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From bugzi...@apache.org
Subject DO NOT REPLY [Bug 35746] New: - session manager should be immune to system clock time changes (solution provided)
Date Thu, 14 Jul 2005 19:56:38 GMT
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http://issues.apache.org/bugzilla/show_bug.cgi?id=35746

           Summary: session manager should be immune to system clock time
                    changes (solution provided)
           Product: Tomcat 5
           Version: 5.0.30
          Platform: Other
        OS/Version: other
            Status: NEW
          Severity: normal
          Priority: P2
         Component: Catalina
        AssignedTo: tomcat-dev@jakarta.apache.org
        ReportedBy: quartz12h@yahoo.com


Hi,
The session manager should be able to age session by age, not by comparison to
system time stamp.

Here is a simple and working time tracker immune to time shifts.
It 'knows' it waited some amount of milliseconds. This cannot be hacked on any
OS. Given that, the time arrow is maintained and session can be aged normally,
even if system time changes on the server, which is more than probable on
appliances and embed system.
 
That would prevent http session to expire and logout user prematurely.
Note that upon the receiver update, 't2' is always the current time (now) and
't1' is usually the last 't2' is no shift was detected.


public void run() {
	long t1 = -1;
	while(true) {
		try {
			long t2 = System.currentTimeMillis();

			//------ time shifting detection --------
			long shift = 0;
			if(t1>0) { //if not first loop
				long expected = t1+intervalMillis;
				shift = t2-expected;
				if(shift > timePositiveShiftTolerance) {
					vlogger.warn("Time shifted in future by more than positive tolerance:
shift="+shift+" ms, tolerance="+timePositiveShiftTolerance);
					//fireTimeDriftEvent(expected, drift);
					t1 = t2-intervalMillis;

				} else if(shift < timeNegativeShiftTolerance) {
					vlogger.warn("Time shifted in past by more than negative tolerance:
shift="+shift+" ms, tolerance="+timeNegativeShiftTolerance);
					//fireTimeDriftEvent(expected, drift);
					t1 = t2-intervalMillis;

				} else {
					shift = 0;
				}
			}


			///////////////
			//someReceiver.update(t1, t2, shift);
			///////////////

			t1 = t2;
			Thread.sleep(intervalMillis);

		} catch(IllegalArgumentException e) {
			vlogger.warn("",e);
			//no break.
		} catch(InterruptedException e) {
			break;
		} catch(Exception e) {
			vlogger.error("",e);
		}
	}
}

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