On Thu, Mar 30, 2023 at 9:58 PM Zack Weinberg <zack@xxxxxxxxxxxx> wrote: We can already say with high confidence that the four checks done by AC_CHECK_HEADERS([a.h b.h c.h d.h]) can be run in parallel, for instance. […] This is getting into things that I'm not sure can be done in M4 at It is not the first email I write about this: for whatever thing can be done in parallel I had written an M4 framework <https://github.com/madmurphy/not-autotools/blob/master/m4/not-parallel-configure.m4> to make life simpler. And so the code above in parallel would become (assuming that we want to check for the headers stddef.h, stdint.h, stdio.h and stdlib.h): m4_include([not-parallel-configure.m4]) # Launch AC_CHECK_HEADERS() in parallel... NC_THREAD_NEW([headers_thread], [AC_CHECK_HEADERS([stddef.h stdint.h stdio.h stdlib.h])]) # Do other stuff in the meanwhile... # ... # Wait until the AC_CHECK_HEADERS thread has returned... NC_JOIN_THREADS([headers_thread]) AS_IF([test "x${ac_cv_header_stddef_h}" = 'xyes'], [AC_MSG_NOTICE([We have stddef.h])], [AC_MSG_NOTICE([We don't have stddef.h])]) A complete configure.ac example is available at madmurphy/not-autotools/examples/not-parallel-configure/configure.ac <https://github.com/madmurphy/not-autotools/blob/master/examples/not-parallel-configure/configure.ac> . --madmurphy On Thu, Mar 30, 2023 at 9:58 PM Zack Weinberg <zack@xxxxxxxxxxxx> wrote: > On Wed, Mar 29, 2023, at 7:05 PM, Thomas Jahns wrote: > > I spent some time thinking about improvements to autoconf configure > > scripts (while waiting for builds to proceed). In my view, it is > > currently still easier to seek small efficiency gains that, in sum, > > could still improve run-time substantially than parallelizing the > > whole would be, because there is so much often untapped potential: > > I do generally agree with this, and I'd also like to remind everyone > that Autoconf has very limited developer resources relative to how > difficult the task of parallelizing _all_ of a configure script will be. > > There _are_ some bits of "low hanging fruit" here. If parallelism > within a configure script is the specific thing what you're interested > in working on, I'd recommend that you start with the macros that check > for a list of things. We can already say with high confidence that the > four checks done by > > AC_CHECK_HEADERS([a.h b.h c.h d.h]) > > can be run in parallel, for instance. > > > Regarding parallelization for autoconf in particular, I think > > autoconf could very much benefit from having first more explicit > > effects of each macro, i.e. which variables end up being set, which > > file will be appended to etc. To my knowledge this is mostly well > > documented for the human reader, but not programmatically available > > in the M4 phase at all. > > This is getting into things that I'm not sure can be done in M4 at > all... > > zw > >
