What makes a pthread defunct ?

Question

i'm working with a multi-threaded program (using pthreads) that currently create a background thread (PTHREAD_DETACHED) and then invokes pthread_exit(0). My problem is that the process is then listed as "defunct" and curiously do not seems to "really exists" in /proc (which defeats my debugging strategies)

I would like the following requirements to be met:

• the program should run function A in a loop and function B once
• given the PID of the program /proc/$pid/exe, /proc/$pid/maps and /proc/$pid/fd must be accessible (when the process is defunct, they are all empty or invalid links)
• it must be possible to suspend/interrupt the program with CTRL+C and CTRL+Z as usual

edit: I hesitate changing the program's interface for having A in the "main" thread and B in a spawned thread (they are currently in the other way). Would it solve the problem ?

Answer 1

Is there a reason you can't do things the other way round: have the main thread run the loop, and do the one-off task in the background thread?

Answer 2

Not the most elegant design but maybe you could block the main thread before exiting with:

 while(1) {
       pause();
 }

Then you can install a signal handler for SIGINT and SIGTERM that breaks the loop. The easiest way for that is: exit(0) :-).

Answer 3

You can either suspend the execution of the main process waiting for a signal, or don't detach the thread (using the default PHTREAD_CRATE_JOINABLE) waiting for its termination with a pthread_join().