pmdaEventClients(3) — Linux manual page


PMDAEVENTCLIENT(3)        Library Functions Manual        PMDAEVENTCLIENT(3)

NAME         top

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

C SYNOPSIS         top

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

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

       cc ... -lpcp_pmda -lpcp

DESCRIPTION         top

       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         top

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

COLOPHON         top

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Performance Co-Pilot                 PCP                  PMDAEVENTCLIENT(3)