commit 0e8df1c7e48bcae2285c7c138bd50f932049bd24
author Neels Hofmeyr <neels@hofmeyr.de> Mon Feb 11 20:32:25 2019 +0100
committer Neels Hofmeyr <nhofmeyr@sysmocom.de> Mon Apr 08 13:47:17 2019 +0000
tree ebc61be55958db4925f412bfb55906cf100d94eb
parent 0c7826e9bd8026b239d320dba49416fd603f17fd

add osmo_use_count API

Provide a common implementation of use counting that supports naming each user
as well as counting more than just one use per user, depending on the rules the
caller implies.

In osmo-msc, we were originally using a simple int counter to see whether a
connection is still in use or should be discarded. For clarity, we later added
names to each user in the form of a bitmask of flags, to figure out exactly
which users are still active: for logging and to debug double get / double put
bugs. This however is still not adequate, since there may be more than one CM
Service Request pending. Also, it is a specialized implementation that is not
re-usable.

With this generalized implementation, we can:

- fix the problem of inadequate counting of multiple concurrent CM Service
  Requests (more than one use count per user category),
- directly use arbitrary names for uses like __func__ or "foo" (no need to
  define enums and value_string[]s),
- re-use the same code for e.g. vlr_subscr and get fairly detailed VLR
  susbscriber usage logging for free.

Change-Id: Ife31e6798b4e728a23913179e346552a7dd338c0