How to tell if a forked process is done?

[John Lin]

Howdy,

I want to know how to tell if a forked process is done.

Actually, my real question is that I want to run a shell script inside
of a python script, and after the shell script has finished running, I
want to do more stuff *condition* on the fact that the shell script
has finished running, inside the same python script.

The only way I can think of is to fork a process and then call the
shell script, as in:
pid = os.fork()
if pid == 0:
os.execl(shells cript_name.sh, "")
but how can I know if the shell script is finished?

In sum, my two questions are:
1. How can I know if a forked shell script is finished?
2. How can I run a shell script inside a python script without
forking a new process, so that I can know the shell script is done
from within the same python script?

thanks in advance,

John

[Klaus Alexander Seistrup]

Erik Max Francis wrote:

killing blindly is bad programming practice.
But he's killing with a signal of 0. From kill(2):

If sig is 0, then no signal is sent, but error checking is
still performed.

It's perfectly reasonable behavior to kill a process with a 0 signal;
it does no harm.

I overlooked that detail, thanks for correcting me.
// Klaus

--<> unselfish actions pay back better

[Donn Cave]

In article <3F************ ***@alcyone.com >,
Erik Max Francis <ma*@alcyone.co m> wrote:

Klaus Alexander Seistrup wrote:

Anyway you look at it, killing blindly is bad programming practice.

But he's killing with a signal of 0. From kill(2):

If sig is 0, then no signal is sent, but error checking is
still performed.

It's perfectly reasonable behavior to kill a process with a 0 signal; it
does no harm.

I think it would be reasonable to posit an implied context
for discussion of any programming technique, that said
technique would be deployed for some purpose.

If that is not too bold of an assumption, I think it follows
that our standard for a good programming practice has to be
a little more stringent that just whether deployment of the
technique causes any harm. In this case, for example, the
proposed technique is use the information returned from kill(0)
to decide whether some process is still alive, and according
to our theory of purposeful programming, we may guess that
the program then acts on the basis of that decision.

If kill(0) actually does not reliably indicate that the process
is alive because process IDs are not unique over time, then
it is arguably harmful as a programming practice even if it
is harmless as a system call.

What actually happens with processes that exited but haven't
been reaped by their parent with wait(2) or similar? Seems
to vary quite a bit, here's what I found -

FreeBSD 5.1 - No such process, ps PID=0, owned by me
Linux 2.4 - kill -0 works
MacOS X/Darwin - No such process, ps original PID, owner root

Donn Cave, do**@u.washingt on.edu