The spring container monitors if it is still used by `exec`

Since all processes run by docker-compose run or exec are parent of -ppid 0 we can use it to count how many shells are in use.

If there are no shells (except run) exit after some grace period.

Output

Initially I run make shell twice, then exited.

docker-compose logs -f spring

+ exec /scripts/startup/spring.sh
Used by 2 processes...
Used by 3 processes...
Used by 1 processes...
Retrying 1...
Used by 1 processes...
Retrying 2...
Used by 1 processes...
Retrying 3...
Used by 1 processes...
Retrying 4...
Used by 1 processes...
Retrying 5...
Used by 1 processes...
Retrying 6...
Used by 1 processes...
Retrying 7...
Used by 1 processes...
Retrying 8...
Used by 1 processes...
Retrying 9...
Used by 1 processes...
Retrying 0...
No more `docker-compose exec` running. Exiting