Port uses of SkLazyPtr to SkOncePtr.

include/core/SkLazyPtr.h

-/*
- * Copyright 2014 Google Inc.
- *
- * Use of this source code is governed by a BSD-style license that can be
- * found in the LICENSE file.
- */
-
-#ifndef SkLazyPtr_DEFINED
-#define SkLazyPtr_DEFINED
-
-/** Declare a lazily-chosen static pointer (or array of pointers) of type T.
- *
- *  Example usage:
- *
- *  Foo* GetSingletonFoo() {
- *      SK_DECLARE_STATIC_LAZY_PTR(Foo, singleton);  // Created with new, destroyed with delete.
- *      return singleton.get();
- *  }
- *
- *  These macros take an optional T* (*Create)() and void (*Destroy)(T*) at the end.
- *  If not given, we'll use new and delete.
- *  These options are most useful when T doesn't have a public constructor or destructor.
- *  Create comes first, so you may use a custom Create with a default Destroy, but not vice versa.
- *
- *  Foo* CustomCreate() { return ...; }
- *  void CustomDestroy(Foo* ptr) { ... }
- *  Foo* GetSingletonFooWithCustomCleanup() {
- *      SK_DECLARE_STATIC_LAZY_PTR(Foo, singleton, CustomCreate, CustomDestroy);
- *      return singleton.get();
- *  }
- *
- *  If you have a bunch of related static pointers of the same type, you can
- *  declare an array of lazy pointers together, and we'll pass the index to Create().
- *
- *  Foo* CreateFoo(int i) { return ...; }
- *  Foo* GetCachedFoo(Foo::Enum enumVal) {
- *      SK_DECLARE_STATIC_LAZY_PTR_ARRAY(Foo, Foo::kEnumCount, cachedFoos, CreateFoo);
- *      return cachedFoos[enumVal];
- *  }
- *
- *
- *  You can think of SK_DECLARE_STATIC_LAZY_PTR as a cheaper specialization of
- *  SkOnce.  There is no mutex or extra storage used past the pointer itself.
- *
- *  We may call Create more than once, but all threads will see the same pointer
- *  returned from get().  Any extra calls to Create will be cleaned up.
- *
- *  These macros must be used in a global scope, not in function scope or as a class member.
- */
-
-#define SK_DECLARE_STATIC_LAZY_PTR(T, name, ...) \
-    namespace {} static Private::SkStaticLazyPtr<T, ##__VA_ARGS__> name
-
-#define SK_DECLARE_STATIC_LAZY_PTR_ARRAY(T, name, N, ...) \
-    namespace {} static Private::SkStaticLazyPtrArray<T, N, ##__VA_ARGS__> name
-
-// namespace {} forces these macros to only be legal in global scopes.  Chrome has thread-safety
-// problems with them in function-local statics because it uses -fno-threadsafe-statics, and even
-// in builds with threadsafe statics, those threadsafe statics are just unnecessary overhead.
-
-// Everything below here is private implementation details.  Don't touch, don't even look.
-
-#include "SkAtomics.h"
-
-// See FIXME below.
-class SkFontConfigInterfaceDirect;
-
-namespace Private {
-
-// Set *dst to ptr if *dst is NULL.  Returns value of *dst, destroying ptr if not swapped in.
-// Issues acquire memory barrier on failure, release on success.
-template <typename P, void (*Destroy)(P)>
-static P try_cas(P* dst, P ptr) {
-    P prev = NULL;
-    if (sk_atomic_compare_exchange(dst, &prev, ptr,
-                                   sk_memory_order_release/*on success*/,
-                                   sk_memory_order_acquire/*on failure*/)) {
-        // We need a release barrier before returning ptr.  The compare_exchange provides it.
-        SkASSERT(!prev);
-        return ptr;
-    } else {
-        Destroy(ptr);
-        // We need an acquire barrier before returning prev.  The compare_exchange provided it.
-        SkASSERT(prev);
-        return prev;
-    }
-}
-
-template <typename T>
-T* sk_new() {
-    return new T;
-}
-template <typename T>
-void sk_delete(T* ptr) {
-    delete ptr;
-}
-
-// We're basing these implementations here on this article:
-//   http://preshing.com/20140709/the-purpose-of-memory_order_consume-in-cpp11/
-//
-// Because the users of SkLazyPtr and SkLazyPtrArray will read the pointers
-// _through_ our atomically set pointer, there is a data dependency between our
-// atomic and the guarded data, and so we only need writer-releases /
-// reader-consumes memory pairing rather than the more general write-releases /
-// reader-acquires convention.
-//
-// This is nice, because a consume load is free on all our platforms: x86,
-// ARM, MIPS.  In contrast, an acquire load issues a memory barrier on non-x86.
-
-template <typename T>
-T consume_load(T* ptr) {
-#if defined(THREAD_SANITIZER)
-    // TSAN gets anxious if we don't tell it what we're actually doing, a consume load.
-    return sk_atomic_load(ptr, sk_memory_order_consume);
-#else
-    // All current compilers blindly upgrade consume memory order to acquire memory order.
-    // For our purposes, though, no memory barrier is required, so we lie and use relaxed.
-    return sk_atomic_load(ptr, sk_memory_order_relaxed);
-#endif
-}
-
-// This has no constructor and must be zero-initalized (the macro above does this).
-template <typename T, T* (*Create)() = sk_new<T>, void (*Destroy)(T*) = sk_delete<T> >
-class SkStaticLazyPtr {
-public:
-    T* get() {
-        // If fPtr has already been filled, we need a consume barrier when loading it.
-        // If not, we need a release barrier when setting it.  try_cas will do that.
-        T* ptr = consume_load(&fPtr);
-        return ptr ? ptr : try_cas<T*, Destroy>(&fPtr, Create());
-    }
-
-private:
-    T* fPtr;
-};
-
-template <typename T>
-T* sk_new_arg(int i) {
-    return new T(i);
-}
-
-// This has no constructor and must be zero-initalized (the macro above does this).
-template <typename T, int N, T* (*Create)(int) = sk_new_arg<T>, void (*Destroy)(T*) = sk_delete<T> >
-class SkStaticLazyPtrArray {
-public:
-    T* operator[](int i) {
-        SkASSERT(i >= 0 && i < N);
-        // If fPtr has already been filled, we need an consume barrier when loading it.
-        // If not, we need a release barrier when setting it.  try_cas will do that.
-        T* ptr = consume_load(&fArray[i]);
-        return ptr ? ptr : try_cas<T*, Destroy>(&fArray[i], Create(i));
-    }
-
-private:
-    T* fArray[N];
-};
-
-}  // namespace Private
-
-// This version is suitable for use as a class member.
-// It's much the same as above except:
-//   - it has a constructor to zero itself;
-//   - it has a destructor to clean up;
-//   - get() calls SkNew(T) to create the pointer;
-//   - get(functor) calls functor to create the pointer.
-template <typename T, void (*Destroy)(T*) = Private::sk_delete<T> >
-class SkLazyPtr : SkNoncopyable {
-public:
-    SkLazyPtr() : fPtr(NULL) {}
-    ~SkLazyPtr() { if (fPtr) { Destroy((T*)fPtr); } }
-
-    T* get() const {
-        T* ptr = Private::consume_load(&fPtr);
-        return ptr ? ptr : Private::try_cas<T*, Destroy>(&fPtr, new T);
-    }
-
-    template <typename Create>
-    T* get(const Create& create) const {
-        T* ptr = Private::consume_load(&fPtr);
-        return ptr ? ptr : Private::try_cas<T*, Destroy>(&fPtr, create());
-    }
-
-private:
-    mutable T* fPtr;
-};
-
-
-#endif//SkLazyPtr_DEFINED