make a shallow-copy so we don't get racy trying to lock/unlock our private bitmap

src/image/SkImage_Raster.cpp

 /*
  * Copyright 2012 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkImage_Base.h"
 #include "SkBitmap.h"
 #include "SkCanvas.h"
@@ skipping 147 matching lines @@
     const SkImageInfo info = fBitmap.info();
     if ((kUnknown_SkColorType == info.colorType()) || !fBitmap.getPixels()) {
         return nullptr;
     }
     *infoPtr = info;
     *rowBytesPtr = fBitmap.rowBytes();
     return fBitmap.getPixels();
 }
 
 void SkImage_Raster::onPreroll(GrContext* ctx) const {
-    fBitmap.lockPixels();
-    fBitmap.unlockPixels();
+    // SkImage can be called from lots of threads, but our fBitmap is *not* thread-safe,
+    // so we have to perform this lock/unlock in a non-racy way... we make a copy!
+    SkBitmap localShallowCopy(fBitmap);
+    localShallowCopy.lockPixels();
+    localShallowCopy.unlockPixels();

[f(malita), 2015/09/10 18:36:37]

This may solve the preRoll race, but don't we have the same issue when drawing
the same SkImage on multiple threads?  I presume internally we still call
lock/unlock on fBitmap in that case.

 }
 
 SkData* SkImage_Raster::onRefEncoded() const {
     SkPixelRef* pr = fBitmap.pixelRef();
     const SkImageInfo prInfo = pr->info();
     const SkImageInfo bmInfo = fBitmap.info();
 
     // we only try if we (the image) cover the entire area of the pixelRef
     if (prInfo.width() == bmInfo.width() && prInfo.height() == bmInfo.height()) {
         return pr->refEncodedData();
@@ skipping 111 matching lines @@
         // pixelref since the caller might call setImmutable() themselves
         // (thus changing our state).
         if (fBitmap.isImmutable()) {
             bitmap->setInfo(fBitmap.info(), fBitmap.rowBytes());
             bitmap->setPixelRef(fBitmap.pixelRef(), fBitmap.pixelRefOrigin());
             return true;
         }
     }
     return this->INHERITED::onAsLegacyBitmap(bitmap, mode);
 }