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# Copyright (C) 2008-2009 Oprea Dan
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# This program is free software; you can redistribute it and/or modify
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# it under the terms of the GNU General Public License as published by
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# the Free Software Foundation; either version 2 of the License, or
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# (at your option) any later version.
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# This program is distributed in the hope that it will be useful,
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# but WITHOUT ANY WARRANTY; without even the implied warranty of
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# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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# GNU General Public License for more details.
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# You should have received a copy of the GNU General Public License along
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# with this program; if not, write to the Free Software Foundation, Inc.,
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# 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
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#class used to handle one application instance mechanism
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class ApplicationInstance:
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#specify the file used to save the application instance pid
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def __init__( self, pid_file, auto_exit = True ):
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self.pid_file = pid_file
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if self.check( True ):
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self.start_application()
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#check if the current application is already running, returns True if this is the application instance
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def check( self, auto_exit = False ):
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#check if the pidfile exists
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if not os.path.isfile( self.pid_file ):
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#read the pid from the file
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file = open( self.pid_file, 'rt' )
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#check if the process with specified by pid exists
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os.kill( pid, 0 ) #this will raise an exception if the pid is not valid
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print "The application is already running !"
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exit(0) #exit raise an exception so don't put it in a try/except block
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#called when the single instance starts to save it's pid
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def start_application( self ):
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file = open( self.pid_file, 'wt' )
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file.write( str( os.getpid() ) )
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#called when the single instance exit ( remove pid file )
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def exit_application( self ):
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os.remove( self.pid_file )
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if __name__ == '__main__':
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#create application instance
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app_instance = ApplicationInstance( '/tmp/myapp.pid' )
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time.sleep(5) #sleep 5 seconds
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app_instance.exit_application()