# 9. Version Numbers and Binary Compatibility

OpenPMIx has two sets of version numbers that are likely of interest to end users / system administrator:

- Software version number

- Shared library version numbers

Both are described below, followed by a discussion of application binary interface (ABI) compatibility implications.

## 9.1. Software Version Number

OpenPMIx’s version numbers are the union of several different values: major, minor, release, and an optional quantifier.

- Major: The major number is the first integer in the version string (e.g., v1.2.3). Changes in the major number typically indicate a significant change in the code base and/or end-user functionality. The major number is always included in the version number.

- Minor: The minor number is the second integer in the version string (e.g., v1.2.3). Changes in the minor number typically indicate a incremental change in the code base and/or end-user functionality. The minor number is always included in the version number:

- Release: The release number is the third integer in the version string (e.g., v1.2.3). Changes in the release number typically indicate a bug fix in the code base and/or end-user functionality.

- Quantifier: OpenPMIx version numbers sometimes have an arbitrary string affixed to the end of the version number. Common strings include:

  - `aX`: Indicates an alpha release. X is an integer indicating the number of the alpha release (e.g., v1.2.3a5 indicates the 5th alpha release of version 1.2.3).

  - `bX`: Indicates a beta release. X is an integer indicating the number of the beta release (e.g., v1.2.3b3 indicates the 3rd beta release of version 1.2.3).

  - `rcX`: Indicates a release candidate. X is an integer indicating the number of the release candidate (e.g., v1.2.3rc4 indicates the 4th release candidate of version 1.2.3).

Although the major, minor, and release values (and optional quantifiers) are reported in OpenPMIx nightly snapshot tarballs, the filenames of these snapshot tarballs follow a slightly different convention.

Specifically, the snapshot tarball filename contains three distinct values:

- Most recent Git tag name on the branch from which the tarball was created.

- An integer indicating how many Git commits have occurred since that Git tag.

- The Git hash of the tip of the branch.

For example, a snapshot tarball filename of `pmix-v1.0.2-57-gb9f1fd9.tar.bz2` indicates that this tarball was created from the v1.0 branch, 57 Git commits after the `v1.0.2` tag, specifically at Git hash gb9f1fd9.

OpenPMIx’s Git master branch contains a single `dev` tag. For example, `pmix-dev-8-gf21c349.tar.bz2` represents a snapshot tarball created from the master branch, 8 Git commits after the “dev” tag, specifically at Git hash gf21c349.

The exact value of the “number of Git commits past a tag” integer is fairly meaningless; its sole purpose is to provide an easy, human-recognizable ordering for snapshot tarballs.

## 9.2. Shared Library Version Number

OpenPMIx uses the GNU Libtool shared library versioning scheme.

Note

Only official releases of OpenPMIx adhere to this versioning scheme. “Beta” releases, release candidates, and nightly tarballs, developer snapshots, and Git snapshot tarballs likely will all have arbitrary/meaningless shared library version numbers.

The GNU Libtool official documentation details how the versioning scheme works. The quick version is that the shared library versions are a triple of integers: (current,revision,age), or `c:r:a`. This triple is not related to the PMIx software version number. There are six simple rules for updating the values (taken almost verbatim from the Libtool docs):

1. Start with version information of `0:0:0` for each shared library.

2. Update the version information only immediately before a public release of your software. More frequent updates are unnecessary, and only guarantee that the current interface number gets larger faster.

3. If the library source code has changed at all since the last update, then increment revision (`c:r:a` becomes `c:r+1:a`).

4. If any interfaces have been added, removed, or changed since the last update, increment current, and set revision to 0.

5. If any interfaces have been added since the last public release, then increment age.

6. If any interfaces have been removed since the last public release, then set age to 0.

## 9.3. Application Binary Interface (ABI) Compatibility

OpenPMIx provides forward ABI compatibility in all versions of a given feature release series and its corresponding super stable series. For example, on a single platform, a PMIx application linked against OpenPMIx v1.3.2 shared libraries can be updated to point to the shared libraries in any successive v1.3.x or v1.4 release and still work properly (e.g., via the `LD_LIBRARY_PATH` environment variable or other operating system mechanism).

OpenPMIx reserves the right to break ABI compatibility at new feature release series. For example, the same PMIx application from above (linked against PMIx v1.3.2 shared libraries) will not work with PMIx v1.5 shared libraries.