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

base/profiler/native_stack_sampler_mac.cc

Index: base/profiler/native_stack_sampler_mac.cc
diff --git a/base/profiler/native_stack_sampler_mac.cc b/base/profiler/native_stack_sampler_mac.cc
index dcaaa6febcaad06b9a292d81c2c0e592fe21d591..1daa0cc8570c74a2da5bd9cfb8bfa07a2d66db69 100644
--- a/base/profiler/native_stack_sampler_mac.cc
+++ b/base/profiler/native_stack_sampler_mac.cc
@@ -323,13 +323,15 @@ class NativeStackSamplerMac : 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:
   // Suspends the thread with |thread_port_|, copies its stack and resumes the
   // thread, then records the stack frames and associated modules into |sample|.
-  void SuspendThreadAndRecordStack(StackSamplingProfiler::Sample* sample);
+  void SuspendThreadAndRecordStack(StackBuffer* stackbuffer,
+                                   StackSamplingProfiler::Sample* sample);
 
   // Weak reference: Mach port for thread being profiled.
   mach_port_t thread_port_;
@@ -341,13 +343,6 @@ class NativeStackSamplerMac : public NativeStackSampler {
   // The stack base address corresponding to |thread_handle_|.
   const void* const thread_stack_base_address_;
 
-  // The size of the |stack_copy_buffer_|.
-  const size_t stack_copy_buffer_size_;
-
-  // 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_ = nullptr;
@@ -367,9 +362,7 @@ NativeStackSamplerMac::NativeStackSamplerMac(
       annotator_(annotator),
       test_delegate_(test_delegate),
       thread_stack_base_address_(
-          pthread_get_stackaddr_np(pthread_from_mach_thread_np(thread_port))),
-      stack_copy_buffer_size_(StackCopyBufferSize()),
-      stack_copy_buffer_(new unsigned char[stack_copy_buffer_size_]) {
+          pthread_get_stackaddr_np(pthread_from_mach_thread_np(thread_port))) {
   DCHECK(annotator_);
 
   // This class suspends threads, and those threads might be suspended in dyld.
@@ -389,17 +382,19 @@ void NativeStackSamplerMac::ProfileRecordingStarting(
 }
 
 void NativeStackSamplerMac::RecordStackSample(
+    StackBuffer* stackbuffer,
     StackSamplingProfiler::Sample* sample) {
   DCHECK(current_modules_);
 
-  SuspendThreadAndRecordStack(sample);
+  SuspendThreadAndRecordStack(stackbuffer, sample);
 }
 
-void NativeStackSamplerMac::ProfileRecordingStopped() {
+void NativeStackSamplerMac::ProfileRecordingStopped(StackBuffer* stackbuffer) {
   current_modules_ = nullptr;
 }
 
 void NativeStackSamplerMac::SuspendThreadAndRecordStack(
+    StackBuffer* stackbuffer,
     StackSamplingProfiler::Sample* sample) {
   x86_thread_state64_t thread_state;
 
@@ -424,18 +419,18 @@ void NativeStackSamplerMac::SuspendThreadAndRecordStack(
       return;
     uintptr_t stack_size = stack_top - stack_bottom;
 
-    if (stack_size > stack_copy_buffer_size_)
+    if (stack_size > stackbuffer->size())
       return;
 
     (*annotator_)(sample);
 
     CopyStackAndRewritePointers(
-        reinterpret_cast<uintptr_t*>(stack_copy_buffer_.get()),
+        reinterpret_cast<uintptr_t*>(stackbuffer->buffer()),
         reinterpret_cast<uintptr_t*>(stack_bottom),
         reinterpret_cast<uintptr_t*>(stack_top), &thread_state);
 
     new_stack_top =
-        reinterpret_cast<uintptr_t>(stack_copy_buffer_.get()) + stack_size;
+        reinterpret_cast<uintptr_t>(stackbuffer->buffer()) + stack_size;
   }  // ScopedSuspendThread
 
   if (test_delegate_)
@@ -468,4 +463,9 @@ std::unique_ptr<NativeStackSampler> NativeStackSampler::Create(
                                                  test_delegate);
 }
 
+std::unique_ptr<NativeStackSampler::StackBuffer>
+NativeStackSampler::CreateStackBuffer() {
+  return MakeUnique<StackBuffer>(StackCopyBufferSize());
+}
+
 }  // namespace base