the last export took longer than the export interval, we
     // calculate the next time from now.
-    next_export_time = absl::Now() + export_interval_;
+    next_export_time = GetNextExportTime();
     Export();
   }
 }
 
+// StatsExporter
+// -------------
+
+// static
+void StatsExporter::SetInterval(absl::Duration interval) {
+  StatsExporterImpl::Get()->SetInterval(interval);
+}
+
+// static
 void StatsExporter::RemoveView(absl::string_view name) {
   StatsExporterImpl::Get()->RemoveView(name);
 }
 
+// static
 void StatsExporter::RegisterPushHandler(std::unique_ptr<Handler> handler) {
   StatsExporterImpl::Get()->RegisterPushHandler(std::move(handler));
 }
 
+// static
 std::vector<std::pair<ViewDescriptor, ViewData>> StatsExporter::GetViewData() {
   return StatsExporterImpl::Get()->GetViewData();
 }
 
+// static
 void StatsExporter::ExportForTesting() { StatsExporterImpl::Get()->Export(); }
 
+// static
 void StatsExporter::ClearHandlersForTesting() {
   StatsExporterImpl::Get()->ClearHandlersForTesting();
 }

opencensus/stats/internal/stats_exporter_impl.h

@@ -33,9 +33,9 @@ namespace stats {
 class StatsExporterImpl {
  public:
   static StatsExporterImpl* Get();
-
+  void SetInterval(absl::Duration interval);
+  absl::Time GetNextExportTime() const;
   void AddView(const ViewDescriptor& view);
-
   void RemoveView(absl::string_view name);
 
   // Adds a handler, which cannot be subsequently removed (except by
@@ -44,27 +44,22 @@ class StatsExporterImpl {
   void RegisterPushHandler(std::unique_ptr<StatsExporter::Handler> handler);
 
   std::vector<std::pair<ViewDescriptor, ViewData>> GetViewData();
-
   void Export();
-
   void ClearHandlersForTesting();
 
  private:
-  StatsExporterImpl() {}
+  StatsExporterImpl() = default;
 
   void StartExportThread() EXCLUSIVE_LOCKS_REQUIRED(mu_);
 
   // Loops forever, calling Export() every export_interval_.
   void RunWorkerLoop();
 
-  const absl::Duration export_interval_ = absl::Seconds(10);
-
   mutable absl::Mutex mu_;
-
+  absl::Duration export_interval_ GUARDED_BY(mu_) = absl::Seconds(10);
   std::vector<std::unique_ptr<StatsExporter::Handler>> handlers_
       GUARDED_BY(mu_);
   std::unordered_map<std::string, std::unique_ptr<View>> views_ GUARDED_BY(mu_);
-
   bool thread_started_ GUARDED_BY(mu_) = false;
   std::thread t_ GUARDED_BY(mu_);
 };

opencensus/stats/internal/stats_exporter_test.cc

@@ -65,6 +65,8 @@ MeasureDouble TestMeasure() {
 
 class StatsExporterTest : public ::testing::Test {
  protected:
+  static void SetUpTestSuite() { StatsExporter::SetInterval(absl::Seconds(5)); }
+
   void SetUp() {
     // Access the measure to ensure it has been registered.
     TestMeasure();
@@ -165,7 +167,7 @@ TEST_F(StatsExporterTest, TimedExport) {
   std::vector<std::pair<ViewDescriptor, ViewData>> exported_data;
   MockExporter::Register(&exported_data);
   descriptor1_.RegisterForExport();
-  absl::SleepFor(absl::Seconds(11));
+  absl::SleepFor(absl::Seconds(6));
   EXPECT_THAT(exported_data,
               ::testing::UnorderedElementsAre(::testing::Key(descriptor1_)));
 }

opencensus/stats/stats_exporter.h

@@ -35,6 +35,13 @@ namespace stats {
 // StatsExporter is thread-safe.
 class StatsExporter final {
  public:
+  // Sets the interval between exports. Takes effect after the current export
+  // finishes.
+  //
+  // Warning: this API may be removed in future, in favor of configuring this
+  // per-exporter.
+  static void SetInterval(absl::Duration interval);
+
   // Removes the view with 'name' from the registry, if one is registered.
   static void RemoveView(absl::string_view name);
 
@@ -59,10 +66,12 @@ class StatsExporter final {
   static std::vector<std::pair<ViewDescriptor, ViewData>> GetViewData();
 
  private:
+  StatsExporter() = delete;
   friend class StatsExporterTest;
 
   // Forces immediate export of data.
   static void ExportForTesting();
+
   static void ClearHandlersForTesting();
 };