[ViewVC] Diff of: cvs/libev/ev.pod

Comparing libev/ev.pod (file contents):
Revision 1.74 by root, Sat Dec 8 14:12:08 2007 UTC vs.
Revision 1.110 by root, Tue Dec 25 07:05:45 2007 UTC

 =head1 SYNOPSIS
   #include <ev.h>
-=head1 EXAMPLE PROGRAM
+=head2 EXAMPLE PROGRAM
   #include <ev.h>
   ev_io stdin_watcher;
   ev_timer timeout_watcher;
 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
+file descriptor being readable or a timeout occurring), and it will manage
 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 I<event loop> handler, and will then
 communicate events via a callback mechanism.
 You register interest in certain events by registering so-called I<event
 watchers>, which are relatively small C structures you initialise with the
 details of the event, and then hand it over to libev by I<starting> the
 watcher.
-=head1 FEATURES
+=head2 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>), the Linux C<inotify> interface
 (for C<ev_stat>), relative timers (C<ev_timer>), absolute timers
 It also is quite fast (see this
 L<benchmark|http://libev.schmorp.de/bench.html> comparing it to libevent
 for example).
-=head1 CONVENTIONS
+=head2 CONVENTIONS
 Libev is very configurable. In this manual the default configuration will
 be described, which supports multiple event loops. For more info about
 various configuration options please have a look at B<EMBED> section in
 this manual. If libev was configured without support for multiple event
 loops, then all functions taking an initial argument of name C<loop>
 (which is always of type C<struct ev_loop *>) will not have this argument.
-=head1 TIME REPRESENTATION
+=head2 TIME REPRESENTATION
 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 C<ev_tstamp>, which is what you should use too. It usually aliases
 to the C<double> type in C, and when you need to do any calculations on
-it, you should treat it as such.
+it, you should treat it as some floatingpoint value. Unlike the name
+component C<stamp> might indicate, it is also used for time differences
+throughout libev.
 =head1 GLOBAL FUNCTIONS
 These functions can be called anytime, even before initialising the
 library in any way.
 Returns the current time as libev would use it. Please note that the
 C<ev_now> function is usually faster and also often returns the timestamp
 you actually want to know.
+=item ev_sleep (ev_tstamp interval)
+Sleep for the given interval: The current thread will be blocked until
+either it is interrupted or the given time interval has passed. Basically
+this is a subsecond-resolution C<sleep ()>.
 =item int ev_version_major ()
 =item 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 C<ev_version_major> and
 C<ev_version_minor>. If you want, you can compare against the global
 symbols C<EV_VERSION_MAJOR> and C<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
 version.
 =item C<EVBACKEND_SELECT>  (value 1, portable select backend)
 This is your standard select(2) backend. Not I<completely> standard, as
 libev tries to roll its own fd_set with no limits on the number of fds,
 but if that fails, expect a fairly low limit on the number of fds when
-using this backend. It doesn't scale too well (O(highest_fd)), but its usually
+using this backend. It doesn't scale too well (O(highest_fd)), but its
-the fastest backend for a low number of fds.
+usually the fastest backend for a low number of (low-numbered :) fds.
+To get good performance out of this backend you need a high amount of
+parallelity (most of the file descriptors should be busy). If you are
+writing a server, you should C<accept ()> in a loop to accept as many
+connections as possible during one iteration. You might also want to have
+a look at C<ev_set_io_collect_interval ()> to increase the amount of
+readyness notifications you get per iteration.
 =item C<EVBACKEND_POLL>    (value 2, poll backend, available everywhere except on windows)
-And this is your standard poll(2) backend. It's more complicated than
+And this is your standard poll(2) backend. It's more complicated
-select, but handles sparse fds better and has no artificial limit on the
+than select, but handles sparse fds better and has no artificial
-number of fds you can use (except it will slow down considerably with a
+limit on the number of fds you can use (except it will slow down
-lot of inactive fds). It scales similarly to select, i.e. O(total_fds).
+considerably with a lot of inactive fds). It scales similarly to select,
+i.e. O(total_fds). See the entry for C<EVBACKEND_SELECT>, above, for
+performance tips.
 =item C<EVBACKEND_EPOLL>   (value 4, Linux)
 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
+but it scales phenomenally better. While poll and select usually scale
-O(total_fds) where n is the total number of fds (or the highest fd), epoll scales
+like O(total_fds) where n is the total number of fds (or the highest fd),
-either O(1) or O(active_fds).
+epoll scales either O(1) or O(active_fds). The epoll design has a number
+of shortcomings, such as silently dropping events in some hard-to-detect
+cases and rewiring a syscall per fd change, no fork support and bad
+support for dup.
-While stopping and starting an I/O watcher in the same iteration will
+While stopping, setting and starting an I/O watcher in the same iteration
-result in some caching, there is still a syscall per such incident
+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
+best to avoid that. Also, C<dup ()>'ed file descriptors might not work
-well if you register events for both fds.
+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.
+Best performance from this backend is achieved by not unregistering all
+watchers for a file descriptor until it has been closed, if possible, i.e.
+keep at least one watcher active per fd at all times.
+While nominally embeddeble in other event loops, this feature is broken in
+all kernel versions tested so far.
 =item C<EVBACKEND_KQUEUE>  (value 8, most BSD clones)
 Kqueue deserves special mention, as at the time of this writing, it
-was broken on all BSDs except NetBSD (usually it doesn't work with
+was broken on all BSDs except NetBSD (usually it doesn't work reliably
-anything but sockets and pipes, except on Darwin, where of course its
+with anything but sockets and pipes, except on Darwin, where of course
-completely useless). For this reason its not being "autodetected"
+it's completely useless). For this reason it's not being "autodetected"
 unless you explicitly specify it explicitly in the flags (i.e. using
-C<EVBACKEND_KQUEUE>).
+C<EVBACKEND_KQUEUE>) or libev was compiled on a known-to-be-good (-enough)
+system like NetBSD.
+You still can embed kqueue into a normal poll or select backend and use it
+only for sockets (after having made sure that sockets work with kqueue on
+the target platform). See C<ev_embed> watchers for more info.
 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
+course). While stopping, setting and starting an I/O watcher does never
-extra syscall as with epoll, it still adds up to four event changes per
+cause an extra syscall as with C<EVBACKEND_EPOLL>, it still adds up to
-incident, so its best to avoid that.
+two event changes per incident, support for C<fork ()> is very bad and it
+drops fds silently in similarly hard-to-detect cases.
+This backend usually performs well under most conditions.
+While nominally embeddable in other event loops, this doesn't work
+everywhere, so you might need to test for this. And since it is broken
+almost everywhere, you should only use it when you have a lot of sockets
+(for which it usually works), by embedding it into another event loop
+(e.g. C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>) and using it only for
+sockets.
 =item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)
-This is not implemented yet (and might never be).
+This is not implemented yet (and might never be, unless you send me an
+implementation). According to reports, C</dev/poll> only supports sockets
+and is not embeddable, which would limit the usefulness of this backend
+immensely.
 =item C<EVBACKEND_PORT>    (value 32, Solaris 10)
-This uses the Solaris 10 port mechanism. As with everything on Solaris,
+This uses the Solaris 10 event 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
+Please note that solaris event ports can deliver 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.
+While this backend scales well, it requires one system call per active
+file descriptor per loop iteration. For small and medium numbers of file
+descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend
+might perform better.
 =item C<EVBACKEND_ALL>
 Try all backends (even potentially broken ones that wouldn't be tried
 with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as
 C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.
+It is definitely not recommended to use this flag.
 =back
 If one or more of these are ored into the flags value, then only these
 backends will be tried (in the reverse order as given here). If none are
 Destroys the default loop again (frees all memory and kernel state
 etc.). None of the active event watchers will be stopped in the normal
 sense, so e.g. C<ev_is_active> might still return true. It is your
 responsibility to either stop all watchers cleanly yoursef I<before>
 calling this function, or cope with the fact afterwards (which is usually
-the easiest thing, youc na just ignore the watchers and/or C<free ()> them
+the easiest thing, you can just ignore the watchers and/or C<free ()> them
 for example).
+Note that certain global state, such as signal state, will not be freed by
+this function, and related watchers (such as signal and child watchers)
+would need to be stopped manually.
+In general it is not advisable to call this function except in the
+rare occasion where you really need to free e.g. the signal handling
+pipe fds. If you need dynamically allocated loops it is better to use
+C<ev_loop_new> and C<ev_loop_destroy>).
 =item ev_loop_destroy (loop)
 Like C<ev_default_destroy>, but destroys an event loop created by an
 earlier call to C<ev_loop_new>.
 Returns the current "event loop time", which is the time the event loop
 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).
+event occurring (or more correctly, libev finding out about it).
 =item ev_loop (loop, int flags)
 Finally, this is it, the event handler. This function usually is called
 after you initialised all your watchers and you want to start handling
 libev watchers. However, a pair of C<ev_prepare>/C<ev_check> watchers is
 usually a better approach for this kind of thing.
 Here are the gory details of what C<ev_loop> does:
+   - 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".
    - Calculate for how long to block.
    - Block the process, waiting for any events.
 Example: For some weird reason, unregister the above signal handler again.
   ev_ref (loop);
   ev_signal_stop (loop, &exitsig);
+=item ev_set_io_collect_interval (loop, ev_tstamp interval)
+=item ev_set_timeout_collect_interval (loop, ev_tstamp interval)
+These advanced functions influence the time that libev will spend waiting
+for events. Both are by default C<0>, meaning that libev will try to
+invoke timer/periodic callbacks and I/O callbacks with minimum latency.
+Setting these to a higher value (the C<interval> I<must> be >= C<0>)
+allows libev to delay invocation of I/O and timer/periodic callbacks to
+increase efficiency of loop iterations.
+The background is that sometimes your program runs just fast enough to
+handle one (or very few) event(s) per loop iteration. While this makes
+the program responsive, it also wastes a lot of CPU time to poll for new
+events, especially with backends like C<select ()> which have a high
+overhead for the actual polling but can deliver many events at once.
+By setting a higher I<io collect interval> you allow libev to spend more
+time collecting I/O events, so you can handle more events per iteration,
+at the cost of increasing latency. Timeouts (both C<ev_periodic> and
+C<ev_timer>) will be not affected. Setting this to a non-null value will
+introduce an additional C<ev_sleep ()> call into most loop iterations.
+Likewise, by setting a higher I<timeout collect interval> you allow libev
+to spend more time collecting timeouts, at the expense of increased
+latency (the watcher callback will be called later). C<ev_io> watchers
+will not be affected. Setting this to a non-null value will not introduce
+any overhead in libev.
+Many (busy) programs can usually benefit by setting the io collect
+interval to a value near C<0.1> or so, which is often enough for
+interactive servers (of course not for games), likewise for timeouts. It
+usually doesn't make much sense to set it to a lower value than C<0.01>,
+as this approsaches the timing granularity of most systems.
 =back
 =head1 ANATOMY OF A WATCHER
 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 C<EVBACKEND_SELECT> and
 C<EVBACKEND_POLL>).
 Another thing you have to watch out for is that it is quite easy to
 play around with an Xlib connection), then you have to seperately re-test
 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).
+=head3 The special problem of disappearing file descriptors
+Some backends (e.g. kqueue, epoll) need to be told about closing a file
+descriptor (either by calling C<close> explicitly or by any other means,
+such as C<dup>). The reason is that you register interest in some file
+descriptor, but when it goes away, the operating system will silently drop
+this interest. If another file descriptor with the same number then is
+registered with libev, there is no efficient way to see that this is, in
+fact, a different file descriptor.
+To avoid having to explicitly tell libev about such cases, libev follows
+the following policy:  Each time C<ev_io_set> is being called, libev
+will assume that this is potentially a new file descriptor, otherwise
+it is assumed that the file descriptor stays the same. That means that
+you I<have> to call C<ev_io_set> (or C<ev_io_init>) when you change the
+descriptor even if the file descriptor number itself did not change.
+This is how one would do it normally anyway, the important point is that
+the libev application should not optimise around libev but should leave
+optimisations to libev.
+=head3 The special problem of dup'ed file descriptors
+Some backends (e.g. epoll), cannot register events for file descriptors,
+but only events for the underlying file descriptions. That means when you
+have C<dup ()>'ed file descriptors or weirder constellations, and register
+events for them, only one file descriptor might actually receive events.
+There is no workaround possible except not registering events
+for potentially C<dup ()>'ed file descriptors, or to resort to
+C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
+=head3 The special problem of fork
+Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit
+useless behaviour. Libev fully supports fork, but needs to be told about
+it in the child.
+To support fork in your programs, you either have to call
+C<ev_default_fork ()> or C<ev_loop_fork ()> after a fork in the child,
+enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or
+C<EVBACKEND_POLL>.
+=head3 Watcher-Specific Functions
 =over 4
 =item ev_io_init (ev_io *, callback, int fd, int events)
 =item ev_io_set (ev_io *, int fd, int events)
    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.
+=head3 Watcher-Specific Functions and Data Members
 =over 4
 =item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
 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 C<ev_timer>, which would trigger
-roughly 10 seconds later and of course not if you reset your system time
+roughly 10 seconds later).
-again).
 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 (C<at>) has been passed, but if multiple periodic timers become ready
 during the same loop iteration then order of execution is undefined.
+=head3 Watcher-Specific Functions and Data Members
 =over 4
 =item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)
 =item ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)
 Lots of arguments, lets sort it out... There are basically three modes of
 operation, and we will explain them from simplest to complex:
 =over 4
-=item * absolute timer (interval = reschedule_cb = 0)
+=item * absolute timer (at = time, interval = reschedule_cb = 0)
 In this configuration the watcher triggers an event at the wallclock time
 C<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.
-=item * non-repeating interval timer (interval > 0, reschedule_cb = 0)
+=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
-C<at + N * interval> time (for some integer N) and then repeat, regardless
+C<at + N * interval> time (for some integer N, which can also be negative)
-of any time jumps.
+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);
 Another way to think about it (for the mathematically inclined) is that
 C<ev_periodic> will try to run the callback in this mode at the next possible
 time where C<time = at (mod interval)>, regardless of any time jumps.
+For numerical stability it is preferable that the C<at> value is near
+C<ev_now ()> (the current time), but there is no range requirement for
+this value.
-=item * manual reschedule mode (reschedule_cb = callback)
+=item * manual reschedule mode (at and interval ignored, reschedule_cb = callback)
 In this mode the values for C<interval> and C<at> 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
 current time as second argument.
 NOTE: I<This callback MUST NOT stop or destroy any periodic watcher,
 ever, or make any event loop modifications>. If you need to stop it,
 return C<now + 1e30> (or so, fudge fudge) and stop it afterwards (e.g. by
-starting a prepare watcher).
+starting an C<ev_prepare> watcher, which is legal).
 Its prototype is C<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)
 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).
+=item ev_tstamp offset [read-write]
+When repeating, this contains the offset value, otherwise this is the
+absolute point in time (the C<at> value passed to C<ev_periodic_set>).
+Can be modified any time, but changes only take effect when the periodic
+timer fires or C<ev_periodic_again> is being called.
 =item ev_tstamp interval [read-write]
 The current interval value. Can be modified any time, but changes only
 take effect when the periodic timer fires or C<ev_periodic_again> is being
 called.
 =item ev_tstamp (*reschedule_cb)(struct ev_periodic *w, ev_tstamp now) [read-write]
 The current reschedule callback, or C<0>, if this functionality is
 switched off. Can be changed any time, but changes only take effect when
 the periodic timer fires or C<ev_periodic_again> is being called.
+=item ev_tstamp at [read-only]
+When active, contains the absolute time that the watcher is supposed to
+trigger next.
 =back
 Example: Call a callback every hour, or, more precisely, whenever the
 system clock is divisible by 3600. The callback invocation times have
 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
 watcher for a signal is stopped libev will reset the signal handler to
 SIG_DFL (regardless of what it was set to before).
+=head3 Watcher-Specific Functions and Data Members
 =over 4
 =item ev_signal_init (ev_signal *, callback, int signum)
 =item ev_signal_set (ev_signal *, int signum)
 =head2 C<ev_child> - watch out for process status changes
 Child watchers trigger when your process receives a SIGCHLD in response to
 some child status changes (most typically when a child of yours dies).
+=head3 Watcher-Specific Functions and Data Members
 =over 4
 =item ev_child_init (ev_child *, callback, int pid)
 semantics of C<ev_stat> watchers, which means that libev sometimes needs
 to fall back to regular polling again even with inotify, but changes are
 usually detected immediately, and if the file exists there will be no
 polling.
+=head3 Inotify
+When C<inotify (7)> support has been compiled into libev (generally only
+available on Linux) and present at runtime, it will be used to speed up
+change detection where possible. The inotify descriptor will be created lazily
+when the first C<ev_stat> watcher is being started.
+Inotify presense does not change the semantics of C<ev_stat> watchers
+except that changes might be detected earlier, and in some cases, to avoid
+making regular C<stat> calls. Even in the presense of inotify support
+there are many cases where libev has to resort to regular C<stat> polling.
+(There is no support for kqueue, as apparently it cannot be used to
+implement this functionality, due to the requirement of having a file
+descriptor open on the object at all times).
+=head3 The special problem of stat time resolution
+The C<stat ()> syscall only supports full-second resolution portably, and
+even on systems where the resolution is higher, many filesystems still
+only support whole seconds.
+That means that, if the time is the only thing that changes, you might
+miss updates: on the first update, C<ev_stat> detects a change and calls
+your callback, which does something. When there is another update within
+the same second, C<ev_stat> will be unable to detect it.
+The solution to this is to delay acting on a change for a second (or till
+the next second boundary), using a roughly one-second delay C<ev_timer>
+(C<ev_timer_set (w, 0., 1.01); ev_timer_again (loop, w)>). The C<.01>
+is added to work around small timing inconsistencies of some operating
+systems.
+=head3 Watcher-Specific Functions and Data Members
 =over 4
 =item ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)
 =item ev_stat_set (ev_stat *, const char *path, ev_tstamp interval)
 =item const char *path [read-only]
 The filesystem path that is being watched.
 =back
+=head3 Examples
 Example: Watch C</etc/passwd> for attribute changes.
   static void
   passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)
   }
   ...
   ev_stat passwd;
-  ev_stat_init (&passwd, passwd_cb, "/etc/passwd");
+  ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);
   ev_stat_start (loop, &passwd);
+Example: Like above, but additionally use a one-second delay so we do not
+miss updates (however, frequent updates will delay processing, too, so
+one might do the work both on C<ev_stat> callback invocation I<and> on
+C<ev_timer> callback invocation).
+  static ev_stat passwd;
+  static ev_timer timer;
+  static void
+  timer_cb (EV_P_ ev_timer *w, int revents)
+  {
+    ev_timer_stop (EV_A_ w);
+    /* now it's one second after the most recent passwd change */
+  }
+  static void
+  stat_cb (EV_P_ ev_stat *w, int revents)
+  {
+    /* reset the one-second timer */
+    ev_timer_again (EV_A_ &timer);
+  }
+  ...
+  ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);
+  ev_stat_start (loop, &passwd);
+  ev_timer_init (&timer, timer_cb, 0., 1.01);
 =head2 C<ev_idle> - when you've got nothing better to do...
 Idle watchers trigger events when no other events of the same or higher
 Apart from keeping your process non-blocking (which is a useful
 effect on its own sometimes), idle watchers are a good place to do
 "pseudo-background processing", or delay processing stuff to after the
 event loop has handled all outstanding events.
+=head3 Watcher-Specific Functions and Data Members
 =over 4
 =item ev_idle_init (ev_signal *, callback)
 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 C<ev_check> watchers highest (C<EV_MAXPRI>)
+priority, to ensure that they are being run before any other watchers
+after the poll. Also, C<ev_check> watchers (and C<ev_prepare> watchers,
+too) should not activate ("feed") events into libev. While libev fully
+supports this, they will be called before other C<ev_check> watchers
+did their job. As C<ev_check> watchers are often used to embed other
+(non-libev) event loops those other event loops might be in an unusable
+state until their C<ev_check> watcher ran (always remind yourself to
+coexist peacefully with others).
+=head3 Watcher-Specific Functions and Data Members
 =over 4
 =item ev_prepare_init (ev_prepare *, callback)
 =item ev_check_init (ev_check *, callback)
 parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>
 macros, but using them is utterly, utterly and completely pointless.
 =back
-Example: To include a library such as adns, you would add IO watchers
+There are a number of principal ways to embed other event loops or modules
-and a timeout watcher in a prepare handler, as required by libadns, and
+into libev. Here are some ideas on how to include libadns into libev
+(there is a Perl module named C<EV::ADNS> that does this, which you could
+use for an actually working example. Another Perl module named C<EV::Glib>
+embeds a Glib main context into libev, and finally, C<Glib::EV> embeds EV
+into the Glib event loop).
+Method 1: Add IO watchers and a timeout watcher in a prepare handler,
-in a check watcher, destroy them and call into libadns. What follows is
+and in a check watcher, destroy them and call into libadns. What follows
-pseudo-code only of course:
+is pseudo-code only of course. This requires you to either use a low
+priority for the check watcher or use C<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
   static void
   adns_prepare_cb (ev_loop *loop, ev_prepare *w, int revents)
     /* the callback is illegal, but won't be called as we stop during check */
     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,
           ((fds [i].events & POLLIN ? EV_READ : 0)
            | (fds [i].events & POLLOUT ? EV_WRITE : 0)));
         fds [i].revents = 0;
-        iow [i].data = fds + i;
         ev_io_start (loop, iow + i);
       }
   }
   // stop all watchers after blocking
   adns_check_cb (ev_loop *loop, ev_check *w, int revents)
   {
     ev_timer_stop (loop, &tw);
     for (int i = 0; i < nfd; ++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);
+        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 C<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 C<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;
   }
 =head2 C<ev_embed> - when one backend isn't enough...
       ev_embed_start (loop_hi, &embed);
     }
   else
     loop_lo = loop_hi;
+=head3 Watcher-Specific Functions and Data Members
 =over 4
 =item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)
 =item ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)
 Make a single, non-blocking sweep over the embedded loop. This works
 similarly to C<ev_loop (embedded_loop, EVLOOP_NONBLOCK)>, but in the most
 apropriate way for embedded loops.
-=item struct ev_loop *loop [read-only]
+=item struct ev_loop *other [read-only]
 The embedded event loop.
 =back
 event loop blocks next and before C<ev_check> watchers are being called,
 and only in the child after the fork. If whoever good citizen calling
 C<ev_default_fork> cheats and calls it in the wrong process, the fork
 handlers will be invoked, too, of course.
+=head3 Watcher-Specific Functions and Data Members
 =over 4
 =item ev_fork_init (ev_signal *, callback)
 Initialises and configures the fork watcher - it has no parameters of any
   myclass obj;
   ev::io iow;
   iow.set <myclass, &myclass::io_cb> (&obj);
-=item w->set (void (*function)(watcher &w, int), void *data = 0)
+=item w->set<function> (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.
+The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.
 See the method-C<set> above for more details.
+Example:
+  static void io_cb (ev::io &w, int revents) { }
+  iow.set <io_cb> ();
 =item w->set (struct ev_loop *)
 Associates a different C<struct ev_loop> with this watcher. You can only
 do this when the watcher is inactive (and not pending either).
 =item w->stop ()
 Stops the watcher if it is active. Again, no C<loop> argument.
-=item w->again ()       C<ev::timer>, C<ev::periodic> only
+=item w->again () (C<ev::timer>, C<ev::periodic> only)
 For C<ev::timer> and C<ev::periodic>, this invokes the corresponding
 C<ev_TYPE_again> function.
-=item w->sweep ()       C<ev::embed> only
+=item w->sweep () (C<ev::embed> only)
 Invokes C<ev_embed_sweep>.
-=item w->update ()      C<ev::stat> only
+=item w->update () (C<ev::stat> only)
 Invokes C<ev_stat_stat>.
 =back
   }
 =head1 MACRO MAGIC
-Libev can be compiled with a variety of options, the most fundemantal is
+Libev can be compiled with a variety of options, the most fundamantal
-C<EV_MULTIPLICITY>. This option determines whether (most) functions and
+of which is C<EV_MULTIPLICITY>. This option determines whether (most)
-callbacks have an initial C<struct ev_loop *> argument.
+functions and callbacks have an initial C<struct ev_loop *> argument.
 To make it easier to write programs that cope with either variant, the
 following macros are defined:
 =over 4
 Libev can (and often is) directly embedded into host
 applications. Examples of applications that embed it include the Deliantra
 Game Server, the EV perl module, the GNU Virtual Private Ethernet (gvpe)
 and rxvt-unicode.
-The goal is to enable you to just copy the neecssary files into your
+The goal is to enable you to just copy the necessary files into your
 source directory without having to change even a single line in them, so
 you can easily upgrade by simply copying (or having a checked-out copy of
 libev somewhere in your source tree).
 =head2 FILESETS
 If defined to be C<1>, libev will try to detect the availability of the
 monotonic clock option at both compiletime and runtime. Otherwise no use
 of the monotonic clock option will be attempted. If you enable this, you
 usually have to link against librt or something similar. Enabling it when
-the functionality isn't available is safe, though, althoguh you have
+the functionality isn't available is safe, though, although you have
 to make sure you link against any libraries where the C<clock_gettime>
 function is hiding in (often F<-lrt>).
 =item EV_USE_REALTIME
 If defined to be C<1>, libev will try to detect the availability of the
 realtime clock option at compiletime (and assume its availability at
 runtime if successful). Otherwise no use of the realtime clock option will
 be attempted. This effectively replaces C<gettimeofday> by C<clock_get
-(CLOCK_REALTIME, ...)> and will not normally affect correctness. See tzhe note about libraries
+(CLOCK_REALTIME, ...)> and will not normally affect correctness. See the
-in the description of C<EV_USE_MONOTONIC>, though.
+note about libraries in the description of C<EV_USE_MONOTONIC>, though.
+=item EV_USE_NANOSLEEP
+If defined to be C<1>, libev will assume that C<nanosleep ()> is available
+and will use it for delays. Otherwise it will use C<select ()>.
 =item EV_USE_SELECT
 If undefined or defined to be C<1>, libev will compile in support for the
 C<select>(2) backend. No attempt at autodetection will be done: if no
 be detected at runtime.
 =item EV_H
 The name of the F<ev.h> header file used to include it. The default if
-undefined is C<< <ev.h> >> in F<event.h> and C<"ev.h"> in F<ev.c>. This
+undefined is C<"ev.h"> in F<event.h> and F<ev.c>. This can be used to
-can be used to virtually rename the F<ev.h> header file in case of conflicts.
+virtually rename the F<ev.h> header file in case of conflicts.
 =item EV_CONFIG_H
 If C<EV_STANDALONE> isn't C<1>, this variable can be used to override
 F<ev.c>'s idea of where to find the F<config.h> file, similarly to
 C<EV_H>, above.
 =item EV_EVENT_H
 Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea
-of how the F<event.h> header can be found.
+of how the F<event.h> header can be found, the dfeault is C<"event.h">.
 =item EV_PROTOTYPES
 If defined to be C<0>, then F<ev.h> will not define any function
 prototypes, but still define all the structs and other symbols. This is
 than enough. If you need to manage thousands of children you might want to
 increase this value (I<must> be a power of two).
 =item EV_INOTIFY_HASHSIZE
-C<ev_staz> watchers use a small hash table to distribute workload by
+C<ev_stat> watchers use a small hash table to distribute workload by
 inotify watch id. The default size is C<16> (or C<1> with C<EV_MINIMAL>),
 usually more than enough. If you need to manage thousands of C<ev_stat>
 watchers you might want to increase this value (I<must> be a power of
 two).
 =item ev_set_cb (ev, cb)
 Can be used to change the callback member declaration in each watcher,
 and the way callbacks are invoked and set. Must expand to a struct member
-definition and a statement, respectively. See the F<ev.v> header file for
+definition and a statement, respectively. See the F<ev.h> header file for
 their default definitions. One possible use for overriding these is to
 avoid the C<struct ev_loop *> as first argument in all cases, or to use
 method calls instead of plain function calls in C++.
+=head2 EXPORTED API SYMBOLS
+If you need to re-export the API (e.g. via a dll) and you need a list of
+exported symbols, you can use the provided F<Symbol.*> files which list
+all public symbols, one per line:
+  Symbols.ev      for libev proper
+  Symbols.event   for the libevent emulation
+This can also be used to rename all public symbols to avoid clashes with
+multiple versions of libev linked together (which is obviously bad in
+itself, but sometimes it is inconvinient to avoid this).
+A sed command like this will create wrapper C<#define>'s that you need to
+include before including F<ev.h>:
+   <Symbols.ev sed -e "s/.*/#define & myprefix_&/" >wrap.h
+This would create a file F<wrap.h> which essentially looks like this:
+   #define ev_backend     myprefix_ev_backend
+   #define ev_check_start myprefix_ev_check_start
+   #define ev_check_stop  myprefix_ev_check_stop
+   ...
 =head2 EXAMPLES
 For a real-world example of a program the includes libev
 verbatim, you can have a look at the EV perl module
 =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.
+have to skip roughly seven (C<ld 100>) of these watchers.
-=item Changing timer/periodic watchers (by autorepeat, again): O(log skipped_other_timers)
+=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)
-That means that for changing a timer costs less than removing/adding them
+That means that 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)
 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))
 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 Finding the next timer in each loop iteration: O(1)
+By virtue of using a binary heap, the next timer is always found at the
+beginning of the storage array.
 =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).
+libev to recalculate its status (and possibly tell the kernel, depending
+on backend and wether C<ev_io_set> was used).
-=item Activating one watcher: O(1)
+=item Activating one watcher (putting it into the pending state): 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.
+linearly search all the priorities, but starting/stopping and activating
+watchers becomes O(1) w.r.t. prioritiy handling.
 =back
 =head1 AUTHOR

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Revision 1.74 by root, Sat Dec 8 14:12:08 2007 UTC vs.
Revision 1.110 by root, Tue Dec 25 07:05:45 2007 UTC