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Re: Python vs C++

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  Re: Python vs C++ Chris Angelico <rosuav@gmail.com> - 2014-08-22 10:26 +1000
    Re: Python vs C++ CHIN Dihedral <dihedral88888@gmail.com> - 2014-08-22 12:00 -0700
      Halfway point between interactive and daemon? Travis Griggs <travisgriggs@gmail.com> - 2014-08-22 12:27 -0700
        Re: Halfway point between interactive and daemon? Marko Rauhamaa <marko@pacujo.net> - 2014-08-22 22:49 +0300
      Re: Halfway point between interactive and daemon? Chris Angelico <rosuav@gmail.com> - 2014-08-23 06:32 +1000

#76758 — Re: Python vs C++

On Fri, Aug 22, 2014 at 4:05 AM, Joseph Martinot-Lagarde
<joseph.martinot-lagarde@m4x.org> wrote:
> For information, Cython works with C++ now:
> http://docs.cython.org/src/userguide/wrapping_CPlusPlus.html.

Now isn't that cool!

Every time Cython gets discussed, I get a renewed desire to learn it.
Trouble is, I don't have any project that calls for it - there's
nothing I'm desperately wanting to do that involves both Python and
C/C++. Anyone got any suggestions? :)

ChrisA

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#76808

On Friday, August 22, 2014 8:26:00 AM UTC+8, Chris Angelico wrote:
> On Fri, Aug 22, 2014 at 4:05 AM, Joseph Martinot-Lagarde
> 
> <joseph.martinot-lagarde@m4x.org> wrote:
> 
> > For information, Cython works with C++ now:
> 
> > http://docs.cython.org/src/userguide/wrapping_CPlusPlus.html.
> 
> 
> 
> Now isn't that cool!
> 
> 
> 
> Every time Cython gets discussed, I get a renewed desire to learn it.
> 
> Trouble is, I don't have any project that calls for it - there's
> 
> nothing I'm desperately wanting to do that involves both Python and
> 
> C/C++. Anyone got any suggestions? :)
> 
> 
> 
> ChrisA

Don't you use C as a portable assembler
in Python?

PYTHON->C->HW_BOUNDED_ASSEMBLY

That is the way to speed up python
programs using critical heavy 
computing functions.

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#76811 — Halfway point between interactive and daemon?

I have a python3 program that performs a long running service on a semi embedded linux device. I've been in the prototyping stage.  I just run it from the command line and use print() statements to let me know the thing is making acceptable process.

At some point, I need to properly daemonize it. Write an init script, find a logging framework/module, batton all the hatches down, so to speak.

I’m curious if there’s a technique one could use to get half way there. Basically, with minimal modifications, I’d like to get it running at startup. So I can put a line like this in rc.local

nohup python3 myMain.py 2>&1 > /var/log/mylog.log &

Then I can “check” on it when I need to with a tail -f /var/log/mylog.log. But then I have the problem of managing the log size. And also I either have to wait for stdout to flush, or insert sys.stdout.flush() after any of my print()’s.

I haven’t done a lot of these daemon processes (and this is my first with python), so I was curious what those with experience do here.

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#76812 — Re: Halfway point between interactive and daemon?

Travis Griggs <travisgriggs@gmail.com>:

> nohup python3 myMain.py 2>&1 > /var/log/mylog.log &

I don't recommend this (ubiquitous) technique. You should keep your
daemon in the foreground until it has reserved and initialized all the
resources it needs and daemonize only then. That way the caller does not
have to guess when the service is really available.

The proper daemonization procedure is here:

  <URL: http://code.activestate.com/recipes/66012-fork-a-dae
  mon-process-on-unix/>

Now, with the new systemd standard, there is a way for you to inform the
system when a service is up even after backgrounding. I have no personal
experience with that technique.


Marko

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#76822 — Re: Halfway point between interactive and daemon?

On Sat, Aug 23, 2014 at 5:27 AM, Travis Griggs <travisgriggs@gmail.com> wrote:
> I’m curious if there’s a technique one could use to get half way there. Basically, with minimal modifications, I’d like to get it running at startup.

Okay, hold on a minute there. There are two quite separate things
here: daemonization, and starting on system startup.

Daemonization is actually unnecessary to the latter, if you use a
modern init system. Just write your program to never fork, and either
Upstart or systemd will happily monitor it. Just create a unit file,
something like this:

[Unit]
Description=Yosemite Project
[Service]
Environment=DISPLAY=:0.0
User=whichever_user_to_run_as
ExecStart=/usr/bin/python /path/to/your/script
# If the network isn't available yet, restart until it is.
Restart=on-failure
RestartSec=10
[Install]
WantedBy=multi-user.target

$ systemctl --system daemon-reload
$ systemctl enable yos.service
$ systemctl start yos.service

(Feel free to steal that for your own purposes. It came from my
MIT-licensed videos server project "Yosemite".)

Daemonization should be optional. The above unit file works fine for
something that doesn't fork itself away. (I'm not sure how systemd
works with daemonizing processes, never tried. In any case, it's
unnecessary.) If you do need it (so the user can start your program
from the command line), I strongly recommend picking up a module off
PyPI; there are actually a lot of little details that people will
expect you to have gotten right. May as well bury it all away in a
little daemonize() call :)

ChrisA

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