1. Transitioning VisIt to CMake
Brad Whitlock
ASQ Division
Lawrence Livermore National Laboratory
VisIt is a visualization and data analysis tool with a complex build system that transforms over 1 million lines of C++ source code into many executables and hundreds of plug-in shared libraries. Historically, VisIt has relied on two distinct build systems to support different platforms. In early 2010, both build systems were replaced with a single build system based on CMake. The resulting build system has proven superior and has eliminated a long-standing maintenance burden.
Introduction:
Methods:
VisIt has a very complex build system that needs to be simplified to boost developer productivity.
We chose to write a new build system that replaces both old ones using CMake (cross-platform make) from Kitware, Inc.
Viewer
Metadata server
Core libraries
CLI
Plug-ins
GUI
Compute server
VisIt comprises:
5 main executables
45+ core libraries
20+ plot plug-ins
45+ operator plug-ins
100+ database plug-ins
Each plug-in consists of 3-6 shared libraries
Incremental replacement of autoconf build system
Detect 3rd party libraries such as VTK, Qt, Python
Add targets for core VisIt libraries
Add targets for most important executables
Add targets for plug-ins
Add advanced features
After creating a basic build system with just the main targets, we started developing on all platforms to avoid problems with portability.
Desired build system properties
CMake
Portable to Windows, MacOS X, UNIX/ Linux
Scriptable
Well supported, widely adopted, free
Generate build system for favorite environment (make, Visual Studio, Xcode)
Flexible
Low barrier to entry
Two build systems: autoconf for UNIX&Mac builds, Microsoft Visual Studio for Windows builds
Each build system represents hundreds of build targets
Responsibility for Windows build was on 1 person, which was not very fair and took an estimated 2 months/year to maintain
Results:
Discussion:
Conversion to a CMake build system took around 2 developer months of effort to achieve all features on all platforms. This also includes enhancements never before present in the old systems: make install, automatic packaging, symbol visibility, static builds.
Our CMake build system works on all platforms and a single source of build-logic informs the entire build process so maintenance going forward will be minimized.
Developers on different platforms can use their preferred development environment instead of a 1 size fits all approach.
Switching to CMake had other benefits:
Out of source build
Better build dependencies
Support for parallel make over all directories
Choosing CMake was the right choice for VisIt since we were able to:
Consolidate all build-logic
Address portability
Target multiple build environments
Simplify the installation and packaging process
Getting started with CMake does not take much time and projects can increase in complexity as needed. Complexity can be managed by using built-in functions and by reusing macros that set up build targets. We have used CMake to replace 2 build systems, ensuring we have a single up-to-date build system at all times. This reduces errors and frees developers to work on actual source code.
This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.
LLNL-POST