argument of name C<loop> (which is always of type C<struct ev_loop *>)
will not have this argument.
-=head1 TIME AND OTHER GLOBAL FUNCTIONS
+=head1 TIME REPRESENTATION
Libev represents time as a single floating point number, representing the
(fractional) number of seconds since the (POSIX) epoch (somewhere near
called C<ev_tstamp>, which is what you should use too. It usually aliases
to the double type in C.
+=head1 GLOBAL FUNCTIONS
+
+These functions can be called anytime, even before initialising the
+library in any way.
+
=over 4
=item ev_tstamp ev_time ()
-Returns the current time as libev would use it.
+Returns the current time as libev would use it. Please note that the
+C<ev_now> function is usually faster and also often returns the timestamp
+you actually want to know.
=item int ev_version_major ()
compatible to older versions, so a larger minor version alone is usually
not a problem.
+=item unsigned int ev_supported_backends ()
+
+Return the set of all backends (i.e. their corresponding C<EV_BACKEND_*>
+value) compiled into this binary of libev (independent of their
+availability on the system you are running on). See C<ev_default_loop> for
+a description of the set values.
+
+=item unsigned int ev_recommended_backends ()
+
+Return the set of all backends compiled into this binary of libev and also
+recommended for this platform. This set is often smaller than the one
+returned by C<ev_supported_backends>, as for example kqueue is broken on
+most BSDs and will not be autodetected unless you explicitly request it
+(assuming you know what you are doing). This is the set of backends that
+C<EVFLAG_AUTO> will probe for.
+
=item ev_set_allocator (void *(*cb)(void *ptr, long size))
Sets the allocation function to use (the prototype is similar to the
events, and dynamically created loops which do not.
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
+in your main thread (or in a separate thread) and for each thread you
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
This will initialise the default event loop if it hasn't been initialised
yet and return it. If the default loop could not be initialised, returns
false. If it already was initialised it simply returns it (and ignores the
-flags).
+flags. If that is troubling you, check C<ev_backend ()> afterwards).
If you don't know what event loop to use, use the one returned from this
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 C<0> (or EVFLAG_AUTO).
It supports the following flags:
useful to try out specific backends to test their performance, or to work
around bugs.
-=item C<EVMETHOD_SELECT> (portable select backend)
+=item C<EVBACKEND_SELECT> (value 1, portable select backend)
-=item C<EVMETHOD_POLL> (poll backend, available everywhere except on windows)
+This is your standard select(2) backend. Not I<completely> standard, as
+libev tries to roll its own fd_set with no limits on the number of fds,
+but if that fails, expect a fairly low limit on the number of fds when
+using this backend. It doesn't scale too well (O(highest_fd)), but its usually
+the fastest backend for a low number of fds.
-=item C<EVMETHOD_EPOLL> (linux only)
+=item C<EVBACKEND_POLL> (value 2, poll backend, available everywhere except on windows)
-=item C<EVMETHOD_KQUEUE> (some bsds only)
+And this is your standard poll(2) backend. It's more complicated than
+select, but handles sparse fds better and has no artificial limit on the
+number of fds you can use (except it will slow down considerably with a
+lot of inactive fds). It scales similarly to select, i.e. O(total_fds).
-=item C<EVMETHOD_DEVPOLL> (solaris 8 only)
+=item C<EVBACKEND_EPOLL> (value 4, Linux)
-=item C<EVMETHOD_PORT> (solaris 10 only)
+For few fds, this backend is a bit little slower than poll and select,
+but it scales phenomenally better. While poll and select usually scale like
+O(total_fds) where n is the total number of fds (or the highest fd), epoll scales
+either O(1) or O(active_fds).
-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
-specified, any backend will do.
+While stopping and starting an I/O watcher in the same iteration will
+result in some caching, there is still a syscall per such incident
+(because the fd could point to a different file description now), so its
+best to avoid that. Also, dup()ed file descriptors might not work very
+well if you register events for both fds.
+
+=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)
+
+Kqueue deserves special mention, as at the time of this writing, it
+was broken on all BSDs except NetBSD (usually it doesn't work with
+anything but sockets and pipes, except on Darwin, where of course its
+completely useless). For this reason its not being "autodetected" unless
+you explicitly specify the flags (i.e. you don't use EVFLAG_AUTO).
+
+It scales in the same way as the epoll backend, but the interface to the
+kernel is more efficient (which says nothing about its actual speed, of
+course). While starting and stopping an I/O watcher does not cause an
+extra syscall as with epoll, it still adds up to four event changes per
+incident, so its best to avoid that.
+
+=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)
+
+This is not implemented yet (and might never be).
+
+=item C<EVBACKEND_PORT> (value 32, Solaris 10)
+
+This uses the Solaris 10 port mechanism. As with everything on Solaris,
+it's really slow, but it still scales very well (O(active_fds)).
+
+=item C<EVBACKEND_ALL>
+
+Try all backends (even potentially broken ones that wouldn't be tried
+with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as
+C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.
=back
+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 none are
+specified, most compiled-in backend will be tried, usually in reverse
+order of their flag values :)
+
=item struct ev_loop *ev_loop_new (unsigned int flags)
Similar to C<ev_default_loop>, but always creates a new event loop that is
after forking, in either the parent or child process (or both, but that
again makes little sense).
-You I<must> call this function after forking if and only if you want to
-use the event library in both processes. If you just fork+exec, you don't
-have to call it.
+You I<must> call this function in the child process after forking if and
+only if you want to 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 it's usually not a problem to call
it just in case after a fork. To make this easy, the function will fit in
pthread_atfork (0, 0, ev_default_fork);
+At the moment, C<EVBACKEND_SELECT> and C<EVBACKEND_POLL> are safe to use
+without calling this function, so if you force one of those backends you
+do not need to care.
+
=item ev_loop_fork (loop)
Like C<ev_default_fork>, but acts on an event loop created by
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_method (loop)
+=item unsigned int ev_backend (loop)
-Returns one of the C<EVMETHOD_*> flags indicating the event backend in
+Returns one of the C<EVBACKEND_*> flags indicating the event backend in
use.
=item ev_tstamp ev_now (loop)
constructs, but the C<prepare> and C<check> watchers provide a better and
more generic mechanism.
+Here are the gory details of what ev_loop does:
+
+ 1. If there are no active watchers (reference count is zero), return.
+ 2. Queue and immediately call all prepare watchers.
+ 3. If we have been forked, recreate the kernel state.
+ 4. Update the kernel state with all outstanding changes.
+ 5. Update the "event loop time".
+ 6. Calculate for how long to block.
+ 7. Block the process, waiting for events.
+ 8. Update the "event loop time" and do time jump handling.
+ 9. Queue all outstanding timers.
+ 10. Queue all outstanding periodics.
+ 11. If no events are pending now, queue all idle watchers.
+ 12. Queue all check watchers.
+ 13. Call all queued watchers in reverse order (i.e. check watchers first).
+ 14. If ev_unloop has been called or EVLOOP_ONESHOT or EVLOOP_NONBLOCK
+ was used, return, otherwise continue with step #1.
+
=item ev_unloop (loop, how)
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_ONE>, 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)
As long as your watcher is active (has been started but not stopped) you
must not touch the values stored in it. Most specifically you must never
-reinitialise it or call its set method.
+reinitialise it or call its set macro.
-You cna check whether an event is active by calling the C<ev_is_active
+You can 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
+callback for it has not been called yet) you can use the C<ev_is_pending
(watcher *)> macro.
Each and every callback receives the event loop pointer as first, the
registered watcher structure as second, and a bitset of received events as
third argument.
-The rceeived events usually include a single bit per event type received
+The received events usually include a single bit per event type received
(you can receive multiple events at the same time). The possible bit masks
are:
=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
Each watcher has, by default, a member C<void *data> that you can change
-and read at any time, libev will completely ignore it. This cna be used
+and read at any time, libev will completely ignore it. This can be used
to associate arbitrary data with your watcher. If you need more data and
don't want to allocate memory and store a pointer to it in that data
member, you can also "subclass" the watcher type and provide your own
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
+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 oer
+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
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.
+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 EVMETHOD_SELECT and
-EVMETHOD_POLL).
+(at the time of this writing, this includes only C<EVBACKEND_SELECT> and
+C<EVBACKEND_POLL>).
=over 4
given time, and optionally repeating in regular intervals after that.
The timers are based on real time, that is, if you register an event that
-times out after an hour and youreset your system clock to last years
+times out after an hour and you reset your system clock to last years
time, it will still time out after (roughly) and hour. "Roughly" because
-detecting time jumps is hard, and soem inaccuracies are unavoidable (the
+detecting time jumps is hard, and some 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:
+of the event triggering whatever timeout you are modifying/starting. If
+you suspect event processing to be delayed and you I<need> to base the timeout
+on the current time, use something like this to adjust for this:
ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);
+The callback is guarenteed to be invoked only when its timeout has passed,
+but if multiple timers become ready during the same loop iteration then
+order of execution is undefined.
+
=over 4
=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
The timer itself will do a best-effort at avoiding drift, that is, if you
configure a timer to trigger every 10 seconds, then it will trigger at
exactly 10 second intervals. If, however, your program cannot keep up with
-the timer (ecause it takes longer than those 10 seconds to do stuff) the
+the timer (because it takes longer than those 10 seconds to do stuff) the
timer will not fire more than once per event loop iteration.
=item ev_timer_again (loop)
=back
-=head2 C<ev_periodic> - to cron or not to cron it
+=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).
They can also be used to implement vastly more complex timers, such as
triggering an event on eahc midnight, local time.
+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.
+
=over 4
=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)
Lots of arguments, lets sort it out... There are basically three modes of
operation, and we will explain them from simplest to complex:
-
=over 4
=item * absolute timer (interval = reschedule_cb = 0)
reschedule callback will be called with the watcher as first, and the
current time as second argument.
-NOTE: I<This callback MUST NOT stop or destroy the periodic or any other
-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.
-
-Also, I<< this callback must always return a time that is later than the
-passed C<now> value >>. Not even C<now> itself will be ok.
+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).
Its prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic *w,
ev_tstamp now)>, e.g.:
will usually be called just before the callback will be triggered, but
might be called at other times, too.
+NOTE: I<< This callback must always return a time that is later than the
+passed C<now> value >>. Not even C<now> itself will do, it I<must> be larger.
+
This can be used to create very complex timers, such as a timer that
triggers on each midnight, local time. To do this, you would calculate the
-next midnight after C<now> and return the timestamp value for this. How you do this
-is, again, up to you (but it is not trivial).
+next midnight after C<now> and return the timestamp value for this. How
+you do this is, again, up to you (but it is not trivial, which is the main
+reason I omitted it as an example).
=back
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
+You can configure as many watchers as you like per signal. Only when the
first watcher gets started will libev actually register a signal watcher
with the kernel (thus it coexists with your own signal handlers as long
as you don't register any with libev). Similarly, when the last signal
Configures the watcher to wait for status changes of process C<pid> (or
I<any> process if C<pid> is specified as C<0>). The callback can look
at the C<rstatus> member of the C<ev_child> watcher structure to see
-the status word (use the macros from C<sys/wait.h>). The C<rpid> member
-contains the pid of the process causing the status change.
+the status word (use the macros from C<sys/wait.h> and see your systems
+C<waitpid> documentation). The C<rpid> member contains the pid of the
+process causing the status change.
=back
=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
-handling sockets or timeouts it will not be called. But when your process
-is idle all idle watchers are being called again and again - until
-stopped, that is, or your process receives more events.
+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 most noteworthy effect is that as long as any idle watchers are
active, the process will not block when waiting for new events.
=back
-=head2 prepare and check - your hooks into the event loop
+=head2 C<ev_prepare> and C<ev_check> - customise your event loop
-Prepare and check watchers usually (but not always) are used in
-tandom. Prepare watchers get invoked before the process blocks and check
-watchers afterwards.
+Prepare and check watchers are usually (but not always) used in tandem:
+prepare watchers get invoked before the process blocks and check watchers
+afterwards.
Their main purpose is to integrate other event mechanisms into libev. This
could be used, for example, to track variable changes, implement your own
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 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.
-
-As another example, the perl Coro module uses these hooks to integrate
+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 checking the pending status of all watchers
+and stopping them) and call back into the library. The I/O and timer
+callbacks will never actually be called (but must be valid nevertheless,
+because you never know, you know?).
+
+As another example, the Perl Coro module uses these hooks to integrate
coroutines into libev programs, by yielding to other active coroutines
during each prepare and only letting the process block if no coroutines
-are ready to run.
+are ready to run (it's actually more complicated: it only runs coroutines
+with priority higher than or equal to the event loop and one coroutine
+of lower priority, but only once, using idle watchers to keep the event
+loop from blocking if lower-priority coroutines are active, thus mapping
+low-priority coroutines to idle/background tasks).
=over 4
Initialises and configures the prepare or check watcher - they have no
parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>
-macros, but using them is utterly, utterly pointless.
+macros, but using them is utterly, utterly and completely pointless.
=back
=head1 OTHER FUNCTIONS
-There are some other fucntions of possible interest. Described. Here. Now.
+There are some other functions of possible interest. Described. Here. Now.
=over 4
This function combines a simple timer and an I/O watcher, calls your
callback on whichever event happens first and automatically stop both
watchers. This is useful if you want to wait for a single event on an fd
-or timeout without havign to allocate/configure/start/stop/free one or
+or timeout without having to allocate/configure/start/stop/free one or
more watchers yourself.
-If C<fd> is less than 0, then no I/O watcher will be started and events is
-ignored. Otherwise, an C<ev_io> watcher for the given C<fd> and C<events> set
-will be craeted and started.
+If C<fd> is less than 0, then no I/O watcher will be started and events
+is being 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 C<ev_timer> watcher with after = C<timeout> (and repeat
-= 0) will be started.
+started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and
+repeat = 0) will be started. While C<0> is a valid timeout, it is of
+dubious value.
-The callback has the type C<void (*cb)(int revents, void *arg)> and
-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>:
+The callback has the type C<void (*cb)(int revents, void *arg)> and gets
+passed an C<revents> set like normal event callbacks (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)
{
if (revents & EV_TIMEOUT)
- /* doh, nothing entered */
+ /* doh, nothing entered */;
else if (revents & EV_READ)
- /* stdin might have data for us, joy! */
+ /* stdin might have data for us, joy! */;
}
- ev_once (STDIN_FILENO, EV_READm 10., stdin_ready, 0);
+ ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
=item ev_feed_event (loop, watcher, int events)
Feeds the given event set into the event loop, as if the specified event
-has happened for the specified watcher (which must be a pointer to an
-initialised but not necessarily active event watcher).
+had happened for the specified watcher (which must be a pointer to an
+initialised but not necessarily started event watcher).
=item ev_feed_fd_event (loop, int fd, int revents)
-Feed an event on the given fd, as if a file descriptor backend detected it.
+Feed an event on the given fd, as if a file descriptor backend detected
+the given events it.
=item ev_feed_signal_event (loop, int signum)
=back
+=head1 LIBEVENT EMULATION
+
+Libev offers a compatibility emulation layer for libevent. It cannot
+emulate the internals of libevent, so here are some usage hints:
+
+=over 4
+
+=item * Use it by including <event.h>, as usual.
+
+=item * The following members are fully supported: ev_base, ev_callback,
+ev_arg, ev_fd, ev_res, ev_events.
+
+=item * Avoid using ev_flags and the EVLIST_*-macros, while it is
+maintained by libev, it does not work exactly the same way as in libevent (consider
+it a private API).
+
+=item * Priorities are not currently supported. Initialising priorities
+will fail and all watchers will have the same priority, even though there
+is an ev_pri field.
+
+=item * Other members are not supported.
+
+=item * The libev emulation is I<not> ABI compatible to libevent, you need
+to use the libev header file and library.
+
+=back
+
+=head1 C++ SUPPORT
+
+TBD.
+
=head1 AUTHOR
Marc Lehmann <libev@schmorp.de>.
projects / software / libev.git / blobdiff