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Make TestFile Image threadsafe. #2225

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Merged
merged 3 commits into from
Sep 14, 2022
Merged

Make TestFile Image threadsafe. #2225

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9fdaac8
Use Interlocked.CompareExchange
JimBobSquarePants Sep 12, 2022
c5d893a
Use simple lock for readability
JimBobSquarePants Sep 13, 2022
2515d80
Initialize the locker!
JimBobSquarePants Sep 13, 2022
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26 changes: 24 additions & 2 deletions tests/ImageSharp.Tests/TestFile.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -4,6 +4,7 @@
using System;
using System.Collections.Concurrent;
using System.IO;
using System.Threading;
using SixLabors.ImageSharp.Advanced;
using SixLabors.ImageSharp.Formats;
using SixLabors.ImageSharp.PixelFormats;
Expand All @@ -29,7 +30,7 @@ public sealed class TestFile
/// <summary>
/// The image (lazy initialized value)
/// </summary>
private Image<Rgba32> image;
private volatile Image<Rgba32> image;

/// <summary>
/// The image bytes
Expand Down Expand Up @@ -65,7 +66,28 @@ public sealed class TestFile
/// <summary>
/// Gets the image with lazy initialization.
/// </summary>
private Image<Rgba32> Image => this.image ??= ImageSharp.Image.Load<Rgba32>(this.Bytes);
private Image<Rgba32> Image
{
get
{
Image<Rgba32> img = this.image;
if (img is null)
{
Image<Rgba32> loadedImg = ImageSharp.Image.Load<Rgba32>(this.Bytes);
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@br3aker br3aker Sep 13, 2022 •
edited
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Well, we can do a double check lock instead so image would never be loaded twice:

// this.image should be marked volatile still
if (this.image is null)
{
    lock (this.lockObject)
    {
        if (this.image is null)
        {
            this.image = ImageSharp.Image.Load<Rgba32>(this.Bytes);
        }
    }
}
return this.image;

I proposed Interlocked solution, I know, but lock solution is a lot more readable IMO and doesn't have a possible flaw of loading the same image twice. It's also isn't slow on reads due to locking as most of the time first if check would be true.

Maybe we should use it instead due to simplicity?

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@JimBobSquarePants JimBobSquarePants Sep 13, 2022

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Definitely far more readable. I’m happy to switch out

img = Interlocked.CompareExchange(location1: ref this.image, value: loadedImg, comparand: null);
if (img is not null)
{
loadedImg.Dispose();
}
else
{
img = loadedImg;
}
}

return img;
}
}

/// <summary>
/// Gets the input image directory.
Expand Down