5 ms·

I have hope for modules because they can improve build times. Not exactly sure they would improve build time but if it's true, it would be a massive improvement

by jokoon 7y ago

I have hope for modules because they can improve build times. Not exactly sure they would improve build time but if it's true, it would be a massive improvement.

Renana 7y ago
Have you tried using IncrediBuild. It's a dedicated solution to reduce C++ build times. If you're working on Windows, you can use it free (sharing the link to download): https://www.incredibuild.com/ibonlinestore/register#/regWindows?utm_source=hackernews&utm_medium=question&utm_campaign=answer&utm_content=download https://www.incredibuild.com/ibonlinestore/register#/regWind...
saurik 7y ago
Meanwhile, I am deeply concerned about modules, as it seems like the kind of feature that is going to massively harm build times by making it much more difficult to do truly independent distributed builds (which right now is pretty easy with C/C++ due to its separate compilation and extremely explicit inter-file dependencies).
- vips7L 7y ago
  Wasn't the point of modules to decrease compilation/build times?
  - saurik 7y ago
    Some claim this, but I haven't seen it play out this way yet in what I have seen for modules; it could be that people are hyper-optimizing for serial performance when the future (and present!) is parallel? If so, :(. This article is possibly out of date--or maybe was wrong to begin with--but it shows how the modules concept from earlier this year simply broke parallel build efforts by enforcing a ton of serial dependencies. https://vector-of-bool.github.io/2019/01/27/modules-doa.html https://vector-of-bool.github.io/2019/01/27/modules-doa.html
    - BubRoss 7y ago
      I have also seen this. My guess is that it highlights more that there are way too many dependencies in the libraries being used and that those dependencies aren't organized well.
- naasking 7y ago
  Modules make separate compilation possible. C++ does not really have separate compilation right now.
  - saurik 7y ago
    I do not understand this comment, as I have done separate compilation every day with C++ for over two two decades: the model inherently only allows this, as every translation unit absolutely must be compiled separately and then linked... you don't even have a choice in the matter. I have also used both off-the-shelf and custom distributed build systems (most recently, I have deployed one which does insanely-parallel builds of a C++2a codebase using AWS Lambda), which pair extremely well with the explicit file-oriented dependencies that can be reported by each translation unit and used to determine which parts of the build are now stale given changes to the filesystem. I have never seen languages with module systems support even basic separate compilation, and it terrifies me; meanwhile, the flags I have seen being added to clang for attempting to preserve separate compilation behavior with the modules spec doesn't leave me feeling good about the endeavor. It could be my fears are unjustified, but it is extremely strange and somewhat annoying that the advocates for it don't ever seem to appreciate the state of the art for the status quo.
    - naasking 7y ago
      > I do not understand this comment, as I have done separate compilation every day with C++ for over two two decades: the model inherently only allows this, as every translation unit absolutely must be compiled separately and then linked... you don't even have a choice in the matter. Except if your headers include macros or templates, which must be evaluated every time. This is not separate compilation. What C/C++ developers have been doing for 20 years is jumping through hoops to incrementally reuse previously compiled results because C/C++ violate basic modularity principles [1]. They call it "separate compilation", but it's a pale shadow of true separate compilation. Proper modules would enforce abstraction boundaries so true separate compilation becomes possible. I can't speak to the specific C++ proposal here, but enabling separate compilation is exactly what modules are for. [1] http://llvm.org/devmtg/2012-11/Gregor-Modules.pdf http://llvm.org/devmtg/2012-11/Gregor-Modules.pdf
- zelly 7y ago
  You can still do distributed builds with modules. You can't have cyclic dependencies anymore though. Your code has to be structured into logical modules that are meant to be built in parallel. It's not going to be free. You could have replicated modules with the old preprocessor style, but this way it is formalized and enforced by the compiler.

by jokoon 7y ago

I have hope for modules because they can improve build times. Not exactly sure they would improve build time but if it's true, it would be a massive improvement.

Renana 7y ago

Have you tried using IncrediBuild. It's a dedicated solution to reduce C++ build times. If you're working on Windows, you can use it free (sharing the link to download): https://www.incredibuild.com/ibonlinestore/register#/regWindows?utm_source=hackernews&utm_medium=question&utm_campaign=answer&utm_content=download https://www.incredibuild.com/ibonlinestore/register#/regWind...

saurik 7y ago

Meanwhile, I am deeply concerned about modules, as it seems like the kind of feature that is going to massively harm build times by making it much more difficult to do truly independent distributed builds (which right now is pretty easy with C/C++ due to its separate compilation and extremely explicit inter-file dependencies).

vips7L 7y ago
Wasn't the point of modules to decrease compilation/build times?
- saurik 7y ago
  Some claim this, but I haven't seen it play out this way yet in what I have seen for modules; it could be that people are hyper-optimizing for serial performance when the future (and present!) is parallel? If so, :(. This article is possibly out of date--or maybe was wrong to begin with--but it shows how the modules concept from earlier this year simply broke parallel build efforts by enforcing a ton of serial dependencies. https://vector-of-bool.github.io/2019/01/27/modules-doa.html https://vector-of-bool.github.io/2019/01/27/modules-doa.html
  - BubRoss 7y ago
    I have also seen this. My guess is that it highlights more that there are way too many dependencies in the libraries being used and that those dependencies aren't organized well.
naasking 7y ago
Modules make separate compilation possible. C++ does not really have separate compilation right now.
- saurik 7y ago
  I do not understand this comment, as I have done separate compilation every day with C++ for over two two decades: the model inherently only allows this, as every translation unit absolutely must be compiled separately and then linked... you don't even have a choice in the matter. I have also used both off-the-shelf and custom distributed build systems (most recently, I have deployed one which does insanely-parallel builds of a C++2a codebase using AWS Lambda), which pair extremely well with the explicit file-oriented dependencies that can be reported by each translation unit and used to determine which parts of the build are now stale given changes to the filesystem. I have never seen languages with module systems support even basic separate compilation, and it terrifies me; meanwhile, the flags I have seen being added to clang for attempting to preserve separate compilation behavior with the modules spec doesn't leave me feeling good about the endeavor. It could be my fears are unjustified, but it is extremely strange and somewhat annoying that the advocates for it don't ever seem to appreciate the state of the art for the status quo.
  - naasking 7y ago
    > I do not understand this comment, as I have done separate compilation every day with C++ for over two two decades: the model inherently only allows this, as every translation unit absolutely must be compiled separately and then linked... you don't even have a choice in the matter. Except if your headers include macros or templates, which must be evaluated every time. This is not separate compilation. What C/C++ developers have been doing for 20 years is jumping through hoops to incrementally reuse previously compiled results because C/C++ violate basic modularity principles [1]. They call it "separate compilation", but it's a pale shadow of true separate compilation. Proper modules would enforce abstraction boundaries so true separate compilation becomes possible. I can't speak to the specific C++ proposal here, but enabling separate compilation is exactly what modules are for. [1] http://llvm.org/devmtg/2012-11/Gregor-Modules.pdf http://llvm.org/devmtg/2012-11/Gregor-Modules.pdf
zelly 7y ago
You can still do distributed builds with modules. You can't have cyclic dependencies anymore though. Your code has to be structured into logical modules that are meant to be built in parallel. It's not going to be free. You could have replicated modules with the old preprocessor style, but this way it is formalized and enforced by the compiler.