Re: [gpsd-dev] Port to QNX: PPS without SHM?

[Hal Murray]

> But QNX does support POSIX shared memory:
> Would it help if gpsd supported POSIX? 

If we go make any non-trivial changes in the shared memory area, we should 
switch to the new scheme that lets the client side be read only.  I don't 
know the name, but it works like this:

Writer:
  Bump X
  update stuff
  Bump Y

Reader:
  Grab Y
  grab stuff
  Grab X
if X == Y, good.  Else try again.

The critical idea is that the reader and writer use X and Y in the opposite 
order.

It needs memory barriers.

Being read only allows multiple clients.


-- 
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