[Omake] multiple generator invokation

[Aleksey Nogin]

On 27.07.2007 14:10, Sam Steingold wrote:

> $(R_GEN) : ./tools/gen_foo.exe
>   foreach($(my_save), $@)
>   $< -by_type -tp foo_tick.ml -ut $(UTDEST)/ut_foo.ml \
>     -map $(UTDEST)/map_foo.ml
>   foreach($(my_diff), $@)
> 
> I noticed that the generator ./tools/gen_foo.exe is invoked 6(!) times
> in quick succession (few seconds). why?

The issue is how the rules with multiple targets work - there is a 
_separate_ rule for each target, and the rules get merged together if 
all the commands and dependencies are the same.

Consider for example:

foo bar:
    touch $@

This would actually create two separate rules:

foo: :effects: bar
    touch foo

bar: :effects: foo
    touch bar

(where the :effects: part makes sure the two would never run in parallel).

If the $@ is not explicitly present in the rule test, different rules 
will get created, but only the first will run - when OMake will come 
around to run the subsequent ones, it will see that there is nothing new 
that needs to be done.

-- 
Aleksey Nogin, Research Scientist
Advanced Technologies Department, Information & System Sciences Lab
HRL Laboratories, LLC, Malibu, CA