How to make child process die after parent exits?

Question

Suppose I have a process which spawns exactly one child process. Now when the parent process exits for whatever reason (normally or abnormally, by kill, ^C, assert failure o

Answer 1

I managed to do a portable, non-polling solution with 3 processes by abusing terminal control and sessions. This is mental masturbation, but works.

The trick is:

• process A is started
• process A creates a pipe P (and never reads from it)
• process A forks into process B
• process B creates a new session
• process B allocates a virtual terminal for that new session
• process B installs SIGCHLD handler to die when the child exits
• process B sets a SIGPIPE handler
• process B forks into process C
• process C does whatever it needs (e.g. exec()s the unmodified binary or runs whatever logic)
• process B writes to pipe P (and blocks that way)
• process A wait()s on process B and exits when it dies

That way:

• if process A dies: process B gets a SIGPIPE and dies
• if process B dies: process A's wait() returns and dies, process C gets a SIGHUP (because when the session leader of a session with a terminal attached dies, all processes in the foreground process group get a SIGHUP)
• if process C dies: process B gets a SIGCHLD and dies, so process A dies

Shortcomings:

• process C can't handle SIGHUP
• process C will be run in a different session
• process C can't use session/process group API because it'll break the brittle setup
• creating a terminal for every such operation is not the best idea ever