Job queue idle.py

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Important.png Note: The correct title of this article is job_queue_idle.py. It appears incorrectly here due to technical restrictions.


Author various
Description A python script that checks the job queue status. Its exit status indicates the number of jobs available for processing on this host. A zero exit status (success) means the job queue is idle and may be terminated.
Supports Version24.png  


This python script checks to see if a job queue server is idle. Its exit status indicates the number of jobs available for processing on this host. A zero exit status (success) means the job queue is idle and may be terminated.

It can be used in a cron job or in a loop in a script that starts and backgrounds mythjobqueue to determine if there are any jobs currently being processed by this host's mythjobqueue or available for this host's mythjobqueue to process. If no jobs are in progress or available for processing, mythjobqueue, or even the computer running mythjobqueue, may be shut down.


PythonIcon.png job_queue_idle.py

#!/usr/bin/env python
# -*- coding: UTF-8 -*-
#---------------------------
# Name: job_queue_idle.py
# Purpose
#   This python script checks to see if a job queue server is idle.
#   If no jobs are listed for, or can be run by, the current host, the
#   script will return 0, indicating mythjobqueue can be safely
#   terminated, allowing the master backend to shut itself down.
#   Otherwise, the script returns the total number of jobs capable of
#   being run by the current host.
#
#   It can also be run in daemon mode, in which case it backgrounds
#   itself, and proceeds to automatically manage the start and stop of
#   mythjobqueue as needed.
#---------------------------

from MythTV import MythDB, Job, MythDBError
from optparse import OptionParser
import subprocess
import time
import sys
import os

DB = None
LEVEL = None

class VERBOSE_LEVEL:
    DEFAULT = 0
    VERBOSE = 1
    DEBUG   = 2

def verbose(level, *messages):
    if (LEVEL >= level):
        print ''.join(map(str,messages))

def get_pid():
    pid = None
    ps = subprocess.Popen(['ps', 'ax'], stdout=-1)
    ps.wait()
    for line in ps.stdout.read().split('\n')
        if 'mythjobqueue' in line:
            pid = int(line.strip().split(' ')[0])
            break
    return pid

def run_jobqueue():
    if subprocess.call(['mythjobqueue', '--daemon']):
        verbose(VERBOSE_LEVEL.DEFAULT, "Daemon failed to run mythjobqueue")
        sys.exit(1)
    return get_pid()

def term_jobqueue(pid):
    subprocess.call(['kill', str(pid)])

def get_job_count():
    currenthost = DB.gethostname()
    verbose(VERBOSE_LEVEL.DEBUG, 'Checking job queue status for host ',
            currenthost)
    jobs = list(Job.getAllEntries(db=DB))
    jobCount=0
    if len(jobs) == 0:
        verbose(VERBOSE_LEVEL.VERBOSE, 'No jobs found')
    else:
        for job in jobs:
            if (len(job.hostname) == 0):
                verbose(VERBOSE_LEVEL.VERBOSE, 'Job ',job.id,
                        'available for processing on any host (',
                        job.comment,')')
                jobCount+=1
            elif ((job.hostname != currenthost)):
                verbose(VERBOSE_LEVEL.DEBUG, 'Job ',job.id,' claimed by ',
                        job.hostname,' (',job.comment,')')
            elif (not(job.status & job.DONE)):
                verbose(VERBOSE_LEVEL.VERBOSE, 'Currently processing job ',
                        job.id,' (',job.comment,')')
                jobCount+=1
            else:
                verbose(VERBOSE_LEVEL.DEBUG, 'Finished processing job ',
                        job.id,' (',job.comment,')')

    verbose(VERBOSE_LEVEL.VERBOSE, 'Found ',jobCount,' jobs.')
    if (jobCount > 0):
        verbose(VERBOSE_LEVEL.DEFAULT, "mythjobqueue is not idle.")
    else:
        verbose(VERBOSE_LEVEL.DEFAULT, "mythjobqueue is idle.")

    return jobCount

def run_daemon():
    # fork once
    try:
        pid = os.fork()
        if pid:
            # parent, exit
            sys.exit(0)
    except OSError, e:
        verbose(VERBOSE_LEVEL.DEFAULT, "Daemon failed fork to background.")
        sys.exit(1)

    os.chdir("/")
    os.setsid()
    os.umask(0)

    # fork twice
    try:
        pid = os.fork()
        if pid:
            # parent, exit
            sys.exit(0)
    except OSError, e:
        verbose(VERBOSE_LEVEL.DEFAULT, "Daemon failed fork to background.")
        sys.exit(1)

    pid = get_pid()
    if pid is None:
        pid = run_jobqueue()

    running = True
    while True:
        try:
            count = get_job_count()
            if running and count==0:
                term_jobqueue(pid)
            elif not running and count:
                pid = run_jobqueue()
        except MythDBError:
            # database is inaccessible
            # wait for bindings to automatically reconnect
            pass
        time.sleep(60)

        
if __name__ == '__main__':
    parser = OptionParser(usage="usage: %prog [options]")

    parser.set_defaults(verbose_level=VERBOSE_LEVEL.DEFAULT)
    parser.add_option('-v', '--verbose', action='store', type='int',
                      dest='verbose_level', default=VERBOSE_LEVEL.DEFAULT,
                      help='Verbosity level')
    parser.add_option('-d', '--daemonize', action='store_true',
                      dest='daemon', default=False,
                      help='Daemonize and manage mythjobqueue')

    opts, args = parser.parse_args()

    LEVEL = opts.verbose_level

    try:
        DB = MythDB()
    except MythDBError:
        verbose(VERBOSE_LEVEL.VERBOSE, 'Failed to connect to the database server.')
        sys.exit(int(opts.daemon))

    if opts.daemon:
        run_daemon()
        sys.exit(1)

    else:
        sys.exit(get_job_count())