Re: [pcp] suitability of PCP for event tracing

[Greg Banks <gnb at evostor dot com>]

Ken McDonell wrote:
> Apologies for my tardiness in responding, but I'm travelling at the 
> moment (typing this on a train and then on a ferry somewhere in Norway).
>
>
>   
Sounds like fun :)
>   
> On 3/09/2010 5:39 AM, Frank Ch. Eigler wrote:
>   
> > ...
> >
> > OK, then it looks like we'd have at least a few separate pieces to
> > work on:
> >
> > * extensions to the PMCD<->PMDA API/protocol to allow PMDAs to push
> >    event data, and corresponding extensions for PMclients<->PMCD
> >     
>
> I'd really like to see some more discussion on how people think this is 
> going to work.  None of the PCP libraries are thread-safe (again a 
> deliberate design decision at the original point of conception),
I've made a brief survey of the place in the libpcp code which are not 
threadsafe; there's *lots* of them but most are easily fixed without 
breaking external interfaces.  I'd estimate a few weeks' work is 
involved.  I'm interested in helping on this for my own reasons (I'd 
like kmchart to be more robust when communication with pmdas is disrupted).

>  and 
> asynchronous delivery of data from pmdas through pmcd to clients 
> increases the likelihood that people will want to use multiple threads 
> to handle PCP calls.  There are some asynchronous calls that were 
> grafted onto libpcp later on, but these have very little use in existing 
> code and no QA coverage.
>
>   
They're also a right bugger to program with, as we've discovered.  I 
would be happy to see them deprecated in favour of full libpcp thread 
safety.

--
Greg.