Make trace export interval and batch size configurable at runtime. (#421

)

Fixes #420.

opencensus/trace/CMakeLists.txt

@@ -49,6 +49,10 @@ opencensus_lib(
   absl::time
   absl::span)
 
+# Define NOMINMAX to fix build errors when compiling with MSVC.
+target_compile_definitions(opencensus_trace PUBLIC
+                           $<$<CXX_COMPILER_ID:MSVC>:NOMINMAX>)
+
 opencensus_lib(
   trace_b3
   PUBLIC

opencensus/trace/exporter/span_exporter.h

@@ -18,6 +18,7 @@
 #include <memory>
 #include <vector>
 
+#include "absl/time/time.h"
 #include "opencensus/trace/exporter/span_data.h"
 
 namespace opencensus {
@@ -27,6 +28,22 @@ namespace exporter {
 // SpanExporter allows Exporters to register. Thread-safe.
 class SpanExporter final {
  public:
+  // Sets the batch size when exporting traces. Takes effect after the next
+  // batch starts. This is not a strict limit, the generated batch may be
+  // slightly larger. If the interval expires before the batch fills up, the
+  // batch will be smaller.
+  //
+  // Warning: this API may be removed in future, in favor of configuring this
+  // per-exporter.
+  static void SetBatchSize(int size);
+
+  // Sets the interval between exporting batches of traces. Takes effect after
+  // the next batch starts.
+  //
+  // Warning: this API may be removed in future, in favor of configuring this
+  // per-exporter.
+  static void SetInterval(absl::Duration interval);
+
   // Handlers allow different tracing services to export recorded data for
   // sampled spans in their own format. Every exporter must provide a static
   // Register() method that takes any arguments needed by the exporter (e.g. a
@@ -41,6 +58,7 @@ class SpanExporter final {
   static void RegisterHandler(std::unique_ptr<Handler> handler);
 
  private:
+  SpanExporter() = delete;
   friend class SpanExporterTestPeer;
 
   // Forces an export, only for testing purposes.

opencensus/trace/internal/span_exporter.cc

@@ -17,12 +17,23 @@
 #include <memory>
 #include <utility>
 
+#include "absl/time/time.h"
 #include "opencensus/trace/internal/span_exporter_impl.h"
 
 namespace opencensus {
 namespace trace {
 namespace exporter {
 
+// static
+void SpanExporter::SetBatchSize(int size) {
+  SpanExporterImpl::Get()->SetBatchSize(size);
+}
+
+// static
+void SpanExporter::SetInterval(absl::Duration interval) {
+  SpanExporterImpl::Get()->SetInterval(interval);
+}
+
 // static
 void SpanExporter::RegisterHandler(std::unique_ptr<Handler> handler) {
   SpanExporterImpl::Get()->RegisterHandler(std::move(handler));

opencensus/trace/internal/span_exporter_impl.cc

@@ -14,6 +14,7 @@
 
 #include "opencensus/trace/internal/span_exporter_impl.h"
 
+#include <algorithm>
 #include <utility>
 
 #include "absl/synchronization/mutex.h"
@@ -24,17 +25,20 @@ namespace opencensus {
 namespace trace {
 namespace exporter {
 
-SpanExporterImpl* SpanExporterImpl::span_exporter_ = nullptr;
-
 SpanExporterImpl* SpanExporterImpl::Get() {
-  static SpanExporterImpl* global_span_exporter_impl = new SpanExporterImpl(
-      kDefaultBufferSize, absl::Milliseconds(kIntervalWaitTimeInMillis));
+  static SpanExporterImpl* global_span_exporter_impl = new SpanExporterImpl;
   return global_span_exporter_impl;
 }
 
-SpanExporterImpl::SpanExporterImpl(uint32_t buffer_size,
-                                   absl::Duration interval)
-    : buffer_size_(buffer_size), interval_(interval) {}
+void SpanExporterImpl::SetBatchSize(int size) {
+  absl::MutexLock l(&handler_mu_);
+  batch_size_ = std::max(1, size);
+}
+
+void SpanExporterImpl::SetInterval(absl::Duration interval) {
+  absl::MutexLock l(&handler_mu_);
+  interval_ = std::max(absl::Seconds(1), interval);
+}
 
 void SpanExporterImpl::RegisterHandler(
     std::unique_ptr<SpanExporter::Handler> handler) {
@@ -59,36 +63,43 @@ void SpanExporterImpl::StartExportThread() {
   collect_spans_ = true;
 }
 
-bool SpanExporterImpl::IsBufferFull() const {
+bool SpanExporterImpl::IsBatchFull() const {
   span_mu_.AssertHeld();
-  return spans_.size() >= buffer_size_;
+  return spans_.size() >= cached_batch_size_;
 }
 
 void SpanExporterImpl::RunWorkerLoop() {
-  std::vector<opencensus::trace::exporter::SpanData> span_data_;
-  std::vector<std::shared_ptr<opencensus::trace::SpanImpl>> batch_;
+  std::vector<opencensus::trace::exporter::SpanData> span_data;
+  std::vector<std::shared_ptr<opencensus::trace::SpanImpl>> batch;
   // Thread loops forever.
   // TODO: Add in shutdown mechanism.
-  absl::Time next_forced_export_time = absl::Now() + interval_;
   while (true) {
+    int size;
+    absl::Time next_forced_export_time;
+    {
+      // Start of loop, update batch size and interval.
+      absl::MutexLock l(&handler_mu_);
+      size = batch_size_;
+      next_forced_export_time = absl::Now() + interval_;
+    }
     {
       absl::MutexLock l(&span_mu_);
+      cached_batch_size_ = size;
       // Wait until batch is full or interval time has been exceeded.
       span_mu_.AwaitWithDeadline(
-          absl::Condition(this, &SpanExporterImpl::IsBufferFull),
+          absl::Condition(this, &SpanExporterImpl::IsBatchFull),
           next_forced_export_time);
-      next_forced_export_time = absl::Now() + interval_;
       if (spans_.empty()) {
         continue;
       }
-      std::swap(batch_, spans_);
+      std::swap(batch, spans_);
     }
-    for (const auto& span : batch_) {
-      span_data_.emplace_back(span->ToSpanData());
+    for (const auto& span : batch) {
+      span_data.emplace_back(span->ToSpanData());
     }
-    batch_.clear();
-    Export(span_data_);
-    span_data_.clear();
+    batch.clear();
+    Export(span_data);
+    span_data.clear();
   }
 }
 

opencensus/trace/internal/span_exporter_impl.h

@@ -44,6 +44,9 @@ class SpanExporterImpl {
   // Returns the global instance of SpanExporterImpl.
   static SpanExporterImpl* Get();
 
+  void SetBatchSize(int size);
+  void SetInterval(absl::Duration interval);
+
   // A shared_ptr to the span is added to a list. The actual conversion to
   // SpanData will take place at a later time via the background thread. This
   // is intended to be called at the Span::End().
@@ -53,11 +56,8 @@ class SpanExporterImpl {
   // initialization.
   void RegisterHandler(std::unique_ptr<SpanExporter::Handler> handler);
 
-  static constexpr uint32_t kDefaultBufferSize = 64;
-  static constexpr uint32_t kIntervalWaitTimeInMillis = 5000;
-
  private:
-  SpanExporterImpl(uint32_t buffer_size, absl::Duration interval);
+  SpanExporterImpl() = default;
   SpanExporterImpl(const SpanExporterImpl&) = delete;
   SpanExporterImpl(SpanExporterImpl&&) = delete;
   SpanExporterImpl& operator=(const SpanExporterImpl&) = delete;
@@ -75,14 +75,15 @@ class SpanExporterImpl {
   // returns when complete.
   void ExportForTesting();
 
-  // Returns true if the spans_ buffer has filled up.
-  bool IsBufferFull() const;
+  // Returns true if the spans_ batch is full.
+  bool IsBatchFull() const;
 
-  static SpanExporterImpl* span_exporter_;
-  const uint32_t buffer_size_;
-  const absl::Duration interval_;
   mutable absl::Mutex span_mu_;
   mutable absl::Mutex handler_mu_;
+  int batch_size_ GUARDED_BY(handler_mu_) = 64;
+  absl::Duration interval_ GUARDED_BY(handler_mu_) = absl::Seconds(5);
+  // Updated in RunWorkerLoop and protected by span_mu_ instead of handler_mu_.
+  int cached_batch_size_ GUARDED_BY(span_mu_);
   std::vector<std::shared_ptr<opencensus::trace::SpanImpl>> spans_
       GUARDED_BY(span_mu_);
   std::vector<std::unique_ptr<SpanExporter::Handler>> handlers_

opencensus/trace/internal/span_exporter_test.cc

@@ -17,6 +17,7 @@
 #include "absl/memory/memory.h"
 #include "absl/synchronization/mutex.h"
 #include "absl/time/clock.h"
+#include "absl/time/time.h"
 #include "gtest/gtest.h"
 #include "opencensus/trace/exporter/span_data.h"
 #include "opencensus/trace/sampler.h"
@@ -63,6 +64,9 @@ class MyExporter : public exporter::SpanExporter::Handler {
 class SpanExporterTest : public ::testing::Test {
  protected:
   static void SetUpTestSuite() {
+    exporter::SpanExporter::SetBatchSize(1);
+    exporter::SpanExporter::SetInterval(absl::Seconds(1));
+
     // Only register once.
     MyExporter::Register();
   }