[BUG] ToTextureImage causes Native Crash (1.68.2-preview.39)

[nor0x]

Description
I'm using an SKGLView on macOS to render some SKImage objects - since the latest preview build introduces ToTextureImage i wanted to use this to create the SKImage object on the GPU. This causes the following native crash for me

Code

=================================================================
	Native Crash Reporting
=================================================================
Got a SIGSEGV while executing native code. This usually indicates
a fatal error in the mono runtime or one of the native libraries 
used by your application.
=================================================================

=================================================================
	Native stacktrace:
=================================================================
	0x109680d38 - /Users/dev/test.MacOS/bin/Debug/test.app/Contents/MacOS/test : mono_dump_native_crash_info
	0x109674555 - /Users/dev/test.MacOS/bin/Debug/test.app/Contents/MacOS/test : mono_handle_native_crash
	0x1099bfb33 - /Users/dev/test.MacOS/bin/Debug/test.app/Contents/MacOS/test : altstack_handle_and_restore.cold.1
	0x1095f26ac - /Users/dev/test.MacOS/bin/Debug/test.app/Contents/MacOS/test : altstack_handle_and_restore
	0x7fff3a333980 - /System/Library/Frameworks/OpenGL.framework/Versions/A/Libraries/libGL.dylib : glGenTextures
	0x10a28226c - /Users/dev/test.MacOS/bin/Debug/test.app/Contents/MonoBundle/libSkiaSharp.dylib : gr_backendrendertarget_get_gl_framebufferinfo
	0x10a281e76 - /Users/dev/test.MacOS/bin/Debug/test.app/Contents/MonoBundle/libSkiaSharp.dylib : gr_backendrendertarget_get_gl_framebufferinfo
	0x10a1a672c - /Users/dev/test.MacOS/bin/Debug/test.app/Contents/MonoBundle/libSkiaSharp.dylib : gr_backendrendertarget_get_gl_framebufferinfo
	0x10a1a67d4 - /Users/dev/test.MacOS/bin/Debug/test.app/Contents/MonoBundle/libSkiaSharp.dylib : gr_backendrendertarget_get_gl_framebufferinfo
	0x10a1cdecb - /Users/dev/test.MacOS/bin/Debug/test.app/Contents/MonoBundle/libSkiaSharp.dylib : gr_backendrendertarget_get_gl_framebufferinfo
	0x10a1b3006 - /Users/dev/test.MacOS/bin/Debug/test.app/Contents/MonoBundle/libSkiaSharp.dylib : gr_backendrendertarget_get_gl_framebufferinfo
	0x10a1cd9f6 - /Users/dev/test.MacOS/bin/Debug/test.app/Contents/MonoBundle/libSkiaSharp.dylib : gr_backendrendertarget_get_gl_framebufferinfo
	0x10a1b4b3f - /Users/dev/test.MacOS/bin/Debug/test.app/Contents/MonoBundle/libSkiaSharp.dylib : gr_backendrendertarget_get_gl_framebufferinfo
	0x10a1e5b17 - /Users/dev/test.MacOS/bin/Debug/test.app/Contents/MonoBundle/libSkiaSharp.dylib : gr_backendrendertarget_get_gl_framebufferinfo
	0x10a1b345c - /Users/dev/test.MacOS/bin/Debug/test.app/Contents/MonoBundle/libSkiaSharp.dylib : gr_backendrendertarget_get_gl_framebufferinfo
	0x10a1eab72 - /Users/dev/test.MacOS/bin/Debug/test.app/Contents/MonoBundle/libSkiaSharp.dylib : gr_backendrendertarget_get_gl_framebufferinfo
	0x10a0fcf0d - /Users/dev/test.MacOS/bin/Debug/test.app/Contents/MonoBundle/libSkiaSharp.dylib : gr_backendrendertarget_get_gl_framebufferinfo
	0x10a0fcfba - /Users/dev/test.MacOS/bin/Debug/test.app/Contents/MonoBundle/libSkiaSharp.dylib : gr_backendrendertarget_get_gl_framebufferinfo
	0x10a1a8d11 - /Users/dev/test.MacOS/bin/Debug/test.app/Contents/MonoBundle/libSkiaSharp.dylib : gr_backendrendertarget_get_gl_framebufferinfo
	0x10a1e776c - /Users/dev/test.MacOS/bin/Debug/test.app/Contents/MonoBundle/libSkiaSharp.dylib : gr_backendrendertarget_get_gl_framebufferinfo
	0x10a1e88ff - /Users/dev/test.MacOS/bin/Debug/test.app/Contents/MonoBundle/libSkiaSharp.dylib : gr_backendrendertarget_get_gl_framebufferinfo
	0x10a2b831b - /Users/dev/test.MacOS/bin/Debug/test.app/Contents/MonoBundle/libSkiaSharp.dylib : gr_backendrendertarget_get_gl_framebufferinfo
	0x10a2b81d1 - /Users/dev/test.MacOS/bin/Debug/test.app/Contents/MonoBundle/libSkiaSharp.dylib : gr_backendrendertarget_get_gl_framebufferinfo
	0x109fc065a - /Users/dev/test.MacOS/bin/Debug/test.app/Contents/MonoBundle/libSkiaSharp.dylib : sk_image_make_texture_image
	0x13f30f4dc - Unknown

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	Telemetry Dumper:
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Pkilling 0x70000a93f000 from 0x700007971000
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Pkilling 0x700006d5f000 from 0x700007971000
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Pkilling 0x700009f30000 from 0x700007971000
Pkilling 0x700007368000 from 0x700007971000
Pkilling 0x70000a539000 from 0x700007971000
Pkilling 0x700007f7a000 from 0x700007971000
Pkilling 0x70000890f000 from 0x700007971000
Pkilling 0x700008583000 from 0x700007971000
Pkilling 0x700008f18000 from 0x700007971000
Pkilling 0x700005fc4000 from 0x700007971000
Pkilling 0x700009521000 from 0x700007971000
Pkilling 0x7000065cd000 from 0x700007971000
Pkilling 0x700009b2a000 from 0x700007971000
Pkilling 0x700006f62000 from 0x700007971000
Pkilling 0x70000a133000 from 0x700007971000
Pkilling 0x70000756b000 from 0x700007971000
Pkilling 0x70000a73c000 from 0x700007971000
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* Assertion: should not be reached at /Users/builder/jenkins/workspace/archive-mono/2019-08/mac/release/mono/metadata/threads.c:6254
Pkilling 0x700009724000 from 0x700007971000
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Pkilling 0x700009d2d000 from 0x700007971000
Pkilling 0x700007165000 from 0x700007971000
Pkilling 0x70000a336000 from 0x700007971000
Pkilling 0x70000776e000 from 0x700007971000
Entering thread summarizer pause from 0x700007971000
Thread started: <Thread Pool> #44
Thread started: <Thread Pool> #45
Finished thread summarizer pause from 0x700007971000.

Waiting for dumping threads to resume

=================================================================
	External Debugger Dump:
=================================================================
(lldb) command source -s 0 '/tmp/mono-gdb-commands.22028'
Executing commands in '/tmp/mono-gdb-commands.22028'.
(lldb) process attach --pid 22028

Expected Behavior
image object should be created on the GPU without errors

Actual Behavior
application crashes

Basic Information

• Version with issue: 1.68.2-preview.29

• IDE: Visual Studio for Mac

• Platform Target Frameworks:

  • macOS: 10.15.3 (19D76)
    Target Devices:
  • MacBook Pro (13-inch, 2018, Four Thunderbolt 3 Ports) | 16 GB 2133 MHz LPDDR3 | 2,3 GHz Quad-Core Intel Core i5 | Intel Iris Plus Graphics 655 1536 MB

Reproduction Link

https://github.com/nor0x/SkiaSharp_PerfomanceExperiments/tree/master/Xamarin.Forms

[mattleibow]

This is a very late reply, but I looked into this and the crash is because macOS doesn't do the correct checks that it should.

However, the reason for any error is that what is happening is that the ToTextureImage is trying to copy the image to the GPU via the current OpenGL context. But, on a button click, the context is not set/valid. This might be because the OS is using the GL context, or some other control is has changed to its own context. Before calling this, you have to make sure that you have set the view to be in control.

Right now, there is no way to indicate that the view must set its GL context to be current, so I would suggest adjusting the logic to rather queue the copy and then wait until the next draw operation to actually copy.

In fact, the way you have your code, you can do this with minimal code changes. Just 2 places:

void AddImage_Clicked() {
//    var im = SKImage.FromEncodedData(_buffer.ElementAt(index)).ToTextureImage(SkiaView.GRContext);
    var im = SKImage.FromEncodedData(_buffer.ElementAt(index));
}

void Handle_PaintSurface() {

    // convert all images to textures
    if (!img.Image.IsTextureBacked)
        img.Image = img.Image.ToTextureImage(SkiaView.GRContext);

    e.Surface.Canvas.DrawImage(img.Image, img.Destination, p);
}

Obviously, we should look into the crash part and see if we can either throw a native exception or return null.