#include <ev.h>
+=head1 EXAMPLE PROGRAM
+
+ #include <ev.h>
+
+ ev_io stdin_watcher;
+ ev_timer timeout_watcher;
+
+ /* called when data readable on stdin */
+ static void
+ stdin_cb (EV_P_ struct ev_io *w, int revents)
+ {
+ /* puts ("stdin ready"); */
+ ev_io_stop (EV_A_ w); /* just a syntax example */
+ ev_unloop (EV_A_ EVUNLOOP_ALL); /* leave all loop calls */
+ }
+
+ static void
+ timeout_cb (EV_P_ struct ev_timer *w, int revents)
+ {
+ /* puts ("timeout"); */
+ ev_unloop (EV_A_ EVUNLOOP_ONE); /* leave one loop call */
+ }
+
+ int
+ main (void)
+ {
+ struct ev_loop *loop = ev_default_loop (0);
+
+ /* initialise an io watcher, then start it */
+ ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ);
+ ev_io_start (loop, &stdin_watcher);
+
+ /* simple non-repeating 5.5 second timeout */
+ ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
+ ev_timer_start (loop, &timeout_watcher);
+
+ /* loop till timeout or data ready */
+ ev_loop (loop, 0);
+
+ return 0;
+ }
+
=head1 DESCRIPTION
+The newest version of this document is also available as a html-formatted
+web page you might find easier to navigate when reading it for the first
+time: L<http://cvs.schmorp.de/libev/ev.html>.
+
Libev is an event loop: you register interest in certain events (such as a
file descriptor being readable or a timeout occuring), and it will manage
these event sources and provide your program with events.
=head1 FEATURES
-Libev supports select, poll, the linux-specific epoll and the bsd-specific
-kqueue mechanisms for file descriptor events, relative timers, absolute
-timers with customised rescheduling, signal events, process status change
-events (related to SIGCHLD), and event watchers dealing with the event
-loop mechanism itself (idle, prepare and check watchers). It also is quite
-fast (see this L<benchmark|http://libev.schmorp.de/bench.html> comparing
-it to libevent for example).
+Libev supports C<select>, C<poll>, the Linux-specific C<epoll>, the
+BSD-specific C<kqueue> and the Solaris-specific event port mechanisms
+for file descriptor events (C<ev_io>), the Linux C<inotify> interface
+(for C<ev_stat>), relative timers (C<ev_timer>), absolute timers
+with customised rescheduling (C<ev_periodic>), synchronous signals
+(C<ev_signal>), process status change events (C<ev_child>), and event
+watchers dealing with the event loop mechanism itself (C<ev_idle>,
+C<ev_embed>, C<ev_prepare> and C<ev_check> watchers) as well as
+file watchers (C<ev_stat>) and even limited support for fork events
+(C<ev_fork>).
+
+It also is quite fast (see this
+L<benchmark|http://libev.schmorp.de/bench.html> comparing it to libevent
+for example).
=head1 CONVENTIONS
-Libev is very configurable. In this manual the default configuration
-will be described, which supports multiple event loops. For more info
-about various configuration options please have a look at the file
-F<README.embed> in the libev distribution. If libev was configured without
-support for multiple event loops, then all functions taking an initial
-argument of name C<loop> (which is always of type C<struct ev_loop *>)
-will not have this argument.
+Libev is very configurable. In this manual the default configuration will
+be described, which supports multiple event loops. For more info about
+various configuration options please have a look at B<EMBED> section in
+this manual. If libev was configured without support for multiple event
+loops, then all functions taking an initial argument of name C<loop>
+(which is always of type C<struct ev_loop *>) will not have this argument.
=head1 TIME REPRESENTATION
to the C<double> type in C, and when you need to do any calculations on
it, you should treat it as such.
-
=head1 GLOBAL FUNCTIONS
These functions can be called anytime, even before initialising the
=item int ev_version_minor ()
-You can find out the major and minor version numbers of the library
+You can find out the major and minor ABI version numbers of the library
you linked against by calling the functions C<ev_version_major> and
C<ev_version_minor>. If you want, you can compare against the global
symbols C<EV_VERSION_MAJOR> and C<EV_VERSION_MINOR>, which specify the
version of the library your program was compiled against.
+These version numbers refer to the ABI version of the library, not the
+release version.
+
Usually, it's a good idea to terminate if the major versions mismatch,
-as this indicates an incompatible change. Minor versions are usually
+as this indicates an incompatible change. Minor versions are usually
compatible to older versions, so a larger minor version alone is usually
not a problem.
-Example: make sure we haven't accidentally been linked against the wrong
-version:
+Example: Make sure we haven't accidentally been linked against the wrong
+version.
assert (("libev version mismatch",
ev_version_major () == EV_VERSION_MAJOR
=item ev_set_allocator (void *(*cb)(void *ptr, long size))
-Sets the allocation function to use (the prototype is similar to the
-realloc C function, the semantics are identical). It is used to allocate
-and free memory (no surprises here). If it returns zero when memory
-needs to be allocated, the library might abort or take some potentially
-destructive action. The default is your system realloc function.
+Sets the allocation function to use (the prototype is similar - the
+semantics is identical - to the realloc C function). It is used to
+allocate and free memory (no surprises here). If it returns zero when
+memory needs to be allocated, the library might abort or take some
+potentially destructive action. The default is your system realloc
+function.
You could override this function in high-availability programs to, say,
free some memory if it cannot allocate memory, to use a special allocator,
or even to sleep a while and retry until some memory is available.
-Example: replace the libev allocator with one that waits a bit and then
-retries: better than mine).
+Example: Replace the libev allocator with one that waits a bit and then
+retries).
static void *
- persistent_realloc (void *ptr, long size)
+ persistent_realloc (void *ptr, size_t size)
{
for (;;)
{
requested operation, or, if the condition doesn't go away, do bad stuff
(such as abort).
-Example: do the same thing as libev does internally:
+Example: This is basically the same thing that libev does internally, too.
static void
fatal_error (const char *msg)
useful to try out specific backends to test their performance, or to work
around bugs.
+=item C<EVFLAG_FORKCHECK>
+
+Instead of calling C<ev_default_fork> or C<ev_loop_fork> manually after
+a fork, you can also make libev check for a fork in each iteration by
+enabling this flag.
+
+This works by calling C<getpid ()> on every iteration of the loop,
+and thus this might slow down your event loop if you do a lot of loop
+iterations and little real work, but is usually not noticeable (on my
+Linux system for example, C<getpid> is actually a simple 5-insn sequence
+without a syscall and thus I<very> fast, but my Linux system also has
+C<pthread_atfork> which is even faster).
+
+The big advantage of this flag is that you can forget about fork (and
+forget about forgetting to tell libev about forking) when you use this
+flag.
+
+This flag setting cannot be overriden or specified in the C<LIBEV_FLAGS>
+environment variable.
+
=item C<EVBACKEND_SELECT> (value 1, portable select backend)
This is your standard select(2) backend. Not I<completely> standard, as
handle signal and child watchers, and attempts to do so will be greeted by
undefined behaviour (or a failed assertion if assertions are enabled).
-Example: try to create a event loop that uses epoll and nothing else.
+Example: Try to create a event loop that uses epoll and nothing else.
struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
if (!epoller)
C<ev_loop_new>. Yes, you have to call this on every allocated event loop
after fork, and how you do this is entirely your own problem.
+=item unsigned int ev_loop_count (loop)
+
+Returns the count of loop iterations for the loop, which is identical to
+the number of times libev did poll for new events. It starts at C<0> and
+happily wraps around with enough iterations.
+
+This value can sometimes be useful as a generation counter of sorts (it
+"ticks" the number of loop iterations), as it roughly corresponds with
+C<ev_prepare> and C<ev_check> calls.
+
=item unsigned int ev_backend (loop)
Returns one of the C<EVBACKEND_*> flags indicating the event backend in
Here are the gory details of what C<ev_loop> does:
+ - Before the first iteration, call any pending watchers.
* If there are no active watchers (reference count is zero), return.
- - Queue prepare watchers and then call all outstanding watchers.
+ - Queue all prepare watchers and then call all outstanding watchers.
- If we have been forked, recreate the kernel state.
- Update the kernel state with all outstanding changes.
- Update the "event loop time".
- If ev_unloop has been called or EVLOOP_ONESHOT or EVLOOP_NONBLOCK
were used, return, otherwise continue with step *.
-Example: queue some jobs and then loop until no events are outsanding
+Example: Queue some jobs and then loop until no events are outsanding
anymore.
... queue jobs here, make sure they register event watchers as long
way to do this for generic recurring timers or from within third-party
libraries. Just remember to I<unref after start> and I<ref before stop>.
-Example: create a signal watcher, but keep it from keeping C<ev_loop>
+Example: Create a signal watcher, but keep it from keeping C<ev_loop>
running when nothing else is active.
- struct dv_signal exitsig;
+ struct ev_signal exitsig;
ev_signal_init (&exitsig, sig_cb, SIGINT);
- ev_signal_start (myloop, &exitsig);
- evf_unref (myloop);
+ ev_signal_start (loop, &exitsig);
+ evf_unref (loop);
-Example: for some weird reason, unregister the above signal handler again.
+Example: For some weird reason, unregister the above signal handler again.
- ev_ref (myloop);
- ev_signal_stop (myloop, &exitsig);
+ ev_ref (loop);
+ ev_signal_stop (loop, &exitsig);
=back
+
=head1 ANATOMY OF A WATCHER
A watcher is a structure that you create and register to record your
The pid specified in the C<ev_child> watcher has received a status change.
+=item C<EV_STAT>
+
+The path specified in the C<ev_stat> watcher changed its attributes somehow.
+
=item C<EV_IDLE>
The C<ev_idle> watcher has determined that you have nothing better to do.
(for example, a C<ev_prepare> watcher might start an idle watcher to keep
C<ev_loop> from blocking).
+=item C<EV_EMBED>
+
+The embedded event loop specified in the C<ev_embed> watcher needs attention.
+
+=item C<EV_FORK>
+
+The event loop has been resumed in the child process after fork (see
+C<ev_fork>).
+
=item C<EV_ERROR>
An unspecified error has occured, the watcher has been stopped. This might
=back
-=head2 SUMMARY OF GENERIC WATCHER FUNCTIONS
+=head2 GENERIC WATCHER FUNCTIONS
In the following description, C<TYPE> stands for the watcher type,
e.g. C<timer> for C<ev_timer> watchers and C<io> for C<ev_io> watchers.
You can reinitialise a watcher at any time as long as it has been stopped
(or never started) and there are no pending events outstanding.
-The callbakc is always of type C<void (*)(ev_loop *loop, ev_TYPE *watcher,
+The callback is always of type C<void (*)(ev_loop *loop, ev_TYPE *watcher,
int revents)>.
=item C<ev_TYPE_set> (ev_TYPE *, [args])
Returns a true value iff the watcher is pending, (i.e. it has outstanding
events but its callback has not yet been invoked). As long as a watcher
is pending (but not active) you must not call an init function on it (but
-C<ev_TYPE_set> is safe) and you must make sure the watcher is available to
-libev (e.g. you cnanot C<free ()> it).
+C<ev_TYPE_set> is safe), you must not change its priority, and you must
+make sure the watcher is available to libev (e.g. you cannot C<free ()>
+it).
-=item callback = ev_cb (ev_TYPE *watcher)
+=item callback ev_cb (ev_TYPE *watcher)
Returns the callback currently set on the watcher.
Change the callback. You can change the callback at virtually any time
(modulo threads).
+=item ev_set_priority (ev_TYPE *watcher, priority)
+
+=item int ev_priority (ev_TYPE *watcher)
+
+Set and query the priority of the watcher. The priority is a small
+integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>
+(default: C<-2>). Pending watchers with higher priority will be invoked
+before watchers with lower priority, but priority will not keep watchers
+from being executed (except for C<ev_idle> watchers).
+
+This means that priorities are I<only> used for ordering callback
+invocation after new events have been received. This is useful, for
+example, to reduce latency after idling, or more often, to bind two
+watchers on the same event and make sure one is called first.
+
+If you need to suppress invocation when higher priority events are pending
+you need to look at C<ev_idle> watchers, which provide this functionality.
+
+You I<must not> change the priority of a watcher as long as it is active or
+pending.
+
+The default priority used by watchers when no priority has been set is
+always C<0>, which is supposed to not be too high and not be too low :).
+
+Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
+fine, as long as you do not mind that the priority value you query might
+or might not have been adjusted to be within valid range.
+
+=item ev_invoke (loop, ev_TYPE *watcher, int revents)
+
+Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
+C<loop> nor C<revents> need to be valid as long as the watcher callback
+can deal with that fact.
+
+=item int ev_clear_pending (loop, ev_TYPE *watcher)
+
+If the watcher is pending, this function returns clears its pending status
+and returns its C<revents> bitset (as if its callback was invoked). If the
+watcher isn't pending it does nothing and returns C<0>.
+
=back
...
}
-More interesting and less C-conformant ways of catsing your callback type
-have been omitted....
+More interesting and less C-conformant ways of casting your callback type
+instead have been omitted.
+
+Another common scenario is having some data structure with multiple
+watchers:
+
+ struct my_biggy
+ {
+ int some_data;
+ ev_timer t1;
+ ev_timer t2;
+ }
+
+In this case getting the pointer to C<my_biggy> is a bit more complicated,
+you need to use C<offsetof>:
+
+ #include <stddef.h>
+
+ static void
+ t1_cb (EV_P_ struct ev_timer *w, int revents)
+ {
+ struct my_biggy big = (struct my_biggy *
+ (((char *)w) - offsetof (struct my_biggy, t1));
+ }
+
+ static void
+ t2_cb (EV_P_ struct ev_timer *w, int revents)
+ {
+ struct my_biggy big = (struct my_biggy *
+ (((char *)w) - offsetof (struct my_biggy, t2));
+ }
=head1 WATCHER TYPES
This section describes each watcher in detail, but will not repeat
-information given in the last section.
+information given in the last section. Any initialisation/set macros,
+functions and members specific to the watcher type are explained.
+
+Members are additionally marked with either I<[read-only]>, meaning that,
+while the watcher is active, you can look at the member and expect some
+sensible content, but you must not modify it (you can modify it while the
+watcher is stopped to your hearts content), or I<[read-write]>, which
+means you can expect it to have some sensible content while the watcher
+is active, but you can also modify it. Modifying it may not do something
+sensible or take immediate effect (or do anything at all), but libev will
+not crash or malfunction in any way.
-=head2 C<ev_io> - is this file descriptor readable or writable
+=head2 C<ev_io> - is this file descriptor readable or writable?
I/O watchers check whether a file descriptor is readable or writable
-in each iteration of the event loop (This behaviour is called
-level-triggering because you keep receiving events as long as the
-condition persists. Remember you can stop the watcher if you don't want to
-act on the event and neither want to receive future events).
+in each iteration of the event loop, or, more precisely, when reading
+would not block the process and writing would at least be able to write
+some data. This behaviour is called level-triggering because you keep
+receiving events as long as the condition persists. Remember you can stop
+the watcher if you don't want to act on the event and neither want to
+receive future events.
In general you can register as many read and/or write event watchers per
fd as you want (as long as you don't confuse yourself). Setting all file
You have to be careful with dup'ed file descriptors, though. Some backends
(the linux epoll backend is a notable example) cannot handle dup'ed file
descriptors correctly if you register interest in two or more fds pointing
-to the same underlying file/socket etc. description (that is, they share
+to the same underlying file/socket/etc. description (that is, they share
the same underlying "file open").
If you must do this, then force the use of a known-to-be-good backend
(at the time of this writing, this includes only C<EVBACKEND_SELECT> and
C<EVBACKEND_POLL>).
+Another thing you have to watch out for is that it is quite easy to
+receive "spurious" readyness notifications, that is your callback might
+be called with C<EV_READ> but a subsequent C<read>(2) will actually block
+because there is no data. Not only are some backends known to create a
+lot of those (for example solaris ports), it is very easy to get into
+this situation even with a relatively standard program structure. Thus
+it is best to always use non-blocking I/O: An extra C<read>(2) returning
+C<EAGAIN> is far preferable to a program hanging until some data arrives.
+
+If you cannot run the fd in non-blocking mode (for example you should not
+play around with an Xlib connection), then you have to seperately re-test
+whether a file descriptor is really ready with a known-to-be good interface
+such as poll (fortunately in our Xlib example, Xlib already does this on
+its own, so its quite safe to use).
+
+=head3 The special problem of disappearing file descriptors
+
+Some backends (e.g kqueue, epoll) need to be told about closing a file
+descriptor (either by calling C<close> explicitly or by any other means,
+such as C<dup>). The reason is that you register interest in some file
+descriptor, but when it goes away, the operating system will silently drop
+this interest. If another file descriptor with the same number then is
+registered with libev, there is no efficient way to see that this is, in
+fact, a different file descriptor.
+
+To avoid having to explicitly tell libev about such cases, libev follows
+the following policy: Each time C<ev_io_set> is being called, libev
+will assume that this is potentially a new file descriptor, otherwise
+it is assumed that the file descriptor stays the same. That means that
+you I<have> to call C<ev_io_set> (or C<ev_io_init>) when you change the
+descriptor even if the file descriptor number itself did not change.
+
+This is how one would do it normally anyway, the important point is that
+the libev application should not optimise around libev but should leave
+optimisations to libev.
+
+
+=head3 Watcher-Specific Functions
+
=over 4
=item ev_io_init (ev_io *, callback, int fd, int events)
=item ev_io_set (ev_io *, int fd, int events)
-Configures an C<ev_io> watcher. The fd is the file descriptor to rceeive
-events for and events is either C<EV_READ>, C<EV_WRITE> or C<EV_READ |
-EV_WRITE> to receive the given events.
-
-Please note that most of the more scalable backend mechanisms (for example
-epoll and solaris ports) can result in spurious readyness notifications
-for file descriptors, so you practically need to use non-blocking I/O (and
-treat callback invocation as hint only), or retest separately with a safe
-interface before doing I/O (XLib can do this), or force the use of either
-C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>, which don't suffer from this
-problem. Also note that it is quite easy to have your callback invoked
-when the readyness condition is no longer valid even when employing
-typical ways of handling events, so its a good idea to use non-blocking
-I/O unconditionally.
+Configures an C<ev_io> watcher. The C<fd> is the file descriptor to
+rceeive events for and events is either C<EV_READ>, C<EV_WRITE> or
+C<EV_READ | EV_WRITE> to receive the given events.
+
+=item int fd [read-only]
+
+The file descriptor being watched.
+
+=item int events [read-only]
+
+The events being watched.
=back
-Example: call C<stdin_readable_cb> when STDIN_FILENO has become, well
+Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well
readable, but only once. Since it is likely line-buffered, you could
-attempt to read a whole line in the callback:
+attempt to read a whole line in the callback.
static void
stdin_readable_cb (struct ev_loop *loop, struct ev_io *w, int revents)
ev_loop (loop, 0);
-=head2 C<ev_timer> - relative and optionally recurring timeouts
+=head2 C<ev_timer> - relative and optionally repeating timeouts
Timer watchers are simple relative timers that generate an event after a
given time, and optionally repeating in regular intervals after that.
but if multiple timers become ready during the same loop iteration then
order of execution is undefined.
+=head3 Watcher-Specific Functions and Data Members
+
=over 4
=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
This will act as if the timer timed out and restart it again if it is
repeating. The exact semantics are:
-If the timer is started but nonrepeating, stop it.
+If the timer is pending, its pending status is cleared.
+
+If the timer is started but nonrepeating, stop it (as if it timed out).
-If the timer is repeating, either start it if necessary (with the repeat
-value), or reset the running timer to the repeat value.
+If the timer is repeating, either start it if necessary (with the
+C<repeat> value), or reset the running timer to the C<repeat> value.
This sounds a bit complicated, but here is a useful and typical
example: Imagine you have a tcp connection and you want a so-called idle
timeout, that is, you want to be called when there have been, say, 60
seconds of inactivity on the socket. The easiest way to do this is to
-configure an C<ev_timer> with after=repeat=60 and calling ev_timer_again each
-time you successfully read or write some data. If you go into an idle
-state where you do not expect data to travel on the socket, you can stop
-the timer, and again will automatically restart it if need be.
+configure an C<ev_timer> with a C<repeat> value of C<60> and then call
+C<ev_timer_again> each time you successfully read or write some data. If
+you go into an idle state where you do not expect data to travel on the
+socket, you can C<ev_timer_stop> the timer, and C<ev_timer_again> will
+automatically restart it if need be.
+
+That means you can ignore the C<after> value and C<ev_timer_start>
+altogether and only ever use the C<repeat> value and C<ev_timer_again>:
+
+ ev_timer_init (timer, callback, 0., 5.);
+ ev_timer_again (loop, timer);
+ ...
+ timer->again = 17.;
+ ev_timer_again (loop, timer);
+ ...
+ timer->again = 10.;
+ ev_timer_again (loop, timer);
+
+This is more slightly efficient then stopping/starting the timer each time
+you want to modify its timeout value.
+
+=item ev_tstamp repeat [read-write]
+
+The current C<repeat> value. Will be used each time the watcher times out
+or C<ev_timer_again> is called and determines the next timeout (if any),
+which is also when any modifications are taken into account.
=back
-Example: create a timer that fires after 60 seconds.
+Example: Create a timer that fires after 60 seconds.
static void
one_minute_cb (struct ev_loop *loop, struct ev_timer *w, int revents)
ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
ev_timer_start (loop, &mytimer);
-Example: create a timeout timer that times out after 10 seconds of
+Example: Create a timeout timer that times out after 10 seconds of
inactivity.
static void
ev_timer_again (&mytimer);
-=head2 C<ev_periodic> - to cron or not to cron
+=head2 C<ev_periodic> - to cron or not to cron?
Periodic watchers are also timers of a kind, but they are very versatile
(and unfortunately a bit complex).
Unlike C<ev_timer>'s, they are not based on real time (or relative time)
but on wallclock time (absolute time). You can tell a periodic watcher
to trigger "at" some specific point in time. For example, if you tell a
-periodic watcher to trigger in 10 seconds (by specifiying e.g. c<ev_now ()
+periodic watcher to trigger in 10 seconds (by specifiying e.g. C<ev_now ()
+ 10.>) and then reset your system clock to the last year, then it will
take a year to trigger the event (unlike an C<ev_timer>, which would trigger
-roughly 10 seconds later and of course not if you reset your system time
-again).
+roughly 10 seconds later).
They can also be used to implement vastly more complex timers, such as
-triggering an event on eahc midnight, local time.
+triggering an event on each midnight, local time or other, complicated,
+rules.
As with timers, the callback is guarenteed to be invoked only when the
time (C<at>) has been passed, but if multiple periodic timers become ready
during the same loop iteration then order of execution is undefined.
+=head3 Watcher-Specific Functions and Data Members
+
=over 4
=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)
=over 4
-=item * absolute timer (interval = reschedule_cb = 0)
+=item * absolute timer (at = time, interval = reschedule_cb = 0)
In this configuration the watcher triggers an event at the wallclock time
C<at> and doesn't repeat. It will not adjust when a time jump occurs,
that is, if it is to be run at January 1st 2011 then it will run when the
system time reaches or surpasses this time.
-=item * non-repeating interval timer (interval > 0, reschedule_cb = 0)
+=item * non-repeating interval timer (at = offset, interval > 0, reschedule_cb = 0)
In this mode the watcher will always be scheduled to time out at the next
-C<at + N * interval> time (for some integer N) and then repeat, regardless
-of any time jumps.
+C<at + N * interval> time (for some integer N, which can also be negative)
+and then repeat, regardless of any time jumps.
This can be used to create timers that do not drift with respect to system
time:
C<ev_periodic> will try to run the callback in this mode at the next possible
time where C<time = at (mod interval)>, regardless of any time jumps.
-=item * manual reschedule mode (reschedule_cb = callback)
+For numerical stability it is preferable that the C<at> value is near
+C<ev_now ()> (the current time), but there is no range requirement for
+this value.
+
+=item * manual reschedule mode (at and interval ignored, reschedule_cb = callback)
In this mode the values for C<interval> and C<at> are both being
ignored. Instead, each time the periodic watcher gets scheduled, the
NOTE: I<This callback MUST NOT stop or destroy any periodic watcher,
ever, or make any event loop modifications>. If you need to stop it,
return C<now + 1e30> (or so, fudge fudge) and stop it afterwards (e.g. by
-starting a prepare watcher).
+starting an C<ev_prepare> watcher, which is legal).
Its prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic *w,
ev_tstamp now)>, e.g.:
a different time than the last time it was called (e.g. in a crond like
program when the crontabs have changed).
+=item ev_tstamp offset [read-write]
+
+When repeating, this contains the offset value, otherwise this is the
+absolute point in time (the C<at> value passed to C<ev_periodic_set>).
+
+Can be modified any time, but changes only take effect when the periodic
+timer fires or C<ev_periodic_again> is being called.
+
+=item ev_tstamp interval [read-write]
+
+The current interval value. Can be modified any time, but changes only
+take effect when the periodic timer fires or C<ev_periodic_again> is being
+called.
+
+=item ev_tstamp (*reschedule_cb)(struct ev_periodic *w, ev_tstamp now) [read-write]
+
+The current reschedule callback, or C<0>, if this functionality is
+switched off. Can be changed any time, but changes only take effect when
+the periodic timer fires or C<ev_periodic_again> is being called.
+
+=item ev_tstamp at [read-only]
+
+When active, contains the absolute time that the watcher is supposed to
+trigger next.
+
=back
-Example: call a callback every hour, or, more precisely, whenever the
+Example: Call a callback every hour, or, more precisely, whenever the
system clock is divisible by 3600. The callback invocation times have
potentially a lot of jittering, but good long-term stability.
ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
ev_periodic_start (loop, &hourly_tick);
-Example: the same as above, but use a reschedule callback to do it:
+Example: The same as above, but use a reschedule callback to do it:
#include <math.h>
ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
-Example: call a callback every hour, starting now:
+Example: Call a callback every hour, starting now:
struct ev_periodic hourly_tick;
ev_periodic_init (&hourly_tick, clock_cb,
ev_periodic_start (loop, &hourly_tick);
-=head2 C<ev_signal> - signal me when a signal gets signalled
+=head2 C<ev_signal> - signal me when a signal gets signalled!
Signal watchers will trigger an event when the process receives a specific
signal one or more times. Even though signals are very asynchronous, libev
watcher for a signal is stopped libev will reset the signal handler to
SIG_DFL (regardless of what it was set to before).
+=head3 Watcher-Specific Functions and Data Members
+
=over 4
=item ev_signal_init (ev_signal *, callback, int signum)
Configures the watcher to trigger on the given signal number (usually one
of the C<SIGxxx> constants).
+=item int signum [read-only]
+
+The signal the watcher watches out for.
+
=back
-=head2 C<ev_child> - wait for pid status changes
+=head2 C<ev_child> - watch out for process status changes
Child watchers trigger when your process receives a SIGCHLD in response to
some child status changes (most typically when a child of yours dies).
+=head3 Watcher-Specific Functions and Data Members
+
=over 4
=item ev_child_init (ev_child *, callback, int pid)
C<waitpid> documentation). The C<rpid> member contains the pid of the
process causing the status change.
+=item int pid [read-only]
+
+The process id this watcher watches out for, or C<0>, meaning any process id.
+
+=item int rpid [read-write]
+
+The process id that detected a status change.
+
+=item int rstatus [read-write]
+
+The process exit/trace status caused by C<rpid> (see your systems
+C<waitpid> and C<sys/wait.h> documentation for details).
+
=back
-Example: try to exit cleanly on SIGINT and SIGTERM.
+Example: Try to exit cleanly on SIGINT and SIGTERM.
static void
sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents)
ev_signal_start (loop, &sigint_cb);
-=head2 C<ev_idle> - when you've got nothing better to do
+=head2 C<ev_stat> - did the file attributes just change?
+
+This watches a filesystem path for attribute changes. That is, it calls
+C<stat> regularly (or when the OS says it changed) and sees if it changed
+compared to the last time, invoking the callback if it did.
-Idle watchers trigger events when there are no other events are pending
-(prepare, check and other idle watchers do not count). That is, as long
-as your process is busy handling sockets or timeouts (or even signals,
-imagine) it will not be triggered. But when your process is idle all idle
-watchers are being called again and again, once per event loop iteration -
-until stopped, that is, or your process receives more events and becomes
-busy.
+The path does not need to exist: changing from "path exists" to "path does
+not exist" is a status change like any other. The condition "path does
+not exist" is signified by the C<st_nlink> field being zero (which is
+otherwise always forced to be at least one) and all the other fields of
+the stat buffer having unspecified contents.
+
+The path I<should> be absolute and I<must not> end in a slash. If it is
+relative and your working directory changes, the behaviour is undefined.
+
+Since there is no standard to do this, the portable implementation simply
+calls C<stat (2)> regularly on the path to see if it changed somehow. You
+can specify a recommended polling interval for this case. If you specify
+a polling interval of C<0> (highly recommended!) then a I<suitable,
+unspecified default> value will be used (which you can expect to be around
+five seconds, although this might change dynamically). Libev will also
+impose a minimum interval which is currently around C<0.1>, but thats
+usually overkill.
+
+This watcher type is not meant for massive numbers of stat watchers,
+as even with OS-supported change notifications, this can be
+resource-intensive.
+
+At the time of this writing, only the Linux inotify interface is
+implemented (implementing kqueue support is left as an exercise for the
+reader). Inotify will be used to give hints only and should not change the
+semantics of C<ev_stat> watchers, which means that libev sometimes needs
+to fall back to regular polling again even with inotify, but changes are
+usually detected immediately, and if the file exists there will be no
+polling.
+
+=head3 Watcher-Specific Functions and Data Members
+
+=over 4
+
+=item ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)
+
+=item ev_stat_set (ev_stat *, const char *path, ev_tstamp interval)
+
+Configures the watcher to wait for status changes of the given
+C<path>. The C<interval> is a hint on how quickly a change is expected to
+be detected and should normally be specified as C<0> to let libev choose
+a suitable value. The memory pointed to by C<path> must point to the same
+path for as long as the watcher is active.
+
+The callback will be receive C<EV_STAT> when a change was detected,
+relative to the attributes at the time the watcher was started (or the
+last change was detected).
+
+=item ev_stat_stat (ev_stat *)
+
+Updates the stat buffer immediately with new values. If you change the
+watched path in your callback, you could call this fucntion to avoid
+detecting this change (while introducing a race condition). Can also be
+useful simply to find out the new values.
+
+=item ev_statdata attr [read-only]
+
+The most-recently detected attributes of the file. Although the type is of
+C<ev_statdata>, this is usually the (or one of the) C<struct stat> types
+suitable for your system. If the C<st_nlink> member is C<0>, then there
+was some error while C<stat>ing the file.
+
+=item ev_statdata prev [read-only]
+
+The previous attributes of the file. The callback gets invoked whenever
+C<prev> != C<attr>.
+
+=item ev_tstamp interval [read-only]
+
+The specified interval.
+
+=item const char *path [read-only]
+
+The filesystem path that is being watched.
+
+=back
+
+Example: Watch C</etc/passwd> for attribute changes.
+
+ static void
+ passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)
+ {
+ /* /etc/passwd changed in some way */
+ if (w->attr.st_nlink)
+ {
+ printf ("passwd current size %ld\n", (long)w->attr.st_size);
+ printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);
+ printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);
+ }
+ else
+ /* you shalt not abuse printf for puts */
+ puts ("wow, /etc/passwd is not there, expect problems. "
+ "if this is windows, they already arrived\n");
+ }
+
+ ...
+ ev_stat passwd;
+
+ ev_stat_init (&passwd, passwd_cb, "/etc/passwd");
+ ev_stat_start (loop, &passwd);
+
+
+=head2 C<ev_idle> - when you've got nothing better to do...
+
+Idle watchers trigger events when no other events of the same or higher
+priority are pending (prepare, check and other idle watchers do not
+count).
+
+That is, as long as your process is busy handling sockets or timeouts
+(or even signals, imagine) of the same or higher priority it will not be
+triggered. But when your process is idle (or only lower-priority watchers
+are pending), the idle watchers are being called once per event loop
+iteration - until stopped, that is, or your process receives more events
+and becomes busy again with higher priority stuff.
The most noteworthy effect is that as long as any idle watchers are
active, the process will not block when waiting for new events.
"pseudo-background processing", or delay processing stuff to after the
event loop has handled all outstanding events.
+=head3 Watcher-Specific Functions and Data Members
+
=over 4
=item ev_idle_init (ev_signal *, callback)
=back
-Example: dynamically allocate an C<ev_idle>, start it, and in the
-callback, free it. Alos, use no error checking, as usual.
+Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the
+callback, free it. Also, use no error checking, as usual.
static void
idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents)
ev_idle_start (loop, idle_cb);
-=head2 C<ev_prepare> and C<ev_check> - customise your event loop
+=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
Prepare and check watchers are usually (but not always) used in tandem:
prepare watchers get invoked before the process blocks and check watchers
afterwards.
+You I<must not> call C<ev_loop> or similar functions that enter
+the current event loop from either C<ev_prepare> or C<ev_check>
+watchers. Other loops than the current one are fine, however. The
+rationale behind this is that you do not need to check for recursion in
+those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,
+C<ev_check> so if you have one watcher of each kind they will always be
+called in pairs bracketing the blocking call.
+
Their main purpose is to integrate other event mechanisms into libev and
their use is somewhat advanced. This could be used, for example, to track
variable changes, implement your own watchers, integrate net-snmp or a
-coroutine library and lots more.
+coroutine library and lots more. They are also occasionally useful if
+you cache some data and want to flush it before blocking (for example,
+in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>
+watcher).
This is done by examining in each prepare call which file descriptors need
to be watched by the other library, registering C<ev_io> watchers for
loop from blocking if lower-priority coroutines are active, thus mapping
low-priority coroutines to idle/background tasks).
+It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)
+priority, to ensure that they are being run before any other watchers
+after the poll. Also, C<ev_check> watchers (and C<ev_prepare> watchers,
+too) should not activate ("feed") events into libev. While libev fully
+supports this, they will be called before other C<ev_check> watchers did
+their job. As C<ev_check> watchers are often used to embed other event
+loops those other event loops might be in an unusable state until their
+C<ev_check> watcher ran (always remind yourself to coexist peacefully with
+others).
+
+=head3 Watcher-Specific Functions and Data Members
+
=over 4
=item ev_prepare_init (ev_prepare *, callback)
=back
-Example: *TODO*.
+There are a number of principal ways to embed other event loops or modules
+into libev. Here are some ideas on how to include libadns into libev
+(there is a Perl module named C<EV::ADNS> that does this, which you could
+use for an actually working example. Another Perl module named C<EV::Glib>
+embeds a Glib main context into libev, and finally, C<Glib::EV> embeds EV
+into the Glib event loop).
+
+Method 1: Add IO watchers and a timeout watcher in a prepare handler,
+and in a check watcher, destroy them and call into libadns. What follows
+is pseudo-code only of course. This requires you to either use a low
+priority for the check watcher or use C<ev_clear_pending> explicitly, as
+the callbacks for the IO/timeout watchers might not have been called yet.
+
+ static ev_io iow [nfd];
+ static ev_timer tw;
+
+ static void
+ io_cb (ev_loop *loop, ev_io *w, int revents)
+ {
+ }
+
+ // create io watchers for each fd and a timer before blocking
+ static void
+ adns_prepare_cb (ev_loop *loop, ev_prepare *w, int revents)
+ {
+ int timeout = 3600000;
+ struct pollfd fds [nfd];
+ // actual code will need to loop here and realloc etc.
+ adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
+
+ /* the callback is illegal, but won't be called as we stop during check */
+ ev_timer_init (&tw, 0, timeout * 1e-3);
+ ev_timer_start (loop, &tw);
+
+ // create one ev_io per pollfd
+ for (int i = 0; i < nfd; ++i)
+ {
+ ev_io_init (iow + i, io_cb, fds [i].fd,
+ ((fds [i].events & POLLIN ? EV_READ : 0)
+ | (fds [i].events & POLLOUT ? EV_WRITE : 0)));
+
+ fds [i].revents = 0;
+ ev_io_start (loop, iow + i);
+ }
+ }
+
+ // stop all watchers after blocking
+ static void
+ adns_check_cb (ev_loop *loop, ev_check *w, int revents)
+ {
+ ev_timer_stop (loop, &tw);
+
+ for (int i = 0; i < nfd; ++i)
+ {
+ // set the relevant poll flags
+ // could also call adns_processreadable etc. here
+ struct pollfd *fd = fds + i;
+ int revents = ev_clear_pending (iow + i);
+ if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;
+ if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;
+
+ // now stop the watcher
+ ev_io_stop (loop, iow + i);
+ }
+
+ adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
+ }
+
+Method 2: This would be just like method 1, but you run C<adns_afterpoll>
+in the prepare watcher and would dispose of the check watcher.
+
+Method 3: If the module to be embedded supports explicit event
+notification (adns does), you can also make use of the actual watcher
+callbacks, and only destroy/create the watchers in the prepare watcher.
+
+ static void
+ timer_cb (EV_P_ ev_timer *w, int revents)
+ {
+ adns_state ads = (adns_state)w->data;
+ update_now (EV_A);
+
+ adns_processtimeouts (ads, &tv_now);
+ }
+
+ static void
+ io_cb (EV_P_ ev_io *w, int revents)
+ {
+ adns_state ads = (adns_state)w->data;
+ update_now (EV_A);
+
+ if (revents & EV_READ ) adns_processreadable (ads, w->fd, &tv_now);
+ if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now);
+ }
+
+ // do not ever call adns_afterpoll
+
+Method 4: Do not use a prepare or check watcher because the module you
+want to embed is too inflexible to support it. Instead, youc na override
+their poll function. The drawback with this solution is that the main
+loop is now no longer controllable by EV. The C<Glib::EV> module does
+this.
+
+ static gint
+ event_poll_func (GPollFD *fds, guint nfds, gint timeout)
+ {
+ int got_events = 0;
+
+ for (n = 0; n < nfds; ++n)
+ // create/start io watcher that sets the relevant bits in fds[n] and increment got_events
+
+ if (timeout >= 0)
+ // create/start timer
+ // poll
+ ev_loop (EV_A_ 0);
-=head2 C<ev_embed> - when one backend isn't enough
+ // stop timer again
+ if (timeout >= 0)
+ ev_timer_stop (EV_A_ &to);
+
+ // stop io watchers again - their callbacks should have set
+ for (n = 0; n < nfds; ++n)
+ ev_io_stop (EV_A_ iow [n]);
+
+ return got_events;
+ }
+
+
+=head2 C<ev_embed> - when one backend isn't enough...
This is a rather advanced watcher type that lets you embed one event loop
into another (currently only C<ev_io> events are supported in the embedded
else
loop_lo = loop_hi;
+=head3 Watcher-Specific Functions and Data Members
+
=over 4
=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)
similarly to C<ev_loop (embedded_loop, EVLOOP_NONBLOCK)>, but in the most
apropriate way for embedded loops.
+=item struct ev_loop *loop [read-only]
+
+The embedded event loop.
+
+=back
+
+
+=head2 C<ev_fork> - the audacity to resume the event loop after a fork
+
+Fork watchers are called when a C<fork ()> was detected (usually because
+whoever is a good citizen cared to tell libev about it by calling
+C<ev_default_fork> or C<ev_loop_fork>). The invocation is done before the
+event loop blocks next and before C<ev_check> watchers are being called,
+and only in the child after the fork. If whoever good citizen calling
+C<ev_default_fork> cheats and calls it in the wrong process, the fork
+handlers will be invoked, too, of course.
+
+=head3 Watcher-Specific Functions and Data Members
+
+=over 4
+
+=item ev_fork_init (ev_signal *, callback)
+
+Initialises and configures the fork watcher - it has no parameters of any
+kind. There is a C<ev_fork_set> macro, but using it is utterly pointless,
+believe me.
+
=back
=head1 C++ SUPPORT
-TBD.
+Libev comes with some simplistic wrapper classes for C++ that mainly allow
+you to use some convinience methods to start/stop watchers and also change
+the callback model to a model using method callbacks on objects.
+
+To use it,
+
+ #include <ev++.h>
+
+This automatically includes F<ev.h> and puts all of its definitions (many
+of them macros) into the global namespace. All C++ specific things are
+put into the C<ev> namespace. It should support all the same embedding
+options as F<ev.h>, most notably C<EV_MULTIPLICITY>.
+
+Care has been taken to keep the overhead low. The only data member the C++
+classes add (compared to plain C-style watchers) is the event loop pointer
+that the watcher is associated with (or no additional members at all if
+you disable C<EV_MULTIPLICITY> when embedding libev).
+
+Currently, functions, and static and non-static member functions can be
+used as callbacks. Other types should be easy to add as long as they only
+need one additional pointer for context. If you need support for other
+types of functors please contact the author (preferably after implementing
+it).
+
+Here is a list of things available in the C<ev> namespace:
+
+=over 4
+
+=item C<ev::READ>, C<ev::WRITE> etc.
+
+These are just enum values with the same values as the C<EV_READ> etc.
+macros from F<ev.h>.
+
+=item C<ev::tstamp>, C<ev::now>
+
+Aliases to the same types/functions as with the C<ev_> prefix.
+
+=item C<ev::io>, C<ev::timer>, C<ev::periodic>, C<ev::idle>, C<ev::sig> etc.
+
+For each C<ev_TYPE> watcher in F<ev.h> there is a corresponding class of
+the same name in the C<ev> namespace, with the exception of C<ev_signal>
+which is called C<ev::sig> to avoid clashes with the C<signal> macro
+defines by many implementations.
+
+All of those classes have these methods:
+
+=over 4
+
+=item ev::TYPE::TYPE ()
+
+=item ev::TYPE::TYPE (struct ev_loop *)
+
+=item ev::TYPE::~TYPE
+
+The constructor (optionally) takes an event loop to associate the watcher
+with. If it is omitted, it will use C<EV_DEFAULT>.
+
+The constructor calls C<ev_init> for you, which means you have to call the
+C<set> method before starting it.
+
+It will not set a callback, however: You have to call the templated C<set>
+method to set a callback before you can start the watcher.
+
+(The reason why you have to use a method is a limitation in C++ which does
+not allow explicit template arguments for constructors).
+
+The destructor automatically stops the watcher if it is active.
+
+=item w->set<class, &class::method> (object *)
+
+This method sets the callback method to call. The method has to have a
+signature of C<void (*)(ev_TYPE &, int)>, it receives the watcher as
+first argument and the C<revents> as second. The object must be given as
+parameter and is stored in the C<data> member of the watcher.
+
+This method synthesizes efficient thunking code to call your method from
+the C callback that libev requires. If your compiler can inline your
+callback (i.e. it is visible to it at the place of the C<set> call and
+your compiler is good :), then the method will be fully inlined into the
+thunking function, making it as fast as a direct C callback.
+
+Example: simple class declaration and watcher initialisation
+
+ struct myclass
+ {
+ void io_cb (ev::io &w, int revents) { }
+ }
+
+ myclass obj;
+ ev::io iow;
+ iow.set <myclass, &myclass::io_cb> (&obj);
+
+=item w->set<function> (void *data = 0)
+
+Also sets a callback, but uses a static method or plain function as
+callback. The optional C<data> argument will be stored in the watcher's
+C<data> member and is free for you to use.
+
+The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.
+
+See the method-C<set> above for more details.
+
+Example:
+
+ static void io_cb (ev::io &w, int revents) { }
+ iow.set <io_cb> ();
+
+=item w->set (struct ev_loop *)
+
+Associates a different C<struct ev_loop> with this watcher. You can only
+do this when the watcher is inactive (and not pending either).
+
+=item w->set ([args])
+
+Basically the same as C<ev_TYPE_set>, with the same args. Must be
+called at least once. Unlike the C counterpart, an active watcher gets
+automatically stopped and restarted when reconfiguring it with this
+method.
+
+=item w->start ()
+
+Starts the watcher. Note that there is no C<loop> argument, as the
+constructor already stores the event loop.
+
+=item w->stop ()
+
+Stops the watcher if it is active. Again, no C<loop> argument.
+
+=item w->again () (C<ev::timer>, C<ev::periodic> only)
+
+For C<ev::timer> and C<ev::periodic>, this invokes the corresponding
+C<ev_TYPE_again> function.
+
+=item w->sweep () (C<ev::embed> only)
+
+Invokes C<ev_embed_sweep>.
+
+=item w->update () (C<ev::stat> only)
+
+Invokes C<ev_stat_stat>.
+
+=back
+
+=back
+
+Example: Define a class with an IO and idle watcher, start one of them in
+the constructor.
+
+ class myclass
+ {
+ ev_io io; void io_cb (ev::io &w, int revents);
+ ev_idle idle void idle_cb (ev::idle &w, int revents);
+
+ myclass ();
+ }
+
+ myclass::myclass (int fd)
+ {
+ io .set <myclass, &myclass::io_cb > (this);
+ idle.set <myclass, &myclass::idle_cb> (this);
+
+ io.start (fd, ev::READ);
+ }
+
+
+=head1 MACRO MAGIC
+
+Libev can be compiled with a variety of options, the most fundamantal
+of which is C<EV_MULTIPLICITY>. This option determines whether (most)
+functions and callbacks have an initial C<struct ev_loop *> argument.
+
+To make it easier to write programs that cope with either variant, the
+following macros are defined:
+
+=over 4
+
+=item C<EV_A>, C<EV_A_>
+
+This provides the loop I<argument> for functions, if one is required ("ev
+loop argument"). The C<EV_A> form is used when this is the sole argument,
+C<EV_A_> is used when other arguments are following. Example:
+
+ ev_unref (EV_A);
+ ev_timer_add (EV_A_ watcher);
+ ev_loop (EV_A_ 0);
+
+It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,
+which is often provided by the following macro.
+
+=item C<EV_P>, C<EV_P_>
+
+This provides the loop I<parameter> for functions, if one is required ("ev
+loop parameter"). The C<EV_P> form is used when this is the sole parameter,
+C<EV_P_> is used when other parameters are following. Example:
+
+ // this is how ev_unref is being declared
+ static void ev_unref (EV_P);
+
+ // this is how you can declare your typical callback
+ static void cb (EV_P_ ev_timer *w, int revents)
+
+It declares a parameter C<loop> of type C<struct ev_loop *>, quite
+suitable for use with C<EV_A>.
+
+=item C<EV_DEFAULT>, C<EV_DEFAULT_>
+
+Similar to the other two macros, this gives you the value of the default
+loop, if multiple loops are supported ("ev loop default").
+
+=back
+
+Example: Declare and initialise a check watcher, utilising the above
+macros so it will work regardless of whether multiple loops are supported
+or not.
+
+ static void
+ check_cb (EV_P_ ev_timer *w, int revents)
+ {
+ ev_check_stop (EV_A_ w);
+ }
+
+ ev_check check;
+ ev_check_init (&check, check_cb);
+ ev_check_start (EV_DEFAULT_ &check);
+ ev_loop (EV_DEFAULT_ 0);
+
+=head1 EMBEDDING
+
+Libev can (and often is) directly embedded into host
+applications. Examples of applications that embed it include the Deliantra
+Game Server, the EV perl module, the GNU Virtual Private Ethernet (gvpe)
+and rxvt-unicode.
+
+The goal is to enable you to just copy the neecssary files into your
+source directory without having to change even a single line in them, so
+you can easily upgrade by simply copying (or having a checked-out copy of
+libev somewhere in your source tree).
+
+=head2 FILESETS
+
+Depending on what features you need you need to include one or more sets of files
+in your app.
+
+=head3 CORE EVENT LOOP
+
+To include only the libev core (all the C<ev_*> functions), with manual
+configuration (no autoconf):
+
+ #define EV_STANDALONE 1
+ #include "ev.c"
+
+This will automatically include F<ev.h>, too, and should be done in a
+single C source file only to provide the function implementations. To use
+it, do the same for F<ev.h> in all files wishing to use this API (best
+done by writing a wrapper around F<ev.h> that you can include instead and
+where you can put other configuration options):
+
+ #define EV_STANDALONE 1
+ #include "ev.h"
+
+Both header files and implementation files can be compiled with a C++
+compiler (at least, thats a stated goal, and breakage will be treated
+as a bug).
+
+You need the following files in your source tree, or in a directory
+in your include path (e.g. in libev/ when using -Ilibev):
+
+ ev.h
+ ev.c
+ ev_vars.h
+ ev_wrap.h
+
+ ev_win32.c required on win32 platforms only
+
+ ev_select.c only when select backend is enabled (which is enabled by default)
+ ev_poll.c only when poll backend is enabled (disabled by default)
+ ev_epoll.c only when the epoll backend is enabled (disabled by default)
+ ev_kqueue.c only when the kqueue backend is enabled (disabled by default)
+ ev_port.c only when the solaris port backend is enabled (disabled by default)
+
+F<ev.c> includes the backend files directly when enabled, so you only need
+to compile this single file.
+
+=head3 LIBEVENT COMPATIBILITY API
+
+To include the libevent compatibility API, also include:
+
+ #include "event.c"
+
+in the file including F<ev.c>, and:
+
+ #include "event.h"
+
+in the files that want to use the libevent API. This also includes F<ev.h>.
+
+You need the following additional files for this:
+
+ event.h
+ event.c
+
+=head3 AUTOCONF SUPPORT
+
+Instead of using C<EV_STANDALONE=1> and providing your config in
+whatever way you want, you can also C<m4_include([libev.m4])> in your
+F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then
+include F<config.h> and configure itself accordingly.
+
+For this of course you need the m4 file:
+
+ libev.m4
+
+=head2 PREPROCESSOR SYMBOLS/MACROS
+
+Libev can be configured via a variety of preprocessor symbols you have to define
+before including any of its files. The default is not to build for multiplicity
+and only include the select backend.
+
+=over 4
+
+=item EV_STANDALONE
+
+Must always be C<1> if you do not use autoconf configuration, which
+keeps libev from including F<config.h>, and it also defines dummy
+implementations for some libevent functions (such as logging, which is not
+supported). It will also not define any of the structs usually found in
+F<event.h> that are not directly supported by the libev core alone.
+
+=item EV_USE_MONOTONIC
+
+If defined to be C<1>, libev will try to detect the availability of the
+monotonic clock option at both compiletime and runtime. Otherwise no use
+of the monotonic clock option will be attempted. If you enable this, you
+usually have to link against librt or something similar. Enabling it when
+the functionality isn't available is safe, though, althoguh you have
+to make sure you link against any libraries where the C<clock_gettime>
+function is hiding in (often F<-lrt>).
+
+=item EV_USE_REALTIME
+
+If defined to be C<1>, libev will try to detect the availability of the
+realtime clock option at compiletime (and assume its availability at
+runtime if successful). Otherwise no use of the realtime clock option will
+be attempted. This effectively replaces C<gettimeofday> by C<clock_get
+(CLOCK_REALTIME, ...)> and will not normally affect correctness. See tzhe note about libraries
+in the description of C<EV_USE_MONOTONIC>, though.
+
+=item EV_USE_SELECT
+
+If undefined or defined to be C<1>, libev will compile in support for the
+C<select>(2) backend. No attempt at autodetection will be done: if no
+other method takes over, select will be it. Otherwise the select backend
+will not be compiled in.
+
+=item EV_SELECT_USE_FD_SET
+
+If defined to C<1>, then the select backend will use the system C<fd_set>
+structure. This is useful if libev doesn't compile due to a missing
+C<NFDBITS> or C<fd_mask> definition or it misguesses the bitset layout on
+exotic systems. This usually limits the range of file descriptors to some
+low limit such as 1024 or might have other limitations (winsocket only
+allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation, might
+influence the size of the C<fd_set> used.
+
+=item EV_SELECT_IS_WINSOCKET
+
+When defined to C<1>, the select backend will assume that
+select/socket/connect etc. don't understand file descriptors but
+wants osf handles on win32 (this is the case when the select to
+be used is the winsock select). This means that it will call
+C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,
+it is assumed that all these functions actually work on fds, even
+on win32. Should not be defined on non-win32 platforms.
+
+=item EV_USE_POLL
+
+If defined to be C<1>, libev will compile in support for the C<poll>(2)
+backend. Otherwise it will be enabled on non-win32 platforms. It
+takes precedence over select.
+
+=item EV_USE_EPOLL
+
+If defined to be C<1>, libev will compile in support for the Linux
+C<epoll>(7) backend. Its availability will be detected at runtime,
+otherwise another method will be used as fallback. This is the
+preferred backend for GNU/Linux systems.
+
+=item EV_USE_KQUEUE
+
+If defined to be C<1>, libev will compile in support for the BSD style
+C<kqueue>(2) backend. Its actual availability will be detected at runtime,
+otherwise another method will be used as fallback. This is the preferred
+backend for BSD and BSD-like systems, although on most BSDs kqueue only
+supports some types of fds correctly (the only platform we found that
+supports ptys for example was NetBSD), so kqueue might be compiled in, but
+not be used unless explicitly requested. The best way to use it is to find
+out whether kqueue supports your type of fd properly and use an embedded
+kqueue loop.
+
+=item EV_USE_PORT
+
+If defined to be C<1>, libev will compile in support for the Solaris
+10 port style backend. Its availability will be detected at runtime,
+otherwise another method will be used as fallback. This is the preferred
+backend for Solaris 10 systems.
+
+=item EV_USE_DEVPOLL
+
+reserved for future expansion, works like the USE symbols above.
+
+=item EV_USE_INOTIFY
+
+If defined to be C<1>, libev will compile in support for the Linux inotify
+interface to speed up C<ev_stat> watchers. Its actual availability will
+be detected at runtime.
+
+=item EV_H
+
+The name of the F<ev.h> header file used to include it. The default if
+undefined is C<< <ev.h> >> in F<event.h> and C<"ev.h"> in F<ev.c>. This
+can be used to virtually rename the F<ev.h> header file in case of conflicts.
+
+=item EV_CONFIG_H
+
+If C<EV_STANDALONE> isn't C<1>, this variable can be used to override
+F<ev.c>'s idea of where to find the F<config.h> file, similarly to
+C<EV_H>, above.
+
+=item EV_EVENT_H
+
+Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea
+of how the F<event.h> header can be found.
+
+=item EV_PROTOTYPES
+
+If defined to be C<0>, then F<ev.h> will not define any function
+prototypes, but still define all the structs and other symbols. This is
+occasionally useful if you want to provide your own wrapper functions
+around libev functions.
+
+=item EV_MULTIPLICITY
+
+If undefined or defined to C<1>, then all event-loop-specific functions
+will have the C<struct ev_loop *> as first argument, and you can create
+additional independent event loops. Otherwise there will be no support
+for multiple event loops and there is no first event loop pointer
+argument. Instead, all functions act on the single default loop.
+
+=item EV_MINPRI
+
+=item EV_MAXPRI
+
+The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to
+C<EV_MAXPRI>, but otherwise there are no non-obvious limitations. You can
+provide for more priorities by overriding those symbols (usually defined
+to be C<-2> and C<2>, respectively).
+
+When doing priority-based operations, libev usually has to linearly search
+all the priorities, so having many of them (hundreds) uses a lot of space
+and time, so using the defaults of five priorities (-2 .. +2) is usually
+fine.
+
+If your embedding app does not need any priorities, defining these both to
+C<0> will save some memory and cpu.
+
+=item EV_PERIODIC_ENABLE
+
+If undefined or defined to be C<1>, then periodic timers are supported. If
+defined to be C<0>, then they are not. Disabling them saves a few kB of
+code.
+
+=item EV_IDLE_ENABLE
+
+If undefined or defined to be C<1>, then idle watchers are supported. If
+defined to be C<0>, then they are not. Disabling them saves a few kB of
+code.
+
+=item EV_EMBED_ENABLE
+
+If undefined or defined to be C<1>, then embed watchers are supported. If
+defined to be C<0>, then they are not.
+
+=item EV_STAT_ENABLE
+
+If undefined or defined to be C<1>, then stat watchers are supported. If
+defined to be C<0>, then they are not.
+
+=item EV_FORK_ENABLE
+
+If undefined or defined to be C<1>, then fork watchers are supported. If
+defined to be C<0>, then they are not.
+
+=item EV_MINIMAL
+
+If you need to shave off some kilobytes of code at the expense of some
+speed, define this symbol to C<1>. Currently only used for gcc to override
+some inlining decisions, saves roughly 30% codesize of amd64.
+
+=item EV_PID_HASHSIZE
+
+C<ev_child> watchers use a small hash table to distribute workload by
+pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more
+than enough. If you need to manage thousands of children you might want to
+increase this value (I<must> be a power of two).
+
+=item EV_INOTIFY_HASHSIZE
+
+C<ev_staz> watchers use a small hash table to distribute workload by
+inotify watch id. The default size is C<16> (or C<1> with C<EV_MINIMAL>),
+usually more than enough. If you need to manage thousands of C<ev_stat>
+watchers you might want to increase this value (I<must> be a power of
+two).
+
+=item EV_COMMON
+
+By default, all watchers have a C<void *data> member. By redefining
+this macro to a something else you can include more and other types of
+members. You have to define it each time you include one of the files,
+though, and it must be identical each time.
+
+For example, the perl EV module uses something like this:
+
+ #define EV_COMMON \
+ SV *self; /* contains this struct */ \
+ SV *cb_sv, *fh /* note no trailing ";" */
+
+=item EV_CB_DECLARE (type)
+
+=item EV_CB_INVOKE (watcher, revents)
+
+=item ev_set_cb (ev, cb)
+
+Can be used to change the callback member declaration in each watcher,
+and the way callbacks are invoked and set. Must expand to a struct member
+definition and a statement, respectively. See the F<ev.v> header file for
+their default definitions. One possible use for overriding these is to
+avoid the C<struct ev_loop *> as first argument in all cases, or to use
+method calls instead of plain function calls in C++.
+
+=head2 EXAMPLES
+
+For a real-world example of a program the includes libev
+verbatim, you can have a look at the EV perl module
+(L<http://software.schmorp.de/pkg/EV.html>). It has the libev files in
+the F<libev/> subdirectory and includes them in the F<EV/EVAPI.h> (public
+interface) and F<EV.xs> (implementation) files. Only the F<EV.xs> file
+will be compiled. It is pretty complex because it provides its own header
+file.
+
+The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file
+that everybody includes and which overrides some configure choices:
+
+ #define EV_MINIMAL 1
+ #define EV_USE_POLL 0
+ #define EV_MULTIPLICITY 0
+ #define EV_PERIODIC_ENABLE 0
+ #define EV_STAT_ENABLE 0
+ #define EV_FORK_ENABLE 0
+ #define EV_CONFIG_H <config.h>
+ #define EV_MINPRI 0
+ #define EV_MAXPRI 0
+
+ #include "ev++.h"
+
+And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
+
+ #include "ev_cpp.h"
+ #include "ev.c"
+
+
+=head1 COMPLEXITIES
+
+In this section the complexities of (many of) the algorithms used inside
+libev will be explained. For complexity discussions about backends see the
+documentation for C<ev_default_init>.
+
+All of the following are about amortised time: If an array needs to be
+extended, libev needs to realloc and move the whole array, but this
+happens asymptotically never with higher number of elements, so O(1) might
+mean it might do a lengthy realloc operation in rare cases, but on average
+it is much faster and asymptotically approaches constant time.
+
+=over 4
+
+=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)
+
+This means that, when you have a watcher that triggers in one hour and
+there are 100 watchers that would trigger before that then inserting will
+have to skip those 100 watchers.
+
+=item Changing timer/periodic watchers (by autorepeat, again): O(log skipped_other_timers)
+
+That means that for changing a timer costs less than removing/adding them
+as only the relative motion in the event queue has to be paid for.
+
+=item Starting io/check/prepare/idle/signal/child watchers: O(1)
+
+These just add the watcher into an array or at the head of a list.
+=item Stopping check/prepare/idle watchers: O(1)
+
+=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))
+
+These watchers are stored in lists then need to be walked to find the
+correct watcher to remove. The lists are usually short (you don't usually
+have many watchers waiting for the same fd or signal).
+
+=item Finding the next timer per loop iteration: O(1)
+
+=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
+
+A change means an I/O watcher gets started or stopped, which requires
+libev to recalculate its status (and possibly tell the kernel).
+
+=item Activating one watcher: O(1)
+
+=item Priority handling: O(number_of_priorities)
+
+Priorities are implemented by allocating some space for each
+priority. When doing priority-based operations, libev usually has to
+linearly search all the priorities.
+
+=back
+
=head1 AUTHOR
projects / software / libev.git / blobdiff