1 files changed, 66 insertions, 3 deletions

diff --git a/tools/memory_watcher/call_stack.h b/tools/memory_watcher/call_stack.h
index 5af7ed6..2c026bc 100644
--- a/tools/memory_watcher/call_stack.h
+++ b/tools/memory_watcher/call_stack.h
@@ -51,8 +51,14 @@ class CallStack {
   // every frame in each is identical to the corresponding frame in the other.
   bool IsEqual(const CallStack &target);
 
+  typedef std::basic_string<char, std::char_traits<char>,
+                            PrivateHookAllocator<char> > PrivateAllocatorString;
+
   // Convert the callstack to a string stored in output.
-  void CallStack::ToString(std::string* output);
+  void CallStack::ToString(PrivateAllocatorString* output);
+
+  //
+  bool Valid() const { return valid_; }
 
  private:
   // The maximum number of frames to trace.
@@ -68,14 +74,67 @@ class CallStack {
   // Functions for manipulating the frame list.
   void ClearFrames();
 
+  // Dynamically load the DbgHelp library and supporting routines that we
+  // will use.
+  static bool LoadDbgHelp();
+
+  static void LockDbgHelp() {
+    dbghelp_lock_.Acquire();
+    active_thread_id_ = GetCurrentThreadId();
+  }
+
+  static void UnlockDbgHelp() {
+    active_thread_id_ = GetCurrentThreadId();
+    dbghelp_lock_.Release();
+  }
+
+  class AutoDbgHelpLock {
+  public:
+    AutoDbgHelpLock() {
+      CallStack::LockDbgHelp();
+    }
+    ~AutoDbgHelpLock() {
+      CallStack::UnlockDbgHelp();
+    }
+  };
+
+  // Check to see if this thread is already processing a stack.
+  bool LockedRecursionDetected() const;
+
+  // According to http://msdn2.microsoft.com/en-us/library/ms680650(VS.85).aspx
+  // "All DbgHelp functions, such as this one, are single threaded.  Therefore,
+  // calls from more than one thread to this function will likely result in
+  // unexpected behavior or memory corruption.  To avoid this, you must
+  // synchromize all concurrent calls from one thread to this function."
+  //
+  // dbghelp_lock_ is used to serialize access across all calls to the DbgHelp
+  // library.  This may be overly conservative (serializing them all together),
+  // but does guarantee correctness.
+  static Lock dbghelp_lock_;
+
+  // Record the fact that dbghelp has been loaded.
+  // Changes to this variable are protected by dbghelp_lock_.
+  // It will only changes once... from false to true.
+  static bool dbghelp_loaded_;
+
+  // To prevent infinite recursion due to unexpected side effects in libraries,
+  // we track the thread_id of the thread currently holding the dbghelp_lock_.
+  // We avoid re-aquiring said lock and return an !valid_ instance when we
+  // detect recursion.
+  static DWORD active_thread_id_;
+
   int frame_count_;  // Current size (in frames)
   DWORD_PTR frames_[kMaxTraceFrames];
   int32 hash_;
   int32 id_;
 
+  // Indicate is this is a valid stack.
+  // This is false if recursion precluded a real stack generation.
+  bool valid_;
+
   // Cache ProgramCounter -> Symbol lookups.
   // This cache is not thread safe.
-  typedef std::map<int32, std::string, std::less<int32>,
+  typedef std::map<int32, PrivateAllocatorString, std::less<int32>,
                    PrivateHookAllocator<int32> > SymbolCache;
   static SymbolCache* symbol_cache_;
 
@@ -88,14 +147,18 @@ class CallStack {
 // free instances.
 class AllocationStack : public CallStack {
  public:
-  AllocationStack() : next_(NULL), CallStack() {}
+  explicit AllocationStack(int32 size)
+      : next_(NULL), size_(size), CallStack() {}
 
   // We maintain a freelist of the AllocationStacks.
   void* operator new(size_t s);
   void operator delete(void*p);
 
+  int32 size() const { return size_; }
+
  private:
   AllocationStack* next_;     // Pointer used when on the freelist.
+  int32 size_;                // Size of block allocated.
   static AllocationStack* freelist_;
   static Lock freelist_lock_;