Re: errlogVprintf does not print messages to console

[Eric Norum <norume@aps.anl.gov>]

On Nov 3, 2008, at 2:40 PM, Andrew Johnson wrote:
> ......
> The middle sentence "by the same thread" is important in  
> understanding why the
> existing code is like it is.  Developers don't particularly like it  
> if their
> errlogPrintf() output doesn't come out immediately; they expect the  
> sequence
> of calls
> 	printf("A\n");
> 	errlogPrintf("B\n");
> 	printf("C\n");
> to generate "A" "B" and "C" in order, which is why the "by the same  
> thread"
> part was added.  Now if epicsThreadIsOkToBlock() returns false we  
> must avoid
> blocking the thread (any kind of printf() to a file descriptor is  
> potentially
> blocking) so we have no choice but to punt the printf() to the  
> errlogThread,
> but where blocking isn't a problem it's nicer to do the printf()  
> directly in
> the calling thread.
>
> ..............
> The question I have for any core-talk readers still paying attention  
> is:
>
>    How important is it that errlogPrintf() and friends directly call
>    fprintf(stderr) when called in a thread that is allowed to block?
>
>    My inclination would be to do what Lewis proposes and do all the
>    console output from the errlogThread, but that would often cause
>    the example above to output "A", "C" and then later "B".
The decision comes down to how heavily you weight the expectations  
that you mention in the first paragraph above.  As you pointed out,  
the developer's guide does state (or at least imply pretty strongly)  
that
 	printf("A\n");
	errlogPrintf("B\n");
	printf("C\n");
will generate "A" "B" and "C" in order.  Now this promise is to be  
rescinded.   About par for the course at this time of year in this  
country, I suppose.........

I think that it is fairly easy to argue that there should not be any  
expectation that errlogPrintf output appear in any fixed relation to  
printf/fprintf output.
--
Eric Norum <norume@aps.anl.gov>
Advanced Photon Source
Argonne National Laboratory
(630) 252-4793