QNX (was: Re: Raspberry Pi NTP config with fudge factors

[Gary E. Miller]

Yo Frank!

On Fri, 6 May 2016 17:32:12 -0400
Frank Nicholas <frank at nicholasfamilycentral.com> wrote:

> > On May 6, 2016, at 4:19 PM, Gary E. Miller <gem at rellim.com> wrote:
> > 
> >       "System  V  shared  memory (shmget(2), shmop(2), etc.) is an
> > older shared memory API.  POSIX shared memory provides a  simpler,
> > and better  designed interface; on the other hand POSIX shared
> > memory is somewhat less widely available (especially on  older
> > systems) than System V shared memory.”  
> 
> Does one or the other have better performance, or introduce more/less
> delays?  Would that be a reason to stick with one or change to the
> other?

The end result is both processes have the shared memory mapped into their
data space.  So things get updated at raw RAM speed.  Knowing it changed
needs polls, semaphores, etc.

shmctl() is dumber, shared memory persists until reboot or explicit kill.

shm_open() has file system semantics, with all the good that implies.
It also gets automatically removed whenn all consumers exit or
explicitly delete.

But both end up giving you direct access to some RAM, possibly R, W, or RW.


> > Never underestiate the power of large numbers of stupid people.  
> 
> Look at all the Trump supporters!  (sorry to mention politics on this
> list, but I couldn’t resist...)

And look at all the Hillary supporters...

How about we not go there?

RGDS
GARY
---------------------------------------------------------------------------
Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97703
	gem at rellim.com  Tel:+1 541 382 8588
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