tsJensen

A quest for software excellence...

Bad Code Leads to Worse Code

It is 100% my fault. I wrote a small library for accessing files in Azure Storage. It has an Exists method. But rather than returning false when the path does not exist, it throws a 404 Not Found exception. This is bad code. It should just return false. And not having time to fix it, I wrote the following worse code.

try
{
   var exists = await _blobIo.Exists(fileName);
}
catch (Exception e)
{
   if (null != e.InnerException && e.InnerException.Message.Contains("404"))
   {
      fileName = $"other/{key}/{id}.{ext}";
      try
      {
         var exists = await _blobIo.Exists(fileName);
      }
      catch (Exception ie)
      {
         if (null != ie.InnerException && ie.InnerException.Message.Contains("404"))
         {
            throw new HttpResponseException(
               new HttpResponseMessage(HttpStatusCode.NotFound)
               {
                  Content = new JsonContent(new 
                  { 
                     Error = "Not Found", 
                     Message = "Content not found." 
                  })
               });
         }
      }
   }
}

I hang my head in shame. Lesson: fix the bad code. Don’t write worse code to work around the bad code.

Update
Once the fire was put out, I fixed the original library and now have this code. It's better. Could be improved, but it's not as ugly as before.

if (false == await _blobIo.Exists(fileName))
{
   fileName = $"other/{key}/{id}.{ext}";
   if (false == await _blobIo.Exists(fileName))
   {
      throw new HttpResponseException(
         new HttpResponseMessage(HttpStatusCode.NotFound)
         {
            Content = new JsonContent(new 
               { 
                  Error = "Not Found", 
                  Message = "Content not found."
               })
         });
   }
}

Second lesson: Don't let stinky code lie around too long. Clean up your messes.

Context Switching and Task<Result>.ConfigureAwait Method

While heavily involved in a few ASP.NET Web API 2 projects over the past year, I’ve learned from experience that context switching, marshaling between threads when using the async and await constructs in C# can be undesirable.

To avoid the context switching which is undeniably needed in a UI application where you’re offloading work from the UI thread, the default value of “true” for the ConfigureAwait Method on the Task<Result> class, one must set the “continueOnCapturedContext” to false. Like this:

var user = await repo.GetUser(id).ConfigureAwait(false);

There is some debate as to whether this is helpful in an ASP.NET application given the request is handled on a thread pool thread which is returned to the pool while the asynchronous task is running.

The issue I’ve noticed is that in some cases setting the “continueOnCapturedContext” to false, eliminates the need to marshal the continuation of your code back to the original context and use of another thread pool thread. While there are no noticeable performance advantages, I have noticed that I experience fewer threading exceptions when I allow the execution to continue on the thread that just executed my asynchronous work.

Exploring .NET Core 1.0

After a busy year working on coding up REST services with ASP.NET Web API 2.0 and doing zero blogging, I’m finally taking a little time to explore the .NET Core 1.0 bits released recently in RC2 and watching a number of presentations. I’m very excited about what I’m learning and will blog more about it but here’s a list of links that I’ve found most instructive and useful.

First, the announcement of RC2: announcing-asp-net-core-rc2

Next, the install: https://www.microsoft.com/net 

The unforgettable Scotts at TechEd: Introducing ASP.NET Core 1.0 

And the ASP.NET Core Deep Dive into MVC that followed.

After some experimentation with the preview tooling, trying to figure out how to create a .NET Core class library NuGet package was made easier with this very helpful article: how-to-create-a-nuget-package-with-your-library

And understanding the IIS deployment story was made so much more clear just the other day by the always helpful Rick Strahl: Publishing-and-Running-ASPNET-Core-Applications-with-IIS

Then I went looking for something similar for using Apache as the reverse proxy in front of a Kestrel app and found this: linuxproduction

Which finally led me to clone the KestrelHttpServer.

Exploring the code and the repo has been interesting. I especially noted with interest the recent pull request to Downtarget Kestrel to NETStandard 1.3.

The comment that Kestrel needed no functionality beyond 1.3 and that this allowed greater flexibility with current scenarios was very interesting.

The most important piece of learning so far has been the very brief discussion of the Libuv library used by Kestrel: http://libuv.org/

This amazing little library is used by Node.js and now by the ASP.NET Core web server called Kestrel and according to reports in Microsoft presentations has served up 3.2 million requests per second on a single bare metal machine. Even with a beefy machine, that is impressive.

Seeing how Kestrel uses Libuv is even more interesting and makes me think I ought to explore it as the next engine for a ServiceWire and ServiceMq implementation that could be deployed as a Docker container.

I was especially interested to see how .NET Core 1.0 utilizes native libraries in the Kestrel integration and use of Libuv as a NuGet package: KestrelHttpServer Internal Networking

The runtimes contained in the Libuv package used by Kestrel were also interesting to note:

libuv_runtimes

This concludes about a week of research on the side where I could sneak in an hour or two here or there. I’m eager to keep learning.

A Software Development Allegory

Farmer Brown has a tractor. Farmer Jones has a tractor. Both tractors break down every Monday.

Farmer Brown spends every Monday afternoon fixing his tractor and then gets a good five days of work in before he rests on Sunday.

Farmer Jones spends Monday afternoon evaluating the tractor and Monday evening discussing it with his wife writing up a plan and reviewing that plan for fixing it.

Tuesday morning Farmer Jones goes to the diner for coffee and a donut and to discuss his tractor woes with his pals, showing off his plan for fixing the tractor. One of the pals suggests it might not a problem with the doohickey as Farmer Jones suspects. He recommends that Farmer Brown take the tractor to the mechanic for further diagnosis and discussion. So Farmer Jones spends the rest of the day loading up his tractor onto the trailer and hauling it into town whereupon the mechanic tells him he can get to it first thing in the morning.

On Wednesday morning after coffee at the diner, Farmer Jones ambles on over to the mechanic shop and learns that the problem was indeed what he had suspected all along and that he could have fixed the problem in an hour or two on Monday afternoon. So farmer Jones loads up the tractor and takes it home only to find that his wife has baked a nice apple pie and so he spends a lazy afternoon eating pie and talking with his wife and the neighbor who has come over to gossip. That evening he fixes the tractor.

Now first thing Thursday morning, Farmer Jones gets to work and works through Sunday, making his wife cross with him for not attending Services at the church. Farmer Jones is too tired to listen and flops down in bed in need of rest.

And on Monday morning both tractors break down again.

Farmer Brown gets 20% more work done and rests one day a week.

Farmer Jones later gives up on farming and gets a job managing the parts store at the mechanic shop.

What kind of farmer are you?

Hiberfile.sys Removal Note to Self

A very large portion of my system drive, a 250GB SSD, seemed to be gobbled up with my fresh Windows 8.1 install and after install all my tools, I was fast running out of disk space on the C: drive. A quick search for culprits using Effective Search from SowSoft turned up a 64GB file called hiberfil.sys.

After a little hunting and poking, I found the GUI for power management options and tried to turn off hibernate. But that did not get rid of the file.

Not until I found and used the following in an “as Administrator” cmd window did I recover the 64GB of SSD space:

powercfg -h off

And yes, I have 64GB of RAM. Call me spoiled.

MongoDB C# Driver 2.0 AsQueryable Alternative

I’m a fan of LINQ and the IQueryable<T> interface power to compose dynamic queries based on input parameters. So when I needed to compose just such a query in a repository for a MongoDB collection, I found that the MongoDB C# 2.0.1 driver is currently missing the AsQueryable method which is slated for 2.1 release of the driver.

After a little searching, I found the Filter Definition Builder documentation and a happy alternative to building up or composing a query based on the presence of query parameters.

And here is a code sample:

public async Task<IEnumerable<MyData>> GetByQuery(MyDataQuery query)
{
    var filter = ComposeFilter(query);
    if (!query.Ascending)
    {
        var responses = await _invoiceCollection
            .Find(filter)
            .SortByDescending(x => x.TransactionDate)
            .Skip(query.Index)
            .Limit(query.Limit)
            .ToListAsync();
        return responses;
    }
    var ascResponses = await _invoiceCollection
        .Find(filter)
        .SortBy(x => x.TransactionDate)
        .Skip(query.Index)
        .Limit(query.Limit)
        .ToListAsync();
    return ascResponses;
}

private FilterDefinition<MyData> ComposeFilter(MyDataQuery query)
{
    var builder = Builders<MyData>.Filter;
    var filter = builder.Eq(x => x.CustomerId, query.CustomerId);
    if (query.StartDate.HasValue)
    {
        filter = filter & builder.Gte(x => x.TransactionDate, query.StartDate.Value);
    }

    if (query.EndDate.HasValue)
    {
        filter = filter & builder.Lt(x => x.TransactionDate, query.EndDate.Value);
    }

    if (query.InvoiceId != null)
    {
        filter = filter & builder.Eq(x => x.InvoiceID, query.InvoiceId);
    }

    if (query.ItemId != null)
    {
        filter = filter & builder.Eq(x => x.ItemID, query.ItemId);
    }
    return filter;
}

So now you have a dynamic query based on composition logic. Of course this is a very simple example and there are bound to be far more sophisticated ways of doing the same thing, but I found this one worked very well for me.

Microsoft Graph Engine

This tweet from Scott Hanselman caught my eye because I spent nearly all of 2014 working on a graph solution for my employer that had it’s genesis in my study of Neo4J but primarily in my reading of this Microsoft Research paper (Sakr, Elnikety, and He) produced in 2012.

graphtweet

The essence of the Microsoft Research paper is storing edges (node relationships) in memory. So that’s what I did with unmanaged memory allocated in blocks using the Marshal.AllocHGlobal method. My own efforts were very specific with respect to my employer’s needs at the time and not really useable as a general purpose tool, so I was very pleased to see that Microsoft Research had an ongoing project called Trinity working to produce a more general purpose tool based on many of the same concepts originally explored by Sakr, Elnikety and He.

That tool was recently quietly released as the Microsoft Graph Engine. I’ve only had a little time to explore and understand it and look forward to spending more time using it soon. The essence is the same. Store the data in sequential chunks in raw unmanaged memory. Graph Engine uses Visual Studio to generate code on the fly using a meta language called Trinity Specification Language (TSL). Have a look through the documentation. If you’re considering graph database work, put Microsoft’s Graph Engine on your list of items to evaluate.

Blog Vacation is Over

It's been seven months and two job changes and crazy busy with family, work and life.

Vacation is over.

List of things to blog about.

So much to say, so little time to say it.