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import os, time
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import sys
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from warnings import warn
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class LockHeld(Exception):pass
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class DaemonLock(object):
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'''daemon locking
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USAGE:
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try:
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l = lock()
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main()
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l.release()
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except LockHeld:
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sys.exit(1)
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'''
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def __init__(self, file=None, callbackfn=None,
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desc='daemon lock', debug=False):
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self.pidfile = file if file else os.path.join(os.path.dirname(__file__),
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'running.lock')
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self.callbackfn = callbackfn
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self.desc = desc
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self.debug = debug
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self.held = False
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#run the lock automatically !
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self.lock()
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def __del__(self):
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if self.held:
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# warn("use lock.release instead of del lock",
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# category = DeprecationWarning,
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# stacklevel = 2)
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# ensure the lock will be removed
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self.release()
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def lock(self):
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'''
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locking function, if lock is present it will raise LockHeld exception
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'''
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lockname = '%s' % (os.getpid())
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self.trylock()
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self.makelock(lockname, self.pidfile)
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return True
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def trylock(self):
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running_pid = False
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try:
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pidfile = open(self.pidfile, "r")
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pidfile.seek(0)
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running_pid = pidfile.readline()
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if self.debug:
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print 'lock file present running_pid: %s, checking for execution'\
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% running_pid
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# Now we check the PID from lock file matches to the current
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# process PID
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if running_pid:
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if os.path.exists("/proc/%s" % running_pid):
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print "You already have an instance of the program running"
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print "It is running as process %s" % running_pid
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raise LockHeld
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else:
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print "Lock File is there but the program is not running"
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print "Removing lock file for the: %s" % running_pid
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self.release()
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except IOError, e:
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if e.errno != 2:
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raise
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def release(self):
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'''
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releases the pid by removing the pidfile
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'''
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if self.callbackfn:
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#execute callback function on release
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if self.debug:
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print 'executing callback function %s' % self.callbackfn
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self.callbackfn()
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try:
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if self.debug:
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print 'removing pidfile %s' % self.pidfile
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os.remove(self.pidfile)
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self.held = False
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except OSError, e:
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if self.debug:
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print 'removing pidfile failed %s' % e
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pass
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def makelock(self, lockname, pidfile):
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'''
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this function will make an actual lock
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@param lockname: acctual pid of file
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@param pidfile: the file to write the pid in
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'''
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if self.debug:
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print 'creating a file %s and pid: %s' % (pidfile, lockname)
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pidfile = open(self.pidfile, "wb")
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pidfile.write(lockname)
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pidfile.close
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self.held = True
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def main():
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print 'func is running'
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cnt = 20
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while 1:
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print cnt
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if cnt == 0:
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break
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time.sleep(1)
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cnt -= 1
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if __name__ == "__main__":
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try:
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l = DaemonLock(desc='test lock')
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main()
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l.release()
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except LockHeld:
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sys.exit(1)
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