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

src/core/SkPictureShader.cpp

Index: src/core/SkPictureShader.cpp
diff --git a/src/core/SkPictureShader.cpp b/src/core/SkPictureShader.cpp
index bf312851ab3bb33b81d4a0b116d1549f96eea352..dc5c90b62e8ec7eb14fc31413f2f3d78ec1afabe 100644
--- a/src/core/SkPictureShader.cpp
+++ b/src/core/SkPictureShader.cpp
@@ -49,7 +49,7 @@ void SkPictureShader::flatten(SkWriteBuffer& buffer) const {
     fPicture->flatten(buffer);
 }
 
-bool SkPictureShader::buildBitmapShader(const SkMatrix& matrix) const {
+SkShader* SkPictureShader::refBitmapShader(const SkMatrix& matrix) const {
     SkASSERT(fPicture && fPicture->width() > 0 && fPicture->height() > 0);
 
     SkMatrix m;
@@ -70,17 +70,20 @@ bool SkPictureShader::buildBitmapShader(const SkMatrix& matrix) const {
 
     SkISize tileSize = scaledSize.toRound();
     if (tileSize.isEmpty()) {
-        return false;
+        return NULL;
     }
 
     // The actual scale, compensating for rounding.
     SkSize tileScale = SkSize::Make(SkIntToScalar(tileSize.width()) / fPicture->width(),
                                     SkIntToScalar(tileSize.height()) / fPicture->height());
 
-    if (!fCachedShader || tileScale != fCachedTileScale) {
+    SkAutoMutexAcquire ama(fCachedBitmapShaderMutex);
+
+    if (!fCachedBitmapShader || tileScale != fCachedTileScale ||
+        this->getLocalMatrix() != fCachedLocalMatrix) {
         SkBitmap bm;
         if (!bm.allocN32Pixels(tileSize.width(), tileSize.height())) {
-            return false;
+            return NULL;
         }
         bm.eraseColor(SK_ColorTRANSPARENT);
 
@@ -88,66 +91,91 @@ bool SkPictureShader::buildBitmapShader(const SkMatrix& matrix) const {
         canvas.scale(tileScale.width(), tileScale.height());
         canvas.drawPicture(*fPicture);
 
-        fCachedShader.reset(CreateBitmapShader(bm, fTmx, fTmy));
+        fCachedBitmapShader.reset(CreateBitmapShader(bm, fTmx, fTmy));
         fCachedTileScale = tileScale;
-    }
+        fCachedLocalMatrix = this->getLocalMatrix();
 
-    SkMatrix shaderMatrix = this->getLocalMatrix();
-    shaderMatrix.preScale(1 / tileScale.width(), 1 / tileScale.height());
-    fCachedShader->setLocalMatrix(shaderMatrix);
+        SkMatrix shaderMatrix = this->getLocalMatrix();
+        shaderMatrix.preScale(1 / tileScale.width(), 1 / tileScale.height());
+        fCachedBitmapShader->setLocalMatrix(shaderMatrix);
+    }
 
-    return true;
+    // 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.
+    fCachedBitmapShader.get()->ref();
+    return fCachedBitmapShader;
 }
 
-bool SkPictureShader::setContext(const SkBitmap& device,
-                                 const SkPaint& paint,
-                                 const SkMatrix& matrix) {
-    if (!this->buildBitmapShader(matrix)) {
-        return false;
+SkShader* SkPictureShader::validInternal(const SkBitmap& device, const SkPaint& paint,
+                                         const SkMatrix& matrix, SkMatrix* totalInverse) const {
+    if (!this->INHERITED::validContext(device, paint, matrix, totalInverse)) {
+        return NULL;
     }
 
-    if (!this->INHERITED::setContext(device, paint, matrix)) {
-        return false;
+    SkAutoTUnref<SkShader> bitmapShader(this->refBitmapShader(matrix));
+    if (!bitmapShader || !bitmapShader->validContext(device, paint, matrix)) {
+        return NULL;
     }
 
-    SkASSERT(fCachedShader);
-    if (!fCachedShader->setContext(device, paint, matrix)) {
-        this->INHERITED::endContext();
-        return false;
+    return bitmapShader.detach();
+}
+
+bool SkPictureShader::validContext(const SkBitmap& device, const SkPaint& paint,
+                                   const SkMatrix& matrix, SkMatrix* totalInverse) const {
+    SkAutoTUnref<SkShader> shader(this->validInternal(device, paint, matrix, totalInverse));
+    return shader != NULL;
+}
+
+SkShader::Context* SkPictureShader::createContext(const SkBitmap& device, const SkPaint& paint,
+                                                  const SkMatrix& matrix, void* storage) const {
+    SkAutoTUnref<SkShader> bitmapShader(this->validInternal(device, paint, matrix, NULL));
+    if (!bitmapShader) {
+        return NULL;
     }
 
-    return true;
+    return SkNEW_PLACEMENT_ARGS(storage, PictureShaderContext,
+                                (*this, device, paint, matrix, bitmapShader.detach()));
+}
+
+size_t SkPictureShader::contextSize() const {
+    return sizeof(PictureShaderContext);
 }
 
-void SkPictureShader::endContext() {
-    SkASSERT(fCachedShader);
-    fCachedShader->endContext();
+SkPictureShader::PictureShaderContext::PictureShaderContext(
+        const SkPictureShader& shader, const SkBitmap& device,
+        const SkPaint& paint, const SkMatrix& matrix, SkShader* bitmapShader)
+    : INHERITED(shader, device, paint, matrix)
+    , fBitmapShader(bitmapShader)
+{
+    SkASSERT(fBitmapShader);
+    fBitmapShaderContextStorage = sk_malloc_throw(fBitmapShader->contextSize());
+    fBitmapShaderContext = fBitmapShader->createContext(
+            device, paint, matrix, fBitmapShaderContextStorage);
+    SkASSERT(fBitmapShaderContext);
+}
 
-    this->INHERITED::endContext();
+SkPictureShader::PictureShaderContext::~PictureShaderContext() {
+    fBitmapShaderContext->~Context();
+    sk_free(fBitmapShaderContextStorage);
 }
 
-uint32_t SkPictureShader::getFlags() {
-    if (NULL != fCachedShader) {
-        return fCachedShader->getFlags();
-    }
-    return 0;
+uint32_t SkPictureShader::PictureShaderContext::getFlags() const {
+    return fBitmapShaderContext->getFlags();
 }
 
-SkShader::ShadeProc SkPictureShader::asAShadeProc(void** ctx) {
-    if (fCachedShader) {
-        return fCachedShader->asAShadeProc(ctx);
-    }
-    return NULL;
+SkShader::Context::ShadeProc SkPictureShader::PictureShaderContext::asAShadeProc(void** ctx) {
+    return fBitmapShaderContext->asAShadeProc(ctx);
 }
 
-void SkPictureShader::shadeSpan(int x, int y, SkPMColor dstC[], int count) {
-    SkASSERT(fCachedShader);
-    fCachedShader->shadeSpan(x, y, dstC, count);
+void SkPictureShader::PictureShaderContext::shadeSpan(int x, int y, SkPMColor dstC[], int count) {
+    SkASSERT(fBitmapShaderContext);
+    fBitmapShaderContext->shadeSpan(x, y, dstC, count);
 }
 
-void SkPictureShader::shadeSpan16(int x, int y, uint16_t dstC[], int count) {
-    SkASSERT(fCachedShader);
-    fCachedShader->shadeSpan16(x, y, dstC, count);
+void SkPictureShader::PictureShaderContext::shadeSpan16(int x, int y, uint16_t dstC[], int count) {
+    SkASSERT(fBitmapShaderContext);
+    fBitmapShaderContext->shadeSpan16(x, y, dstC, count);
 }
 
 #ifndef SK_IGNORE_TO_STRING
@@ -168,10 +196,10 @@ void SkPictureShader::toString(SkString* str) const {
 
 #if SK_SUPPORT_GPU
 GrEffectRef* SkPictureShader::asNewEffect(GrContext* context, const SkPaint& paint) const {
-    if (!this->buildBitmapShader(context->getMatrix())) {
+    SkAutoTUnref<SkShader> bitmapShader(this->refBitmapShader(context->getMatrix()));
+    if (!bitmapShader) {
         return NULL;
     }
-    SkASSERT(fCachedShader);
-    return fCachedShader->asNewEffect(context, paint);
+    return bitmapShader->asNewEffect(context, paint);
 }
 #endif