Check for span ended within End() (#70)

Adding check for span ended in End() so it does not populate exporters
with 2 copies of the span.

Author: Vizerai

opencensus/trace/internal/span.cc

@@ -201,7 +201,7 @@ void Span::SetStatus(StatusCode canonical_code, absl::string_view message) {
 }
 
 void Span::End() {
-  if (IsRecording()) {
+  if (IsRecording() && !span_impl_->HasEnded()) {
     span_impl_->End();
     exporter::RunningSpanStoreImpl::Get()->RemoveSpan(span_impl_);
     exporter::LocalSpanStoreImpl::Get()->AddSpan(span_impl_);

opencensus/trace/internal/span_impl.cc

@@ -136,6 +136,11 @@ void SpanImpl::SetStatus(exporter::Status&& status) {
 
 void SpanImpl::End() { EndWithTime(absl::Now()); }
 
+bool SpanImpl::HasEnded() const {
+  absl::MutexLock l(&mu_);
+  return has_ended_;
+}
+
 void SpanImpl::EndWithLatencyForTesting(absl::Duration latency) {
   EndWithTime(start_time_ + latency);
 }

opencensus/trace/internal/span_impl.h

@@ -87,6 +87,8 @@ class SpanImpl final {
 
   // Marks the end of the Span and sets its end_time_.
   void End() LOCKS_EXCLUDED(mu_);
+  // Returns true if the span has ended.
+  bool HasEnded() const LOCKS_EXCLUDED(mu_);
 
   absl::string_view name() const { return name_; }