openmpi @4.0.1: opportunistic linking to libevent

[p-bro]

Several subports of openmpi (I saw it for openmpi-gcc5 openmpi-gcc7 openmpi-gcc8 openmpi-default) opportunistically link to /opt/local/lib/libevent-#.#.#.dylib, a library provided by the libevent port.

Could not open /opt/local/lib/libevent-2.1.6.dylib: Error opening or reading file (referenced from /opt/local/lib/openmpi-mp/libmca_common_monitoring.50.dylib)
...
 openmpi-gcc5 @4.0.1+fortran
 openmpi-gcc7 @4.0.1+fortran
 openmpi-gcc8 @4.0.1+fortran
 openmpi-default @4.0.1+gcc8

libevent is not listed as one of the dependencies of openmpi (not even indirectly), thus an upgrade of libevent triggers a rev-upgrade rebuild of openmpi, and uninstallation of libevent breaks openmpi.

Here's the section from the openmpi configure process confirming its recognition of libevent and then linking to it:

--- MCA component event:external (m4 configuration macro, priority 90)
checking for MCA component event:external compile mode... static
checking --with-libevent-libdir value... simple ok (unspecified value)
checking for external libevent in... (default search paths)
checking event2/event.h usability... yes
checking event2/event.h presence... yes
checking for event2/event.h... yes
looking for library without search path
checking for library containing event_config_new... -levent
checking for evthread_set_lock_callbacks in -levent... yes
checking for evthread_use_pthreads in -levent_pthreads... yes
checking if external libevent version is 2.0.22 or greater... yes
checking if MCA component event:external can compile... yes

[mascguy (Christopher Nielsen)]

I'll take this. Can someone please assign to me?

[mascguy (Christopher Nielsen)]

Reviewed the OpenMPI developer docs, and apparently an external libevent is preferred starting with release 4.0.

So we need to decide whether we want the MacPorts version (in which case a formal dependency on libevent is needed), or force OpenMPI to build and use it's own private version.

This decision is beyond my pay grade, however. MacPorts maintainers/managers?

[mascguy (Christopher Nielsen)]

Draft pull requested created. Final decision of internal vs. external libevent usage is still being discussed, but hopefully we'll be able to get consensus within the next few days.

​https://github.com/macports/macports-ports/pull/9684

[mascguy (Christopher Nielsen)]

Updated status of PR from draft, to ready-for-review.

[Christopher Nielsen <mascguy@…>]

In acc4e389631220a06f9bb1a454b4ca7dae461da3/macports-ports (master):

openmpi: force use of macports libevent, to eliminate implicit use when already installed

Fixes: #59626