5.11. Advice for packagers

5.11.1. Components (“plugins”): DSO or no?

PMIx contains a large number of components (sometimes called “plugins”) to effect different types of functionality in PMIx. For example, some components provide support for networks and may link against specialized libraries to do so.

PMIx v5.0.3rc1 has two configure-time defaults regarding the treatment of components that may be of interest to packagers:

PMIx’s libraries default to building as shared libraries (vs. static libraries). For example, on Linux, PMIx will default to building libpmix.so (vs. libpmix.a).

Note

See the descriptions of --disable-shared and --enable-static in this section for more details about how to change this default.

Also be sure to see this warning about building static apps.
PMIx will default to including its components in its libraries (as opposed to being compiled as dynamic shared objects, or DSOs). For example, libpmix.so on Linux systems will contain the OPA PNET component, instead of the OPA PNET being compiled into mca_pnet_opa.so and dynamically opened at run time via dlopen(3).

Note

See the descriptions of --enable-mca-dso and --enable-mca-static in this section for more details about how to change this defaults.

A side effect of these two defaults is that all the components included in the PMIx libraries will bring their dependencies with them. For example (on Linux), if the XYZ PNET component requires libXYZ.so, then these defaults mean that libpmix.so will depend on libXYZ.so. This dependency will likely be telegraphed into the PMIx binary package that includes libpmix.so.

Conversely, if the XYZ PNET component was built as a DSO, then — assuming no other parts of PMIx require libXYZ.so — libpmix.so would not be dependent on libXYZ.so. Instead, the mca_pnet_xyz.so DSO would have the dependency upon libXYZ.so.

Packagers can use these facts to potentially create multiple binary PMIx packages, each with different dependencies by, for example, using --enable-mca-dso to selectively build some components as DSOs and leave the others included in their respective PMIx libraries.

# Build all the "pnet" components as DSOs (all other
# components will default to being built in their respective
# libraries)
shell$ ./configure --enable-mca-dso=pnet ...

This allows packaging $libdir as part of the “main” PMIx binary package, but then packaging $libdir/pmix/mca_pnet_*.so as sub-packages. These sub-packages may inherit dependencies on their own. Users can always install the “main” PMIx binary package, and can install the additional “pnet” PMIx binary sub-package if they actually have network hardware installed (which will cause the installation of additional dependencies).