ev_io - is this file descriptor readable or writableev_timer - relative and optionally recurring timeoutsev_periodic - to cron or not to cronev_signal - signal me when a signal gets signalledev_child - wait for pid status changesev_idle - when you've got nothing better to doev_prepare and ev_check - customise your event loopev_embed - when one backend isn't enoughLibev 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 event loop handler, and will then communicate events via a callback mechanism.
@@ -73,31 +78,46 @@ watcher. 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 benchmark comparing +it to libevent for example).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
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 loop (which is always of type struct ev_loop *)
will not have this argument.
Libev represents time as a single floating point number, representing the
(fractional) number of seconds since the (POSIX) epoch (somewhere near
the beginning of 1970, details are complicated, don't ask). This type is
called ev_tstamp, which is what you should use too. It usually aliases
-to the double type in C.
double type in C, and when you need to do any calculations on
+it, you should treat it as such.
+
+
+
+
+
+These functions can be called anytime, even before initialising the +library in any way.
Returns the current time as libev would use it.
+Returns the current time as libev would use it. Please note that the
+ev_now function is usually faster and also often returns the timestamp
+you actually want to know.
ev_version_major and
ev_version_minor. If you want, you can compare against the global
symbols EV_VERSION_MAJOR and 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.
+Example: make sure we haven't accidentally been linked against the wrong +version:
+ assert (("libev version mismatch",
+ ev_version_major () == EV_VERSION_MAJOR
+ && ev_version_minor () >= EV_VERSION_MINOR));
+
+
+
+ Return the set of all backends (i.e. their corresponding EV_BACKEND_*
+value) compiled into this binary of libev (independent of their
+availability on the system you are running on). See ev_default_loop for
+a description of the set values.
Example: make sure we have the epoll method, because yeah this is cool and +a must have and can we have a torrent of it please!!!11
+ assert (("sorry, no epoll, no sex",
+ ev_supported_backends () & EVBACKEND_EPOLL));
+
+
+ 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 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
+libev will probe for if you specify no backends explicitly.
Returns the set of backends that are embeddable in other event loops. This
+is the theoretical, all-platform, value. To find which backends
+might be supported on the current system, you would need to look at
+ev_embeddable_backends () & ev_supported_backends (), likewise for
+recommended ones.
See the description of ev_embed watchers for more info.
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, 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).
+ static void *
+ persistent_realloc (void *ptr, long size)
+ {
+ for (;;)
+ {
+ void *newptr = realloc (ptr, size);
+
+ if (newptr)
+ return newptr;
+
+ sleep (60);
+ }
+ }
+
+ ...
+ ev_set_allocator (persistent_realloc);
+
+
Example: do the same thing as libev does internally:
+ static void
+ fatal_error (const char *msg)
+ {
+ perror (msg);
+ abort ();
+ }
+
+ ...
+ ev_set_syserr_cb (fatal_error);
+
+
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).
+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 +done correctly, because it's hideous and inefficient).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, checkev_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)
-It supports the following flags:
+backends to use, and is usually specified as0 (or EVFLAG_AUTO).
+ The following flags are supported:
EVFLAG_AUTOThe 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).
EVFLAG_NOENVIf this flag bit is ored into the flag value (or the program runs setuid
+or setgid) then libev will not look at the environment variable
+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.
EVBACKEND_SELECT (value 1, portable select backend)This is your standard select(2) backend. Not 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.
+EVBACKEND_POLL (value 2, poll backend, available everywhere except on windows)If this flag bit is ored into the flag value then libev will not look
-at the environment variable 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.
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).
EVBACKEND_EPOLL (value 4, Linux)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.
+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).
+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.
+Please note that epoll sometimes generates spurious notifications, so you +need to use non-blocking I/O or other means to avoid blocking when no data +(or space) is available.
+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 it explicitly in the flags (i.e. using
+EVBACKEND_KQUEUE).
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.
+EVBACKEND_DEVPOLL (value 16, Solaris 8)This is not implemented yet (and might never be).
+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)).
+Please note that solaris ports can result in a lot of spurious +notifications, so you need to use non-blocking I/O or other means to avoid +blocking when no data (or space) is available.
+EVBACKEND_ALLTry all backends (even potentially broken ones that wouldn't be tried
+with EVFLAG_AUTO). Since this is a mask, you can do stuff such as
+EVBACKEND_ALL & ~EVBACKEND_KQUEUE.
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 :)
+The most typical usage is like this:
+ if (!ev_default_loop (0))
+ fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
+
+
+ Restrict libev to the select and poll backends, and do not allow +environment settings to be taken into account:
+ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV); + ++
Use whatever libev has to offer, but make sure that kqueue is used if +available (warning, breaks stuff, best use only with your own private +event loop and only if you know the OS supports your types of fds):
+ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE); + +
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)
+ fatal ("no epoll found here, maybe it hides under your chair");
+
+
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 :).ev_loop_new.
one. Despite the name, you can call it anytime, but it makes most sense
after forking, in either the parent or child process (or both, but that
again makes little sense).
- You 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.
-The function itself is quite fast and its usually not a problem to call +
You 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
quite nicely into a call to pthread_atfork:
pthread_atfork (0, 0, ev_default_fork);+
At the moment, EVBACKEND_SELECT and EVBACKEND_POLL are safe to use
+without calling this function, so if you force one of those backends you
+do not need to care.
pthread_atfork:
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.
Returns one of the EVMETHOD_* flags indicating the event backend in
+
Returns one of the EVBACKEND_* flags indicating the event backend in
use.
Returns the current "event loop time", which is the time the event loop -got events and started processing them. This timestamp does not change -as long as callbacks are being processed, and this is also the base time -used for relative timers. You can treat it as the timestamp of the event -occuring (or more correctly, the mainloop finding out about it).
+received events and started processing them. This timestamp does not +change as long as callbacks are being processed, and this is also the base +time used for relative timers. You can treat it as the timestamp of the +event occuring (or more correctly, libev finding out about it).Finally, this is it, the event handler. This function usually is called after you initialised all your watchers and you want to start handling events.
-If the flags argument is specified as 0, it will not return until either
-no event watchers are active anymore or ev_unloop was called.
If the flags argument is specified as 0, it will not return until
+either no event watchers are active anymore or ev_unloop was called.
Please note that an explicit ev_unloop is usually better than
+relying on all watchers to be stopped when deciding when a program has
+finished (especially in interactive programs), but having a program that
+automatically loops as long as it has to and no longer by virtue of
+relying on its watchers stopping correctly is a thing of beauty.
A flags value of 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.
A flags value of 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.
This flags value could be used to implement alternative looping
-constructs, but the prepare and check watchers provide a better and
-more generic mechanism.
ev_prepare/ev_check watchers is
+usually a better approach for this kind of thing.
+ Here are the gory details of what ev_loop does:
* If there are no active watchers (reference count is zero), return. + - Queue 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". + - Calculate for how long to block. + - Block the process, waiting for any events. + - Queue all outstanding I/O (fd) events. + - Update the "event loop time" and do time jump handling. + - Queue all outstanding timers. + - Queue all outstanding periodics. + - If no events are pending now, queue all idle watchers. + - Queue all check watchers. + - Call all queued watchers in reverse order (i.e. check watchers first). + Signals and child watchers are implemented as I/O watchers, and will + be handled here by queueing them when their watcher gets executed. + - 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 +anymore.
+... queue jobs here, make sure they register event watchers as long + ... as they still have work to do (even an idle watcher will do..) + ev_loop (my_loop, 0); + ... jobs done. yeah! + +
Can be used to make a call to ev_loop return early. The how argument
-must be either EVUNLOOP_ONCE, which will make the innermost ev_loop
-call return, or EVUNLOOP_ALL, which will make all nested ev_loop
-calls return.
Can be used to make a call to ev_loop return early (but only after it
+has processed all outstanding events). The how argument must be either
+EVUNLOOP_ONE, which will make the innermost ev_loop call return, or
+EVUNLOOP_ALL, which will make all nested ev_loop calls return.
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 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, ev_loop will not return on its own. If you have
+a watcher you never unregister that should not keep 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 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 unref after start and ref before stop.
Example: create a signal watcher, but keep it from keeping ev_loop
+running when nothing else is active.
struct dv_signal exitsig; + ev_signal_init (&exitsig, sig_cb, SIGINT); + ev_signal_start (myloop, &exitsig); + evf_unref (myloop); + ++
Example: for some weird reason, unregister the above signal handler again.
+ev_ref (myloop); + ev_signal_stop (myloop, &exitsig); + +
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 anev_io watcher for that:
static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents)
{
ev_io_stop (w);
@@ -317,56 +538,52 @@ with a watcher-specific start function (ev_<type>_start (loop, watch
corresponding stop function (ev_<type>_stop (loop, watcher *).
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.
-You cna check wether an event is active by calling the ev_is_active
-(watcher *) macro. To see wether an event is outstanding (but the
-callback for it has not been called yet) you cna use the ev_is_pending
-(watcher *) macro.
+reinitialise it or call its set 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:
- - EV_READ
- - EV_WRITE
+ EV_READEV_WRITE-
-
The file descriptor in the ev_io watcher has become readable and/or
+
The file descriptor in the ev_io watcher has become readable and/or
writable.
- - EV_TIMEOUT
+ EV_TIMEOUT-
-
The ev_timer watcher has timed out.
+ The ev_timer watcher has timed out.
- - EV_PERIODIC
+ EV_PERIODIC-
-
The ev_periodic watcher has timed out.
+ The ev_periodic watcher has timed out.
- - EV_SIGNAL
+ EV_SIGNAL-
-
The signal specified in the ev_signal watcher has been received by a thread.
+ The signal specified in the ev_signal watcher has been received by a thread.
- - EV_CHILD
+ EV_CHILD-
-
The pid specified in the ev_child watcher has received a status change.
+ The pid specified in the ev_child watcher has received a status change.
- - EV_IDLE
+ EV_IDLE-
-
The ev_idle watcher has determined that you have nothing better to do.
+ The ev_idle watcher has determined that you have nothing better to do.
- - EV_PREPARE
- - EV_CHECK
+ EV_PREPAREEV_CHECK-
-
All ev_prepare watchers are invoked just before ev_loop starts
-to gather new events, and all ev_check watchers are invoked just after
+
All ev_prepare watchers are invoked just before ev_loop starts
+to gather new events, and all ev_check watchers are invoked just after
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 ev_prepare watcher might start an idle watcher to keep
ev_loop from blocking).
- - EV_ERROR
+ 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
@@ -381,11 +598,89 @@ programs, though, so beware.
+In the following description, TYPE stands for the watcher type,
+e.g. timer for ev_timer watchers and io for ev_io watchers.
ev_init (ev_TYPE *watcher, callback)This macro initialises the generic portion of a watcher. The contents
+of the watcher object can be arbitrary (so malloc will do). Only
+the generic parts of the watcher are initialised, you need to call
+the type-specific ev_TYPE_set macro afterwards to initialise the
+type-specific parts. For each type there is also a ev_TYPE_init macro
+which rolls both calls into one.
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 void (*)(ev_loop *loop, ev_TYPE *watcher,
+int revents).
ev_TYPE_set (ev_TYPE *, [args])This macro initialises the type-specific parts of a watcher. You need to
+call ev_init at least once before you call this macro, but you can
+call ev_TYPE_set any number of times. You must not, however, call this
+macro on a watcher that is active (it can be pending, however, which is a
+difference to the ev_init macro).
Although some watcher types do not have type-specific arguments
+(e.g. ev_prepare) you still need to call its set macro.
ev_TYPE_init (ev_TYPE *watcher, callback, [args])This convinience macro rolls both ev_init and ev_TYPE_set macro
+calls into a single call. This is the most convinient method to initialise
+a watcher. The same limitations apply, of course.
ev_TYPE_start (loop *, ev_TYPE *watcher)Starts (activates) the given watcher. Only active watchers will receive +events. If the watcher is already active nothing will happen.
+ev_TYPE_stop (loop *, ev_TYPE *watcher)Stops the given watcher again (if active) and clears the pending
+status. It is possible that stopped watchers are pending (for example,
+non-repeating timers are being stopped when they become pending), but
+ev_TYPE_stop ensures that the watcher is neither active nor pending. If
+you want to free or reuse the memory used by the watcher it is therefore a
+good idea to always call its ev_TYPE_stop function.
Returns a true value iff the watcher is active (i.e. it has been started +and not yet been stopped). As long as a watcher is active you must not modify +it.
+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
+ev_TYPE_set is safe) and you must make sure the watcher is available to
+libev (e.g. you cnanot free () it).
Returns the callback currently set on the watcher.
+Change the callback. You can change the callback at virtually any time +(modulo threads).
+Each watcher has, by default, a member 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
@@ -421,34 +716,92 @@ have been omitted....
This section describes each watcher in detail, but will not repeat information given in the last section.
+ + + +I/O watchers check wether a file descriptor is readable or writable +
ev_io - is this file descriptor readable or writableI/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 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 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 EVBACKEND_SELECT and
+EVBACKEND_POLL).
Configures an ev_io watcher. The fd is the file descriptor to rceeive +
Configures an ev_io watcher. The fd is the file descriptor to rceeive
events for and events is either EV_READ, EV_WRITE or 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
+EVBACKEND_SELECT or 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.
Example: call 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:
static void
+ stdin_readable_cb (struct ev_loop *loop, struct ev_io *w, int revents)
+ {
+ ev_io_stop (loop, w);
+ .. read from stdin here (or from w->fd) and haqndle any I/O errors
+ }
+
+ ...
+ struct ev_loop *loop = ev_default_init (0);
+ struct ev_io stdin_readable;
+ ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
+ ev_io_start (loop, &stdin_readable);
+ ev_loop (loop, 0);
+
+
+
+
+
ev_timer - relative and optionally recurring timeoutsTimer watchers are simple relative timers that generate an event after a 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 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
+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.
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.
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.
Example: create a timer that fires after 60 seconds.
+ static void
+ one_minute_cb (struct ev_loop *loop, struct ev_timer *w, int revents)
+ {
+ .. one minute over, w is actually stopped right here
+ }
+
+ struct ev_timer mytimer;
+ 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 +inactivity.
+ static void
+ timeout_cb (struct ev_loop *loop, struct ev_timer *w, int revents)
+ {
+ .. ten seconds without any activity
+ }
+
+ struct ev_timer mytimer;
+ ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
+ ev_timer_again (&mytimer); /* start timer */
+ ev_loop (loop, 0);
+
+ // and in some piece of code that gets executed on any "activity":
+ // reset the timeout to start ticking again at 10 seconds
+ ev_timer_again (&mytimer);
+
+
+
+
+
ev_periodic - to cron or not to cronPeriodic 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 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 ev_timer, which would trigger
roughly 10 seconds later and of course not if you reset your system time
again).
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 (at) has been passed, but if multiple periodic timers become ready
+during the same loop iteration then order of execution is undefined.
Lots of arguments, lets sort it out... There are basically three modes of operation, and we will explain them from simplest to complex:
- - - -
This doesn't mean there will always be 3600 seconds in between triggers, but only that the the callback will be called when the system time shows a -full hour (UTC), or more correct, when the system time is evenly divisible +full hour (UTC), or more correctly, when the system time is evenly divisible 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
+ev_periodic will try to run the callback in this mode at the next possible
time where time = at (mod interval), regardless of any time jumps.
time = at (mod interval), regardless of any time jumps.<
ignored. Instead, each time the periodic watcher gets scheduled, the
reschedule callback will be called with the watcher as first, and the
current time as second argument.
- NOTE: This callback MUST NOT stop or destroy the periodic or any other -periodic watcher, ever, or make any event loop modificstions. If you need -to stop it, return 1e30 (or so, fudge fudge) and stop it afterwards.
-Its prototype is c<ev_tstamp (*reschedule_cb)(struct ev_periodic *w, -ev_tstamp now)>, e.g.:
+NOTE: This callback MUST NOT stop or destroy any periodic watcher,
+ever, or make any event loop modifications. If you need to stop it,
+return now + 1e30 (or so, fudge fudge) and stop it afterwards (e.g. by
+starting a prepare watcher).
Its prototype is ev_tstamp (*reschedule_cb)(struct ev_periodic *w,
+ev_tstamp now), e.g.:
static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)
{
return now + 60.;
@@ -554,10 +940,13 @@ ev_tstamp now)>, e.g.:
(that is, the lowest time value larger than to the second argument). It
will usually be called just before the callback will be triggered, but
might be called at other times, too.
+ NOTE: This callback must always return a time that is later than the
+passed now value. Not even now itself will do, it 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 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 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).
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.
+ static void
+ clock_cb (struct ev_loop *loop, struct ev_io *w, int revents)
+ {
+ ... its now a full hour (UTC, or TAI or whatever your clock follows)
+ }
+
+ struct ev_periodic hourly_tick;
+ 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:
+ #include <math.h>
+
+ static ev_tstamp
+ my_scheduler_cb (struct ev_periodic *w, ev_tstamp now)
+ {
+ return fmod (now, 3600.) + 3600.;
+ }
+
+ ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
+
+
+Example: call a callback every hour, starting now:
+struct ev_periodic hourly_tick; + ev_periodic_init (&hourly_tick, clock_cb, + fmod (ev_now (loop), 3600.), 3600., 0); + ev_periodic_start (loop, &hourly_tick); + + + + +
ev_signal - signal me when a signal gets signalledSignal 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 +
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
@@ -593,9 +1018,13 @@ of the SIGxxx constants).
ev_child - wait for pid status changesChild watchers trigger when your process receives a SIGCHLD in response to some child status changes (most typically when a child of yours dies).
Configures the watcher to wait for status changes of process pid (or
any process if pid is specified as 0). The callback can look
at the rstatus member of the ev_child watcher structure to see
-the status word (use the macros from sys/wait.h). The rpid member
-contains the pid of the process causing the status change.
sys/wait.h and see your systems
+waitpid documentation). The rpid member contains the pid of the
+process causing the status change.
Example: try to exit cleanly on SIGINT and SIGTERM.
+ static void
+ sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents)
+ {
+ ev_unloop (loop, EVUNLOOP_ALL);
+ }
+
+ struct ev_signal signal_watcher;
+ ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
+ ev_signal_start (loop, &sigint_cb);
+
+
+
+
+
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.
+ev_idle - when you've got nothing better to doIdle 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.
Apart from keeping your process non-blocking (which is a useful
@@ -632,85 +1079,233 @@ kind. There is a ev_idle_set macro, but using it is utterly pointle
believe me.
Example: dynamically allocate an ev_idle, start it, and in the
+callback, free it. Alos, use no error checking, as usual.
static void
+ idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents)
+ {
+ free (w);
+ // now do something you wanted to do when the program has
+ // no longer asnything immediate to do.
+ }
+
+ struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle));
+ ev_idle_init (idle_watcher, idle_cb);
+ ev_idle_start (loop, idle_cb);
+
+
+
+
+
Prepare and check watchers usually (but not always) are used in -tandom. 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.
+ev_prepare and ev_check - customise your event loopPrepare 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 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.
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 -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 ev_io watchers for
+them and starting an 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).Initialises and configures the prepare or check watcher - they have no
parameters of any kind. There are ev_prepare_set and ev_check_set
-macros, but using them is utterly, utterly pointless.
Example: *TODO*.
+ + + + + +ev_embed - when one backend isn't enoughThis is a rather advanced watcher type that lets you embed one event loop
+into another (currently only ev_io events are supported in the embedded
+loop, other types of watchers might be handled in a delayed or incorrect
+fashion and must not be used).
There are primarily two reasons you would want that: work around bugs and +prioritise I/O.
+As an example for a bug workaround, the kqueue backend might only support +sockets on some platform, so it is unusable as generic backend, but you +still want to make use of it because you have many sockets and it scales +so nicely. In this case, you would create a kqueue-based loop and embed it +into your default loop (which might use e.g. poll). Overall operation will +be a bit slower because first libev has to poll and then call kevent, but +at least you can use both at what they are best.
+As for prioritising I/O: rarely you have the case where some fds have +to be watched and handled very quickly (with low latency), and even +priorities and idle watchers might have too much overhead. In this case +you would put all the high priority stuff in one loop and all the rest in +a second one, and embed the second one in the first.
+As long as the watcher is active, the callback will be invoked every time
+there might be events pending in the embedded loop. The callback must then
+call ev_embed_sweep (mainloop, watcher) to make a single sweep and invoke
+their callbacks (you could also start an idle watcher to give the embedded
+loop strictly lower priority for example). You can also set the callback
+to 0, in which case the embed watcher will automatically execute the
+embedded loop sweep.
As long as the watcher is started it will automatically handle events. The
+callback will be invoked whenever some events have been handled. You can
+set the callback to 0 to avoid having to specify one if you are not
+interested in that.
Also, there have not currently been made special provisions for forking:
+when you fork, you not only have to call ev_loop_fork on both loops,
+but you will also have to stop and restart any ev_embed watchers
+yourself.
Unfortunately, not all backends are embeddable, only the ones returned by
+ev_embeddable_backends are, which, unfortunately, does not include any
+portable one.
So when you want to use this feature you will always have to be prepared +that you cannot get an embeddable loop. The recommended way to get around +this is to have a separate variables for your embeddable loop, try to +create it, and if that fails, use the normal loop for everything:
+ struct ev_loop *loop_hi = ev_default_init (0);
+ struct ev_loop *loop_lo = 0;
+ struct ev_embed embed;
+
+ // see if there is a chance of getting one that works
+ // (remember that a flags value of 0 means autodetection)
+ loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
+ ? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
+ : 0;
+
+ // if we got one, then embed it, otherwise default to loop_hi
+ if (loop_lo)
+ {
+ ev_embed_init (&embed, 0, loop_lo);
+ ev_embed_start (loop_hi, &embed);
+ }
+ else
+ loop_lo = loop_hi;
+
+
+Configures the watcher to embed the given loop, which must be
+embeddable. If the callback is 0, then ev_embed_sweep will be
+invoked automatically, otherwise it is the responsibility of the callback
+to invoke it (it will continue to be called until the sweep has been done,
+if you do not want thta, you need to temporarily stop the embed watcher).
Make a single, non-blocking sweep over the embedded loop. This works
+similarly to ev_loop (embedded_loop, EVLOOP_NONBLOCK), but in the most
+apropriate way for embedded loops.
There are some other fucntions of possible interest. Described. Here. Now.
+There are some other functions of possible interest. Described. Here. Now.
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 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 fd and events set
-will be craeted and started.
If fd is less than 0, then no I/O watcher will be started and events
+is being ignored. Otherwise, an ev_io watcher for the given fd and
+events set will be craeted and started.
If timeout is less than 0, then no timeout watcher will be
-started. Otherwise an ev_timer watcher with after = timeout (and repeat
-= 0) will be started.
The callback has the type 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 arg value passed to ev_once:
ev_timer watcher with after = timeout (and
+repeat = 0) will be started. While 0 is a valid timeout, it is of
+dubious value.
+ The callback has the type void (*cb)(int revents, void *arg) and gets
+passed an revents set like normal event callbacks (a combination of
+EV_ERROR, EV_READ, EV_WRITE or EV_TIMEOUT) and the arg
+value passed to 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);
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).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.
Feed an event as if the given signal occured (loop must be the default loop!).
+Feed an event as if the given signal occured (loop must be the default
+loop!).
Libev offers a compatibility emulation layer for libevent. It cannot +emulate the internals of libevent, so here are some usage hints:
+TBD.
+