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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 con‐
text, 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 con‐
sumed by the PMDA may have to be forwarded on to any number of
monitoring tools (or "client contexts"). These tools may be re‐
questing events at different sampling intervals, and are very un‐
likely to request an event at the exact moment it arrives at the
PMDA, making some form of event buffering and queuing scheme a ne‐
cessity. Events must be held by the PMDA until either all regis‐
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 devel‐
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 pmdaEvent‐
NewQueue or pmdaEventNewActiveQueue. These are passed an identi‐
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 begin‐
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 pmdaEvent‐
NewActiveQueue interface should be used, with the additional
nclients parameter indicating the count of active client connec‐
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 iden‐
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 pmdaEven‐
tQueueRecords routine should be used. It is passed the queue han‐
dle and the avp pmAtomValue structure to fill with event records,
for the client making that fetch request (identified by the con‐
text parameter). Finally, the PMDA must also pass in an event de‐
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 - pm‐
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. In‐
formation about the project can be found at ⟨http://www.pcp.io/⟩.
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 ⟨https://github.com/performancecopilot/pcp.git⟩ on
2025-02-02. (At that time, the date of the most recent commit
that was found in the repository was 2025-01-30.) 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 2025-02-02 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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