Extract most of the mutable state of SkShader into a separate Context object.

src/effects/gradients/SkGradientShader.cpp

Index: src/effects/gradients/SkGradientShader.cpp
diff --git a/src/effects/gradients/SkGradientShader.cpp b/src/effects/gradients/SkGradientShader.cpp
index 2e92076b3add195c08158967c451a6e8b324dc40..46e0c9502dd089fda6cb27d77df7da64d9118497 100644
--- a/src/effects/gradients/SkGradientShader.cpp
+++ b/src/effects/gradients/SkGradientShader.cpp
@@ -15,8 +15,6 @@
 SkGradientShaderBase::SkGradientShaderBase(const Descriptor& desc) {
     SkASSERT(desc.fCount > 1);
 
-    fCacheAlpha = 256;  // init to a value that paint.getAlpha() can't return
-
     fMapper = desc.fMapper;
     SkSafeRef(fMapper);
     fGradFlags = SkToU8(desc.fGradFlags);
@@ -26,10 +24,6 @@ SkGradientShaderBase::SkGradientShaderBase(const Descriptor& desc) {
     fTileMode = desc.fTileMode;
     fTileProc = gTileProcs[desc.fTileMode];
 
-    fCache16 = fCache16Storage = NULL;
-    fCache32 = NULL;
-    fCache32PixelRef = NULL;
-
     /*  Note: we let the caller skip the first and/or last position.
         i.e. pos[0] = 0.3, pos[1] = 0.7
         In these cases, we insert dummy entries to ensure that the final data
@@ -146,14 +140,8 @@ static uint32_t unpack_flags(uint32_t packed) {
 }
 
 SkGradientShaderBase::SkGradientShaderBase(SkReadBuffer& buffer) : INHERITED(buffer) {
-    fCacheAlpha = 256;
-
     fMapper = buffer.readUnitMapper();
 
-    fCache16 = fCache16Storage = NULL;
-    fCache32 = NULL;
-    fCache32PixelRef = NULL;
-
     int colorCount = fColorCount = buffer.getArrayCount();
     if (colorCount > kColorStorageCount) {
         size_t allocSize = (sizeof(SkColor) + sizeof(SkPMColor) + sizeof(Rec)) * colorCount;
@@ -188,10 +176,6 @@ SkGradientShaderBase::SkGradientShaderBase(SkReadBuffer& buffer) : INHERITED(buf
 }
 
 SkGradientShaderBase::~SkGradientShaderBase() {
-    if (fCache16Storage) {
-        sk_free(fCache16Storage);
-    }
-    SkSafeUnref(fCache32PixelRef);
     if (fOrigColors != fStorage) {
         sk_free(fOrigColors);
     }
@@ -199,7 +183,6 @@ SkGradientShaderBase::~SkGradientShaderBase() {
 }
 
 void SkGradientShaderBase::initCommon() {
-    fFlags = 0;
     unsigned colorAlpha = 0xFF;
     for (int i = 0; i < fColorCount; i++) {
         colorAlpha &= SkColorGetA(fOrigColors[i]);
@@ -267,49 +250,50 @@ bool SkGradientShaderBase::isOpaque() const {
     return fColorsAreOpaque;
 }
 
-bool SkGradientShaderBase::setContext(const SkBitmap& device,
-                                 const SkPaint& paint,
-                                 const SkMatrix& matrix) {
-    if (!this->INHERITED::setContext(device, paint, matrix)) {
-        return false;
-    }
-
+SkGradientShaderBase::GradientShaderBaseContext::GradientShaderBaseContext(
+        const SkGradientShaderBase& shader, const SkBitmap& device,
+        const SkPaint& paint, const SkMatrix& matrix)
+    : INHERITED(shader, device, paint, matrix)
+    , fCache(shader.refCache(getPaintAlpha()))
+{
     const SkMatrix& inverse = this->getTotalInverse();
 
-    fDstToIndex.setConcat(fPtsToUnit, inverse);
+    fDstToIndex.setConcat(shader.fPtsToUnit, inverse);
+
     fDstToIndexProc = fDstToIndex.getMapXYProc();
-    fDstToIndexClass = (uint8_t)SkShader::ComputeMatrixClass(fDstToIndex);
+    fDstToIndexClass = (uint8_t)SkShader::Context::ComputeMatrixClass(fDstToIndex);
 
     // now convert our colors in to PMColors
     unsigned paintAlpha = this->getPaintAlpha();
 
     fFlags = this->INHERITED::getFlags();
-    if (fColorsAreOpaque && paintAlpha == 0xFF) {
+    if (shader.fColorsAreOpaque && paintAlpha == 0xFF) {
         fFlags |= kOpaqueAlpha_Flag;
     }
     // we can do span16 as long as our individual colors are opaque,
     // regardless of the paint's alpha
-    if (fColorsAreOpaque) {
+    if (shader.fColorsAreOpaque) {
         fFlags |= kHasSpan16_Flag;
     }
+}
 
-    this->setCacheAlpha(paintAlpha);
-    return true;
+SkGradientShaderBase::GradientShaderCache::GradientShaderCache(
+        U8CPU alpha, const SkGradientShaderBase& shader)
+    : fCacheAlpha(alpha)
+    , fShader(shader)
+    , fCache16Inited(false)
+    , fCache32Inited(false)
+{
+    // Only initialize the cache in getCache16/32.
+    fCache16 = NULL;
+    fCache32 = NULL;
+    fCache16Storage = NULL;
+    fCache32PixelRef = NULL;
 }
 
-void SkGradientShaderBase::setCacheAlpha(U8CPU alpha) const {
-    // if the new alpha differs from the previous time we were called, inval our cache
-    // this will trigger the cache to be rebuilt.
-    // we don't care about the first time, since the cache ptrs will already be NULL
-    if (fCacheAlpha != alpha) {
-        fCache16 = NULL;            // inval the cache
-        fCache32 = NULL;            // inval the cache
-        fCacheAlpha = alpha;        // record the new alpha
-        // inform our subclasses
-        if (fCache32PixelRef) {
-            fCache32PixelRef->notifyPixelsChanged();
-        }
-    }
+SkGradientShaderBase::GradientShaderCache::~GradientShaderCache() {
+    sk_free(fCache16Storage);
+    SkSafeUnref(fCache32PixelRef);
 }
 
 #define Fixed_To_Dot8(x)        (((x) + 0x80) >> 8)
@@ -318,8 +302,8 @@ void SkGradientShaderBase::setCacheAlpha(U8CPU alpha) const {
     build a 16bit table as long as the original colors are opaque, even if the
     paint specifies a non-opaque alpha.
 */
-void SkGradientShaderBase::Build16bitCache(uint16_t cache[], SkColor c0, SkColor c1,
-                                      int count) {
+void SkGradientShaderBase::GradientShaderCache::Build16bitCache(
+        uint16_t cache[], SkColor c0, SkColor c1, int count) {
     SkASSERT(count > 1);
     SkASSERT(SkColorGetA(c0) == 0xFF);
     SkASSERT(SkColorGetA(c1) == 0xFF);
@@ -367,8 +351,9 @@ void SkGradientShaderBase::Build16bitCache(uint16_t cache[], SkColor c0, SkColor
  */
 typedef uint32_t SkUFixed;
 
-void SkGradientShaderBase::Build32bitCache(SkPMColor cache[], SkColor c0, SkColor c1,
-                                      int count, U8CPU paintAlpha, uint32_t gradFlags) {
+void SkGradientShaderBase::GradientShaderCache::Build32bitCache(
+        SkPMColor cache[], SkColor c0, SkColor c1,
+        int count, U8CPU paintAlpha, uint32_t gradFlags) {
     SkASSERT(count > 1);
 
     // need to apply paintAlpha to our two endpoints
@@ -511,97 +496,121 @@ static inline U16CPU bitsTo16(unsigned x, const unsigned bits) {
     return 0;
 }
 
-const uint16_t* SkGradientShaderBase::getCache16() const {
-    if (fCache16 == NULL) {
-        // double the count for dither entries
-        const int entryCount = kCache16Count * 2;
-        const size_t allocSize = sizeof(uint16_t) * entryCount;
+const uint16_t* SkGradientShaderBase::GradientShaderCache::getCache16() {
+    SkOnce(&fCache16Inited, &fCache16Mutex, SkGradientShaderBase::GradientShaderCache::initCache16,
+           this);
+    SkASSERT(fCache16);
+    return fCache16;
+}
 
-        if (fCache16Storage == NULL) { // set the storage and our working ptr
-            fCache16Storage = (uint16_t*)sk_malloc_throw(allocSize);
-        }
-        fCache16 = fCache16Storage;
-        if (fColorCount == 2) {
-            Build16bitCache(fCache16, fOrigColors[0], fOrigColors[1],
-                            kCache16Count);
-        } else {
-            Rec* rec = fRecs;
-            int prevIndex = 0;
-            for (int i = 1; i < fColorCount; i++) {
-                int nextIndex = SkFixedToFFFF(rec[i].fPos) >> kCache16Shift;
-                SkASSERT(nextIndex < kCache16Count);
-
-                if (nextIndex > prevIndex)
-                    Build16bitCache(fCache16 + prevIndex, fOrigColors[i-1], fOrigColors[i], nextIndex - prevIndex + 1);
-                prevIndex = nextIndex;
-            }
+void SkGradientShaderBase::GradientShaderCache::initCache16(GradientShaderCache* cache) {
+    // double the count for dither entries
+    const int entryCount = kCache16Count * 2;
+    const size_t allocSize = sizeof(uint16_t) * entryCount;
+
+    SkASSERT(NULL == cache->fCache16Storage);
+    cache->fCache16Storage = (uint16_t*)sk_malloc_throw(allocSize);
+    cache->fCache16 = cache->fCache16Storage;
+    if (cache->fShader.fColorCount == 2) {
+        Build16bitCache(cache->fCache16, cache->fShader.fOrigColors[0],
+                        cache->fShader.fOrigColors[1], kCache16Count);
+    } else {
+        Rec* rec = cache->fShader.fRecs;
+        int prevIndex = 0;
+        for (int i = 1; i < cache->fShader.fColorCount; i++) {
+            int nextIndex = SkFixedToFFFF(rec[i].fPos) >> kCache16Shift;
+            SkASSERT(nextIndex < kCache16Count);
+
+            if (nextIndex > prevIndex)
+                Build16bitCache(cache->fCache16 + prevIndex, cache->fShader.fOrigColors[i-1],
+                                cache->fShader.fOrigColors[i], nextIndex - prevIndex + 1);
+            prevIndex = nextIndex;
         }
+    }
 
-        if (fMapper) {
-            fCache16Storage = (uint16_t*)sk_malloc_throw(allocSize);
-            uint16_t* linear = fCache16;         // just computed linear data
-            uint16_t* mapped = fCache16Storage;  // storage for mapped data
-            SkUnitMapper* map = fMapper;
-            for (int i = 0; i < kCache16Count; i++) {
-                int index = map->mapUnit16(bitsTo16(i, kCache16Bits)) >> kCache16Shift;
-                mapped[i] = linear[index];
-                mapped[i + kCache16Count] = linear[index + kCache16Count];
-            }
-            sk_free(fCache16);
-            fCache16 = fCache16Storage;
+    if (cache->fShader.fMapper) {
+        cache->fCache16Storage = (uint16_t*)sk_malloc_throw(allocSize);
+        uint16_t* linear = cache->fCache16;         // just computed linear data
+        uint16_t* mapped = cache->fCache16Storage;  // storage for mapped data
+        SkUnitMapper* map = cache->fShader.fMapper;
+        for (int i = 0; i < kCache16Count; i++) {
+            int index = map->mapUnit16(bitsTo16(i, kCache16Bits)) >> kCache16Shift;
+            mapped[i] = linear[index];
+            mapped[i + kCache16Count] = linear[index + kCache16Count];
         }
+        sk_free(cache->fCache16);
+        cache->fCache16 = cache->fCache16Storage;
     }
-    return fCache16;
 }
 
-const SkPMColor* SkGradientShaderBase::getCache32() const {
-    if (fCache32 == NULL) {
-        SkImageInfo info;
-        info.fWidth = kCache32Count;
-        info.fHeight = 4;   // for our 4 dither rows
-        info.fAlphaType = kPremul_SkAlphaType;
-        info.fColorType = kN32_SkColorType;
+const SkPMColor* SkGradientShaderBase::GradientShaderCache::getCache32() {
+    SkOnce(&fCache32Inited, &fCache32Mutex, SkGradientShaderBase::GradientShaderCache::initCache32,
+           this);
+    SkASSERT(fCache32);
+    return fCache32;
+}
 
-        if (NULL == fCache32PixelRef) {
-            fCache32PixelRef = SkMallocPixelRef::NewAllocate(info, 0, NULL);
-        }
-        fCache32 = (SkPMColor*)fCache32PixelRef->getAddr();
-        if (fColorCount == 2) {
-            Build32bitCache(fCache32, fOrigColors[0], fOrigColors[1],
-                            kCache32Count, fCacheAlpha, fGradFlags);
-        } else {
-            Rec* rec = fRecs;
-            int prevIndex = 0;
-            for (int i = 1; i < fColorCount; i++) {
-                int nextIndex = SkFixedToFFFF(rec[i].fPos) >> kCache32Shift;
-                SkASSERT(nextIndex < kCache32Count);
-
-                if (nextIndex > prevIndex)
-                    Build32bitCache(fCache32 + prevIndex, fOrigColors[i-1],
-                                    fOrigColors[i], nextIndex - prevIndex + 1,
-                                    fCacheAlpha, fGradFlags);
-                prevIndex = nextIndex;
-            }
+void SkGradientShaderBase::GradientShaderCache::initCache32(GradientShaderCache* cache) {
+    SkImageInfo info;
+    info.fWidth = kCache32Count;
+    info.fHeight = 4;   // for our 4 dither rows
+    info.fAlphaType = kPremul_SkAlphaType;
+    info.fColorType = kN32_SkColorType;
+
+    SkASSERT(NULL == cache->fCache32PixelRef);
+    cache->fCache32PixelRef = SkMallocPixelRef::NewAllocate(info, 0, NULL);
+    cache->fCache32 = (SkPMColor*)cache->fCache32PixelRef->getAddr();
+    if (cache->fShader.fColorCount == 2) {
+        Build32bitCache(cache->fCache32, cache->fShader.fOrigColors[0],
+                        cache->fShader.fOrigColors[1], kCache32Count, cache->fCacheAlpha,
+                        cache->fShader.fGradFlags);
+    } else {
+        Rec* rec = cache->fShader.fRecs;
+        int prevIndex = 0;
+        for (int i = 1; i < cache->fShader.fColorCount; i++) {
+            int nextIndex = SkFixedToFFFF(rec[i].fPos) >> kCache32Shift;
+            SkASSERT(nextIndex < kCache32Count);
+
+            if (nextIndex > prevIndex)
+                Build32bitCache(cache->fCache32 + prevIndex, cache->fShader.fOrigColors[i-1],
+                                cache->fShader.fOrigColors[i], nextIndex - prevIndex + 1,
+                                cache->fCacheAlpha, cache->fShader.fGradFlags);
+            prevIndex = nextIndex;
         }
+    }
 
-        if (fMapper) {
-            SkMallocPixelRef* newPR = SkMallocPixelRef::NewAllocate(info, 0, NULL);
-            SkPMColor* linear = fCache32;           // just computed linear data
-            SkPMColor* mapped = (SkPMColor*)newPR->getAddr();    // storage for mapped data
-            SkUnitMapper* map = fMapper;
-            for (int i = 0; i < kCache32Count; i++) {
-                int index = map->mapUnit16((i << 8) | i) >> 8;
-                mapped[i + kCache32Count*0] = linear[index + kCache32Count*0];
-                mapped[i + kCache32Count*1] = linear[index + kCache32Count*1];
-                mapped[i + kCache32Count*2] = linear[index + kCache32Count*2];
-                mapped[i + kCache32Count*3] = linear[index + kCache32Count*3];
-            }
-            fCache32PixelRef->unref();
-            fCache32PixelRef = newPR;
-            fCache32 = (SkPMColor*)newPR->getAddr();
+    if (cache->fShader.fMapper) {
+        SkMallocPixelRef* newPR = SkMallocPixelRef::NewAllocate(info, 0, NULL);
+        SkPMColor* linear = cache->fCache32;           // just computed linear data
+        SkPMColor* mapped = (SkPMColor*)newPR->getAddr();    // storage for mapped data
+        SkUnitMapper* map = cache->fShader.fMapper;
+        for (int i = 0; i < kCache32Count; i++) {
+            int index = map->mapUnit16((i << 8) | i) >> 8;
+            mapped[i + kCache32Count*0] = linear[index + kCache32Count*0];
+            mapped[i + kCache32Count*1] = linear[index + kCache32Count*1];
+            mapped[i + kCache32Count*2] = linear[index + kCache32Count*2];
+            mapped[i + kCache32Count*3] = linear[index + kCache32Count*3];
         }
+        cache->fCache32PixelRef->unref();
+        cache->fCache32PixelRef = newPR;
+        cache->fCache32 = (SkPMColor*)newPR->getAddr();
     }
-    return fCache32;
+}
+
+/*
+ *  The gradient holds a cache for the most recent value of alpha. Successive
+ *  callers with the same alpha value will share the same cache.
+ */
+SkGradientShaderBase::GradientShaderCache* SkGradientShaderBase::refCache(U8CPU alpha) const {
+    SkAutoMutexAcquire ama(fCacheMutex);
+    if (!fCache || fCache->getAlpha() != alpha) {
+        fCache.reset(SkNEW_ARGS(GradientShaderCache, (alpha, *this)));
+    }
+    // Increment the ref counter inside the mutex to ensure the returned pointer is still valid.
+    // Otherwise, the pointer may have been overwritten on a different thread before the object's
+    // ref count was incremented.
+    fCache.get()->ref();
+    return fCache;
 }
 
 /*
@@ -615,14 +624,14 @@ const SkPMColor* SkGradientShaderBase::getCache32() const {
 void SkGradientShaderBase::getGradientTableBitmap(SkBitmap* bitmap) const {
     // our caller assumes no external alpha, so we ensure that our cache is
     // built with 0xFF
-    this->setCacheAlpha(0xFF);
+    SkAutoTUnref<GradientShaderCache> cache(this->refCache(0xFF));
 
     // don't have a way to put the mapper into our cache-key yet
     if (fMapper) {
-        // force our cahce32pixelref to be built
-        (void)this->getCache32();
+        // force our cache32pixelref to be built
+        (void)cache->getCache32();
         bitmap->setConfig(SkImageInfo::MakeN32Premul(kCache32Count, 1));
-        bitmap->setPixelRef(fCache32PixelRef);
+        bitmap->setPixelRef(cache->getCache32PixelRef());
         return;
     }
 
@@ -661,9 +670,9 @@ void SkGradientShaderBase::getGradientTableBitmap(SkBitmap* bitmap) const {
 
     if (!gCache->find(storage.get(), size, bitmap)) {
         // force our cahce32pixelref to be built
-        (void)this->getCache32();
+        (void)cache->getCache32();
         bitmap->setConfig(SkImageInfo::MakeN32Premul(kCache32Count, 1));
-        bitmap->setPixelRef(fCache32PixelRef);
+        bitmap->setPixelRef(cache->getCache32PixelRef());
 
         gCache->add(storage.get(), size, *bitmap);
     }