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

base/profiler/native_stack_sampler_win.cc

Index: base/profiler/native_stack_sampler_win.cc
diff --git a/base/profiler/native_stack_sampler_win.cc b/base/profiler/native_stack_sampler_win.cc
index e1605109fe960d769523733b2a1190700b250d28..47c14f41470110efea91e5dfb20b9167715da1d2 100644
--- a/base/profiler/native_stack_sampler_win.cc
+++ b/base/profiler/native_stack_sampler_win.cc
@@ -18,6 +18,7 @@
 #include "base/lazy_instance.h"
 #include "base/logging.h"
 #include "base/macros.h"
+#include "base/memory/ptr_util.h"
 #include "base/profiler/win32_stack_frame_unwinder.h"
 #include "base/strings/string_util.h"
 #include "base/strings/stringprintf.h"
@@ -386,6 +387,24 @@ void SuspendThreadAndRecordStack(
 
 class NativeStackSamplerWin : public NativeStackSampler {
  public:
+  enum {
+    // Intended to hold the largest stack used by Chrome. The default Win32
+    // reserved stack size is 1 MB and Chrome Windows threads currently always
+    // use the default, but this allows for expansion if it occurs. The size
+    // beyond the actual stack size consists of unallocated virtual memory pages
+    // so carries little cost (just a bit of wasted address space).
+    kStackCopyBufferSize = 2 * 1024 * 1024
+  };
+
+  class StackBufferWin : public StackBuffer {
+   public:
+    StackBufferWin() {}
+    ~StackBufferWin() override {}
+
+    // Buffer to use for copies of the stack.
+    unsigned char stack_copy_buffer_[kStackCopyBufferSize];
+  };
+
   NativeStackSamplerWin(win::ScopedHandle thread_handle,
                         AnnotateCallback annotator,
                         NativeStackSamplerTestDelegate* test_delegate);
@@ -394,19 +413,11 @@ class NativeStackSamplerWin : public NativeStackSampler {
   // StackSamplingProfiler::NativeStackSampler:
   void ProfileRecordingStarting(
       std::vector<StackSamplingProfiler::Module>* modules) override;
-  void RecordStackSample(StackSamplingProfiler::Sample* sample) override;
-  void ProfileRecordingStopped() override;
+  void RecordStackSample(StackBuffer* stackbuffer,
+                         StackSamplingProfiler::Sample* sample) override;
+  void ProfileRecordingStopped(StackBuffer* stackbuffer) override;
 
  private:
-  enum {
-    // Intended to hold the largest stack used by Chrome. The default Win32
-    // reserved stack size is 1 MB and Chrome Windows threads currently always
-    // use the default, but this allows for expansion if it occurs. The size
-    // beyond the actual stack size consists of unallocated virtual memory pages
-    // so carries little cost (just a bit of wasted address space).
-    kStackCopyBufferSize = 2 * 1024 * 1024
-  };
-
   // Attempts to query the module filename, base address, and id for
   // |module_handle|, and store them in |module|. Returns true if it succeeded.
   static bool GetModuleForHandle(HMODULE module_handle,
@@ -433,10 +444,6 @@ class NativeStackSamplerWin : public NativeStackSampler {
   // The stack base address corresponding to |thread_handle_|.
   const void* const thread_stack_base_address_;
 
-  // Buffer to use for copies of the stack. We use the same buffer for all the
-  // samples to avoid the overhead of multiple allocations and frees.
-  const std::unique_ptr<unsigned char[]> stack_copy_buffer_;
-
   // Weak. Points to the modules associated with the profile being recorded
   // between ProfileRecordingStarting() and ProfileRecordingStopped().
   std::vector<StackSamplingProfiler::Module>* current_modules_;
@@ -456,8 +463,7 @@ NativeStackSamplerWin::NativeStackSamplerWin(
       annotator_(annotator),
       test_delegate_(test_delegate),
       thread_stack_base_address_(
-          GetThreadEnvironmentBlock(thread_handle_.Get())->Tib.StackBase),
-      stack_copy_buffer_(new unsigned char[kStackCopyBufferSize]) {
+          GetThreadEnvironmentBlock(thread_handle_.Get())->Tib.StackBase) {
   DCHECK(annotator_);
 }
 
@@ -471,20 +477,20 @@ void NativeStackSamplerWin::ProfileRecordingStarting(
 }
 
 void NativeStackSamplerWin::RecordStackSample(
+    StackBuffer* stackbuffer,
     StackSamplingProfiler::Sample* sample) {
+  DCHECK(stackbuffer);
   DCHECK(current_modules_);
 
-  if (!stack_copy_buffer_)
-    return;
-
   std::vector<RecordedFrame> stack;
-  SuspendThreadAndRecordStack(thread_handle_.Get(), thread_stack_base_address_,
-                              stack_copy_buffer_.get(), kStackCopyBufferSize,
-                              &stack, annotator_, sample, test_delegate_);
+  SuspendThreadAndRecordStack(
+      thread_handle_.Get(), thread_stack_base_address_,
+      static_cast<StackBufferWin*>(stackbuffer)->stack_copy_buffer_,
+      kStackCopyBufferSize, &stack, annotator_, sample, test_delegate_);
   CopyToSample(stack, sample, current_modules_);
 }
 
-void NativeStackSamplerWin::ProfileRecordingStopped() {
+void NativeStackSamplerWin::ProfileRecordingStopped(StackBuffer* stackbuffer) {
   current_modules_ = nullptr;
 }
 
@@ -563,4 +569,9 @@ std::unique_ptr<NativeStackSampler> NativeStackSampler::Create(
   return std::unique_ptr<NativeStackSampler>();
 }
 
+std::unique_ptr<NativeStackSampler::StackBuffer>
+NativeStackSampler::CreateStackBuffer() {
+  return MakeUnique<NativeStackSamplerWin::StackBufferWin>();
+}
+
 }  // namespace base