Bug 910881 - Do not call RasterImage::DoError off the main thread. r=jdm

--HG--
extra : rebase_source : 9d76763242a351dfbdcf8a35db98a5dceed0d838

image/src/RasterImage.cpp

@@ -401,6 +401,7 @@ RasterImage::RasterImage(imgStatusTracker* aStatusTracker,
   mFinishing(false),
   mInUpdateImageContainer(false),
   mWantFullDecode(false),
+  mPendingError(false),
   mScaleRequest(nullptr)
 {
   // Set up the discard tracker node.
@@ -2822,13 +2823,19 @@ RasterImage::DoError()
   if (mError)
     return;
 
+  // We can't safely handle errors off-main-thread, so dispatch a worker to do it.
+  if (!NS_IsMainThread()) {
+    HandleErrorWorker::DispatchIfNeeded(this);
+    return;
+  }
+
   // If we're mid-decode, shut down the decoder.
   if (mDecoder) {
     MutexAutoLock lock(mDecodingMutex);
     FinishedSomeDecoding(eShutdownIntent_Error);
   }
 
-  // Put the container in an error state
+  // Put the container in an error state.
   mError = true;
 
   if (mDecodeRequest) {
@@ -2841,6 +2848,30 @@ RasterImage::DoError()
   LOG_CONTAINER_ERROR;
 }
 
+/* static */ void
+RasterImage::HandleErrorWorker::DispatchIfNeeded(RasterImage* aImage)
+{
+  if (!aImage->mPendingError) {
+    aImage->mPendingError = true;
+    nsRefPtr<HandleErrorWorker> worker = new HandleErrorWorker(aImage);
+    NS_DispatchToMainThread(worker);
+  }
+}
+
+RasterImage::HandleErrorWorker::HandleErrorWorker(RasterImage* aImage)
+  : mImage(aImage)
+{
+  MOZ_ASSERT(mImage, "Should have image");
+}
+
+NS_IMETHODIMP
+RasterImage::HandleErrorWorker::Run()
+{
+  mImage->DoError();
+
+  return NS_OK;
+}
+
 // nsIInputStream callback to copy the incoming image data directly to the
 // RasterImage without processing. The RasterImage is passed as the closure.
 // Always reads everything it gets, even if the data is erroneous.
@@ -3188,6 +3219,7 @@ RasterImage::DecodePool::DecodeJob::Run()
   // this request to the back of the list.
   else if (mImage->mDecoder &&
            !mImage->mError &&
+           !mImage->mPendingError &&
            !mImage->IsDecodeFinished() &&
            bytesDecoded < mRequest->mBytesToDecode &&
            bytesDecoded > 0) {

image/src/RasterImage.h

@@ -667,6 +667,11 @@ private: // data
   // off a full decode.
   bool                       mWantFullDecode:1;
 
+  // Set when a decode worker detects an error off-main-thread. Once the error
+  // is handled on the main thread, mError is set, but mPendingError is used to
+  // stop decode work immediately.
+  bool                       mPendingError:1;
+
   // Decoding
   nsresult WantDecodedFrames();
   nsresult SyncDecode();
@@ -699,8 +704,28 @@ private: // data
 
   nsresult ShutdownDecoder(eShutdownIntent aIntent);
 
-  // Helpers
+  // Error handling.
   void DoError();
+
+  class HandleErrorWorker : public nsRunnable
+  {
+  public:
+    /**
+     * Called from decoder threads when DoError() is called, since errors can't
+     * be handled safely off-main-thread. Dispatches an event which reinvokes
+     * DoError on the main thread if there isn't one already pending.
+     */
+    static void DispatchIfNeeded(RasterImage* aImage);
+
+    NS_IMETHOD Run();
+
+  private:
+    HandleErrorWorker(RasterImage* aImage);
+
+    nsRefPtr<RasterImage> mImage;
+  };
+
+  // Helpers
   bool CanDiscard();
   bool CanForciblyDiscard();
   bool DiscardingActive();