Try fix WriteableBitmap hangs when source bitmap is rendered on other thread

[lindexi]

Fixes Issue #4396

Description

See #4396

Why

Why the background task will dead lock? Because the background task will get the lock in WriteableBitmap.InitFromBitmapSource method.

    public sealed class WriteableBitmap : BitmapSource
    {
        private void InitFromBitmapSource(
            BitmapSource source
            )
        {
        	// Ignore code
        	 _syncObject = source.SyncObject;
            lock (_syncObject)
            {
            	// Ignore code
            }
        }
    }

And the source is a TransformedBitmap which was created in ProcessImageAsync method and running in background task.

// The Demo code
		private void ProcessImageAsync(string filePath)
		{
			TransformedBitmap tb = new TransformedBitmap(new BitmapImage(new Uri(filePath)), new RotateTransform(90));

			CopyBitmapSourceToUi(tb);

			_ = new WriteableBitmap(tb);
		}

But the source.SyncObject will be used in main thread when Render.

 	PresentationCore.dll!System.Windows.Media.Imaging.BitmapSource.UpdateBitmapSourceResource(System.Windows.Media.Composition.DUCE.Channel channel = {System.Windows.Media.Composition.DUCE.Channel}, bool skipOnChannelCheck)
 	PresentationCore.dll!System.Windows.Media.Imaging.BitmapSource.UpdateResource(System.Windows.Media.Composition.DUCE.Channel channel, bool skipOnChannelCheck)
 	PresentationCore.dll!System.Windows.Media.Imaging.BitmapSource.AddRefOnChannelCore(System.Windows.Media.Composition.DUCE.Channel channel = {System.Windows.Media.Composition.DUCE.Channel})
 	PresentationCore.dll!System.Windows.Media.Imaging.BitmapSource.System.Windows.Media.Composition.DUCE.IResource.AddRefOnChannel(System.Windows.Media.Composition.DUCE.Channel channel)
 	PresentationCore.dll!System.Windows.Media.RenderData.System.Windows.Media.Composition.DUCE.IResource.AddRefOnChannel(System.Windows.Media.Composition.DUCE.Channel channel = {System.Windows.Media.Composition.DUCE.Channel})
 	PresentationCore.dll!System.Windows.UIElement.RenderContent(System.Windows.Media.RenderContext ctx, bool isOnChannel)
 	PresentationCore.dll!System.Windows.Media.Visual.UpdateContent(System.Windows.Media.RenderContext ctx = {System.Windows.Media.RenderContext}, System.Windows.Media.VisualProxyFlags flags, bool isOnChannel)
 	PresentationCore.dll!System.Windows.Media.Visual.RenderRecursive(System.Windows.Media.RenderContext ctx = {System.Windows.Media.RenderContext})

The main thread will use the same SyncObject in BitmapSource.UpdateBitmapSourceResource

     public abstract class BitmapSource : ImageSource, DUCE.IResource
     {
        internal virtual void UpdateBitmapSourceResource(DUCE.Channel channel, bool skipOnChannelCheck)
        {
                // Ignore code
                // We may end up loading in the bitmap bits so it's necessary to take the sync lock here.
                lock (_syncObject)
                {
                    channel.SendCommandBitmapSource(
                        _duceResource.GetHandle(channel),
                        DUCECompatiblePtr
                        );
                }
            }
        }
     }

The main thread will waitting the _syncObject which be used in background task in WriteableBitmap.InitFromBitmapSource method.

But the background task now waitting the main thread in MediaSystem.Startup. So the main thread wait background task to release the _syncObject lock and the background task wait main thread.

How

By splitting the original Unlock method, we are able to enter the InitFromBitmapSource method when creating a WriteableBitmap object in the background thread without having to wait for the main thread to complete and release the lock. This allows the _syncObject lock to be released as quickly as possible when creating a WriteableBitmap object in the background thread. Since the lock is released before the background thread enters waiting for the main thread, the main thread can safely wait for the lock. The main thread will not wait for each other with the background thread.

Customer Impact

Regression

Testing

Demo test: https://github.com/lindexi/lindexi_gd/tree/82c1dc09816d7a15214a167cae78f215a3393d6c/BitmapSourceTest

Risk

[lindexi]

@ryalanms @fabiant3 Any news?

[miloush]

@lindexi can you please be more descriptive in the PR, what is the bug and how does your PR fix it?

[lindexi]

@miloush Yes, I will add

[Kuldeep-MS]

@lindexi - Could you please rebase this PR and resolve the build error? I attempted to do it myself, but I don't have the necessary access.

[lindexi]

@Kuldeep-MS Thank you and I rebase the PR.

[h3xds1nz]

@lindexi The build fails due to "Void" instead of "void" in method signatures:

• UnlockWithoutSubscribeToCommittingBatch
• SubscribeToCommittingBatchAndWritePostscript

I also don't like the var, that should fail by default 😀