wait for all subprocesses in a list to exit

gistfile1.py

import signal

def wait_for_subprocs(procs, cb=lambda proc: 0):
    # do-nothing handler for SIGCHLD, just so it's something other than SIG_DFL.
    # otherwise, Python won't interrupt syscalls.
    oldhandler = signal.signal(signal.SIGCHLD, lambda *_: None)
    try:
        while procs:
            signal.pause()
            aliveprocs = []
            for p in procs:
                if p.poll() is None:
                    aliveprocs.append(p)
                else:
                    cb(p)
            procs = aliveprocs
    finally:
        signal.signal(signal.SIGCHLD, oldhandler)