NAME

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

C SYNOPSIS

       #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

       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 discard‐
       ed 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 queuing mechanism provided by pm‐
       daEventNewQueue(3) and friends, client connections and disconnections must be tracked via  calls  to  pm‐
       daEventNewClient  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).

Performance Co-Pilot                                   PCP                                    PMDAEVENTCLIENT(3)