Modernize and trim down SkOnce.

The API and implementation are very much simplified.
You may not want to bother reading the diff.

As is our trend, SkOnce now uses <atomic> directly.

Member initialization means we don't need SK_DECLARE_STATIC_ONCE.
SkSpinlock already works this same way.

All uses of the old API taking an external bool* and Lock* were pessimal,
so I have not carried this sort of API forward.  It's simpler, faster,
and more space-efficient to always use this single SkOnce class interface.

SkOnce weighs 2 bytes: a done bool and an SkSpinlock, also a bool internally.
This API refactoring opens up the opportunity to fuse those into a single
three-state byte if we'd like.

No public API changes.
TBR=reed@google.com

BUG=skia:
GOLD_TRYBOT_URL= https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&issue=1894893002

Review URL: https://codereview.chromium.org/1894893002

2 files changed, 4 insertions, 8 deletions

diff --git a/src/effects/gradients/SkGradientShader.cpp b/src/effects/gradients/SkGradientShader.cpp
index 6c141dcf80..779756f3ba 100644
--- a/src/effects/gradients/SkGradientShader.cpp
+++ b/src/effects/gradients/SkGradientShader.cpp
@@ -322,8 +322,6 @@ SkGradientShaderBase::GradientShaderCache::GradientShaderCache(
     : fCacheAlpha(alpha)
     , fCacheDither(dither)
     , fShader(shader)
-    , fCache16Inited(false)
-    , fCache32Inited(false)
 {
     // Only initialize the cache in getCache16/32.
     fCache16 = nullptr;
@@ -545,8 +543,7 @@ static inline int SkFixedToFFFF(SkFixed x) {
 }
 
 const uint16_t* SkGradientShaderBase::GradientShaderCache::getCache16() {
-    SkOnce(&fCache16Inited, &fCache16Mutex, SkGradientShaderBase::GradientShaderCache::initCache16,
-           this);
+    fCache16InitOnce(SkGradientShaderBase::GradientShaderCache::initCache16, this);
     SkASSERT(fCache16);
     return fCache16;
 }
@@ -579,8 +576,7 @@ void SkGradientShaderBase::GradientShaderCache::initCache16(GradientShaderCache*
 }
 
 const SkPMColor* SkGradientShaderBase::GradientShaderCache::getCache32() {
-    SkOnce(&fCache32Inited, &fCache32Mutex, SkGradientShaderBase::GradientShaderCache::initCache32,
-           this);
+    fCache32InitOnce(SkGradientShaderBase::GradientShaderCache::initCache32, this);
     SkASSERT(fCache32);
     return fCache32;
 }
diff --git a/src/effects/gradients/SkGradientShaderPriv.h b/src/effects/gradients/SkGradientShaderPriv.h
index 881f1eb836..0677cf0fd3 100644
--- a/src/effects/gradients/SkGradientShaderPriv.h
+++ b/src/effects/gradients/SkGradientShaderPriv.h
@@ -142,8 +142,8 @@ public:
         const SkGradientShaderBase& fShader;
 
         // Make sure we only initialize the caches once.
-        bool    fCache16Inited, fCache32Inited;
-        SkMutex fCache16Mutex, fCache32Mutex;
+        SkOnce fCache16InitOnce,
+               fCache32InitOnce;
 
         static void initCache16(GradientShaderCache* cache);
         static void initCache32(GradientShaderCache* cache);