[Mac] Capture -dealloc backtrace to log with CrZombie messages.

base/debug/stack_trace.h

 // Copyright (c) 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef BASE_DEBUG_STACK_TRACE_H_
 #define BASE_DEBUG_STACK_TRACE_H_
 #pragma once
 
 #include <iosfwd>
 
 #include "base/base_export.h"
 #include "build/build_config.h"
 
 #if defined(OS_WIN)
 struct _EXCEPTION_POINTERS;
 #endif
 
 namespace base {
 namespace debug {
 
 // A stacktrace can be helpful in debugging. For example, you can include a
 // stacktrace member in a object (probably around #ifndef NDEBUG) so that you
 // can later see where the given object was created from.
 class BASE_EXPORT StackTrace {
  public:
   // Creates a stacktrace from the current location.
   StackTrace();
 
+  // Creates a stacktrace from an existing buffer gotten elsewhere.
+  // Useful for sharing PrintBacktrace().
+  StackTrace(const void* const* trace, int count);

[Mark Mentovai, 2011/08/27 00:29:02]

Since this is part of the public interface now, you kind of need to say what the
trace argument is all about. I can see from the implementation file that it’s
dumped right into trace_, but that doesn’t really help someone who doesn’t know
any better because the contents of trace_ isn’t defined below other than to say
that it’s an array of up to kMaxTraces pointers.

[Scott Hess - ex-Googler, 2011/08/27 05:15:40]

OK, I'll document it as accepting an array of instruction pointers such as
returned by Addresses().

Given that, would it make sense to have the zombie code generate an instance and
store results from Addresses(), or to continue using backtrace() directly?  I'm
a bit paranoid about overhead, but I find that a hard decision (it's called a
lot, arguing for low overhead, and this class of code is hardly abstract in the
first place).

+
 #if defined(OS_WIN)
   // Creates a stacktrace for an exception.
   // Note: this function will throw an import not found (StackWalk64) exception
   // on system without dbghelp 5.1.
   StackTrace(_EXCEPTION_POINTERS* exception_pointers);
 #endif
 
   // Copying and assignment are allowed with the default functions.
 
   ~StackTrace();
@@ skipping 16 matching lines @@
   static const int kMaxTraces = 62;
 
   void* trace_[kMaxTraces];
   int count_;
 };
 
 }  // namespace debug
 }  // namespace base
 
 #endif  // BASE_DEBUG_STACK_TRACE_H_