Crash when writing PNG in Parallel.ForEach on Magick.NET-Q8-x64 14.10.2

[junji19750412-lab]

Magick.NET version

14.10.2

Environment (Operating system, version and so on)

Windows 11 x64

Description

Summary

After upgrading to Magick.NET-Q8-x64 14.10.2, the process crashes when saving PNG images in parallel.
This did not occur in 14.10.1. JPEG are not affected.

The crash happens even when only loading and saving a PNG (no resize, no colorspace change).

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Environment

• OS: Windows 11 x64
• .NET Runtime: .NET 10.0.2
• Magick.NET: Magick.NET-Q8-x64 14.10.2
• CPU: x64
• Execution model: Parallel.ForEach

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Behavior

• Saving PNG images in Parallel.ForEach causes a process crash

• Exception observed:

  • ExecutionEngineException
  • Native crash during PNG write

• try/catch cannot catch the error (process terminates)

• The same code works correctly when executed sequentially

• The same code works correctly with Magick.NET-Q8-x64 14.10.1

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Not affected

• JPEG save (parallel): OK
• PNG save (sequential): OK
• PNG load only (parallel): OK

Steps to Reproduce

Reproduction steps

1. Prepare multiple PNG files

2. Run a Parallel.ForEach loop

3. Inside the loop:

   • Create a MagickImage from a PNG file
   • Immediately call Write() to save as PNG

4. Set MaxDegreeOfParallelism to 2 or higher

5. The process crashes during execution

Even a simple read + write of PNG files causes the crash.

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Additional notes

• ResourceLimits.Thread = 1 does not prevent the crash
• Q16-x64 was also tested and showed similar instability
• Setting ColorSpace or resizing is not required to reproduce
• The issue appears to be specific to the PNG encoder in 14.10.2

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Regression

✔ Works in 14.10.1
❌ Crashes in 14.10.2

This appears to be a regression related to PNG writing in multithreaded scenarios.

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Expected behavior

PNG images should be writable safely in parallel, or at least fail gracefully without crashing the process.

Thank you for your work on Magick.NET.

Images

Images: Not applicable (process crashes before output can be generated)

[junji19750412-lab]

Update / Clarification

After further investigation, I was able to narrow down the conditions.

• Saving PNG files in parallel without any modification works correctly.
• The crash occurs only when Resize is performed before saving PNG in a parallel loop.

In other words, the following combination causes the crash:

• PNG input
• Resize (e.g. Resize(new MagickGeometry("x1000")))
• Parallel.ForEach
• PNG Write

The same code works correctly:

• when executed sequentially
• or when Resize is skipped

This suggests the issue is related to PNG resize + write in multithreaded scenarios, not PNG write alone.

Additional observation (possibly related)

I also observed a similar crash with JPEG resizing in parallel:

• When img.ColorSpace = ColorSpace.sRGB is called before img.Resize(...), the process may crash.
• Moving the ColorSpace conversion after the Resize avoids the crash.

This does not occur in 14.10.1 and appears to be order-dependent in 14.10.2.

I am not sure if this is directly related to the PNG issue, but it may indicate a regression in color space handling during resize operations.

[dlemstra]

How can I reproduce this?

[junji19750412-lab]

Reproduction details update

I was able to further narrow down the root cause.

The crash is caused by the combination of:

Environment.SetEnvironmentVariable("MAGICK_OCL_DEVICE", "GPU")

Calling img.Resize(...)

Important observations:

If only MAGICK_OCL_DEVICE=GPU is set → no crash

If only img.Resize(...) is used → no crash

Both together cause a crash

This happens regardless of:

Image format (PNG or JPEG)

Execution model (Parallel.ForEach or sequential / single image)

The following minimal examples reproduce the issue.

Parallel case:

Environment.SetEnvironmentVariable("MAGICK_OCL_DEVICE", "GPU")

Parallel.ForEach(imgFiles,
New ParallelOptions With {.MaxDegreeOfParallelism = 10},
Sub(path)
Using img As New MagickImage(path)
img.Resize(New MagickGeometry("x1000"))
img.Write(outputPath)
End Using
End Sub)

Sequential case:

Environment.SetEnvironmentVariable("MAGICK_OCL_DEVICE", "GPU")

Using img As New MagickImage("01.jpg")
img.Resize(New MagickGeometry("x1000"))
img.Write("01_NEW.jpg")
End Using

In both cases, removing either the environment variable or the Resize call prevents the crash.

This suggests a problem related to OpenCL (GPU) acceleration combined with resize operations.

[dlemstra]

Earlier today I pushed a patch to fix something in the OpenCL initialization. I suspect that this is also causing the issue that you are experiencing. This will be resolved in the next release.

[junji19750412-lab]

Thank you for the quick investigation and fix.

I will test again once the release is available and report back if needed.