How to set up build bots for libwebrtc

I. Introduction

Following My previous posts, I got a lot of e-mails concerning setting up the build bots. I have to admit that my previous post did not address that in detail, and that the documentation about it is sparse and confusing, as the recommended way to do it in the cmake community changed through the 15 years of the (vtk, itk) projects. So here is a post to describe, step by step, how to set up your own bots in a matter of hours, and manage them remotely through git, without ever having to connect to them again (in theory, in practice, s#$%^ happens, and you might also want to connect from time to time to debug problems directly.)

It is good policy to keep the build bot script separated from the main code, as they might contain sensitive information about your infrastructure. For example, you might put access key to upload the result of the build (packaged libraries) and that had better be private. Moreover, with the current setting, anybody that manage to have access to your build script end up being able to run anything on your build bot, which is also something you don’t want 🙂 In our case, it’s more a tutorial, and all scripts are accessible here.

II. Scripting CTest

So far, I touched on two ways of using ctest:

  • as an extension of CMake, to handle test suite directly from within the CMake files.
  • as an CDash client, to run CMake and automatically send the results of the upgrade, configure, build and test steps to a CDash server. 

There is a third way to use ctest: through scripting. You can write a files, using cmake syntax to prepopulate CTEST_<> variables to run ctest in a controlled way. You then call “ctest -S” with your file as argument to run ctest in script mode.

Some very useful variables are defined for you to use, to set CTEST cache, or environment variables, or hardcode compilers, and any given program or cmake variable before hand. That allow for example to run 32 bits and 64 bits builds, debug and release, on a single machine. Another example is to have multiple versions of compilers on a given machine, and use ctest scripts to use a specific one at a time. One of th best script I saw, written by gaethan lehman, was handling different versions of MSVC and Java on windows. Hat off.

One can get more information about CTest capacity on the old page written when people were still using purify (here, here and here),  and a more recent version here, .

III. What about libwebrtc?

For this example, I used the latest method, developed for ITK v4. A very fast overview is here. This version was focussed on git, and implement some nice tricks to handle different branches, which makes setting up bots for development branches easier.

1. A generic script that does all the heavy lifting

The idea is to have a very generic script that handle most of the problems for you, and to leave only a few variables to be defined to the user. I ported the generic script to be usable for libwebrtc: libwebrtc_common.cmake. Unless you’re a purist, I do not recommend modifying it, or even looking at it. It now allows you to define a set of parameters, some of the usual CMAKE or CTEST variables, but some new dashboard_ variables as well, to control your build.

  • dashboard_model = Nightly | Experimental | Continuous
  • dashboard_track = Optional track to submit dashboard to
  • dashboard_loop = Repeat until N seconds have elapsed
  • dashboard_root_name = Change name of “My Tests” directory
  • dashboard_source_name = Name of source directory (libwebrtc)
  • dashboard_binary_name = Name of binary directory (libwebrtc-build)
  • dashboard_data_name = Name of ExternalData store (ExternalData)
  • dashboard_cache = Initial CMakeCache.txt file content
  • dashboard_do_cache = Always write CMakeCache.txt
  • dashboard_do_coverage = True to enable coverage (ex: gcov)
  • dashboard_do_memcheck = True to enable memcheck (ex: valgrind)
  • dashboard_no_clean = True to skip build tree wipeout
  • dashboard_no_update = True to skip source tree update
  • CTEST_UPDATE_COMMAND = path to git command-line client
  • CTEST_BUILD_FLAGS = build tool arguments (ex: -j2)
  • CTEST_BUILD_TARGET = A specific target to be built (instead of all)
  • CTEST_DASHBOARD_ROOT = Where to put source and build trees
  • CTEST_TEST_CTEST = Whether to run long CTestTest* tests
  • CTEST_TEST_TIMEOUT = Per-test timeout length
  • CTEST_COVERAGE_ARGS = ctest_coverage command args
  • CTEST_TEST_ARGS = ctest_test args (ex: PARALLEL_LEVEL 4)
  • CTEST_MEMCHECK_ARGS = ctest_memcheck args (defaults to CTEST_TEST_ARGS)
  • CMAKE_MAKE_PROGRAM = Path to “make” tool to use
  • Options to configure builds from experimental git repository:
  • dashboard_git_url = Custom git clone url
  • dashboard_git_branch = Custom remote branch to track
  • dashboard_git_crlf = Value of core.autocrlf for repository

If you want to extend the capacity of this core script, some hooks are also provided to keep things clean and compartementalized.

  • dashboard_hook_init = End of initialization, before loop
  • dashboard_hook_start = Start of loop body, before ctest_start
  • dashboard_hook_started = After ctest_start
  • dashboard_hook_build = Before ctest_build
  • dashboard_hook_test = Before ctest_test
  • dashboard_hook_coverage = Before ctest_coverage
  • dashboard_hook_memcheck = Before ctest_memcheck
  • dashboard_hook_submit = Before ctest_submit
  • dashboard_hook_end = End of loop body, after ctest_submit

2. A very simple file to define a bot

Eventually, that makes writing a build script very easy indeed:

  1. set(CTEST_SITE “Bill_._Our_fearless_leader” )
  2. set(CTEST_BUILD_NAME “Ubuntu-12.04-32-Deb” )
  3. set(CTEST_BUILD_FLAGS -j8 )
  4. set(CTEST_DASHBOARD_ROOT “/home/ubuntu/Dashboards” )
  5. set(CTEST_TEST_TIMEOUT 1500 )
  7. set(CTEST_CMAKE_GENERATOR “Unix Makefiles” )
  8. set(dashboard_model Experimental )
  9. include(libwebrtc_common.cmake)

And … voila! you have a linux build bot all set up! Replace ‘Debug’ by ‘Release’, and you have your release build ready. To change from 32 to 64 bits, since we use ninja, you have to set up the right env variable, but it’s not difficult either:

  2.   “GYP_DEFINES=’target_arch=x64′” # or ia32 for 32 bits
  3. )

The corresponding file is here.

A word of warning though, installing the dev environment for libwebrtc is hard. First, it will almost only work under ubuntu, second, the environment install scripts provided do not seem to work, so you will end up having to manually install quite a few libs yourself before being able to compile. The good news is, you will only have to do that once. 

3. How to automate it all?

Now you are armed with several files for each build you want to run. You might very well run many build on the same machine, e.g. 32/64, Debug/Release. For Linux machines, you might want to cross-compile the android binaries as well (more on the mobile target in another post). 

However, you still need to have access to the machine, and manually launch

  1. ctest -S My_Build_script.cmake

For it to work.

One way around this is to define a (shell) script that run those commands for you. However, whenever you make a modification to the script, you have to connect to the machine again, and manually update the local script to the new version, grrrrr

That’s where cron (on linux or mac) and Scheduled tasks (on windows) comes in handy, as it can run a command at a given time for a given user. Here you have two schools: the original cmake members designed everything so that people could configure their always-on desktops to be used during sleeping hours. More recent developers will want to set up either a dedicated build bot, or a hosted build bot, and might want to reduce the cost by switching the machine off when the job is done. I will illustrate the later for linux (and mac) and the files for windows will be provided in the github account for those interested. Note that for windows build bot specifically, it has been shown that you’d better reboot the machine once a day in any case if you want it to work ….

Starting devices remotely is easy, all the cloud providers provide command line API, and you can maintain a build master (very tiny instance) whose sole job will be to wake up the bots once  day for them to fetch the latest code, configure, build test, and submit to the dashboard. In AWS EC2, that means playing with IAM, but nothing too hard there, and it’s very well documented. On linux, the cron daemon accept the ‘reboot’ keyword, and will run the corresponding task whenever the device is started.

  1. @reboot /home/ubuntu/Dashboards/Scripts/

Finally, you can just use the shutdown command in your script to stop the instance when they’re done.

  1. shutdown -h now

We’re only left with automated updating of the scripts. 

The trick used by the ITK community is to keep the scripts (and the cron table) in a git repository, and to update this repository first. In this example, you can see from the shell script that we expect a ~/Dashboard/Scripts directory to contain the build scripts, a ~/Dashboard/Logs directory to be present, and that the crontable also get updated on the fly. Now I can just commit to my git repository, and the build bot will auto update itself. Sweet.

  1. # Go to the working directory
  2. cd /home/ubuntu/Dashboards/Scripts
  3. # get the latest scripts
  4. git pull –rebase -q
  5. # update the crontable
  6. crontab ./Bill-crontab
  7. # Run the builds
  8. ctest -S ./Bill-32-Debug.cmake
  9. ctest -S ./Bill-32-Release.cmake
  10. # done, let’s shutdown the instance to avoid paying too much
    sudo shutdown -h now

The full script with some additional features is here.

IV. Conclusion

It should now be pretty clear that setting up a build bot for libwebrtc is actually quite easy. The code provided in github should actually make it even easier. Feel free to set up your own build bot, hopefully with settings that are to yet present in any of the bots contributing to the dashboard today, and contribute to the fun. I should update to a bigger CDash server that will allow for more than 10 builds a day very soon. I would love to see people contributing for arm, android, iOS, …..

If you find this useful, let other know, and nice comments are also appreciated. 😉