Delivering the FIRST_NONEMPTY_PAINT phase changing event to base/

base/tracked_objects.h

Index: base/tracked_objects.h
diff --git a/base/tracked_objects.h b/base/tracked_objects.h
index 964326511b23355f0bca71b1671919d8cb3e8548..6c881039633c810b3cd09b1fd18d30cb0f8d3ccb 100644
--- a/base/tracked_objects.h
+++ b/base/tracked_objects.h
@@ -258,6 +258,18 @@ class BASE_EXPORT Births: public BirthOnThread {
 // single birthplace (fixed Location).  Used both on specific threads, and also
 // in snapshots when integrating assembled data.
 
+struct DeathDataPhaseSnapshot;
+
+//------------------------------------------------------------------------------
+// Information about deaths of a task on a given thread, called "death thread".
+// Access to members of this class is never protected by the lock. The fields
+// are accessed in such a way that corruptions resulting from race conditions
+// are not significant, and don't accumulate as a result of multiple accesses.
+// All snapshots and phase change notifications must be called from the same
+// thread. It doesn't matter what thread it is, but it's important the same
+// thread is used as a snapshot thread during the whole process lifetime.
+// All fields except sample_probability_count_ can be snapshotted.
+
 class BASE_EXPORT DeathData {
  public:
   // Default initializer.
@@ -268,13 +280,16 @@ class BASE_EXPORT DeathData {
   // a corresponding death.
   explicit DeathData(int count);
 
+  ~DeathData();
+
   // Update stats for a task destruction (death) that had a Run() time of
   // |duration|, and has had a queueing delay of |queue_duration|.
   void RecordDeath(const int32 queue_duration,
                    const int32 run_duration,
                    const uint32 random_number);
 
-  // Metrics accessors, used only for serialization and in tests.
+  // Metrics and past snapshots accessors, used only for serialization and in
+  // tests.
   int count() const;
   int32 run_duration_sum() const;
   int32 run_duration_max() const;
@@ -282,26 +297,47 @@ class BASE_EXPORT DeathData {
   int32 queue_duration_sum() const;
   int32 queue_duration_max() const;
   int32 queue_duration_sample() const;
+  DeathDataPhaseSnapshot* last_phase_snapshot() const;
 
-  // Reset all tallies to zero. This is used as a hack on realtime data.
-  void Clear();
+  // Called when the current profiling phase, identified by |profiling_phase|,
+  // ends.
+  // Must be called only on the snapshot thread.

[Alexei Svitkine (slow), 2015/04/08 21:57:50]

Is there a way to enforce these threading requirements in debug builds using
some of the helper classes we have, such as ThreadChecker?

[vadimt, 2015/04/08 23:31:24]

Speaking of birth and death threads, I’d not bother. The very fact that methods
like ThreadData::TallyADeath happen on an instance of ThreadData taken from to a
certain thread’s TLS, guarantee that the operations happen in a correct thread.
Also, I’m hesitant to overload pretty frequently executed code (task
start/finish) with more checks even in debug mode. YMMV.

I’ve included checks for the snapshot thread. Not using LazyInstance because in
non-debug mode the instance resolves to an empty structure without a
constructor.

+  void OnProfilingPhaseCompleted(int profiling_phase);
 
  private:
   // Members are ordered from most regularly read and updated, to least
   // frequently used.  This might help a bit with cache lines.
   // Number of runs seen (divisor for calculating averages).
+  // Can be incremented only on the death thread.
   int count_;
-  // Basic tallies, used to compute averages.
+
+  // Count used in determining probability of selecting exec/queue times from a
+  // recorded death as samples.
+  // Gets incremented only on the death thread, but can be set to 0 by
+  // OnProfilingPhaseCompleted() on the snapshot thread.
+  int sample_probability_count_;
+
+  // Basic tallies, used to compute averages. Can be incremented only on the
+  // death thread.
   int32 run_duration_sum_;
   int32 queue_duration_sum_;
   // Max values, used by local visualization routines.  These are often read,
-  // but rarely updated.
+  // but rarely updated. The max values get assigned only on the death thread,
+  // but these fields can be set to 0 by OnProfilingPhaseCompleted() on the
+  // snapshot thread.
   int32 run_duration_max_;
   int32 queue_duration_max_;
   // Samples, used by crowd sourcing gatherers.  These are almost never read,
-  // and rarely updated.
+  // and rarely updated. They can be modified only on the death thread.
   int32 run_duration_sample_;
   int32 queue_duration_sample_;
+
+  // Snapshot of this death data made at the last profiling phase completion, if
+  // any. DeathData owns the whole list starting with this pointer.
+  // Can be accessed only on the snapshot thread.
+  DeathDataPhaseSnapshot* last_phase_snapshot_;
+
+  DISALLOW_COPY_AND_ASSIGN(DeathData);
 };
 
 //------------------------------------------------------------------------------
@@ -312,6 +348,10 @@ struct BASE_EXPORT DeathDataSnapshot {
   explicit DeathDataSnapshot(const DeathData& death_data);
   ~DeathDataSnapshot();
 
+  // Calculates delta between this snapshot and an earlier snapshot of the same
+  // task |older| and assigns it back to this object.
+  void CalculateDelta(const DeathDataSnapshot& older);
+
   int count;
   int32 run_duration_sum;
   int32 run_duration_max;
@@ -322,6 +362,21 @@ struct BASE_EXPORT DeathDataSnapshot {
 };
 
 //------------------------------------------------------------------------------
+// A "snapshotted" representation of the DeathData for a particular profiling
+// phase. Used as an element of the list of phase snapshots owned by DeathData.
+
+struct DeathDataPhaseSnapshot {
+  DeathDataPhaseSnapshot(int profiling_phase, const DeathData& death_data);
+
+  // Profiling phase at which completion this snapshot was taken.
+  int profiling_phase;
+  // Death data snapshot.
+  DeathDataSnapshot death_data;
+  // Pointer to a snapshot from the previous phase.
+  DeathDataPhaseSnapshot* prev;
+};
+
+//------------------------------------------------------------------------------
 // A temporary collection of data that can be sorted and summarized.  It is
 // gathered (carefully) from many threads.  Instances are held in arrays and
 // processed, filtered, and rendered.
@@ -330,12 +385,14 @@ struct BASE_EXPORT DeathDataSnapshot {
 
 struct BASE_EXPORT TaskSnapshot {
   TaskSnapshot();
-  TaskSnapshot(const BirthOnThread& birth,
-               const DeathData& death_data,
+  TaskSnapshot(const BirthOnThreadSnapshot& birth,
+               const DeathDataSnapshot& death_data,
                const std::string& death_thread_name);
   ~TaskSnapshot();
 
   BirthOnThreadSnapshot birth;
+  // Delta between death data for a thread for a certain profiling phase and the
+  // snapshot for the pervious phase, if any. Otherwise, just a snapshot.
   DeathDataSnapshot death_data;
   std::string death_thread_name;
 };
@@ -388,8 +445,21 @@ class BASE_EXPORT ThreadData {
   static ThreadData* Get();
 
   // Fills |process_data_snapshot| with phased snapshots of all profiling
-  // phases, including the current one.
-  static void Snapshot(ProcessDataSnapshot* process_data_snapshot);
+  // phases, including the current one, identified by |current_profiling_phase|.
+  // |current_profiling_phase| is necessary because a child process can start
+  // after several phase-changing events, so it needs to receive the current
+  // phase number from the browser process to fill the correct entry for the
+  // current phase in the |process_data_snapshot| map.
+  static void Snapshot(int current_profiling_phase,
+                       ProcessDataSnapshot* process_data_snapshot);
+
+  // Called when the current profiling phase, identified by |profiling_phase|,
+  // ends.
+  // |profiling_phase| is necessary because a child process can start after
+  // several phase-changing events, so it needs to receive the phase number from
+  // the browser process to fill the correct entry in the
+  // completed_phases_snapshots_ map.
+  static void OnProfilingPhaseCompleted(int profiling_phase);
 
   // Finds (or creates) a place to count births from the given location in this
   // thread, and increment that tally.
@@ -415,13 +485,13 @@ class BASE_EXPORT ThreadData {
   // the task.
   // The |end_of_run| was just obtained by a call to Now() (just after the task
   // finished).
-  static void TallyRunOnWorkerThreadIfTracking(const Births* birth,
+  static void TallyRunOnWorkerThreadIfTracking(const Births* births,
                                                const TrackedTime& time_posted,
                                                const TaskStopwatch& stopwatch);
 
   // Record the end of execution in region, generally corresponding to a scope
   // being exited.
-  static void TallyRunInAScopedRegionIfTracking(const Births* birth,
+  static void TallyRunInAScopedRegionIfTracking(const Births* births,
                                                 const TaskStopwatch& stopwatch);
 
   const std::string& thread_name() const { return thread_name_; }
@@ -493,6 +563,9 @@ class BASE_EXPORT ThreadData {
 
   typedef std::map<const BirthOnThread*, int> BirthCountMap;
 
+  typedef std::vector<std::pair<const Births*, DeathDataPhaseSnapshot>>
+      DeathsSnapshot;
+
   // Worker thread construction creates a name since there is none.
   explicit ThreadData(int thread_number);
 
@@ -517,37 +590,35 @@ class BASE_EXPORT ThreadData {
   Births* TallyABirth(const Location& location);
 
   // Find a place to record a death on this thread.
-  void TallyADeath(const Births& birth,
+  void TallyADeath(const Births& births,
                    int32 queue_duration,
                    const TaskStopwatch& stopwatch);
 
-  // Snapshot (under a lock) the profiled data for the tasks in each ThreadData
-  // instance.  Also updates the |birth_counts| tally for each task to keep
-  // track of the number of living instances of the task.
-  static void SnapshotAllExecutedTasks(
-      ProcessDataPhaseSnapshot* process_data_phase,
-      BirthCountMap* birth_counts);
-
-  // Fills |process_data_phase| with all the recursive results in our process.
-  static void SnapshotCurrentPhase(
-      ProcessDataPhaseSnapshot* process_data_phase);
-
   // Snapshots (under a lock) the profiled data for the tasks for this thread
-  // and writes all of the executed tasks' data -- i.e. the data for the tasks
-  // with with entries in the death_map_ -- into |process_data_phase|.  Also
-  // updates the |birth_counts| tally for each task to keep track of the number
-  // of living instances of the task -- that is, each task maps to the number of
-  // births for the task that have not yet been balanced by a death.
-  void SnapshotExecutedTasks(ProcessDataPhaseSnapshot* process_data_phase,
-                             BirthCountMap* birth_counts);
+  // and writes all of the executed tasks' data -- i.e. the data for all
+  // profiling phases (including the current one: |current_profiling_phase|) for
+  // the tasks with with entries in the death_map_ -- into
+  // |return_of_snapshot_hrenina|. Also updates the |birth_counts| tally for
+  // each task to keep track of the number of living instances of the task --
+  // that is, each task maps to the number of births for the task that have not
+  // yet been balanced by a death.
+  void SnapshotExecutedTasks(
+      int current_profiling_phase,
+      PhasedProcessDataSnapshotMap* phased_process_data_snapshots,
+      BirthCountMap* birth_counts);
 
   // Using our lock, make a copy of the specified maps.  This call may be made
   // on  non-local threads, which necessitate the use of the lock to prevent
   // the map(s) from being reallocated while they are copied.
-  void SnapshotMaps(BirthMap* birth_map,
-                    DeathMap* death_map,
+  void SnapshotMaps(int profiling_phase,
+                    BirthMap* birth_map,
+                    DeathsSnapshot* deaths,
                     ParentChildSet* parent_child_set);
 
+  // Called for this thread when the current profiling phase, identified by
+  // |profiling_phase|, ends.
+  void OnProfilingPhaseCompletionOnThread(int profiling_phase);
+
   // This method is called by the TLS system when a thread terminates.
   // The argument may be NULL if this thread has never tracked a birth or death.
   static void OnThreadTermination(void* thread_data);