Re: [Wrapper-user] Wrapper and Time

[Leif M. <le...@ta...>]

Grant,
    Thanks for pointing this out.  The Wrapper has always worked great 
in an environment
where the system time is reliable but I agree that the changes you 
suggest would be a
good idea.  The changes are easy on the Java side, let me look into ways 
of making things
work in the native code.  I'll see if I can get this into the next 
release.  I'll post back if I
run into any problems.

Cheers,
Leif

Grant (ProtectionNET) wrote:

>Leif,
>
>Another thing, when DST comes into effect, some regions change +- by 2 hours
>so this is going to cause a problem relying on time in the wrapper code.
>
>I poked around in the wrapper.c and WrapperManager.java source and I
>absolutely think you could modify the code to include a no-time dependant
>counter.
>
>This would require you to create your own timer thread that polls every
>second and increments an unsigned long.
>
>I use this code in some of my Java apps to get a counter that continues
>forward independant of the actual system time.
>
>private long secondTimer = 0;
>
>Thread t = new Thread()
>{
> public void run()
> {
>  while (true)
>  {
>   try
>   {
>    secondTimer++;
>    if (secondTimer == Long.MAX_VALUE-1) secondTimer = 0;
>    sleep(1000);
>   }
>   catch (Exception e)
>   {
>   }
>  }
> }
>
>};
>t.start();
>
>I'm sure it wouldn't take long to develop the same code for the wrapper.c on
>Win32 and Unix ? The lack of standard threads in unix could be an issue? but
>using time the way you have will definitely cause an issue every DST
>adjustment or when the user changes the system time. They'll need to restart
>wrapper to fix this.
>
>I would continue to use a date based timer for understanding CPU load but
>ignore anything that jumps by more than 10 seconds as time adjustment above
>this is likely a time change. 10 seconds with no CPU time is a LONG time. If
>everything else moves to a CPU timer (on unix you could just count every 1/4
>second or adjust that sleep to 1 second and continue counting).
>
>When using NTP, the systems tend to drift time upwards and downwards
>gracefully so that apps don't notice the change - most hwclocks will only
>loose 1 second a day at worst so this would not really be worth worrying
>about.
>
>Grant
>
>----- Original Message ----- 
>From: "Leif Mortenson" <le...@ta...>
>To: <wra...@li...>
>Sent: Friday, December 26, 2003 10:33 AM
>Subject: Re: [Wrapper-user] Wrapper and Time
>
>
>  
>
>>Grant,
>>    :-/  That doesn't surprise me in the least that you are having
>>problems there.  The
>>Wrapper makes extensive use of time both in its native and Java
>>components to keep
>>track of various timeouts.   The Wrapper currently relies on the system
>>time being
>>fairly reliable.
>>
>>    I could probably add some code to reset the various timeouts in the
>>event that either
>>component of the Wrapper detects that the system time appears to have
>>been changed.
>>Ie when the time decreases or is increased by a large amount.
>>
>>    Small forward adjustments of the system time would be very difficult
>>to detect
>>because the Wrapper contains features to detect when the system has been
>>heavily
>>loaded.  I am not sure that it would be possible to differentiate
>>between the cases where
>>the process is not given any CPU for a minute vs the clock being
>>instantly set ahead
>>by a minute.
>>
>>    Could you describe how you are adjusting the time?  Ie by how much,
>>in which
>>direction and why?  It will help me to prioritize this.   If you know
>>that the Wrapper
>>simply does not like having the clock changed, would it be unreasonable
>>to just not
>>do this? Or is changing the clock a common operation?
>>
>>    I know I can make the Wrapper behave better than it is now, but am
>>unsure of how
>>perfect I can make it perform under all situations.
>>
>>Cheers,
>>Leif
>>
>>Grant (ProtectionNET) wrote:
>>
>>    
>>
>>>Hi,
>>>
>>>I have a case where the Java app changes the system time (via OS calls
>>>etc) and when Wrapper is running, I have sometimes seen strange
>>>problems and the wrapper service shuts down or goes crazy when the
>>>time is changed around.
>>>
>>>I'm only starting to investigate this now, so I don't have all the
>>>facts yet.
>>>
>>>Can someone explain to me what reliance Wrapper has to time and how it
>>>uses it... that would help me track this problem down...
>>>
>>>Thanks a billion.... and merry-xmas and all that ;-)
>>>
>>>Regards,
>>>
>>>Grant
>>>      
>>>
>>
>>
>>
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