FAQ
Hello.

I am going to write python script which will read python command from
socket, run it and return some values back to socket.

My problem is, that I need some timeout. I need to say for example:

os.system("someapplication.exe")

and kill it, if it waits longer than let's say 100 seconds

I want to call command on separate thread, then after given timeout -
kill thread, but I realized (after reading Usenet archive) that there is
no way to kill a thread in Python.

How can I implement my script then?

PS. it should be portable - Linux, Windows, QNX, etc


From http Tue Sep 6 11:31:06 2005
From: http (Paul Rubin)
Date: 06 Sep 2005 02:31:06 -0700
Subject: Job Offer in Paris, France : R&D Engineer (Plone)
References: <mailman.132.1125914440.4249.python-list@python.org>
<7xbr37u8ut.fsf@ruckus.brouhaha.com>
<mailman.138.1125921981.4249.python-list@python.org>
<7xpsrn3100.fsf@ruckus.brouhaha.com>
<mailman.182.1125995848.4249.python-list@python.org>
Message-ID: <7x4q8y35lx.fsf@ruckus.brouhaha.com>

Huron <huron at sopinspace.com> writes:
1) whether there would be legal or procedural obstacles for a
non-European wanting to work in Paris for a while; and
If you are a member of the EU (the netherlands ?), there no such problem on
our side. Only _you_ would have some paperwork to do.
I'm in the US and have no EU papers. Still feasible?
2) whether it was mandatory to be able to speak and write in French (I
can do so, but very badly for now).
I would say that it is mandatory to speak a bit and to be willing/able to
lean ... but this is not _mandatory_ to speak perfectly. This should not
stop you if you're interested.
(A test could be : whether or not you understand the position description
pdf.)
I can understand the main points but I had to figure out some parts
from context. I had a good French class many years ago and could read
French pretty well at that time, and could converse ok if the other
person was a little bit patient. I've forgotten most of it since
then, but I expect (or hope) that it would come back.

Another issue: I have most of the qualifications in the pdf (I've been
involved with free software for a long time and am a former FSF staff
member, I'm knowledgeable about web server implementation and web
applications, and I'm pretty good with Python), but I've never used
Zope or Plone. I do have a strong interest in collaborative web site
implementation but have been wanting to code something with higher
performance than what I see the traditional LAMP architecture as
capable of.
I'm sure you will get lots of good French-speaking candidates though.
Dont be too sure of that ;-) ... and dont hesitate to apply if you are
interested.
If you still think this, I'd be interested in chatting a little
further. Does the email address in the pdf go to you? If not, should
I write you directly? Can I call on the phone (you can leave me a
number at http://paulrubin.com)? Thanks.

Search Discussions

  • Jacek Popławski at Sep 6, 2005 at 9:48 am
    After reading more archive I think that solution may be to raise an
    Exception after timeout, but how to do it portable?
  • Sp1d3rx at Sep 6, 2005 at 4:43 pm
    You'll need a watchdog thread that handles the other threads. The
    watchdog thread just builds a table of when threads were started, and
    after a certain # of seconds, expires those threads and kills them.
  • Bryan Olson at Sep 6, 2005 at 8:03 pm
    Jacek Poplawski had written:
    I am going to write python script which will read python
    command from socket, run it and return some values back to
    socket.
    >>
    My problem is, that I need some timeout.
    Jacek Poplawski wrote:
    After reading more archive I think that solution may be to raise an
    Exception after timeout, but how to do it portable?
    Python allows any thread to raise a KeyboardInterrupt in the
    main thread (see thread.interrupt_main), but I don't think there
    is any standard facility to raise an exception in any other
    thread. I also believe, and hope, there is no support for lower-
    level killing of threads; doing so is almost always a bad idea.
    At arbitrary kill-times, threads may have important business
    left to do, such as releasing locks, closing files, and other
    kinds of clean-up.

    Processes look like a better choice than threads here. Any
    decent operating system will put a deceased process's affairs
    in order.


    Anticipating the next issues: we need to spawn and connect to
    the various worker processes, and we need to time-out those
    processes.

    First, a portable worker-process timeout: In the child process,
    create a worker daemon thread, and let the main thread wait
    until either the worker signals that it is done, or the timeout
    duration expires. As the Python Library Reference states in
    section 7.5.6:

    A thread can be flagged as a "daemon thread". The
    significance of this flag is that the entire Python program
    exits when only daemon threads are left.

    The following code outlines the technique:

    import threading

    work_is_done = threading.Event()

    def work_to_do(*args):
    # ... Do the work.
    work_is_done.set()

    if __name__ == '__main__':
    # ... Set stuff up.
    worker_thread = threading.Thread(
    target = work_to_do,
    args = whatever_params)
    worker_thread.setDaemon(True)
    worker_thread.start()
    work_is_done.wait(timeout_duration)



    Next, how do we connect the clients to the worker processes?

    If Unix-only is acceptable, we can set up the accepting socket,
    and then fork(). The child processes can accept() incomming
    connections on its copy of the socket. Be aware that select() on
    the process-shared socket is tricky, in that that the socket can
    select as readable, but the accept() can block because some
    other processes took the connection.


    If we need to run on Windows (and Unix), we can have one main
    process handle the socket connections, and pipe the data to and
    from worker processes. See the popen2 module in the Python
    Standard Library.


    --
    --Bryan
  • Bryan Olson at Sep 6, 2005 at 8:23 pm
    Bryan Olson wrote:
    [Some stuff he thinks is right, but might not answer the real
    question]

    Definitely look into Peter Hanson's answer.

    Olson's answer was about timing-out one's own Python code.


    Bryan Olson has heretofore avoided referring to himself in the
    third person, and will hence forth endeavor to return to his
    previous ways.

    --
    --Bryan
  • Jacek Popławski at Sep 8, 2005 at 11:26 am

    Bryan Olson wrote:
    First, a portable worker-process timeout: In the child process,
    create a worker daemon thread, and let the main thread wait
    until either the worker signals that it is done, or the timeout
    duration expires.
    It works on QNX, thanks a lot, your reply was very helpful!
    If we need to run on Windows (and Unix), we can have one main
    process handle the socket connections, and pipe the data to and
    from worker processes. See the popen2 module in the Python
    Standard Library.
    popen will not work in thread on QNX/Windows, same problem with spawnl
    currently I am using:

    os.system(command+">file 2>file2")

    it works, I just need to finish implementing everything and check how it
    may fail...

    One more time - thanks for great idea!
  • Jacek Popławski at Sep 8, 2005 at 1:06 pm

    Paul Rubin wrote:
    Maybe the child process can just use sigalarm instead of a separate
    thread, to implement the timeout.
    Already tried that, signals works only in main thread.
    To get even more OS-specific, AF_UNIX sockets (at least on Linux) have
    a feature called ancillary messages that allow passing file
    descriptors between processes. It's currently not supported by the
    Python socket lib, but one of these days... . But I don't think
    Windows has anything like it. No idea about QNX.
    I have solved problem with additional process, just like Bryan Olson
    proposed. Looks like all features I wanted are working... :)
  • Bryan Olson at Sep 8, 2005 at 4:00 pm

    Paul Rubin wrote:
    To get even more OS-specific, AF_UNIX sockets (at least on Linux) have
    a feature called ancillary messages that allow passing file
    descriptors between processes. It's currently not supported by the
    Python socket lib, but one of these days... . But I don't think
    Windows has anything like it.
    It can be done on on Windows.

    http://tangentsoft.net/wskfaq/articles/passing-sockets.html


    --
    --Bryan
  • Steve Horsley at Sep 6, 2005 at 6:06 pm

    Jacek Pop?awski wrote:
    Hello.

    I am going to write python script which will read python command from
    socket, run it and return some values back to socket.

    My problem is, that I need some timeout. I need to say for example:

    os.system("someapplication.exe")

    and kill it, if it waits longer than let's say 100 seconds

    I want to call command on separate thread, then after given timeout -
    kill thread, but I realized (after reading Usenet archive) that there is
    no way to kill a thread in Python.

    How can I implement my script then?

    PS. it should be portable - Linux, Windows, QNX, etc

    Probably the easiest way is to use select with a timeout (see the
    docs for library module select). eg.

    a, b c = select.select([mySocket], [], [], timeout)
    if len(a) == 0:
    print 'We timed out'
    else:
    print 'the socket has something for us'


    Steve
  • Peter Hansen at Sep 6, 2005 at 7:19 pm

    Jacek Pop?awski wrote:
    I am going to write python script which will read python command from
    socket, run it and return some values back to socket.
    (Sounds like a huge security risk, unless you have tight control over
    who can connect to that socket.)
    My problem is, that I need some timeout. I need to say for example:

    os.system("someapplication.exe")

    and kill it, if it waits longer than let's say 100 seconds

    I want to call command on separate thread, then after given timeout -
    kill thread, but I realized (after reading Usenet archive) that there is
    no way to kill a thread in Python.
    The issue isn't killing a thread in Python, it's killing the *new
    process* which that thread has started. To do that you have to rely on
    OS-specific (i.e. non-portable) techniques. Googling for "python kill
    process" would probably get you off to a good start.

    -Peter

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