Take ownership of cairo_pattern_t in canvas_state_t with refcounts

src/CanvasRenderingContext2d.cc

@@ -242,18 +242,25 @@ Context2d::Context2d(const Napi::CallbackInfo& info) : Napi::ObjectWrap<Context2
  */
 
 Context2d::~Context2d() {
+  while (!states.empty()) states.pop();
+  state = nullptr;
   if (_layout) g_object_unref(_layout);
   if (_context) cairo_destroy(_context);
-  _resetPersistentHandles();
+  // _resetPersistentHandles() is intentionally NOT called here. It calls
+  // napi_delete_reference, which is unsafe when the destructor runs from
+  // inside GC (FATAL ERROR: "Finalizer is calling a function that may
+  // affect GC state"). Persistent handles are reset from Finalize(env)
+  // which is deferred via node_api_post_finalizer.
 }
 
 /*
  * Reset canvas state.
  */
 
 void Context2d::resetState() {
-  states.pop();
+  while (!states.empty()) states.pop();
   states.emplace();
+  state = &states.top();
   pango_layout_set_font_description(_layout, state->fontDescription);
   _resetPersistentHandles();
 }
@@ -1966,13 +1973,13 @@ Context2d::SetFillStyle(const Napi::CallbackInfo& info, const Napi::Value& value
     InstanceData *data = env.GetInstanceData<InstanceData>();
     Napi::Object obj = value.As<Napi::Object>();
     if (obj.InstanceOf(data->CanvasGradientCtor.Value()).UnwrapOr(false)) {
-      _fillStyle.Reset(obj);
+      _fillStyle.Reset(obj, 1);
       Gradient *grad = Gradient::Unwrap(obj);
-      state->fillGradient = grad->pattern();
+      state->setFillGradient(grad->pattern());
     } else if (obj.InstanceOf(data->CanvasPatternCtor.Value()).UnwrapOr(false)) {
-      _fillStyle.Reset(obj);
+      _fillStyle.Reset(obj, 1);
       Pattern *pattern = Pattern::Unwrap(obj);
-      state->fillPattern = pattern->pattern();
+      state->setFillPattern(pattern->pattern());
     }
   }
 }
@@ -2006,13 +2013,13 @@ Context2d::SetStrokeStyle(const Napi::CallbackInfo& info, const Napi::Value& val
     InstanceData *data = env.GetInstanceData<InstanceData>();
     Napi::Object obj = value.As<Napi::Object>();
     if (obj.InstanceOf(data->CanvasGradientCtor.Value()).UnwrapOr(false)) {
-      _strokeStyle.Reset(obj);
+      _strokeStyle.Reset(obj, 1);
       Gradient *grad = Gradient::Unwrap(obj);
-      state->strokeGradient = grad->pattern();
+      state->setStrokeGradient(grad->pattern());
     } else if (obj.InstanceOf(data->CanvasPatternCtor.Value()).UnwrapOr(false)) {
-      _strokeStyle.Reset(value);
+      _strokeStyle.Reset(value, 1);
       Pattern *pattern = Pattern::Unwrap(obj);
-      state->strokePattern = pattern->pattern();
+      state->setStrokePattern(pattern->pattern());
     }
   }
 }
@@ -2193,7 +2200,7 @@ Context2d::_setFillColor(Napi::Value arg) {
     if (status != napi_ok) return;
     uint32_t rgba = rgba_from_string(buf, &ok);
     if (!ok) return;
-    state->fillPattern = state->fillGradient = NULL;
+    state->clearFillPattern();
     state->fill = rgba_create(rgba);
   }
 }
@@ -2219,7 +2226,7 @@ Context2d::_setStrokeColor(Napi::Value arg) {
   std::string str = arg.As<Napi::String>();
   uint32_t rgba = rgba_from_string(str.c_str(), &ok);
   if (!ok) return;
-  state->strokePattern = state->strokeGradient = NULL;
+  state->clearStrokePattern();
   state->stroke = rgba_create(rgba);
 }
 

src/CanvasRenderingContext2d.h

@@ -47,10 +47,10 @@ struct canvas_state_t {
     fill = other.fill;
     stroke = other.stroke;
     patternQuality = other.patternQuality;
-    fillPattern = other.fillPattern;
-    strokePattern = other.strokePattern;
-    fillGradient = other.fillGradient;
-    strokeGradient = other.strokeGradient;
+    fillPattern = referencePattern(other.fillPattern);
+    strokePattern = referencePattern(other.strokePattern);
+    fillGradient = referencePattern(other.fillGradient);
+    strokeGradient = referencePattern(other.strokeGradient);
     globalAlpha = other.globalAlpha;
     textAlignment = other.textAlignment;
     textBaseline = other.textBaseline;
@@ -66,9 +66,93 @@ struct canvas_state_t {
     lang = other.lang;
   }
 
+  canvas_state_t& operator=(const canvas_state_t& other) {
+    if (this == &other) return *this;
+
+    fill = other.fill;
+    stroke = other.stroke;
+    patternQuality = other.patternQuality;
+    releasePattern(fillPattern);
+    releasePattern(strokePattern);
+    releasePattern(fillGradient);
+    releasePattern(strokeGradient);
+    fillPattern = referencePattern(other.fillPattern);
+    strokePattern = referencePattern(other.strokePattern);
+    fillGradient = referencePattern(other.fillGradient);
+    strokeGradient = referencePattern(other.strokeGradient);
+    globalAlpha = other.globalAlpha;
+    textAlignment = other.textAlignment;
+    textBaseline = other.textBaseline;
+    shadow = other.shadow;
+    shadowBlur = other.shadowBlur;
+    shadowOffsetX = other.shadowOffsetX;
+    shadowOffsetY = other.shadowOffsetY;
+    textDrawingMode = other.textDrawingMode;
+    pango_font_description_free(fontDescription);
+    fontDescription = pango_font_description_copy(other.fontDescription);
+    font = other.font;
+    imageSmoothingEnabled = other.imageSmoothingEnabled;
+    direction = other.direction;
+    lang = other.lang;
+
+    return *this;
+  }
+
   ~canvas_state_t() {
+    releasePattern(fillPattern);
+    releasePattern(strokePattern);
+    releasePattern(fillGradient);
+    releasePattern(strokeGradient);
     pango_font_description_free(fontDescription);
   }
+
+  void setFillPattern(cairo_pattern_t* pattern) {
+    releasePattern(fillGradient);
+    replacePattern(fillPattern, pattern);
+  }
+
+  void setStrokePattern(cairo_pattern_t* pattern) {
+    releasePattern(strokeGradient);
+    replacePattern(strokePattern, pattern);
+  }
+
+  void setFillGradient(cairo_pattern_t* pattern) {
+    releasePattern(fillPattern);
+    replacePattern(fillGradient, pattern);
+  }
+
+  void setStrokeGradient(cairo_pattern_t* pattern) {
+    releasePattern(strokePattern);
+    replacePattern(strokeGradient, pattern);
+  }
+
+  void clearFillPattern() {
+    releasePattern(fillPattern);
+    releasePattern(fillGradient);
+  }
+
+  void clearStrokePattern() {
+    releasePattern(strokePattern);
+    releasePattern(strokeGradient);
+  }
+
+  static cairo_pattern_t* referencePattern(cairo_pattern_t* pattern) {
+    if (pattern) cairo_pattern_reference(pattern);
+    return pattern;
+  }
+
+  static void releasePattern(cairo_pattern_t*& pattern) {
+    if (pattern) {
+      cairo_pattern_destroy(pattern);
+      pattern = nullptr;
+    }
+  }
+
+  static void replacePattern(cairo_pattern_t*& current, cairo_pattern_t* next) {
+    if (current == next) return;
+    releasePattern(current);
+    current = referencePattern(next);
+  }
 };
 
 /*