Re: [9fans] `mk` (from Plan9 ports) efficiency related issue

["Federico G. Benavento" <benavento@gmail.com>]

when you have a clean mkfile, doing mk clean; mk install is faster than all the
dependency checking you'd want to do, specially is the project is a big bloat

take X11 for instance.... how long does it take to build it?

On Mon, Jan 17, 2011 at 2:31 PM, Ciprian Dorin Craciun
<ciprian.craciun@gmail.com> wrote:
> On Mon, Jan 17, 2011 at 17:53, Robert Raschke <rtrlists@googlemail.com> wrote:
>>
>> On Mon, Jan 17, 2011 at 3:33 PM, Ciprian Dorin Craciun
>> <ciprian.craciun@gmail.com> wrote:
>>>
>>> On Mon, Jan 17, 2011 at 17:00, Robert Raschke <rtrlists@googlemail.com>
>>> wrote:
>>> > Your email also doesn't explain why you cannot generate a "normal"
>>> > mk file.
>>>
>>>    I'm afraid I don't understand the question. What do you mean by
>>> "generating a normal mk file"?
>>>    A) Do you mean why am I using a generator that writes the `mk`
>>> script instead of writing the `mk` script myself by hand? The answer
>>> to this is complexity: writing `mk` is Ok when you have a simple
>>> application to build, but as the application grows larger so does the
>>> make script. (And using meta rules is not always possible.)
>>>    B) Why isn't the output script a "normal" `mk` script? Actually is
>>> a very simple script (no meta-rules, no shell expansion, etc.). It's
>>> just big. :)
>>>
>>
>> Sorry, I meant an idiomatic mk file, in the sense as they are used within
>> the Plan 9 distribution. Have a look at "Plan 9 Mkfiles"
>> (http://www.cs.bell-labs.com/sys/doc/mkfiles.html) and "Maintaining Files on
>> Plan 9 with Mk" (http://www.cs.bell-labs.com/sys/doc/mk.html), if you
>> haven't already done so.
>>
>> I think by listing all your dependencies one by one, step by step, you are
>> bypassing a lot of the strengths of a make system. I would expect your
>> generator to produce a mk include file with the meta rules plus the mk file
>> itself which lists file dependencies in a concise manner.
>>
>> Robby
>
> On Mon, Jan 17, 2011 at 17:51, Federico G. Benavento
> <benavento@gmail.com> wrote:
>>
>> a normal mkfile does have meta-rules and if you have so many targets
>> wouldn't it make sense to have more mkfiles?
>>
>> --
>> Federico G. Benavento
>
>
>    I'll respond to both Robert and Federico in the same email, as
> their observations an suggestions are on the same topic.
>
>    So for starters I've read both mentioned papers "Plan9 Mkfiles"
> and "Maintaining Files on Plan9 with Mk", and I have the following
> observations:
>    * the second paper "Maintaining Files on ..." is more a general
> guide that describes the semantic and syntax of `mk` files;
>    * the first paper "Plan9 Mkfiles" focuses entirely and exclusively
> on writing `mk` files for building Plan9 native applications; that is
> it describes the general rules on how to write short and simple `mk`
> files that take advantage on the existing Plan9 build infrastructure;
>    * as a consequence both of them seem to suggest writing small `mk`
> scripts that individually build each application or library;
>    * unfortunately what they don't deal with is inter-dependencies
> between multiple projects or libraries each with it's own `mk` script;
>    * thus if looking into the `plan9port` source code, inside the
> `src/mkfile` I see the following snippet (and I count about 50 other
> similar instances):
> ~~~~
> libs-%:V:
>        for i in $LIBDIRS
>        do
>                (cd $i; echo cd `pwd`';' mk $MKFLAGS $stem; mk $MKFLAGS $stem)
>        done
> ~~~~
>
>    But after reading the paper "Recursive Make Considered Harmful", I
> see that this approach poses at least the following problems:
>    * when developing and updating a single library, there is no way
> in which I can instruct `mk` to rebuild all dependent applications --
> unless I know about them and enumerate them one by one; as a
> consequence -- unless I know very well the real dependency graph --
> `mk` doesn't help me at all and I have to `mk clean all`;
>    * second, there is a performance bottleneck as now libraries can't
> be built in parallel; (this is fine if a library is quite big, but if
> I have libraries with a number of files on par with the number of
> processors I have wasted time;)
>    * third, it's almost impossible to make a dependency between one
> library to another; the dependency is encoded in their order in the
> variables like `LIBDIRS`;
>
>    I hope that these observations answer the first question of why
> don't I just create a number of separate files one for each project or
> library.
>
>    (The cited paper is at http://aegis.sourceforge.net/auug97.pdf .)
>
>    For the second question about why no "meta-rules", the answer is
> somehow trickier, thus I'll give a few problems which arise when using
> meta-rules:
>    * not all files of the same type are built by using the same rule;
> (for example for some files I want to enable debugging, for others
> not); thus I don't see how a meta-rule would solve this problem;
> (unless I create separate `mk` files or I resort to filename tags --
> for example I would call `*.debug.c` all C files that I want to be
> debugged, and `*.release.c` for those I don't);
>    * second, each file has a unique dependency graph -- for example
> one `*.c` file might include other headers than another `*.c` file in
> the same project; thus when updating a single header I want to be able
> to build only those `*.c` files that actually depend on it; (this
> observation is less important for C applications, but for other type
> of programs -- like Java -- this fine grained dependency tracking
> means a lot of saved computing power);
>    * third, in my brief experience with make files, meta-rules are
> quite hard to get right... furthermore it is impossible to have two
> patterns like: `%.%.x`; just imagine I have two types of images:
> background and foreground and I want to superimpose them, then I would
> like to be able to write `%{foreground}.%{background}.jpg :
> %{foreground}.jpg %{background}.jpg ..."; (I know that I can resort
> here to "<| generating command" but it seems just plain wrong...)
>
>    Now I hope nobody was offended by my observations regarding the
> way `mk` scripts are currently written. I am sure that for the purpose
> of building Plan9 applications this way is the best trade-off. But
> applying the same techniques to more complex programming languages or
> other systems is quite hard... Thus I just wanted to use the good `mk`
> tool as a backend for a build script generator that is more intimately
> acquainted with what it tries to build. (I want to extend my generator
> to Python -- as a replacement for `setup.py` -- and Java -- as a
> replacement for all the awful tools that exist in that ecosystem,
> especially Ant.)
>
>    Ciprian.
>
>



-- 
Federico G. Benavento