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CentOS 7.0 - man page for __pmafregister (centos section 3)

PMAF(3) 			     Library Functions Manual				  PMAF(3)

       __pmAFregister,	__pmAFunregister, __pmAFblock, __pmAFunblock, __pmAFisempty - event queue
       services for periodic asynchronous callbacks

       #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

       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-

       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-

       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


       __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

       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.

       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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