Add a 'unique' method to SkRefCnt, document the usage, and add support.

include/core/SkThread_platform.h

 
 /*
  * Copyright 2006 The Android Open Source Project
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 
 #ifndef SkThread_platform_DEFINED
@@ skipping 70 matching lines @@
 }
 static inline __attribute__((always_inline)) void sk_membar_aquire__after_atomic_conditional_inc() {
     //HACK: Android is actually using full memory barriers.
     //      Should this change, uncomment below.
     //int dummy;
     //android_atomic_aquire_store(0, &dummy);
 }
 
 #endif // SK_BUILD_FOR_ANDROID_FRAMEWORK
 
+int32_t sk_atomic_unprotected_read(const volatile int32_t & x) {

[bsalomon, 2013/07/15 13:04:08]

We've got several implementations of this that are all the same. Would it be
different on any platform?

[bungeman-skia, 2013/07/15 16:02:41]

Yes, we need to clean this up in general. Note that the one which would be in
Chromium is different.

+    return x;
+}
+
 #else  // !SK_BUILD_FOR_ANDROID
 
 /** Implemented by the porting layer, this function adds one to the int
     specified by the address (in a thread-safe manner), and returns the
     previous value.
     No additional memory barrier is required.
     This must act as a compiler barrier.
 */
 SK_API int32_t sk_atomic_inc(int32_t* addr);
 
@@ skipping 22 matching lines @@
     No additional memory barrier is required.
     This must act as a compiler barrier.
 */
 SK_API int32_t sk_atomic_conditional_inc(int32_t*);
 /** If sk_atomic_conditional_inc does not act as an aquire (L/SL) barrier, this
     is expected to act as an aquire (L/SL) memory barrier and as a compiler
     barrier.
 */
 SK_API void sk_membar_aquire__after_atomic_conditional_inc();
 
+/** Forces an atomic read of 'x' and marks the read as a benign race.
+    No additional memory barrier is required.
+    This does not need to act as a compiler barrier.
+*/
+SK_API int32_t sk_atomic_unprotected_read(const volatile int32_t & x);
+
 #endif // !SK_BUILD_FOR_ANDROID
 
 #ifdef SK_USE_POSIX_THREADS
 
 #include <pthread.h>
 
 // A SkBaseMutex is a POD structure that can be directly initialized
 // at declaration time with SK_DECLARE_STATIC/GLOBAL_MUTEX. This avoids the
 // generation of a static initializer in the final machine code (and
 // a corresponding static finalizer).
@@ skipping 42 matching lines @@
 
 typedef SkMutex SkBaseMutex;
 
 #define SK_DECLARE_STATIC_MUTEX(name)           static SkBaseMutex  name
 #define SK_DECLARE_GLOBAL_MUTEX(name)           SkBaseMutex  name
 
 #endif // !SK_USE_POSIX_THREADS
 
 
 #endif