Re: [CMake] [cmake-developers] Need ideas/opinions on third party library management

[Ruslan Baratov via CMake]

On 17-Aug-16 04:29, Florent Castelli wrote:


The Boost source download is cached outside of the build directory 
in a unique folder.

So it’s effectively only done once for all platforms and then reused.
This is true for local machines and for custom build servers like 
your personal Jenkins. For Travis/AppVeyor you have to create root 
folder with 3rd parties from scratch for each build (at least for 
free public accounts).
Yes. If you're using a free shared service, that's not something you 
can count on.
If you host your CI, you can do neat tricks like this, use ccache or 
other similar techs.

What if you don't need "tricks" and make everything plain and simple?







You’ll also have symbols and the sources available for debugging 
properly, and they’re

not always available with a binary distribution.
Just to clarify: with Hunter you're creating binaries from sources, 
so everything you install with `cmake --build _builds --target 
install` (or `./b2 install` for Boost) is available.
So you build each dependency separately, install them, and then use 
them in your top level dependency.

No, in shared root folder.

That works, but you have the extra overhead of the instrumentation for 
the whole build.
Even a no-op build will have to recurse in the build folder for each 
dependency and run again, which is slow.
This is why I prefer Ninja to the Makefile generator: it has a global 
view of everything and you get a quick no-op build.

Not sure I understand that. What is the overhead?








Of course building from source is not an option for such monsters 
like Qt or OpenCV. Ready-to-use binaries is something critical for 
real life applications. There is no way to test everything on 
Travis/AppVeyor without this feature.


Well, you don’t have to use Travis or AppVeyor.
It's the most powerful and easy to setup services I know. If you know 
any better solutions please share.
Well, you don't have a full control on the environment, so I wouldn't 
say it's the most powerful.
Please share your solution. I have worked with Jenkins before and will 
not say that it's something easy customizable. Shareable folder - yes, 
good, but other stuff is a complete pain.
You can setup Travis in a seconds, add AppVeyor and you got Linux, OSX, 
Windows testing. How much time will take to start and tune Jenkins 
master and connect several slaves with different OSes on them?
Then add bunch of projects and tune them, then create dev branches for 
testing and so on.



Convenient for sure. It probably fits smaller structures very well.
Bigger companies have the resources to host their own service most of 
the time and requirements that
force them to do so. Those are probably the ones that will have the 
manpower to handle a super-build type

build system.
Why do not have both? Hunter can share downloads/root/cache on local 
folder for such CIs like Jenkins/custom so you don't need to rebuild 
everything.
At the same time binaries from server can be downloaded for 
"build-from-scratch" environment like Travis.


Anyway what about users? So you think it's okay to spend several hours 
of building from sources to just to run simple example of your product?







Spotify isn’t at the same scale as most
projects hosted there and we have different requirements and resources.
Admittedly, Spotify doesn’t use Qt anymore, so this isn’t a problem 
for us.
It's not about Qt, it's about expandability. Use 20 of smaller 
libraries and you will have quite the same issues.
As I said before, if I have build scripts for 20 small libraries and I 
want to update a build flag affecting the ABI, I don't have to do 
anything but just change the flag once.
In your case, you'll have to tweak the 20 build scripts for each 
library to reflect it.
The dependencies are only intermediate products you use for the final 
one. I don't want to deal with them constantly.
It's not true, I don't need to tweak 20 scripts, I just need to tweak 
one toolchain file.








Note that by integrating everything in the same project, you also 
have proper dependencies
and you will only build what you need. You may save some time by 
doing that.

And caching is important, when done in the right way!
With Hunter you're installing only what you need too, it does respect 
options like FOO_WITH_OPENSSL or FOO_WITH_QT, it download only 
binaries for toolchain you're currently working on, etc.


Don't want to make a discussion too broad. You said that it's hard to 
manage binaries for a lot of configuration, I'm saying that it's 
possible and is very handy.
I'm not saying it's impossible. I'm saying the overhead of managing 
binaries is just a burden we shouldn't have to accept in the C/C++ world.
If you can build build everything from source all the time in a 
super-build, why wouldn't you do it?
Because it's not practical. I have such experience with Gentoo, I prefer 
do something useful instead of watching on "emerge world" progress. 
Super-build doesn't scale, what if 

Re: [CMake] [cmake-developers] Need ideas/opinions on third party library management

[Ruslan Baratov via CMake]

On 17-Aug-16 08:36, Elizabeth A. Fischer wrote:

> > I don't think CMake is the best place to do it,
> Can you provide any details? I personally think that CMake is a
> natural and the only place where it should be done.

The most important reason here is because there are combinatorially
many versions of a package you COULD install, depending on what
versions of its dependencies you link with, and CMake provides nothing
to address that issue.

CMake provides an abstraction. "Slots" that you need to fill:

  if(FOO_WITH_TESTS)
# need to have GTest installed
find_package(GTest)
  endif()
  if(FOO_WITH_OPENSSL)
# need to have OpenSSL installed
find_package(OpenSSL)
  endif()

And it should drive package manager. At least I find that approach 
natural and convenient, see no problems with it.
You can have as much combinations of versions/options/dependencies as 
you need:

* https://docs.hunter.sh/en/latest/overview/customization/hunter-id.html
* https://docs.hunter.sh/en/latest/overview/customization/config-id.html


  See here for an overview of how Spack
addresses the combinatorial versioning issue (which no other
auto-builder does, to the best of my knowledge):

http://hpcugent.github.io/easybuild/files/SC14_BoF_Spack.pdf
That's what I was talking about. I think that there is no need to 
introduce new funky syntax like "spack install mpileaks@1.1.2 %gcc@4.7.3 
+debug".
We already have CMAKE_CXX_COMPILER and 
CMAKE_BUILD_TYPE/CMAKE_CONFIGURATION_TYPES. Version can be set by CMake 
options too.

Effectively you can do:

  option(FOO_STABLE_BUILD "Stable build" ON)
  option(FOO_EXPERIMENTAL_BUILD "Experimental build" OFF)

  if(APPLE AND IOS AND FOO_STABLE_BUILD)
hunter_config(BooPackage VERSION "1.0")
  endif()

  if(WIN32 AND FOO_EXPERIMENTAL_BUILD)
hunter_config(BooPackage VERSION "2.0-beta" CMAKE_ARGS 
BOO_NEW_STUFF=YES)

  endif()



Once you've built something, it's nice to be able to re-use it.  If I
have a top-level CMake project that automatically builds three
dependencies, will other projects be able to make use of those
dependencies I've built?

Yes, libraries should be installed to the shared root, not to local folder:
* https://docs.hunter.sh/en/latest/overview/shareable.html


  Or do they become private?
No. Though you can make it private by setting CMake variable. It will 
use separate directory just like virtualenv do.



  If libraries
cannot be shared between applications, you will get a LOT of library
bloat, especially among the low-level libraries that get repeated
numerous times.  Admittedly, this may not be such an issue in some
environments where people are really only focused on building one
thing.

If you make a project, you might see it as a "top-level" project.  But 
someone else might want to build something bigger on top of your 
work.  You can never assume that "this package is top-level and no one 
will ever depend on it."

No issue here, see notes above.



Another obvious problem with using CMake for everything is that not
all packages come with CMake builds; most do not, in fact. Even if we
CAN re-write all the buils into CMake, that is a lot of extra effort.
As Florent has discovered, upstream authors do not always see a CMake
build in a favorable light, and these re-worked builds are not always
as functional as the original.  Moreover... writing a Spack recipe is 
an order of magnitude easier than writing a CMake build.  Usually, 
it's just a matter of calling `configure` or `cmake` with the right 
options.
Again, converting to CMake is a best option, but not the only possible 
one. E.g. OpenSSL, Boost, autotool-based package like X11 can be used as is:
* 
https://github.com/ruslo/hunter/blob/b4c370e32798cc3da74c37e4156c3bfc77add379/cmake/projects/Boost/hunter.cmake#L21
* 
https://github.com/ruslo/hunter/blob/b4c370e32798cc3da74c37e4156c3bfc77add379/cmake/projects/OpenSSL/hunter.cmake#L17
* 
https://github.com/ruslo/hunter/blob/b4c370e32798cc3da74c37e4156c3bfc77add379/cmake/projects/x11/hunter.cmake#L20




Although we can maybe imagine a world in which everyone eventually
abandons Autotools for CMake, it is still not realistic to expect that
Python, Haskell or Java programs will ever come with CMake builds.
This would be OK if each language exited in its own silo. But they
don't.  Python packages (built with setuptools) routinely depend on
C-based packages (built with Autotools or CMake).  By being agnostic
to the build system, auto-builders (like Spack, Macports, HomeBrew,
etc) are able to make packages work together, regardless of the build
system chosen for each one.

That's exactly what Hunter do, but using CMake as a driver.



In the sense that CMake is a Turing-complete language, there's no
fundamental reason you CAN'T write a meta-builder in CMake.  But
gosh... the language sure is arcane (but still better than Autotools
by a long shot).  I like to imagine that if CMake were starting off
today, it would be written in Python.
Language is a 

Re: [CMake] [cmake-developers] Need ideas/opinions on third party library management

[Elizabeth A. Fischer]

Well, I tried upstreaming the new build scripts to some projects and it
didn’t go well.
Some of the reasons I’ve heard of:

> I installed CMake 2.8.6 five years ago and I don’t want to update yet
> again!  People relying on old versions is quite common and any attempt
> to raise the min version will be frowned upon (see the discussion in
> the LLVM mailing lists for example).

Spack is really good at installing dependencies, and makes this a LOT
easier.  In your Spack recipe, you just tell it which version of CMake
your package needs.  If Spack hasn't already built that
version, it will download and install it for you.  Building packages by
hand, and configuring their dependencies, needs to go the way of stone
spears.

> We prefer to use autotools and don’t want to have to learn CMake.
> That’s fair. But also, no one likes to build an autotools backed
> project for Android or iOS.

I suppose it's fair.  But a Google search of "convert CMake to
Autotools" results in 9:1 stories of people abandoning Autotools for
CMake.  Except for the fact that it works well for users, I can't say
enough evil things about Autotools.

Part of the benefit of Autotools is it "just works" without
requiring the user to install anything.  This benefit is of little
value once you move to an auto-builder like Spack.  The days when
you can get any interesting software to work without installing
a zillion dependencies first are long gone.

> I’ve never heard of Spack before. It looks better than other solutions
> I’ve seen before.

The great and unique thing about Spack is it can install a zillion versions
of each package.  For example... if Package B uses MPI, I can build B-1.7
two (or more) times --- once with OpenMPI and once with MPICH.  And I can
install them side-by-side.  If you change any of the dependencies of a
package, Spack will see that as a new and separate version.  Most
auto-builders let you build one software distro, with only one build of
each package (or sometimes one build per numerical version of the package
or compiler or something).  Spack's versioning is a lot more powerful.

> But you still have to manage all the options from your build script

Not sure what you mean by this.  True, there is some redundancy building
code.  First you put the options and dependencies in a package's CMake
build.  And then you put them into the Spack build again.  Some things
could be simplified if we assumed our CMake-based packages would only ever
be built with Spack.  But we still need to create CMake-based software that
can be installed by hand.  Hence the redundancy between the CMake build
scripts and the Spack package.  In practice, this has not been the
end of the world.

Another nice thing about Spack is there is no difference between your
libraries and Third-party libraries.

> and publish the binaries somewhere.

In its original incarnation, Spack builds from source.  It does not publish
or install from binary distros (because the build you asked for, with all
its dependency variants, is likely not a build that's ever been built
before).  There's currently work on a project to use Spack to produce
binary RPMs, and maybe other forms of binary distribution.

> Then you need to teach your build scripts to get the right version.

Your build scripts know nothing about Spack.  Spack is an auto-builder that
sits ON TOP of your build scripts.

> I won’t trade my builds from source for a set of prebuilt binaries
anytime soon I think :)

Spack builds from source, it is not prebuilt binaries.

> > I don't think CMake is the best place to do it,
> Can you provide any details? I personally think that CMake is a
> natural and the only place where it should be done.

The most important reason here is because there are combinatorially
many versions of a package you COULD install, depending on what
versions of its dependencies you link with, and CMake provides nothing
to address that issue.  See here for an overview of how Spack
addresses the combinatorial versioning issue (which no other
auto-builder does, to the best of my knowledge):

http://hpcugent.github.io/easybuild/files/SC14_BoF_Spack.pdf

Once you've built something, it's nice to be able to re-use it.  If I
have a top-level CMake project that automatically builds three
dependencies, will other projects be able to make use of those
dependencies I've built?  Or do they become private?  If libraries
cannot be shared between applications, you will get a LOT of library
bloat, especially among the low-level libraries that get repeated
numerous times.  Admittedly, this may not be such an issue in some
environments where people are really only focused on building one
thing.

If you make a project, you might see it as a "top-level" project.  But
someone else might want to build something bigger on top of your work.  You
can never assume that "this package is top-level and no one will ever
depend on it."

Another obvious problem with using CMake for everything is that not
all packages 

Re: [CMake] [cmake-developers] Need ideas/opinions on third party library management

[Ruslan Baratov via CMake]

On 16-Aug-16 16:37, Florent Castelli wrote:
Well, I tried upstreaming the new build scripts to some projects and 
it didn’t go well.

Some of the reasons I’ve heard of:
- Windows developpers don’t use CMake, they have project files on the 
repository.

  The CMake files for Windows will never be updated.
They can coexists, it's easier then maintaining forks. If only C++ code 
changed you got new version "for free".


- I installed CMake 2.8.6 five years ago and I don’t want to update 
yet again!
  People relying on old versions is quite common and any attempt to 
raise the min
  version will be frowned upon (see the discussion in the LLVM mailing 
lists for example).
You can add `if(CMAKE_VERSION VERSION_LESS ...)` condition. It's hard to 
support such hairy configuration but anyway.



- We prefer to use autotools and don’t want to have to learn CMake.
  That’s fair. But also, no one likes to build an autotools backed 
project for Android or iOS.
Just for your info Hunter use build scheme for autotools project: 
https://github.com/ruslo/hunter/blob/b4c370e32798cc3da74c37e4156c3bfc77add379/cmake/modules/hunter_autotools_project.cmake
It can create universal iOS libraries and works for Android. There are a 
lot of efforts made by Alexandre Pretyman so this can be possible, it 
has some peculiarities. I guess he can clarify anything if you need details.


Ruslo
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Re: [CMake] [cmake-developers] Need ideas/opinions on third party library management

[Ruslan Baratov via CMake]

On 16-Aug-16 17:04, Florent Castelli wrote:


On 16 Aug 2016, at 15:29, Ruslan Baratov > wrote:


On 16-Aug-16 13:52, Florent Castelli wrote:
For example, Boost is used by 5 platforms: Windows, OSX, Linux, 
Android and iOS.

Each platform has a different CPU target (or many 32/64bit, x86/ARM).
Each platform has many compilers.
Some platforms have instrumentation options (Debug / Release, ASan, 
MSan…) and really need

to be compiled properly, otherwise you’ll end up with false positives.
The matrix of builds is REALLY hard to track. Each time we update 
Boost, we had to update

a lot of things.

Not a problem for Hunter.

Linux, OSX, Windows, iOS 9.3, iOS 8.2, Android, GCC, Clang, ASan, 
LeakSan, ThreadSan, Static Analyzer,  libstdc++, libc++, MinGW, 
Visual Studio 2008-2015:

* https://travis-ci.org/ingenue/hunter/builds/140317830
* https://ci.appveyor.com/project/ingenue/hunter/build/1.0.665

This list is not even full, I guess I can add more toolchains in 
future (GCC variations and C++ standards).


To test all matrix I need to push one commit to pkg.boost branch, to 
upload binaries to server I need to push one commit to upload.boost 
branch (upload ALL toolchains at one shot). To reuse all updates 
users just need to set new URL/SHA1 of HunterGate module: 
https://github.com/ruslo/hunter/releases


Overall, building boost takes 10s on our developers’ machines. The 
sources aren’t changed often,

so the cost is pretty low.
What kind of hardware do they have? And what libraries you mean? It 
takes about 20 seconds on my Linux machine just to unpack 80 MB of 
Boost release archive. It's even worse on Windows, it takes several 
minutes for some strange reason even on SSD + Core i7. Using binaries 
in such cases is a huge time saver because there is no need to 
compile anything and there is no a lot of junk that they put into 
release archive (if you remove docs and tests 80 MB became 15 MB).


I consider the time to download Boost isn’t part of the build.
I'm not counting that. It takes 20 seconds just to unpack archive that 
already downloaded. Anyway I'm just wondering what is possible to do 
with Boost for 10 seconds. Install header-only libraries? Build 1-2 
libraries? All of them? :)


The Boost source download is cached outside of the build directory in 
a unique folder.

So it’s effectively only done once for all platforms and then reused.
This is true for local machines and for custom build servers like your 
personal Jenkins. For Travis/AppVeyor you have to create root folder 
with 3rd parties from scratch for each build (at least for free public 
accounts).




You’ll also have symbols and the sources available for debugging 
properly, and they’re

not always available with a binary distribution.
Just to clarify: with Hunter you're creating binaries from sources, so 
everything you install with `cmake --build _builds --target install` (or 
`./b2 install` for Boost) is available.





Of course building from source is not an option for such monsters 
like Qt or OpenCV. Ready-to-use binaries is something critical for 
real life applications. There is no way to test everything on 
Travis/AppVeyor without this feature.


Well, you don’t have to use Travis or AppVeyor.
It's the most powerful and easy to setup services I know. If you know 
any better solutions please share.



Spotify isn’t at the same scale as most
projects hosted there and we have different requirements and resources.
Admittedly, Spotify doesn’t use Qt anymore, so this isn’t a problem 
for us.
It's not about Qt, it's about expandability. Use 20 of smaller libraries 
and you will have quite the same issues.




Note that by integrating everything in the same project, you also have 
proper dependencies
and you will only build what you need. You may save some time by doing 
that.

And caching is important, when done in the right way!
With Hunter you're installing only what you need too, it does respect 
options like FOO_WITH_OPENSSL or FOO_WITH_QT, it download only binaries 
for toolchain you're currently working on, etc.


Don't want to make a discussion too broad. You said that it's hard to 
manage binaries for a lot of configuration, I'm saying that it's 
possible and is very handy.


Ruslo
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Re: [CMake] [cmake-developers] Need ideas/opinions on third party library management

[Ruslan Baratov via CMake]

On 16-Aug-16 13:52, Florent Castelli wrote:

For example, Boost is used by 5 platforms: Windows, OSX, Linux, Android and iOS.
Each platform has a different CPU target (or many 32/64bit, x86/ARM).
Each platform has many compilers.
Some platforms have instrumentation options (Debug / Release, ASan, MSan…) and 
really need
to be compiled properly, otherwise you’ll end up with false positives.
The matrix of builds is REALLY hard to track. Each time we update Boost, we had 
to update
a lot of things.

Not a problem for Hunter.

Linux, OSX, Windows, iOS 9.3, iOS 8.2, Android, GCC, Clang, ASan, 
LeakSan, ThreadSan, Static Analyzer,  libstdc++, libc++, MinGW, Visual 
Studio 2008-2015:

* https://travis-ci.org/ingenue/hunter/builds/140317830
* https://ci.appveyor.com/project/ingenue/hunter/build/1.0.665

This list is not even full, I guess I can add more toolchains in future 
(GCC variations and C++ standards).


To test all matrix I need to push one commit to pkg.boost branch, to 
upload binaries to server I need to push one commit to upload.boost 
branch (upload ALL toolchains at one shot). To reuse all updates users 
just need to set new URL/SHA1 of HunterGate module: 
https://github.com/ruslo/hunter/releases



Overall, building boost takes 10s on our developers’ machines. The sources 
aren’t changed often,
so the cost is pretty low.
What kind of hardware do they have? And what libraries you mean? It 
takes about 20 seconds on my Linux machine just to unpack 80 MB of Boost 
release archive. It's even worse on Windows, it takes several minutes 
for some strange reason even on SSD + Core i7. Using binaries in such 
cases is a huge time saver because there is no need to compile anything 
and there is no a lot of junk that they put into release archive (if you 
remove docs and tests 80 MB became 15 MB).


Of course building from source is not an option for such monsters like 
Qt or OpenCV. Ready-to-use binaries is something critical for real life 
applications. There is no way to test everything on Travis/AppVeyor 
without this feature.


Ruslo
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Re: [CMake] [cmake-developers] Need ideas/opinions on third party library management

[Elizabeth A. Fischer]

CMake builds for existing libraries are certainly an interesting and useful
thing, and deserve to be posted in a GitHub repo somewhere.  They should
also serve as the basis of a campaign to get the library authors to
incorporate the CMake build directly in their repos.

But any approach that requires every build to be ported to CMake will be
difficult and labor-prone to scale.  Writing a meta-build recipe is usually
much easier.

Spack handles the combinatorial dependencies you mention in a
sophisticated, graceful way that most meta-builders do not.  Its only
problem is it does not (yet) run on Windows.  There's no fundamental reason
why not; we just need someone to get involved and start trying it on
Windows.

-- Elizabeth


On Tue, Aug 16, 2016 at 6:52 AM, Florent Castelli <
florent.caste...@gmail.com> wrote:

> At Spotify, we use CMake a lot for our large C++ library shared by all the
> clients.
> After trying to build libraries for each platform and variant, we
> basically gave up and we now
> use a super-build approach.
>
> For example, Boost is used by 5 platforms: Windows, OSX, Linux, Android
> and iOS.
> Each platform has a different CPU target (or many 32/64bit, x86/ARM).
> Each platform has many compilers.
> Some platforms have instrumentation options (Debug / Release, ASan, MSan…)
> and really need
> to be compiled properly, otherwise you’ll end up with false positives.
> The matrix of builds is REALLY hard to track. Each time we update Boost,
> we had to update
> a lot of things.
> I tried using ExternalProject and use b2 (build tool from Boost) to build
> it and instead of having
> lots of build jobs with a mirror of the flags, you end up mirroring the
> flags in your CMake files
> instead, which is still not good enough.
>
> In the end, I looked at how Boost is actually built. And for most
> libraries, it’s plain simple.
> A static library with a few files, some define, sometimes a platform
> specific source file.
> What if instead of having an external build tool, I built it from CMake
> instead?
> It would propagate all the build flags, target, instrumentation and
> compiler information from the main
> build to it and just work.
> I tried it and it worked in no time! We replaced our Boost 1.59 binary
> distribution with the source
> distribution and it’s much easier. When people build our library for a
> different target, they don’t have
> to download new binaries, they just reuse the same sources.
> Later on, we found a bug in Boost 1.59 (fixed in later versions) and
> patched it. We updated our source
> bundle and everything was smooth.
> Much later on, we wanted to use 1.61. We just updated the source bundle
> again, the list of source
> files or compilation flags for the libraries we use didn’t change. It was
> again effortless.
>
> Overall, building boost takes 10s on our developers’ machines. The sources
> aren’t changed often,
> so the cost is pretty low. It needs attention when we upgrade it, but
> that’s quite rare.
>
> We try now to use the same approach for other libraries when we add them.
> Some of them are
> already using CMake and it’s somewhat easier, but since most people still
> target version 2.8 (or 2.6...),
> we find it better to rewrite the build scripts ourselves and use modern
> features (as in, everything is
> a target that propagates requirements, we don’t propagate variables).
> It makes it also much easier to build a library for another platform that
> wasn’t targeted by the original
> project.
>
> If people are interested, I could share the CMakeLists.txt file we use for
> Boost. It doesn’t build all
> the libraries (some are hard like Context) and uses some internal macros,
> but it should be plain
> simple to tweak for your use.
>
> /Florent
>
> > On 12 Aug 2016, at 21:59, Robert Dailey 
> wrote:
> >
> > Hello,
> >
> > There is an internal C++ product at the company I work for which I
> > have written a series of CMake scripts for. This project actually has
> > dependencies on several open source libraries, such as boost,
> > freetype, openssl, etc.
> >
> > Right now what we do is build each of these third party libraries *by
> > hand*, once for every platform we support (Windows, Linux x86, Android
> > NDK). Then we stuff the includes (headers) and libraries
> > (static/shared) in a submodule and the primary code base's CMake
> > scripts pull them in as interface targets.
> >
> > This works well and is light-weight but is a pain when upgrading or
> > changing libraries. It's a pain because if I want to upgrade boost, I
> > have to build it up to 6 times (once for each platform and once for
> > each configuration).
> >
> > I've been thinking of a different approach for a while. I've done some
> > toying around with the "Super Build" concept, where I have a separate
> > CMake project that does nothing but use the ExternalProject module to
> > build libraries in real time along with our project. So the order of
> > operations would be 

Re: [CMake] [cmake-developers] Need ideas/opinions on third party library management

[Benjamin Ballet via CMake]

Very interesting discussion, we have the same issues here.

Florent Castelli, how many third parties libraries do you use ? I think a
super build can be a very good solution but I'm wondering how much third
party code you have to build. Here we use OpenCV, with, boost, and poco,
and other things... So it may be too long.

I was personnaly considering having an hybrid solution : include small
libraries (like jsoncpp) and pre-build the other for each platforms.


2016-08-16 12:52 GMT+02:00 Florent Castelli :

> At Spotify, we use CMake a lot for our large C++ library shared by all the
> clients.
> After trying to build libraries for each platform and variant, we
> basically gave up and we now
> use a super-build approach.
>
> For example, Boost is used by 5 platforms: Windows, OSX, Linux, Android
> and iOS.
> Each platform has a different CPU target (or many 32/64bit, x86/ARM).
> Each platform has many compilers.
> Some platforms have instrumentation options (Debug / Release, ASan, MSan…)
> and really need
> to be compiled properly, otherwise you’ll end up with false positives.
> The matrix of builds is REALLY hard to track. Each time we update Boost,
> we had to update
> a lot of things.
> I tried using ExternalProject and use b2 (build tool from Boost) to build
> it and instead of having
> lots of build jobs with a mirror of the flags, you end up mirroring the
> flags in your CMake files
> instead, which is still not good enough.
>
> In the end, I looked at how Boost is actually built. And for most
> libraries, it’s plain simple.
> A static library with a few files, some define, sometimes a platform
> specific source file.
> What if instead of having an external build tool, I built it from CMake
> instead?
> It would propagate all the build flags, target, instrumentation and
> compiler information from the main
> build to it and just work.
> I tried it and it worked in no time! We replaced our Boost 1.59 binary
> distribution with the source
> distribution and it’s much easier. When people build our library for a
> different target, they don’t have
> to download new binaries, they just reuse the same sources.
> Later on, we found a bug in Boost 1.59 (fixed in later versions) and
> patched it. We updated our source
> bundle and everything was smooth.
> Much later on, we wanted to use 1.61. We just updated the source bundle
> again, the list of source
> files or compilation flags for the libraries we use didn’t change. It was
> again effortless.
>
> Overall, building boost takes 10s on our developers’ machines. The sources
> aren’t changed often,
> so the cost is pretty low. It needs attention when we upgrade it, but
> that’s quite rare.
>
> We try now to use the same approach for other libraries when we add them.
> Some of them are
> already using CMake and it’s somewhat easier, but since most people still
> target version 2.8 (or 2.6...),
> we find it better to rewrite the build scripts ourselves and use modern
> features (as in, everything is
> a target that propagates requirements, we don’t propagate variables).
> It makes it also much easier to build a library for another platform that
> wasn’t targeted by the original
> project.
>
> If people are interested, I could share the CMakeLists.txt file we use for
> Boost. It doesn’t build all
> the libraries (some are hard like Context) and uses some internal macros,
> but it should be plain
> simple to tweak for your use.
>
> /Florent
>
> > On 12 Aug 2016, at 21:59, Robert Dailey 
> wrote:
> >
> > Hello,
> >
> > There is an internal C++ product at the company I work for which I
> > have written a series of CMake scripts for. This project actually has
> > dependencies on several open source libraries, such as boost,
> > freetype, openssl, etc.
> >
> > Right now what we do is build each of these third party libraries *by
> > hand*, once for every platform we support (Windows, Linux x86, Android
> > NDK). Then we stuff the includes (headers) and libraries
> > (static/shared) in a submodule and the primary code base's CMake
> > scripts pull them in as interface targets.
> >
> > This works well and is light-weight but is a pain when upgrading or
> > changing libraries. It's a pain because if I want to upgrade boost, I
> > have to build it up to 6 times (once for each platform and once for
> > each configuration).
> >
> > I've been thinking of a different approach for a while. I've done some
> > toying around with the "Super Build" concept, where I have a separate
> > CMake project that does nothing but use the ExternalProject module to
> > build libraries in real time along with our project. So the order of
> > operations would be as follows (for our automated build server):
> >
> > 1. Clone our "Third Party" repository
> > 2. Use CMake to generate & build the "Super Build" project (this
> > builds boost, openssl, freetype, etc for the current platform).
> > 3. Clone the main code base's repository
> > 4. Use