__pmAFregister, __pmAFunregister, __pmAFblock, __pmAFunblock,
__pmAFisempty - event queue services for periodic asynchronous
int __pmAFregister(const struct timeval *delta, void *data, void (*func)(int, void *))
int __pmAFunregister(int afid)
cc ... -lpcp
The routines implement an event queue and callback framework that
supports periodic evaluation of a series 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
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.
__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.
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
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
argument to __pmAFregister.