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
       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).