[ViewVC] Diff of: cvs/libev/ev.3

Comparing libev/ev.3 (file contents):
Revision 1.34 by root, Thu Nov 29 12:21:21 2007 UTC vs.
Revision 1.57 by root, Sat Dec 22 11:49:17 2007 UTC

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-.IX Title ""<STANDARD INPUT>" 1"
+.IX Title "EV 1"
-.TH "<STANDARD INPUT>" 1 "2007-11-29" "perl v5.8.8" "User Contributed Perl Documentation"
+.TH EV 1 "2007-12-22" "perl v5.8.8" "User Contributed Perl Documentation"
 .SH "NAME"
 libev \- a high performance full\-featured event loop written in C
 .SH "SYNOPSIS"
 .IX Header "SYNOPSIS"
 .Vb 1
 \&    return 0;
 \&  }
 .Ve
 .SH "DESCRIPTION"
 .IX Header "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: <http://cvs.schmorp.de/libev/ev.html>.
+.PP
 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.
 .PP
 To do this, it must take more or less complete control over your process
 (or thread) by executing the \fIevent loop\fR handler, and will then
 communicate events via a callback mechanism.
 Libev represents time as a single floating point number, representing the
 (fractional) number of seconds since the (\s-1POSIX\s0) epoch (somewhere near
 the beginning of 1970, details are complicated, don't ask). This type is
 called \f(CW\*(C`ev_tstamp\*(C'\fR, which is what you should use too. It usually aliases
 to the \f(CW\*(C`double\*(C'\fR 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 \f(CW\*(C`stamp\*(C'\fR might indicate, it is also used for time differences
+throughout libev.
 .SH "GLOBAL FUNCTIONS"
 .IX Header "GLOBAL FUNCTIONS"
 These functions can be called anytime, even before initialising the
 library in any way.
 .IP "ev_tstamp ev_time ()" 4
 .IX Item "ev_tstamp ev_time ()"
 Returns the current time as libev would use it. Please note that the
 \&\f(CW\*(C`ev_now\*(C'\fR function is usually faster and also often returns the timestamp
 you actually want to know.
+.IP "ev_sleep (ev_tstamp interval)" 4
+.IX 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 \f(CW\*(C`sleep ()\*(C'\fR.
 .IP "int ev_version_major ()" 4
 .IX Item "int ev_version_major ()"
 .PD 0
 .IP "int ev_version_minor ()" 4
 .IX Item "int ev_version_minor ()"
 .PD
-You can find out the major and minor version numbers of the library
+You can find out the major and minor \s-1ABI\s0 version numbers of the library
 you linked against by calling the functions \f(CW\*(C`ev_version_major\*(C'\fR and
 \&\f(CW\*(C`ev_version_minor\*(C'\fR. If you want, you can compare against the global
 symbols \f(CW\*(C`EV_VERSION_MAJOR\*(C'\fR and \f(CW\*(C`EV_VERSION_MINOR\*(C'\fR, which specify the
 version of the library your program was compiled against.
 .Sp
+These version numbers refer to the \s-1ABI\s0 version of the library, not the
+release version.
+.Sp
 Usually, it's a good idea to terminate if the major versions mismatch,
-as this indicates an incompatible change.  Minor versions are usually
+as this indicates an incompatible change. Minor versions are usually
 compatible to older versions, so a larger minor version alone is usually
 not a problem.
 .Sp
 Example: Make sure we haven't accidentally been linked against the wrong
 version.
 or setgid) then libev will \fInot\fR look at the environment variable
 \&\f(CW\*(C`LIBEV_FLAGS\*(C'\fR. Otherwise (the default), this environment variable will
 override the flags completely if it is found in the environment. This is
 useful to try out specific backends to test their performance, or to work
 around bugs.
+.ie n .IP """EVFLAG_FORKCHECK""" 4
+.el .IP "\f(CWEVFLAG_FORKCHECK\fR" 4
+.IX Item "EVFLAG_FORKCHECK"
+Instead of calling \f(CW\*(C`ev_default_fork\*(C'\fR or \f(CW\*(C`ev_loop_fork\*(C'\fR manually after
+a fork, you can also make libev check for a fork in each iteration by
+enabling this flag.
+.Sp
+This works by calling \f(CW\*(C`getpid ()\*(C'\fR 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, \f(CW\*(C`getpid\*(C'\fR is actually a simple 5\-insn sequence
+without a syscall and thus \fIvery\fR fast, but my Linux system also has
+\&\f(CW\*(C`pthread_atfork\*(C'\fR which is even faster).
+.Sp
+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.
+.Sp
+This flag setting cannot be overriden or specified in the \f(CW\*(C`LIBEV_FLAGS\*(C'\fR
+environment variable.
 .ie n .IP """EVBACKEND_SELECT""  (value 1, portable select backend)" 4
 .el .IP "\f(CWEVBACKEND_SELECT\fR  (value 1, portable select backend)" 4
 .IX Item "EVBACKEND_SELECT  (value 1, portable select backend)"
 This is your standard \fIselect\fR\|(2) backend. Not \fIcompletely\fR standard, as
 libev tries to roll its own fd_set with no limits on the number of fds,
 lot of inactive fds). It scales similarly to select, i.e. O(total_fds).
 .ie n .IP """EVBACKEND_EPOLL""   (value 4, Linux)" 4
 .el .IP "\f(CWEVBACKEND_EPOLL\fR   (value 4, Linux)" 4
 .IX Item "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:
 .Sp
-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, \fIdup()\fRed file descriptors might not work very
+best to avoid that. Also, \f(CW\*(C`dup ()\*(C'\fR'ed file descriptors might not work
-well if you register events for both fds.
+very well if you register events for both fds.
 .Sp
 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.
 .ie n .IP """EVBACKEND_KQUEUE""  (value 8, most \s-1BSD\s0 clones)" 4
 .el .IP "\f(CWEVBACKEND_KQUEUE\fR  (value 8, most \s-1BSD\s0 clones)" 4
 .IX Item "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 \*(L"autodetected\*(R"
+it's completely useless). For this reason it's not being \*(L"autodetected\*(R"
 unless you explicitly specify it explicitly in the flags (i.e. using
-\&\f(CW\*(C`EVBACKEND_KQUEUE\*(C'\fR).
+\&\f(CW\*(C`EVBACKEND_KQUEUE\*(C'\fR) or libev was compiled on a known-to-be-good (\-enough)
+system like NetBSD.
+.Sp
+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 \f(CW\*(C`ev_embed\*(C'\fR watchers for more info.
 .Sp
 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 \f(CW\*(C`EVBACKEND_EPOLL\*(C'\fR, it still adds up to
-incident, so its best to avoid that.
+two event changes per incident, support for \f(CW\*(C`fork ()\*(C'\fR is very bad and it
+drops fds silently in similarly hard-to-detect cases.
 .ie n .IP """EVBACKEND_DEVPOLL"" (value 16, Solaris 8)" 4
 .el .IP "\f(CWEVBACKEND_DEVPOLL\fR (value 16, Solaris 8)" 4
 .IX Item "EVBACKEND_DEVPOLL (value 16, Solaris 8)"
 This is not implemented yet (and might never be).
 .ie n .IP """EVBACKEND_PORT""    (value 32, Solaris 10)" 4
 .el .IP "\f(CWEVBACKEND_PORT\fR    (value 32, Solaris 10)" 4
 .IX Item "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)).
 .Sp
-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.
 .ie n .IP """EVBACKEND_ALL""" 4
 .el .IP "\f(CWEVBACKEND_ALL\fR" 4
 .IX Item "EVBACKEND_ALL"
 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. \f(CW\*(C`ev_is_active\*(C'\fR might still return true. It is your
 responsibility to either stop all watchers cleanly yoursef \fIbefore\fR
 calling this function, or cope with the fact afterwards (which is usually
-the easiest thing, youc na just ignore the watchers and/or \f(CW\*(C`free ()\*(C'\fR them
+the easiest thing, you can just ignore the watchers and/or \f(CW\*(C`free ()\*(C'\fR them
 for example).
+.Sp
+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.
+.Sp
+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
+\&\f(CW\*(C`ev_loop_new\*(C'\fR and \f(CW\*(C`ev_loop_destroy\*(C'\fR).
 .IP "ev_loop_destroy (loop)" 4
 .IX Item "ev_loop_destroy (loop)"
 Like \f(CW\*(C`ev_default_destroy\*(C'\fR, but destroys an event loop created by an
 earlier call to \f(CW\*(C`ev_loop_new\*(C'\fR.
 .IP "ev_default_fork ()" 4
 .IP "ev_loop_fork (loop)" 4
 .IX Item "ev_loop_fork (loop)"
 Like \f(CW\*(C`ev_default_fork\*(C'\fR, but acts on an event loop created by
 \&\f(CW\*(C`ev_loop_new\*(C'\fR. Yes, you have to call this on every allocated event loop
 after fork, and how you do this is entirely your own problem.
+.IP "unsigned int ev_loop_count (loop)" 4
+.IX 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 \f(CW0\fR and
+happily wraps around with enough iterations.
+.Sp
+This value can sometimes be useful as a generation counter of sorts (it
+\&\*(L"ticks\*(R" the number of loop iterations), as it roughly corresponds with
+\&\f(CW\*(C`ev_prepare\*(C'\fR and \f(CW\*(C`ev_check\*(C'\fR calls.
 .IP "unsigned int ev_backend (loop)" 4
 .IX Item "unsigned int ev_backend (loop)"
 Returns one of the \f(CW\*(C`EVBACKEND_*\*(C'\fR flags indicating the event backend in
 use.
 .IP "ev_tstamp ev_now (loop)" 4
 .IX Item "ev_tstamp ev_now (loop)"
 Returns the current \*(L"event loop time\*(R", 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).
 .IP "ev_loop (loop, int flags)" 4
 .IX 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
 events.
 libev watchers. However, a pair of \f(CW\*(C`ev_prepare\*(C'\fR/\f(CW\*(C`ev_check\*(C'\fR watchers is
 usually a better approach for this kind of thing.
 .Sp
 Here are the gory details of what \f(CW\*(C`ev_loop\*(C'\fR does:
 .Sp
-.Vb 18
+.Vb 19
+\&   - Before the first iteration, call any pending watchers.
 \&   * If there are no active watchers (reference count is zero), return.
-\&   - Queue prepare watchers and then call all outstanding watchers.
+\&   - Queue all prepare watchers and then call all outstanding watchers.
 \&   - If we have been forked, recreate the kernel state.
 \&   - Update the kernel state with all outstanding changes.
 \&   - Update the "event loop time".
 \&   - Calculate for how long to block.
 \&   - Block the process, waiting for any events.
 .Sp
 .Vb 2
 \&  ev_ref (loop);
 \&  ev_signal_stop (loop, &exitsig);
 .Ve
+.IP "ev_set_io_collect_interval (loop, ev_tstamp interval)" 4
+.IX Item "ev_set_io_collect_interval (loop, ev_tstamp interval)"
+.PD 0
+.IP "ev_set_timeout_collect_interval (loop, ev_tstamp interval)" 4
+.IX Item "ev_set_timeout_collect_interval (loop, ev_tstamp interval)"
+.PD
+These advanced functions influence the time that libev will spend waiting
+for events. Both are by default \f(CW0\fR, meaning that libev will try to
+invoke timer/periodic callbacks and I/O callbacks with minimum latency.
+.Sp
+Setting these to a higher value (the \f(CW\*(C`interval\*(C'\fR \fImust\fR be >= \f(CW0\fR)
+allows libev to delay invocation of I/O and timer/periodic callbacks to
+increase efficiency of loop iterations.
+.Sp
+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 \s-1CPU\s0 time to poll for new
+events, especially with backends like \f(CW\*(C`select ()\*(C'\fR which have a high
+overhead for the actual polling but can deliver many events at once.
+.Sp
+By setting a higher \fIio collect interval\fR 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 \f(CW\*(C`ev_periodic\*(C'\fR and
+\&\f(CW\*(C`ev_timer\*(C'\fR) will be not affected. Setting this to a non-null bvalue will
+introduce an additional \f(CW\*(C`ev_sleep ()\*(C'\fR call into most loop iterations.
+.Sp
+Likewise, by setting a higher \fItimeout collect interval\fR you allow libev
+to spend more time collecting timeouts, at the expense of increased
+latency (the watcher callback will be called later). \f(CW\*(C`ev_io\*(C'\fR watchers
+will not be affected. Setting this to a non-null value will not introduce
+any overhead in libev.
+.Sp
+Many (busy) programs can usually benefit by setting the io collect
+interval to a value near \f(CW0.1\fR 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 \f(CW0.01\fR,
+as this approsaches the timing granularity of most systems.
 .SH "ANATOMY OF A WATCHER"
 .IX Header "ANATOMY OF A WATCHER"
 A watcher is a structure that you create and register to record your
 interest in some event. For instance, if you want to wait for \s-1STDIN\s0 to
 become readable, you would create an \f(CW\*(C`ev_io\*(C'\fR watcher for that:
 .IP "bool ev_is_pending (ev_TYPE *watcher)" 4
 .IX Item "bool ev_is_pending (ev_TYPE *watcher)"
 Returns a true value iff the watcher is pending, (i.e. it has outstanding
 events but its callback has not yet been invoked). As long as a watcher
 is pending (but not active) you must not call an init function on it (but
-\&\f(CW\*(C`ev_TYPE_set\*(C'\fR is safe) and you must make sure the watcher is available to
+\&\f(CW\*(C`ev_TYPE_set\*(C'\fR is safe), you must not change its priority, and you must
-libev (e.g. you cnanot \f(CW\*(C`free ()\*(C'\fR it).
+make sure the watcher is available to libev (e.g. you cannot \f(CW\*(C`free ()\*(C'\fR
+it).
 .IP "callback ev_cb (ev_TYPE *watcher)" 4
 .IX Item "callback ev_cb (ev_TYPE *watcher)"
 Returns the callback currently set on the watcher.
 .IP "ev_cb_set (ev_TYPE *watcher, callback)" 4
 .IX Item "ev_cb_set (ev_TYPE *watcher, callback)"
 Change the callback. You can change the callback at virtually any time
 (modulo threads).
+.IP "ev_set_priority (ev_TYPE *watcher, priority)" 4
+.IX Item "ev_set_priority (ev_TYPE *watcher, priority)"
+.PD 0
+.IP "int ev_priority (ev_TYPE *watcher)" 4
+.IX Item "int ev_priority (ev_TYPE *watcher)"
+.PD
+Set and query the priority of the watcher. The priority is a small
+integer between \f(CW\*(C`EV_MAXPRI\*(C'\fR (default: \f(CW2\fR) and \f(CW\*(C`EV_MINPRI\*(C'\fR
+(default: \f(CW\*(C`\-2\*(C'\fR). Pending watchers with higher priority will be invoked
+before watchers with lower priority, but priority will not keep watchers
+from being executed (except for \f(CW\*(C`ev_idle\*(C'\fR watchers).
+.Sp
+This means that priorities are \fIonly\fR 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.
+.Sp
+If you need to suppress invocation when higher priority events are pending
+you need to look at \f(CW\*(C`ev_idle\*(C'\fR watchers, which provide this functionality.
+.Sp
+You \fImust not\fR change the priority of a watcher as long as it is active or
+pending.
+.Sp
+The default priority used by watchers when no priority has been set is
+always \f(CW0\fR, which is supposed to not be too high and not be too low :).
+.Sp
+Setting a priority outside the range of \f(CW\*(C`EV_MINPRI\*(C'\fR to \f(CW\*(C`EV_MAXPRI\*(C'\fR is
+fine, as long as you do not mind that the priority value you query might
+or might not have been adjusted to be within valid range.
+.IP "ev_invoke (loop, ev_TYPE *watcher, int revents)" 4
+.IX Item "ev_invoke (loop, ev_TYPE *watcher, int revents)"
+Invoke the \f(CW\*(C`watcher\*(C'\fR with the given \f(CW\*(C`loop\*(C'\fR and \f(CW\*(C`revents\*(C'\fR. Neither
+\&\f(CW\*(C`loop\*(C'\fR nor \f(CW\*(C`revents\*(C'\fR need to be valid as long as the watcher callback
+can deal with that fact.
+.IP "int ev_clear_pending (loop, ev_TYPE *watcher)" 4
+.IX Item "int ev_clear_pending (loop, ev_TYPE *watcher)"
+If the watcher is pending, this function returns clears its pending status
+and returns its \f(CW\*(C`revents\*(C'\fR bitset (as if its callback was invoked). If the
+watcher isn't pending it does nothing and returns \f(CW0\fR.
 .Sh "\s-1ASSOCIATING\s0 \s-1CUSTOM\s0 \s-1DATA\s0 \s-1WITH\s0 A \s-1WATCHER\s0"
 .IX Subsection "ASSOCIATING CUSTOM DATA WITH A WATCHER"
 Each watcher has, by default, a member \f(CW\*(C`void *data\*(C'\fR that you can change
 and read at any time, libev will completely ignore it. This can be used
 to associate arbitrary data with your watcher. If you need more data and
 it is best to always use non-blocking I/O: An extra \f(CW\*(C`read\*(C'\fR(2) returning
 \&\f(CW\*(C`EAGAIN\*(C'\fR is far preferable to a program hanging until some data arrives.
 .PP
 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).
+.PP
+\fIThe special problem of disappearing file descriptors\fR
+.IX Subsection "The special problem of disappearing file descriptors"
+.PP
+Some backends (e.g. kqueue, epoll) need to be told about closing a file
+descriptor (either by calling \f(CW\*(C`close\*(C'\fR explicitly or by any other means,
+such as \f(CW\*(C`dup\*(C'\fR). 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.
+.PP
+To avoid having to explicitly tell libev about such cases, libev follows
+the following policy:  Each time \f(CW\*(C`ev_io_set\*(C'\fR 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 \fIhave\fR to call \f(CW\*(C`ev_io_set\*(C'\fR (or \f(CW\*(C`ev_io_init\*(C'\fR) when you change the
+descriptor even if the file descriptor number itself did not change.
+.PP
+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.
+.PP
+\fIThe special problem of dup'ed file descriptors\fR
+.IX Subsection "The special problem of dup'ed file descriptors"
+.PP
+Some backends (e.g. epoll), cannot register events for file descriptors,
+but only events for the underlying file descriptions. That menas when you
+have \f(CW\*(C`dup ()\*(C'\fR'ed file descriptors and register events for them, only one
+file descriptor might actually receive events.
+.PP
+There is no workaorund possible except not registering events
+for potentially \f(CW\*(C`dup ()\*(C'\fR'ed file descriptors or to resort to
+\&\f(CW\*(C`EVBACKEND_SELECT\*(C'\fR or \f(CW\*(C`EVBACKEND_POLL\*(C'\fR.
+.PP
+\fIThe special problem of fork\fR
+.IX Subsection "The special problem of fork"
+.PP
+Some backends (epoll, kqueue) do not support \f(CW\*(C`fork ()\*(C'\fR at all or exhibit
+useless behaviour. Libev fully supports fork, but needs to be told about
+it in the child.
+.PP
+To support fork in your programs, you either have to call
+\&\f(CW\*(C`ev_default_fork ()\*(C'\fR or \f(CW\*(C`ev_loop_fork ()\*(C'\fR after a fork in the child,
+enable \f(CW\*(C`EVFLAG_FORKCHECK\*(C'\fR, or resort to \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR or
+\&\f(CW\*(C`EVBACKEND_POLL\*(C'\fR.
+.PP
+\fIWatcher-Specific Functions\fR
+.IX Subsection "Watcher-Specific Functions"
 .IP "ev_io_init (ev_io *, callback, int fd, int events)" 4
 .IX Item "ev_io_init (ev_io *, callback, int fd, int events)"
 .PD 0
 .IP "ev_io_set (ev_io *, int fd, int events)" 4
 .IX Item "ev_io_set (ev_io *, int fd, int events)"
 .Ve
 .PP
 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.
+.PP
+\fIWatcher-Specific Functions and Data Members\fR
+.IX Subsection "Watcher-Specific Functions and Data Members"
 .IP "ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)" 4
 .IX Item "ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)"
 .PD 0
 .IP "ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)" 4
 .IX Item "ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)"
 but on wallclock time (absolute time). You can tell a periodic watcher
 to trigger \*(L"at\*(R" some specific point in time. For example, if you tell a
 periodic watcher to trigger in 10 seconds (by specifiying e.g. \f(CW\*(C`ev_now ()
 + 10.\*(C'\fR) and then reset your system clock to the last year, then it will
 take a year to trigger the event (unlike an \f(CW\*(C`ev_timer\*(C'\fR, which would trigger
-roughly 10 seconds later and of course not if you reset your system time
+roughly 10 seconds later).
-again).
 .PP
 They can also be used to implement vastly more complex timers, such as
-triggering an event on eahc midnight, local time.
+triggering an event on each midnight, local time or other, complicated,
+rules.
 .PP
 As with timers, the callback is guarenteed to be invoked only when the
 time (\f(CW\*(C`at\*(C'\fR) has been passed, but if multiple periodic timers become ready
 during the same loop iteration then order of execution is undefined.
+.PP
+\fIWatcher-Specific Functions and Data Members\fR
+.IX Subsection "Watcher-Specific Functions and Data Members"
 .IP "ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)" 4
 .IX Item "ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)"
 .PD 0
 .IP "ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)" 4
 .IX Item "ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)"
 .PD
 Lots of arguments, lets sort it out... There are basically three modes of
 operation, and we will explain them from simplest to complex:
 .RS 4
-.IP "* absolute timer (interval = reschedule_cb = 0)" 4
+.IP "* absolute timer (at = time, interval = reschedule_cb = 0)" 4
-.IX Item "absolute timer (interval = reschedule_cb = 0)"
+.IX Item "absolute timer (at = time, interval = reschedule_cb = 0)"
 In this configuration the watcher triggers an event at the wallclock time
 \&\f(CW\*(C`at\*(C'\fR and doesn't repeat. It will not adjust when a time jump occurs,
 that is, if it is to be run at January 1st 2011 then it will run when the
 system time reaches or surpasses this time.
-.IP "* non-repeating interval timer (interval > 0, reschedule_cb = 0)" 4
+.IP "* non-repeating interval timer (at = offset, interval > 0, reschedule_cb = 0)" 4
-.IX Item "non-repeating interval timer (interval > 0, reschedule_cb = 0)"
+.IX Item "non-repeating interval timer (at = offset, interval > 0, reschedule_cb = 0)"
 In this mode the watcher will always be scheduled to time out at the next
-\&\f(CW\*(C`at + N * interval\*(C'\fR time (for some integer N) and then repeat, regardless
+\&\f(CW\*(C`at + N * interval\*(C'\fR time (for some integer N, which can also be negative)
-of any time jumps.
+and then repeat, regardless of any time jumps.
 .Sp
 This can be used to create timers that do not drift with respect to system
 time:
 .Sp
 .Vb 1
 by 3600.
 .Sp
 Another way to think about it (for the mathematically inclined) is that
 \&\f(CW\*(C`ev_periodic\*(C'\fR will try to run the callback in this mode at the next possible
 time where \f(CW\*(C`time = at (mod interval)\*(C'\fR, regardless of any time jumps.
+.Sp
+For numerical stability it is preferable that the \f(CW\*(C`at\*(C'\fR value is near
+\&\f(CW\*(C`ev_now ()\*(C'\fR (the current time), but there is no range requirement for
+this value.
-.IP "* manual reschedule mode (reschedule_cb = callback)" 4
+.IP "* manual reschedule mode (at and interval ignored, reschedule_cb = callback)" 4
-.IX Item "manual reschedule mode (reschedule_cb = callback)"
+.IX Item "manual reschedule mode (at and interval ignored, reschedule_cb = callback)"
 In this mode the values for \f(CW\*(C`interval\*(C'\fR and \f(CW\*(C`at\*(C'\fR are both being
 ignored. Instead, each time the periodic watcher gets scheduled, the
 reschedule callback will be called with the watcher as first, and the
 current time as second argument.
 .Sp
 \&\s-1NOTE:\s0 \fIThis callback \s-1MUST\s0 \s-1NOT\s0 stop or destroy any periodic watcher,
 ever, or make any event loop modifications\fR. If you need to stop it,
 return \f(CW\*(C`now + 1e30\*(C'\fR (or so, fudge fudge) and stop it afterwards (e.g. by
-starting a prepare watcher).
+starting an \f(CW\*(C`ev_prepare\*(C'\fR watcher, which is legal).
 .Sp
 Its prototype is \f(CW\*(C`ev_tstamp (*reschedule_cb)(struct ev_periodic *w,
 ev_tstamp now)\*(C'\fR, e.g.:
 .Sp
 .Vb 4
 .IX Item "ev_periodic_again (loop, ev_periodic *)"
 Simply stops and restarts the periodic watcher again. This is only useful
 when you changed some parameters or the reschedule callback would return
 a different time than the last time it was called (e.g. in a crond like
 program when the crontabs have changed).
+.IP "ev_tstamp offset [read\-write]" 4
+.IX Item "ev_tstamp offset [read-write]"
+When repeating, this contains the offset value, otherwise this is the
+absolute point in time (the \f(CW\*(C`at\*(C'\fR value passed to \f(CW\*(C`ev_periodic_set\*(C'\fR).
+.Sp
+Can be modified any time, but changes only take effect when the periodic
+timer fires or \f(CW\*(C`ev_periodic_again\*(C'\fR is being called.
 .IP "ev_tstamp interval [read\-write]" 4
 .IX Item "ev_tstamp interval [read-write]"
 The current interval value. Can be modified any time, but changes only
 take effect when the periodic timer fires or \f(CW\*(C`ev_periodic_again\*(C'\fR is being
 called.
 .IP "ev_tstamp (*reschedule_cb)(struct ev_periodic *w, ev_tstamp now) [read\-write]" 4
 .IX Item "ev_tstamp (*reschedule_cb)(struct ev_periodic *w, ev_tstamp now) [read-write]"
 The current reschedule callback, or \f(CW0\fR, if this functionality is
 switched off. Can be changed any time, but changes only take effect when
 the periodic timer fires or \f(CW\*(C`ev_periodic_again\*(C'\fR is being called.
+.IP "ev_tstamp at [read\-only]" 4
+.IX Item "ev_tstamp at [read-only]"
+When active, contains the absolute time that the watcher is supposed to
+trigger next.
 .PP
 Example: Call a callback every hour, or, more precisely, whenever the
 system clock is divisible by 3600. The callback invocation times have
 potentially a lot of jittering, but good long-term stability.
 .PP
 first watcher gets started will libev actually register a signal watcher
 with the kernel (thus it coexists with your own signal handlers as long
 as you don't register any with libev). Similarly, when the last signal
 watcher for a signal is stopped libev will reset the signal handler to
 \&\s-1SIG_DFL\s0 (regardless of what it was set to before).
+.PP
+\fIWatcher-Specific Functions and Data Members\fR
+.IX Subsection "Watcher-Specific Functions and Data Members"
 .IP "ev_signal_init (ev_signal *, callback, int signum)" 4
 .IX Item "ev_signal_init (ev_signal *, callback, int signum)"
 .PD 0
 .IP "ev_signal_set (ev_signal *, int signum)" 4
 .IX Item "ev_signal_set (ev_signal *, int signum)"
 .ie n .Sh """ev_child"" \- watch out for process status changes"
 .el .Sh "\f(CWev_child\fP \- watch out for process status changes"
 .IX Subsection "ev_child - watch out for process status changes"
 Child watchers trigger when your process receives a \s-1SIGCHLD\s0 in response to
 some child status changes (most typically when a child of yours dies).
+.PP
+\fIWatcher-Specific Functions and Data Members\fR
+.IX Subsection "Watcher-Specific Functions and Data Members"
 .IP "ev_child_init (ev_child *, callback, int pid)" 4
 .IX Item "ev_child_init (ev_child *, callback, int pid)"
 .PD 0
 .IP "ev_child_set (ev_child *, int pid)" 4
 .IX Item "ev_child_set (ev_child *, int pid)"
 reader). Inotify will be used to give hints only and should not change the
 semantics of \f(CW\*(C`ev_stat\*(C'\fR 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.
+.PP
+\fIWatcher-Specific Functions and Data Members\fR
+.IX Subsection "Watcher-Specific Functions and Data Members"
 .IP "ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)" 4
 .IX Item "ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)"
 .PD 0
 .IP "ev_stat_set (ev_stat *, const char *path, ev_tstamp interval)" 4
 .IX Item "ev_stat_set (ev_stat *, const char *path, ev_tstamp interval)"
 \&  ev_stat_start (loop, &passwd);
 .Ve
 .ie n .Sh """ev_idle"" \- when you've got nothing better to do..."
 .el .Sh "\f(CWev_idle\fP \- when you've got nothing better to do..."
 .IX Subsection "ev_idle - when you've got nothing better to do..."
-Idle watchers trigger events when there are no other events are pending
+Idle watchers trigger events when no other events of the same or higher
-(prepare, check and other idle watchers do not count). That is, as long
+priority are pending (prepare, check and other idle watchers do not
-as your process is busy handling sockets or timeouts (or even signals,
+count).
-imagine) it will not be triggered. But when your process is idle all idle
+.PP
-watchers are being called again and again, once per event loop iteration \-
+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
-until stopped, that is, or your process receives more events and becomes
+iteration \- until stopped, that is, or your process receives more events
-busy.
+and becomes busy again with higher priority stuff.
 .PP
 The most noteworthy effect is that as long as any idle watchers are
 active, the process will not block when waiting for new events.
 .PP
 Apart from keeping your process non-blocking (which is a useful
 effect on its own sometimes), idle watchers are a good place to do
 \&\*(L"pseudo\-background processing\*(R", or delay processing stuff to after the
 event loop has handled all outstanding events.
+.PP
+\fIWatcher-Specific Functions and Data Members\fR
+.IX Subsection "Watcher-Specific Functions and Data Members"
 .IP "ev_idle_init (ev_signal *, callback)" 4
 .IX Item "ev_idle_init (ev_signal *, callback)"
 Initialises and configures the idle watcher \- it has no parameters of any
 kind. There is a \f(CW\*(C`ev_idle_set\*(C'\fR macro, but using it is utterly pointless,
 believe me.
 are ready to run (it's actually more complicated: it only runs coroutines
 with priority higher than or equal to the event loop and one coroutine
 of lower priority, but only once, using idle watchers to keep the event
 loop from blocking if lower-priority coroutines are active, thus mapping
 low-priority coroutines to idle/background tasks).
+.PP
+It is recommended to give \f(CW\*(C`ev_check\*(C'\fR watchers highest (\f(CW\*(C`EV_MAXPRI\*(C'\fR)
+priority, to ensure that they are being run before any other watchers
+after the poll. Also, \f(CW\*(C`ev_check\*(C'\fR watchers (and \f(CW\*(C`ev_prepare\*(C'\fR watchers,
+too) should not activate (\*(L"feed\*(R") events into libev. While libev fully
+supports this, they will be called before other \f(CW\*(C`ev_check\*(C'\fR watchers
+did their job. As \f(CW\*(C`ev_check\*(C'\fR watchers are often used to embed other
+(non\-libev) event loops those other event loops might be in an unusable
+state until their \f(CW\*(C`ev_check\*(C'\fR watcher ran (always remind yourself to
+coexist peacefully with others).
+.PP
+\fIWatcher-Specific Functions and Data Members\fR
+.IX Subsection "Watcher-Specific Functions and Data Members"
 .IP "ev_prepare_init (ev_prepare *, callback)" 4
 .IX Item "ev_prepare_init (ev_prepare *, callback)"
 .PD 0
 .IP "ev_check_init (ev_check *, callback)" 4
 .IX Item "ev_check_init (ev_check *, callback)"
 .PD
 Initialises and configures the prepare or check watcher \- they have no
 parameters of any kind. There are \f(CW\*(C`ev_prepare_set\*(C'\fR and \f(CW\*(C`ev_check_set\*(C'\fR
 macros, but using them is utterly, utterly and completely pointless.
 .PP
-Example: To include a library such as adns, you would add \s-1IO\s0 watchers
+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 \f(CW\*(C`EV::ADNS\*(C'\fR that does this, which you could
+use for an actually working example. Another Perl module named \f(CW\*(C`EV::Glib\*(C'\fR
+embeds a Glib main context into libev, and finally, \f(CW\*(C`Glib::EV\*(C'\fR embeds \s-1EV\s0
+into the Glib event loop).
+.PP
+Method 1: Add \s-1IO\s0 watchers and a timeout watcher in a prepare handler,
-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 \f(CW\*(C`ev_clear_pending\*(C'\fR explicitly, as
+the callbacks for the IO/timeout watchers might not have been called yet.
 .PP
 .Vb 2
 \&  static ev_io iow [nfd];
 \&  static ev_timer tw;
 .Ve
 .PP
-.Vb 9
+.Vb 4
 \&  static void
 \&  io_cb (ev_loop *loop, ev_io *w, int revents)
 \&  {
-\&    // set the relevant poll flags
-\&    // could also call adns_processreadable etc. here
-\&    struct pollfd *fd = (struct pollfd *)w->data;
-\&    if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;
-\&    if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;
 \&  }
 .Ve
 .PP
-.Vb 7
+.Vb 8
 \&  // create io watchers for each fd and a timer before blocking
 \&  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 ()));
 .Ve
 .PP
 .Vb 3
 \&    ev_timer_init (&tw, 0, timeout * 1e-3);
 \&    ev_timer_start (loop, &tw);
 .Ve
 .PP
 .Vb 6
-\&    // create on ev_io per pollfd
+\&    // create one ev_io per pollfd
 \&    for (int i = 0; i < nfd; ++i)
 \&      {
 \&        ev_io_init (iow + i, io_cb, fds [i].fd,
 \&          ((fds [i].events & POLLIN ? EV_READ : 0)
 \&           | (fds [i].events & POLLOUT ? EV_WRITE : 0)));
 .Ve
 .PP
-.Vb 5
+.Vb 4
 \&        fds [i].revents = 0;
-\&        iow [i].data = fds + i;
 \&        ev_io_start (loop, iow + i);
 \&      }
 \&  }
 .Ve
 .PP
 \&  adns_check_cb (ev_loop *loop, ev_check *w, int revents)
 \&  {
 \&    ev_timer_stop (loop, &tw);
 .Ve
 .PP
-.Vb 2
+.Vb 8
 \&    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;
+.Ve
+.PP
+.Vb 3
+\&        // now stop the watcher
-\&      ev_io_stop (loop, iow + i);
+\&        ev_io_stop (loop, iow + i);
+\&      }
 .Ve
 .PP
 .Vb 2
 \&    adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
+\&  }
+.Ve
+.PP
+Method 2: This would be just like method 1, but you run \f(CW\*(C`adns_afterpoll\*(C'\fR
+in the prepare watcher and would dispose of the check watcher.
+.PP
+Method 3: If the module to be embedded supports explicit event
+notification (adns does), you can also make use of the actual watcher
+callbacks, and only destroy/create the watchers in the prepare watcher.
+.PP
+.Vb 5
+\&  static void
+\&  timer_cb (EV_P_ ev_timer *w, int revents)
+\&  {
+\&    adns_state ads = (adns_state)w->data;
+\&    update_now (EV_A);
+.Ve
+.PP
+.Vb 2
+\&    adns_processtimeouts (ads, &tv_now);
+\&  }
+.Ve
+.PP
+.Vb 5
+\&  static void
+\&  io_cb (EV_P_ ev_io *w, int revents)
+\&  {
+\&    adns_state ads = (adns_state)w->data;
+\&    update_now (EV_A);
+.Ve
+.PP
+.Vb 3
+\&    if (revents & EV_READ ) adns_processreadable  (ads, w->fd, &tv_now);
+\&    if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now);
+\&  }
+.Ve
+.PP
+.Vb 1
+\&  // do not ever call adns_afterpoll
+.Ve
+.PP
+Method 4: Do not use a prepare or check watcher because the module you
+want to embed is too inflexible to support it. Instead, youc na override
+their poll function.  The drawback with this solution is that the main
+loop is now no longer controllable by \s-1EV\s0. The \f(CW\*(C`Glib::EV\*(C'\fR module does
+this.
+.PP
+.Vb 4
+\&  static gint
+\&  event_poll_func (GPollFD *fds, guint nfds, gint timeout)
+\&  {
+\&    int got_events = 0;
+.Ve
+.PP
+.Vb 2
+\&    for (n = 0; n < nfds; ++n)
+\&      // create/start io watcher that sets the relevant bits in fds[n] and increment got_events
+.Ve
+.PP
+.Vb 2
+\&    if (timeout >= 0)
+\&      // create/start timer
+.Ve
+.PP
+.Vb 2
+\&    // poll
+\&    ev_loop (EV_A_ 0);
+.Ve
+.PP
+.Vb 3
+\&    // stop timer again
+\&    if (timeout >= 0)
+\&      ev_timer_stop (EV_A_ &to);
+.Ve
+.PP
+.Vb 3
+\&    // stop io watchers again - their callbacks should have set
+\&    for (n = 0; n < nfds; ++n)
+\&      ev_io_stop (EV_A_ iow [n]);
+.Ve
+.PP
+.Vb 2
+\&    return got_events;
 \&  }
 .Ve
 .ie n .Sh """ev_embed"" \- when one backend isn't enough..."
 .el .Sh "\f(CWev_embed\fP \- when one backend isn't enough..."
 .IX Subsection "ev_embed - when one backend isn't enough..."
 \&      ev_embed_start (loop_hi, &embed);
 \&    }
 \&  else
 \&    loop_lo = loop_hi;
 .Ve
+.PP
+\fIWatcher-Specific Functions and Data Members\fR
+.IX Subsection "Watcher-Specific Functions and Data Members"
 .IP "ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)" 4
 .IX Item "ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)"
 .PD 0
 .IP "ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)" 4
 .IX Item "ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)"
 .IP "ev_embed_sweep (loop, ev_embed *)" 4
 .IX Item "ev_embed_sweep (loop, ev_embed *)"
 Make a single, non-blocking sweep over the embedded loop. This works
 similarly to \f(CW\*(C`ev_loop (embedded_loop, EVLOOP_NONBLOCK)\*(C'\fR, but in the most
 apropriate way for embedded loops.
-.IP "struct ev_loop *loop [read\-only]" 4
+.IP "struct ev_loop *other [read\-only]" 4
-.IX Item "struct ev_loop *loop [read-only]"
+.IX Item "struct ev_loop *other [read-only]"
 The embedded event loop.
 .ie n .Sh """ev_fork"" \- the audacity to resume the event loop after a fork"
 .el .Sh "\f(CWev_fork\fP \- the audacity to resume the event loop after a fork"
 .IX Subsection "ev_fork - the audacity to resume the event loop after a fork"
 Fork watchers are called when a \f(CW\*(C`fork ()\*(C'\fR was detected (usually because
 \&\f(CW\*(C`ev_default_fork\*(C'\fR or \f(CW\*(C`ev_loop_fork\*(C'\fR). The invocation is done before the
 event loop blocks next and before \f(CW\*(C`ev_check\*(C'\fR watchers are being called,
 and only in the child after the fork. If whoever good citizen calling
 \&\f(CW\*(C`ev_default_fork\*(C'\fR cheats and calls it in the wrong process, the fork
 handlers will be invoked, too, of course.
+.PP
+\fIWatcher-Specific Functions and Data Members\fR
+.IX Subsection "Watcher-Specific Functions and Data Members"
 .IP "ev_fork_init (ev_signal *, callback)" 4
 .IX Item "ev_fork_init (ev_signal *, callback)"
 Initialises and configures the fork watcher \- it has no parameters of any
 kind. There is a \f(CW\*(C`ev_fork_set\*(C'\fR macro, but using it is utterly pointless,
 believe me.
 .PP
 .Vb 1
 \&  #include <ev++.h>
 .Ve
 .PP
-(it is not installed by default). This automatically includes \fIev.h\fR
+This automatically includes \fIev.h\fR and puts all of its definitions (many
-and puts all of its definitions (many of them macros) into the global
+of them macros) into the global namespace. All \*(C+ specific things are
-namespace. All \*(C+ specific things are put into the \f(CW\*(C`ev\*(C'\fR namespace.
+put into the \f(CW\*(C`ev\*(C'\fR namespace. It should support all the same embedding
+options as \fIev.h\fR, most notably \f(CW\*(C`EV_MULTIPLICITY\*(C'\fR.
 .PP
-It should support all the same embedding options as \fIev.h\fR, most notably
+Care has been taken to keep the overhead low. The only data member the \*(C+
-\&\f(CW\*(C`EV_MULTIPLICITY\*(C'\fR.
+classes add (compared to plain C\-style watchers) is the event loop pointer
+that the watcher is associated with (or no additional members at all if
+you disable \f(CW\*(C`EV_MULTIPLICITY\*(C'\fR when embedding libev).
+.PP
+Currently, functions, and static and non-static member functions can be
+used as callbacks. Other types should be easy to add as long as they only
+need one additional pointer for context. If you need support for other
+types of functors please contact the author (preferably after implementing
+it).
 .PP
 Here is a list of things available in the \f(CW\*(C`ev\*(C'\fR namespace:
 .ie n .IP """ev::READ""\fR, \f(CW""ev::WRITE"" etc." 4
 .el .IP "\f(CWev::READ\fR, \f(CWev::WRITE\fR etc." 4
 .IX Item "ev::READ, ev::WRITE etc."
 which is called \f(CW\*(C`ev::sig\*(C'\fR to avoid clashes with the \f(CW\*(C`signal\*(C'\fR macro
 defines by many implementations.
 .Sp
 All of those classes have these methods:
 .RS 4
-.IP "ev::TYPE::TYPE (object *, object::method *)" 4
+.IP "ev::TYPE::TYPE ()" 4
-.IX Item "ev::TYPE::TYPE (object *, object::method *)"
+.IX Item "ev::TYPE::TYPE ()"
 .PD 0
-.IP "ev::TYPE::TYPE (object *, object::method *, struct ev_loop *)" 4
+.IP "ev::TYPE::TYPE (struct ev_loop *)" 4
-.IX Item "ev::TYPE::TYPE (object *, object::method *, struct ev_loop *)"
+.IX Item "ev::TYPE::TYPE (struct ev_loop *)"
 .IP "ev::TYPE::~TYPE" 4
 .IX Item "ev::TYPE::~TYPE"
 .PD
-The constructor takes a pointer to an object and a method pointer to
+The constructor (optionally) takes an event loop to associate the watcher
-the event handler callback to call in this class. The constructor calls
+with. If it is omitted, it will use \f(CW\*(C`EV_DEFAULT\*(C'\fR.
-\&\f(CW\*(C`ev_init\*(C'\fR for you, which means you have to call the \f(CW\*(C`set\*(C'\fR method
+.Sp
-before starting it. If you do not specify a loop then the constructor
+The constructor calls \f(CW\*(C`ev_init\*(C'\fR for you, which means you have to call the
-automatically associates the default loop with this watcher.
+\&\f(CW\*(C`set\*(C'\fR method before starting it.
+.Sp
+It will not set a callback, however: You have to call the templated \f(CW\*(C`set\*(C'\fR
+method to set a callback before you can start the watcher.
+.Sp
+(The reason why you have to use a method is a limitation in \*(C+ which does
+not allow explicit template arguments for constructors).
 .Sp
 The destructor automatically stops the watcher if it is active.
+.IP "w\->set<class, &class::method> (object *)" 4
+.IX Item "w->set<class, &class::method> (object *)"
+This method sets the callback method to call. The method has to have a
+signature of \f(CW\*(C`void (*)(ev_TYPE &, int)\*(C'\fR, it receives the watcher as
+first argument and the \f(CW\*(C`revents\*(C'\fR as second. The object must be given as
+parameter and is stored in the \f(CW\*(C`data\*(C'\fR member of the watcher.
+.Sp
+This method synthesizes efficient thunking code to call your method from
+the C callback that libev requires. If your compiler can inline your
+callback (i.e. it is visible to it at the place of the \f(CW\*(C`set\*(C'\fR call and
+your compiler is good :), then the method will be fully inlined into the
+thunking function, making it as fast as a direct C callback.
+.Sp
+Example: simple class declaration and watcher initialisation
+.Sp
+.Vb 4
+\&  struct myclass
+\&  {
+\&    void io_cb (ev::io &w, int revents) { }
+\&  }
+.Ve
+.Sp
+.Vb 3
+\&  myclass obj;
+\&  ev::io iow;
+\&  iow.set <myclass, &myclass::io_cb> (&obj);
+.Ve
+.IP "w\->set<function> (void *data = 0)" 4
+.IX Item "w->set<function> (void *data = 0)"
+Also sets a callback, but uses a static method or plain function as
+callback. The optional \f(CW\*(C`data\*(C'\fR argument will be stored in the watcher's
+\&\f(CW\*(C`data\*(C'\fR member and is free for you to use.
+.Sp
+The prototype of the \f(CW\*(C`function\*(C'\fR must be \f(CW\*(C`void (*)(ev::TYPE &w, int)\*(C'\fR.
+.Sp
+See the method\-\f(CW\*(C`set\*(C'\fR above for more details.
+.Sp
+Example:
+.Sp
+.Vb 2
+\&  static void io_cb (ev::io &w, int revents) { }
+\&  iow.set <io_cb> ();
+.Ve
 .IP "w\->set (struct ev_loop *)" 4
 .IX Item "w->set (struct ev_loop *)"
 Associates a different \f(CW\*(C`struct ev_loop\*(C'\fR with this watcher. You can only
 do this when the watcher is inactive (and not pending either).
 .IP "w\->set ([args])" 4
 .IX Item "w->set ([args])"
 Basically the same as \f(CW\*(C`ev_TYPE_set\*(C'\fR, with the same args. Must be
-called at least once.  Unlike the C counterpart, an active watcher gets
+called at least once. Unlike the C counterpart, an active watcher gets
-automatically stopped and restarted.
+automatically stopped and restarted when reconfiguring it with this
+method.
 .IP "w\->start ()" 4
 .IX Item "w->start ()"
-Starts the watcher. Note that there is no \f(CW\*(C`loop\*(C'\fR argument as the
+Starts the watcher. Note that there is no \f(CW\*(C`loop\*(C'\fR argument, as the
-constructor already takes the loop.
+constructor already stores the event loop.
 .IP "w\->stop ()" 4
 .IX Item "w->stop ()"
 Stops the watcher if it is active. Again, no \f(CW\*(C`loop\*(C'\fR argument.
-.ie n .IP "w\->again ()       ""ev::timer""\fR, \f(CW""ev::periodic"" only" 4
+.ie n .IP "w\->again () (""ev::timer""\fR, \f(CW""ev::periodic"" only)" 4
-.el .IP "w\->again ()       \f(CWev::timer\fR, \f(CWev::periodic\fR only" 4
+.el .IP "w\->again () (\f(CWev::timer\fR, \f(CWev::periodic\fR only)" 4
-.IX Item "w->again ()       ev::timer, ev::periodic only"
+.IX Item "w->again () (ev::timer, ev::periodic only)"
 For \f(CW\*(C`ev::timer\*(C'\fR and \f(CW\*(C`ev::periodic\*(C'\fR, this invokes the corresponding
 \&\f(CW\*(C`ev_TYPE_again\*(C'\fR function.
-.ie n .IP "w\->sweep ()       ""ev::embed"" only" 4
+.ie n .IP "w\->sweep () (""ev::embed"" only)" 4
-.el .IP "w\->sweep ()       \f(CWev::embed\fR only" 4
+.el .IP "w\->sweep () (\f(CWev::embed\fR only)" 4
-.IX Item "w->sweep ()       ev::embed only"
+.IX Item "w->sweep () (ev::embed only)"
 Invokes \f(CW\*(C`ev_embed_sweep\*(C'\fR.
-.ie n .IP "w\->update ()      ""ev::stat"" only" 4
+.ie n .IP "w\->update () (""ev::stat"" only)" 4
-.el .IP "w\->update ()      \f(CWev::stat\fR only" 4
+.el .IP "w\->update () (\f(CWev::stat\fR only)" 4
-.IX Item "w->update ()      ev::stat only"
+.IX Item "w->update () (ev::stat only)"
 Invokes \f(CW\*(C`ev_stat_stat\*(C'\fR.
 .RE
 .RS 4
 .RE
 .PP
 .Vb 2
 \&    myclass ();
 \&  }
 .Ve
 .PP
-.Vb 6
+.Vb 4
 \&  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);
+.Ve
+.PP
+.Vb 2
 \&    io.start (fd, ev::READ);
 \&  }
 .Ve
 .SH "MACRO MAGIC"
 .IX Header "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
-\&\f(CW\*(C`EV_MULTIPLICITY\*(C'\fR. This option determines wether (most) functions and
+of which is \f(CW\*(C`EV_MULTIPLICITY\*(C'\fR. This option determines whether (most)
-callbacks have an initial \f(CW\*(C`struct ev_loop *\*(C'\fR argument.
+functions and callbacks have an initial \f(CW\*(C`struct ev_loop *\*(C'\fR argument.
 .PP
 To make it easier to write programs that cope with either variant, the
 following macros are defined:
 .ie n .IP """EV_A""\fR, \f(CW""EV_A_""" 4
 .el .IP "\f(CWEV_A\fR, \f(CWEV_A_\fR" 4
 .el .IP "\f(CWEV_DEFAULT\fR, \f(CWEV_DEFAULT_\fR" 4
 .IX Item "EV_DEFAULT, EV_DEFAULT_"
 Similar to the other two macros, this gives you the value of the default
 loop, if multiple loops are supported (\*(L"ev loop default\*(R").
 .PP
-Example: Declare and initialise a check watcher, working regardless of
+Example: Declare and initialise a check watcher, utilising the above
-wether multiple loops are supported or not.
+macros so it will work regardless of whether multiple loops are supported
+or not.
 .PP
 .Vb 5
 \&  static void
 \&  check_cb (EV_P_ ev_timer *w, int revents)
 \&  {
 Libev can (and often is) directly embedded into host
 applications. Examples of applications that embed it include the Deliantra
 Game Server, the \s-1EV\s0 perl module, the \s-1GNU\s0 Virtual Private Ethernet (gvpe)
 and rxvt\-unicode.
 .PP
-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).
 .Sh "\s-1FILESETS\s0"
 .IX Subsection "FILESETS"
 .Vb 1
 \&  ev_win32.c      required on win32 platforms only
 .Ve
 .PP
 .Vb 5
-\&  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_port.c       only when the solaris port backend is enabled (disabled by default)
 .Ve
 .IX Item "EV_USE_MONOTONIC"
 If defined to be \f(CW1\fR, 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 \f(CW\*(C`clock_gettime\*(C'\fR
 function is hiding in (often \fI\-lrt\fR).
 .IP "\s-1EV_USE_REALTIME\s0" 4
 .IX Item "EV_USE_REALTIME"
 If defined to be \f(CW1\fR, 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 \f(CW\*(C`gettimeofday\*(C'\fR by \f(CW\*(C`clock_get
-(CLOCK_REALTIME, ...)\*(C'\fR and will not normally affect correctness. See tzhe note about libraries
+(CLOCK_REALTIME, ...)\*(C'\fR and will not normally affect correctness. See the
-in the description of \f(CW\*(C`EV_USE_MONOTONIC\*(C'\fR, though.
+note about libraries in the description of \f(CW\*(C`EV_USE_MONOTONIC\*(C'\fR, though.
+.IP "\s-1EV_USE_NANOSLEEP\s0" 4
+.IX Item "EV_USE_NANOSLEEP"
+If defined to be \f(CW1\fR, libev will assume that \f(CW\*(C`nanosleep ()\*(C'\fR is available
+and will use it for delays. Otherwise it will use \f(CW\*(C`select ()\*(C'\fR.
 .IP "\s-1EV_USE_SELECT\s0" 4
 .IX Item "EV_USE_SELECT"
 If undefined or defined to be \f(CW1\fR, libev will compile in support for the
 \&\f(CW\*(C`select\*(C'\fR(2) backend. No attempt at autodetection will be done: if no
 other method takes over, select will be it. Otherwise the select backend
 If undefined or defined to \f(CW1\fR, then all event-loop-specific functions
 will have the \f(CW\*(C`struct ev_loop *\*(C'\fR as first argument, and you can create
 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.
+.IP "\s-1EV_MINPRI\s0" 4
+.IX Item "EV_MINPRI"
+.PD 0
+.IP "\s-1EV_MAXPRI\s0" 4
+.IX Item "EV_MAXPRI"
+.PD
+The range of allowed priorities. \f(CW\*(C`EV_MINPRI\*(C'\fR must be smaller or equal to
+\&\f(CW\*(C`EV_MAXPRI\*(C'\fR, but otherwise there are no non-obvious limitations. You can
+provide for more priorities by overriding those symbols (usually defined
+to be \f(CW\*(C`\-2\*(C'\fR and \f(CW2\fR, respectively).
+.Sp
+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.
+.Sp
+If your embedding app does not need any priorities, defining these both to
+\&\f(CW0\fR will save some memory and cpu.
 .IP "\s-1EV_PERIODIC_ENABLE\s0" 4
 .IX Item "EV_PERIODIC_ENABLE"
 If undefined or defined to be \f(CW1\fR, then periodic timers are supported. If
+defined to be \f(CW0\fR, then they are not. Disabling them saves a few kB of
+code.
+.IP "\s-1EV_IDLE_ENABLE\s0" 4
+.IX Item "EV_IDLE_ENABLE"
+If undefined or defined to be \f(CW1\fR, then idle watchers are supported. If
 defined to be \f(CW0\fR, then they are not. Disabling them saves a few kB of
 code.
 .IP "\s-1EV_EMBED_ENABLE\s0" 4
 .IX Item "EV_EMBED_ENABLE"
 If undefined or defined to be \f(CW1\fR, then embed watchers are supported. If
 .IP "ev_set_cb (ev, cb)" 4
 .IX Item "ev_set_cb (ev, cb)"
 .PD
 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 \fIev.v\fR header file for
+definition and a statement, respectively. See the \fIev.h\fR header file for
 their default definitions. One possible use for overriding these is to
 avoid the \f(CW\*(C`struct ev_loop *\*(C'\fR as first argument in all cases, or to use
 method calls instead of plain function calls in \*(C+.
+.Sh "\s-1EXPORTED\s0 \s-1API\s0 \s-1SYMBOLS\s0"
+.IX Subsection "EXPORTED API SYMBOLS"
+If you need to re-export the \s-1API\s0 (e.g. via a dll) and you need a list of
+exported symbols, you can use the provided \fISymbol.*\fR files which list
+all public symbols, one per line:
+.Sp
+.Vb 2
+\&  Symbols.ev      for libev proper
+\&  Symbols.event   for the libevent emulation
+.Ve
+.Sp
+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).
+.Sp
+A sed command like this will create wrapper \f(CW\*(C`#define\*(C'\fR's that you need to
+include before including \fIev.h\fR:
+.Sp
+.Vb 1
+\&   <Symbols.ev sed -e "s/.*/#define & myprefix_&/" >wrap.h
+.Ve
+.Sp
+This would create a file \fIwrap.h\fR which essentially looks like this:
+.Sp
+.Vb 4
+\&   #define ev_backend     myprefix_ev_backend
+\&   #define ev_check_start myprefix_ev_check_start
+\&   #define ev_check_stop  myprefix_ev_check_stop
+\&   ...
+.Ve
 .Sh "\s-1EXAMPLES\s0"
 .IX Subsection "EXAMPLES"
 For a real-world example of a program the includes libev
 verbatim, you can have a look at the \s-1EV\s0 perl module
 (<http://software.schmorp.de/pkg/EV.html>). It has the libev files in
 interface) and \fI\s-1EV\s0.xs\fR (implementation) files. Only the \fI\s-1EV\s0.xs\fR file
 will be compiled. It is pretty complex because it provides its own header
 file.
 .Sp
 The usage in rxvt-unicode is simpler. It has a \fIev_cpp.h\fR header file
-that everybody includes and which overrides some autoconf choices:
+that everybody includes and which overrides some configure choices:
 .Sp
-.Vb 4
+.Vb 9
+\&  #define EV_MINIMAL 1
 \&  #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_MINPRI 0
+\&  #define EV_MAXPRI 0
 .Ve
 .Sp
 .Vb 1
 \&  #include "ev++.h"
 .Ve
 .SH "COMPLEXITIES"
 .IX Header "COMPLEXITIES"
 In this section the complexities of (many of) the algorithms used inside
 libev will be explained. For complexity discussions about backends see the
 documentation for \f(CW\*(C`ev_default_init\*(C'\fR.
+.Sp
+All of the following are about amortised time: If an array needs to be
+extended, libev needs to realloc and move the whole array, but this
+happens asymptotically never with higher number of elements, so O(1) might
+mean it might do a lengthy realloc operation in rare cases, but on average
+it is much faster and asymptotically approaches constant time.
 .RS 4
 .IP "Starting and stopping timer/periodic watchers: O(log skipped_other_timers)" 4
 .IX Item "Starting and stopping timer/periodic watchers: O(log skipped_other_timers)"
-.PD 0
+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.
 .IP "Changing timer/periodic watchers (by autorepeat, again): O(log skipped_other_timers)" 4
 .IX 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.
 .IP "Starting io/check/prepare/idle/signal/child watchers: O(1)" 4
 .IX Item "Starting io/check/prepare/idle/signal/child watchers: O(1)"
-.IP "Stopping check/prepare/idle watchers: O(1)" 4
+These just add the watcher into an array or at the head of a list.
-.IX Item "Stopping check/prepare/idle watchers: O(1)"
+=item Stopping check/prepare/idle watchers: O(1)
 .IP "Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % \s-1EV_PID_HASHSIZE\s0))" 4
 .IX Item "Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))"
+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).
 .IP "Finding the next timer per loop iteration: O(1)" 4
 .IX Item "Finding the next timer per loop iteration: O(1)"
+.PD 0
 .IP "Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)" 4
 .IX Item "Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)"
+.PD
+A change means an I/O watcher gets started or stopped, which requires
+libev to recalculate its status (and possibly tell the kernel).
 .IP "Activating one watcher: O(1)" 4
 .IX Item "Activating one watcher: O(1)"
+.PD 0
+.IP "Priority handling: O(number_of_priorities)" 4
+.IX Item "Priority handling: O(number_of_priorities)"
+.PD
+Priorities are implemented by allocating some space for each
+priority. When doing priority-based operations, libev usually has to
+linearly search all the priorities.
 .RE
 .RS 4
-.PD
 .SH "AUTHOR"
 .IX Header "AUTHOR"
 Marc Lehmann <libev@schmorp.de>.

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Revision 1.57 by root, Sat Dec 22 11:49:17 2007 UTC