=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.
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
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
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)
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
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
-wether a file descriptor is really ready with a known-to-be good interface
+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).
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 C<after>=C<repeat>=C<60> and calling
+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 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 stop the timer, and again will automatically restart it if
-need be.
+socket, you can C<ev_timer_stop> the timer, and C<ev_timer_again> will
+automatically restart it if need be.
-You can also ignore the C<after> value and C<ev_timer_start> altogether
-and only ever use the C<repeat> value:
+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 = 10.;
ev_timer_again (loop, timer);
-This is more efficient then stopping/starting the timer eahc time you want
-to modify its timeout value.
+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]
=head2 C<ev_idle> - when you've got nothing better to do...
-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.
+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.
=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
static void
adns_prepare_cb (ev_loop *loop, ev_prepare *w, int revents)
{
- int timeout = 3600000;truct pollfd fds [nfd];
+ 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 ()));
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>.
-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 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);
}
=head1 MACRO MAGIC
Libev can be compiled with a variety of options, the most fundemantal is
-C<EV_MULTIPLICITY>. This option determines wether (most) functions and
+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
=back
-Example: Declare and initialise a check watcher, working regardless of
-wether multiple loops are supported or not.
+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_start (EV_DEFAULT_ &check);
ev_loop (EV_DEFAULT_ 0);
-
=head1 EMBEDDING
Libev can (and often is) directly embedded into host
ev_win32.c required on win32 platforms only
- ev_select.c only when select backend is enabled (which is by default)
+ 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)
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
file.
The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file
-that everybody includes and which overrides some autoconf choices:
+that everybody includes and which overrides some configure choices:
+ #define EV_MINIMAL 1
#define EV_USE_POLL 0
#define EV_MULTIPLICITY 0
- #define EV_PERIODICS 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"
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
projects / software / libev.git / blobdiff