Implement standalone event tracing in AppRTCDemo.

webrtc/base/event_tracer.cc

Index: webrtc/base/event_tracer.cc
diff --git a/webrtc/base/event_tracer.cc b/webrtc/base/event_tracer.cc
index 5c6d39f0a49219d24cd307d1d2610eb13a54658f..dbf85a4e9a21e92734ccae6c3a5cda1432885793 100644
--- a/webrtc/base/event_tracer.cc
+++ b/webrtc/base/event_tracer.cc
@@ -7,15 +7,26 @@
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
-
 #include "webrtc/base/event_tracer.h"
 
+#include <inttypes.h>
+
+#include <vector>
+
+#include "webrtc/base/checks.h"
+#include "webrtc/base/criticalsection.h"
+#include "webrtc/base/event.h"
+#include "webrtc/base/logging.h"
+#include "webrtc/base/platform_thread.h"
+#include "webrtc/base/timeutils.h"
+#include "webrtc/base/trace_event.h"
+
 namespace webrtc {
 
 namespace {
 
-GetCategoryEnabledPtr g_get_category_enabled_ptr = 0;
-AddTraceEventPtr g_add_trace_event_ptr = 0;
+GetCategoryEnabledPtr g_get_category_enabled_ptr = nullptr;
+AddTraceEventPtr g_add_trace_event_ptr = nullptr;
 
 }  // namespace
 
@@ -25,7 +36,6 @@ void SetupEventTracer(GetCategoryEnabledPtr get_category_enabled_ptr,
   g_add_trace_event_ptr = add_trace_event_ptr;
 }
 
-// static
 const unsigned char* EventTracer::GetCategoryEnabled(const char* name) {
   if (g_get_category_enabled_ptr)
     return g_get_category_enabled_ptr(name);
@@ -34,7 +44,8 @@ const unsigned char* EventTracer::GetCategoryEnabled(const char* name) {
   return reinterpret_cast<const unsigned char*>("\0");
 }
 
-// static
+// Arguments to this function (phase, etc.) are as defined in
+// webrtc/base/trace_event.h.
 void EventTracer::AddTraceEvent(char phase,
                                 const unsigned char* category_enabled,
                                 const char* name,
@@ -58,3 +69,197 @@ void EventTracer::AddTraceEvent(char phase,
 }
 
 }  // namespace webrtc
+
+namespace rtc {
+namespace tracing {
+namespace {
+
+static bool EventTracingThreadFunc(void* params);
+
+// Atomic-int fast path for avoiding logging when disabled.
+static volatile int g_event_logging_active = 0;
+
+// TODO(pbos): Log metadata for all threads, etc.
+class EventLogger final {
+ public:
+  EventLogger()
+      : logging_thread_(EventTracingThreadFunc, this, "EventTracingThread"),
+        shutdown_event_(false, false) {}
+  ~EventLogger() { RTC_DCHECK(thread_checker_.CalledOnValidThread()); }
+
+  void AddTraceEvent(const char* name,
+                     const unsigned char* category_enabled,
+                     char phase,
+                     uint64_t timestamp,
+                     int pid,
+                     rtc::PlatformThreadId thread_id) {
+    rtc::CritScope lock(&crit_);
+    trace_events_.push_back(
+        {name, category_enabled, phase, timestamp, 1, thread_id});
+  }
+
+// The TraceEvent format is documented here:
+// https://docs.google.com/document/d/1CvAClvFfyA5R-PhYUmn5OOQtYMH4h6I0nSsKchNAySU/preview
+  void Log() {
+    RTC_DCHECK(output_file_);
+    static const int kLoggingIntervalMs = 100;
+    fprintf(output_file_, "{ \"traceEvents\": [\n");
+    bool has_logged_event = false;
+    while (true) {
+      bool shutting_down = shutdown_event_.Wait(kLoggingIntervalMs);
+      std::vector<TraceEvent> events;
+      {
+        rtc::CritScope lock(&crit_);
+        trace_events_.swap(events);
+      }
+      for (const TraceEvent& e : events) {
+        fprintf(output_file_,
+                "%s{ \"name\": \"%s\""
+                ", \"cat\": \"%s\""
+                ", \"ph\": \"%c\""
+                ", \"ts\": %" PRIu64
+                ", \"pid\": %d"
+                ", \"tid\": %d}\n",
+                has_logged_event ? "," : " ", e.name, e.category_enabled,
+                e.phase, e.timestamp, e.pid, e.tid);
+        has_logged_event = true;
+      }
+      if (shutting_down)
+        break;
+    }
+    fprintf(output_file_, "]}\n");
+    if (output_file_owned_)
+      fclose(output_file_);
+    output_file_ = nullptr;
+  }
+
+  void Start(FILE* file, bool owned) {
+    RTC_DCHECK(file);
+    RTC_DCHECK(!output_file_);
+    output_file_ = file;
+    output_file_owned_ = owned;
+    {
+      rtc::CritScope lock(&crit_);
+      // Since the atomic fast-path for adding events to the queue can be
+      // bypassed while the logging thread is shutting down there may be some
+      // stale events in the queue, hence the vector needs to be cleared to not
+      // log events from a previous logging session (which may be days old).
+      trace_events_.clear();
+    }
+    // Enable event logging (fast-path). This should be disabled since starting
+    // shouldn't be done twice.
+    RTC_CHECK_EQ(0,
+                 rtc::AtomicOps::CompareAndSwap(&g_event_logging_active, 0, 1));
+
+    // Finally start, everything should be set up now.
+    logging_thread_.Start();
+  }
+
+  void Stop() {
+    // Try to stop. Abort if we're not currently logging.
+    if (rtc::AtomicOps::CompareAndSwap(&g_event_logging_active, 1, 0) == 0)
+      return;
+
+    // Wake up logging thread to finish writing.
+    shutdown_event_.Set();
+    // Join the logging thread.
+    logging_thread_.Stop();
+  }
+
+ private:
+  struct TraceEvent {
+    const char* name;
+    const unsigned char* category_enabled;
+    char phase;
+    uint64_t timestamp;
+    int pid;
+    rtc::PlatformThreadId tid;
+  };
+
+  rtc::CriticalSection crit_;
+  std::vector<TraceEvent> trace_events_ GUARDED_BY(crit_);
+  rtc::PlatformThread logging_thread_;
+  rtc::Event shutdown_event_;
+  rtc::ThreadChecker thread_checker_;
+  FILE* output_file_ = nullptr;
+  bool output_file_owned_ = false;
+};
+
+static bool EventTracingThreadFunc(void* params) {
+  static_cast<EventLogger*>(params)->Log();
+  return true;
+}
+
+static EventLogger* volatile g_event_logger = nullptr;
+static const char* const kDisabledTracePrefix = TRACE_DISABLED_BY_DEFAULT("");
+const unsigned char* InternalGetCategoryEnabled(const char* name) {
+  const char* prefix_ptr = &kDisabledTracePrefix[0];
+  const char* name_ptr = name;
+  // Check whether name contains the default-disabled prefix.
+  while (*prefix_ptr == *name_ptr && *prefix_ptr != '\0') {
+    ++prefix_ptr;
+    ++name_ptr;
+  }
+  return reinterpret_cast<const unsigned char*>(*prefix_ptr == '\0' ? ""
+                                                                    : name);
+}
+
+void InternalAddTraceEvent(char phase,
+                           const unsigned char* category_enabled,
+                           const char* name,
+                           unsigned long long id,
+                           int num_args,
+                           const char** arg_names,
+                           const unsigned char* arg_types,
+                           const unsigned long long* arg_values,
+                           unsigned char flags) {
+  // Fast path for when event tracing is inactive.
+  if (rtc::AtomicOps::AcquireLoad(&g_event_logging_active) == 0)
+    return;
+
+  g_event_logger->AddTraceEvent(name, category_enabled, phase,
+                                rtc::TimeMicros(), 1, rtc::CurrentThreadId());
+}
+
+}  // namespace
+
+void SetupInternalTracer() {
+  RTC_CHECK(rtc::AtomicOps::CompareAndSwapPtr(
+                &g_event_logger, static_cast<EventLogger*>(nullptr),
+                new EventLogger()) == nullptr);
+  g_event_logger = new EventLogger();
+  webrtc::SetupEventTracer(InternalGetCategoryEnabled, InternalAddTraceEvent);
+}
+
+void StartInternalCaptureToFile(FILE* file) {
+  g_event_logger->Start(file, false);
+}
+
+bool StartInternalCapture(const char* filename) {
+  FILE* file = fopen(filename, "w");
+  if (!file) {
+    LOG(LS_ERROR) << "Failed to open trace file '" << filename
+                  << "' for writing.";
+    return false;
+  }
+  g_event_logger->Start(file, true);
+  return true;
+}
+
+void StopInternalCapture() {
+  g_event_logger->Stop();
+}
+
+void ShutdownInternalTracer() {
+  StopInternalCapture();
+  EventLogger* old_logger = rtc::AtomicOps::AtomicLoadPtr(&g_event_logger);
+  RTC_DCHECK(old_logger);
+  RTC_CHECK(rtc::AtomicOps::CompareAndSwapPtr(
+                &g_event_logger, old_logger,
+                static_cast<EventLogger*>(nullptr)) == old_logger);
+  delete old_logger;
+  webrtc::SetupEventTracer(nullptr, nullptr);
+}
+
+}  // namespace tracing
+}  // namespace rtc