[systemd-devel] Journald logging handler for Python 3 and AsyncIO integration

[Zbigniew Jędrzejewski-Szmek]

On Sat, May 02, 2015 at 05:22:49PM +0200, Jörg Thalheim wrote:
> On Sat, 2 May 2015 16:31:44 +0200
> Ludovic Gasc <gmludo at gmail.com> wrote:
> 
> > 2015-05-02 16:18 GMT+02:00 Zbigniew Jędrzejewski-Szmek
> > <zbyszek at in.waw.pl>:
> > 
> > > On Sat, May 02, 2015 at 03:34:52PM +0200, Ludovic Gasc wrote:
> > > > Ok, my bad, I didn't see JournalHandler class to use with Python
> > > > logging:
> > > >
> > > http://www.freedesktop.org/software/systemd/python-systemd/journal.html#journalhandler-class
> > > >
> > > > Nevertheless, my question about communication between Python and
> > > > journald remains.
> > > Can you rephrase the question? I don't quite understand what
> > > functionality you're missing from
> > >
> > > http://www.freedesktop.org/software/systemd/python-systemd/journal.html#systemd.journal.send
> > > .
> > >
> > >
> > In AsyncIO, when you interact with the outside world, you need to use
> > "yield from", for example:
> > https://docs.python.org/3/library/asyncio-stream.html#tcp-echo-client-using-streams
> > 
> > "yield from" means to the Python interpreter to "pause" the coroutine
> > to work on another coroutine until data arrive.
> > To be efficient, I/O should handled by AsyncIO, even if some
> > workarounds are possible if the raw socket isn't accessible.
> > 
> > If this pattern is useful for HTTP requests, for logging where you
> > shouldn't wait a return, it isn't very critical, especially if you use
> > syslog protocol with UNIX socket.
> > 
> > Nevertheless, to be sure, I wish to understand how the communication
> > works between my process and journald daemon.
> 
> AsyncIO was not their, when these bindings were written. Inventing a
> asynchron API on top of a synchron API (as provided by sd_journal_sendv) might be hard.
> So I have two ideas here:
I'm not sure if it is worth the trouble. Sending to the journal should be very
fast, and the overhead of dispatching to a separate thread is likely to only slow
things down.

Zbyszek

> 1. use a background thread, which writes messages to journald from a ring buffer and fill this ringbuffer from your application.
> 2. write to the unix socket /run/systemd/journal/socket directly with python and asyncIO, 
>    this is not as hard as it sounds because it is still some kind of text protocol. The coreos guys did this in go here:
>    https://github.com/coreos/go-systemd/blob/master/journal/send.go#L68



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