Port SkLazyFnPtr users to SkOncePtr.

First baby step on road to replacing SkLazyFnPtr, SkLazyPtr, and SkOnce.

One of those very unusual times you get to use a function type,
not a function pointer type!

BUG=skia:

Review URL: https://codereview.chromium.org/1317263007

2 files changed, 15 insertions, 88 deletions

diff --git a/src/core/SkLazyFnPtr.h b/src/core/SkLazyFnPtr.h
deleted file mode 100644
index 153578201a..0000000000
--- a/src/core/SkLazyFnPtr.h
+++ /dev/null
@@ -1,66 +0,0 @@
-/*
- * 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 SkLazyFnPtr_DEFINED
-#define SkLazyFnPtr_DEFINED
-
-/** Declare a lazily-chosen static function pointer of type F.
- *
- *  Example usage:
- *
- *  typedef int (*FooImpl)(int, int);
- *
- *  static FooImpl choose_foo() { return ... };
- *
- *  int Foo(int a, int b) {
- *     SK_DECLARE_STATIC_LAZY_FN_PTR(FooImpl, foo, choose_foo);
- *     return foo.get()(a, b);
- *  }
- *
- *  You can think of SK_DECLARE_STATIC_LAZY_FN_PTR as a cheaper specialization of SkOnce.
- *  There is no mutex, and in the fast path, no memory barriers are issued.
- *
- *  This must be used in a global or function scope, not as a class member.
- */
-#define SK_DECLARE_STATIC_LAZY_FN_PTR(F, name, Choose) static Private::SkLazyFnPtr<F, Choose> name
-
-
-// Everything below here is private implementation details.  Don't touch, don't even look.
-
-#include "SkAtomics.h"
-
-namespace Private {
-
-// This has no constructor and must be zero-initialized (the macro above does this).
-template <typename F, F (*Choose)()>
-class SkLazyFnPtr {
-public:
-    F get() {
-        // First, try reading to see if it's already set.
-        F fn = (F)sk_atomic_load(&fPtr, sk_memory_order_relaxed);
-        if (fn != nullptr) {
-            return fn;
-        }
-
-        // We think it's not already set.
-        fn = Choose();
-
-        // No particular memory barriers needed; we're not guarding anything but the pointer itself.
-        F prev = (F)sk_atomic_cas(&fPtr, nullptr, (void*)fn);
-
-        // If prev != nullptr, someone snuck in and set fPtr concurrently.
-        // If prev == nullptr, we did write fn to fPtr.
-        return prev != nullptr ? prev : fn;
-    }
-
-private:
-    void* fPtr;
-};
-
-}  // namespace Private
-
-#endif//SkLazyFnPtr_DEFINED
diff --git a/src/ports/SkFontHost_mac.cpp b/src/ports/SkFontHost_mac.cpp
index 343936c673..7d90d84695 100644
--- a/src/ports/SkFontHost_mac.cpp
+++ b/src/ports/SkFontHost_mac.cpp
@@ -28,7 +28,6 @@
 #include "SkFontDescriptor.h"
 #include "SkFontMgr.h"
 #include "SkGlyph.h"
-#include "SkLazyFnPtr.h"
 #include "SkMaskGamma.h"
 #include "SkMutex.h"
 #include "SkOTTable_glyf.h"
@@ -36,6 +35,7 @@
 #include "SkOTTable_hhea.h"
 #include "SkOTTable_loca.h"
 #include "SkOTUtils.h"
+#include "SkOncePtr.h"
 #include "SkPaint.h"
 #include "SkPath.h"
 #include "SkSFNTHeader.h"
@@ -770,34 +770,27 @@ SkScalerContext_Mac::SkScalerContext_Mac(SkTypeface_Mac* typeface,
     fFUnitMatrix.preScale(emPerFUnit, -emPerFUnit);
 }
 
-extern "C" {
-
-/** CTFontDrawGlyphs was introduced in 10.7. */
-typedef void (*CTFontDrawGlyphsProc)(CTFontRef, const CGGlyph[], const CGPoint[],
-                                     size_t, CGContextRef);
-
-/** This is an implementation of CTFontDrawGlyphs for 10.6. */
-static void sk_legacy_CTFontDrawGlyphs(CTFontRef, const CGGlyph glyphs[], const CGPoint points[],
-                                       size_t count, CGContextRef cg)
-{
+/** This is an implementation of CTFontDrawGlyphs for 10.6; it was introduced in 10.7. */
+static void legacy_CTFontDrawGlyphs(CTFontRef, const CGGlyph glyphs[], const CGPoint points[],
+                                    size_t count, CGContextRef cg) {
     CGContextShowGlyphsAtPositions(cg, glyphs, points, count);
 }
 
-}
+typedef decltype(legacy_CTFontDrawGlyphs) CTFontDrawGlyphsProc;
 
-CTFontDrawGlyphsProc SkChooseCTFontDrawGlyphs() {
-    CTFontDrawGlyphsProc realCTFontDrawGlyphs;
-    *reinterpret_cast<void**>(&realCTFontDrawGlyphs) = dlsym(RTLD_DEFAULT, "CTFontDrawGlyphs");
-    return realCTFontDrawGlyphs ? realCTFontDrawGlyphs : sk_legacy_CTFontDrawGlyphs;
-};
+static CTFontDrawGlyphsProc* choose_CTFontDrawGlyphs() {
+    if (void* real = dlsym(RTLD_DEFAULT, "CTFontDrawGlyphs")) {
+        return (CTFontDrawGlyphsProc*)real;
+    }
+    return &legacy_CTFontDrawGlyphs;
+}
 
-SK_DECLARE_STATIC_LAZY_FN_PTR(CTFontDrawGlyphsProc, gCTFontDrawGlyphs, SkChooseCTFontDrawGlyphs);
+SK_DECLARE_STATIC_ONCE_PTR(CTFontDrawGlyphsProc, gCTFontDrawGlyphs);
 
 CGRGBPixel* Offscreen::getCG(const SkScalerContext_Mac& context, const SkGlyph& glyph,
                              CGGlyph glyphID, size_t* rowBytesPtr,
-                             bool generateA8FromLCD)
-{
-    CTFontDrawGlyphsProc ctFontDrawGlyphs = gCTFontDrawGlyphs.get();
+                             bool generateA8FromLCD) {
+    auto ctFontDrawGlyphs = gCTFontDrawGlyphs.get(choose_CTFontDrawGlyphs);
 
     if (!fRGBSpace) {
         //It doesn't appear to matter what color space is specified.
@@ -867,7 +860,7 @@ CGRGBPixel* Offscreen::getCG(const SkScalerContext_Mac& context, const SkGlyph&
         fDoAA = !doAA;
         fDoLCD = !doLCD;
 
-        if (sk_legacy_CTFontDrawGlyphs == ctFontDrawGlyphs) {
+        if (legacy_CTFontDrawGlyphs == ctFontDrawGlyphs) {
             // CTFontDrawGlyphs will apply the font, font size, and font matrix to the CGContext.
             // Our 'fake' one does not, so set up the CGContext here.
             CGContextSetFont(fCG, context.fCGFont);