rc(8) parallel tasks

[Cyril Vechera]

Hi there.

We've got a small launcher script (~250 loc) for parallel services 
start/stop etc. It is used on our embedded systems and our users 
containers. And I've done a proof of concept for implanting it to the 
FreeBSD's standard /etc/rc for execution starting scripts in parallel. 
It gave me a boot time reduction of rc part from 27 to 7 seconds, mostly 
on eliminating jams for network or other long-latency resources waiting.

The launcher is written in pure POSIX shell and uses FIFOs (named pipes) 
as a mutexes for synchronization. So it is embedded into /etc/rc and 
/etc/rc.d preserving rc.subr preloading. As a primary requirement, it 
guarantees topological order (strict partial order) defined by 
dependencies. It requires only POSIX shell, FreeBSD or Linux kernel, 
mkfifo and a writeable file system. Due to last requirement, it can be 
run on the late stage or should be supplied by some kinf of writtable 
fs, ie tmpfs. The FreeBSD-integrated version uses standard rcorder 
annotations (REQUIRE, BEFORE and PROVIDE) and there's no need to change 
rc.d scripts

It's not a full init replacement or a kind of services supervision tool. 
It only starts or invokes a group of scripts in parallel with resolving 
and assuring execution in dependencies order.

Please take a look at the script and patch set for FreeBSD:

https://github.com/cvss/jet9-multitask-init/blob/master/jet9-multitask-init
https://github.com/cvss/jet9-multitask-init/tree/master/examples/freebsd


-- 
Cyril Vechera