01e4570af7
The Autoconf AC_CONFIG_* macros can only be instantiated exacly once
for any given file, *and* they must be in a code execution path at run
time for the target file to be generated at the end of configure.
For example, if you want to generate file ABC at the end of configure,
you must invoke the AC_CONFIG_FILES(ABC) macro in a code path that
will get executed when configure is run.
That's pretty straightforward.
What's not straightforward is two corner cases:
1. You cannot invoke the AC_CONFIG_FILES(ABC) macro for the same file
more than once. If you do, autoreconf will fail (even before you
can run configure).
2. If AC_CONFIG_FILES(ABC) is not in a code path that is executed by
configure, the file ABC is not registered properly, and ABC will
not be generated at the end of configure.
This applies to hwloc because hwloc's HWLOC_SETUP_CORE macro calls
both AC_CONFIG_FILES and AC_CONFIG_HEADER to setup its Makefiles
(etc.) so that targets like "make distclean" and "make distcheck" will
work properly. Hence, we *have* to invoke HWLOC_SETUP_CORE.
However, the MCA_opal_hwloc_hwloc201_CONFIG macro has a few side
effects. It would be nice to do able to do something like this:
```
if hwloc:extern is going to be used:
Invoke minimal HWLOC_SETUP_CORE (with no side effects)
else
Invoke full HWLOC_SETUP_CORE (with side effects)
fi
```
But we can't, because autoreconf will detect that AC_CONFIG_FILES has
been invoked on the same files more than once (regardless of whether
those code paths will be executed at run time or not). Kaboom.
Similarly, we can't do this:
```
if hwloc:extern is not going to be used:
Invoke full HWLOC_SETUP_CORE (with side effects)
fi
```
Because then hwloc's AC_CONFIG_FILES won't be registered properly when
hwloc:external *is* used (i.e., when the HWLOC_SETUP_CORE macro is not
in a code path that is executed at run time), and targets like "make
distclean" will fail because hwloc's Makefiles won't have been setup.
Kaboom.
But remember that the hwloc framework is a bit special: there will
only ever be 2 comoponents: external and internal. External is
guaranteed to be configured first because of its priority. So the
internal component (i.e., this component) immediately knows if it is
going to be used or not based on whether the external component
configuration succeeded or failed.
Specifically: regardless of whether the internal component (i.e., this
component) is going to be used, we have to invoke HWLOC_SETUP_CORE.
But we can manage the side effects: allow the side effects when
this/internal component is going to be used, and avoid the side
effects when this/internal component is not going to be used.
This is a little less clean than I would have liked, but because of
Autoconf's oddity about its AC_CONFIG_* macros, this is the only
solution I could come up with.
Signed-off-by: Jeff Squyres <jsquyres@cisco.com>
|
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|---|---|---|
| .. | ||
| base | ||
| external | ||
| hwloc201 | ||
| autogen.options | ||
| configure.m4 | ||
| hwloc-internal.h | ||
| Makefile.am | ||
| README.txt | ||
12 Sep 2011 Notes for hwloc component maintainers: 1. There can only be *1* hwloc version component at a time. Specifically: if there are multiple hwlocXYZ components (i.e., different versions of hwloc), then they must all be .ompi_ignore'd except for 1. This is because we currently m4_include all of the underlying hwloc's .m4 files -- if there are multiple hwlocXYZ components, I don't know if m4 will barf at the multiple, conflicting AC_DEFUNs, or whether it'll just do something completely undefined. 1a. As a consequence, if you're adding a new hwloc version component, you'll need to .ompi_ignore all others while you're testing the new one. 2. If someone wants to fix #1 someday, we might be able to do what we do for libevent: OPAL_CONFIG_SUBDIR (instead of slurping in hwloc's .m4 files).