=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.
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".
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)
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 :).
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
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).
+
=over 4
=item ev_prepare_init (ev_prepare *, callback)
=back
-Example: To include a library such as adns, you would add IO watchers
-and a timeout watcher in a prepare handler, as required by libadns, and
-in a check watcher, destroy them and call into libadns. What follows is
-pseudo-code only of course:
+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)
{
- // set the relevant poll flags
- // could also call adns_processreadable etc. here
- struct pollfd *fd = (struct pollfd *)w->data;
- if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;
- if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;
}
// create io watchers for each fd and a timer before blocking
ev_timer_init (&tw, 0, timeout * 1e-3);
ev_timer_start (loop, &tw);
- // create on ev_io per pollfd
+ // 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 & POLLOUT ? EV_WRITE : 0)));
fds [i].revents = 0;
- iow [i].data = fds + i;
ev_io_start (loop, iow + i);
}
}
ev_timer_stop (loop, &tw);
for (int i = 0; i < nfd; ++i)
- ev_io_stop (loop, iow + 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);
+
+ // 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...
#include <ev++.h>
-(it is not installed by default). 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.
+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).
-It should support all the same embedding options as F<ev.h>, most notably
-C<EV_MULTIPLICITY>.
+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 ev::TYPE::TYPE (object *, object::method *)
+=item ev::TYPE::TYPE ()
-=item ev::TYPE::TYPE (object *, object::method *, struct ev_loop *)
+=item ev::TYPE::TYPE (struct ev_loop *)
=item ev::TYPE::~TYPE
-The constructor takes a pointer to an object and a method pointer to
-the event handler callback to call in this class. The constructor calls
-C<ev_init> for you, which means you have to call the C<set> method
-before starting it. If you do not specify a loop then the constructor
-automatically associates the default loop with this watcher.
+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
=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.
+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 takes the loop.
+Starts the watcher. Note that there is no C<loop> argument, as the
+constructor already stores the event loop.
=item w->stop ()
}
myclass::myclass (int fd)
- : io (this, &myclass::io_cb),
- idle (this, &myclass::idle_cb)
{
+ io .set <myclass, &myclass::io_cb > (this);
+ idle.set <myclass, &myclass::idle_cb> (this);
+
io.start (fd, ev::READ);
}
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
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
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