Use a common buffer across all instances for stack-copy.

base/profiler/native_stack_sampler.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_NATIVE_STACK_SAMPLER_H_
 #define BASE_PROFILER_NATIVE_STACK_SAMPLER_H_
 
 #include <memory>
 
 #include "base/base_export.h"
 #include "base/macros.h"
 #include "base/profiler/stack_sampling_profiler.h"
 #include "base/threading/platform_thread.h"
 
 namespace base {
 
 class NativeStackSamplerTestDelegate;
 
 // NativeStackSampler is an implementation detail of StackSamplingProfiler. It
 // abstracts the native implementation required to record a stack sample for a
 // given thread.
 class NativeStackSampler {
  public:
+  // This class contains data structures that can be shared across multiple
+  // instances of NativeStackSampler so long as they do not run concurrently.
+  // This supports having a single instance of large structures such as copy
+  // buffers.
+  class Common {

[Mike Wittman, 2017/01/24 17:20:56]

We should just call this StackBuffer. If the concept needs to be generalized in
the future the name can be updated then.

[bcwhite, 2017/02/07 15:16:35]

Done.

+   public:
+    virtual ~Common() {}
+
+   protected:
+    Common() {}
+  };

[Mike Wittman, 2017/01/24 17:20:56]

DISALLOW_COPY_AND_ASSIGN

[bcwhite, 2017/02/07 15:16:35]

Done.

+
   // The callback type used to add annotations to a sample during collection.
   // This is passed to the native sampler to be applied at the most appropriate
   // time. It is a simple function-pointer because the generated code must be
   // completely predictable and do nothing that could acquire a mutex; a
   // Callback object is code outside the control of this object and could,
   // for example, acquire a mutex as part of allocating memory for a LOG
   // message.
   using AnnotateCallback = void (*)(StackSamplingProfiler::Sample*);
 
   virtual ~NativeStackSampler();
 
   // Creates a stack sampler that records samples for |thread_handle|. Returns
   // null if this platform does not support stack sampling.
   static std::unique_ptr<NativeStackSampler> Create(
       PlatformThreadId thread_id,
       AnnotateCallback annotator,
       NativeStackSamplerTestDelegate* test_delegate);
 
   // The following functions are all called on the SamplingThread (not the
   // thread being sampled).
 
+  // Creates an instance of "common" data buffers.
+  virtual std::unique_ptr<Common> CreateCommon();

[Mike Wittman, 2017/01/24 17:20:56]

This function doesn't depend on the instance so should be static.

[bcwhite, 2017/02/07 15:16:35]

Done.

+
   // Notifies the sampler that we're starting to record a new profile. Modules
   // shared across samples in the profile should be recorded in |modules|.
   virtual void ProfileRecordingStarting(
+      Common* common,

[Mike Wittman, 2017/01/24 17:20:57]

No need to pass this to ProfileRecordingStarting or ProfileRecordingStopped. If
someone wants this at some later point it can be added then.

[bcwhite, 2017/02/07 15:16:35]

Done.

       std::vector<StackSamplingProfiler::Module>* modules) = 0;
 
   // Records a stack sample to |sample|.
-  virtual void RecordStackSample(StackSamplingProfiler::Sample* sample) = 0;
+  virtual void RecordStackSample(Common* common,

[Mike Wittman, 2017/01/24 17:20:57]

Doesn't the calling code need to be updated?

[bcwhite, 2017/02/07 15:16:35]

Yes but since the calling code is in the middle of a rewrite to support
multi-sampling, I'm waiting to do that until after that CL lands.

+                                 StackSamplingProfiler::Sample* sample) = 0;
 
   // Notifies the sampler that we've stopped recording the current
   // profile.
-  virtual void ProfileRecordingStopped() = 0;
+  virtual void ProfileRecordingStopped(Common* common) = 0;
 
  protected:
   NativeStackSampler();
 
  private:
   DISALLOW_COPY_AND_ASSIGN(NativeStackSampler);
 };
 
 // NativeStackSamplerTestDelegate provides seams for test code to execute during
 // stack collection.
 class BASE_EXPORT NativeStackSamplerTestDelegate {
  public:
   virtual ~NativeStackSamplerTestDelegate();
 
   // Called after copying the stack and resuming the target thread, but prior to
   // walking the stack. Invoked on the SamplingThread.
   virtual void OnPreStackWalk() = 0;
 
  protected:
   NativeStackSamplerTestDelegate();
 
  private:
   DISALLOW_COPY_AND_ASSIGN(NativeStackSamplerTestDelegate);
 };
 
 }  // namespace base
 
 #endif  // BASE_PROFILER_NATIVE_STACK_SAMPLER_H_