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Jeremy Jameson - Founder and Principal



Large Visual Studio Solutions and Loading/Unloading Projects

This post originally appeared on my MSDN blog:

Since I no longer work for Microsoft, I have copied it here in case that blog ever goes away.

As I noted in my previous post, I typically work with "large" Visual Studio solutions. Note that I put this in quotes, because the definition of "large" will likely vary widely based on your individual experience. Note that I'm not referring to "large" like the source for the .NET Framework itself, but rather "large" like most enterprise customers that I typically engage with. If you want a number, then let's say somewhere in the range of 50-75 projects in a single Visual Studio solution.

On my previous project, we had 52 projects in our solution. On my current project, there are 30.

You may very well have more or less, but the following concepts and tips should still apply. If you are on a development team with several hundred projects, then either you are a member of the NetFx team or you more than likely already know about what I'm about to tell you in this post ;-)

If you work with multiple Visual Studio solutions that only have a handful of projects, but this is simply because your team decided to break up one big solution into several smaller ones, then this post is intended especially for you.

As you start adding more and more projects to a solution, you'll inevitably discover the following to be true:

  • Load time increases (i.e. the time it takes to start Visual Studio and open your solution)
  • Incremental build time increases, even when the only changes that have been made are in "leaf" projects (i.e. projects that don't reference other projects)

Obviously we should expect the build time to take a while whenever we make a change in one project that is referenced by many others (e.g. a "CoreServices" project like I've described in the past).

If, like me, you've grown accustomed to Test Driven Development (TDD) however, then you know that it's essential to minimize the "Red, Green, Refactor" cycle. If your incremental build time requires 28 seconds, then your developer productivity is going to take a hit in a big, big way.

So, what can we do to mitigate these issues?

One approach is to create multiple Visual Studio solutions with a subset of projects. Developers could then open the specific solution (or, possibly, solutions -- plural) containing a subset of the projects they need to work on at any given time.

I really don't like -- or obviously recommend -- this approach, because it can be very problematic (for example, having to synchronize changes to the build configuration). Even worse, though, is that depending on how you partition your solution, you may end up having to switch from project references to file references for assembly dependencies. Anyone who has ever used file references for their own code should tell you that this is something to avoid.

Note that the recommendation to use a single, "master" solution is nothing new. We've had this prescriptive guidance out for a number of years now (please forgive the fact that MSDN still refers to using Visual SourceSafe instead of Team Foundation Server in this article -- there may very well be an updated article that I simply haven't bothered to take the time and find).

Unfortunately, what was fundamentally missing from the original prescriptive guidance was any mention of the feature in Visual Studio that allows you to effectively work with a solution containing numerous projects. This has become critical in light of the shift to TDD.

If you right-click a project in Visual Studio, you'll see the Unload Project option way down near the bottom of the context menu. When you unload a project, Visual Studio completely ignores the project (and all of the items in the project). Unloaded projects are not compiled when you press CTRL+SHIFT+B, which can substantially reduce your incremental build time, thereby making you a much more productive TDD developer! You will also find the time required to open the solution can be greatly reduced by unloading projects.

Whenever you need to change something in an unloaded project, simply right-click the project and click Reload Project.

Unloading a project is also useful whenever you need to edit the MSBuild file -- for example, to rebuild a CAB or WSP whenever a dependency changes.

An important thing to understand about loading and unloading projects is that the settings are stored in the solutions options (.suo) file which is specific to each developer and should never be stored in source control. In other words, if I unload a project in my workspace, this has no effect on other team members. Removing a project, on the other hand, changes the solution file (.sln) itself and therefore impacts other members of the development team.

Note that you can quickly unload or reload multiple projects at a time by using solution folders within Visual Studio. If you right-click a solution folder, you will see the option to Unload Projects in Solution Folder. I typically structure my Visual Studio solutions in a hierarchical fashion (i.e. nested solution folders) to make it very easy to load or unload various "subsystems" or features.

Also note that you can use Visual Studio macros to quickly unload or reload all of the projects in a solution with a single click (well, actually a double-click, but you get the point).

I'll share the macros that I developed and have been using for years in a separate post.

There is one caveat that you should be aware of when unloading projects. Visual Studio warns you when you attempt to unload projects with pending changes in source control. Generally speaking, you want to avoid proceeding whenever Visual Studio displays the warning for this scenario.

Note that modified files in unloaded projects are still shown in the Pending Changes window when using TFS as the source code control provider. However, this isn't true for all providers (e.g. Visual SourceSafe).

I've been using the loading/unloading project feature since my old Visual C++ 4.2 days, but -- at least based on my experience -- there seem to be a number of developers who are unaware of this great feature in Visual Studio. If I recall correctly, this was missing in the original Visual Studio.NET but, thankfully, was added back in a subsequent version, either Visual Studio .NET 2003 or Visual Studio 2005 (honestly, it's been too long to remember). Perhaps that the reason why the original prescriptive guidance on MSDN makes no mention of unloading/loading projects. Thank goodness it's back!


  1. # re: Large Visual Studio Solutions and Loading/Unloading Projects

    February 27, 2011 1:45 PM

    A great tip. Moreover, when I unloaded a project following this post  the compiler complained and I found out I was erroneously using a file reference in one of my dependant projects :-)

  2. # Random Musings of Jeremy Jameson : Why I'm Not a Fan of WspBuilder

    March 5, 2009 9:19 PM
  3. # Tracing and Logging from Visual Studio Macros

    March 10, 2009 7:59 PM

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