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..d78a93d9369f37730fe379bc8e59071b14d0c998 100644
--- a/base/profiler/native_stack_sampler.h
+++ b/base/profiler/native_stack_sampler.h
@@ -21,6 +21,26 @@ class NativeStackSamplerTestDelegate;
 // given thread.
 class NativeStackSampler {
  public:
+  // This class contains data structures that can be shared across multiple

[Mike Wittman, 2017/05/11 21:07:02]

nit: data structures => a buffer for stack copies

"data structures" is a more opaque descriptor than necessary.

[bcwhite, 2017/05/12 13:11:30]

Done.

+  // instances of NativeStackSampler.
+  class StackBuffer {
+   public:
+    StackBuffer(size_t buffer_size);
+    ~StackBuffer();
+
+    void* buffer() const { return buffer_.get(); }
+    size_t size() const { return size_; }
+
+   private:
+    // The word-aligned buffer.
+    const std::unique_ptr<uintptr_t[]> buffer_;
+
+    // The size of the buffer.
+    const size_t size_;
+
+    DISALLOW_COPY_AND_ASSIGN(StackBuffer);
+  };
+
   // 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
@@ -39,6 +59,13 @@ class NativeStackSampler {
       AnnotateCallback annotator,
       NativeStackSamplerTestDelegate* test_delegate);
 
+  // Gets the required size of the stack buffer.
+  static size_t GetStackBufferSize();
+
+  // Creates an instance of the a stack buffer that can be used for calls to
+  // any NativeStackSampler object.
+  static std::unique_ptr<StackBuffer> CreateStackBuffer();
+
   // The following functions are all called on the SamplingThread (not the
   // thread being sampled).
 
@@ -48,11 +75,12 @@ class NativeStackSampler {
       std::vector<StackSamplingProfiler::Module>* modules) = 0;
 
   // Records a stack sample to |sample|.
-  virtual void RecordStackSample(StackSamplingProfiler::Sample* sample) = 0;
+  virtual void RecordStackSample(StackBuffer* stackbuffer,
+                                 StackSamplingProfiler::Sample* sample) = 0;
 
   // Notifies the sampler that we've stopped recording the current
   // profile.
-  virtual void ProfileRecordingStopped() = 0;
+  virtual void ProfileRecordingStopped(StackBuffer* stackbuffer) = 0;
 
  protected:
   NativeStackSampler();