Provided by: pcp_3.5.11_amd64 bug


       pmdaEventNewQueue, pmdaEventQueueHandle, pmdaEventQueueAppend, pmdaEventQueueRecords,
       pmdaEventQueueClients, pmdaEventQueueCounter, pmdaEventQueueBytes, pmdaEventQueueMemory -
       utilities for PMDAs managing event queues


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

       int pmdaEventNewQueue(const char *name, size_t maxmem);
       int pmdaEventQueueHandle(const char *name);
       int pmdaEventQueueAppend(int handle, void *buffer, size_t bytes, struct timeval *tv);

       typedef int (*pmdaEventDecodeCallBack)(int, void *, int, void *);
       int     pmdaEventQueueRecords(int     handle,     pmAtomValue     *avp,    int    context,
               pmdaEventDecodeCallBack decoder, void *data);
       int pmdaEventQueueClients(int handle, pmAtomValue *avp);
       int pmdaEventQueueCounter(int handle, pmAtomValue *avp);
       int pmdaEventQueueBytes(int handle, pmAtomValue *avp);
       int pmdaEventQueueMemory(int handle, pmAtomValue *avp);

       cc ... -lpcp_pmda -lpcp


       A Performance Metrics Domain Agent (PMDA) that exports event records must effectively  act
       an  event  multiplexer.   Events  consumed  by the PMDA may have to be forwarded on to any
       number of monitoring tools (or "client contexts").  These tools may be  requesting  events
       at  different  sampling  intervals, and are very unlikely to request an event at the exact
       moment it arrives at the PMDA, making some form of event buffering and queueing  scheme  a
       necessity.   Events must be held by the PMDA until either all registered clients have been
       sent them, or until a memory limit has been reached by the PMDA at  which  point  it  must
       discard older events as new ones arrive.

       The  routines  described  here  are designed to assist the PMDA developer in managing both
       client contexts and queues of events at a high level.  These  fit  logically  above  lower
       level  primitives, such as those described in pmdaEventNewArray(3), and shield the average
       PMDA from the details of directly building  event  record  arrays  for  individual  client

       The  PMDA  registers  a  new  queue  of events using pmdaEventNewQueue.  This is passed an
       identifying   name   (for   diagnostic   purposes,   and   for   subsequent   lookup    by
       pmdaEventQueueLookup)  and  maxmem,  an  upper  bound on the memory (in bytes) that can be
       consumed by events in this queue, before beginning to discard them (resulting in  "missed"
       events  for  any  client  that  has  not kept up).  The return is a negative error code on
       failure, suitable for  decoding  by  the  pmErrStr(3)  routine.   Any  non-negative  value
       indicates success, and provides a handle suitable for passing into the other API routines.

       For  each  new  event  received  by  the  PMDA, the pmdaEventQueueAppend routine should be
       called, placing that event into the queue identified by handle.  The event itself must  be
       contained in the passed in buffer, having bytes length.  The timestamp associated with the
       event (time at which the event occurred) is passed in via the final tv parameter.

       In the PMDAs specific implementation of its fetch  callback,  when  values  for  an  event
       metric  have  been  requested,  the  pmdaEventQueueRecords  routine should be used.  It is
       passed the queue handle and the avp pmAtomValue structure to fill with event records,  for
       the  client making that fetch request (identified by the context parameter).  Finally, the
       PMDA must also pass in an event decoding routine, which is responsible  for  decoding  the
       fields  of  a  single  event into the individual event parameters of that event.  The data
       parameter is an opaque cookie that can be used to pass situation-specific information into
       each decoder invocation.

       Under some situations it is useful for the PMDA to export state about the queues under its
       control.   The   accessor   routines   -   pmdaEventQueueClients,   pmdaEventQueueCounter,
       pmdaEventQueueBytes  and  pmdaEventQueueMemory provide a mechanism for querying a queue by
       its handle and filling in a pmAtomValue structure that the pmdaFetchCallBack method should


       PMAPI(3), PMDA(3), pmdaEventClient(3).  and pmdaEventArray(3).