Software Engineering

Improved Application Performance with .NET 7

January 25, 2023January 25, 2023 Pranav Negandhi

Speed has been a big selling point for .NET 7. Stephen Toub has written an extremely lengthy and detailed article back in August 2022 about all the performance improvements that went into it. And it’s ridiculously easy to take advantage of the speed boost in your own applications. In most cases, it only requires recompiling your project to target the new runtime. Developers who don’t make the switch are leaving a lot of performance gains on the table. I took some effort to measure the speed improvements by running some benchmarks on my own projects.

Shades is a .NET port of the Python module of the same name, for creating generative art. The module was originally authored by Ben Rutter. The library operates by decomposing any drawing operation, no matter how complex, into a series of single-pixel modifications, executed one at a time, across the entire bitmap. To draw a line, the library first calculates every pixel that makes the line, then iterates through that list to compute its colour value, and making a discrete set pixel call for it. Drawing primitive shapes using solid colours is delegated to the much faster SkiaSharp library. But all the more advanced effects which have no equivalent operation in SkiaSharp have to be done with custom routines.

So of course it is slow. And anything that makes it go faster is a welcome improvement.

For this exercise, I chose the PixelsInsideEdge method, which operates on the coordinates that make up the outer edge of a shape, and identifies the pixels that fall within that boundary. It uses a simplified implementation of a ray-casting algorithm to determine whether a point is within the shape boundary or falls outside of it.

public ICollection<SKPoint> PixelsInsideEdge(ICollection<SKPoint> edgePixels)
{
    /// Contains a list of distinct values along the X axis, extracted from edgePixels.
    /// Each unique value along the X axis corresponds to a list of unique values along
    /// the Y axis that intersect with the X coordinate.
    var xs = new SortedDictionary<int, SortedSet<int>>();
    int minX = int.MaxValue, minY = int.MaxValue, maxX = int.MinValue, maxY = int.MinValue;
    foreach (var e in edgePixels)
    {
        var ex = Convert.ToInt32(e.X);
        var ey = Convert.ToInt32(e.Y);
        maxX = Math.Max(maxX, ex);
        minX = Math.Min(minX, ex);
        maxY = Math.Max(maxY, ey);
        minY = Math.Min(minY, ey);

        if (xs.TryGetValue(ex, out var points))
        {
            points.Add(ey);
        }
        else
        {
            xs[ex] = new SortedSet<int>() { ey };
        }
    }

    /// Contains a list of points that make up the inside of the shape formed by the
    /// bounds of edgePixels.
    var innerPixels = new List<SKPoint>();
    for (var x = minX; x <= maxX; x++)
    {
        var ys = xs[x];

        /// Find the lowest values along the Y axis, i.e. values
        /// that make up the lower edge of the shape.
        var temp = new SortedSet<int>();
        foreach (var y in ys)
        {
            if (!ys.TryGetValue(y - 1, out var _))
            {
                temp.Add(y);
            }
        }

        var rayCount = 0;
        for (var y = temp.Min; y <= temp.Max; y++)
        {
            if (temp.TryGetValue(y, out var _))
            {
                rayCount++;
            }

            if (rayCount % 2 == 1)
            {
                innerPixels.Add(new SKPoint(x, y));
            }
        }
    }

    innerPixels.AddRange(edgePixels);

    return innerPixels;
}

It was executed on a circular shape having a radius of 2048 pixels. This method identified 12869 points enclosed within its boundary. The location of the shape on the canvas had no effect. Negative coordinates were also calculated and stored in the result. The benchmark only ran the geometric computations. It did not perform any modifications on the image itself.

[Benchmark]
[ArgumentsSource(nameof(LargeDataSource))]
public ICollection<SKPoint> PixelsInsideEdgeCollection(SKPoint[] Edges) => shade.PixelsInsideEdge(Edges);

public static IEnumerable<SKPoint[]> LargeDataSource()
{
    var shade = new BlockShade(SKColor.Empty);

    yield return shade.GetCircleEdge(new SKPoint(0, 0), 2048.0f).ToArray();
}

The results of this benchmark are shown below.

dotnet run -c Release --filter PixelsInsideEdgeCollection --runtimes \
net5.0 net6.0 net7.0

// * Summary *

BenchmarkDotNet=v0.13.4, OS=Windows 11 (10.0.22621.1105)
AMD Ryzen 5 5600H with Radeon Graphics, 1 CPU, 12 logical and 6 physical cores
.NET SDK=7.0.102
[Host] : .NET 5.0.17 (5.0.1722.21314), X64 RyuJIT AVX2
Job-SOHORL : .NET 5.0.17 (5.0.1722.21314), X64 RyuJIT AVX2
Job-PPCKCW : .NET 6.0.13 (6.0.1322.58009), X64 RyuJIT AVX2
Job-EBVIPG : .NET 7.0.2 (7.0.222.60605), X64 RyuJIT AVX2


|           Method |  Runtime |          Edges |     Mean | Ratio |
|----------------- |--------- |--------------- |---------:|------:|
| PixelsInsideEdge | .NET 5.0 | SKPoint[12869] | 217.7 ms |  1.00 |
| PixelsInsideEdge | .NET 6.0 | SKPoint[12869] | 213.2 ms |  0.98 |
| PixelsInsideEdge | .NET 7.0 | SKPoint[12869] | 161.9 ms |  0.75 |

But what does this mean for the performance of the application as a whole? To test this, I ran Doom Fire, which replicates the effect from the title screen of the classic video game. I generated a 5 second animated sequence of images in sizes of 128 × 128, 256 × 128, 512 × 128 and 1024 × 128 pixels.

These three videos show the output of the effect at 128 × 128 pixels (top left), 256 × 128 pixels (top centre), and 512 × 128 pixels (above).

The height of the image was restricted to minimise the amount of empty pixels being pushed during the test. Time elapsed was measured with an instance of System.Diagnostics.Stopwatch. Each test was first run 5 times to warm up the JIT and allow the progressive compiler to thoroughly kick in and optimise the code. The results of these warm-up tests were discarded. Then 3 further iterations were run, and the fastest result was considered for comparison.

|  Runtime |           Size |    Time |
|--------- |---------------:|--------:|
| .NET 5.0 |   128 x 128 px | 13.59 s |
| .NET 5.0 |   256 x 128 px | 13.74 s |
| .NET 5.0 |   512 x 128 px | 25.67 s |
| .NET 5.0 |  1024 x 128 px | 49.17 s |

|  Runtime |           Size |    Time |
|--------- |---------------:|--------:|
| .NET 7.0 |   128 x 128 px | 13.35 s |
| .NET 7.0 |   256 x 128 px | 13.52 s |
| .NET 7.0 |   512 x 128 px | 23.23 s |
| .NET 7.0 |  1024 x 128 px | 44.53 s |

This wasn’t quite as stark an improvement as a standalone microbenchmark. A single method being executed in quick succession has vastly different performance characteristics from a complete application. This benchmark also saved the frame to disk, which adds an I/O penalty. As expected, smaller data sets showed minimal variation. The numbers started diverging as the magnitude of data increased.

Conclusion

Based on the standard benchmarks, .NET 5 and 6 show similar performance. With .NET 5 now out of support, and .NET 7 being earmarked as a short-term support release, developers are likely to upgrade to .NET 6 instead of .NET 7. And .NET 6 has an additional 6 months of support over .NET 7. There are many customers who would accept the tradeoff of slower runtime execution for longer official support. If your application is performance sensitive, it’s a no-brainer that you must move to .NET 7. But even otherwise, if you can risk the shorter support cycle (and .NET 8 will certainly be released by then), it may be a worthwhile investment to consider targeting your application for .NET 7 instead.

Breaking Circular Dependencies in Microsoft DI with Lazy Resolution

January 18, 2023January 19, 2023 Pranav Negandhi

The service locator pattern is understandably looked down upon. I’m not the kind to get swept away with hubris, but injecting a service provider into other classes, and telling them to pick whatever they like out of it is just global variables with more steps.

There are certain cases where this is the most straightforward solution to a problem. But this anti-pattern can still be avoided with a bit of thought. This is a real-world scenario that I faced few months back.

Background

A wizard is a UI pattern that is used to guide the user through the stages of a process (a license key verification and user registration in this case). I wrote a simple application that would lead the user through each step.

Welcome and short instruction note.
License Key Entry and verification.
Registration Form input and validation.
Review form input.
Completion.

But there may be cases when somebody might need to change their license key after it has been entered. For this, the application had a button to go back to the previous screen.

Each screen was implemented in its own class as a window object. It would be ideal if the screen object would be injected wherever needed through Microsoft Dependency Injection. The Welcome class would receive a reference to License Key Entry, which would receive a reference to the Registration Form, and so on. But some of the screens also needed a reference to the previous screen. Registration Form would require a reference to License Key Entry. Confirmation would require a reference to the Registration Form.

This would create a circular dependency, which is not supported by Microsoft Dependency Injection.

public class LicenseKeyEntry : Form
{
    public LicenseKeyEntry(RegistrationForm next) { … }
}

public class RegistrationForm : Form
{
    public RegistrationForm(LicenseKeyEntry previous, Confirmation next) { … }
}

private static void ConfigureHostServices(HostBuilderContext _, IServiceCollection services)
{
    …
    services.AddSingleton<LicenseKeyEntry>();
    services.AddSingleton<RegistrationForm>(); /// Welp! Circular dependency!
    …
}

System.InvalidOperationException: A circular dependency was detected for the service of type ‘LicenseKeyEntry’.

My first instinct was that this was an impossible problem to solve. Classes need references. References must come from the DI container. The container won’t allow creating circular dependencies between types. Just hand over a reference to the service provider to the objects, and let them ask for whatever objects they need at runtime.

public class RegistrationForm : Form
{
    private IServiceProvider _services;

    /// Don't do this!
    public RegistrationForm(IServiceProvider services)
    {
        _services = services;
    }

    public void Next()
    {
        var next = services.GetRequiredService<Confirmation>();
        …
    }

    public void Previous()
    {
        var previous = services.GetRequiredService<LicenseKeyEntry>();
        …
    }
}

But this reeks of a code smell. The class was now bound to the types in the specific dependency injection framework. Switching over to another framework or removing it altogether would be difficult. Testing and mocking became more complicated, because the unit tests would now have to inject DI container, which would contain the mock types.

A Workaround

While the approach shown above is not advisable, it does demonstrate the strategy of using lazy resolution to break circular dependencies. .NET contains a built-in Lazy<T> type that can be leveraged for the job.

Begin by changing the constructor signatures to use Lazy<T>, where T is the actual type that is required.

public RegistrationForm(Lazy<LicenseKeyEntry> previous, Lazy<Confirmation> next) { … }

Then, inject the Lazy types into the service container.

services.AddSingleton<LicenseKeyEntry>();
services.AddSingleton<RegistrationForm>();
services.AddSingleton<Confirmation>();
services.AddTransient<Lazy<RegistrationForm>>();
services.AddTransient<Lazy<LicenseKeyEntry>>();
services.AddTransient<Lazy<Confirmation>>();

This removes the circular dependency because these types don’t have a direct reference to each other. But it’s important that the value of the dependent types is not realised in the constructor. They should continue to hold a reference to the Lazy<T> type instead, and only reify the underlying instance later down the line.

public class RegistrationForm : Form
{
    private Lazy<LicenseKeyEntry> _previous;
    private Lazy<Confirmation> _next;

    public RegistrationForm(Lazy<LicenseKeyEntry> previous, Lazy<Confirmation> next)
    {
        _previous = previous;
        _next = next;
    }

    public void Next()
    {
        var next = _next.Value;
        …
    }

    public void Previous()
    {
        var previous = _previous.Value;
        …
    }
}

Addendum

Thomas Levesque wrapped this into an elegant implementation that is exposed by a simple extension method on the service collection. The full article is available on his blog.

public static class ServiceCollectionExtensions
{
    public static IServiceCollection AddLazyResolution(this IServiceCollection services)
    {
        return services.AddTransient(typeof(Lazy<>), typeof(LazilyResolved<>));
    }

    private class LazilyResolved<T> : Lazy<T>
    {
        public LazilyResolved(IServiceProvider serviceProvider) : base(serviceProvider.GetRequiredService<T>)
        {
        }
    }
}

Porting a Windows Forms Application to .NET – Part 2

December 28, 2022January 18, 2023 Pranav Negandhi

Previously, I described the legacy of the Vertika Player, the bottlenecks in its initial development, some elementary efforts to refactor the code, and a major roadblock that came from the deprecation of the Flash Player.

Once we decided to move to .NET, work began in full earnest. Enthusiasm was running high, and nothing seemed impossible. Don’t mind the old code. It was trash. We’d rewrite everything from scratch! Heck, we were so smart, we could do it twice over. But this fervour lasted all of 15 minutes before we folded up and rolled back all our changes.

I’m exaggerating, of course. We did write a new application shell from scratch, using newer APIs like the Microsoft.Extensions.Hosting.IHost interface and its dependency injection framework for some of the most fundamental classes that were needed. But there was immense pressure to get the product out of the door. Remember that the Flash Player uninstaller was well and truly active now, and support staff were working overtime to keep up with restoring it every time it got nuked. After a couple of weeks of this effort, the enormity of the exercise hit us and we fell back to copying files wholesale from the old code-base. On the brighter side, in spite of rewriting only a small portion of the code, the groundwork had been laid for more significant breakthroughs in the near future.

The singular monolith had been deconstructed into separate projects based on functionality, such as the primary executable, model classes, and the web API host. Over the following months, we added more projects to isolate critical portions of data synchronisation, the network download library (eventually replaced by the Downloader library, written by Behzad Khosravifar) and background services.

A SOAP-y Muddle

There’s a significant chunk of the application functionality that depends on communicating with a remote SOAP service (stop sniggering; this stuff is from 15 years ago). Visual Studio continues to provide tools to automatically generate a SOAP client from a service. But the output does not maintain API compatibility with the client generated with earlier versions of the tool. Among the methods missing from the new client are the synchronous variants of the service calls, which, unfortunately, were a mainstay in the earlier application code.

That’s right. Microsoft used to ship tools that allowed developers to make synchronous network calls.

But this is all gone now. And I had a problem on my hands.

public void ClickHandler(object sender, MouseEvent e)
{
    var users = serviceClient.GetUsers();
}

CS1061	'ServiceClient' does not contain a definition for 'GetUsers' and no accessible extension method 'GetUsers' accepting a first argument of type 'object' could be found (are you missing a using directive or an assembly reference?)

Welp!

Calling asynchronous code from previously written synchronous methods was not going to be easy. Web service calls were tightly integrated in many classes that were still oversized even after aggressive refactoring. Stephen Cleary’s AsyncEx library came to our rescue. Asynchronous method invocations were wrapped inside calls to AsyncContext.Run(), which we liberally abused to build a synchronous abstraction over the TAP interface.

public void ClickHandler(object sender, MouseEvent e)
{
    var users = AsyncContext.Run(serviceClient.GetUsersAsync());
}

This was much better than the alternative of calling Wait() or Result directly on the task. In addition to blocking what could potentially be the UI thread, it would also wrap any exceptions thrown during the invocation into an additional AggregateException. And anybody who’s dealt with InnerException hell knows how bad that can be.

The second API incompatibility was in the collection types returned from the service. The earlier service client returned a System.Data.DataSet type for collections. This was changed to a new type called ArrayOfXElement. Fortunately, this was an easy fix with a simple extension method to convert the ArrayOfXElement into a DataSet.

Wrapping Up and Rolling Out

The hour of reckoning arrived about 5 months later, when we finally removed references to the Flash Player ActiveX control from the project, replacing them with the WebView2 control. The minuscule amount of effort required of this step belies the enormity of its significance. Flash had been our rendering mainstay for over a decade. All those thousands of man-hours invested into the application were gone in a blink of an eye, replaced with a still-wet-behind-the-ears port to Blazor. This was the first time in the history of the company that legacy code was discarded entirely, and rewritten from scratch on an empty slate.

The new product was deployed to several test sites for a month to ensure that everything worked as expected. And other than a few basic layout errors, there were no problems that we encountered. The porting exercise was a success, and offered a major lifeline to the business.

Porting a Windows Forms Application to .NET – Part 1

December 24, 2022January 18, 2023 Pranav Negandhi

In a time when every dinky software company is writing massive systems that run in The Cloud™, it’s a source of astonishment for some to hear about my continued work on a desktop application. It’s not quite the same effort as synchronising 5K posts per second with millions of followers. But it does have its high notes nevertheless.

Understanding the Legacy

Like many products from early-stage startups, the first iteration of the Vertika Player was built as a proof-of-concept. The objective was to fetch text, video and images from a web service and play it on a large screen. But the underlying Windows Forms framework wasn’t really geared towards rendering multimedia content. So a separate application was written in ActionScript, which was hosted inside the Windows Forms application through the Flash Player ActiveX control.

Even during those days, web development was topping the list of desired programming skills. Nobody on the original team had significant experience engineering a desktop application. As a result, it came to be that most of the code got piled into the main window class, a couple of static utility classes, and a single god class containing approximately 200 public fields to maintain application state. The latter was referenced hither and yon all over the project. It was awful. The project was so fragile that even changing a simple network port number was fraught with risk of breakages in parts of the application that had nothing to do with networking.

Apparently, none of the programmers understood the significance of the UI thread, or even basic threading in general. Resource contentions were handled with a hail Mary running inside an infinite loop.

while (!result)
{
    try
    {
        xmlDoc.Save(FilePath);
        result = true;
    }
    catch (Exception exception)
    {
        log.Error("An error occurred while saving to disk");
    }
}

There were some hard to replicate bugs that reared their heads at times. Support incidents came up occasionally about missing content, or false alarms were raised when the telemetry and monitoring thread went awry. A particularly egregious bug was the cause for occasional runaway file downloads that never stopped, appending the same sequence of bytes in a file ad infinitum. To the end user, the file would seem to grow continuously until it filled the entire hard disk.

But in spite of all these issues, the application worked as expected more often than it didn’t. It generated steady revenue from paying customers who were mostly pleased with its performance. Support staff had formulated scripts for almost every scenario that they were likely to encounter. They could identify symptoms and were able to get in and resolve the problem quickly.

Ringing in the New

Teams changed, until there was nobody left who had worked on the first iteration of the product.

New features were gradually added over time. But architectural issues continued to fester, while more lines of code were added to already expansive classes. At one time, the main window class exceeded 5,000 lines of code. It wasn’t a pleasant experience maintaining this project. But the one thing that we all agreed upon was that we would never discard the project and start from scratch. We bided our time and waited for an opportunity to refactor the application.

We got our foot in when customers started reporting stutter during playback after minor update. Telemetry reports had to include a screen shot of the running application. But due to data caps at many locations, captured images used to be down-sampled to postage stamp sizes before uploading. Network capacities had recently been improved, and screen shot dimensions were increased accordingly.

Herein lay the catch. A 100 pixel square image is about 2 KB in size. But a 500 pixel square accounts for a 25x increase in data. The code to upload the image was being executed on the UI thread, blocking it while the network request was completing. This was imperceptible when the file sizes were small. But it became immediately noticeable once the images sizes were increased. It was glaringly obvious during playback of video because of periodic frame freeze that occurred while an image was uploaded.

We chose the expeditious fix for the time being. Instead of directly calling the upload method, it was wrapped into a WaitCallback delegate and queued for later execution through ThreadPool.QueueUserWorkItem(). The UI thread was freed up again, solving the playback stutters. But we made dozens of commits in the project while working our way to these few lines of change. This was the chance we were looking for. We had to get the cat out of the bag.

All our early modifications were mechanical and low-risk. Auto-format the code. Reduce the API surface area by hiding unnecessary public members. Remove dead and commented lines of code.

This exercise gave us the exposure to the codebase that was necessary to make further modifications. Further refactoring was driven by some of the SOLID principles. If we found a class that was doing too many things, we’d try to split it into different types with individual responsibilities. Interfaces were scarcely in use so far. So we began to define some new ones, being careful to contain their scope. But dependency inversion wasn’t quite as high on our list of priorities. .NET Framework didn’t ship with built-in DI features, and adding a third-party library for the job would impede our path to upgrade to .NET Core later down the line.

Over time, the quality of the codebase improved, and our knowledge of its internal working increased. There were few changes which were visible to the end user. In general, it was just a little more robust, faster to launch and run, and the UI looked a bit tidier.

The Demise of Flash

Come January 2021, disaster struck. Flash had been on its last legs since a long time. But nobody expected Adobe to pull the rug from under us by forcefully removing the plug-in from all computers. This bricked every deployed instance of the application. Nothing could be displayed on any screen without the Flash Player.

We scrambled to find workarounds, such as installing older versions of Flash Player that did not contain the the self-destruct switch, blocking Windows Updates, and even deploying older versions of Windows that shipped with working versions of Flash. These were all temporary solutions. The juggernaut was unstoppable, and we were fielding support calls every week that involved a missing Flash Player. In addition to the technical complexities, Adobe had also revoked the license to install and run the Flash Player. Continuing to use it was exposing the company to legal ramifications that nobody wanted to deal with. We needed an alternative for Flash as soon as possible.

Blazing Guns of Glory

Our salvation came in the form of the recently released Blazor framework from Microsoft. Built on the C# language, it borrowed a lot of concepts from ASP.NET and MVC. A crack team of developers was assembled, with the singular motive of porting the entire Flash application into Blazor. This was a significant diversion from our ground rule to never throw away everything and start from scratch.

Blazor generates a web application that runs in a browser. Embed a browser control into a Windows Forms project, and voila! It works just the same as the Flash application. The only significant difference was the communication protocol across process boundaries. Flash used to expose a TCP sockets API to communicate with the host process. Since web browsers don’t expose any such interface, we had to fall back upon standard HTTP. The hosting process would expose a web API that would be accessible on localhost over the HTTP protocol.

The last item was a significant pivot point. Hosting a HTTP API would require a web server, for which there were limited options that worked within the .NET Framework ecosystem. HttpListener was far too low-level. Cassini wasn’t as tightly integrated. GenHttp came with its own learning curve. In the long-term, it was going to be far better to switch from .NET Framework to .NET 5. And it shipped with its own built-in web server that supported running ASP.NET Web API out of the box.

The writing was on the wall. We would be porting to .NET 5.

Valknut – JSON Serialization

September 8, 2020January 5, 2023 Pranav Negandhi

Many service responses are returned as JSON objects. For this, the application must implement some basic configuration and error handling in each method. By utilising the cross-cutting facet of attributes, this code is unified into a common location and applied wherever required.

Signalling

Firstly, the action method that returns JSON has to be marked. The JsonHandlerAttribute class inherits from ActionFilterAttribute. It is applied to the method in question. When the method is invoked, the ASP.NET pipeline executes the OnActionExecuted method on its attribute. The method converts the System.Web.Mvc.JsonResult result into a custom-written class called FitNet.Web.Infrastructure.JsonNetResult. This class inherits from JsonResult and adds some shared functionality.

Error Handling and Serialization

The conversion from JsonResult to JsonNetResult is performed inside the JsonHandlerAttribute class. The Result property of the current filter context is typed into JsonNetResult. If the conversion is successful, then a new instance of JsonNetResult is created and the copies of the current result copied over.

Finally, the ExecuteResult method is invoked on the newly created result instance. This step performs the following error checks.

Deny GET requests by default, unless it is explicitly allowed in the method.
Set the content type of the response to application/json.
Configure the underlying serializer to throw an error in case of looping references.

If all the checks pass, then the response data is serialized and the output is assigned to the Output property of the current response.

This structure of the code removes the need to have all these checks in each method that has to return a JSON response.

Category: Software Engineering