Copyright (c) 2016 Jaeheum Han <jay.han@gmail.com>
Licensed under Apache License v2.0 - see LICENSE file for details 

q)\l qac.q
q)c:init 0;n:123456789
q)do[n;inc c];print c
123456789
q)do[n;dec c];0~print c
1b
q)

o:.z.i; do[.z.c;if[o~.z.i;pids,:fork[]]]; ... ; wait[]
wait[] / blocks until all fork[]ed children are dead
kill[pids] / kill all pids
c:init j / c~(kc(-KJ);kj(intptr_t))
c:restart fname / `:/dev/rszshm_xxxxxx/0 or fname c
f:fname c / f~`:/dev/rszshm_xxxxxx/0 (useful for restart f)
detach c / detach c from current process, all ops but fname and rm are no-ops afterwards
rm c / rm the underlying shm file, preventing future processes from accessing it
xx:inc,dec,print c / xx:the value of counter, or nothing after detach or rm