Singleton

google 'python prevent duplication process'

http://pastebin.com/f66169fef

http://www.garyrobinson.net/2004/03/python_singleto.html

http://stackoverflow.com/questions/1900979/how-to-avoid-multiple-instances-of-a-program

http://stackoverflow.com/questions/7464000/how-to-prevent-duplicate-values-in-a-shared-queue