[ntp:hackers] [Gpsd-dev] Single-writer/many-reader consistency

Dave Hart davehart_gmail_exchange_tee at davehart.net
Sat Mar 26 21:56:46 UTC 2011


[dropping gpsd-dev@ from this ntpd-specific comment]

On Sat, Mar 26, 2011 at 21:26 UTC, Terje Mathisen <terje at tmsw.no> wrote:
> 3) It overlays the current mode value, and none of the 8 bytes contain
> either 1 or 0 which are the only legal values for the current interface,
> i.e. a current-generation ntpd shm driver will never pick up any bogus
> timestamps from a new-model gpsd.

Assuming we're switching from SysV to POSIX named shared memory, and
we change the Windows refclock_shm shared memory naming convention, we
need not concern ourselves with interaction with the previous
refclock_shm shared memory layout, right?

I wonder if anyone is using refclock_shm on Windows.  The bk history
isn't any help, rev 1.1 of refclock_shm.c (dating to 1999 and the
introduction of RCS for NTP) contains the Windows stuff.  I didn't
glean anything useful from CommitLog-4.1.0 either.  Google Code Search
might turn something up, but a few quick tries suggest won't be easy
to sift out the bazillion copies of the NTP distribution posted around
the web.

The search did point out we're carrying around a util/sht.c test
program associated with refclock_shm which hasn't been updated in
ages.

Terje, I've been debating whether I have the focus and energy to dive
into a test program to try out your idea at an accelerated rate
(specified on the command line) with a producer and a couple of
consumers forked or threaded off pounding away attempting to detect
corruption.  Are you interested in trying something like that?

Cheers,
Dave Hart


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