Re: Enhancement: make -j4 by default

[Paul Smith]

On Wed, 2013-05-29 at 17:22 -0400, Andrew Pennebaker wrote:
> On Wed, May 29, 2013 at 5:14 PM, Paul Smith <address@hidden> wrote:
> > On Wed, 2013-05-29 at 16:57 -0400, Andrew Pennebaker wrote:
> > > Could we turn on concurrency for make by default?
> >
> > No.  This would break far too many makefiles and be very unexpected.
> 
> How would this break a makefile?

We prefer to avoid top-posting on technical lists.

Many makefiles which have never been run with parallel builds enabled
will break the first time it's run that way, because the makefile has
imperfectly-defined prerequisite rules.  Make always builds its targets
in a well-defined order, so during serialized builds you can rely on
that ordering (perhaps not even intentionally) to get correct builds.

Once parallel builds are enabled, such a makefile could break as rules
can start and finish in a different order than they would during serial
builds.