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From: Cecil Westerhof <Cecil@decebal.nl>
Newsgroups: comp.lang.python
Subject: Re: Best way to prevent zombie processes
Organization: Decebal Computing
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Date: Mon, 01 Jun 2015 15:03:52 +0200
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Op Monday 1 Jun 2015 14:16 CEST schreef Cecil Westerhof:

> Op Sunday 31 May 2015 23:33 CEST schreef Cecil Westerhof:
>
>> At the moment I have the following code:
>> os.chdir(directory)
>> for document in documents:
>> subprocess.Popen(['evince', document])
>>
>> With this I can open several documents at once. But there is no way
>> to know when those documents are going to be closed. This
>> could/will lead to zombie processes. (I run it on Linux.) What is
>> the best solution to circumvent this?
>>
>> I was thinking about putting all Popen instances in a list. And
>> then every five minutes walk through the list and check with poll
>> if the process has terminated. If it has it can be released from
>> the list. Of-course I need to synchronise those events. Is that a
>> good way to do it?
>
> With some investigation I decided on something completely different.
>
> I made a class:
> import os
> import subprocess
>
> from os.path    import expanduser
> from threading  import Thread
>
> class DocumentsToShow:
> def show_documents(self):
> if self._desktop != -1:
> subprocess.check_call(['wmctrl', '-s', str(self._desktop - 1)])
> os.chdir(self._directory)
> for document in self._documents:
> Popen_without_zombie(['evince', document])
>
> def __init__(self, name, desktop, directory, documents):
> '''Initialise the class'''
>
> self._name      = name
> self._desktop   = desktop
> self._directory = expanduser(directory)
> self._documents = documents
>
> And this class uses the following function:
> def Popen_without_zombie(command):
> p = subprocess.Popen(command)
> Thread(target = p.wait).start()
>
> The class takes a name for the collection, which desktop to display
> it on, the directory that contains the documents and a list of
> documents. With show_documents they are displayed.
>
> How about this way of solving it?
>
>
> About the improvement of the class. Now it is always evince that is
> used to open a document. But it would be nice if it was a little
> less picky. What is the preferred way to solve this? - Defining a
> set the user can choose from. - Making it a string parameter and
> expecting the user to know what he is doing.

I let the user give the command to open the documents, but check if
the command exists:
    class DocumentsToShow:
        def show_documents(self):
            if self._desktop != -1:
                subprocess.check_call(['wmctrl', '-s', str(self._desktop - 1)])
            os.chdir(self._directory)
            for document in self._documents:
                Popen_without_zombie([self._command, document])

        def __init__(self, name, desktop, command, directory, documents):
            '''Initialise the class'''

            try:
                subprocess.check_call(['which', command])
            except subprocess.CalledProcessError:
                raise ValueError('Command \'{0}\' is not known'.format(command))

            self._name      = name
            self._desktop   = desktop
            self._command   = command
            self._directory = expanduser(directory)
            self._documents = documents


-- 
Cecil Westerhof
Senior Software Engineer
LinkedIn: http://www.linkedin.com/in/cecilwesterhof