StackSamplingProfiler clean up

base/profiler/stack_sampling_profiler.h

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef BASE_PROFILER_STACK_SAMPLING_PROFILER_H_
 #define BASE_PROFILER_STACK_SAMPLING_PROFILER_H_
 
 #include <string>
 #include <vector>
 
 #include "base/base_export.h"
 #include "base/callback.h"
 #include "base/files/file_path.h"
 #include "base/memory/scoped_ptr.h"
 #include "base/strings/string16.h"
 #include "base/threading/platform_thread.h"
 #include "base/time/time.h"
 
 namespace base {
 
 // StackSamplingProfiler periodically stops a thread to sample its stack, for
 // the purpose of collecting information about which code paths are
 // executing. This information is used in aggregate by UMA to identify hot
 // and/or janky code paths.
 //
-// Sample StackStackSamplingProfiler usage:
+// Sample StackSamplingProfiler usage:
 //
 //   // Create and customize params as desired.
 //   base::StackStackSamplingProfiler::SamplingParams params;
 //   // Any thread's ID may be passed as the target.
 //   base::StackSamplingProfiler profiler(base::PlatformThread::CurrentId()),
 //       params);
 //
 //   // To process the profiles within Chrome rather than via UMA, set a custom
 //   // completed callback:
-//   base::Callback<void(const std::vector<Profile>&)>
+//   base::StackStackSamplingProfiler::CompletedCallback
 //       thread_safe_callback = ...;
 //   profiler.SetCustomCompletedCallback(thread_safe_callback);
 //
 //   profiler.Start();
 //   // ... work being done on the target thread here ...
 //   profiler.Stop();  // optional, stops collection before complete per params
 //
+// The default SamplingParams causes stacks to be recorded in a single burst at
+// a 10Hz interval for a total of 30 seconds. All of these parameters may be
+// altered as desired.
+//
 // When all profiles are complete or the profiler is stopped, if the custom
-// completed callback was set it will be called from the profiler thread with
-// the completed profiles. If no callback was set, the profiles are stored
-// internally and retrieved for UMA through
-// GetPendingProfiles(). GetPendingProfiles() should never be called by other
-// code; to retrieve profiles for in-process processing, set a completed
-// callback.
+// completed callback was set it is called from the profiler thread with the
+// completed profiles. A profile is considered complete if all requested samples
+// were recorded for the profile (i.e. it was not stopped prematurely). If no
+// callback was set, the completed profiles are stored internally and retrieved
+// for UMA through GetPendingProfiles().  GetPendingProfiles() should never be
+// called by other code; to retrieve profiles for in-process processing, set a
+// completed callback.
+//
+// The results of the profiling are passed to the completed callback and consist
+// of a vector of Profiles. Each Profile corresponds to a burst as specified in
+// SamplingParams and contains a set of Samples and Modules. One Sample
+// corresponds to a single recorded stack, and the Modules record those modules
+// associated with the recorded stack frames.
 class BASE_EXPORT StackSamplingProfiler {
  public:
   // Module represents the module (DLL or exe) corresponding to a stack frame.
   struct Module {
     Module();
     ~Module();
 
     // Points to the base address of the module.
     const void* base_address;
     // An opaque binary string that uniquely identifies a particular program
     // version with high probability. This is parsed from headers of the loaded
     // module.
     // For binaries generated by GNU tools:
     //   Contents of the .note.gnu.build-id field.
     // On Windows:
     //   GUID + AGE in the debug image headers of a module.
     std::string id;
     // The filename of the module.
     FilePath filename;
   };
 
   // Frame represents an individual sampled stack frame with module information.
   struct Frame {
-    Frame();
+    Frame(const void* instruction_pointer, size_t module_index);
     ~Frame();
 
     // The sampled instruction pointer within the function.
     const void* instruction_pointer;
-    // Index of the module in the array of modules. We don't represent module
-    // state directly here to save space.
-    int module_index;
+    // Index of the module in Profile::modules. We don't represent module state
+    // directly here to save space.
+    size_t module_index;
+
+    // Identifies a unknown module.
+    static const size_t kUnknownModuleIndex = static_cast<size_t>(-1);
   };
 
   // Sample represents a set of stack frames.
   using Sample = std::vector<Frame>;
 
   // Profile represents a set of samples.
   struct BASE_EXPORT Profile {
     Profile();
     ~Profile();
 
     std::vector<Module> modules;
     std::vector<Sample> samples;
     // Duration of this profile.
     TimeDelta profile_duration;
     // Time between samples.
     TimeDelta sampling_period;
     // True if sample ordering is important and should be preserved if and when
     // this profile is compressed and processed.
     bool preserve_sample_ordering;
   };
 
   // NativeStackSampler abstracts the native implementation required to record a
   // stack sample for a given thread.
   class NativeStackSampler {
    public:
     virtual ~NativeStackSampler();
 
-    // Create a stack sampler that records samples for |thread_handle|. Returns
+    // Creates a stack sampler that records samples for |thread_handle|. Returns
     // null if this platform does not support stack sampling.
     static scoped_ptr<NativeStackSampler> Create(PlatformThreadId thread_id);
 
-    // Notify the sampler that we're starting to record a new profile. This
-    // function is called on the SamplingThread.
+    // Notifies the sampler that we're starting to record a new profile. This
+    // function is called on the thread used for sampling.
     virtual void ProfileRecordingStarting(Profile* profile) = 0;
 
-    // Record a stack sample. This function is called on the SamplingThread.
+    // Records a stack sample. This function is called on the thread used for
+    // sampling.
     virtual void RecordStackSample(Sample* sample) = 0;
 
-    // Notify the sampler that we've stopped recording the current profile. This
-    // function is called on the SamplingThread.
+    // Notifies the sampler that we've stopped recording the current
+    // profile. This function is called on the thread used for sampling.
     virtual void ProfileRecordingStopped() = 0;
 
    protected:
     NativeStackSampler();
 
    private:
     DISALLOW_COPY_AND_ASSIGN(NativeStackSampler);
   };
 
   // Represents parameters that configure the sampling.
   struct BASE_EXPORT SamplingParams {
     SamplingParams();
 
     // Time to delay before first samples are taken. Defaults to 0.
     TimeDelta initial_delay;
     // Number of sampling bursts to perform. Defaults to 1.
     int bursts;
     // Interval between sampling bursts. This is the desired duration from the
     // start of one burst to the start of the next burst. Defaults to 10s.
     TimeDelta burst_interval;
     // Number of samples to record per burst. Defaults to 300.
     int samples_per_burst;
     // Interval between samples during a sampling burst. This is the desired
-    // duration from the start of one burst to the start of the next
-    // burst. Defaults to 100ms.
+    // duration from the start of one sample to the start of the next
+    // sample. Defaults to 100ms.
     TimeDelta sampling_interval;
     // True if sample ordering is important and should be preserved if and when
     // this profile is compressed and processed. Defaults to false.
     bool preserve_sample_ordering;
   };
 
+  using CompletedCallback = Callback<void(const std::vector<Profile>&)>;
+
   StackSamplingProfiler(PlatformThreadId thread_id,
                         const SamplingParams& params);
   ~StackSamplingProfiler();
 
   // Initializes the profiler and starts sampling.
   void Start();
+
   // Stops the profiler and any ongoing sampling. Calling this function is
-  // optional; if not invoked profiling will terminate when all the profiling
-  // bursts specified in the SamplingParams are completed.
+  // optional; if not invoked profiling terminates when all the profiling bursts
+  // specified in the SamplingParams are completed.
   void Stop();
 
-  // Gets the pending profiles into *|profiles| and clears the internal
-  // storage. This function is thread safe.
+  // Moves all pending profiles from internal storage to |profiles|. This
+  // function is thread safe.
   //
   // ***This is intended for use only by UMA.*** Callers who want to process the
   // collected profiles should use SetCustomCompletedCallback.
   static void GetPendingProfiles(std::vector<Profile>* profiles);
 
   // By default, collected profiles are stored internally and can be retrieved
   // by GetPendingProfiles. If a callback is provided via this function,
-  // however, it will be called with the collected profiles instead. Note that
-  // this call to the callback occurs *on the profiler thread*.
-  void SetCustomCompletedCallback(
-      Callback<void(const std::vector<Profile>&)> callback);
+  // however, it is called with the collected profiles instead. Note that the
+  // call to the callback occurs *on the profiler thread*.
+  void set_custom_completed_callback(CompletedCallback callback) {
+    custom_completed_callback_ = callback;
+  }
 
  private:
+  // SamplingThread is a separate thread used to suspend and sample stacks from
+  // the target thread.
   class SamplingThread;
   struct SamplingThreadDeleter {
     void operator() (SamplingThread* thread) const;
   };
 
   // The thread whose stack will be sampled.
   PlatformThreadId thread_id_;
 
   const SamplingParams params_;
 
   scoped_ptr<SamplingThread, SamplingThreadDeleter> sampling_thread_;
   scoped_ptr<NativeStackSampler> native_sampler_;
 
-  Callback<void(const std::vector<Profile>&)> custom_completed_callback_;
+  CompletedCallback custom_completed_callback_;
 
   DISALLOW_COPY_AND_ASSIGN(StackSamplingProfiler);
 };
 
 // Defined to allow equality check of Samples.
 BASE_EXPORT bool operator==(const StackSamplingProfiler::Frame& a,
                             const StackSamplingProfiler::Frame& b);
 // Defined to allow ordering of Samples.
 BASE_EXPORT bool operator<(const StackSamplingProfiler::Frame& a,
                            const StackSamplingProfiler::Frame& b);
 
 }  // namespace base
 
 #endif  // BASE_PROFILER_STACK_SAMPLING_PROFILER_H_
+