Reverting r12635 (Make leak counters thread-safe - https://codereview.chromium.org/99483003) due to compile errors on Mac 10.6 & in Chrome



git-svn-id: http://skia.googlecode.com/svn/trunk/src@12637 2bbb7eff-a529-9590-31e7-b0007b416f81
diff --git a/core/SkOnce.h b/core/SkOnce.h
new file mode 100644
index 0000000..89de112
--- /dev/null
+++ b/core/SkOnce.h
@@ -0,0 +1,155 @@
+/*
+ * 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
+
+// SkOnce.h defines SK_DECLARE_STATIC_ONCE and SkOnce(), which you can use
+// together to create a threadsafe way to call a function just once.  This
+// is particularly useful for lazy singleton initialization. E.g.
+//
+// static void set_up_my_singleton(Singleton** singleton) {
+//     *singleton = new Singleton(...);
+// }
+// ...
+// const Singleton& GetSingleton() {
+//     static Singleton* singleton = NULL;
+//     SK_DECLARE_STATIC_ONCE(once);
+//     SkOnce(&once, set_up_my_singleton, &singleton);
+//     SkASSERT(NULL != singleton);
+//     return *singleton;
+// }
+//
+// OnceTest.cpp also should serve as a few other simple examples.
+
+#include "SkThread.h"
+#include "SkTypes.h"
+
+#ifdef SK_USE_POSIX_THREADS
+#  define SK_ONCE_INIT { false, { PTHREAD_MUTEX_INITIALIZER } }
+#else
+#  define SK_ONCE_INIT { false, SkBaseMutex() }
+#endif
+
+#define SK_DECLARE_STATIC_ONCE(name) static SkOnceFlag name = SK_ONCE_INIT
+
+struct SkOnceFlag;  // If manually created, initialize with SkOnceFlag once = SK_ONCE_INIT
+
+template <typename Func, typename Arg>
+inline void SkOnce(SkOnceFlag* once, Func f, Arg arg);
+
+//  ----------------------  Implementation details below here. -----------------------------
+
+struct SkOnceFlag {
+    bool done;
+    SkBaseMutex mutex;
+};
+
+// TODO(bungeman, mtklein): move all these *barrier* functions to SkThread when refactoring lands.
+
+#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() {
+#ifdef SK_CPU_ARM
+#if SK_ARM_ARCH >= 7
+    asm volatile("dmb" : : : "memory");
+#else
+    asm volatile("mcr p15, 0, %0, c7, c10, 5" : : "r" (0) : "memory");
+#endif
+#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();
+}
+
+// We've pulled a pretty standard double-checked locking implementation apart
+// into its main fast path and a slow path that's called when we suspect the
+// one-time code hasn't run yet.
+
+// This is the guts of the code, called when we suspect the one-time code hasn't been run yet.
+// This should be rarely called, so we separate it from SkOnce and don't mark it as inline.
+// (We don't mind if this is an actual function call, but odds are it'll be inlined anyway.)
+template <typename Func, typename Arg>
+static void sk_once_slow(SkOnceFlag* once, Func f, Arg arg) {
+    const SkAutoMutexAcquire lock(once->mutex);
+    if (!once->done) {
+        f(arg);
+        // 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();
+        once->done = true;
+    }
+}
+
+// We nabbed this code from the dynamic_annotations library, and in their honor
+// we check the same define.  If you find yourself wanting more than just
+// ANNOTATE_BENIGN_RACE, it might make sense to pull that in as a dependency
+// rather than continue to reproduce it here.
+
+#if DYNAMIC_ANNOTATIONS_ENABLED
+// TSAN provides this hook to supress a known-safe apparent race.
+extern "C" {
+void AnnotateBenignRace(const char* file, int line, const volatile void* mem, const char* desc);
+}
+#define ANNOTATE_BENIGN_RACE(mem, desc) AnnotateBenignRace(__FILE__, __LINE__, mem, desc)
+#else
+#define ANNOTATE_BENIGN_RACE(mem, desc)
+#endif
+
+// This is our fast path, called all the time.  We do really want it to be inlined.
+template <typename Func, typename Arg>
+inline void SkOnce(SkOnceFlag* once, Func f, Arg arg) {
+    ANNOTATE_BENIGN_RACE(&(once->done), "Don't worry TSAN, we're sure this is safe.");
+    if (!once->done) {
+        sk_once_slow(once, f, arg);
+    }
+    // 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.
+    //
+    // In version control terms, this is a lot like saying "sync up to the
+    // commit where we wrote once->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
+    // forcing ourselves to also wait until the effects of f(arg) are readble.
+    acquire_barrier();
+}
+
+#undef ANNOTATE_BENIGN_RACE
+
+#endif  // SkOnce_DEFINED