*** empty log message ***

[software/libev.git] / ev.pod

diff --git a/ev.pod b/ev.pod
index 8b57eb449d6ca81e84facd66284cedbd73251dcd..d40456bbde29d5ea0c0070e55bbdd6aebfff4920 100644 (file)
--- a/ev.pod
+++ b/ev.pod
@@ -50,6 +50,10 @@ libev - a high performance full-featured event loop written in C
 
 =head1 DESCRIPTION
 
 
 =head1 DESCRIPTION
 

+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: L<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.
 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.


@@ -65,12 +69,13 @@ watcher.
 
 =head1 FEATURES
 
 
 =head1 FEATURES
 

-Libev supports C<select>, C<poll>, the linux-specific C<epoll>, the
-bsd-specific C<kqueue> and the solaris-specific event port mechanisms
-for file descriptor events (C<ev_io>), relative timers (C<ev_timer>),
-absolute timers with customised rescheduling (C<ev_periodic>), synchronous
-signals (C<ev_signal>), process status change events (C<ev_child>), and
-event watchers dealing with the event loop mechanism itself (C<ev_idle>,
+Libev supports C<select>, C<poll>, the Linux-specific C<epoll>, the
+BSD-specific C<kqueue> and the Solaris-specific event port mechanisms
+for file descriptor events (C<ev_io>), the Linux C<inotify> interface
+(for C<ev_stat>), relative timers (C<ev_timer>), absolute timers
+with customised rescheduling (C<ev_periodic>), synchronous signals
+(C<ev_signal>), process status change events (C<ev_child>), and event
+watchers dealing with the event loop mechanism itself (C<ev_idle>,

 C<ev_embed>, C<ev_prepare> and C<ev_check> watchers) as well as
 file watchers (C<ev_stat>) and even limited support for fork events
 (C<ev_fork>).
 C<ev_embed>, C<ev_prepare> and C<ev_check> watchers) as well as
 file watchers (C<ev_stat>) and even limited support for fork events
 (C<ev_fork>).


@@ -164,13 +169,14 @@ recommended ones.
 
 See the description of C<ev_embed> watchers for more info.
 
 
 See the description of C<ev_embed> watchers for more info.
 

-=item ev_set_allocator (void *(*cb)(void *ptr, size_t size))
+=item ev_set_allocator (void *(*cb)(void *ptr, long size))

 
 

-Sets the allocation function to use (the prototype and semantics are
-identical to the realloc C 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.
+Sets the allocation function to use (the prototype is similar - the
+semantics is identical - to the realloc C 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.

 
 You could override this function in high-availability programs to, say,
 free some memory if it cannot allocate memory, to use a special allocator,
 
 You could override this function in high-availability programs to, say,
 free some memory if it cannot allocate memory, to use a special allocator,


@@ -266,6 +272,26 @@ 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.
 
 useful to try out specific backends to test their performance, or to work
 around bugs.
 

+=item C<EVFLAG_FORKCHECK>
+
+Instead of calling C<ev_default_fork> or C<ev_loop_fork> manually after
+a fork, you can also make libev check for a fork in each iteration by
+enabling this flag.
+
+This works by calling C<getpid ()> on every iteration of the loop,
+and thus this might slow down your event loop if you do a lot of loop
+iterations and little real work, but is usually not noticeable (on my
+Linux system for example, C<getpid> is actually a simple 5-insn sequence
+without a syscall and thus I<very> fast, but my Linux system also has
+C<pthread_atfork> which is even faster).
+
+The big advantage of this flag is that you can forget about fork (and
+forget about forgetting to tell libev about forking) when you use this
+flag.
+
+This flag setting cannot be overriden or specified in the C<LIBEV_FLAGS>
+environment variable.
+

 =item C<EVBACKEND_SELECT>  (value 1, portable select backend)
 
 This is your standard select(2) backend. Not I<completely> standard, as
 =item C<EVBACKEND_SELECT>  (value 1, portable select backend)
 
 This is your standard select(2) backend. Not I<completely> standard, as


@@ -410,6 +436,16 @@ Like C<ev_default_fork>, but acts on an event loop created by
 C<ev_loop_new>. Yes, you have to call this on every allocated event loop
 after fork, and how you do this is entirely your own problem.
 
 C<ev_loop_new>. Yes, you have to call this on every allocated event loop
 after fork, and how you do this is entirely your own problem.
 

+=item unsigned int ev_loop_count (loop)
+
+Returns the count of loop iterations for the loop, which is identical to
+the number of times libev did poll for new events. It starts at C<0> and
+happily wraps around with enough iterations.
+
+This value can sometimes be useful as a generation counter of sorts (it
+"ticks" the number of loop iterations), as it roughly corresponds with
+C<ev_prepare> and C<ev_check> calls.
+

 =item unsigned int ev_backend (loop)
 
 Returns one of the C<EVBACKEND_*> flags indicating the event backend in
 =item unsigned int ev_backend (loop)
 
 Returns one of the C<EVBACKEND_*> flags indicating the event backend in


@@ -714,6 +750,31 @@ Returns the callback currently set on the watcher.
 Change the callback. You can change the callback at virtually any time
 (modulo threads).
 
 Change the callback. You can change the callback at virtually any time
 (modulo threads).
 

+=item ev_set_priority (ev_TYPE *watcher, priority)
+
+=item int ev_priority (ev_TYPE *watcher)
+
+Set and query the priority of the watcher. The priority is a small
+integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>
+(default: C<-2>). Pending watchers with higher priority will be invoked
+before watchers with lower priority, but priority will not keep watchers
+from being executed (except for C<ev_idle> watchers).
+
+This means that priorities are I<only> used for ordering callback
+invocation after new events have been received. This is useful, for
+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 C<ev_idle> watchers, which provide this functionality.
+
+The default priority used by watchers when no priority has been set is
+always C<0>, which is supposed to not be too high and not be too low :).
+
+Setting a priority outside the range of C<EV_MINPRI> to C<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.
+

 =back
 
 
 =back
 
 


@@ -828,7 +889,7 @@ C<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
 
 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).
 
 such as poll (fortunately in our Xlib example, Xlib already does this on
 its own, so its quite safe to use).
 


@@ -916,23 +977,25 @@ timer will not fire more than once per event loop iteration.
 This will act as if the timer timed out and restart it again if it is
 repeating. The exact semantics are:
 
 This will act as if the timer timed out and restart it again if it is
 repeating. The exact semantics are:
 

-If the timer is started but nonrepeating, stop it.
+If the timer is pending, its pending status is cleared.
+
+If the timer is started but nonrepeating, stop it (as if it timed out).

 
 

-If the timer is repeating, either start it if necessary (with the repeat
-value), or reset the running timer to the repeat value.
+If the timer is repeating, either start it if necessary (with the
+C<repeat> value), or reset the running timer to the C<repeat> value.

 
 This sounds a bit complicated, but here is a useful and typical
 
 This sounds a bit complicated, but here is a useful and typical

-example: Imagine you have a tcp connection and you want a so-called
-idle timeout, that is, you want to be called when there have been,
-say, 60 seconds of inactivity on the socket. The easiest way to do
-this is to configure an C<ev_timer> with C<after>=C<repeat>=C<60> and calling
+example: Imagine you have a tcp connection and you want a so-called idle
+timeout, that is, you want to be called when there have been, say, 60
+seconds of inactivity on the socket. The easiest way to do this is to
+configure an C<ev_timer> with a C<repeat> value of C<60> and then call

 C<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
 C<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.
+socket, you can C<ev_timer_stop> the timer, and C<ev_timer_again> will
+automatically restart it if need be.

 
 

-You can also ignore the C<after> value and C<ev_timer_start> altogether
-and only ever use the C<repeat> value:
+That means you can ignore the C<after> value and C<ev_timer_start>
+altogether and only ever use the C<repeat> value and C<ev_timer_again>:

 
    ev_timer_init (timer, callback, 0., 5.);
    ev_timer_again (loop, timer);
 
    ev_timer_init (timer, callback, 0., 5.);
    ev_timer_again (loop, timer);


@@ -943,8 +1006,8 @@ and only ever use the C<repeat> value:
    timer->again = 10.;
    ev_timer_again (loop, timer);
 
    timer->again = 10.;
    ev_timer_again (loop, timer);
 

-This is more efficient then stopping/starting the timer eahc time you want
-to modify its timeout value.
+This is more slightly efficient then stopping/starting the timer each time
+you want to modify its timeout value.

 
 =item ev_tstamp repeat [read-write]
 
 
 =item ev_tstamp repeat [read-write]
 


@@ -1223,6 +1286,9 @@ not exist" is signified by the C<st_nlink> field being zero (which is
 otherwise always forced to be at least one) and all the other fields of
 the stat buffer having unspecified contents.
 
 otherwise always forced to be at least one) and all the other fields of
 the stat buffer having unspecified contents.
 

+The path I<should> be absolute and I<must not> end in a slash. If it is
+relative and your working directory changes, the behaviour is undefined.
+

 Since there is no standard to do this, the portable implementation simply
 calls C<stat (2)> regularly on the path to see if it changed somehow. You
 can specify a recommended polling interval for this case. If you specify
 Since there is no standard to do this, the portable implementation simply
 calls C<stat (2)> regularly on the path to see if it changed somehow. You
 can specify a recommended polling interval for this case. If you specify


@@ -1316,13 +1382,16 @@ Example: Watch C</etc/passwd> for attribute changes.
 
 =head2 C<ev_idle> - when you've got nothing better to do...
 
 
 =head2 C<ev_idle> - when you've got nothing better to do...
 

-Idle watchers trigger events when there are no other 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.
+Idle watchers trigger events when no other events of the same or higher
+priority 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) of the same or higher priority it will not be
+triggered. But when your process is idle (or only lower-priority watchers
+are pending), the idle watchers are being called once per event loop
+iteration - until stopped, that is, or your process receives more events
+and becomes busy again with higher priority stuff.

 
 The most noteworthy effect is that as long as any idle watchers are
 active, the process will not block when waiting for new events.
 
 The most noteworthy effect is that as long as any idle watchers are
 active, the process will not block when waiting for new events.


@@ -1432,7 +1501,8 @@ pseudo-code only of course:
   static void
   adns_prepare_cb (ev_loop *loop, ev_prepare *w, int revents)
   {
   static void
   adns_prepare_cb (ev_loop *loop, ev_prepare *w, int revents)
   {

-    int timeout = 3600000;truct pollfd fds [nfd];
+    int timeout = 3600000;
+    struct pollfd fds [nfd];

     // actual code will need to loop here and realloc etc.
     adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
 
     // actual code will need to loop here and realloc etc.
     adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
 


@@ -1676,12 +1746,21 @@ To use it,
    
   #include <ev++.h>
 
    
   #include <ev++.h>
 

-(it is not installed by default). This automatically includes F<ev.h>
-and puts all of its definitions (many of them macros) into the global
-namespace. All C++ specific things are put into the C<ev> namespace.
+This automatically includes F<ev.h> and puts all of its definitions (many
+of them macros) into the global namespace. All C++ specific things are
+put into the C<ev> namespace. It should support all the same embedding
+options as F<ev.h>, most notably C<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 C<EV_MULTIPLICITY> when embedding libev).

 
 

-It should support all the same embedding options as F<ev.h>, most notably
-C<EV_MULTIPLICITY>.
+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 C<ev> namespace:
 
 
 Here is a list of things available in the C<ev> namespace:
 


@@ -1707,20 +1786,58 @@ All of those classes have these methods:
 
 =over 4
 
 
 =over 4
 

-=item ev::TYPE::TYPE (object *, object::method *)
+=item ev::TYPE::TYPE ()

 
 

-=item ev::TYPE::TYPE (object *, object::method *, struct ev_loop *)
+=item ev::TYPE::TYPE (struct ev_loop *)

 
 =item ev::TYPE::~TYPE
 
 
 =item 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
-C<ev_init> for you, which means you have to call the C<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 C<EV_DEFAULT>.
+
+The constructor calls C<ev_init> for you, which means you have to call the
+C<set> method before starting it.
+
+It will not set a callback, however: You have to call the templated C<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.
 
 
 The destructor automatically stops the watcher if it is active.
 

+=item w->set<class, &class::method> (object *)
+
+This method sets the callback method to call. The method has to have a
+signature of C<void (*)(ev_TYPE &, int)>, it receives the watcher as
+first argument and the C<revents> as second. The object must be given as
+parameter and is stored in the C<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 C<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);
+
+=item w->set (void (*function)(watcher &w, int), void *data = 0)
+
+Also sets a callback, but uses a static method or plain function as
+callback. The optional C<data> argument will be stored in the watcher's
+C<data> member and is free for you to use.
+
+See the method-C<set> above for more details.
+

 =item w->set (struct ev_loop *)
 
 Associates a different C<struct ev_loop> with this watcher. You can only
 =item w->set (struct ev_loop *)
 
 Associates a different C<struct ev_loop> with this watcher. You can only


@@ -1729,13 +1846,14 @@ do this when the watcher is inactive (and not pending either).
 =item w->set ([args])
 
 Basically the same as C<ev_TYPE_set>, with the same args. Must be
 =item w->set ([args])
 
 Basically the same as C<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.

 
 =item w->start ()
 
 
 =item w->start ()
 

-Starts the watcher. Note that there is no C<loop> argument as the
-constructor already takes the loop.
+Starts the watcher. Note that there is no C<loop> argument, as the
+constructor already stores the event loop.

 
 =item w->stop ()
 
 
 =item w->stop ()
 


@@ -1770,9 +1888,10 @@ the constructor.
   }
 
   myclass::myclass (int fd)
   }
 
   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);
   }
 
     io.start (fd, ev::READ);
   }
 


@@ -1780,7 +1899,7 @@ the constructor.
 =head1 MACRO MAGIC
 
 Libev can be compiled with a variety of options, the most fundemantal is
 =head1 MACRO MAGIC
 
 Libev can be compiled with a variety of options, the most fundemantal is

-C<EV_MULTIPLICITY>. This option determines wether (most) functions and
+C<EV_MULTIPLICITY>. This option determines whether (most) functions and

 callbacks have an initial C<struct ev_loop *> argument.
 
 To make it easier to write programs that cope with either variant, the
 callbacks have an initial C<struct ev_loop *> argument.
 
 To make it easier to write programs that cope with either variant, the


@@ -1823,8 +1942,9 @@ loop, if multiple loops are supported ("ev loop default").
 
 =back
 
 
 =back
 

-Example: Declare and initialise a check watcher, working regardless of
-wether multiple loops are supported or not.
+Example: Declare and initialise a check watcher, utilising the above
+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)
 
   static void
   check_cb (EV_P_ ev_timer *w, int revents)


@@ -1837,7 +1957,6 @@ wether multiple loops are supported or not.
   ev_check_start (EV_DEFAULT_ &check);
   ev_loop (EV_DEFAULT_ 0);
 
   ev_check_start (EV_DEFAULT_ &check);
   ev_loop (EV_DEFAULT_ 0);
 

-

 =head1 EMBEDDING
 
 Libev can (and often is) directly embedded into host
 =head1 EMBEDDING
 
 Libev can (and often is) directly embedded into host


@@ -1886,7 +2005,7 @@ in your include path (e.g. in libev/ when using -Ilibev):
 
   ev_win32.c      required on win32 platforms only
 
 
   ev_win32.c      required on win32 platforms only
 

-  ev_select.c     only when select backend is enabled (which is by default)
+  ev_select.c     only when select backend is enabled (which is enabled by default)

   ev_poll.c       only when poll backend is enabled (disabled by default)
   ev_epoll.c      only when the epoll backend is enabled (disabled by default)
   ev_kqueue.c     only when the kqueue backend is enabled (disabled by default)
   ev_poll.c       only when poll backend is enabled (disabled by default)
   ev_epoll.c      only when the epoll backend is enabled (disabled by default)
   ev_kqueue.c     only when the kqueue backend is enabled (disabled by default)


@@ -2059,12 +2178,35 @@ 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.
 
 for multiple event loops and there is no first event loop pointer
 argument. Instead, all functions act on the single default loop.
 

+=item EV_MINPRI
+
+=item EV_MAXPRI
+
+The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to
+C<EV_MAXPRI>, but otherwise there are no non-obvious limitations. You can
+provide for more priorities by overriding those symbols (usually defined
+to be C<-2> and C<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
+C<0> will save some memory and cpu.
+

 =item EV_PERIODIC_ENABLE
 
 If undefined or defined to be C<1>, then periodic timers are supported. If
 defined to be C<0>, then they are not. Disabling them saves a few kB of
 code.
 
 =item EV_PERIODIC_ENABLE
 
 If undefined or defined to be C<1>, then periodic timers are supported. If
 defined to be C<0>, then they are not. Disabling them saves a few kB of
 code.
 

+=item EV_IDLE_ENABLE
+
+If undefined or defined to be C<1>, then idle watchers are supported. If
+defined to be C<0>, then they are not. Disabling them saves a few kB of
+code.
+

 =item EV_EMBED_ENABLE
 
 If undefined or defined to be C<1>, then embed watchers are supported. If
 =item EV_EMBED_ENABLE
 
 If undefined or defined to be C<1>, then embed watchers are supported. If


@@ -2138,12 +2280,17 @@ will be compiled. It is pretty complex because it provides its own header
 file.
 
 The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file
 file.
 
 The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file

-that everybody includes and which overrides some autoconf choices:
+that everybody includes and which overrides some configure choices:

 
 

+  #define EV_MINIMAL 1

   #define EV_USE_POLL 0
   #define EV_MULTIPLICITY 0
   #define EV_USE_POLL 0
   #define EV_MULTIPLICITY 0

-  #define EV_PERIODICS 0
+  #define EV_PERIODIC_ENABLE 0
+  #define EV_STAT_ENABLE 0
+  #define EV_FORK_ENABLE 0

   #define EV_CONFIG_H <config.h>
   #define EV_CONFIG_H <config.h>

+  #define EV_MINPRI 0
+  #define EV_MAXPRI 0

 
   #include "ev++.h"
 
 
   #include "ev++.h"
 


@@ -2159,24 +2306,51 @@ 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 C<ev_default_init>.
 
 libev will be explained. For complexity discussions about backends see the
 documentation for C<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.
+

 =over 4
 
 =item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)
 
 =over 4
 
 =item 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.
+

 =item Changing timer/periodic watchers (by autorepeat, again): O(log skipped_other_timers)
 
 =item 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.
+

 =item Starting io/check/prepare/idle/signal/child watchers: O(1)
 
 =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.

 =item Stopping check/prepare/idle watchers: O(1)
 
 =item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))
 
 =item Stopping check/prepare/idle watchers: O(1)
 
 =item 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).
+

 =item Finding the next timer per loop iteration: O(1)
 
 =item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
 
 =item Finding the next timer per loop iteration: O(1)
 
 =item 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).
+

 =item Activating one watcher: O(1)
 
 =item Activating one watcher: O(1)
 

+=item 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.
+

 =back
 
 
 =back