The newest version of this document is also available as a html-formatted +web page you might find easier to navigate when reading it for the first +time: http://cvs.schmorp.de/libev/ev.html.

Libev is an event loop: you register interest in certain events (such as a file descriptor being readable or a timeout occuring), and it will manage these event sources and provide your program with events.

@@ -184,13 +187,15 @@ you actually want to know.

int ev_version_major ()

int ev_version_minor ()

You can find out the major and minor version numbers of the library +

You can find out the major and minor ABI version numbers of the library you linked against by calling the functions 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.

These version numbers refer to the ABI version of the library, not the +release version.

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.

Example: Make sure we haven't accidentally been linked against the wrong @@ -528,8 +533,9 @@ external event in conjunction with something not expressible using other libev watchers. However, a pair of 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.
+   - Before the first iteration, call any pending watchers.
+   * If there are no active watchers (reference count is zero), return.
+   - 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".
@@ -768,8 +774,9 @@ 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
-ev_TYPE_set is safe) and you must make sure the watcher is available to
-libev (e.g. you cnanot free () it).
+ev_TYPE_set is safe), you must not change its priority, and you must
+make sure the watcher is available to libev (e.g. you cannot free ()
+it).

callback ev_cb (ev_TYPE *watcher)

@@ -794,12 +801,26 @@ example, to reduce latency after idling, or more often, to bind two watchers on the same event and make sure one is called first.

If you need to suppress invocation when higher priority events are pending you need to look at ev_idle watchers, which provide this functionality.

You must not change the priority of a watcher as long as it is active or +pending.

The default priority used by watchers when no priority has been set is always 0, which is supposed to not be too high and not be too low :).

Setting a priority outside the range of EV_MINPRI to EV_MAXPRI is fine, as long as you do not mind that the priority value you query might or might not have been adjusted to be within valid range.

ev_invoke (loop, ev_TYPE *watcher, int revents)

Invoke the watcher with the given loop and revents. Neither +loop nor revents need to be valid as long as the watcher callback +can deal with that fact.

int ev_clear_pending (loop, ev_TYPE *watcher)

If the watcher is pending, this function returns clears its pending status +and returns its revents bitset (as if its callback was invoked). If the +watcher isn't pending it does nothing and returns 0.

@@ -919,7 +940,7 @@ it is best to always use non-blocking I/O: An extra read(2) returni EAGAIN is far preferable to a program hanging until some data arrives.

If you cannot run the fd in non-blocking mode (for example you should not play around with an Xlib connection), then you have to seperately re-test -wether a file descriptor is really ready with a known-to-be good interface +whether a file descriptor is really ready with a known-to-be good interface such as poll (fortunately in our Xlib example, Xlib already does this on its own, so its quite safe to use).

@@ -1080,10 +1101,10 @@ to trigger "at" some specific point in time. For example, if you tell periodic watcher to trigger in 10 seconds (by specifiying e.g.

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 -roughly 10 seconds later and of course not if you reset your system time -again).

+roughly 10 seconds later).

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.

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.

@@ -1095,18 +1116,18 @@ during the same loop iteration then order of execution is undefined.

operation, and we will explain them from simplest to complex:

* absolute timer (interval = reschedule_cb = 0)

* absolute timer (at = time, interval = reschedule_cb = 0)

In this configuration the watcher triggers an event at the wallclock time at 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.

* non-repeating interval timer (interval > 0, reschedule_cb = 0)

* 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 -at + N * interval time (for some integer N) and then repeat, regardless -of any time jumps.

+at + N * interval time (for some integer N, which can also be negative) +and then repeat, regardless of any time jumps.

This can be used to create timers that do not drift with respect to system time:

   ev_periodic_set (&periodic, 0., 3600., 0);
@@ -1119,8 +1140,11 @@ 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
 time where time = at (mod interval), regardless of any time jumps.
+					For numerical stability it is preferable that the at value is near
+ev_now () (the current time), but there is no range requirement for
+this value.

* manual reschedule mode (reschedule_cb = callback)

* manual reschedule mode (at and interval ignored, reschedule_cb = callback)

In this mode the values for interval and at are both being ignored. Instead, each time the periodic watcher gets scheduled, the @@ -1129,7 +1153,7 @@ current time as second argument.

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).

+starting an ev_prepare watcher, which is legal).

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)
@@ -1159,6 +1183,13 @@ reason I omitted it as an example).
 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).
+

ev_tstamp offset [read-write]

When repeating, this contains the offset value, otherwise this is the +absolute point in time (the at value passed to ev_periodic_set).

Can be modified any time, but changes only take effect when the periodic +timer fires or ev_periodic_again is being called.

ev_tstamp interval [read-write]

@@ -1467,6 +1498,15 @@ 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).

It is recommended to give ev_check watchers highest (EV_MAXPRI) +priority, to ensure that they are being run before any other watchers +after the poll. Also, ev_check watchers (and ev_prepare watchers, +too) should not activate ("feed") events into libev. While libev fully +supports this, they will be called before other ev_check watchers did +their job. As ev_check watchers are often used to embed other event +loops those other event loops might be in an unusable state until their +ev_check watcher ran (always remind yourself to coexist peacefully with +others).

ev_prepare_init (ev_prepare *, callback)
ev_check_init (ev_check *, callback)


-Example: To include a library such as adns, you would add IO watchers
-and a timeout watcher in a prepare handler, as required by libadns, and
-in a check watcher, destroy them and call into libadns. What follows is
-pseudo-code only of course:
+There are a number of principal ways to embed other event loops or modules
+into libev. Here are some ideas on how to include libadns into libev
+(there is a Perl module named EV::ADNS that does this, which you could
+use for an actually working example. Another Perl module named EV::Glib
+embeds a Glib main context into libev, and finally, Glib::EV embeds EV
+into the Glib event loop).
+Method 1: Add IO watchers and a timeout watcher in a prepare handler,
+and in a check watcher, destroy them and call into libadns. What follows
+is pseudo-code only of course. This requires you to either use a low
+priority for the check watcher or use ev_clear_pending explicitly, as
+the callbacks for the IO/timeout watchers might not have been called yet.
   static ev_io iow [nfd];
   static ev_timer tw;
 
   static void
   io_cb (ev_loop *loop, ev_io *w, int revents)
   {
-    // set the relevant poll flags
-    // could also call adns_processreadable etc. here
-    struct pollfd *fd = (struct pollfd *)w->data;
-    if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;
-    if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;
   }
 
   // create io watchers for each fd and a timer before blocking
@@ -1506,7 +1548,7 @@ pseudo-code only of course:
     ev_timer_init (&tw, 0, timeout * 1e-3);
     ev_timer_start (loop, &tw);
 
-    // create on ev_io per pollfd
+    // create one ev_io per pollfd
     for (int i = 0; i < nfd; ++i)
       {
         ev_io_init (iow + i, io_cb, fds [i].fd,
@@ -1514,7 +1556,6 @@ pseudo-code only of course:
            | (fds [i].events & POLLOUT ? EV_WRITE : 0)));
 
         fds [i].revents = 0;
-        iow [i].data = fds + i;
         ev_io_start (loop, iow + i);
       }
   }
@@ -1526,11 +1567,79 @@ pseudo-code only of course:
     ev_timer_stop (loop, &tw);
 
     for (int i = 0; i < nfd; ++i)
-      ev_io_stop (loop, iow + i);
+      {
+        // set the relevant poll flags
+        // could also call adns_processreadable etc. here
+        struct pollfd *fd = fds + i;
+        int revents = ev_clear_pending (iow + i);
+        if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;
+        if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;
+
+        // now stop the watcher
+        ev_io_stop (loop, iow + i);
+      }
 
     adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
   }
 
+
+Method 2: This would be just like method 1, but you run adns_afterpoll
+in the prepare watcher and would dispose of the check watcher.
+Method 3: If the module to be embedded supports explicit event
+notification (adns does), you can also make use of the actual watcher
+callbacks, and only destroy/create the watchers in the prepare watcher.
+  static void
+  timer_cb (EV_P_ ev_timer *w, int revents)
+  {
+    adns_state ads = (adns_state)w->data;
+    update_now (EV_A);
+
+    adns_processtimeouts (ads, &tv_now);
+  }
+
+  static void
+  io_cb (EV_P_ ev_io *w, int revents)
+  {
+    adns_state ads = (adns_state)w->data;
+    update_now (EV_A);
+
+    if (revents & EV_READ ) adns_processreadable  (ads, w->fd, &tv_now);
+    if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now);
+  }
+
+  // do not ever call adns_afterpoll
+
+
+Method 4: Do not use a prepare or check watcher because the module you
+want to embed is too inflexible to support it. Instead, youc na override
+their poll function.  The drawback with this solution is that the main
+loop is now no longer controllable by EV. The Glib::EV module does
+this.
+  static gint
+  event_poll_func (GPollFD *fds, guint nfds, gint timeout)
+  {
+    int got_events = 0;
+
+    for (n = 0; n < nfds; ++n)
+      // create/start io watcher that sets the relevant bits in fds[n] and increment got_events
+
+    if (timeout >= 0)
+      // create/start timer
+
+    // poll
+    ev_loop (EV_A_ 0);
+
+    // stop timer again
+    if (timeout >= 0)
+      ev_timer_stop (EV_A_ &to);
+
+    // stop io watchers again - their callbacks should have set
+    for (n = 0; n < nfds; ++n)
+      ev_io_stop (EV_A_ iow [n]);
+
+    return got_events;
+  }
+
 
 
 
@@ -1735,11 +1844,19 @@ the callback model to a model using method callbacks on objects.
   #include <ev++.h>
 
 
-(it is not installed by default). This automatically includes ev.h
-and puts all of its definitions (many of them macros) into the global
-namespace. All C++ specific things are put into the ev namespace.
-It should support all the same embedding options as ev.h, most notably
-EV_MULTIPLICITY.
+This automatically includes ev.h and puts all of its definitions (many
+of them macros) into the global namespace. All C++ specific things are
+put into the ev namespace. It should support all the same embedding
+options as ev.h, most notably EV_MULTIPLICITY.
+Care has been taken to keep the overhead low. The only data member the C++
+classes add (compared to plain C-style watchers) is the event loop pointer
+that the watcher is associated with (or no additional members at all if
+you disable EV_MULTIPLICITY when embedding libev).
+Currently, functions, and static and non-static member functions can be
+used as callbacks. Other types should be easy to add as long as they only
+need one additional pointer for context. If you need support for other
+types of functors please contact the author (preferably after implementing
+it).
 Here is a list of things available in the ev namespace:
 
 	ev::READ, ev::WRITE etc.
@@ -1760,17 +1877,56 @@ defines by many implementations.
 		All of those classes have these methods:
 		
 			

-				ev::TYPE::TYPE (object *, object::method *)
-				ev::TYPE::TYPE (object *, object::method *, struct ev_loop *)
+				ev::TYPE::TYPE ()
+				ev::TYPE::TYPE (struct ev_loop *)
 				ev::TYPE::~TYPE
 				
-					The constructor takes a pointer to an object and a method pointer to
-the event handler callback to call in this class. The constructor calls
-ev_init for you, which means you have to call the set method
-before starting it. If you do not specify a loop then the constructor
-automatically associates the default loop with this watcher.
+					The constructor (optionally) takes an event loop to associate the watcher
+with. If it is omitted, it will use EV_DEFAULT.
+					The constructor calls ev_init for you, which means you have to call the
+set method before starting it.
+					It will not set a callback, however: You have to call the templated set
+method to set a callback before you can start the watcher.
+					(The reason why you have to use a method is a limitation in C++ which does
+not allow explicit template arguments for constructors).
 					The destructor automatically stops the watcher if it is active.
 				
+				w->set<class, &class::method> (object *)
+				
+					This method sets the callback method to call. The method has to have a
+signature of void (*)(ev_TYPE &, int), it receives the watcher as
+first argument and the revents as second. The object must be given as
+parameter and is stored in the data member of the watcher.
+					This method synthesizes efficient thunking code to call your method from
+the C callback that libev requires. If your compiler can inline your
+callback (i.e. it is visible to it at the place of the set call and
+your compiler is good :), then the method will be fully inlined into the
+thunking function, making it as fast as a direct C callback.
+					Example: simple class declaration and watcher initialisation
+  struct myclass
+  {
+    void io_cb (ev::io &w, int revents) { }
+  }
+
+  myclass obj;
+  ev::io iow;
+  iow.set <myclass, &myclass::io_cb> (&obj);
+
+
+				
+				w->set<function> (void *data = 0)
+				
+					Also sets a callback, but uses a static method or plain function as
+callback. The optional data argument will be stored in the watcher's
+data member and is free for you to use.
+					The prototype of the function must be void (*)(ev::TYPE &w, int).
+					See the method-set above for more details.
+					Example:
+  static void io_cb (ev::io &w, int revents) { }
+  iow.set <io_cb> ();
+
+
+				
 				w->set (struct ev_loop *)
 				
 					Associates a different struct ev_loop with this watcher. You can only
@@ -1779,13 +1935,14 @@ do this when the watcher is inactive (and not pending either).
 				
w->set ([args])
 				
 					Basically the same as ev_TYPE_set, with the same args. Must be
-called at least once.  Unlike the C counterpart, an active watcher gets
-automatically stopped and restarted.
+called at least once. Unlike the C counterpart, an active watcher gets
+automatically stopped and restarted when reconfiguring it with this
+method.
 				
 				w->start ()
 				
-					Starts the watcher. Note that there is no loop argument as the
-constructor already takes the loop.
+					Starts the watcher. Note that there is no loop argument, as the
+constructor already stores the event loop.
 				
 				w->stop ()
 				
@@ -1819,9 +1976,10 @@ the constructor.
   }
 
   myclass::myclass (int fd)
-  : io   (this, &myclass::io_cb),
-    idle (this, &myclass::idle_cb)
   {
+    io  .set <myclass, &myclass::io_cb  > (this);
+    idle.set <myclass, &myclass::idle_cb> (this);
+
     io.start (fd, ev::READ);
   }
 
@@ -1834,7 +1992,7 @@ the constructor.
 MACRO MAGIC
 
 Libev can be compiled with a variety of options, the most fundemantal is
-EV_MULTIPLICITY. This option determines wether (most) functions and
+EV_MULTIPLICITY. This option determines whether (most) functions and
 callbacks have an initial struct ev_loop * argument.
 To make it easier to write programs that cope with either variant, the
 following macros are defined:
@@ -1874,7 +2032,7 @@ loop, if multiple loops are supported ("ev loop default").
 	
 
 Example: Declare and initialise a check watcher, utilising the above
-macros so it will work regardless of wether multiple loops are supported
+macros so it will work regardless of whether multiple loops are supported
 or not.
   static void
   check_cb (EV_P_ ev_timer *w, int revents)
@@ -2111,6 +2269,20 @@ will have the struct ev_loop * as first argument, and you can creat
 additional independent event loops. Otherwise there will be no support
 for multiple event loops and there is no first event loop pointer
 argument. Instead, all functions act on the single default loop.
+	
+	EV_MINPRI
+	EV_MAXPRI
+	
+		The range of allowed priorities. EV_MINPRI must be smaller or equal to
+EV_MAXPRI, but otherwise there are no non-obvious limitations. You can
+provide for more priorities by overriding those symbols (usually defined
+to be -2 and 2, respectively).
+		When doing priority-based operations, libev usually has to linearly search
+all the priorities, so having many of them (hundreds) uses a lot of space
+and time, so using the defaults of five priorities (-2 .. +2) is usually
+fine.
+		If your embedding app does not need any priorities, defining these both to
+0 will save some memory and cpu.
 	
 	EV_PERIODIC_ENABLE
 	
@@ -2224,16 +2396,48 @@ that everybody includes and which overrides some configure choices:
 		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 ev_default_init.
+		All of the following are about amortised time: If an array needs to be
+extended, libev needs to realloc and move the whole array, but this
+happens asymptotically never with higher number of elements, so O(1) might
+mean it might do a lengthy realloc operation in rare cases, but on average
+it is much faster and asymptotically approaches constant time.
 		
 			

 				Starting and stopping timer/periodic watchers: O(log skipped_other_timers)
+				
+					This means that, when you have a watcher that triggers in one hour and
+there are 100 watchers that would trigger before that then inserting will
+have to skip those 100 watchers.
+				
 				Changing timer/periodic watchers (by autorepeat, again): O(log skipped_other_timers)
+				
+					That means that for changing a timer costs less than removing/adding them
+as only the relative motion in the event queue has to be paid for.
+				
 				Starting io/check/prepare/idle/signal/child watchers: O(1)
-				Stopping check/prepare/idle watchers: O(1)
+				
+					These just add the watcher into an array or at the head of a list.
+=item Stopping check/prepare/idle watchers: O(1)
+				
 				Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))
+				
+					These watchers are stored in lists then need to be walked to find the
+correct watcher to remove. The lists are usually short (you don't usually
+have many watchers waiting for the same fd or signal).
+				
 				Finding the next timer per loop iteration: O(1)
 				Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
+				
+					A change means an I/O watcher gets started or stopped, which requires
+libev to recalculate its status (and possibly tell the kernel).
+				
 				Activating one watcher: O(1)
+				Priority handling: O(number_of_priorities)
+				
+					Priorities are implemented by allocating some space for each
+priority. When doing priority-based operations, libev usually has to
+linearly search all the priorities.
+

DESCRIPTION

MACRO MAGIC