From: gwtmp01@...
Date: 2005-06-28T04:48:18+09:00
Subject: Re: redirecting STDOUT


On Jun 27, 2005, at 1:37 PM, Joe Van Dyk wrote:
> Why doesn't this work?

Disclaimer: I'm pretty good with Unix System stuff
but still learning on the Ruby so...

> (#executable is a function that returns a string that contains a test
> application that spits out some data)
>
>   def start
>     pid = fork
>     if pid.nil?              # In child
>       log = File.open(executable + ".log", "w")
>       STDOUT.reopen(log)
>       STDERR.reopen(log)
>       exec executable        # Start program
>       exit
>     else                     # In parent
>       @pid = pid             # Record new process id
>       Process.detach @pid    # If the process dies, let it die
>       monitor                # Start monitoring the process' status
>     end
>   end

This worked for me (Mac OS X 10.4, Ruby 1.8.2).  Check the permissions
on the log file. If was created in earlier tests as a read-only file  
maybe
that is why the program fails now.

If you have something like ktrace or truss on your system, trace
the ruby program and then look at the dump.  You can see exactly
what system calls are being made (open/read/write/etc) and also
what errors, if any, are being returned.

Try using some standard program such as /bin/date instead of executable
just to make sure it isn't a problem with your test program.  You'll
probably want a different path for the log file in that case.

If 'monitor' is going to watch the child process then just incorporate
calls to Process.wait(@pid) as part of 'monitor' instead of
Process.detach.  If you have both Process.detach and monitor  
periodically
calling Process.wait, you'll never be sure which thread is going to
catch the exiting child.



Gary Wright