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rpoll(3) BEGEMOT Library rpoll(3)
NAME
rpoll - callback functions for file descriptors and timers
SYNOPSIS
# include <rpoll.h>
typedef void (*poll_f)(int fd, int mask, void *arg);
typedef void (*timer_f)(int tid, void *arg);
int poll_register(int fd, poll_f func, void *arg, int mask);
void poll_unregister(int handle);
int poll_start_timer(u_int msecs, int repeat, timer_f func,
void *arg);
void poll_stop_timer(int handle);
int poll_start_utimer(unsigned long long usecs, int repeat,
timer_f func, void *arg);
void poll_dispatch(int wait);
DESCRIPTION
Many programs need to read from several file descriptors at the same
time. Typically in these programs one of select(3c) or poll(2) is
used. These calls are however clumsy to use and the usage of one of
these calls is probably not portable to other systems - not all systems
support both calls.
The rpoll(l) family of functions is designed to overcome these
restrictions. They support the well known and understood technique of
event driven programing and, in addition to select(3c) and poll(2) also
support timers.
Each event on a file descriptor or each timer event is translated into
a call to a user defined callback function. These functions need to be
registered. A file descriptor is registered with poll_register. fd is
the file descriptor to watch, mask is an event mask. It may be any
combination of POLL_IN to get informed when input on the file
descriptor is possible, POLL_OUT to get informed when output is
possible or POLL_EXCEPT to get informed when an exceptional condition
occures. An example of an exceptional condition is the arrival of
urgent data. (Note, that an end of file condition is signaled via
POLL_IN). func is the user function to be called and arg is a user
supplied argument for this function. The callback functions is called
with the file descriptor, a mask describing the actual events (from the
set supplied in the registration) and the user argument. poll_register
returns a handle, which may be used later to de-register the file
descriptor. A file descriptor may be registered more than once, if the
function, the user arguments or both differ in the call to
poll_register. If func and arg are the same, then no new registration
is done, instead the event mask of the registration is changed to
reflect the new mask.
A registered file descriptor may be de-registered by calling
poll_unregister with the handle returned by poll_register.
0). A one-short timer will automatically unregistered after expiry.
func is the user function which will be called with a timer id and the
user supplied arg. poll_start_timer and poll_start_utimer return a
timer id, which may be used to cancel the timer with poll_stop_timer.
A one-short timer should be canceled only if it has not yet fired.
poll_dispatch must be called to actually dispatch events. wait is a
flag, which should be 0, if only a poll should be done. In this case,
the function returns, after polling the registered file descriptors and
timers. If wait is not 0, poll_dispatch waits until an event occures.
All events are dispatch (i.e. callback functions called) and
poll_dispatch returns.
Typical use is:
while(1)
poll_dispatch(1);
SEE ALSO
poll(2),select(3C)
RETURN VALUES
poll_register , poll_start_timer and poll_start_utimer return a handle
which may be used to unregister the file descriptor or cancel the
timer.
Both functions and poll_dispatch call xrealloc(l) and can end in
panic(l).
ERRORS
System call or memory allocation errors are fatal and are handle by
calling panic(l). The one exception is a return of EINTR from
select(3c) or poll(2) in poll_dispatch. In this case poll_dispatch
simply returns.
BUGS
Obscure sequences of poll_start_timer and poll_stop_timer in callback
functions may probably break the code.
The semantics of POLL_EXCEPT are not clear.
AUTHORS
Hartmut Brandt, harti@freebsd.org
BEGEMOT 8 Dec 2006 rpoll(3)