Re: Ruby redirection woes

Hi Brian,

Firstly, thanks for the help.

> I don't think you said anything about the platform you are running under.
> When I run your test under ruby 1.8.2p2 and FreeBSD 4.10, I get:
> 
> $ ruby command_runner_shell_test.rb 
> Hello, world! 2 times!
> $ 
>
> which looks pretty good to me too.

You actually need to run the test script with a shell redirection. Like
in the example output I gave, I redirected output of the script to a
file, output.txt, and then cat'ed it:

    $ ruby command_runner_shell_test.rb > output.txt
    $ cat output.txt
    Hello, world! 2 times!
    Hello, world! 2 times!
    Hello, world! 2 times!

Hopefully that will reproduce the same results I am seeing? Otherwise if
this problem just happens on mine... well that is just going to make it
even more difficult for me to track. :(

> If you are running under cygwin plus some Microsoft operating system

I am running this on Debian Linux 3.1, the testing branch of the
distribution. Ruby v1.8.2. Maybe the Debian package maintainers applied
some patches, but I doubt that would be the cause... but maybe.

> Seriously, Windows is badly broken with regard to processes and pipes.

I would agree there. I once had to write a sh-like shell that compiled
and ran on both Windows and Linux, for a uni project. :) I never
finished the windows part by the deadline (I did start a bit last minute
though)...

> Why is this a problem? You can call waitpid on the child pid, and if it has
> already terminated, then it will still be in the process table (as a zombie)
> waiting for you to reap its exit status. That's unless someone has messed
> with SIGCHLD.

That is just the handy little fact I needed. Now I guess I can remove
all that part of the code and be confident it works.  Thanks!

> And even if the process had gone completely, you'd just get an error from
> waitpid saying that the child did not exist (which is fine, since you know
> it did exist at the time you forked, so it must have died since then). Only
> if another process on the system had forked and re-used the same PID in the
> mean time would that be a problem.

Which was the (unlikely) problem I was trying to protect myself from. I
know it won't happen... but the fact that it "technically" could made me
uncomfortable. :P

I've attached the 'updated' command_runner with the threading stuff
removed. Hopefully with that cruft gone, it is easier to read.

Steven
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Steven Wong
Undergraduate Software Engineer

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