Can I use DrawImage on the same image from different threads?

[Raildex]

I generate "Buckets" which represent a small portion of a bigger image. The bucket images have their own memory.
Each bucket belongs to a thread.
Each Thread then uses

image.Mutate(l => l.DrawImage(bucketImage,new Point(bucket.X,bucket.Y),new Rectangle(0,0,bucket.W,bucket.H), PixelColorBlendingMode.Add, 1.0f));

The bucket dimensions (Bucket.X,Bucket.Y,Bucket.W,Bucket.H) do not overlap.

[JimBobSquarePants]

ImageSharp already stores larger buffers using discontiguous chunks so it's likely already split up.

It should be thread safe though so your approach should work.

[antonfirsov]

Do we guarantee Image APIs to be thread-safe though?

I would advice against this for performance reasons. Depending on the bucket sizes, and the size of image, this it might end up being very inefficient because of false sharing.

I would rather implement this with producer/consumer pattern, where the bucket threads post work to a thread owning the big image. Maybe System.Threading.Channels can help implementing this?

[JimBobSquarePants]

There’s no written guarantee but the implementations should be. Brushes were an issue in the past but we fixed that together.

Good link re false sharing!

[Raildex]

I've come back to Imagesharp and noticed that DrawImage isn't threadsafe.
My code is fairly complex and I will try to make an example, but Imagesharp does not seem to be thread safe when concurrently writing to an image.

Just as in my OP, i have a big image and use many smaller images (using Image.Wrap onto a RgbaVector Memory) to draw onto the bigger image.

The result when using C#'s lock on the big image:

the Result when not locking the big image:

Of course this is highly dependent on what I do and how many threads I use and like all race conditions this is not easy to reproduce. however, I get fairly consistent "artifacts" when removing the lock.

[JimBobSquarePants]

You’ll need to share some code here so I can replicate.