ImageSharp-762: Added methods to pre-seed AoT compiler on iOS #767
Conversation
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Hi @dmanning23 I've been putting some thought to this and I think I've come up with a good class design that will let us incrementally add workarounds for AOT compiler limitations without negatively impact the public API. This design allows you to call a single method at startup that will allow you to easily seed the compiler. // Seed a single pixel format.
AotCompiler.Seed<Rgba32>();
// Seed two pixel formats.
AotCompiler.Seed<Rgba24, Rgba32>();
// Seed three pixel formats.
AotCompiler.Seed<Gray8, Rgba24, Rgba32>();I'm assuming, I could be wrong of course, that you need to tell the compiler about each pixel format you intend to use. If not, great, we can simplify. // Copyright (c) Six Labors and contributors.
// Licensed under the Apache License, Version 2.0.
using SixLabors.ImageSharp.PixelFormats;
namespace SixLabors.ImageSharp.Advanced
{
/// <summary>
/// Unlike traditional Mono/.NET, code on the iPhone is statically compiled ahead of time instead of being
/// compiled on demand by a JIT compiler. This means there are a few limitations with respect to generics,
/// these are caused because not every possible generic instantiation can be determined up front at compile time.
/// The Aot Compiler is designed to overcome the limitations of this compiler.
/// </summary>
public static class AotCompiler
{
/// <summary>
/// Seeds the compiler using the given pixel format.
/// </summary>
/// <typeparam name="TPixel">The pixel format.</typeparam>
public static void Seed<TPixel>()
where TPixel : struct, IPixel<TPixel>
{
// This is we actually call all the individual methods you need to seed.
// TODO: Do the discovery work to figure out what works and what doesn't.
}
/// <summary>
/// Seeds the compiler using the given pixel formats.
/// </summary>
/// <typeparam name="TPixel">The first pixel format.</typeparam>
/// <typeparam name="TPixel2">The second pixel format.</typeparam>
public static void Seed<TPixel, TPixel2>()
where TPixel : struct, IPixel<TPixel>
where TPixel2 : struct, IPixel<TPixel2>
{
Seed<TPixel>();
Seed<TPixel2>();
}
/// <summary>
/// Seeds the compiler using the given pixel formats.
/// </summary>
/// <typeparam name="TPixel">The first pixel format.</typeparam>
/// <typeparam name="TPixel2">The second pixel format.</typeparam>
/// <typeparam name="TPixel3">The third pixel format.</typeparam>
public static void Seed<TPixel, TPixel2, TPixel3>()
where TPixel : struct, IPixel<TPixel>
where TPixel2 : struct, IPixel<TPixel2>
where TPixel3 : struct, IPixel<TPixel3>
{
Seed<TPixel, TPixel2>();
Seed<TPixel3>();
}
}
}Do you think this is a sensible approach? |
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Yeah, that makes perfect sense 👍 |
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@dmanning23 Glad you agree, thanks for your help on this. The build is failing just now due to trailing whitespace errors. I've got a pretty draconian set of rules in the repo that seem harsh but have kept us sane over the last few years. If you build locally in release you'll see the errors. |
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naw I dig it. All yall using StyleCopAnalyzer to setup those rules? I might set it up on a few projects of my own ;) |
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@dmanning thanks for this contribution! If it works for you I would say it's fine. One minor thing: I know there is no good way for testing this stuff without adding an AOT target in our CI, but I would feel more safe if there were unit tests which at least make sure these methods can be inoked without causing trouble. (Eg Exceptions) |
…ptions are thrown by AotCompiler
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@dmanning23 Is there anything else you would like to add, or does this cover it? |
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@JimBobSquarePants @dmanning23 just one other thing: How about ˛renaming |
YES! Much better 👍 |
Codecov Report
@@ Coverage Diff @@
## master #767 +/- ##
==========================================
- Coverage 88.52% 88.52% -0.01%
==========================================
Files 1003 1005 +2
Lines 42738 42763 +25
Branches 3150 3150
==========================================
+ Hits 37834 37854 +20
- Misses 4212 4218 +6
+ Partials 692 691 -1
Continue to review full report at Codecov.
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Aight, got that last change in to rename to AotCompilerTools. @JimBobSquarePants Yeah, this is ready to merge in whenever yall are OK with it 👍 |
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Merged and thanks you! |
Prerequisites
Description
These changes add a few methods to get around the problems described in #762.
Basically, the heavy use of generics in ImageSharp is too much to figure out for the ahead-of-time compiler used in Xamarin.iOS. When a user tries to call the SaveAsGif method on an iOS device, it has to spin up the JIT compiler to build the necessary code... however iOS is strictly AoT, so this is an illegal op and throws an exception.
All these changes do is add a few methods that can be used to pre-seed the necessary code in the AoT compiler on iOS for the OctreeQuantizer used in the SaveAsGif method. I saw a few more of these exceptions in the WuQuantizer and the dithering processors. If yall are ok with this recipe for fixing these errors, I can add a few more of these stubs.
Cheers!