Stack sampling profiler: handle unloaded and unloading modules

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 "base/base_export.h"
 #include "base/memory/scoped_ptr.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:
   virtual ~NativeStackSampler();
 
   // 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);
+  static scoped_ptr<NativeStackSampler> Create(
+      PlatformThreadId thread_id,
+      NativeStackSamplerTestDelegate* test_delegate);
 
   // The following functions are all called on the SamplingThread (not the
   // thread being sampled).
 
   // 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(
       std::vector<StackSamplingProfiler::Module>* modules) = 0;
 
   // Records a stack sample to |sample|.
   virtual void RecordStackSample(StackSamplingProfiler::Sample* sample) = 0;
 
   // Notifies the sampler that we've stopped recording the current
   // profile.
   virtual void ProfileRecordingStopped() = 0;
 
  protected:
   NativeStackSampler();
 
  private:
   DISALLOW_COPY_AND_ASSIGN(NativeStackSampler);
 };
 
+// NativeStackSamplerTestDelegate provides seams for test code to execute during

[brucedawson, 2015/10/30 00:15:59]

I'm not sure what you mean by 'seams' here, although the later comment makes the
purpose of this class clear. It this a technical use of 'seams' that I just
haven't encountered yet?

[Mike Wittman, 2015/10/30 17:08:06]

Yes, I believe it's originally from _Working Effectively with Legacy Code_. A
seam a place where the behavior of code can be altered without altering the code
itself, usually for unit testing testing purposes.

http://www.informit.com/articles/article.aspx?p=359417&seqNum=2

+// 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_