import threading
import bz2

comp = bz2.BZ2File('bz2locktest', 'w')

data = "1"*(1024*1024)

def docomp(index):
    print "before", index
    comp.write(data)
    print "after", index

t1=threading.Thread(target=docomp, args=(1,))
t2=threading.Thread(target=docomp, args=(2,))
t1.start()
t2.start()