Add process lifetime annotations to stack samples.

base/profiler/stack_sampling_profiler.h

Index: base/profiler/stack_sampling_profiler.h
diff --git a/base/profiler/stack_sampling_profiler.h b/base/profiler/stack_sampling_profiler.h
index cf1daf7e16d4b1846fa1b20a3c79f0f2578ce100..abc3a8fa76bfa022f0fdc861d62ac14556d1c124 100644
--- a/base/profiler/stack_sampling_profiler.h
+++ b/base/profiler/stack_sampling_profiler.h
@@ -11,6 +11,7 @@
 #include <string>
 #include <vector>
 
+#include "base/atomicops.h"
 #include "base/base_export.h"
 #include "base/callback.h"
 #include "base/files/file_path.h"
@@ -107,8 +108,28 @@ class BASE_EXPORT StackSamplingProfiler {
     size_t module_index;
   };
 
-  // Sample represents a set of stack frames.
-  using Sample = std::vector<Frame>;
+  // Sample represents a set of stack frames with some extra information.
+  struct BASE_EXPORT Sample {
+    Sample();
+    Sample(const Sample& sample);
+    ~Sample();
+
+    // These constructors are used only during testing.
+    Sample(const Frame& frame);
+    Sample(const std::vector<Frame>& frames);
+
+    // The entire stack frame when the sample is taken.
+    std::vector<Frame> frames;
+
+    // A bit-field indicating which process phases have passed. This can be
+    // used to tell where in the process lifetime the samples are taken. See
+    // ProcessPhase, above.

[Alexei Svitkine (slow), 2016/11/07 23:22:07]

This comment is not correct anymore since there's no ProcessPhase above now,
right?

Same for the one below.

Please rephrase to mention what these are now. (Even if the answer that these
are defined elsewhere and pass through function x).

[bcwhite, 2016/11/08 01:02:36]

Done.

+    uint32_t process_phases = 0;
+
+    // A bit-field indicating activities which were active when the frame was
+    // captured. See ProcessActivity, above.

[Alexei Svitkine (slow), 2016/11/07 23:22:07]

I think there needs to be a more in depth comment somewhere discussing the
distinction between phases and activities because it's not obvious to me.

[bcwhite, 2016/11/08 01:02:36]

Done.

+    uint32_t current_activities = 0;
+  };
 
   // CallStackProfile represents a set of samples.
   struct BASE_EXPORT CallStackProfile {
@@ -201,6 +222,17 @@ class BASE_EXPORT StackSamplingProfiler {
   // whichever occurs first.
   void Stop();
 
+  // Set the current system state that is recorded with each captured stack
+  // frame. These are all thread-safe so can be called from anywhere. The
+  // parameter values should be from an enumeration of the appropriate type
+  // with values ranging from 0 to 31, inclusive, and set bits within Sample
+  // fields of |process_phases| and |current_activities|. The actual meanings
+  // of these bits are defined (globally) by the caller(s).
+  static void SetProcessPhase(int phase);
+  static void RecordActivityBegin(int activity);
+  static void RecordActivityEnd(int activity);
+  static void ResetPhaseAndActivityForTesting();
+
  private:
   // SamplingThread is a separate thread used to suspend and sample stacks from
   // the target thread.
@@ -243,6 +275,17 @@ class BASE_EXPORT StackSamplingProfiler {
     DISALLOW_COPY_AND_ASSIGN(SamplingThread);
   };
 
+  // Adds "phases" and "activities" annotations to a Sample.
+  static void RecordAnnotations(Sample* sample);
+
+  // These global variables hold current system state. These values are
+  // recorded with every captured sample, done on a separate thread which is
+  // why updates to these must be atomic. A PostTask to move the the updates
+  // to that thread would skew the timing and a lock could result in deadlock
+  // if the thread making a change was also being profiled and got stopped.
+  static subtle::Atomic32 process_phases_;
+  static subtle::Atomic32 current_activities_;
+
   // The thread whose stack will be sampled.
   PlatformThreadId thread_id_;
 
@@ -263,6 +306,12 @@ class BASE_EXPORT StackSamplingProfiler {
 // done in tests and by the metrics provider code.
 BASE_EXPORT bool operator==(const StackSamplingProfiler::Module& a,
                             const StackSamplingProfiler::Module& b);
+BASE_EXPORT bool operator==(const StackSamplingProfiler::Sample& a,
+                            const StackSamplingProfiler::Sample& b);
+BASE_EXPORT bool operator!=(const StackSamplingProfiler::Sample& a,
+                            const StackSamplingProfiler::Sample& b);
+BASE_EXPORT bool operator<(const StackSamplingProfiler::Sample& a,
+                           const StackSamplingProfiler::Sample& b);
 BASE_EXPORT bool operator==(const StackSamplingProfiler::Frame& a,
                             const StackSamplingProfiler::Frame& b);
 BASE_EXPORT bool operator<(const StackSamplingProfiler::Frame& a,