107 lines
2.8 KiB
Python
Executable File
107 lines
2.8 KiB
Python
Executable File
#
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# Module vtime - Keep virtual time between two nodes.
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#
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# We try for synchronised clocks by sending a packet of the for
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# (1,mytime,0) to the other side, and waiting (at most) a second for
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# a reply. This reply has the form (2,mytime,histime), and we can
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# estimate the time difference by defining histime to be exactly half-way
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# between the time we sent our message and got our reply. We send a
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# final (3,mynewtime,histime) message to allow the other side to do the
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# same computations.
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#
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# Note that the protocol suffers heavily from the 2-army problem.
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# It'll have to do until I can read up on time-sync protocols, though.
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#
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from socket import *
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import time
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MSGSIZE = 100
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MSGTIMEOUT = 1000
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recv_timeout = 'receive timeout'
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bad_connect = 'Bad connection'
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def timeavg(a,b):
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return int((long(a)+b)/2L)
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def tryrecv(s):
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cnt = 0
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while 1:
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if s.avail():
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return s.recvfrom(MSGSIZE)
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time.millisleep(100)
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cnt = cnt + 100
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if cnt > MSGTIMEOUT:
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raise recv_timeout
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class VTime():
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def init(self,(client,host,port)):
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s = socket(AF_INET, SOCK_DGRAM)
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host = gethostbyname(host)
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localhost = gethostbyname(gethostname())
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raddr = (host,port)
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s.bind((localhost,port))
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if client:
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#
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# We loop here because we want the *second* measurement
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# for accuracy
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for loopct in (0,2):
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curtijd = time.millitimer()
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check = `(loopct,curtijd,0)`
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s.sendto(check,raddr)
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while 1:
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try:
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if loopct:
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data, other = s.recvfrom(MSGSIZE)
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else:
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data, other = tryrecv(s)
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newtijd = time.millitimer()
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if other <> raddr:
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print 'Someone else syncing to us: ', other
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raise bad_connect
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data = eval(data)
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if data[:2] = (loopct+1,curtijd):
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break
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if data[0] <> 2:
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print 'Illegal sync reply: ', data
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raise bad_connect
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except recv_timeout:
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curtijd = time.millitimer()
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check = `(loopct,curtijd,0)`
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s.sendto(check,raddr)
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histime = data[2]
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s.sendto(`(4,newtijd,histime)`,raddr)
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mytime = timeavg(curtijd,newtijd)
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#mytime = curtijd
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self.timediff = histime - mytime
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else:
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while 1:
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data,other = s.recvfrom(MSGSIZE)
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if other <> raddr:
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print 'Someone else syncing to us: ', other, ' Wanted ', raddr
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raise bad_connect
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data = eval(data)
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if data[0] in (0,2):
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curtijd = time.millitimer()
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s.sendto(`(data[0]+1,data[1],curtijd)`,raddr)
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elif data[0] = 4:
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newtijd = time.millitimer()
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histime = data[1]
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mytime = timeavg(curtijd,newtijd)
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#mytime = curtijd
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self.timediff = histime-mytime
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break
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else:
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print 'Funny data: ', data
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raise bad_connect
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return self
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#
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def his2mine(self,tijd):
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return tijd - self.timediff
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#
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def mine2his(self, tijd):
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return tijd + self.timediff
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def test(clt, host, port):
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xx = VTime().init(clt,host,port)
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print 'Time diff: ', xx.his2mine(0)
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