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 evaluation of  a  se‐
       ries of events with varying frequencies for Performance Co-Pilot (PCP) applications.

       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 occurs the function func will be called with the event number and
       the event data as arguments.

       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  entry  from  the
       event queue.

       To  control the event queue processing, __pmAFblock and __pmAFunblock may be used to explicitly 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 proba‐
       bly ill-suited for applications that require direct and concurrent  access  to  these  services  and  re‐
       sources.

       If  the  callback functions are slow, or delayed, it is possible that the event scheduling could fall be‐
       hind 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 argument 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 en‐
       forced 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)