I am working on a project in which I need to loosely recreate supervisord(job control system) in D. I am using spawnShell() as opposed to spawnProcess() for ease of configuring arguments etc. This has the effect of running sh -c "command". However, it returns the PID of sh NOT of the child process(for obvious reasons). This becomes a problem because my program needs to be able to send a SIGKILL to the process if it doesn't respond to a SIGTERM after a certain period of time. I am able to send a SIGTERM no problem(presumably because sh catches the SIGTERM and passes it to it's child process/processes before exiting). However, for again obvious reasons, SIGKILL stops sh before it gets a chance to send a signal to the child process and it's left orphaned. Which brings me to my questions:
A: Can I safely assume that the PID of the spawned process will always be one higher than the PID of sh? It has behaved as such in all my testing so far.
B: If not, then is there a more elegant way(system call or such) to get a child process's PID knowing only the parent process's PID than having my program just execute pgrep -P <sh PID>?
You just need:
sh -c 'exec command'
the shell replaces itself with your command and gets out of the way, so there is no intermediate process.
No, you cannot assume pids will differ by one.