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Reduced some allocations in QRCodeGenerator (NETCORE_APP only)#595

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codebude merged 10 commits intoShane32:masterfrom
gfoidl:perf
Sep 30, 2025
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Reduced some allocations in QRCodeGenerator (NETCORE_APP only)#595
codebude merged 10 commits intoShane32:masterfrom
gfoidl:perf

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@gfoidl gfoidl commented Jun 16, 2025

Profiling showed that there are some allocations in QRCodeGenerator that can be quite easily avoided.

simple console app for profiling 
using System.Diagnostics;
using QRCoder;

string payload = $"""
    Time    : {DateTimeOffset.Now:O}
    Machine : {Environment.MachineName}
    Activity: {Activity.Current?.RootId}
    """;

int len = 0;

for (int i = 0; i < 1_000; ++i)
{
    string imgSrc = GetQRCode("sdfsdf");
    len += imgSrc.Length;
}

Console.WriteLine(len);

static string GetQRCode(string payload)
{
    using QRCodeGenerator qrCodeGenerator = new();
    using QRCodeData qrCodeData = qrCodeGenerator.CreateQrCode(payload, QRCodeGenerator.ECCLevel.Q);
    using Base64QRCode qrCodeBase64 = new(qrCodeData);
    string base64QRCode = qrCodeBase64.GetGraphic(20);
    return $"data:image/png;base64,{base64QRCode}";
}

Allocations are removed / avoided for:

  • Dictionary<,>.Entry[]
  • QRCodeGenerator.PolynomItem[]
  • Dictionary<,>

The change is done only for .NET (Core) targets, as Span<T> is used.
By adding a reference to System.Memory package this change could also be done for .NET Desktop.

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Before

before

After

after

Benchmarks

Before

| Method              | Mean        | Error     | StdDev    | Gen0   | Allocated |
|-------------------- |------------:|----------:|----------:|-------:|----------:|
| CreateQRCode        |    235.2 μs |   4.50 μs |   5.00 μs | 2.1973 |    7.2 KB |
| CreateQRCodeLong    |  2,684.9 μs |  48.00 μs |  44.89 μs | 7.8125 |  33.25 KB |
| CreateQRCodeLongest | 16,264.4 μs | 317.90 μs | 485.47 μs |      - |  79.69 KB |

After

| Method              | Mean        | Error     | StdDev    | Gen0   | Allocated |
|-------------------- |------------:|----------:|----------:|-------:|----------:|
| CreateQRCode        |    232.0 μs |   4.63 μs |   6.64 μs | 0.9766 |   4.38 KB |
| CreateQRCodeLong    |  2,574.1 μs |  41.97 μs |  39.26 μs | 3.9063 |     12 KB |
| CreateQRCodeLongest | 15,573.7 μs | 292.90 μs | 259.65 μs |      - |  48.24 KB |

gfoidl
gfoidl commented Jun 16, 2025
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Shane32
Shane32 reviewed Jun 16, 2025
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Shane32 commented Jun 16, 2025

By adding a reference to System.Memory package this change could also be done for .NET Desktop.

I wouldn't. There has been so many performance enhancements in .NET Core since .NET Framework, that if anyone wants better performance, they should use .NET Core. And I'm sure the fallback performance is plenty good enough anyway.

@Shane32
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Shane32 commented Jun 16, 2025

The reduction in allocations is very impressive!

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Shane32 commented Jun 16, 2025

I fixed the CI scripts in #592 btw

Shane32
Shane32 approved these changes Jun 16, 2025
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Looks good to me! (subject to tests passing, of course)

@gfoidl
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gfoidl commented Jun 17, 2025

I fixed the CI scripts in #592 btw

Should that change be separated into a own PR to fix CI?

Otherwise every PR has to re-do the same until your PR gets merged.

@Shane32 thanks for your review and comments 👍🏻

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Shane32 commented Jun 17, 2025

Should that change be separated into a own PR to fix CI?

Honestly yes…

@gfoidl
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gfoidl commented Jun 17, 2025

Found some more allocation that can be quite easily avoided.

| Method              | Mean        | Error     | StdDev    | Gen0   | Allocated |
|-------------------- |------------:|----------:|----------:|-------:|----------:|
| CreateQRCode        |    240.0 μs |   4.57 μs |   4.89 μs | 1.2207 |   4.07 KB |
| CreateQRCodeLong    |  2,730.3 μs |  41.85 μs |  37.10 μs |      - |  11.05 KB |
| CreateQRCodeLongest | 17,367.9 μs | 345.33 μs | 657.03 μs |      - |  46.42 KB |

(note: time column isn't really comparable to results in top post (different machine), so only allocations count here)

gfoidl
gfoidl commented Jun 17, 2025
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codebude commented Sep 27, 2025

Hi @gfoidl ,

since QRCoder will reach its end of life and the repository will be archived on November 1st, 2025, I’d like to clarify how to proceed with this PR.

Would you prefer me to merge it before the archival, or should I close it instead?
Please let me know what you think – I want to handle your contribution in the way that feels most appropriate to you.

Thanks again for your effort and contribution!

@gfoidl
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gfoidl commented Sep 28, 2025

As written in #605 (comment) I'd like that the repo here continues to live, and don't be archived, so please merge the PR as it brings goodness to your baby QRCoder.

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Shane32 commented Sep 30, 2025

@gfoidl if you merge in master, tests should run properly now

@codebude codebude merged commit 9ed6c79 into Shane32:master Sep 30, 2025
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@gfoidl gfoidl deleted the perf branch September 30, 2025 22:17
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