Daemonizing and my plugin

[Thomas Heller-2]

I have a cherrypy application that, in addition to the
normal work, needs to respond to UDP broadcasts.

The UDP server is implemented in a SimplePlugin subclass.
The plugin's start() method starts a thread.

However, this doesn't work correctly when the application
is daemonized.  It looks like the thread is started before
the forking occurs.  Here's the logfile (the timestamps
are wrong because this is running on an embedded system
that has no hardware clock):

[01/Jan/1970:01:03:49] ENGINE Listening for SIGHUP.
[01/Jan/1970:01:03:49] ENGINE Listening for SIGTERM.
[01/Jan/1970:01:03:49] ENGINE Listening for SIGUSR1.
[01/Jan/1970:01:03:49] ENGINE Bus STARTING
[01/Jan/1970:01:03:49] ENGINE There are [<_MainThread(MainThread, started 1073872192)>, <Thread(Thread-1, started daemon 1087337616)>] active threads. Daemonizing now may cause strange failures.
[01/Jan/1970:01:03:49] ENGINE Forking once.
[01/Jan/1970:01:03:49] ENGINE Forking twice.
[01/Jan/1970:01:03:49] ENGINE Daemonized to PID: 844
[01/Jan/1970:01:03:49] ENGINE PID 844 written to '/var/run/hvampd.pid'.
[01/Jan/1970:01:03:49] ENGINE Started monitor thread '_TimeoutMonitor'.
[01/Jan/1970:01:03:49] ENGINE Serving on 0.0.0.0:8080
[01/Jan/1970:01:03:49] ENGINE Bus STARTED


Any ideas how this can be solved?

--
Thanks,
Thomas


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[Robert Brewer-4]

Thomas Heller wrote:
> I have a cherrypy application that, in addition to the
> normal work, needs to respond to UDP broadcasts.
>
> The UDP server is implemented in a SimplePlugin subclass.
> The plugin's start() method starts a thread.

I hope the plugin's stop() method stops that thread for your continued
Ctrl-C sanity. ;)

> However, this doesn't work correctly when the application
> is daemonized.  It looks like the thread is started before
> the forking occurs.  Here's the logfile (the timestamps
> are wrong because this is running on an embedded system
> that has no hardware clock):
>
> [01/Jan/1970:01:03:49] ENGINE Listening for SIGHUP.
> [01/Jan/1970:01:03:49] ENGINE Listening for SIGTERM.
> [01/Jan/1970:01:03:49] ENGINE Listening for SIGUSR1.
> [01/Jan/1970:01:03:49] ENGINE Bus STARTING
> [01/Jan/1970:01:03:49] ENGINE There are [<_MainThread(MainThread,
> started 1073872192)>, <Thread(Thread-1, started daemon 1087337616)>]
> active threads. Daemonizing now may cause strange failures.
> [01/Jan/1970:01:03:49] ENGINE Forking once.
> [01/Jan/1970:01:03:49] ENGINE Forking twice.
> [01/Jan/1970:01:03:49] ENGINE Daemonized to PID: 844
> [01/Jan/1970:01:03:49] ENGINE PID 844 written to

'/var/run/hvampd.pid'.
> [01/Jan/1970:01:03:49] ENGINE Started monitor thread
'_TimeoutMonitor'.
> [01/Jan/1970:01:03:49] ENGINE Serving on 0.0.0.0:8080
> [01/Jan/1970:01:03:49] ENGINE Bus STARTED
>
>
> Any ideas how this can be solved?

Yup, cherrypy.process.plugins.Daemonizer.start.priority = 65. Just set a
priority on your start method that's higher than that so it runs after
Daemonizer.start; for example:

    def start(self):
        start_my_udp_server()
    start.priority = 80

Priorities of other builtin start listeners:
   
   default            50
   Daemonizer.start   65
   ThreadMonitor      70
   Autoreload         70
   PIDFile            70
   cherrypy.server    75
   DropPrivileges     77

...you can override any of these at your leisure (and at your own
risk--the "strange failures" message you received, for example, is there
for a good reason; see the source code for further comments about
default priorities).


Robert Brewer
fumanchu@...


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