PMDAEVENTARRAY(3)

NAME
pmdaEventNewArray, pmdaEventResetArray, pmdaEventReleaseArray, pmdaEventAddRecord, pmdaEventAddMissedRecord, pmdaEventAddParam, pmdaEventGetAddr, pmdaEventNewHighResArray, pmdaEventResetHighResArray, pmdaEventReleaseHighResArray, pmdaEventAddHighResRecord, pmdaEventAddHighResMissedRecord, pmdaEventHighResAddParam, pmdaEventHighResGetAddr - utilities for PMDAs to build packed arrays of event records

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

int pmdaEventNewArray(void);
int pmdaEventResetArray(int idx);
int pmdaEventReleaseArray(int idx);
int pmdaEventAddRecord(int idx, struct timeval *tp, int flags);
int pmdaEventAddMissedRecord(int idx, struct timeval *tp, int nmissed);
int pmdaEventAddParam(int idx, pmID pmid, int type, pmAtomValue *avp);
pmEventArray *pmdaEventGetAddr(int idx);

int pmdaEventNewHighResArray(void);
int pmdaEventResetHighResArray(int idx);
int pmdaEventReleaseHighResArray(int idx);
int pmdaEventAddHighResRecord(int idx, struct timespec *ts, int flags);
int pmdaEventAddHighResMissedRecord(int idx, struct timespec *ts, int nmissed);
int pmdaEventHighResAddParam(int idx, pmID pmid, int type, pmAtomValue *avp);
pmHighResEventArray *pmdaEventHighResGetAddr(int idx);

cc ... -lpcp

DESCRIPTION
A Performance Metrics Domain Agent (PMDA) that wishes to export event records (or trace records) is encouraged to use a metric of either type PM_TYPE_EVENT or PM_TYPE_HIGHRES_EVENT to encode a group of event records into a single packed array.

The only difference between the two metric types is the resolution of the timestamp associated with each - in high resolution form it is nanosecond scale (see clock_gettime(2)), otherwise it is microseconds (see gettimeofday(2)). For simplicity, we will only refer to the lower resolution API and data structures hereafter - however, the higher resolution variants are all named similarly and are used in the same way.

The packed array of event records format is defined in <pcp/pmapi.h> and consists of a pmEventArray structure containing a variable number of pmEventRecord structures, each of which contains a variable number of pmEventParameter structures, which in turn may contain a variable length value for each parameter of each event record.

The higher resolution equivalents are defined in the same location, and the structures are named the same. Note that the pmEventParameter structure has no timestamp associated with it, hence it this does not have a high resolution counterpart.

The routines described here are designed to assist the PMDA developer in building a packed array of event records, and managing all of the memory allocations required to hold each instance of an array of event records in a contiguous buffer. Normal use would be as part of PMDA's pmdaFetchCallBack method.

pmdaEventNewArray is used to create a new event array. The return value is a small integer that is used as the idx parameter to the other routines to identify a specific event array. If needed, a PMDA can create and use multiple event arrays.

To start a new cycle and refill an event array from the beginning, call pmdaEventResetArray.

If the PMDA has finished with an event array, pmdaEventReleaseArray may be used to release the underlying storage and ``close'' the event array so that subsequent attempts to use idx will return PM_ERR_NOCONTEXT.

To start a new event record, use pmdaEventAddRecord. The timestamp for the event record is given via tp and the flags parameter may be used to set the control field that determines the type of the event record - flags may be the bit-wise ``or'' of one or more of the PM_EVENT_FLAG_* values defined in <pcp/pmapi.h> (but note that PM_EVENT_FLAG_MISSED should not be used in this context).

If event records have been missed, either because the PMDA cannot keep up or because the PMAPI client cannot keep up, then pmdaEventAddMissedRecord may be used. idx and tp have the same meaning as for pmdaEventAddRecord and nmissed is the number of event records that have been missed at this point in the time-series of event records. pmdaEventAddMissedRecord may be called multiple times for a single batch of event records if there are more than one ``missed event record'' episode.

Once an event record has been started by calling pmdaEventAddRecord, one or more event parameters may be added using pmdaEventAddParam. The pmid and type parameters decribe the PMID of the parameter and the data type (one of the PM_TYPE_* values from <pcp/pmapi.h>) of the value that is passed via avp. type should one where the size of the value is implied by the type or by the length of a string value (for PM_TYPE_STRING) or encoded within avp->vbp (for PM_TYPE_AGGREGATE).

Once the packed array has been constructed, pmdaEventGetAddr should be used to initialize the ea_type and ea_len fields at the start of the pmEventArray and return the base address of the event array that is assigned to the vp field of the pmAtomValue structure that the pmdaFetchCallBack method should return.

EXAMPLE
The following skeletal code shows how these routines might be used.

int             sts;
int             myarray;
int             first = 1;
pmEventArray    eap;
if (first) {
   first = 0;
   if ((myarray = pmdaEventNewArray()) < 0) {
      // report error and fail
   }
}
pmdaEventResetArray(myarray);
// loop over all event records to be exported
... {
   struct timeval   stamp;
   int              flags;
   // establish timestamp and set flags to 0 or some combination
   // of PM_EVENT_FLAG_POINT, PM_EVENT_FLAG_START, PM_EVENT_FLAG_ID,
   // etc
   if ((sts = pmdaEventAddRecord(myarray, &stamp, flags)) < 0) {
      // report error and fail
   }
   // loop over all parameters for this event record
   ... {
      pmID          pmid;
      int           type;
      pmAtomValue   atom;

      // construct pmid, type and atom for the parameter and
      // its value
      if ((sts = pmdaEventAddParam(myarray, pmid, type, &atom)) < 0) {
	 // report error and fail
      }
   }
   // if some event records were missed (could be at the start
   // of the exported set, or at the end, or in the middle, or
   // a combination of multiple missed record episodes)
   ... {
      int              nmiss;
      struct timeval   stamp;
      if ((sts = pmdaEventAddMissedRecord(myarray, &stamp, nmiss)) < 0) {
	 // report error and fail
      }
   }
}
// finish up
eap = pmdaEventGetAddr(myarray);

SEE ALSO
clock_gettime(2), gettimeofday(2), pmdaEventNewQueue(3), pmdaEventNewClient(3), PMDA(3) and pmEventFlagsStr(3).