Re: [reSIProcate] Timers: why system time?
To qualify things further, though: in order for this bug to be
triggered, you would need to have no calls to "Timer::getTimeMs()" for
over two minutes (131.07 seconds, to be more precise) as the 49.7-day
boundary rolls around. In a normally operating SIP stack, the chances of
this happening seem vanishingly small.
So, it's a corner case on top of a corner case. And it only happens on
WIN32 systems.
/a
Byron Campen wrote:
Ok, so this is in the "much more serious" category. I would not be
comfortable leaving this be.
Best regards,
Byron Campen
Byron Campen wrote:
Let's say one of these timers is at the top of the heap, and
whatever error you're thinking about happens. Are you saying that
not only will that timer be 49 days late, but everything else in the
heap will be too?
Not new timers. But, if we miss the rollover, then everything in the
heap at that time will instantaneously appear to be 49.7 days later
than their original expiration time. New timers will be inserted in
the heap just fine (ahead of the "lost" timers), and expire correctly.
The behavior would be similar to using our current stack and setting
the system time to be 49 days in the past while timers are pending.
/a
Best regards,
Byron Campen
Technically, they won't be "lost" as much as "over 49 days late."
From a SIP protocol perspective, 49 days is long enough to consider
the timer lost for all practical purposes.
/a
Byron Campen wrote:
I can see how we would miss a roll-over with low timer activity,
but I am not sure what you mean by "lose timers". If we have lost
a timer from a timer heap, that implies the heap is now broken,
because that is the only way to "lose" anything. So this is either
much more serious, or much less serious than you have stated.
Best regards,
Byron Campen
Scott (and any other Windows developers on the list):
The Windows 49.7-day rollover fix in this patch uses heuristics
to handle the rollover in an efficient manner -- you can actually
lose timers if you have relatively low timer activity and a
multi-minute timer running when the tick count rolls over. The
chances of this happening are, admittedly, vanishingly small
(especially in normal SIP usage). In any case, you might want to
give that code a quick review to ensure that you're comfortable
with it.
Also, I think it's safe to say that it's difficult to test the
correctness of the code, as step one of any such test plan
necessarily involves something like: "boot a Windows machine and
wait 49.6 days." Make sure you're comfortable with that fact as
well.
/a
Alexander wrote:
Hi
Here is a patch to use monotonic clock.
It is 3 modified files from reSIProcate 1.4.
Attached files have Windows (CLRF) eof-style.
Windows
=======
GetTickCount() with 16 ms inaccuracy used.
It is very simple to change it to timeGetTime() etc with 1 ms
accuracy,
but it will require init/fini calls on application level and
linking
with Winmm.lib
Tested on Windows XP SP2, compiled with VS7.1
Not tested on Windows CE
Linux
=====
If monotonic clock is not available (compile time and runtime)
it will
fall back to gettimeofday()
I am not familiar with reSIProcate build system so I use
workaround to
avoid linking with librt:
syscall( __NR_clock_gettime, ... )
instead of clock_gettime(...)
IMHO it may not work on other POSIX compliant platforms.
Pass only some basic tests on my Linux PC (2.6.18 kernel)
Any feedbacks appreciated.
Regards
Alexander Altshuler
Xeepe team
http://xeepe.com
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