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pmdaeventclient(3)


NAME

   pmdaEventNewClient, pmdaEventEndClient, pmdaEventClients - client
   context tracking interfaces for event queues

C SYNOPSIS

   #include <pcp/pmapi.h>
   #include <pcp/impl.h>
   #include <pcp/pmda.h>

   int pmdaEventNewClient(int context);
   int pmdaEventEndClient(int context);
   int pmdaEventClients(pmAtomValue *avp);

   cc ... -lpcp_pmda -lpcp

DESCRIPTION

   A Performance Metrics Domain Agent (PMDA) that  exports  event  records
   needs  to track which clients are connected to it, in order that it can
   track which events have been sent to which clients so far.   Only  once
   an  event  has  been  sent  to  all monitoring tools that registered an
   interest can the event be discarded and any memory reclaimed.

   The PMDA(3) library provides callback routines for PMDA  developers  to
   provide  custom  handling of client connections and disconnections.  If
   the PMDA is making use of the  event  queueing  mechanism  provided  by
   pmdaEventNewQueue(3) and friends, client connections and disconnections
   must be tracked via calls to pmdaEventNewClient and  pmdaEventEndClient
   respectively.  This allows the library to keep track of when events can
   be discarded from a queue, for  example,  for  the  context  specified.
   This  parameter is passed into the e_endCallBack function directly, and
   for other callback functions is available via the  e_context  field  of
   the  pmdaExt  structure.   Additionally,  it can be queried at any time
   using pmdaGetContext(3).

   Sometimes it is useful for the PMDA to export a metric  indicating  the
   current  count  of  attached  clients  -  this  is  available using the
   pmdaEventClients routine,  which  will  fill  in  the  avp  pmAtomValue
   structure on behalf of a PMDA fetch callback routine.

SEE ALSO

   pmdaEventNewArray(3),   pmdaEventNewQueue(3),   PMAPI(3),  PMDA(3)  and
   pmEventFlagsStr(3).



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