[CMake] How would I use parallel make on ExternalProjects?

[David Cole]

On the other hand, with Visual Studio, it's all a big hairy mess.....
because the setting for "how many parallel projects to build simultaneously"
is a single top level global setting. So when we spawn sub-VS instances in
VS 2008, for example, each one uses "N" for its parallel setting.

In that case, I typically recommend setting that "N" to be half to a quarter
of your processors available, assuming that there will be between 2 and 4
(on average) projects building simultaneously.


On Thu, Oct 7, 2010 at 11:55 AM, David Cole <david.cole at kitware.com> wrote:

> If you use "$(MAKE)" in a BUILD_COMMAND, then the literal "$(MAKE)" appears
> in the generated makefiles.
>
> That tells the top level make to spawn sub-makes with the job controller
> from the top level make.
>
> Then you do not need to specify any -j flags anywhere except at the top
> level.
>
> And then, the top level job controller makes sure there are only N
> concurrent things happening regardless of the level of sub-makes...
>
> Does that "make" sense?
>
>
> :-)
> David
>
>
> On Thu, Oct 7, 2010 at 11:52 AM, kent williams <nkwmailinglists at gmail.com>wrote:
>
>> 1. Is that $(MAKE) or is it ${MAKE} ?  One thing missing from the
>> CMake documentation -- unless I'm mistaken there's not much
>> explanation of CMake syntax in the documentation.
>>
>> 2. I think it's probably not what one intends to have 'make -j4' (for
>> example) used every time make is invoked.  If you configure a program
>> that includes several ExternalProjects, then it would spawn 4
>> concurrent builds of those ExternalProjects, and then each of those
>> builds would spawn 4 make steps at once, for 16 concurrent processes.
>>
>>
>> On Thu, Oct 7, 2010 at 10:36 AM, Bill Hoffman <bill.hoffman at kitware.com>
>> wrote:
>> > On 10/7/2010 11:25 AM, kent williams wrote:
>> >>
>> >> On Wed, Oct 6, 2010 at 5:01 PM, Clifford Yapp<cliffyapp at gmail.com>
>>  wrote:
>> >>>
>> >>> I use $(MAKE) in my BUILD_COMMAND and that seems to do OK, although I
>> >>> don't know if it works universally.
>> >>>
>> >>
>> >> That's an environment variable, as near as I can tell and isn't
>> >> mentioned in the current CMake documentation. So it's probably not the
>> >> best thing to do.
>> >>
>> >> upon reflection, this would be a little safer:
>> >>
>> >> if("${CMAKE_GENERATOR}" STREQUAL "Unix Makefiles")
>> >> set(BUILD_COMMAND_STRING "${CMAKE_MAKE_PROGRAM} -j4")
>> >> else()
>> >> set(BUILD_COMMAND_STRING "$(CMAKE_MAKE_PROGRAM)")
>> >> endif()
>> >
>> > By using $(MAKE), the toplevel -j N option should be passed down.  The
>> 2.8.3
>> > RC that is out now has some fixes in this area.
>> >
>> >
>> > -Bill
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