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