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In my company, we are using Visual Studio 2019 and we would like to reduce the build times of our C++ solution. It is about 21 projects and it takes roughly 8.5 minutes for a debug build and a lot more for a release build. I am wondering if there is a way to make projects with dependencies on each other compile in parallel. I am already aware and make use of multiprocess compilation (/MP flag). Indeed, each project in the solution is built using multiple cores. Also when two projects, let's say A and B, don't depend on each other they build in parallel. However with our current settings, if A depends on B, the build of B has to complete before A starts. As far as I understand, the compilation of files in A can start even before B finishes, and only linking of A has to really wait until B finishes (let's assume that A generates either a .dll or a .exe). Is there a way to achieve this?
In addition to your query, are you also using Precompiled Headers correctly to reduce the build time?
Yes, sure.
Among other things, we use something like unity build on precompiled headers for projects that rarely change.
Also to fasten the link-time I added:: /DEBUG:FASTLINK, and related parameters
Now I'm working on implementing Pimpl and reducing the size of the files included in the headers.
Hi,
The /MP option causes the compiler to create one or more copies of itself, each in a separate process. As far as I'm concerned, this is based on each project, and this will not let all projects build in parallel. To do that you have to pass in -M[:num] or -maxcpucount (max cpu count) to msbuild.exe. For more details, I suggest you could refer to the Doc: https://learn.microsoft.com/zh-cn/visualstudio/msbuild/msbuild-command-line-reference?view=vs-2019&redirectedfrom=MSDN&viewFallbackFrom=vs-2015
I am wondering if there is a way to make projects with dependencies on each other compile in parallel.
If the two projects that depend on each other, are in the same solution and the dependencies between each other are clearly marked, then the cpp files can be compiled at the same time, but not linked at the same time. The linking must occur in order of how they depend on one another.
Best Regards,
Jeanine
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Hi Jeanine,
You wrote: "If the two projects that depend on each other, are in the same solution and the dependencies between each other are clearly marked". So, I can't understand "clearly marked", what does it mean? And how to properly set dependency between projects. I use the standard mechanism now (right-click on a project -> Build Dependencies -> Project Dependencies). And in this case, my project is being built consistently.
ЗP.S -maxcpucount is set to zero (via Visual Studio of course), and it means that scheduler uses all the available cores and create as much separate process as possible.
P.P.S And the number of available parallel builds is equal to available logic cores(12).
Glen
What do you mean"my project is being built consistently"? Compile and build are different.
-maxcpucount is set to zero
The value must be an integer greater then zero. You could without specifying a value, MSBuild will use up to the number of processors on the computer.
About "my project is being built consistently":
Let's imagine that I have 2 projects. Y depends on X. Project Y starts compiling only when the linking of project X completes.
I want project Y to start compiling at the same time as project X. But they must be linked strictly sequentially. I want the linker on the Y project to start immediately after the completion of the linking of the X project
@Jeanine Zhang-MSFT Apparently there are differences between how Visual Studio builds projects and how MSBuild acts when it is run outside of Visual Studio. According to Visual Studio builds vs. MSBuild.exe builds
So, I think that @Glen Sand is asking about altering how dependencies are evaluated and handled for Visual Studio builds, including building inside the IDE.
@Glen Sand , please correct me if I misunderstand your question.
Yes, I wanted to learn how to build projects in parallel in Visual Studio. Your answer helped me, before I did not understand what is the difference between these assembly methods. However, I still don't know if the assembly can be made more parallel. I know for sure that I need it, I experimented with dependencies, and I realized that I can win another 50 seconds if I do what I want.
Can you give us an example of the dependencies that you are working with? For example, does one project reference another (a dependency is created) because it needs an import library for functions imported from a dll?
Yes, I have about 10 dlls or static libraries inside the solution that the larger dll depends on. For example:
If you want to know how dependencies are evaluated and handled for Visual Studio builds, including building inside the IDE.
As far as I'm concerned, this problem needs help from the visual studio product group.
I suggest you could post the issue to DC for better help.
Have you tried using MSBuild in a developer command prompt to build the solution to see if it makes a difference compared to building with Visual Studio in the IDE?
I tried to run the build through MsBuild.exe through the console, I did not notice the difference.
By the way, production builds are assembled like this.
If you want to eliminate the project dependencies related to the use of import libraries you could use runtime dynamic linking (LoadLibrary/GetProcAddress) or pre-build the import libraries. One way to accomplish this without needing any binary inputs is to use a .def file. So in a preliminary step create the needed import libraries as described at building-an-import-library-and-export-file. Then any project can use that import library in its linker step without a dependency on the project that creates the dll.