X-Git-Url: https://git.llucax.com/software/libev.git/blobdiff_plain/1ef940ed393da8f8d74505196399215d6bb21016..ae1704c5ed25ba151cb448264ada4b96c9b88225:/ev.3 diff --git a/ev.3 b/ev.3 index 6aaee67..4f3bfef 100644 --- a/ev.3 +++ b/ev.3 @@ -129,7 +129,7 @@ .\" ======================================================================== .\" .IX Title """ 1" -.TH "" 1 "2007-12-07" "perl v5.8.8" "User Contributed Perl Documentation" +.TH "" 1 "2007-12-09" "perl v5.8.8" "User Contributed Perl Documentation" .SH "NAME" libev \- a high performance full\-featured event loop written in C .SH "SYNOPSIS" @@ -261,14 +261,17 @@ you actually want to know. .IP "int ev_version_minor ()" 4 .IX Item "int ev_version_minor ()" .PD -You can find out the major and minor version numbers of the library +You can find out the major and minor \s-1ABI\s0 version numbers of the library you linked against by calling the functions \f(CW\*(C`ev_version_major\*(C'\fR and \&\f(CW\*(C`ev_version_minor\*(C'\fR. If you want, you can compare against the global symbols \f(CW\*(C`EV_VERSION_MAJOR\*(C'\fR and \f(CW\*(C`EV_VERSION_MINOR\*(C'\fR, which specify the version of the library your program was compiled against. .Sp +These version numbers refer to the \s-1ABI\s0 version of the library, not the +release version. +.Sp Usually, it's a good idea to terminate if the major versions mismatch, -as this indicates an incompatible change. Minor versions are usually +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. .Sp @@ -636,9 +639,10 @@ usually a better approach for this kind of thing. .Sp Here are the gory details of what \f(CW\*(C`ev_loop\*(C'\fR does: .Sp -.Vb 18 +.Vb 19 +\& - Before the first iteration, call any pending watchers. \& * If there are no active watchers (reference count is zero), return. -\& - Queue prepare watchers and then call all outstanding watchers. +\& - Queue all prepare watchers and then call all outstanding watchers. \& - If we have been forked, recreate the kernel state. \& - Update the kernel state with all outstanding changes. \& - Update the "event loop time". @@ -891,8 +895,9 @@ 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 -\&\f(CW\*(C`ev_TYPE_set\*(C'\fR is safe) and you must make sure the watcher is available to -libev (e.g. you cnanot \f(CW\*(C`free ()\*(C'\fR it). +\&\f(CW\*(C`ev_TYPE_set\*(C'\fR is safe), you must not change its priority, and you must +make sure the watcher is available to libev (e.g. you cannot \f(CW\*(C`free ()\*(C'\fR +it). .IP "callback ev_cb (ev_TYPE *watcher)" 4 .IX Item "callback ev_cb (ev_TYPE *watcher)" Returns the callback currently set on the watcher. @@ -920,12 +925,25 @@ 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 \f(CW\*(C`ev_idle\*(C'\fR watchers, which provide this functionality. .Sp +You \fImust not\fR change the priority of a watcher as long as it is active or +pending. +.Sp The default priority used by watchers when no priority has been set is always \f(CW0\fR, which is supposed to not be too high and not be too low :). .Sp Setting a priority outside the range of \f(CW\*(C`EV_MINPRI\*(C'\fR to \f(CW\*(C`EV_MAXPRI\*(C'\fR 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. +.IP "ev_invoke (loop, ev_TYPE *watcher, int revents)" 4 +.IX Item "ev_invoke (loop, ev_TYPE *watcher, int revents)" +Invoke the \f(CW\*(C`watcher\*(C'\fR with the given \f(CW\*(C`loop\*(C'\fR and \f(CW\*(C`revents\*(C'\fR. Neither +\&\f(CW\*(C`loop\*(C'\fR nor \f(CW\*(C`revents\*(C'\fR need to be valid as long as the watcher callback +can deal with that fact. +.IP "int ev_clear_pending (loop, ev_TYPE *watcher)" 4 +.IX Item "int ev_clear_pending (loop, ev_TYPE *watcher)" +If the watcher is pending, this function returns clears its pending status +and returns its \f(CW\*(C`revents\*(C'\fR bitset (as if its callback was invoked). If the +watcher isn't pending it does nothing and returns \f(CW0\fR. .Sh "\s-1ASSOCIATING\s0 \s-1CUSTOM\s0 \s-1DATA\s0 \s-1WITH\s0 A \s-1WATCHER\s0" .IX Subsection "ASSOCIATING CUSTOM DATA WITH A WATCHER" Each watcher has, by default, a member \f(CW\*(C`void *data\*(C'\fR that you can change @@ -1222,11 +1240,11 @@ to trigger \*(L"at\*(R" some specific point in time. For example, if you tell a periodic watcher to trigger in 10 seconds (by specifiying e.g. \f(CW\*(C`ev_now () + 10.\*(C'\fR) and then reset your system clock to the last year, then it will take a year to trigger the event (unlike an \f(CW\*(C`ev_timer\*(C'\fR, which would trigger -roughly 10 seconds later and of course not if you reset your system time -again). +roughly 10 seconds later). .PP They can also be used to implement vastly more complex timers, such as -triggering an event on eahc midnight, local time. +triggering an event on each midnight, local time or other, complicated, +rules. .PP As with timers, the callback is guarenteed to be invoked only when the time (\f(CW\*(C`at\*(C'\fR) has been passed, but if multiple periodic timers become ready @@ -1240,17 +1258,17 @@ 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: .RS 4 -.IP "* absolute timer (interval = reschedule_cb = 0)" 4 -.IX Item "absolute timer (interval = reschedule_cb = 0)" +.IP "* absolute timer (at = time, interval = reschedule_cb = 0)" 4 +.IX Item "absolute timer (at = time, interval = reschedule_cb = 0)" In this configuration the watcher triggers an event at the wallclock time \&\f(CW\*(C`at\*(C'\fR and doesn't repeat. It will not adjust when a time jump occurs, that is, if it is to be run at January 1st 2011 then it will run when the system time reaches or surpasses this time. -.IP "* non-repeating interval timer (interval > 0, reschedule_cb = 0)" 4 -.IX Item "non-repeating interval timer (interval > 0, reschedule_cb = 0)" +.IP "* non-repeating interval timer (at = offset, interval > 0, reschedule_cb = 0)" 4 +.IX Item "non-repeating interval timer (at = offset, interval > 0, reschedule_cb = 0)" In this mode the watcher will always be scheduled to time out at the next -\&\f(CW\*(C`at + N * interval\*(C'\fR time (for some integer N) and then repeat, regardless -of any time jumps. +\&\f(CW\*(C`at + N * interval\*(C'\fR time (for some integer N, which can also be negative) +and then repeat, regardless of any time jumps. .Sp This can be used to create timers that do not drift with respect to system time: @@ -1267,8 +1285,12 @@ by 3600. Another way to think about it (for the mathematically inclined) is that \&\f(CW\*(C`ev_periodic\*(C'\fR will try to run the callback in this mode at the next possible time where \f(CW\*(C`time = at (mod interval)\*(C'\fR, regardless of any time jumps. -.IP "* manual reschedule mode (reschedule_cb = callback)" 4 -.IX Item "manual reschedule mode (reschedule_cb = callback)" +.Sp +For numerical stability it is preferable that the \f(CW\*(C`at\*(C'\fR value is near +\&\f(CW\*(C`ev_now ()\*(C'\fR (the current time), but there is no range requirement for +this value. +.IP "* manual reschedule mode (at and interval ignored, reschedule_cb = callback)" 4 +.IX Item "manual reschedule mode (at and interval ignored, reschedule_cb = callback)" In this mode the values for \f(CW\*(C`interval\*(C'\fR and \f(CW\*(C`at\*(C'\fR are both being ignored. Instead, each time the periodic watcher gets scheduled, the reschedule callback will be called with the watcher as first, and the @@ -1277,7 +1299,7 @@ current time as second argument. \&\s-1NOTE:\s0 \fIThis callback \s-1MUST\s0 \s-1NOT\s0 stop or destroy any periodic watcher, ever, or make any event loop modifications\fR. If you need to stop it, return \f(CW\*(C`now + 1e30\*(C'\fR (or so, fudge fudge) and stop it afterwards (e.g. by -starting a prepare watcher). +starting an \f(CW\*(C`ev_prepare\*(C'\fR watcher, which is legal). .Sp Its prototype is \f(CW\*(C`ev_tstamp (*reschedule_cb)(struct ev_periodic *w, ev_tstamp now)\*(C'\fR, e.g.: @@ -1311,6 +1333,13 @@ Simply stops and restarts the periodic watcher again. This is only useful when you changed some parameters or the reschedule callback would return a different time than the last time it was called (e.g. in a crond like program when the crontabs have changed). +.IP "ev_tstamp offset [read\-write]" 4 +.IX Item "ev_tstamp offset [read-write]" +When repeating, this contains the offset value, otherwise this is the +absolute point in time (the \f(CW\*(C`at\*(C'\fR value passed to \f(CW\*(C`ev_periodic_set\*(C'\fR). +.Sp +Can be modified any time, but changes only take effect when the periodic +timer fires or \f(CW\*(C`ev_periodic_again\*(C'\fR is being called. .IP "ev_tstamp interval [read\-write]" 4 .IX Item "ev_tstamp interval [read-write]" The current interval value. Can be modified any time, but changes only @@ -1622,6 +1651,16 @@ 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). +.PP +It is recommended to give \f(CW\*(C`ev_check\*(C'\fR watchers highest (\f(CW\*(C`EV_MAXPRI\*(C'\fR) +priority, to ensure that they are being run before any other watchers +after the poll. Also, \f(CW\*(C`ev_check\*(C'\fR watchers (and \f(CW\*(C`ev_prepare\*(C'\fR watchers, +too) should not activate (\*(L"feed\*(R") events into libev. While libev fully +supports this, they will be called before other \f(CW\*(C`ev_check\*(C'\fR watchers did +their job. As \f(CW\*(C`ev_check\*(C'\fR watchers are often used to embed other event +loops those other event loops might be in an unusable state until their +\&\f(CW\*(C`ev_check\*(C'\fR watcher ran (always remind yourself to coexist peacefully with +others). .IP "ev_prepare_init (ev_prepare *, callback)" 4 .IX Item "ev_prepare_init (ev_prepare *, callback)" .PD 0 @@ -1632,25 +1671,28 @@ Initialises and configures the prepare or check watcher \- they have no parameters of any kind. There are \f(CW\*(C`ev_prepare_set\*(C'\fR and \f(CW\*(C`ev_check_set\*(C'\fR macros, but using them is utterly, utterly and completely pointless. .PP -Example: To include a library such as adns, you would add \s-1IO\s0 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 \f(CW\*(C`EV::ADNS\*(C'\fR that does this, which you could +use for an actually working example. Another Perl module named \f(CW\*(C`EV::Glib\*(C'\fR +embeds a Glib main context into libev, and finally, \f(CW\*(C`Glib::EV\*(C'\fR embeds \s-1EV\s0 +into the Glib event loop). +.PP +Method 1: Add \s-1IO\s0 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 \f(CW\*(C`ev_clear_pending\*(C'\fR explicitly, as +the callbacks for the IO/timeout watchers might not have been called yet. .PP .Vb 2 \& static ev_io iow [nfd]; \& static ev_timer tw; .Ve .PP -.Vb 9 +.Vb 4 \& 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; \& } .Ve .PP @@ -1672,7 +1714,7 @@ pseudo-code only of course: .Ve .PP .Vb 6 -\& // 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, @@ -1680,9 +1722,8 @@ pseudo-code only of course: \& | (fds [i].events & POLLOUT ? EV_WRITE : 0))); .Ve .PP -.Vb 5 +.Vb 4 \& fds [i].revents = 0; -\& iow [i].data = fds + i; \& ev_io_start (loop, iow + i); \& } \& } @@ -1696,15 +1737,110 @@ pseudo-code only of course: \& ev_timer_stop (loop, &tw); .Ve .PP -.Vb 2 +.Vb 8 \& 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; +.Ve +.PP +.Vb 3 +\& // now stop the watcher +\& ev_io_stop (loop, iow + i); +\& } .Ve .PP .Vb 2 \& adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop)); \& } .Ve +.PP +Method 2: This would be just like method 1, but you run \f(CW\*(C`adns_afterpoll\*(C'\fR +in the prepare watcher and would dispose of the check watcher. +.PP +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. +.PP +.Vb 5 +\& static void +\& timer_cb (EV_P_ ev_timer *w, int revents) +\& { +\& adns_state ads = (adns_state)w->data; +\& update_now (EV_A); +.Ve +.PP +.Vb 2 +\& adns_processtimeouts (ads, &tv_now); +\& } +.Ve +.PP +.Vb 5 +\& static void +\& io_cb (EV_P_ ev_io *w, int revents) +\& { +\& adns_state ads = (adns_state)w->data; +\& update_now (EV_A); +.Ve +.PP +.Vb 3 +\& if (revents & EV_READ ) adns_processreadable (ads, w->fd, &tv_now); +\& if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now); +\& } +.Ve +.PP +.Vb 1 +\& // do not ever call adns_afterpoll +.Ve +.PP +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 \s-1EV\s0. The \f(CW\*(C`Glib::EV\*(C'\fR module does +this. +.PP +.Vb 4 +\& static gint +\& event_poll_func (GPollFD *fds, guint nfds, gint timeout) +\& { +\& int got_events = 0; +.Ve +.PP +.Vb 2 +\& for (n = 0; n < nfds; ++n) +\& // create/start io watcher that sets the relevant bits in fds[n] and increment got_events +.Ve +.PP +.Vb 2 +\& if (timeout >= 0) +\& // create/start timer +.Ve +.PP +.Vb 2 +\& // poll +\& ev_loop (EV_A_ 0); +.Ve +.PP +.Vb 3 +\& // stop timer again +\& if (timeout >= 0) +\& ev_timer_stop (EV_A_ &to); +.Ve +.PP +.Vb 3 +\& // stop io watchers again - their callbacks should have set +\& for (n = 0; n < nfds; ++n) +\& ev_io_stop (EV_A_ iow [n]); +.Ve +.PP +.Vb 2 +\& return got_events; +\& } +.Ve .ie n .Sh """ev_embed"" \- when one backend isn't enough..." .el .Sh "\f(CWev_embed\fP \- when one backend isn't enough..." .IX Subsection "ev_embed - when one backend isn't enough..." @@ -1896,12 +2032,21 @@ To use it, \& #include .Ve .PP -(it is not installed by default). This automatically includes \fIev.h\fR -and puts all of its definitions (many of them macros) into the global -namespace. All \*(C+ specific things are put into the \f(CW\*(C`ev\*(C'\fR namespace. +This automatically includes \fIev.h\fR and puts all of its definitions (many +of them macros) into the global namespace. All \*(C+ specific things are +put into the \f(CW\*(C`ev\*(C'\fR namespace. It should support all the same embedding +options as \fIev.h\fR, most notably \f(CW\*(C`EV_MULTIPLICITY\*(C'\fR. .PP -It should support all the same embedding options as \fIev.h\fR, most notably -\&\f(CW\*(C`EV_MULTIPLICITY\*(C'\fR. +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 \f(CW\*(C`EV_MULTIPLICITY\*(C'\fR when embedding libev). +.PP +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). .PP Here is a list of things available in the \f(CW\*(C`ev\*(C'\fR namespace: .ie n .IP """ev::READ""\fR, \f(CW""ev::WRITE"" etc." 4 @@ -1923,21 +2068,70 @@ defines by many implementations. .Sp All of those classes have these methods: .RS 4 -.IP "ev::TYPE::TYPE (object *, object::method *)" 4 -.IX Item "ev::TYPE::TYPE (object *, object::method *)" +.IP "ev::TYPE::TYPE ()" 4 +.IX Item "ev::TYPE::TYPE ()" .PD 0 -.IP "ev::TYPE::TYPE (object *, object::method *, struct ev_loop *)" 4 -.IX Item "ev::TYPE::TYPE (object *, object::method *, struct ev_loop *)" +.IP "ev::TYPE::TYPE (struct ev_loop *)" 4 +.IX Item "ev::TYPE::TYPE (struct ev_loop *)" .IP "ev::TYPE::~TYPE" 4 .IX Item "ev::TYPE::~TYPE" .PD -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 -\&\f(CW\*(C`ev_init\*(C'\fR for you, which means you have to call the \f(CW\*(C`set\*(C'\fR 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 \f(CW\*(C`EV_DEFAULT\*(C'\fR. +.Sp +The constructor calls \f(CW\*(C`ev_init\*(C'\fR for you, which means you have to call the +\&\f(CW\*(C`set\*(C'\fR method before starting it. +.Sp +It will not set a callback, however: You have to call the templated \f(CW\*(C`set\*(C'\fR +method to set a callback before you can start the watcher. +.Sp +(The reason why you have to use a method is a limitation in \*(C+ which does +not allow explicit template arguments for constructors). .Sp The destructor automatically stops the watcher if it is active. +.IP "w\->set (object *)" 4 +.IX Item "w->set (object *)" +This method sets the callback method to call. The method has to have a +signature of \f(CW\*(C`void (*)(ev_TYPE &, int)\*(C'\fR, it receives the watcher as +first argument and the \f(CW\*(C`revents\*(C'\fR as second. The object must be given as +parameter and is stored in the \f(CW\*(C`data\*(C'\fR member of the watcher. +.Sp +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 \f(CW\*(C`set\*(C'\fR 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. +.Sp +Example: simple class declaration and watcher initialisation +.Sp +.Vb 4 +\& struct myclass +\& { +\& void io_cb (ev::io &w, int revents) { } +\& } +.Ve +.Sp +.Vb 3 +\& myclass obj; +\& ev::io iow; +\& iow.set (&obj); +.Ve +.IP "w\->set (void *data = 0)" 4 +.IX Item "w->set (void *data = 0)" +Also sets a callback, but uses a static method or plain function as +callback. The optional \f(CW\*(C`data\*(C'\fR argument will be stored in the watcher's +\&\f(CW\*(C`data\*(C'\fR member and is free for you to use. +.Sp +The prototype of the \f(CW\*(C`function\*(C'\fR must be \f(CW\*(C`void (*)(ev::TYPE &w, int)\*(C'\fR. +.Sp +See the method\-\f(CW\*(C`set\*(C'\fR above for more details. +.Sp +Example: +.Sp +.Vb 2 +\& static void io_cb (ev::io &w, int revents) { } +\& iow.set (); +.Ve .IP "w\->set (struct ev_loop *)" 4 .IX Item "w->set (struct ev_loop *)" Associates a different \f(CW\*(C`struct ev_loop\*(C'\fR with this watcher. You can only @@ -1945,12 +2139,13 @@ do this when the watcher is inactive (and not pending either). .IP "w\->set ([args])" 4 .IX Item "w->set ([args])" Basically the same as \f(CW\*(C`ev_TYPE_set\*(C'\fR, 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. .IP "w\->start ()" 4 .IX Item "w->start ()" -Starts the watcher. Note that there is no \f(CW\*(C`loop\*(C'\fR argument as the -constructor already takes the loop. +Starts the watcher. Note that there is no \f(CW\*(C`loop\*(C'\fR argument, as the +constructor already stores the event loop. .IP "w\->stop ()" 4 .IX Item "w->stop ()" Stops the watcher if it is active. Again, no \f(CW\*(C`loop\*(C'\fR argument. @@ -1986,11 +2181,14 @@ the constructor. \& } .Ve .PP -.Vb 6 +.Vb 4 \& myclass::myclass (int fd) -\& : io (this, &myclass::io_cb), -\& idle (this, &myclass::idle_cb) \& { +\& io .set (this); +\& idle.set (this); +.Ve +.PP +.Vb 2 \& io.start (fd, ev::READ); \& } .Ve @@ -2406,6 +2604,12 @@ And a \fIev_cpp.C\fR implementation file that contains libev proper and is compi In this section the complexities of (many of) the algorithms used inside libev will be explained. For complexity discussions about backends see the documentation for \f(CW\*(C`ev_default_init\*(C'\fR. +.Sp +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. .RS 4 .IP "Starting and stopping timer/periodic watchers: O(log skipped_other_timers)" 4 .IX Item "Starting and stopping timer/periodic watchers: O(log skipped_other_timers)" @@ -2418,16 +2622,10 @@ 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. .IP "Starting io/check/prepare/idle/signal/child watchers: O(1)" 4 .IX 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. If -the array needs to be extended libev needs to realloc and move the whole -array, but this happen asymptotically less and less with more watchers, -thus amortised O(1). -.IP "Stopping check/prepare/idle watchers: O(1)" 4 -.IX Item "Stopping check/prepare/idle watchers: O(1)" -.PD 0 +These just add the watcher into an array or at the head of a list. +=item Stopping check/prepare/idle watchers: O(1) .IP "Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % \s-1EV_PID_HASHSIZE\s0))" 4 .IX Item "Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))" -.PD 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).