Tag all tracked objects, including Tasks, with the program counter at the site of FROM_HERE.

base/tracked.h

Index: base/tracked.h
===================================================================
--- base/tracked.h	(revision 85540)
+++ base/tracked.h	(working copy)
@@ -41,7 +41,10 @@
   // Constructor should be called with a long-lived char*, such as __FILE__.
   // It assumes the provided value will persist as a global constant, and it
   // will not make a copy of it.
-  Location(const char* function_name, const char* file_name, int line_number);
+  Location(const char* function_name,
+           const char* file_name,
+           int line_number,
+           void* program_counter);
 
   // Provide a default constructor for easy of debugging.
   Location();
@@ -63,6 +66,7 @@
   const char* function_name() const { return function_name_; }
   const char* file_name()     const { return file_name_; }
   int line_number()           const { return line_number_; }
+  void* program_counter()     const { return program_counter_; }
 
   void Write(bool display_filename, bool display_function_name,
              std::string* output) const;
@@ -74,13 +78,19 @@
   const char* const function_name_;
   const char* const file_name_;
   const int line_number_;
+  void* program_counter_;

[awong, 2011/05/17 23:54:01]

This does fundamentally change the nature of this object.  If you look at the
rest of the definition of Location, it's written such that it is effectively a
constant.

I recall jar@ saying that this was done carefully to allow the compiler to
possibly even elide instances since the "class" is effectively a constant.

Adding in program_counter() breaks that performance characteristic.  This
functionality seems like a worthwhile inclusion, but we are changing some of the
fundamental semantics of tracked objects.

[cpu_(ooo_6.6-7.5), 2011/05/18 00:52:26]

But what if the program counter is const void* ?

On 2011/05/17 23:54:01, awong wrote:

[awong, 2011/05/18 01:02:45]

I don't think that const really matters too much (we should add it anyways
though).

The difference is that __FUNCTION__, __FILE__, and __LINE__ are all constants
that can be resolved in at compile time.

GetProgramCounterRegister() is specifically not such a thing.

I'm not saying there's necessarily a problem here...but I just remember jar@
noting that the Location was carefully crafted to be compile time resolvable.



On 2011/05/18 00:52:26, cpu wrote:

[apatrick_chromium, 2011/05/18 21:09:47]

I made it "const void* const" for consistency. I don't think it will help the
compiler though.

[apatrick_chromium, 2011/05/18 21:09:47]

I agree the result of GetProgramCounterRegister() is not compile time
resolvable. I examined the code generated for an optimized windows build prior
to this change (no global optimization) and the compiler was not doing anything
special for FROM_HERE:

5C50BD18  push        293h 
5C50BD1D  push        offset string ".\\browser\\safe_browsing\\safe_bro"...
(5D25874Ch) 
5C50BD22  push        offset string "SafeBrowsingService::MakeDatabas"...
(5D258C2Ch) 
5C50BD27  lea         ecx,[esp+2Ch] 
5C50BD2B  call        dword ptr [__imp_tracked_objects::Location::Location
(5D1B4C98h)] 

This change adds the overhead for invoking GetProgramCounterRegister() and
pushing it as an argument for the Location constructor.

I didn't figure out how to do an LTCG build.

 };
 
+BASE_API void* GetProgramCounterRegister();
 
 //------------------------------------------------------------------------------
 // Define a macro to record the current source location.
 
-#define FROM_HERE tracked_objects::Location(__FUNCTION__, __FILE__, __LINE__)
+#define FROM_HERE tracked_objects::Location(                                   \
+    __FUNCTION__,                                                              \
+    __FILE__,                                                                  \
+    __LINE__,                                                                  \
+    tracked_objects::GetProgramCounterRegister())                              \
 
 
 //------------------------------------------------------------------------------
@@ -110,6 +120,8 @@
   base::TimeTicks tracked_birth_time() const { return base::TimeTicks::Now(); }
 #endif  // defined(TRACK_ALL_TASK_OBJECTS)
 
+  void* get_birth_program_counter() const { return birth_program_counter_; }
+
  private:
 #if defined(TRACK_ALL_TASK_OBJECTS)
 
@@ -123,6 +135,8 @@
 
 #endif  // defined(TRACK_ALL_TASK_OBJECTS)
 
+  void* birth_program_counter_;
+
   DISALLOW_COPY_AND_ASSIGN(Tracked);
 };