[mej/nhc] 5dcd2e: nhc: Add concurrency checking via PID file

[Michael Jennings]

Branch: refs/heads/mej/dev/40-context-aware-concurrency
Home: https://github.com/mej/nhc
Commit: 5dcd2e50b78671f3173f59a78c7c82f14b64a025
https://github.com/mej/nhc/commit/5dcd2e50b78671f3173f59a78c7c82f14b64a025
Author: Michael Jennings <m...@lanl.gov>
Date: 2023-08-29 (Tue, 29 Aug 2023)

Changed paths:
M nhc

Log Message:
-----------
nhc: Add concurrency checking via PID file

This changeset adds the use of a PID file to record the running NHC's
process ID and to check if an existing NHC (of the same context) is
already running. There are also several sanity checks to try and
avoid misbehavior and/or race conditions.

Closes #40.