create cairo before we hand-off the surface, in case the surface is destroyed

skia/ext/bitmap_platform_device_cairo.cc

 // Copyright 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "skia/ext/bitmap_platform_device_cairo.h"
 #include "skia/ext/platform_canvas.h"
 
 #if defined(OS_OPENBSD)
 #include <cairo.h>
 #else
 #include <cairo/cairo.h>
 #endif
 
 namespace skia {
 
 namespace {
 
 void CairoSurfaceReleaseProc(void*, void* context) {
   SkASSERT(context);
   cairo_surface_destroy(static_cast<cairo_surface_t*>(context));
 }
 
 // Back the destination bitmap by a Cairo surface.  The bitmap's
 // pixelRef takes ownership of the passed-in surface and will call
 // cairo_surface_destroy() upon destruction.
+//
+// Note: it may immediately destroy the surface, if it fails to create a bitmap
+// with pixels, thus the caller must either ref() the surface before hand, or
+// it must not refer to the surface after this call.
 bool InstallCairoSurfacePixels(SkBitmap* dst,
                                cairo_surface_t* surface,
                                bool is_opaque) {
   SkASSERT(dst);
   if (!surface) {
     return false;
   }
   SkImageInfo info
       = SkImageInfo::MakeN32Premul(cairo_image_surface_get_width(surface),
                                    cairo_image_surface_get_height(surface));
@@ skipping 56 matching lines @@
 // required so that we can call the base class' constructor with the pixel
 // data.
 BitmapPlatformDevice* BitmapPlatformDevice::Create(int width, int height,
                                                    bool is_opaque,
                                                    cairo_surface_t* surface) {
   if (cairo_surface_status(surface) != CAIRO_STATUS_SUCCESS) {
     cairo_surface_destroy(surface);
     return NULL;
   }
 
+  // must call this before trying to install the surface, since that may result
+  // in the surface being destroyed.
+  cairo_t* cairo = cairo_create(surface);
+
   SkBitmap bitmap;
   if (!InstallCairoSurfacePixels(&bitmap, surface, is_opaque)) {
+    cairo_destroy(cairo);
     return NULL;
   }
 
   // The device object will take ownership of the graphics context.
-  return new BitmapPlatformDevice(bitmap, surface);
+  return new BitmapPlatformDevice(bitmap, cairo);
 }
 
 BitmapPlatformDevice* BitmapPlatformDevice::Create(int width, int height,
                                                    bool is_opaque) {
   // This initializes the bitmap to all zeros.
   cairo_surface_t* surface = cairo_image_surface_create(CAIRO_FORMAT_ARGB32,
                                                         width, height);
 
   BitmapPlatformDevice* device = Create(width, height, is_opaque, surface);
 
@@ skipping 16 matching lines @@
 BitmapPlatformDevice* BitmapPlatformDevice::Create(int width, int height,
                                                    bool is_opaque,
                                                    uint8_t* data) {
   cairo_surface_t* surface = cairo_image_surface_create_for_data(
       data, CAIRO_FORMAT_ARGB32, width, height,
       cairo_format_stride_for_width(CAIRO_FORMAT_ARGB32, width));
 
   return Create(width, height, is_opaque, surface);
 }
 
-// The device will own the bitmap, which corresponds to also owning the pixel
-// data. Therefore, we do not transfer ownership to the SkBitmapDevice's bitmap.
+// Ownership of the cairo object is transferred.
 BitmapPlatformDevice::BitmapPlatformDevice(
     const SkBitmap& bitmap,
-    cairo_surface_t* surface)
+    cairo_t* cairo)
     : SkBitmapDevice(bitmap),
-      cairo_(cairo_create(surface)),
+      cairo_(cairo),
       config_dirty_(true),
       transform_(SkMatrix::I()) {  // Want to load the config next time.
   SetPlatformDevice(this, this);
 }
 
 BitmapPlatformDevice::~BitmapPlatformDevice() {
   cairo_destroy(cairo_);
 }
 
 SkBaseDevice* BitmapPlatformDevice::onCreateCompatibleDevice(
@@ skipping 51 matching lines @@
       width,
       height);
   if (cairo_surface_status(surf) != CAIRO_STATUS_SUCCESS) {
     cairo_surface_destroy(surf);
     return false;
   }
   return InstallCairoSurfacePixels(&bitmap_, surf, is_opaque);
 }
 
 }  // namespace skia