Fix thread unsafe mutex initialization.

include/core/SkInstCnt.h

 /*
  * Copyright 2012 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 
 #ifndef SkInstCnt_DEFINED
 #define SkInstCnt_DEFINED
@@ skipping 55 matching lines @@
         static int32_t* GetInstanceCountPtr() {                             \
             static int32_t gInstanceCount;                                  \
             return &gInstanceCount;                                         \
         }                                                                   \
                                                                             \
         static SkTArray<int (*)(int, bool)>*& GetChildren() {               \
             static SkTArray<int (*)(int, bool)>* gChildren;                 \
             return gChildren;                                               \
         }                                                                   \
                                                                             \
+        static void create_mutex(SkMutex** mutex) {                         \
+            *mutex = SkNEW(SkMutex);                                        \
+        }                                                                   \
         static SkBaseMutex& GetChildrenMutex() {                            \
-            SK_DECLARE_STATIC_MUTEX(childrenMutex);                         \
-            return childrenMutex;                                           \
+            static SkMutex* childrenMutex = (SkMutex*)className::SkInstanceCountHelper::nil; \

[mtklein, 2014/07/25 12:35:33]

Just curious, how come static SkMutex* childrenMutex; is no good?  Or = NULL?

[bungeman-skia, 2014/07/25 14:40:40]

Because that would require an out of line definition (only static const
primitives are allowed to be defined in a class). We did a bunch of work before
to get away from the error prone two part declare and define of this instance
counting class, and I'd like to avoid it for just this. One would think to get
around this with intptr_t, but it would still have to be static const and the
compiler can ignore where it's used and use the class value directly.

+            SK_DECLARE_STATIC_ONCE(once);                                   \

[mtklein, 2014/07/25 12:35:33]

Can't we still use SK_DECLARE_STATIC_MUTEX to make the mutex a static member?

[bungeman-skia, 2014/07/25 14:40:40]

See above, it's the same situation as the pointer, requiring a top level
definition.

+            SkOnce(&once, create_mutex, &childrenMutex);                    \
+            return *childrenMutex;                                          \
         }                                                                   \
+        static const intptr_t nil = (intptr_t)NULL;                         \
                                                                             \
     } fInstanceCountHelper;                                                 \
                                                                             \
     static int32_t GetInstanceCount() {                                     \
         return *SkInstanceCountHelper::GetInstanceCountPtr();               \
     }                                                                       \
                                                                             \
     static void exitPrint() {                                               \
         CheckInstanceCount(0, true);                                        \
     }                                                                       \
@@ skipping 43 matching lines @@
 #define SK_DECLARE_INST_COUNT(className) static void AddInstChild() { INHERITED::AddInstChild(); }
 #define SK_DECLARE_INST_COUNT_ROOT(className) static void AddInstChild() { }
 #endif
 
 // Following are deprecated. They are defined only for backwards API compatibility.
 #define SK_DECLARE_INST_COUNT_TEMPLATE(className) SK_DECLARE_INST_COUNT(className)
 #define SK_DEFINE_INST_COUNT(className)
 #define SK_DEFINE_INST_COUNT_TEMPLATE(templateInfo, className)
 
 #endif // SkInstCnt_DEFINED