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..e7d83a1b909618de56e661ef7a71195d2cc41dba 100644
--- a/base/profiler/native_stack_sampler_win.cc
+++ b/base/profiler/native_stack_sampler_win.cc
@@ -15,13 +15,16 @@
 #include <utility>
 #include <vector>
 
+#include "base/atomicops.h"

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

No longer needed.

[bcwhite, 2017/02/07 15:16:36]

Done.

 #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"
 #include "base/strings/utf_string_conversions.h"
+#include "base/synchronization/lock.h"

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

No longer needed.

[bcwhite, 2017/02/07 15:16:36]

Done.

 #include "base/time/time.h"
 #include "base/win/pe_image.h"
 #include "base/win/scoped_handle.h"
@@ -392,10 +395,13 @@ class NativeStackSamplerWin : public NativeStackSampler {
   ~NativeStackSamplerWin() override;
 
   // StackSamplingProfiler::NativeStackSampler:
+  std::unique_ptr<Common> CreateCommon() override;
   void ProfileRecordingStarting(
+      Common* common,
       std::vector<StackSamplingProfiler::Module>* modules) override;
-  void RecordStackSample(StackSamplingProfiler::Sample* sample) override;
-  void ProfileRecordingStopped() override;
+  void RecordStackSample(Common* common,
+                         StackSamplingProfiler::Sample* sample) override;
+  void ProfileRecordingStopped(Common* common) override;
 
  private:
   enum {
@@ -407,6 +413,15 @@ class NativeStackSamplerWin : public NativeStackSampler {
     kStackCopyBufferSize = 2 * 1024 * 1024
   };
 
+  class WinCommon : public Common {

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

WinCommon => CommonWin (or actually StackBufferWin per previous comment)

Convention in Chrome is to use the platform specific name as suffix.

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

Done.

+   public:
+    WinCommon() {}
+    ~WinCommon() override {}
+
+    // Buffer to use for copies of the stack.
+    unsigned char stack_copy_buffer_[kStackCopyBufferSize];
+  };
+
   // 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 +448,6 @@ 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_;
@@ -445,6 +456,11 @@ class NativeStackSamplerWin : public NativeStackSampler {
   // current_modules_.
   std::map<HMODULE, size_t> profile_module_index_;
 
+  // This "in use" flag is used to validate the assumption that there are no
+  // concurrent stack sampling requests regardless of how many instances of
+  // this class are currently active.
+  static subtle::AtomicWord stack_copy_buffer_in_use_;

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

No longer needed.

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

Done.

+
   DISALLOW_COPY_AND_ASSIGN(NativeStackSamplerWin);
 };
 
@@ -456,35 +472,40 @@ 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_);
 }
 
 NativeStackSamplerWin::~NativeStackSamplerWin() {
 }
 
+std::unique_ptr<NativeStackSampler::Common>
+NativeStackSamplerWin::CreateCommon() {
+  return MakeUnique<WinCommon>();
+}
+
 void NativeStackSamplerWin::ProfileRecordingStarting(
+    Common* common,
     std::vector<StackSamplingProfiler::Module>* modules) {
   current_modules_ = modules;
   profile_module_index_.clear();
 }
 
 void NativeStackSamplerWin::RecordStackSample(
+    Common* common,
     StackSamplingProfiler::Sample* sample) {
+  DCHECK(common);
   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_,
+      reinterpret_cast<WinCommon*>(common)->stack_copy_buffer_,

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

static_cast for downcast

[bcwhite, 2017/02/07 15:16:36]

Done.

+      kStackCopyBufferSize, &stack, annotator_, sample, test_delegate_);
   CopyToSample(stack, sample, current_modules_);
 }
 
-void NativeStackSamplerWin::ProfileRecordingStopped() {
+void NativeStackSamplerWin::ProfileRecordingStopped(Common* common) {
   current_modules_ = nullptr;
 }