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PMAF(3) PMAF(3)
NAME
__pmAFregister, __pmAFunregister, __pmAFblock, __pmAFunblock, __pmAFisempty - event queue
services for periodic asynchronous callbacks
C SYNOPSIS
#include <pcp/pmapi.h>
#include <pcp/impl.h>
int __pmAFregister(const struct timeval *delta, void *data, void (*func)(int, void *));
int __pmAFunregister(int afid);
void __pmAFblock(void);
void __pmAFunblock(void);
int __pmAFisempty(void);
cc ... -lpcp
DESCRIPTION
The routines implement an event queue and callback framework that supports periodic evalu-
ation of a series of events with varying frequencies for Performance Co-Pilot (PCP) appli-
cations.
The pmlogger(1) application, the pmdatrace(1) PMDA and the pmdahotproc(1) PMDA are the
principal users of these services.
An event is registered by calling __pmAFregister, and on success the return value is an
event number greater than zero. The event has associated event data identified by the
opaque pointer data. The event will occur with frequency delta (the first instance will
be delta after the current time when the event is registered), and each time the event oc-
curs the function func will be called with the event number and the event data as argu-
ments.
Once the event occurs and the callback has been executed, the event will be rescheduled
for delta into the future, except if all the fields of delta are zero, in which case the
event will not be rescheduled (a ``one trip'' event).
Internally, events are processed serially so there is no possibility of nested callbacks
or re-entrant callbacks from the event management routines.
Given an event number afid, __pmAFunregister will permanently remove the corresponding en-
try from the event queue.
To control the event queue processing, __pmAFblock and __pmAFunblock may be used to ex-
plicitly block and unblock the dispatch of events. This is most useful when the caller
wishes to set up a number of events via __pmAFregister and complete the registration phase
before the first event callback occurs.
A call to __pmAFisempty returns 1 or 0 depending on whether the event queue is empty or
not.
SEE ALSO
PMAPI(3)
DIAGNOSTICS
__pmAFregister and __pmAFunregister return values less than zero in the case of an error.
These values are PCP error codes, and may be used to produce error messages via
pmErrStr(3).
The routines support the standard PCP debug tracing, and the value DBG_TRACE_AF (or -D af
on the command line) will produce diagnostics on standard error that trace the enqueueing
and execution of events.
CAVEATS
These routines rely on setitimer(2) and manipulate the handling of SIGALRM signals, and
hence are probably ill-suited for applications that require direct and concurrent access
to these services and resources.
If the callback functions are slow, or delayed, it is possible that the event scheduling
could fall behind and never catchup. When this begins to happen, events are silently
skipped and rescheduled at the earliest possible time on the future according to the fixed
schedule defined by the time of the call to __pmAFregister and the value of the delta ar-
gument to __pmAFregister.
In addition, the semantics of the interval timer(s) and the global state needed to support
these services demand that applications calling these routines must do so from a single
thread. This restriction is enforced at the PMAPI(3), where routines may return the error
code PM_ERR_THREAD if the library detects calls from more than one thread.
Performance Co-Pilot PCP PMAF(3) |
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