Add TRACE_EVENT_IS_NEW_TRACE as a way to snapshot objects at start of recording

R=dsinclair,enne
NOTRY=True

Android test failures are flake.

Review URL: https://chromiumcodereview.appspot.com/15774010

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@203810 0039d316-1c4b-4281-b951-d872f2087c98

4 files changed, 71 insertions, 1 deletions

diff --git a/base/debug/trace_event.h b/base/debug/trace_event.h
index abd3901..aa4cc75 100644
--- a/base/debug/trace_event.h
+++ b/base/debug/trace_event.h
@@ -678,6 +678,22 @@
       } \
     } while (0)
 
+// Macro to efficiently determine, through polling, if a new trace has begun.
+#define TRACE_EVENT_IS_NEW_TRACE(ret) \
+    do { \
+      static int INTERNAL_TRACE_EVENT_UID(lastRecordingNumber) = 0; \
+      int num_traces_recorded = TRACE_EVENT_API_GET_NUM_TRACES_RECORDED(); \
+      if (num_traces_recorded != -1 && \
+          num_traces_recorded != \
+          INTERNAL_TRACE_EVENT_UID(lastRecordingNumber)) { \
+        INTERNAL_TRACE_EVENT_UID(lastRecordingNumber) = \
+            num_traces_recorded; \
+        *ret = true; \
+      } else { \
+        *ret = false; \
+      } \
+    } while (0)
+
 ////////////////////////////////////////////////////////////////////////////////
 // Implementation specific tracing API definitions.
 
@@ -694,6 +710,12 @@
 #define TRACE_EVENT_API_GET_CATEGORY_GROUP_ENABLED \
     base::debug::TraceLog::GetCategoryGroupEnabled
 
+// Get the number of times traces have been recorded. This is used to implement
+// the TRACE_EVENT_IS_NEW_TRACE facility.
+// unsigned int TRACE_EVENT_API_GET_NUM_TRACES_RECORDED()
+#define TRACE_EVENT_API_GET_NUM_TRACES_RECORDED \
+    base::debug::TraceLog::GetInstance()->GetNumTracesRecorded
+
 // Add a trace event to the platform tracing system.
 // void TRACE_EVENT_API_ADD_TRACE_EVENT(
 //                    char phase,
diff --git a/base/debug/trace_event_impl.cc b/base/debug/trace_event_impl.cc
index 34f26f6..6e3516e 100644
--- a/base/debug/trace_event_impl.cc
+++ b/base/debug/trace_event_impl.cc
@@ -773,6 +773,7 @@ TraceLog::Options TraceLog::TraceOptionsFromString(const std::string& options) {
 
 TraceLog::TraceLog()
     : enable_count_(0),
+      num_traces_recorded_(0),
       logged_events_(NULL),
       dispatching_to_observer_list_(false),
       watch_category_(NULL),
@@ -933,6 +934,8 @@ void TraceLog::SetEnabled(const CategoryFilter& category_filter,
     return;
   }
 
+  num_traces_recorded_++;
+
   dispatching_to_observer_list_ = true;
   FOR_EACH_OBSERVER(EnabledStateChangedObserver, enabled_state_observer_list_,
                     OnTraceLogWillEnable());
@@ -1007,6 +1010,13 @@ void TraceLog::SetDisabled() {
   AddThreadNameMetadataEvents();
 }
 
+int TraceLog::GetNumTracesRecorded() {
+  AutoLock lock(lock_);
+  if (enable_count_ == 0)
+    return -1;
+  return num_traces_recorded_;
+}
+
 void TraceLog::AddEnabledStateObserver(EnabledStateChangedObserver* listener) {
   enabled_state_observer_list_.AddObserver(listener);
 }
@@ -1517,4 +1527,3 @@ ScopedTrace::~ScopedTrace() {
 }
 
 }  // namespace trace_event_internal
-
diff --git a/base/debug/trace_event_impl.h b/base/debug/trace_event_impl.h
index da70b4b..b3be02a 100644
--- a/base/debug/trace_event_impl.h
+++ b/base/debug/trace_event_impl.h
@@ -317,6 +317,13 @@ class BASE_EXPORT TraceLog {
   void SetDisabled();
   bool IsEnabled() { return !!enable_count_; }
 
+  // The number of times we have begun recording traces. If tracing is off,
+  // returns -1. If tracing is on, then it returns the number of times we have
+  // recorded a trace. By watching for this number to increment, you can
+  // passively discover when a new trace has begun. This is then used to
+  // implement the TRACE_EVENT_IS_NEW_TRACE() primitive.
+  int GetNumTracesRecorded();
+
 #if defined(OS_ANDROID)
   void StartATrace();
   void StopATrace();
@@ -526,6 +533,7 @@ class BASE_EXPORT TraceLog {
   // This lock protects TraceLog member accesses from arbitrary threads.
   Lock lock_;
   int enable_count_;
+  int num_traces_recorded_;
   NotificationCallback notification_callback_;
   scoped_ptr<TraceBuffer> logged_events_;
   EventCallback event_callback_;
diff --git a/base/debug/trace_event_unittest.cc b/base/debug/trace_event_unittest.cc
index 26e79c0..02bb899 100644
--- a/base/debug/trace_event_unittest.cc
+++ b/base/debug/trace_event_unittest.cc
@@ -905,6 +905,37 @@ TEST_F(TraceEventTestFixture, EnabledObserverFiresOnDisable) {
   TraceLog::GetInstance()->RemoveEnabledStateObserver(&observer);
 }
 
+bool IsNewTrace() {
+  bool is_new_trace;
+  TRACE_EVENT_IS_NEW_TRACE(&is_new_trace);
+  return is_new_trace;
+}
+
+TEST_F(TraceEventTestFixture, NewTraceRecording) {
+  ManualTestSetUp();
+  ASSERT_FALSE(IsNewTrace());
+  TraceLog::GetInstance()->SetEnabled(CategoryFilter("*"),
+                                      TraceLog::RECORD_UNTIL_FULL);
+  // First call to IsNewTrace() should succeed. But, the second shouldn't.
+  ASSERT_TRUE(IsNewTrace());
+  ASSERT_FALSE(IsNewTrace());
+  EndTraceAndFlush();
+
+  // IsNewTrace() should definitely be false now.
+  ASSERT_FALSE(IsNewTrace());
+
+  // Start another trace. IsNewTrace() should become true again, briefly, as
+  // before.
+  TraceLog::GetInstance()->SetEnabled(CategoryFilter("*"),
+                                      TraceLog::RECORD_UNTIL_FULL);
+  ASSERT_TRUE(IsNewTrace());
+  ASSERT_FALSE(IsNewTrace());
+
+  // Cleanup.
+  EndTraceAndFlush();
+}
+
+
 // Test that categories work.
 TEST_F(TraceEventTestFixture, Categories) {
   ManualTestSetUp();