Add example_startup_trace.cc
Change-Id: I9125b10980077399a817d757d0030448880fee4e
diff --git a/examples/sdk/example_startup_trace.cc b/examples/sdk/example_startup_trace.cc
new file mode 100644
index 0000000..3a3afe3
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+++ b/examples/sdk/example_startup_trace.cc
@@ -0,0 +1,175 @@
+/*
+ * Copyright (C) 2022 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 startup tracing with a custom data source.
+// Startup tracing can work only with kSystemBackend. Before running
+// this example, `traced` must already be running in a separate process.
+
+// Run system tracing: ninja -C out/default/ traced && ./out/default/traced
+// And then run this example: ninja -C out/default example_startup_trace &&
+// ./out/default/example_startup_trace
+
+#if defined(PERFETTO_SDK_EXAMPLE_USE_INTERNAL_HEADERS)
+#include "perfetto/tracing.h"
+#include "perfetto/tracing/core/data_source_descriptor.h"
+#include "perfetto/tracing/core/trace_config.h"
+#include "perfetto/tracing/data_source.h"
+#include "perfetto/tracing/tracing.h"
+#include "protos/perfetto/trace/test_event.pbzero.h"
+#else
+#include <perfetto.h>
+#endif
+
+#include <unistd.h>
+#include <fstream>
+#include <iostream>
+#include <thread>
+
+namespace {
+
+class EventObserver {
+ public:
+ // Wait until OnEvent is ever called.
+ // Returns immediately if OnEvent was already called.
+ void Wait() {
+ std::unique_lock<std::mutex> lock(mutex);
+ cv.wait(lock, [&]() { return event_occurred_; });
+ }
+ void OnEvent() {
+ {
+ std::unique_lock<std::mutex> lock(mutex);
+ event_occurred_ = true;
+ }
+ cv.notify_all();
+ }
+ EventObserver() = default;
+
+ private:
+ EventObserver(const EventObserver&) = delete;
+ EventObserver& operator=(const EventObserver&) = delete;
+
+ std::mutex mutex;
+ std::condition_variable cv;
+ bool event_occurred_ = false;
+};
+
+// The definition of our custom data source. Instances of this class will be
+// automatically created and destroyed by Perfetto.
+class CustomDataSource : public perfetto::DataSource<CustomDataSource> {
+ public:
+ CustomDataSource(EventObserver* event_observer)
+ : event_observer_(event_observer) {}
+ void OnStart(const StartArgs&) override { event_observer_->OnEvent(); }
+
+ private:
+ EventObserver* event_observer_;
+};
+
+void InitializePerfetto(EventObserver* event_observer) {
+ perfetto::TracingInitArgs args;
+ // The backends determine where trace events are recorded. For this example we
+ // are going to use the system-wide tracing service, because the in-process
+ // backend doesn't support startup tracing.
+ args.backends = perfetto::kSystemBackend;
+ perfetto::Tracing::Initialize(args);
+
+ // Register our custom data source. Only the name is required, but other
+ // properties can be advertised too.
+ perfetto::DataSourceDescriptor dsd;
+ dsd.set_name("com.example.startup_trace");
+ CustomDataSource::Register(dsd, event_observer);
+}
+
+// The trace config defines which types of data sources are enabled for
+// recording.
+perfetto::TraceConfig GetTraceConfig() {
+ perfetto::TraceConfig cfg;
+ cfg.add_buffers()->set_size_kb(1024);
+ auto* ds_cfg = cfg.add_data_sources()->mutable_config();
+ ds_cfg->set_name("com.example.startup_trace");
+ return cfg;
+}
+
+void StartStartupTracing() {
+ perfetto::Tracing::SetupStartupTracingOpts args;
+ args.backend = perfetto::kSystemBackend;
+ perfetto::Tracing::SetupStartupTracing(GetTraceConfig(), args);
+}
+
+std::unique_ptr<perfetto::TracingSession> StartTracing() {
+ auto tracing_session = perfetto::Tracing::NewTrace();
+ tracing_session->Setup(GetTraceConfig());
+ tracing_session->StartBlocking();
+ return tracing_session;
+}
+
+void StopTracing(std::unique_ptr<perfetto::TracingSession> tracing_session) {
+ // Flush to make sure the last written event ends up in the trace.
+ CustomDataSource::Trace(
+ [](CustomDataSource::TraceContext ctx) { ctx.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;
+ const char* filename = "example_startup_trace.pftrace";
+ output.open(filename, std::ios::out | std::ios::binary);
+ output.write(&trace_data[0], static_cast<std::streamsize>(trace_data.size()));
+ output.close();
+ PERFETTO_LOG(
+ "Trace written in %s file. To read this trace in "
+ "text form, run `./tools/traceconv text %s`",
+ filename, filename);
+}
+
+} // namespace
+
+PERFETTO_DECLARE_DATA_SOURCE_STATIC_MEMBERS(CustomDataSource);
+PERFETTO_DEFINE_DATA_SOURCE_STATIC_MEMBERS(CustomDataSource);
+
+int main(int, const char**) {
+ EventObserver event_observer;
+ InitializePerfetto(&event_observer);
+
+ StartStartupTracing();
+ // TODO(mohitms): Once we support `SetupStartupTracingBlocking`,
+ // it won't be required.
+ event_observer.Wait();
+
+ // Write an event using our custom data source before starting tracing
+ // session.
+ CustomDataSource::Trace([](CustomDataSource::TraceContext ctx) {
+ auto packet = ctx.NewTracePacket();
+ packet->set_timestamp(41);
+ packet->set_for_testing()->set_str("Startup Event");
+ });
+
+ auto tracing_session = StartTracing();
+
+ // Write an event using our custom data source.
+ CustomDataSource::Trace([](CustomDataSource::TraceContext ctx) {
+ auto packet = ctx.NewTracePacket();
+ packet->set_timestamp(42);
+ packet->set_for_testing()->set_str("Main Event");
+ });
+ StopTracing(std::move(tracing_session));
+
+ return 0;
+}
