in reply to Re^6: Best way to kill a child process
in thread Best way to kill a child process
$SIG{CHLD} = sub {while (waitpid(-1, WNOHANG) > 0){} };
This shouldn't hang if there are no children to reap. And it will reap all available children to reap (0,1,20,150).
Somewhere in the last couple of threads about this, there was a question about grandchildren. There can be "big trouble in Dodge City" if children are creating grandchildren. Maybe the grandchild dies and expects its parent who was a "child" to reap it, but if that child dies, I suspect that there could be some race conditions about who reaps that - maybe the "step-child" is still running?
The parent should only be responsible for reaping it own children. I highly recommend against the idea of children making further grandchildren. After a fork(), the child should close the passive socket.
As a general "rule" children should not spawn more grandchildren. I mean a child is supposed to do its job of talking to a client and then die. But things can get "out of wack" if that child has its own child. So the first "step child" is supposed to die and get reaped, but that can't happen if it itself has as a child that is supposed to be active? I think there is a problem here. We have a "dead" parent, that can't be reaped because it has a child that can't be reaped.
I think things will be ok if you do not allow children to make other children. First thing that a child should do is close the passive socket.
First thing that a parent (server) should do after the fork() is close the active socket. Parents (servers) should only listen for new client connections. Children should only deal with their currently active socket (to the client).
Yes, there are models where parents coordinate children activities, but that is an advanced topic and I don't think that we are talking about that here. That is into the range of not only complicated, but darn complicated!