☰
OpenCensus is being archived! Read the blog post to learn more
OpenCensus is being archived! Read the blog post to learn more
Navigation :

Trace exporter

In this quickstart, we’ll learn how to write a custom exporter for tracing.

Requirements

Brief overview

By the end of this tutorial, we would have done these two things using OpenCensus:

  1. Write a custom exporter for tracing.
  2. Show how to use this exporter in an example program.

Getting started

The exporter has two components:

Let’s put the API in latency_exporter.h:

class LatencyExporter {
 public:
  LatencyExporter() = delete;
  static void Register();
};

And the implementation in latency_exporter.cc:

#include "latency_exporter.h"

#include <iostream>
#include <vector>

#include "absl/memory/memory.h"
#include "opencensus/trace/exporter/span_data.h"
#include "opencensus/trace/exporter/span_exporter.h"

namespace {

// Implement the Handler interface.
class Handler : public ::opencensus::trace::exporter::SpanExporter::Handler {
 public:
  // OpenCensus will call Export() periodically with a batch of spans.
  void Export(const std::vector<::opencensus::trace::exporter::SpanData>& spans)
      override {
    // Export each span we were given.
    for (const auto& span : spans) {
      std::cout << "Span \"" << span.name() << "\" took "
                << (span.end_time() - span.start_time()) << ".\n";
    }
  }
};

}  // namespace

// static
void LatencyExporter::Register() {
  ::opencensus::trace::exporter::SpanExporter::RegisterHandler(
      absl::make_unique<Handler>());
}

Add a cc_library target to the BUILD file:

cc_library(
    name = "latency_exporter",
    srcs = ["latency_exporter.cc"],
    hdrs = ["latency_exporter.h"],
    deps = [
        "@com_google_absl//absl/memory",
        "@io_opencensus_cpp//opencensus/trace",
    ],
)

Exercise

Adapt the tracing quickstart to use this exporter:

Every five seconds, the exporter will produce output like:

Span "readLine" took 1.862484838s.
Span "processLine" took 37.702us.
Span "repl" took 1.862748259s.

References

A good reference is opencensus/exporters/trace/stdout/ which implements a simple exporter.

Resource URL
OpenCensus C++ https://github.com/census-instrumentation/opencensus-cpp
Bazel build system https://bazel.build/