waiting for a program run by popen3() to end

[Donn Cave]

Quoth Rajarshi Guha <rajarshi at presidency.com>:

|  I have some code that runs an interactive program via popen3(). The program generates
| output which is then used later on. My script looks like this:
|
|
|
|         o,i,e = os.popen3('/usr/local/adapt/bin/descmng -g')
|         o.write('\n%s\n\n' % (redpick))
|         o.close()
|         time.sleep(1)
|         os.system('mv set5 gendes.in && rm set? outputdesc.txt')
|
| The program (descmng) produces the files set?, outputdesc.txt
|
| However on some systems, the program takes more than 1 sec to complete
| and as a result the os.system() command fails.
|
| Increasing the sleep time to 5 sec solves the problem but it does'nt seem to
| be reliable.
|
| I have considered using fork() and wait() but that does'nt let me run the
| program interactively.
|
| Is there any other way out (apart from dumping commands to a file and
| piping them to my program in a fork())?

You should look at the popen2 module in the library.  You're using
it already, via os.popen3, but the classes in popen2.py provide more
features.  However, it seems to me that you should be able to synch
with the child process by simply reading from its output or error
files.  Whether it actually outputs any data or not, when the process
exits, those pipes should close and the read will finish.  If you're
not interested in the data, though, I would not redirect error output
and throw it away as you're doing here, and if you redirect only the
regular output, that will greatly reduce odds of a deadlock.

Or even simpler, you can add the other statements to the command
to be run by os.popen3.

	Donn Cave, donn at drizzle.com