InstallProgress.waitChild spins if read fails immediately

[Colin Watson]

    def waitChild(self):
        while True:
            (pid, res) = os.waitpid(self.child_pid,os.WNOHANG)
            if pid == self.child_pid:
                break
            self.updateInterface()
        return os.WEXITSTATUS(res)

In the event that the read() in updateInterface immediately returns EAGAIN (and by the way you should refer to that as errno.EAGAIN rather than as the hardcoded 11 and check errno.EWOULDBLOCK as well for compatibility with hppa etc.), then this will spin. select()ing on self.statusfd.fileno() would be much better, and you could install a SIGCHLD handler rather than checking with waitpid() every time.

[Colin Watson (cjwatson)]

And, of course, because this file descriptor is non-blocking it spins nearly all the time. I bet fixing this would speed ubiquity's final stages up a fair bit; it would certainly make the strace a lot less noisy!

[Michael Vogt (mvo)]

Thanks for those suggestions.

I added select() in waitChild() to make sure that it does not spin unnecessarly. It will timeout every 0.1s (default, can be changed via self.selectTimeout) to keep a possible GUI alive.

Cheers,
 Michael

The reason why waitChild() is implemented as a function and not as a signal handler is that e.g. vte does not work with that. It installs its own signal handler and you need to use the reaper object to catch children exiting.