службы очереди событий для периодических асинхронных обратных вызовов (event queue services for periodic asynchronous callbacks)
Имя (Name)
__pmAFsetup, __pmAFregister, __pmAFunregister, __pmAFblock,
__pmAFunblock, __pmAFisempty - event queue services for periodic
asynchronous callbacks
Синопсис C (C Synopsis)
#include "pmapi.h"
#include "libpcp.h"
int __pmAFsetup(const struct timeval *start, const struct timeval
*delta, void *data, void (*func)(int, void *));
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
Предостережение (Caveat)
This documentation is intended for internal Performance Co-Pilot
(PCP) developer use.
These interfaces are not part of the PCP APIs that are guaranteed
to remain fixed across releases, and they may not work, or may
provide different semantics at some point in the future.
Описание (Description)
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 created by calling __pmAFsetup or __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 and each
time the event occurs the function func will be called with the
event number and the event data as arguments.
If __pmAFsetup is used then the first event is scheduled for the
current time plus start, else if __pmAFregister is used then the
first event is scheduled for the current time plus delta.
func is called in a SIGALRM signal handler context and so the
routines that may be safely called from func are restricted to
the so-called async-signal-safe set. In particular there must be
no Standard I/O calls nor calls to any of the malloc(3) routines
to modify the state of the heap. Refer to the Pointer to a
Function Section of the POSIX.1-2013 document at
http://pubs.opengroup.org/onlinepubs/9699919799/functions/V2_chap02.html
for a fuller description.
The safest and simplest class of func routines are those that do
minimal processing, set some global state and return. The real
work associated with the event is done subsequently from the
application's main loop when the global state change is detected.
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 __pmAFsetup or __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.
Предостережение (Caveat)
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 in the future according
to the fixed schedule defined by the time of the call to
__pmAFsetup and the value of the start and delta arguments (or
defined by the time of the call to __pmAFregister and the value
of the delta argument).
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.
Диагностика (Diagnostic)
__pmAFsetup, __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 af
option (or -D af on the command line) will produce diagnostics on
standard error that trace the enqueuing and execution of events.
Смотри также (See also)
PMAPI(3)
