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 events.
+these event sources and provide your program with events.
To do this, it must take more or less complete control over your process
(or thread) by executing the I<event loop> handler, and will then
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).
+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).
=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 configuraiton options please have a look at the file
+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 *>)
symbols C<EV_VERSION_MAJOR> and C<EV_VERSION_MINOR>, which specify the
version of the library your program was compiled against.
-Usually, its a good idea to terminate if the major versions mismatch,
+Usually, it's a good idea to terminate if the major versions mismatch,
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.
=item ev_set_allocator (void *(*cb)(void *ptr, long size))
Sets the allocation function to use (the prototype is similar to the
-realloc 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.
+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.
You could override this function in high-availability programs to, say,
free some memory if it cannot allocate memory, to use a special allocator,
as failed select, poll, epoll_wait). The message is a printable string
indicating the system call or subsystem causing the problem. If this
callback is set, then libev will expect it to remedy the sitution, no
-matter what, when it returns. That is, libev will geenrally retry the
+matter what, when it returns. That is, libev will generally retry the
requested operation, or, if the condition doesn't go away, do bad stuff
(such as abort).
If you use threads, a common model is to run the default event loop
in your main thread (or in a separate thrad) and for each thread you
-create, you also create another event loop. Libev itself does no lockign
-whatsoever, so if you mix calls to different event loops, make sure you
-lock (this is usually a bad idea, though, even if done right).
+create, you also create another event loop. Libev itself does no locking
+whatsoever, so if you mix calls to the same event loop in different
+threads, make sure you lock (this is usually a bad idea, though, even if
+done correctly, because it's hideous and inefficient).
=over 4
function.
The flags argument can be used to specify special behaviour or specific
-backends to use, and is usually specified as 0 (or EVFLAG_AUTO)
+backends to use, and is usually specified as 0 (or EVFLAG_AUTO).
It supports the following flags:
=over 4
-=item EVFLAG_AUTO
+=item C<EVFLAG_AUTO>
-The default flags value. Use this if you have no clue (its the right
+The default flags value. Use this if you have no clue (it's the right
thing, believe me).
-=item EVFLAG_NOENV
+=item C<EVFLAG_NOENV>
-If this flag bit is ored into the flag value then libev will I<not> look
-at the environment variable C<LIBEV_FLAGS>. Otherwise (the default), this
-environment variable will override the flags completely. This is useful
-to try out specific backends to tets their performance, or to work around
-bugs.
+If this flag bit is ored into the flag value (or the program runs setuid
+or setgid) then libev will I<not> look at the environment variable
+C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will
+override the flags completely if it is found in the environment. This is
+useful to try out specific backends to test their performance, or to work
+around bugs.
-=item EVMETHOD_SELECT portable select backend
+=item C<EVMETHOD_SELECT> (portable select backend)
-=item EVMETHOD_POLL poll backend (everywhere except windows)
+=item C<EVMETHOD_POLL> (poll backend, available everywhere except on windows)
-=item EVMETHOD_EPOLL linux only
+=item C<EVMETHOD_EPOLL> (linux only)
-=item EVMETHOD_KQUEUE some bsds only
+=item C<EVMETHOD_KQUEUE> (some bsds only)
-=item EVMETHOD_DEVPOLL solaris 8 only
+=item C<EVMETHOD_DEVPOLL> (solaris 8 only)
-=item EVMETHOD_PORT solaris 10 only
+=item C<EVMETHOD_PORT> (solaris 10 only)
If one or more of these are ored into the flags value, then only these
backends will be tried (in the reverse order as given here). If one are
Destroys the default loop again (frees all memory and kernel state
etc.). This stops all registered event watchers (by not touching them in
-any way whatsoever, although you cnanot rely on this :).
+any way whatsoever, although you cannot rely on this :).
=item ev_loop_destroy (loop)
use the event library in both processes. If you just fork+exec, you don't
have to call it.
-The function itself is quite fast and its usually not a problem to call
+The function itself is quite fast and it's usually not a problem to call
it just in case after a fork. To make this easy, the function will fit in
quite nicely into a call to C<pthread_atfork>:
Returns one of the C<EVMETHOD_*> flags indicating the event backend in
use.
-=item ev_tstamp = ev_now (loop)
+=item ev_tstamp ev_now (loop)
Returns the current "event loop time", which is the time the event loop
got events and started processing them. This timestamp does not change
A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle
those events and any outstanding ones, but will not block your process in
-case there are no events.
+case there are no events and will return after one iteration of the loop.
A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if
neccessary) and will handle those and any outstanding ones. It will block
-your process until at least one new event arrives.
+your process until at least one new event arrives, and will return after
+one iteration of the loop.
This flags value could be used to implement alternative looping
constructs, but the C<prepare> and C<check> watchers provide a better and
=item ev_unloop (loop, how)
-Can be used to make a call to C<ev_loop> return early. The C<how> argument
-must be either C<EVUNLOOP_ONCE>, which will make the innermost C<ev_loop>
-call return, or C<EVUNLOOP_ALL>, which will make all nested C<ev_loop>
-calls return.
+Can be used to make a call to C<ev_loop> return early (but only after it
+has processed all outstanding events). The C<how> argument must be either
+C<EVUNLOOP_ONCE>, which will make the innermost C<ev_loop> call return, or
+C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.
=item ev_ref (loop)
=item ev_unref (loop)
-Ref/unref can be used to add or remove a refcount on the event loop: Every
-watcher keeps one reference. If you have a long-runing watcher you never
-unregister that should not keep ev_loop from running, ev_unref() after
-starting, and ev_ref() before stopping it. Libev itself uses this for
-example for its internal signal pipe: It is not visible to you as a user
-and should not keep C<ev_loop> from exiting if the work is done. It is
-also an excellent way to do this for generic recurring timers or from
-within third-party libraries. Just remember to unref after start and ref
-before stop.
+Ref/unref can be used to add or remove a reference count on the event
+loop: Every watcher keeps one reference, and as long as the reference
+count is nonzero, C<ev_loop> will not return on its own. If you have
+a watcher you never unregister that should not keep C<ev_loop> from
+returning, ev_unref() after starting, and ev_ref() before stopping it. For
+example, libev itself uses this for its internal signal pipe: It is not
+visible to the libev user and should not keep C<ev_loop> from exiting if
+no event watchers registered by it are active. It is also an excellent
+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>.
=back
A watcher is a structure that you create and register to record your
interest in some event. For instance, if you want to wait for STDIN to
-become readable, you would create an ev_io watcher for that:
+become readable, you would create an C<ev_io> watcher for that:
static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents)
{
must not touch the values stored in it. Most specifically you must never
reinitialise it or call its set method.
-You cna check wether an event is active by calling the C<ev_is_active
-(watcher *)> macro. To see wether an event is outstanding (but the
+You cna check whether an event is active by calling the C<ev_is_active
+(watcher *)> macro. To see whether an event is outstanding (but the
callback for it has not been called yet) you cna use the C<ev_is_pending
(watcher *)> macro.
=over 4
-=item EV_READ
+=item C<EV_READ>
-=item EV_WRITE
+=item C<EV_WRITE>
-The file descriptor in the ev_io watcher has become readable and/or
+The file descriptor in the C<ev_io> watcher has become readable and/or
writable.
-=item EV_TIMEOUT
+=item C<EV_TIMEOUT>
-The ev_timer watcher has timed out.
+The C<ev_timer> watcher has timed out.
-=item EV_PERIODIC
+=item C<EV_PERIODIC>
-The ev_periodic watcher has timed out.
+The C<ev_periodic> watcher has timed out.
-=item EV_SIGNAL
+=item C<EV_SIGNAL>
-The signal specified in the ev_signal watcher has been received by a thread.
+The signal specified in the C<ev_signal> watcher has been received by a thread.
-=item EV_CHILD
+=item C<EV_CHILD>
-The pid specified in the ev_child watcher has received a status change.
+The pid specified in the C<ev_child> watcher has received a status change.
-=item EV_IDLE
+=item C<EV_IDLE>
-The ev_idle watcher has determined that you have nothing better to do.
+The C<ev_idle> watcher has determined that you have nothing better to do.
-=item EV_PREPARE
+=item C<EV_PREPARE>
-=item EV_CHECK
+=item C<EV_CHECK>
-All ev_prepare watchers are invoked just I<before> C<ev_loop> starts
-to gather new events, and all ev_check watchers are invoked just after
+All C<ev_prepare> watchers are invoked just I<before> C<ev_loop> starts
+to gather new events, and all C<ev_check> watchers are invoked just after
C<ev_loop> has gathered them, but before it invokes any callbacks for any
received events. Callbacks of both watcher types can start and stop as
many watchers as they want, and all of them will be taken into account
-(for example, a ev_prepare watcher might start an idle watcher to keep
+(for example, a C<ev_prepare> watcher might start an idle watcher to keep
C<ev_loop> from blocking).
-=item EV_ERROR
+=item C<EV_ERROR>
An unspecified error has occured, the watcher has been stopped. This might
happen because the watcher could not be properly started because libev
This section describes each watcher in detail, but will not repeat
information given in the last section.
-=head2 struct ev_io - is my file descriptor readable or writable
+=head2 C<ev_io> - is this file descriptor readable or writable
-I/O watchers check wether a file descriptor is 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 cna 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 oer
+fd as you want (as long as you don't confuse yourself). Setting all file
+descriptors to non-blocking mode is also usually a good idea (but not
+required if you know what you are doing).
+
+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 file/socket etc. description.
+
+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 EVMETHOD_SELECT and
+EVMETHOD_POLL).
+
=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 ev_io watcher. The fd is the file descriptor to rceeive
+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.
=back
-=head2 struct ev_timer - relative and optionally recurring timeouts
+=head2 C<ev_timer> - relative and optionally recurring timeouts
Timer watchers are simple relative timers that generate an event after a
given time, and optionally repeating in regular intervals after that.
detecting time jumps is hard, and soem inaccuracies are unavoidable (the
monotonic clock option helps a lot here).
+The relative timeouts are calculated relative to the C<ev_now ()>
+time. This is usually the right thing as this timestamp refers to the time
+of the event triggering whatever timeout you are modifying/starting. If
+you suspect event processing to be delayed and you *need* to base the timeout
+ion the current time, use something like this to adjust for this:
+
+ ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);
+
=over 4
=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
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 ev_timer with after=repeat=60 and calling ev_timer_again each
+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.
=back
-=head2 ev_periodic
+=head2 C<ev_periodic> - to cron or not to cron it
Periodic watchers are also timers of a kind, but they are very versatile
(and unfortunately a bit complex).
-Unlike ev_timer's, they are not based on real time (or relative time)
+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 ()
+ 10.>) and then reset your system clock to the last year, then it will
-take a year to trigger the event (unlike an ev_timer, which would trigger
+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).
by 3600.
Another way to think about it (for the mathematically inclined) is that
-ev_periodic will try to run the callback in this mode at the next possible
+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)
=back
-=head2 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
-will try its best to deliver signals synchronously, i.e. as part of the
+will try it's best to deliver signals synchronously, i.e. as part of the
normal event processing, like any other event.
You cna configure as many watchers as you like per signal. Only when the
=back
-=head2 ev_child - wait for pid status changes
+=head2 C<ev_child> - wait for pid 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).
=back
-=head2 ev_idle - when you've got nothing better to do
+=head2 C<ev_idle> - when you've got nothing better to do
Idle watchers trigger events when there are no other I/O or timer (or
periodic) events pending. That is, as long as your process is busy
watchers, integrate net-snmp or a coroutine library and lots more.
This is done by examining in each prepare call which file descriptors need
-to be watched by the other library, registering ev_io watchers for them
-and starting an ev_timer watcher for any timeouts (many libraries provide
+to be watched by the other library, registering C<ev_io> watchers for them
+and starting an C<ev_timer> watcher for any timeouts (many libraries provide
just this functionality). Then, in the check watcher you check for any
events that occured (by making your callbacks set soem flags for example)
and call back into the library.
more watchers yourself.
If C<fd> is less than 0, then no I/O watcher will be started and events is
-ignored. Otherwise, an ev_io watcher for the given C<fd> and C<events> set
+ignored. Otherwise, an C<ev_io> watcher for the given C<fd> and C<events> set
will be craeted and started.
If C<timeout> is less than 0, then no timeout watcher will be
-started. Otherwise an ev_timer watcher with after = C<timeout> (and repeat
+started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and repeat
= 0) will be started.
The callback has the type C<void (*cb)(int revents, void *arg)> and
-gets passed an events set (normally a combination of EV_ERROR, EV_READ,
-
EV_WRITE or EV_TIMEOUT) and the C<arg> value passed to C<ev_once>:
+gets passed an events set (normally a combination of C<EV_ERROR>, C<EV_READ>,
+
C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg> value passed to C<ev_once>:
static void stdin_ready (int revents, void *arg)
{
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