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

base/profiler/native_stack_sampler.h

Index: base/profiler/native_stack_sampler.h
diff --git a/base/profiler/native_stack_sampler.h b/base/profiler/native_stack_sampler.h
index 8d7e441b69306b072ed67321a531ac76aee4e28c..b5b07b148e6c88b2d1fafa405a3a8f6810ace697 100644
--- a/base/profiler/native_stack_sampler.h
+++ b/base/profiler/native_stack_sampler.h
@@ -21,6 +21,18 @@ class NativeStackSamplerTestDelegate;
 // 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
@@ -42,17 +54,22 @@ class NativeStackSampler {
   // 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();