Hello world quickstart example. (#85)

* Hello world quickstart example.

Author: Vizerai

examples/helloworld/BUILD

@@ -0,0 +1,33 @@
+# Copyright 2018, OpenCensus Authors
+#
+# 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.
+
+load("//opencensus:copts.bzl", "DEFAULT_COPTS", "TEST_COPTS")
+
+licenses(["notice"])  # Apache License 2.0
+
+package(default_visibility = ["//visibility:private"])
+
+cc_binary(
+    name = "hello_world",
+    srcs = ["hello_world.cc"],
+    copts = DEFAULT_COPTS,
+    linkopts = ["-pthread"],
+    deps = [
+        "//opencensus/exporters/stats/stdout:stdout_exporter",
+        "//opencensus/exporters/trace/stdout:stdout_exporter",
+        "//opencensus/trace",
+        "//opencensus/stats",
+        "@com_google_absl//absl/strings",
+    ],
+)

examples/helloworld/hello_world.cc

@@ -0,0 +1,106 @@
+// Copyright 2018, OpenCensus Authors
+//
+// 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.
+
+#include <time.h>
+#include <cstdlib>
+#include <iostream>
+#include <memory>
+#include <string>
+
+#include "absl/strings/string_view.h"
+#include "absl/time/clock.h"
+#include "absl/time/time.h"
+#include "opencensus/exporters/stats/stdout/stdout_exporter.h"
+#include "opencensus/exporters/trace/stdout/stdout_exporter.h"
+#include "opencensus/stats/stats.h"
+#include "opencensus/trace/sampler.h"
+#include "opencensus/trace/span.h"
+
+namespace {
+
+ABSL_CONST_INIT const absl::string_view kFrontendKey = "my.org/keys/frontend";
+ABSL_CONST_INIT const absl::string_view kVideoSizeViewName =
+    "my.org/views/video_size";
+ABSL_CONST_INIT const absl::string_view kVideoSizeMeasureName =
+    "my.org/measure/video_size";
+
+// The resource owner defines and registers a measure. A function exposing a
+// function-local static is the recommended style, ensuring that the measure is
+// only registered once.
+opencensus::stats::MeasureInt VideoSizeMeasure() {
+  static const opencensus::stats::MeasureInt video_size =
+      opencensus::stats::MeasureRegistry::RegisterInt(
+          kVideoSizeMeasureName, "MBy", "size of processed videos");
+  return video_size;
+}
+
+}  // namespace
+
+// Simple program that collects data for video size.
+int main(int argc, char **argv) {
+  if (argc != 1) {
+    std::cerr << "Usage: " << argv[0] << "\n";
+    return 1;
+  }
+  srand(time(NULL));
+
+  // Register stdout exporters.
+  opencensus::exporters::stats::StdoutExporter::Register();
+  opencensus::exporters::trace::StdoutExporter::Register();
+
+  // Call measure so that it is initialized.
+  VideoSizeMeasure();
+
+  // Create view to see the processed video size distribution broken down by
+  // frontend. The view has bucket boundaries (0, 256, 65536) that will group
+  // measure values into histogram buckets.
+  const opencensus::stats::ViewDescriptor video_size_view =
+      opencensus::stats::ViewDescriptor()
+          .set_name(kVideoSizeViewName)
+          .set_description("processed video size over time")
+          .set_measure(kVideoSizeMeasureName)
+          .set_aggregation(opencensus::stats::Aggregation::Distribution(
+              opencensus::stats::BucketBoundaries::Exponential(8, 1 << 8, 2)))
+          .add_column(kFrontendKey);
+  opencensus::stats::View view(video_size_view);
+  video_size_view.RegisterForExport();
+
+  opencensus::trace::AlwaysSampler sampler;
+  auto span = opencensus::trace::Span::StartSpan("my.org/ProcessVideo", nullptr,
+                                                 {&sampler});
+
+  // Process video.
+  // Record the processed video size.
+  span.AddAnnotation("Start processing video.");
+  // Sleep for [1,10] milliseconds to fake work.
+  absl::SleepFor(absl::Milliseconds(rand() % 10 + 1));
+  opencensus::stats::Record({{VideoSizeMeasure(), 25648}},
+                            {{kFrontendKey, "video size"}});
+  span.AddAnnotation("Finished processing video.");
+  span.End();
+
+  // Sleep for ~5 seconds to ensure that exporters will process the span.
+  std::cout << "Wait longer than the reporting duration...\n";
+  absl::SleepFor(absl::Milliseconds(5100));
+
+  // Sleep while exporters run in the background.
+  std::cout << "Views:\n" << video_size_view.DebugString() << "\n";
+  const auto data = view.GetData();
+  if (data.type() == opencensus::stats::ViewData::Type::kDistribution) {
+    for (auto &it : data.distribution_data()) {
+      for (auto &name : it.first) std::cout << name << " : ";
+      std::cout << it.second.DebugString() << "\n";
+    }
+  }
+}