Add SkBarriers to ports.

include/core/SkOnce.h

 /*
  * Copyright 2013 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef SkOnce_DEFINED
 #define SkOnce_DEFINED
 
@@ skipping 53 matching lines @@
 
     int32_t thisIsPrivate;
     SkDEBUGCODE(int32_t shouldBeZero;)
 };
 
 struct SkOnceFlag {
     bool done;
     SkSpinlock lock;
 };
 
-// TODO(bungeman, mtklein): move all these *barrier* functions to SkThread when refactoring lands.

[bungeman-skia, 2014/05/29 18:02:52]

yay!!

-
-#ifdef SK_BUILD_FOR_WIN
-#  include <intrin.h>
-inline static void compiler_barrier() {
-    _ReadWriteBarrier();
-}
-#else
-inline static void compiler_barrier() {
-    asm volatile("" : : : "memory");
-}
-#endif
-
-inline static void full_barrier_on_arm() {
-#if (defined(SK_CPU_ARM) && SK_ARM_ARCH >= 7) || defined(SK_CPU_ARM64)
-    asm volatile("dmb ish" : : : "memory");
-#elif defined(SK_CPU_ARM)
-    asm volatile("mcr p15, 0, %0, c7, c10, 5" : : "r" (0) : "memory");
-#endif
-}
-
-// On every platform, we issue a compiler barrier to prevent it from reordering
-// code.  That's enough for platforms like x86 where release and acquire
-// barriers are no-ops.  On other platforms we may need to be more careful;
-// ARM, in particular, needs real code for both acquire and release.  We use a
-// full barrier, which acts as both, because that the finest precision ARM
-// provides.
-
-inline static void release_barrier() {
-    compiler_barrier();
-    full_barrier_on_arm();
-}
-
-inline static void acquire_barrier() {
-    compiler_barrier();
-    full_barrier_on_arm();
-}
-
 // Works with SkSpinlock or SkMutex.
 template <typename Lock>
 class SkAutoLockAcquire {
 public:
     explicit SkAutoLockAcquire(Lock* lock) : fLock(lock) { fLock->acquire(); }
     ~SkAutoLockAcquire() { fLock->release(); }
 private:
     Lock* fLock;
 };
 
@@ skipping 14 matching lines @@
         }
         // Also known as a store-store/load-store barrier, this makes sure that the writes
         // done before here---in particular, those done by calling f(arg)---are observable
         // before the writes after the line, *done = true.
         //
         // In version control terms this is like saying, "check in the work up
         // to and including f(arg), then check in *done=true as a subsequent change".
         //
         // We'll use this in the fast path to make sure f(arg)'s effects are
         // observable whenever we observe *done == true.
-        release_barrier();
-        *done = true;
+        sk_release_store(done, true);
     }
 }
 
 // This is our fast path, called all the time.  We do really want it to be inlined.
 template <typename Lock, typename Func, typename Arg>
 inline void SkOnce(bool* done, Lock* lock, Func f, Arg arg, void(*atExit)()) {
     if (!SK_ANNOTATE_UNPROTECTED_READ(*done)) {
         sk_once_slow(done, lock, f, arg, atExit);
     }
     // Also known as a load-load/load-store barrier, this acquire barrier makes
     // sure that anything we read from memory---in particular, memory written by
-    // calling f(arg)---is at least as current as the value we read from once->done.
+    // calling f(arg)---is at least as current as the value we read from done.
     //
     // In version control terms, this is a lot like saying "sync up to the
-    // commit where we wrote once->done = true".
+    // commit where we wrote done = true".
     //
-    // The release barrier in sk_once_slow guaranteed that once->done = true
-    // happens after f(arg), so by syncing to once->done = true here we're
+    // The release barrier in sk_once_slow guaranteed that done = true
+    // happens after f(arg), so by syncing to done = true here we're
     // forcing ourselves to also wait until the effects of f(arg) are readble.
-    acquire_barrier();
+    SkAssertResult(sk_acquire_load(done));
 }
 
 template <typename Func, typename Arg>
 inline void SkOnce(SkOnceFlag* once, Func f, Arg arg, void(*atExit)()) {
     return SkOnce(&once->done, &once->lock, f, arg, atExit);
 }
 
 #undef SK_ANNOTATE_BENIGN_RACE
 
 #endif  // SkOnce_DEFINED