Path: csiph.com!v102.xanadu-bbs.net!xanadu-bbs.net!eternal-september.org!feeder.eternal-september.org!news.stack.nl!newsfeed.xs4all.nl!newsfeed2a.news.xs4all.nl!xs4all!post.news.xs4all.nl!not-for-mail
Content-Type: text/plain; charset=windows-1252
Mime-Version: 1.0 (Mac OS X Mail 7.3 \(1878.6\))
Subject: Re: Example of python service running under systemd?
From: Travis Griggs <travisgriggs@gmail.com>
In-Reply-To: <20140911212921.GB26465@arxnet.hu>
Date: Thu, 11 Sep 2014 16:45:56 -0700
Content-Transfer-Encoding: quoted-printable
References: <FE4C3550-8958-4F72-8AFE-62AA7248D6AF@gmail.com> <CAMw+j7+LQL_+77ejCFVSqWap7Rk9gS_Wu5d3y0gT1UpB8hiZAA@mail.gmail.com> <6B97B7A5-0816-401E-9BDD-A23FFC646985@gmail.com> <20140911212921.GB26465@arxnet.hu>
To: python-list@python.org
Precedence: list
Newsgroups: comp.lang.python
Message-ID: <mailman.13949.1410479578.18130.python-list@python.org>
Lines: 82
NNTP-Posting-Host: 2001:888:2000:d::a6
Xref: csiph.com comp.lang.python:77785


On Sep 11, 2014, at 2:29 PM, Ervin Heged=FCs <airween@gmail.com> wrote:

> Hi Travis,
>=20
> On Thu, Sep 11, 2014 at 02:06:48PM -0700, Travis Griggs wrote:
>>=20
>> On Sep 11, 2014, at 11:18 AM, Chris =93Kwpolska=94 Warrick =
<kwpolska@gmail.com> wrote:
>>=20
>>> Depends what you want.=20
>>=20
>> Mine is not a web service. My main.py looks like this:
>>=20
>> #!/usr/bin/env python3
>>=20
>> import cycle
>> import pushTelemetry
>> from threading import Thread
>>=20
>> def main():
>>    Thread(target=3DpushTelemetry.udpLoop).start()
>>    Thread(target=3Dcycle.cycleLoop).start()
>>=20
>> if __name__ =3D=3D '__main__':
>>    main()
>>=20
>> It basically creates two threads, one which does some local =
processing and control, the other which periodically does reporting via =
udp packets. I use the dual threads because they both work with a shared =
serial port at times, so I have to synchronize access through that.
>>=20
>> What I want is to have this startup, after my board has it=92s =
networking layer up and running (and hopefully a valid ip address by =
then), and to just keep running forever
>=20
> may be you think about the fork(), eg:
>=20
> if __name__ =3D=3D "__main__":
>    ...other codes, eg. drop root privileges, ...
>    ...check arguments...
>    try:
>      pid =3D os.fork()
>      if pid > 0:
>          #print "Daemon started (pid: %d)" % (pid)
>          sys.exit(0)
>    except OSError, e:
>      print >>sys.stderr, "fork #1 failed: %d (%s)" % (e.errno, =
e.strerror)
>      sys.exit(1)
>=20
>    os.chdir("/")
>    os.setsid()
>    os.umask(0)
>=20
>    # do second fork
>    try:
>      pid =3D os.fork()
>      if pid > 0:
>          #print "Daemon started (pid: %d)" % (pid)
>          sys.exit(0)
>    except OSError, e:
>      print >>sys.stderr, "fork #2 failed: %d (%s)" % (e.errno, =
e.strerror)
>      sys.exit(1)
>=20
>    main()

OK, I=92m probably going to show my naivety about something simple here=85=


I thought a =93fork=94 essentially created a memory copy of the original =
process and let it go off running. The problem is, in the bowels of the =
code executing in those loops, I access a single instance of a =
threading.RLock, so that I can avoid both threads trying to do =
transactions with a single serial port at the same time. If I end up =
with two copies of the base process, unhooked from their parent, does =
that RLock still remain valid between the two? I thought since they were =
complete different copies of the same memory, they would no longer be =
coordinated.

Is this a day where I discover something new?=