examples/sdk/example.cc

/*
 * Copyright (C) 2020 The Android Open Source Project
 *
 * 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.
 */

// This example demonstrates in-process tracing with Perfetto.

#include "trace_categories.h"

#include <chrono>
#include <fstream>
#include <thread>

void InitializePerfetto() {
  perfetto::TracingInitArgs args;
  // The backends determine where trace events are recorded. For this example we
  // are going to use the in-process tracing service, which only includes in-app
  // events.
  args.backends = perfetto::kInProcessBackend;

  perfetto::Tracing::Initialize(args);
  perfetto::TrackEvent::Register();
}

std::unique_ptr<perfetto::TracingSession> StartTracing() {
  // The trace config defines which types of data sources are enabled for
  // recording. In this example we just need the "track_event" data source,
  // which corresponds to the TRACE_EVENT trace points.
  perfetto::TraceConfig cfg;
  cfg.add_buffers()->set_size_kb(1024);
  auto* ds_cfg = cfg.add_data_sources()->mutable_config();
  ds_cfg->set_name("track_event");

  auto tracing_session = perfetto::Tracing::NewTrace();
  tracing_session->Setup(cfg);
  tracing_session->StartBlocking();
  return tracing_session;
}

void StopTracing(std::unique_ptr<perfetto::TracingSession> tracing_session) {
  // Make sure the last event is closed for this example.
  perfetto::TrackEvent::Flush();

  // Stop tracing and read the trace data.
  tracing_session->StopBlocking();
  std::vector<char> trace_data(tracing_session->ReadTraceBlocking());

  // Write the result into a file.
  // Note: To save memory with longer traces, you can tell Perfetto to write
  // directly into a file by passing a file descriptor into Setup() above.
  std::ofstream output;
  output.open("example.pftrace", std::ios::out | std::ios::binary);
  output.write(&trace_data[0], trace_data.size());
  output.close();
}

void DrawPlayer(int player_number) {
  TRACE_EVENT("rendering", "DrawPlayer", "player_number", player_number);
  // Sleep to simulate a long computation.
  std::this_thread::sleep_for(std::chrono::milliseconds(500));
}

void DrawGame() {
  // This is an example of an unscoped slice, which begins and ends at specific
  // points (instead of at the end of the current block scope).
  TRACE_EVENT_BEGIN("rendering", "DrawGame");
  DrawPlayer(1);
  DrawPlayer(2);
  TRACE_EVENT_END("rendering");

  // Record the rendering framerate as a counter sample.
  TRACE_COUNTER("rendering", "Framerate", 120);
}

int main(int, const char**) {
  InitializePerfetto();
  auto tracing_session = StartTracing();

  // Give a custom name for the traced process.
  perfetto::ProcessTrack process_track = perfetto::ProcessTrack::Current();
  perfetto::protos::gen::TrackDescriptor desc = process_track.Serialize();
  desc.mutable_process()->set_process_name("Example");
  perfetto::TrackEvent::SetTrackDescriptor(process_track, desc);

  // Simulate some work that emits trace events.
  DrawGame();

  StopTracing(std::move(tracing_session));
  return 0;
}