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NAME | C SYNOPSIS | DESCRIPTION | SEE ALSO | COLOPHON |
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PMDAEVENTQUEUE(3) Library Functions Manual PMDAEVENTQUEUE(3)
pmdaEventNewQueue, pmdaEventNewActiveQueue, pmdaEventQueueHandle,
pmdaEventQueueAppend, pmdaEventQueueShutdown,
pmdaEventQueueRecords, pmdaEventQueueClients,
pmdaEventQueueCounter, pmdaEventQueueBytes, pmdaEventQueueMemory -
utilities for PMDAs managing event queues
#include <pcp/pmapi.h>
#include <pcp/pmda.h>
int pmdaEventNewQueue(const char *name, size_t maxmem);
int pmdaEventNewActiveQueue(const char *name, size_t maxmem,
int nclients);
int pmdaEventQueueHandle(const char *name);
int pmdaEventQueueAppend(int handle, void *buffer, size_t bytes,
struct timeval *tv);
int pmdaEventQueueShutdown(int handle);
typedef int (*pmdaEventDecodeCallBack)(int, void *, int,
struct timeval *, 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 conâ
sumed by the PMDA may have to be forwarded on to any number of
monitoring tools (or "client contexts"). These tools may be reâ
questing events at different sampling intervals, and are very unâ
likely to request an event at the exact moment it arrives at the
PMDA, making some form of event buffering and queuing scheme a neâ
cessity. Events must be held by the PMDA until either all regisâ
tered 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 develâ
oper 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 contexts.
The PMDA registers a new queue of events using either pmdaEventâ
NewQueue or pmdaEventNewActiveQueue. These are passed an identiâ
fying name (for diagnostic purposes, and for subsequent lookup by
pmdaEventQueueHandle) and maxmem, an upper bound on the memory (in
bytes) that can be consumed by events in this queue, before beginâ
ning to discard them (resulting in "missed" events for any client
that has not kept up). If a queue is dynamically allocated (such
that the PMDA may already have clients connected) the pmdaEventâ
NewActiveQueue interface should be used, with the additional
nclients parameter indicating the count of active client connecâ
tions. 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 idenâ
tified 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 pmdaEvenâ
tQueueRecords routine should be used. It is passed the queue hanâ
dle and the avp pmAtomValue structure to fill with event records,
for the client making that fetch request (identified by the conâ
text parameter). Finally, the PMDA must also pass in an event deâ
coding 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 - pmâ
daEventQueueClients, 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 return.
PMAPI(3), PMDA(3), pmdaEventNewClient(3) and pmdaEventNewArray(3).
This page is part of the PCP (Performance Co-Pilot) project. Inâ
formation about the project can be found at âĻhttp://www.pcp.io/âĐ.
If you have a bug report for this manual page, send it to
pcp@groups.io. This page was obtained from the project's upstream
Git repository âĻhttps://github.com/performancecopilot/pcp.gitâĐ on
2026-05-24. (At that time, the date of the most recent commit
that was found in the repository was 2026-05-24.) If you discover
any rendering problems in this HTML version of the page, or you
believe there is a better or more up-to-date source for the page,
or you have corrections or improvements to the information in this
COLOPHON (which is not part of the original manual page), send a
mail to man-pages@man7.org
Performance Co-Pilot PCP PMDAEVENTQUEUE(3)
Pages that refer to this page: pmdaeventarray(3), pmdaeventclient(3)
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HTML rendering created 2026-05-30 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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