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

Comparing libev/ev.3 (file contents):
Revision 1.76 by root, Wed Jan 7 20:45:52 2009 UTC vs.
Revision 1.79 by root, Fri Jul 17 14:43:38 2009 UTC

-.\" Automatically generated by Pod::Man 2.16 (Pod::Simple 3.05)
+.\" Automatically generated by Pod::Man 2.22 (Pod::Simple 3.07)
 .\"
 .\" Standard preamble:
 .\" ========================================================================
-.de Sh \" Subsection heading
-.br
-.if t .Sp
-.ne 5
-.PP
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-.\" titles (.TH), headers (.SH), subsections (.Sh), items (.Ip), and index
+.\" titles (.TH), headers (.SH), subsections (.SS), items (.Ip), and index
 .\" entries marked with X<> in POD.  Of course, you'll have to process the
 .\" output yourself in some meaningful fashion.
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 .IX Title "LIBEV 3"
-.TH LIBEV 3 "2008-12-14" "libev-3.52" "libev - high performance full featured event loop"
+.TH LIBEV 3 "2009-07-15" "libev-3.7" "libev - high performance full featured event loop"
 .\" For nroff, turn off justification.  Always turn off hyphenation; it makes
 .\" way too many mistakes in technical documents.
 .if n .ad l
 .nh
 .SH "NAME"
 .SH "SYNOPSIS"
 .IX Header "SYNOPSIS"
 .Vb 1
 \&   #include <ev.h>
 .Ve
-.Sh "\s-1EXAMPLE\s0 \s-1PROGRAM\s0"
+.SS "\s-1EXAMPLE\s0 \s-1PROGRAM\s0"
 .IX Subsection "EXAMPLE PROGRAM"
 .Vb 2
 \&   // a single header file is required
 \&   #include <ev.h>
 \&
 \&
 \&     // unloop was called, so exit
 \&     return 0;
 \&   }
 .Ve
-.SH "DESCRIPTION"
+.SH "ABOUT THIS DOCUMENT"
-.IX Header "DESCRIPTION"
+.IX Header "ABOUT THIS DOCUMENT"
+This document documents the libev software package.
+.PP
 The newest version of this document is also available as an html-formatted
 web page you might find easier to navigate when reading it for the first
 time: <http://pod.tst.eu/http://cvs.schmorp.de/libev/ev.pod>.
 .PP
+While this document tries to be as complete as possible in documenting
+libev, its usage and the rationale behind its design, it is not a tutorial
+on event-based programming, nor will it introduce event-based programming
+with libev.
+.PP
+Familarity with event based programming techniques in general is assumed
+throughout this document.
+.SH "ABOUT LIBEV"
+.IX Header "ABOUT LIBEV"
 Libev is an event loop: you register interest in certain events (such as a
 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
 .PP
 You register interest in certain events by registering so-called \fIevent
 watchers\fR, which are relatively small C structures you initialise with the
 details of the event, and then hand it over to libev by \fIstarting\fR the
 watcher.
-.Sh "\s-1FEATURES\s0"
+.SS "\s-1FEATURES\s0"
 .IX Subsection "FEATURES"
 Libev supports \f(CW\*(C`select\*(C'\fR, \f(CW\*(C`poll\*(C'\fR, the Linux-specific \f(CW\*(C`epoll\*(C'\fR, the
 BSD-specific \f(CW\*(C`kqueue\*(C'\fR and the Solaris-specific event port mechanisms
 for file descriptor events (\f(CW\*(C`ev_io\*(C'\fR), the Linux \f(CW\*(C`inotify\*(C'\fR interface
 (for \f(CW\*(C`ev_stat\*(C'\fR), relative timers (\f(CW\*(C`ev_timer\*(C'\fR), absolute timers
 \&\f(CW\*(C`ev_embed\*(C'\fR, \f(CW\*(C`ev_prepare\*(C'\fR and \f(CW\*(C`ev_check\*(C'\fR watchers) as well as
 file watchers (\f(CW\*(C`ev_stat\*(C'\fR) and even limited support for fork events
 (\f(CW\*(C`ev_fork\*(C'\fR).
 .PP
 It also is quite fast (see this
-benchmark comparing it to libevent
+<benchmark> comparing it to libevent
 for example).
-.Sh "\s-1CONVENTIONS\s0"
+.SS "\s-1CONVENTIONS\s0"
 .IX Subsection "CONVENTIONS"
 Libev is very configurable. In this manual the default (and most common)
 configuration will be described, which supports multiple event loops. For
 more info about various configuration options please have a look at
 \&\fB\s-1EMBED\s0\fR section in this manual. If libev was configured without support
 for multiple event loops, then all functions taking an initial argument of
 name \f(CW\*(C`loop\*(C'\fR (which is always of type \f(CW\*(C`ev_loop *\*(C'\fR) will not have
 this argument.
-.Sh "\s-1TIME\s0 \s-1REPRESENTATION\s0"
+.SS "\s-1TIME\s0 \s-1REPRESENTATION\s0"
 .IX Subsection "TIME REPRESENTATION"
-Libev represents time as a single floating point number, representing the
+Libev represents time as a single floating point number, representing
-(fractional) number of seconds since the (\s-1POSIX\s0) epoch (somewhere near
+the (fractional) number of seconds since the (\s-1POSIX\s0) epoch (somewhere
-the beginning of 1970, details are complicated, don't ask). This type is
+near the beginning of 1970, details are complicated, don't ask). This
-called \f(CW\*(C`ev_tstamp\*(C'\fR, which is what you should use too. It usually aliases
+type is called \f(CW\*(C`ev_tstamp\*(C'\fR, which is what you should use too. It usually
-to the \f(CW\*(C`double\*(C'\fR type in C, and when you need to do any calculations on
+aliases to the \f(CW\*(C`double\*(C'\fR type in C. When you need to do any calculations
-it, you should treat it as some floating point value. Unlike the name
+on it, you should treat it as some floating point value. Unlike the name
 component \f(CW\*(C`stamp\*(C'\fR might indicate, it is also used for time differences
 throughout libev.
 .SH "ERROR HANDLING"
 .IX Header "ERROR HANDLING"
 Libev knows three classes of errors: operating system errors, usage errors
 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_loop_depth (loop)" 4
+.IX Item "unsigned int ev_loop_depth (loop)"
+Returns the number of times \f(CW\*(C`ev_loop\*(C'\fR was entered minus the number of
+times \f(CW\*(C`ev_loop\*(C'\fR was exited, in other words, the recursion depth.
+.Sp
+Outside \f(CW\*(C`ev_loop\*(C'\fR, this number is zero. In a callback, this number is
+\&\f(CW1\fR, unless \f(CW\*(C`ev_loop\*(C'\fR was invoked recursively (or from another thread),
+in which case it is higher.
+.Sp
+Leaving \f(CW\*(C`ev_loop\*(C'\fR abnormally (setjmp/longjmp, cancelling the thread
+etc.), doesn't count as exit.
 .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
 This function is rarely useful, but when some event callback runs for a
 very long time without entering the event loop, updating libev's idea of
 the current time is a good idea.
 .Sp
 See also \*(L"The special problem of time updates\*(R" in the \f(CW\*(C`ev_timer\*(C'\fR section.
+.IP "ev_suspend (loop)" 4
+.IX Item "ev_suspend (loop)"
+.PD 0
+.IP "ev_resume (loop)" 4
+.IX Item "ev_resume (loop)"
+.PD
+These two functions suspend and resume a loop, for use when the loop is
+not used for a while and timeouts should not be processed.
+.Sp
+A typical use case would be an interactive program such as a game:  When
+the user presses \f(CW\*(C`^Z\*(C'\fR to suspend the game and resumes it an hour later it
+would be best to handle timeouts as if no time had actually passed while
+the program was suspended. This can be achieved by calling \f(CW\*(C`ev_suspend\*(C'\fR
+in your \f(CW\*(C`SIGTSTP\*(C'\fR handler, sending yourself a \f(CW\*(C`SIGSTOP\*(C'\fR and calling
+\&\f(CW\*(C`ev_resume\*(C'\fR directly afterwards to resume timer processing.
+.Sp
+Effectively, all \f(CW\*(C`ev_timer\*(C'\fR watchers will be delayed by the time spend
+between \f(CW\*(C`ev_suspend\*(C'\fR and \f(CW\*(C`ev_resume\*(C'\fR, and all \f(CW\*(C`ev_periodic\*(C'\fR watchers
+will be rescheduled (that is, they will lose any events that would have
+occured while suspended).
+.Sp
+After calling \f(CW\*(C`ev_suspend\*(C'\fR you \fBmust not\fR call \fIany\fR function on the
+given loop other than \f(CW\*(C`ev_resume\*(C'\fR, and you \fBmust not\fR call \f(CW\*(C`ev_resume\*(C'\fR
+without a previous call to \f(CW\*(C`ev_suspend\*(C'\fR.
+.Sp
+Calling \f(CW\*(C`ev_suspend\*(C'\fR/\f(CW\*(C`ev_resume\*(C'\fR has the side effect of updating the
+event loop time (see \f(CW\*(C`ev_now_update\*(C'\fR).
 .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.
 .Sp
 If you have a watcher you never unregister that should not keep \f(CW\*(C`ev_loop\*(C'\fR
 from returning, call \fIev_unref()\fR after starting, and \fIev_ref()\fR before
 stopping it.
 .Sp
-As an example, libev itself uses this for its internal signal pipe: It is
+As an example, libev itself uses this for its internal signal pipe: It
-not visible to the libev user and should not keep \f(CW\*(C`ev_loop\*(C'\fR from exiting
+is not visible to the libev user and should not keep \f(CW\*(C`ev_loop\*(C'\fR from
-if no event watchers registered by it are active. It is also an excellent
+exiting if no event watchers registered by it are active. It is also an
-way to do this for generic recurring timers or from within third-party
+excellent way to do this for generic recurring timers or from within
-libraries. Just remember to \fIunref after start\fR and \fIref before stop\fR
+third-party libraries. Just remember to \fIunref after start\fR and \fIref
-(but only if the watcher wasn't active before, or was active before,
+before stop\fR (but only if the watcher wasn't active before, or was active
-respectively).
+before, respectively. Note also that libev might stop watchers itself
+(e.g. non-repeating timers) in which case you have to \f(CW\*(C`ev_ref\*(C'\fR
+in the callback).
 .Sp
 Example: Create a signal watcher, but keep it from keeping \f(CW\*(C`ev_loop\*(C'\fR
 running when nothing else is active.
 .Sp
 .Vb 4
 .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 value will
-introduce an additional \f(CW\*(C`ev_sleep ()\*(C'\fR call into most loop iterations.
+introduce an additional \f(CW\*(C`ev_sleep ()\*(C'\fR call into most loop iterations. The
+sleep time ensures that libev will not poll for I/O events more often then
+once per this interval, on average.
 .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/jitter/inexactness (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
 .Sp
 Many (busy) programs can usually benefit by setting the I/O 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 approaches the timing granularity of most systems.
+as this approaches the timing granularity of most systems. Note that if
+you do transactions with the outside world and you can't increase the
+parallelity, then this setting will limit your transaction rate (if you
+need to poll once per transaction and the I/O collect interval is 0.01,
+then you can't do more than 100 transations per second).
 .Sp
 Setting the \fItimeout collect interval\fR can improve the opportunity for
 saving power, as the program will \*(L"bundle\*(R" timer callback invocations that
 are \*(L"near\*(R" in time together, by delaying some, thus reducing the number of
 times the process sleeps and wakes up again. Another useful technique to
 reduce iterations/wake\-ups is to use \f(CW\*(C`ev_periodic\*(C'\fR watchers and make sure
 they fire on, say, one-second boundaries only.
+.Sp
+Example: we only need 0.1s timeout granularity, and we wish not to poll
+more often than 100 times per second:
+.Sp
+.Vb 2
+\&   ev_set_timeout_collect_interval (EV_DEFAULT_UC_ 0.1);
+\&   ev_set_io_collect_interval (EV_DEFAULT_UC_ 0.01);
+.Ve
+.IP "ev_invoke_pending (loop)" 4
+.IX Item "ev_invoke_pending (loop)"
+This call will simply invoke all pending watchers while resetting their
+pending state. Normally, \f(CW\*(C`ev_loop\*(C'\fR does this automatically when required,
+but when overriding the invoke callback this call comes handy.
+.IP "int ev_pending_count (loop)" 4
+.IX Item "int ev_pending_count (loop)"
+Returns the number of pending watchers \- zero indicates that no watchers
+are pending.
+.IP "ev_set_invoke_pending_cb (loop, void (*invoke_pending_cb)(\s-1EV_P\s0))" 4
+.IX Item "ev_set_invoke_pending_cb (loop, void (*invoke_pending_cb)(EV_P))"
+This overrides the invoke pending functionality of the loop: Instead of
+invoking all pending watchers when there are any, \f(CW\*(C`ev_loop\*(C'\fR will call
+this callback instead. This is useful, for example, when you want to
+invoke the actual watchers inside another context (another thread etc.).
+.Sp
+If you want to reset the callback, use \f(CW\*(C`ev_invoke_pending\*(C'\fR as new
+callback.
+.IP "ev_set_loop_release_cb (loop, void (*release)(\s-1EV_P\s0), void (*acquire)(\s-1EV_P\s0))" 4
+.IX Item "ev_set_loop_release_cb (loop, void (*release)(EV_P), void (*acquire)(EV_P))"
+Sometimes you want to share the same loop between multiple threads. This
+can be done relatively simply by putting mutex_lock/unlock calls around
+each call to a libev function.
+.Sp
+However, \f(CW\*(C`ev_loop\*(C'\fR can run an indefinite time, so it is not feasible to
+wait for it to return. One way around this is to wake up the loop via
+\&\f(CW\*(C`ev_unloop\*(C'\fR and \f(CW\*(C`av_async_send\*(C'\fR, another way is to set these \fIrelease\fR
+and \fIacquire\fR callbacks on the loop.
+.Sp
+When set, then \f(CW\*(C`release\*(C'\fR will be called just before the thread is
+suspended waiting for new events, and \f(CW\*(C`acquire\*(C'\fR is called just
+afterwards.
+.Sp
+Ideally, \f(CW\*(C`release\*(C'\fR will just call your mutex_unlock function, and
+\&\f(CW\*(C`acquire\*(C'\fR will just call the mutex_lock function again.
+.Sp
+While event loop modifications are allowed between invocations of
+\&\f(CW\*(C`release\*(C'\fR and \f(CW\*(C`acquire\*(C'\fR (that's their only purpose after all), no
+modifications done will affect the event loop, i.e. adding watchers will
+have no effect on the set of file descriptors being watched, or the time
+waited. USe an \f(CW\*(C`ev_async\*(C'\fR watcher to wake up \f(CW\*(C`ev_loop\*(C'\fR when you want it
+to take note of any changes you made.
+.Sp
+In theory, threads executing \f(CW\*(C`ev_loop\*(C'\fR will be async-cancel safe between
+invocations of \f(CW\*(C`release\*(C'\fR and \f(CW\*(C`acquire\*(C'\fR.
+.Sp
+See also the locking example in the \f(CW\*(C`THREADS\*(C'\fR section later in this
+document.
+.IP "ev_set_userdata (loop, void *data)" 4
+.IX Item "ev_set_userdata (loop, void *data)"
+.PD 0
+.IP "ev_userdata (loop)" 4
+.IX Item "ev_userdata (loop)"
+.PD
+Set and retrieve a single \f(CW\*(C`void *\*(C'\fR associated with a loop. When
+\&\f(CW\*(C`ev_set_userdata\*(C'\fR has never been called, then \f(CW\*(C`ev_userdata\*(C'\fR returns
+\&\f(CW0.\fR
+.Sp
+These two functions can be used to associate arbitrary data with a loop,
+and are intended solely for the \f(CW\*(C`invoke_pending_cb\*(C'\fR, \f(CW\*(C`release\*(C'\fR and
+\&\f(CW\*(C`acquire\*(C'\fR callbacks described above, but of course can be (ab\-)used for
+any other purpose as well.
 .IP "ev_loop_verify (loop)" 4
 .IX Item "ev_loop_verify (loop)"
 This function only does something when \f(CW\*(C`EV_VERIFY\*(C'\fR support has been
 compiled in, which is the default for non-minimal builds. It tries to go
 through all internal structures and checks them for validity. If anything
 \&\f(CW\*(C`ev_fork\*(C'\fR).
 .ie n .IP """EV_ASYNC""" 4
 .el .IP "\f(CWEV_ASYNC\fR" 4
 .IX Item "EV_ASYNC"
 The given async watcher has been asynchronously notified (see \f(CW\*(C`ev_async\*(C'\fR).
+.ie n .IP """EV_CUSTOM""" 4
+.el .IP "\f(CWEV_CUSTOM\fR" 4
+.IX Item "EV_CUSTOM"
+Not ever sent (or otherwise used) by libev itself, but can be freely used
+by libev users to signal watchers (e.g. via \f(CW\*(C`ev_feed_event\*(C'\fR).
 .ie n .IP """EV_ERROR""" 4
 .el .IP "\f(CWEV_ERROR\fR" 4
 .IX Item "EV_ERROR"
 An unspecified error has occurred, the watcher has been stopped. This might
 happen because the watcher could not be properly started because libev
 example it might indicate that a fd is readable or writable, and if your
 callbacks is well-written it can just attempt the operation and cope with
 the error from \fIread()\fR or \fIwrite()\fR. This will not work in multi-threaded
 programs, though, as the fd could already be closed and reused for another
 thing, so beware.
-.Sh "\s-1GENERIC\s0 \s-1WATCHER\s0 \s-1FUNCTIONS\s0"
+.SS "\s-1GENERIC\s0 \s-1WATCHER\s0 \s-1FUNCTIONS\s0"
 .IX Subsection "GENERIC WATCHER FUNCTIONS"
 .ie n .IP """ev_init"" (ev_TYPE *watcher, callback)" 4
 .el .IP "\f(CWev_init\fR (ev_TYPE *watcher, callback)" 4
 .IX Item "ev_init (ev_TYPE *watcher, callback)"
 This macro initialises the generic portion of a watcher. The contents
 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 clamped to the valid range.
+.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
+See \*(L"\s-1WATCHER\s0 \s-1PRIORITY\s0 \s-1MODELS\s0\*(R", below, for a more thorough treatment of
+priorities.
 .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, as both are simply passed through to the
 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.
 .Sp
 Sometimes it can be useful to \*(L"poll\*(R" a watcher instead of waiting for its
 callback to be invoked, which can be accomplished with this function.
-.Sh "\s-1ASSOCIATING\s0 \s-1CUSTOM\s0 \s-1DATA\s0 \s-1WITH\s0 A \s-1WATCHER\s0"
+.SS "\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
 don't want to allocate memory and store a pointer to it in that data
 \&   #include <stddef.h>
 \&
 \&   static void
 \&   t1_cb (EV_P_ ev_timer *w, int revents)
 \&   {
-\&     struct my_biggy big = (struct my_biggy *
+\&     struct my_biggy big = (struct my_biggy *)
 \&       (((char *)w) \- offsetof (struct my_biggy, t1));
 \&   }
 \&
 \&   static void
 \&   t2_cb (EV_P_ ev_timer *w, int revents)
 \&   {
-\&     struct my_biggy big = (struct my_biggy *
+\&     struct my_biggy big = (struct my_biggy *)
 \&       (((char *)w) \- offsetof (struct my_biggy, t2));
 \&   }
 .Ve
+.SS "\s-1WATCHER\s0 \s-1PRIORITY\s0 \s-1MODELS\s0"
+.IX Subsection "WATCHER PRIORITY MODELS"
+Many event loops support \fIwatcher priorities\fR, which are usually small
+integers that influence the ordering of event callback invocation
+between watchers in some way, all else being equal.
+.PP
+In libev, Watcher priorities can be set using \f(CW\*(C`ev_set_priority\*(C'\fR. See its
+description for the more technical details such as the actual priority
+range.
+.PP
+There are two common ways how these these priorities are being interpreted
+by event loops:
+.PP
+In the more common lock-out model, higher priorities \*(L"lock out\*(R" invocation
+of lower priority watchers, which means as long as higher priority
+watchers receive events, lower priority watchers are not being invoked.
+.PP
+The less common only-for-ordering model uses priorities solely to order
+callback invocation within a single event loop iteration: Higher priority
+watchers are invoked before lower priority ones, but they all get invoked
+before polling for new events.
+.PP
+Libev uses the second (only-for-ordering) model for all its watchers
+except for idle watchers (which use the lock-out model).
+.PP
+The rationale behind this is that implementing the lock-out model for
+watchers is not well supported by most kernel interfaces, and most event
+libraries will just poll for the same events again and again as long as
+their callbacks have not been executed, which is very inefficient in the
+common case of one high-priority watcher locking out a mass of lower
+priority ones.
+.PP
+Static (ordering) priorities are most useful when you have two or more
+watchers handling the same resource: a typical usage example is having an
+\&\f(CW\*(C`ev_io\*(C'\fR watcher to receive data, and an associated \f(CW\*(C`ev_timer\*(C'\fR to handle
+timeouts. Under load, data might be received while the program handles
+other jobs, but since timers normally get invoked first, the timeout
+handler will be executed before checking for data. In that case, giving
+the timer a lower priority than the I/O watcher ensures that I/O will be
+handled first even under adverse conditions (which is usually, but not
+always, what you want).
+.PP
+Since idle watchers use the \*(L"lock-out\*(R" model, meaning that idle watchers
+will only be executed when no same or higher priority watchers have
+received events, they can be used to implement the \*(L"lock-out\*(R" model when
+required.
+.PP
+For example, to emulate how many other event libraries handle priorities,
+you can associate an \f(CW\*(C`ev_idle\*(C'\fR watcher to each such watcher, and in
+the normal watcher callback, you just start the idle watcher. The real
+processing is done in the idle watcher callback. This causes libev to
+continously poll and process kernel event data for the watcher, but when
+the lock-out case is known to be rare (which in turn is rare :), this is
+workable.
+.PP
+Usually, however, the lock-out model implemented that way will perform
+miserably under the type of load it was designed to handle. In that case,
+it might be preferable to stop the real watcher before starting the
+idle watcher, so the kernel will not have to process the event in case
+the actual processing will be delayed for considerable time.
+.PP
+Here is an example of an I/O watcher that should run at a strictly lower
+priority than the default, and which should only process data when no
+other events are pending:
+.PP
+.Vb 2
+\&   ev_idle idle; // actual processing watcher
+\&   ev_io io;     // actual event watcher
+\&
+\&   static void
+\&   io_cb (EV_P_ ev_io *w, int revents)
+\&   {
+\&     // stop the I/O watcher, we received the event, but
+\&     // are not yet ready to handle it.
+\&     ev_io_stop (EV_A_ w);
+\&
+\&     // start the idle watcher to ahndle the actual event.
+\&     // it will not be executed as long as other watchers
+\&     // with the default priority are receiving events.
+\&     ev_idle_start (EV_A_ &idle);
+\&   }
+\&
+\&   static void
+\&   idle_cb (EV_P_ ev_idle *w, int revents)
+\&   {
+\&     // actual processing
+\&     read (STDIN_FILENO, ...);
+\&
+\&     // have to start the I/O watcher again, as
+\&     // we have handled the event
+\&     ev_io_start (EV_P_ &io);
+\&   }
+\&
+\&   // initialisation
+\&   ev_idle_init (&idle, idle_cb);
+\&   ev_io_init (&io, io_cb, STDIN_FILENO, EV_READ);
+\&   ev_io_start (EV_DEFAULT_ &io);
+.Ve
+.PP
+In the \*(L"real\*(R" world, it might also be beneficial to start a timer, so that
+low-priority connections can not be locked out forever under load. This
+enables your program to keep a lower latency for important connections
+during short periods of high load, while not completely locking out less
+important ones.
 .SH "WATCHER TYPES"
 .IX Header "WATCHER TYPES"
 This section describes each watcher in detail, but will not repeat
 information given in the last section. Any initialisation/set macros,
 functions and members specific to the watcher type are explained.
 watcher is stopped to your hearts content), or \fI[read\-write]\fR, which
 means you can expect it to have some sensible content while the watcher
 is active, but you can also modify it. Modifying it may not do something
 sensible or take immediate effect (or do anything at all), but libev will
 not crash or malfunction in any way.
-.ie n .Sh """ev_io"" \- is this file descriptor readable or writable?"
+.ie n .SS """ev_io"" \- is this file descriptor readable or writable?"
-.el .Sh "\f(CWev_io\fP \- is this file descriptor readable or writable?"
+.el .SS "\f(CWev_io\fP \- is this file descriptor readable or writable?"
 .IX Subsection "ev_io - is this file descriptor readable or writable?"
 I/O watchers check whether a file descriptor is readable or writable
 in each iteration of the event loop, or, more precisely, when reading
 would not block the process and writing would at least be able to write
 some data. This behaviour is called level-triggering because you keep
 descriptors to non-blocking mode is also usually a good idea (but not
 required if you know what you are doing).
 .PP
 If you cannot use non-blocking mode, then force the use of a
 known-to-be-good backend (at the time of this writing, this includes only
-\&\f(CW\*(C`EVBACKEND_SELECT\*(C'\fR and \f(CW\*(C`EVBACKEND_POLL\*(C'\fR).
+\&\f(CW\*(C`EVBACKEND_SELECT\*(C'\fR and \f(CW\*(C`EVBACKEND_POLL\*(C'\fR). The same applies to file
+descriptors for which non-blocking operation makes no sense (such as
+files) \- libev doesn't guarentee any specific behaviour in that case.
 .PP
 Another thing you have to watch out for is that it is quite easy to
 receive \*(L"spurious\*(R" readiness notifications, that is your callback might
 be called with \f(CW\*(C`EV_READ\*(C'\fR but a subsequent \f(CW\*(C`read\*(C'\fR(2) will actually block
 because there is no data. Not only are some backends known to create a
 \&   ev_io stdin_readable;
 \&   ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
 \&   ev_io_start (loop, &stdin_readable);
 \&   ev_loop (loop, 0);
 .Ve
-.ie n .Sh """ev_timer"" \- relative and optionally repeating timeouts"
+.ie n .SS """ev_timer"" \- relative and optionally repeating timeouts"
-.el .Sh "\f(CWev_timer\fP \- relative and optionally repeating timeouts"
+.el .SS "\f(CWev_timer\fP \- relative and optionally repeating timeouts"
 .IX Subsection "ev_timer - relative and optionally repeating timeouts"
 Timer watchers are simple relative timers that generate an event after a
 given time, and optionally repeating in regular intervals after that.
 .PP
 The timers are based on real time, that is, if you register an event that
 year, it will still time out after (roughly) one hour. \*(L"Roughly\*(R" because
 detecting time jumps is hard, and some inaccuracies are unavoidable (the
 monotonic clock option helps a lot here).
 .PP
 The callback is guaranteed to be invoked only \fIafter\fR its timeout has
-passed, but if multiple timers become ready during the same loop iteration
+passed (not \fIat\fR, so on systems with very low-resolution clocks this
-then order of execution is undefined.
+might introduce a small delay). If multiple timers become ready during the
+same loop iteration then the ones with earlier time-out values are invoked
+before ones of the same priority with later time-out values (but this is
+no longer true when a callback calls \f(CW\*(C`ev_loop\*(C'\fR recursively).
 .PP
 \fIBe smart about timeouts\fR
 .IX Subsection "Be smart about timeouts"
 .PP
 Many real-world problems involve some kind of timeout, usually for error
 member and \f(CW\*(C`ev_timer_again\*(C'\fR.
 .Sp
 At start:
 .Sp
 .Vb 3
-\&   ev_timer_init (timer, callback);
+\&   ev_init (timer, callback);
 \&   timer\->repeat = 60.;
 \&   ev_timer_again (loop, timer);
 .Ve
 .Sp
 Each time there is some activity:
 To start the timer, simply initialise the watcher and set \f(CW\*(C`last_activity\*(C'\fR
 to the current time (meaning we just have some activity :), then call the
 callback, which will \*(L"do the right thing\*(R" and start the timer:
 .Sp
 .Vb 3
-\&   ev_timer_init (timer, callback);
+\&   ev_init (timer, callback);
 \&   last_activity = ev_now (loop);
 \&   callback (loop, timer, EV_TIMEOUT);
 .Ve
 .Sp
 And when there is some activity, simply store the current time in
 .Ve
 .PP
 If the event loop is suspended for a long time, you can also force an
 update of the time returned by \f(CW\*(C`ev_now ()\*(C'\fR by calling \f(CW\*(C`ev_now_update
 ()\*(C'\fR.
+.PP
+\fIThe special problems of suspended animation\fR
+.IX Subsection "The special problems of suspended animation"
+.PP
+When you leave the server world it is quite customary to hit machines that
+can suspend/hibernate \- what happens to the clocks during such a suspend?
+.PP
+Some quick tests made with a Linux 2.6.28 indicate that a suspend freezes
+all processes, while the clocks (\f(CW\*(C`times\*(C'\fR, \f(CW\*(C`CLOCK_MONOTONIC\*(C'\fR) continue
+to run until the system is suspended, but they will not advance while the
+system is suspended. That means, on resume, it will be as if the program
+was frozen for a few seconds, but the suspend time will not be counted
+towards \f(CW\*(C`ev_timer\*(C'\fR when a monotonic clock source is used. The real time
+clock advanced as expected, but if it is used as sole clocksource, then a
+long suspend would be detected as a time jump by libev, and timers would
+be adjusted accordingly.
+.PP
+I would not be surprised to see different behaviour in different between
+operating systems, \s-1OS\s0 versions or even different hardware.
+.PP
+The other form of suspend (job control, or sending a \s-1SIGSTOP\s0) will see a
+time jump in the monotonic clocks and the realtime clock. If the program
+is suspended for a very long time, and monotonic clock sources are in use,
+then you can expect \f(CW\*(C`ev_timer\*(C'\fRs to expire as the full suspension time
+will be counted towards the timers. When no monotonic clock source is in
+use, then libev will again assume a timejump and adjust accordingly.
+.PP
+It might be beneficial for this latter case to call \f(CW\*(C`ev_suspend\*(C'\fR
+and \f(CW\*(C`ev_resume\*(C'\fR in code that handles \f(CW\*(C`SIGTSTP\*(C'\fR, to at least get
+deterministic behaviour in this case (you can do nothing against
+\&\f(CW\*(C`SIGSTOP\*(C'\fR).
 .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)"
 If the timer is repeating, either start it if necessary (with the
 \&\f(CW\*(C`repeat\*(C'\fR value), or reset the running timer to the \f(CW\*(C`repeat\*(C'\fR value.
 .Sp
 This sounds a bit complicated, see \*(L"Be smart about timeouts\*(R", above, for a
 usage example.
+.IP "ev_timer_remaining (loop, ev_timer *)" 4
+.IX Item "ev_timer_remaining (loop, ev_timer *)"
+Returns the remaining time until a timer fires. If the timer is active,
+then this time is relative to the current event loop time, otherwise it's
+the timeout value currently configured.
+.Sp
+That is, after an \f(CW\*(C`ev_timer_set (w, 5, 7)\*(C'\fR, \f(CW\*(C`ev_timer_remaining\*(C'\fR returns
+\&\f(CW5\fR. When the timer is started and one second passes, \f(CW\*(C`ev_timer_remain\*(C'\fR
+will return \f(CW4\fR. When the timer expires and is restarted, it will return
+roughly \f(CW7\fR (likely slightly less as callback invocation takes some time,
+too), and so on.
 .IP "ev_tstamp repeat [read\-write]" 4
 .IX Item "ev_tstamp repeat [read-write]"
 The current \f(CW\*(C`repeat\*(C'\fR value. Will be used each time the watcher times out
 or \f(CW\*(C`ev_timer_again\*(C'\fR is called, and determines the next timeout (if any),
 which is also when any modifications are taken into account.
 \&
 \&   // and in some piece of code that gets executed on any "activity":
 \&   // reset the timeout to start ticking again at 10 seconds
 \&   ev_timer_again (&mytimer);
 .Ve
-.ie n .Sh """ev_periodic"" \- to cron or not to cron?"
+.ie n .SS """ev_periodic"" \- to cron or not to cron?"
-.el .Sh "\f(CWev_periodic\fP \- to cron or not to cron?"
+.el .SS "\f(CWev_periodic\fP \- to cron or not to cron?"
 .IX Subsection "ev_periodic - to cron or not to cron?"
 Periodic watchers are also timers of a kind, but they are very versatile
 (and unfortunately a bit complex).
 .PP
-Unlike \f(CW\*(C`ev_timer\*(C'\fR's, they are not based on real time (or relative time)
+Unlike \f(CW\*(C`ev_timer\*(C'\fR, periodic watchers are not based on real time (or
-but on wall clock time (absolute time). You can tell a periodic watcher
+relative time, the physical time that passes) but on wall clock time
-to trigger after some specific point in time. For example, if you tell a
+(absolute time, the thing you can read on your calender or clock). The
-periodic watcher to trigger in 10 seconds (by specifying e.g. \f(CW\*(C`ev_now ()
+difference is that wall clock time can run faster or slower than real
-+ 10.\*(C'\fR, that is, an absolute time not a delay) and then reset your system
+time, and time jumps are not uncommon (e.g. when you adjust your
-clock to January of the previous year, then it will take more than year
+wrist-watch).
-to trigger the event (unlike an \f(CW\*(C`ev_timer\*(C'\fR, which would still trigger
-roughly 10 seconds later as it uses a relative timeout).
 .PP
+You can tell a periodic watcher to trigger after some specific point
+in time: for example, if you tell a periodic watcher to trigger \*(L"in 10
+seconds\*(R" (by specifying e.g. \f(CW\*(C`ev_now () + 10.\*(C'\fR, that is, an absolute time
+not a delay) and then reset your system clock to January of the previous
+year, then it will take a year or more to trigger the event (unlike an
+\&\f(CW\*(C`ev_timer\*(C'\fR, which would still trigger roughly 10 seconds after starting
+it, as it uses a relative timeout).
+.PP
-\&\f(CW\*(C`ev_periodic\*(C'\fRs can also be used to implement vastly more complex timers,
+\&\f(CW\*(C`ev_periodic\*(C'\fR watchers can also be used to implement vastly more complex
-such as triggering an event on each \*(L"midnight, local time\*(R", or other
+timers, such as triggering an event on each \*(L"midnight, local time\*(R", or
-complicated rules.
+other complicated rules. This cannot be done with \f(CW\*(C`ev_timer\*(C'\fR watchers, as
+those cannot react to time jumps.
 .PP
 As with timers, the callback is guaranteed to be invoked only when the
-time (\f(CW\*(C`at\*(C'\fR) has passed, but if multiple periodic timers become ready
+point in time where it is supposed to trigger has passed. If multiple
-during the same loop iteration, then order of execution is undefined.
+timers become ready during the same loop iteration then the ones with
+earlier time-out values are invoked before ones with later time-out values
+(but this is no longer true when a callback calls \f(CW\*(C`ev_loop\*(C'\fR recursively).
 .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
+.IP "ev_periodic_init (ev_periodic *, callback, ev_tstamp offset, ev_tstamp interval, reschedule_cb)" 4
-.IX Item "ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)"
+.IX Item "ev_periodic_init (ev_periodic *, callback, ev_tstamp offset, ev_tstamp interval, reschedule_cb)"
 .PD 0
-.IP "ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)" 4
+.IP "ev_periodic_set (ev_periodic *, ev_tstamp offset, ev_tstamp interval, reschedule_cb)" 4
-.IX Item "ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)"
+.IX Item "ev_periodic_set (ev_periodic *, ev_tstamp offset, ev_tstamp interval, reschedule_cb)"
 .PD
-Lots of arguments, lets sort it out... There are basically three modes of
+Lots of arguments, let's sort it out... There are basically three modes of
 operation, and we will explain them from simplest to most complex:
 .RS 4
 .IP "\(bu" 4
-absolute timer (at = time, interval = reschedule_cb = 0)
+absolute timer (offset = absolute time, interval = 0, reschedule_cb = 0)
 .Sp
 In this configuration the watcher triggers an event after the wall clock
-time \f(CW\*(C`at\*(C'\fR has passed. It will not repeat and will not adjust when a time
+time \f(CW\*(C`offset\*(C'\fR has passed. It will not repeat and will not adjust when a
-jump occurs, that is, if it is to be run at January 1st 2011 then it will
+time jump occurs, that is, if it is to be run at January 1st 2011 then it
-only run when the system clock reaches or surpasses this time.
+will be stopped and invoked when the system clock reaches or surpasses
+this point in time.
 .IP "\(bu" 4
-repeating interval timer (at = offset, interval > 0, reschedule_cb = 0)
+repeating interval timer (offset = offset within interval, interval > 0, reschedule_cb = 0)
 .Sp
 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, which can also be negative)
+\&\f(CW\*(C`offset + N * interval\*(C'\fR time (for some integer N, which can also be
-and then repeat, regardless of any time jumps.
+negative) and then repeat, regardless of any time jumps. The \f(CW\*(C`offset\*(C'\fR
+argument is merely an offset into the \f(CW\*(C`interval\*(C'\fR periods.
 .Sp
 This can be used to create timers that do not drift with respect to the
-system clock, for example, here is a \f(CW\*(C`ev_periodic\*(C'\fR that triggers each
+system clock, for example, here is an \f(CW\*(C`ev_periodic\*(C'\fR that triggers each
-hour, on the hour:
+hour, on the hour (with respect to \s-1UTC\s0):
 .Sp
 .Vb 1
 \&   ev_periodic_set (&periodic, 0., 3600., 0);
 .Ve
 .Sp
 full hour (\s-1UTC\s0), or more correctly, when the system time is evenly divisible
 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.
+time where \f(CW\*(C`time = offset (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
+For numerical stability it is preferable that the \f(CW\*(C`offset\*(C'\fR value is near
 \&\f(CW\*(C`ev_now ()\*(C'\fR (the current time), but there is no range requirement for
 this value, and in fact is often specified as zero.
 .Sp
 Note also that there is an upper limit to how often a timer can fire (\s-1CPU\s0
 speed for example), so if \f(CW\*(C`interval\*(C'\fR is very small then timing stability
 will of course deteriorate. Libev itself tries to be exact to be about one
 millisecond (if the \s-1OS\s0 supports it and the machine is fast enough).
 .IP "\(bu" 4
-manual reschedule mode (at and interval ignored, reschedule_cb = callback)
+manual reschedule mode (offset ignored, interval ignored, reschedule_cb = callback)
 .Sp
-In this mode the values for \f(CW\*(C`interval\*(C'\fR and \f(CW\*(C`at\*(C'\fR are both being
+In this mode the values for \f(CW\*(C`interval\*(C'\fR and \f(CW\*(C`offset\*(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,
+\&\s-1NOTE:\s0 \fIThis callback \s-1MUST\s0 \s-1NOT\s0 stop or destroy any periodic watcher, ever,
-ever, or make \s-1ANY\s0 event loop modifications whatsoever\fR.
+or make \s-1ANY\s0 other event loop modifications whatsoever, unless explicitly
+allowed by documentation here\fR.
 .Sp
 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 an \f(CW\*(C`ev_prepare\*(C'\fR watcher, which is the
 only event loop modification you are allowed to do).
 .Sp
 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 ev_periodic_at (ev_periodic *)" 4
 .IX Item "ev_tstamp ev_periodic_at (ev_periodic *)"
-When active, returns the absolute time that the watcher is supposed to
+When active, returns the absolute time that the watcher is supposed
-trigger next.
+to trigger next. This is not the same as the \f(CW\*(C`offset\*(C'\fR argument to
+\&\f(CW\*(C`ev_periodic_set\*(C'\fR, but indeed works even in interval and manual
+rescheduling modes.
 .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).
+absolute point in time (the \f(CW\*(C`offset\*(C'\fR value passed to \f(CW\*(C`ev_periodic_set\*(C'\fR,
+although libev might modify this value for better numerical stability).
 .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]"
 \&   ev_periodic hourly_tick;
 \&   ev_periodic_init (&hourly_tick, clock_cb,
 \&                     fmod (ev_now (loop), 3600.), 3600., 0);
 \&   ev_periodic_start (loop, &hourly_tick);
 .Ve
-.ie n .Sh """ev_signal"" \- signal me when a signal gets signalled!"
+.ie n .SS """ev_signal"" \- signal me when a signal gets signalled!"
-.el .Sh "\f(CWev_signal\fP \- signal me when a signal gets signalled!"
+.el .SS "\f(CWev_signal\fP \- signal me when a signal gets signalled!"
 .IX Subsection "ev_signal - signal me when a signal gets signalled!"
 Signal watchers will trigger an event when the process receives a specific
 signal one or more times. Even though signals are very asynchronous, libev
 will try it's best to deliver signals synchronously, i.e. as part of the
 normal event processing, like any other event.
 \&
 \&   ev_signal signal_watcher;
 \&   ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
 \&   ev_signal_start (loop, &signal_watcher);
 .Ve
-.ie n .Sh """ev_child"" \- watch out for process status changes"
+.ie n .SS """ev_child"" \- watch out for process status changes"
-.el .Sh "\f(CWev_child\fP \- watch out for process status changes"
+.el .SS "\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 or
 exits). It is permissible to install a child watcher \fIafter\fR the child
 has been forked (which implies it might have already exited), as long
 as the event loop isn't entered (or is continued from a watcher), i.e.,
 forking and then immediately registering a watcher for the child is fine,
-but forking and registering a watcher a few event loop iterations later is
+but forking and registering a watcher a few event loop iterations later or
-not.
+in the next callback invocation is not.
 .PP
 Only the default event loop is capable of handling signals, and therefore
 you can only register child watchers in the default event loop.
+.PP
+Due to some design glitches inside libev, child watchers will always be
+handled at maximum priority (their priority is set to \f(CW\*(C`EV_MAXPRI\*(C'\fR by
+libev)
 .PP
 \fIProcess Interaction\fR
 .IX Subsection "Process Interaction"
 .PP
 Libev grabs \f(CW\*(C`SIGCHLD\*(C'\fR as soon as the default event loop is
 \&     {
 \&       ev_child_init (&cw, child_cb, pid, 0);
 \&       ev_child_start (EV_DEFAULT_ &cw);
 \&     }
 .Ve
-.ie n .Sh """ev_stat"" \- did the file attributes just change?"
+.ie n .SS """ev_stat"" \- did the file attributes just change?"
-.el .Sh "\f(CWev_stat\fP \- did the file attributes just change?"
+.el .SS "\f(CWev_stat\fP \- did the file attributes just change?"
 .IX Subsection "ev_stat - did the file attributes just change?"
 This watches a file system path for attribute changes. That is, it calls
 \&\f(CW\*(C`stat\*(C'\fR on that path in regular intervals (or when the \s-1OS\s0 says it changed)
 and sees if it changed compared to the last time, invoking the callback if
 it did.
 \&   ...
 \&   ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);
 \&   ev_stat_start (loop, &passwd);
 \&   ev_timer_init (&timer, timer_cb, 0., 1.02);
 .Ve
-.ie n .Sh """ev_idle"" \- when you've got nothing better to do..."
+.ie n .SS """ev_idle"" \- when you've got nothing better to do..."
-.el .Sh "\f(CWev_idle\fP \- when you've got nothing better to do..."
+.el .SS "\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 no other events of the same or higher
 priority are pending (prepare, check and other idle watchers do not count
 as receiving \*(L"events\*(R").
 .PP
 \&\*(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
+.IP "ev_idle_init (ev_idle *, callback)" 4
-.IX Item "ev_idle_init (ev_signal *, callback)"
+.IX Item "ev_idle_init (ev_idle *, 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.
 .PP
 \fIExamples\fR
 \&     // no longer anything immediate to do.
 \&   }
 \&
 \&   ev_idle *idle_watcher = malloc (sizeof (ev_idle));
 \&   ev_idle_init (idle_watcher, idle_cb);
-\&   ev_idle_start (loop, idle_cb);
+\&   ev_idle_start (loop, idle_watcher);
 .Ve
-.ie n .Sh """ev_prepare""\fP and \f(CW""ev_check"" \- customise your event loop!"
+.ie n .SS """ev_prepare"" and ""ev_check"" \- customise your event loop!"
-.el .Sh "\f(CWev_prepare\fP and \f(CWev_check\fP \- customise your event loop!"
+.el .SS "\f(CWev_prepare\fP and \f(CWev_check\fP \- customise your event loop!"
 .IX Subsection "ev_prepare and ev_check - customise your event loop!"
 Prepare and check watchers are usually (but not always) used in pairs:
 prepare watchers get invoked before the process blocks and check watchers
 afterwards.
 .PP
 \&     struct pollfd fds [nfd];
 \&     // actual code will need to loop here and realloc etc.
 \&     adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
 \&
 \&     /* the callback is illegal, but won\*(Aqt be called as we stop during check */
-\&     ev_timer_init (&tw, 0, timeout * 1e\-3);
+\&     ev_timer_init (&tw, 0, timeout * 1e\-3, 0.);
 \&     ev_timer_start (loop, &tw);
 \&
 \&     // create one ev_io per pollfd
 \&     for (int i = 0; i < nfd; ++i)
 \&       {
 \&       ev_io_stop (EV_A_ iow [n]);
 \&
 \&     return got_events;
 \&   }
 .Ve
-.ie n .Sh """ev_embed"" \- when one backend isn't enough..."
+.ie n .SS """ev_embed"" \- when one backend isn't enough..."
-.el .Sh "\f(CWev_embed\fP \- when one backend isn't enough..."
+.el .SS "\f(CWev_embed\fP \- when one backend isn't enough..."
 .IX Subsection "ev_embed - when one backend isn't enough..."
 This is a rather advanced watcher type that lets you embed one event loop
 into another (currently only \f(CW\*(C`ev_io\*(C'\fR events are supported in the embedded
 loop, other types of watchers might be handled in a delayed or incorrect
 fashion and must not be used).
 \&   if (!loop_socket)
 \&     loop_socket = loop;
 \&
 \&   // now use loop_socket for all sockets, and loop for everything else
 .Ve
-.ie n .Sh """ev_fork"" \- the audacity to resume the event loop after a fork"
+.ie n .SS """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"
+.el .SS "\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
 whoever is a good citizen cared to tell libev about it by calling
 \&\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
+\fIThe special problem of life after fork \- how is it possible?\fR
+.IX Subsection "The special problem of life after fork - how is it possible?"
+.PP
+Most uses of \f(CW\*(C`fork()\*(C'\fR consist of forking, then some simple calls to ste
+up/change the process environment, followed by a call to \f(CW\*(C`exec()\*(C'\fR. This
+sequence should be handled by libev without any problems.
+.PP
+This changes when the application actually wants to do event handling
+in the child, or both parent in child, in effect \*(L"continuing\*(R" after the
+fork.
+.PP
+The default mode of operation (for libev, with application help to detect
+forks) is to duplicate all the state in the child, as would be expected
+when \fIeither\fR the parent \fIor\fR the child process continues.
+.PP
+When both processes want to continue using libev, then this is usually the
+wrong result. In that case, usually one process (typically the parent) is
+supposed to continue with all watchers in place as before, while the other
+process typically wants to start fresh, i.e. without any active watchers.
+.PP
+The cleanest and most efficient way to achieve that with libev is to
+simply create a new event loop, which of course will be \*(L"empty\*(R", and
+use that for new watchers. This has the advantage of not touching more
+memory than necessary, and thus avoiding the copy-on-write, and the
+disadvantage of having to use multiple event loops (which do not support
+signal watchers).
+.PP
+When this is not possible, or you want to use the default loop for
+other reasons, then in the process that wants to start \*(L"fresh\*(R", call
+\&\f(CW\*(C`ev_default_destroy ()\*(C'\fR followed by \f(CW\*(C`ev_default_loop (...)\*(C'\fR. Destroying
+the default loop will \*(L"orphan\*(R" (not stop) all registered watchers, so you
+have to be careful not to execute code that modifies those watchers. Note
+also that in that case, you have to re-register any signal watchers.
+.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.
-.ie n .Sh """ev_async"" \- how to wake up another event loop"
+.ie n .SS """ev_async"" \- how to wake up another event loop"
-.el .Sh "\f(CWev_async\fP \- how to wake up another event loop"
+.el .SS "\f(CWev_async\fP \- how to wake up another event loop"
 .IX Subsection "ev_async - how to wake up another event loop"
 In general, you cannot use an \f(CW\*(C`ev_loop\*(C'\fR from multiple threads or other
 asynchronous sources such as signal handlers (as opposed to multiple event
 loops \- those are of course safe to use in different threads).
 .PP
 an \f(CW\*(C`EV_ASYNC\*(C'\fR event on the watcher into the event loop. Unlike
 \&\f(CW\*(C`ev_feed_event\*(C'\fR, this call is safe to do from other threads, signal or
 similar contexts (see the discussion of \f(CW\*(C`EV_ATOMIC_T\*(C'\fR in the embedding
 section below on what exactly this means).
 .Sp
+Note that, as with other watchers in libev, multiple events might get
+compressed into a single callback invocation (another way to look at this
+is that \f(CW\*(C`ev_async\*(C'\fR watchers are level-triggered, set on \f(CW\*(C`ev_async_send\*(C'\fR,
+reset when the event loop detects that).
+.Sp
-This call incurs the overhead of a system call only once per loop iteration,
+This call incurs the overhead of a system call only once per event loop
-so while the overhead might be noticeable, it doesn't apply to repeated
+iteration, so while the overhead might be noticeable, it doesn't apply to
-calls to \f(CW\*(C`ev_async_send\*(C'\fR.
+repeated calls to \f(CW\*(C`ev_async_send\*(C'\fR for the same event loop.
 .IP "bool = ev_async_pending (ev_async *)" 4
 .IX Item "bool = ev_async_pending (ev_async *)"
 Returns a non-zero value when \f(CW\*(C`ev_async_send\*(C'\fR has been called on the
 watcher but the event has not yet been processed (or even noted) by the
 event loop.
 \&\f(CW\*(C`ev_async_send\*(C'\fR sets a flag in the watcher and wakes up the loop. When
 the loop iterates next and checks for the watcher to have become active,
 it will reset the flag again. \f(CW\*(C`ev_async_pending\*(C'\fR can be used to very
 quickly check whether invoking the loop might be a good idea.
 .Sp
-Not that this does \fInot\fR check whether the watcher itself is pending, only
+Not that this does \fInot\fR check whether the watcher itself is pending,
-whether it has been requested to make this watcher pending.
+only whether it has been requested to make this watcher pending: there
+is a time window between the event loop checking and resetting the async
+notification, and the callback being invoked.
 .SH "OTHER FUNCTIONS"
 .IX Header "OTHER FUNCTIONS"
 There are some other functions of possible interest. Described. Here. Now.
 .IP "ev_once (loop, int fd, int events, ev_tstamp timeout, callback)" 4
 .IX Item "ev_once (loop, int fd, int events, ev_tstamp timeout, callback)"
 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
+.ie n .IP """ev::READ"", ""ev::WRITE"" etc." 4
 .el .IP "\f(CWev::READ\fR, \f(CWev::WRITE\fR etc." 4
 .IX Item "ev::READ, ev::WRITE etc."
 These are just enum values with the same values as the \f(CW\*(C`EV_READ\*(C'\fR etc.
 macros from \fIev.h\fR.
-.ie n .IP """ev::tstamp""\fR, \f(CW""ev::now""" 4
+.ie n .IP """ev::tstamp"", ""ev::now""" 4
 .el .IP "\f(CWev::tstamp\fR, \f(CWev::now\fR" 4
 .IX Item "ev::tstamp, ev::now"
 Aliases to the same types/functions as with the \f(CW\*(C`ev_\*(C'\fR prefix.
-.ie n .IP """ev::io""\fR, \f(CW""ev::timer""\fR, \f(CW""ev::periodic""\fR, \f(CW""ev::idle""\fR, \f(CW""ev::sig"" etc." 4
+.ie n .IP """ev::io"", ""ev::timer"", ""ev::periodic"", ""ev::idle"", ""ev::sig"" etc." 4
 .el .IP "\f(CWev::io\fR, \f(CWev::timer\fR, \f(CWev::periodic\fR, \f(CWev::idle\fR, \f(CWev::sig\fR etc." 4
 .IX Item "ev::io, ev::timer, ev::periodic, ev::idle, ev::sig etc."
 For each \f(CW\*(C`ev_TYPE\*(C'\fR watcher in \fIev.h\fR there is a corresponding class of
 the same name in the \f(CW\*(C`ev\*(C'\fR namespace, with the exception of \f(CW\*(C`ev_signal\*(C'\fR
 which is called \f(CW\*(C`ev::sig\*(C'\fR to avoid clashes with the \f(CW\*(C`signal\*(C'\fR macro
 Starts the watcher. Note that there is no \f(CW\*(C`loop\*(C'\fR argument, as the
 constructor already stores the event loop.
 .IP "w\->stop ()" 4
 .IX Item "w->stop ()"
 Stops the watcher if it is active. Again, no \f(CW\*(C`loop\*(C'\fR argument.
-.ie n .IP "w\->again () (""ev::timer""\fR, \f(CW""ev::periodic"" only)" 4
+.ie n .IP "w\->again () (""ev::timer"", ""ev::periodic"" 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)"
 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
 It can be found and installed via \s-1CPAN\s0, its homepage is at
 <http://software.schmorp.de/pkg/EV>.
 .IP "Python" 4
 .IX Item "Python"
 Python bindings can be found at <http://code.google.com/p/pyev/>. It
-seems to be quite complete and well-documented. Note, however, that the
+seems to be quite complete and well-documented.
-patch they require for libev is outright dangerous as it breaks the \s-1ABI\s0
-for everybody else, and therefore, should never be applied in an installed
-libev (if python requires an incompatible \s-1ABI\s0 then it needs to embed
-libev).
 .IP "Ruby" 4
 .IX Item "Ruby"
 Tony Arcieri has written a ruby extension that offers access to a subset
 of the libev \s-1API\s0 and adds file handle abstractions, asynchronous \s-1DNS\s0 and
 more on top of it. It can be found via gem servers. Its homepage is at
 <http://rev.rubyforge.org/>.
 .Sp
 Roger Pack reports that using the link order \f(CW\*(C`\-lws2_32 \-lmsvcrt\-ruby\-190\*(C'\fR
 makes rev work even on mingw.
+.IP "Haskell" 4
+.IX Item "Haskell"
+A haskell binding to libev is available at
+<http://hackage.haskell.org/cgi\-bin/hackage\-scripts/package/hlibev>.
 .IP "D" 4
 .IX Item "D"
 Leandro Lucarella has written a D language binding (\fIev.d\fR) for libev, to
 be found at <http://proj.llucax.com.ar/wiki/evd>.
 .IP "Ocaml" 4
 of which is \f(CW\*(C`EV_MULTIPLICITY\*(C'\fR. This option determines whether (most)
 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
+.ie n .IP """EV_A"", ""EV_A_""" 4
 .el .IP "\f(CWEV_A\fR, \f(CWEV_A_\fR" 4
 .IX Item "EV_A, EV_A_"
 This provides the loop \fIargument\fR for functions, if one is required (\*(L"ev
 loop argument\*(R"). The \f(CW\*(C`EV_A\*(C'\fR form is used when this is the sole argument,
 \&\f(CW\*(C`EV_A_\*(C'\fR is used when other arguments are following. Example:
 \&   ev_loop (EV_A_ 0);
 .Ve
 .Sp
 It assumes the variable \f(CW\*(C`loop\*(C'\fR of type \f(CW\*(C`struct ev_loop *\*(C'\fR is in scope,
 which is often provided by the following macro.
-.ie n .IP """EV_P""\fR, \f(CW""EV_P_""" 4
+.ie n .IP """EV_P"", ""EV_P_""" 4
 .el .IP "\f(CWEV_P\fR, \f(CWEV_P_\fR" 4
 .IX Item "EV_P, EV_P_"
 This provides the loop \fIparameter\fR for functions, if one is required (\*(L"ev
 loop parameter\*(R"). The \f(CW\*(C`EV_P\*(C'\fR form is used when this is the sole parameter,
 \&\f(CW\*(C`EV_P_\*(C'\fR is used when other parameters are following. Example:
 \&   static void cb (EV_P_ ev_timer *w, int revents)
 .Ve
 .Sp
 It declares a parameter \f(CW\*(C`loop\*(C'\fR of type \f(CW\*(C`struct ev_loop *\*(C'\fR, quite
 suitable for use with \f(CW\*(C`EV_A\*(C'\fR.
-.ie n .IP """EV_DEFAULT""\fR, \f(CW""EV_DEFAULT_""" 4
+.ie n .IP """EV_DEFAULT"", ""EV_DEFAULT_""" 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").
-.ie n .IP """EV_DEFAULT_UC""\fR, \f(CW""EV_DEFAULT_UC_""" 4
+.ie n .IP """EV_DEFAULT_UC"", ""EV_DEFAULT_UC_""" 4
 .el .IP "\f(CWEV_DEFAULT_UC\fR, \f(CWEV_DEFAULT_UC_\fR" 4
 .IX Item "EV_DEFAULT_UC, EV_DEFAULT_UC_"
 Usage identical to \f(CW\*(C`EV_DEFAULT\*(C'\fR and \f(CW\*(C`EV_DEFAULT_\*(C'\fR, but requires that the
 default loop has been initialised (\f(CW\*(C`UC\*(C'\fR == unchecked). Their behaviour
 is undefined when the default loop has not been initialised by a previous
 .PP
 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"
+.SS "\s-1FILESETS\s0"
 .IX Subsection "FILESETS"
 Depending on what features you need you need to include one or more sets of files
 in your application.
 .PP
 \fI\s-1CORE\s0 \s-1EVENT\s0 \s-1LOOP\s0\fR
 For this of course you need the m4 file:
 .PP
 .Vb 1
 \&   libev.m4
 .Ve
-.Sh "\s-1PREPROCESSOR\s0 \s-1SYMBOLS/MACROS\s0"
+.SS "\s-1PREPROCESSOR\s0 \s-1SYMBOLS/MACROS\s0"
 .IX Subsection "PREPROCESSOR SYMBOLS/MACROS"
 Libev can be configured via a variety of preprocessor symbols you have to
 define before including any of its files. The default in the absence of
 autoconf is documented for every option.
 .IP "\s-1EV_STANDALONE\s0" 4
 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). See also \f(CW\*(C`EV_USE_CLOCK_SYSCALL\*(C'\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
-real-time clock option at compile time (and assume its availability at
+real-time clock option at compile time (and assume its availability
-runtime if successful). Otherwise no use of the real-time clock option will
+at runtime if successful). Otherwise no use of the real-time clock
-be attempted. This effectively replaces \f(CW\*(C`gettimeofday\*(C'\fR by \f(CW\*(C`clock_get
+option will be attempted. This effectively replaces \f(CW\*(C`gettimeofday\*(C'\fR
-(CLOCK_REALTIME, ...)\*(C'\fR and will not normally affect correctness. See the
+by \f(CW\*(C`clock_get (CLOCK_REALTIME, ...)\*(C'\fR and will not normally affect
-note about libraries in the description of \f(CW\*(C`EV_USE_MONOTONIC\*(C'\fR, though.
+correctness. See the note about libraries in the description of
+\&\f(CW\*(C`EV_USE_MONOTONIC\*(C'\fR, though. Defaults to the opposite value of
+\&\f(CW\*(C`EV_USE_CLOCK_SYSCALL\*(C'\fR.
 .IP "\s-1EV_USE_CLOCK_SYSCALL\s0" 4
 .IX Item "EV_USE_CLOCK_SYSCALL"
 If defined to be \f(CW1\fR, libev will try to use a direct syscall instead
 of calling the system-provided \f(CW\*(C`clock_gettime\*(C'\fR function. This option
 exists because on GNU/Linux, \f(CW\*(C`clock_gettime\*(C'\fR is in \f(CW\*(C`librt\*(C'\fR, but \f(CW\*(C`librt\*(C'\fR
 If undefined or defined to be \f(CW1\fR, then async watchers are supported. If
 defined to be \f(CW0\fR, then they are not.
 .IP "\s-1EV_MINIMAL\s0" 4
 .IX Item "EV_MINIMAL"
 If you need to shave off some kilobytes of code at the expense of some
-speed, define this symbol to \f(CW1\fR. Currently this is used to override some
+speed (but with the full \s-1API\s0), define this symbol to \f(CW1\fR. Currently this
-inlining decisions, saves roughly 30% code size on amd64. It also selects a
+is used to override some inlining decisions, saves roughly 30% code size
-much smaller 2\-heap for timer management over the default 4\-heap.
+on amd64. It also selects a much smaller 2\-heap for timer management over
+the default 4\-heap.
+.Sp
+You can save even more by disabling watcher types you do not need
+and setting \f(CW\*(C`EV_MAXPRI\*(C'\fR == \f(CW\*(C`EV_MINPRI\*(C'\fR. Also, disabling \f(CW\*(C`assert\*(C'\fR
+(\f(CW\*(C`\-DNDEBUG\*(C'\fR) will usually reduce code size a lot.
+.Sp
+Defining \f(CW\*(C`EV_MINIMAL\*(C'\fR to \f(CW2\fR will additionally reduce the core \s-1API\s0 to
+provide a bare-bones event library. See \f(CW\*(C`ev.h\*(C'\fR for details on what parts
+of the \s-1API\s0 are still available, and do not complain if this subset changes
+over time.
 .IP "\s-1EV_PID_HASHSIZE\s0" 4
 .IX Item "EV_PID_HASHSIZE"
 \&\f(CW\*(C`ev_child\*(C'\fR watchers use a small hash table to distribute workload by
 pid. The default size is \f(CW16\fR (or \f(CW1\fR with \f(CW\*(C`EV_MINIMAL\*(C'\fR), usually more
 than enough. If you need to manage thousands of children you might want to
 and the way callbacks are invoked and set. Must expand to a struct member
 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"
+.SS "\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 \s-1DLL\s0) and you need a list of
 exported symbols, you can use the provided \fISymbol.*\fR files which list
 all public symbols, one per line:
 .PP
 \&   #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"
+.SS "\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
 the \fIlibev/\fR subdirectory and includes them in the \fI\s-1EV/EVAPI\s0.h\fR (public
 \&   #include "ev_cpp.h"
 \&   #include "ev.c"
 .Ve
 .SH "INTERACTION WITH OTHER PROGRAMS OR LIBRARIES"
 .IX Header "INTERACTION WITH OTHER PROGRAMS OR LIBRARIES"
-.Sh "\s-1THREADS\s0 \s-1AND\s0 \s-1COROUTINES\s0"
+.SS "\s-1THREADS\s0 \s-1AND\s0 \s-1COROUTINES\s0"
 .IX Subsection "THREADS AND COROUTINES"
 \fI\s-1THREADS\s0\fR
 .IX Subsection "THREADS"
 .PP
 All libev functions are reentrant and thread-safe unless explicitly
 An example use would be to communicate signals or other events that only
 work in the default loop by registering the signal watcher with the
 default loop and triggering an \f(CW\*(C`ev_async\*(C'\fR watcher from the default loop
 watcher callback into the event loop interested in the signal.
 .PP
+\s-1THREAD\s0 \s-1LOCKING\s0 \s-1EXAMPLE\s0
+.IX Subsection "THREAD LOCKING EXAMPLE"
+.PP
+Here is a fictitious example of how to run an event loop in a different
+thread than where callbacks are being invoked and watchers are
+created/added/removed.
+.PP
+For a real-world example, see the \f(CW\*(C`EV::Loop::Async\*(C'\fR perl module,
+which uses exactly this technique (which is suited for many high-level
+languages).
+.PP
+The example uses a pthread mutex to protect the loop data, a condition
+variable to wait for callback invocations, an async watcher to notify the
+event loop thread and an unspecified mechanism to wake up the main thread.
+.PP
+First, you need to associate some data with the event loop:
+.PP
+.Vb 6
+\&   typedef struct {
+\&     mutex_t lock; /* global loop lock */
+\&     ev_async async_w;
+\&     thread_t tid;
+\&     cond_t invoke_cv;
+\&   } userdata;
+\&
+\&   void prepare_loop (EV_P)
+\&   {
+\&      // for simplicity, we use a static userdata struct.
+\&      static userdata u;
+\&
+\&      ev_async_init (&u\->async_w, async_cb);
+\&      ev_async_start (EV_A_ &u\->async_w);
+\&
+\&      pthread_mutex_init (&u\->lock, 0);
+\&      pthread_cond_init (&u\->invoke_cv, 0);
+\&
+\&      // now associate this with the loop
+\&      ev_set_userdata (EV_A_ u);
+\&      ev_set_invoke_pending_cb (EV_A_ l_invoke);
+\&      ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
+\&
+\&      // then create the thread running ev_loop
+\&      pthread_create (&u\->tid, 0, l_run, EV_A);
+\&   }
+.Ve
+.PP
+The callback for the \f(CW\*(C`ev_async\*(C'\fR watcher does nothing: the watcher is used
+solely to wake up the event loop so it takes notice of any new watchers
+that might have been added:
+.PP
+.Vb 5
+\&   static void
+\&   async_cb (EV_P_ ev_async *w, int revents)
+\&   {
+\&      // just used for the side effects
+\&   }
+.Ve
+.PP
+The \f(CW\*(C`l_release\*(C'\fR and \f(CW\*(C`l_acquire\*(C'\fR callbacks simply unlock/lock the mutex
+protecting the loop data, respectively.
+.PP
+.Vb 6
+\&   static void
+\&   l_release (EV_P)
+\&   {
+\&     userdata *u = ev_userdata (EV_A);
+\&     pthread_mutex_unlock (&u\->lock);
+\&   }
+\&
+\&   static void
+\&   l_acquire (EV_P)
+\&   {
+\&     userdata *u = ev_userdata (EV_A);
+\&     pthread_mutex_lock (&u\->lock);
+\&   }
+.Ve
+.PP
+The event loop thread first acquires the mutex, and then jumps straight
+into \f(CW\*(C`ev_loop\*(C'\fR:
+.PP
+.Vb 4
+\&   void *
+\&   l_run (void *thr_arg)
+\&   {
+\&     struct ev_loop *loop = (struct ev_loop *)thr_arg;
+\&
+\&     l_acquire (EV_A);
+\&     pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
+\&     ev_loop (EV_A_ 0);
+\&     l_release (EV_A);
+\&
+\&     return 0;
+\&   }
+.Ve
+.PP
+Instead of invoking all pending watchers, the \f(CW\*(C`l_invoke\*(C'\fR callback will
+signal the main thread via some unspecified mechanism (signals? pipe
+writes? \f(CW\*(C`Async::Interrupt\*(C'\fR?) and then waits until all pending watchers
+have been called (in a while loop because a) spurious wakeups are possible
+and b) skipping inter-thread-communication when there are no pending
+watchers is very beneficial):
+.PP
+.Vb 4
+\&   static void
+\&   l_invoke (EV_P)
+\&   {
+\&     userdata *u = ev_userdata (EV_A);
+\&
+\&     while (ev_pending_count (EV_A))
+\&       {
+\&         wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
+\&         pthread_cond_wait (&u\->invoke_cv, &u\->lock);
+\&       }
+\&   }
+.Ve
+.PP
+Now, whenever the main thread gets told to invoke pending watchers, it
+will grab the lock, call \f(CW\*(C`ev_invoke_pending\*(C'\fR and then signal the loop
+thread to continue:
+.PP
+.Vb 4
+\&   static void
+\&   real_invoke_pending (EV_P)
+\&   {
+\&     userdata *u = ev_userdata (EV_A);
+\&
+\&     pthread_mutex_lock (&u\->lock);
+\&     ev_invoke_pending (EV_A);
+\&     pthread_cond_signal (&u\->invoke_cv);
+\&     pthread_mutex_unlock (&u\->lock);
+\&   }
+.Ve
+.PP
+Whenever you want to start/stop a watcher or do other modifications to an
+event loop, you will now have to lock:
+.PP
+.Vb 2
+\&   ev_timer timeout_watcher;
+\&   userdata *u = ev_userdata (EV_A);
+\&
+\&   ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
+\&
+\&   pthread_mutex_lock (&u\->lock);
+\&   ev_timer_start (EV_A_ &timeout_watcher);
+\&   ev_async_send (EV_A_ &u\->async_w);
+\&   pthread_mutex_unlock (&u\->lock);
+.Ve
+.PP
+Note that sending the \f(CW\*(C`ev_async\*(C'\fR watcher is required because otherwise
+an event loop currently blocking in the kernel will have no knowledge
+about the newly added timer. By waking up the loop it will pick up any new
+watchers in the next event loop iteration.
+.PP
 \fI\s-1COROUTINES\s0\fR
 .IX Subsection "COROUTINES"
 .PP
 Libev is very accommodating to coroutines (\*(L"cooperative threads\*(R"):
 libev fully supports nesting calls to its functions from different
 coroutines (e.g. you can call \f(CW\*(C`ev_loop\*(C'\fR on the same loop from two
-different coroutines, and switch freely between both coroutines running the
+different coroutines, and switch freely between both coroutines running
-loop, as long as you don't confuse yourself). The only exception is that
+the loop, as long as you don't confuse yourself). The only exception is
-you must not do this from \f(CW\*(C`ev_periodic\*(C'\fR reschedule callbacks.
+that you must not do this from \f(CW\*(C`ev_periodic\*(C'\fR reschedule callbacks.
 .PP
 Care has been taken to ensure that libev does not keep local state inside
 \&\f(CW\*(C`ev_loop\*(C'\fR, and other calls do not usually allow for coroutine switches as
 they do not call any callbacks.
-.Sh "\s-1COMPILER\s0 \s-1WARNINGS\s0"
+.SS "\s-1COMPILER\s0 \s-1WARNINGS\s0"
 .IX Subsection "COMPILER WARNINGS"
 Depending on your compiler and compiler settings, you might get no or a
 lot of warnings when compiling libev code. Some people are apparently
 scared by this.
 .PP
 While libev is written to generate as few warnings as possible,
 \&\*(L"warn-free\*(R" code is not a goal, and it is recommended not to build libev
 with any compiler warnings enabled unless you are prepared to cope with
 them (e.g. by ignoring them). Remember that warnings are just that:
 warnings, not errors, or proof of bugs.
-.Sh "\s-1VALGRIND\s0"
+.SS "\s-1VALGRIND\s0"
 .IX Subsection "VALGRIND"
 Valgrind has a special section here because it is a popular tool that is
 highly useful. Unfortunately, valgrind reports are very hard to interpret.
 .PP
 If you think you found a bug (memory leak, uninitialised data access etc.)
 .PP
 If you need, for some reason, empty reports from valgrind for your project
 I suggest using suppression lists.
 .SH "PORTABILITY NOTES"
 .IX Header "PORTABILITY NOTES"
-.Sh "\s-1WIN32\s0 \s-1PLATFORM\s0 \s-1LIMITATIONS\s0 \s-1AND\s0 \s-1WORKAROUNDS\s0"
+.SS "\s-1WIN32\s0 \s-1PLATFORM\s0 \s-1LIMITATIONS\s0 \s-1AND\s0 \s-1WORKAROUNDS\s0"
 .IX Subsection "WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS"
 Win32 doesn't support any of the standards (e.g. \s-1POSIX\s0) that libev
 requires, and its I/O model is fundamentally incompatible with the \s-1POSIX\s0
 model. Libev still offers limited functionality on this platform in
 the form of the \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR backend, and only supports socket
 way (note also that glib is the slowest event library known to man).
 .PP
 There is no supported compilation method available on windows except
 embedding it into other applications.
 .PP
+Sensible signal handling is officially unsupported by Microsoft \- libev
+tries its best, but under most conditions, signals will simply not work.
+.PP
 Not a libev limitation but worth mentioning: windows apparently doesn't
 accept large writes: instead of resulting in a partial write, windows will
 either accept everything or return \f(CW\*(C`ENOBUFS\*(C'\fR if the buffer is too large,
 so make sure you only write small amounts into your sockets (less than a
 megabyte seems safe, but this apparently depends on the amount of memory
 the abysmal performance of winsockets, using a large number of sockets
 is not recommended (and not reasonable). If your program needs to use
 more than a hundred or so sockets, then likely it needs to use a totally
 different implementation for windows, as libev offers the \s-1POSIX\s0 readiness
 notification model, which cannot be implemented efficiently on windows
-(Microsoft monopoly games).
+(due to Microsoft monopoly games).
 .PP
 A typical way to use libev under windows is to embed it (see the embedding
 section for details) and use the following \fIevwrap.h\fR header file instead
 of \fIev.h\fR:
 .PP
 .Sp
 Early versions of winsocket's select only supported waiting for a maximum
 of \f(CW64\fR handles (probably owning to the fact that all windows kernels
 can only wait for \f(CW64\fR things at the same time internally; Microsoft
 recommends spawning a chain of threads and wait for 63 handles and the
-previous thread in each. Great).
+previous thread in each. Sounds great!).
 .Sp
 Newer versions support more handles, but you need to define \f(CW\*(C`FD_SETSIZE\*(C'\fR
 to some high number (e.g. \f(CW2048\fR) before compiling the winsocket select
-call (which might be in libev or elsewhere, for example, perl does its own
+call (which might be in libev or elsewhere, for example, perl and many
-select emulation on windows).
+other interpreters do their own select emulation on windows).
 .Sp
 Another limit is the number of file descriptors in the Microsoft runtime
-libraries, which by default is \f(CW64\fR (there must be a hidden \fI64\fR fetish
+libraries, which by default is \f(CW64\fR (there must be a hidden \fI64\fR
-or something like this inside Microsoft). You can increase this by calling
+fetish or something like this inside Microsoft). You can increase this
-\&\f(CW\*(C`_setmaxstdio\*(C'\fR, which can increase this limit to \f(CW2048\fR (another
+by calling \f(CW\*(C`_setmaxstdio\*(C'\fR, which can increase this limit to \f(CW2048\fR
-arbitrary limit), but is broken in many versions of the Microsoft runtime
+(another arbitrary limit), but is broken in many versions of the Microsoft
-libraries.
-.Sp
-This might get you to about \f(CW512\fR or \f(CW2048\fR sockets (depending on
+runtime libraries. This might get you to about \f(CW512\fR or \f(CW2048\fR sockets
-windows version and/or the phase of the moon). To get more, you need to
+(depending on windows version and/or the phase of the moon). To get more,
-wrap all I/O functions and provide your own fd management, but the cost of
+you need to wrap all I/O functions and provide your own fd management, but
-calling select (O(nA\*^X)) will likely make this unworkable.
+the cost of calling select (O(nA\*^X)) will likely make this unworkable.
-.Sh "\s-1PORTABILITY\s0 \s-1REQUIREMENTS\s0"
+.SS "\s-1PORTABILITY\s0 \s-1REQUIREMENTS\s0"
 .IX Subsection "PORTABILITY REQUIREMENTS"
 In addition to a working ISO-C implementation and of course the
 backend-specific APIs, libev relies on a few additional extensions:
-.ie n .IP """void (*)(ev_watcher_type *, int revents)""\fR must have compatible calling conventions regardless of \f(CW""ev_watcher_type *""." 4
+.ie n .IP """void (*)(ev_watcher_type *, int revents)"" must have compatible calling conventions regardless of ""ev_watcher_type *""." 4
 .el .IP "\f(CWvoid (*)(ev_watcher_type *, int revents)\fR must have compatible calling conventions regardless of \f(CWev_watcher_type *\fR." 4
 .IX Item "void (*)(ev_watcher_type *, int revents) must have compatible calling conventions regardless of ev_watcher_type *."
 Libev assumes not only that all watcher pointers have the same internal
 structure (guaranteed by \s-1POSIX\s0 but not by \s-1ISO\s0 C for example), but it also
 assumes that the same (machine) code can be used to call any watcher
 .el .IP "\f(CWdouble\fR must hold a time value in seconds with enough accuracy" 4
 .IX Item "double must hold a time value in seconds with enough accuracy"
 The type \f(CW\*(C`double\*(C'\fR is used to represent timestamps. It is required to
 have at least 51 bits of mantissa (and 9 bits of exponent), which is good
 enough for at least into the year 4000. This requirement is fulfilled by
-implementations implementing \s-1IEEE\s0 754 (basically all existing ones).
+implementations implementing \s-1IEEE\s0 754, which is basically all existing
+ones. With \s-1IEEE\s0 754 doubles, you get microsecond accuracy until at least
+2200.
 .PP
 If you know of other additional requirements drop me a note.
 .SH "ALGORITHMIC COMPLEXITIES"
 .IX Header "ALGORITHMIC COMPLEXITIES"
 In this section the complexities of (many of) the algorithms used inside
 .IX Item "Processing signals: O(max_signal_number)"
 .PD
 Sending involves a system call \fIiff\fR there were no other \f(CW\*(C`ev_async_send\*(C'\fR
 calls in the current loop iteration. Checking for async and signal events
 involves iterating over all running async watchers or all signal numbers.
+.SH "GLOSSARY"
+.IX Header "GLOSSARY"
+.IP "active" 4
+.IX Item "active"
+A watcher is active as long as it has been started (has been attached to
+an event loop) but not yet stopped (disassociated from the event loop).
+.IP "application" 4
+.IX Item "application"
+In this document, an application is whatever is using libev.
+.IP "callback" 4
+.IX Item "callback"
+The address of a function that is called when some event has been
+detected. Callbacks are being passed the event loop, the watcher that
+received the event, and the actual event bitset.
+.IP "callback invocation" 4
+.IX Item "callback invocation"
+The act of calling the callback associated with a watcher.
+.IP "event" 4
+.IX Item "event"
+A change of state of some external event, such as data now being available
+for reading on a file descriptor, time having passed or simply not having
+any other events happening anymore.
+.Sp
+In libev, events are represented as single bits (such as \f(CW\*(C`EV_READ\*(C'\fR or
+\&\f(CW\*(C`EV_TIMEOUT\*(C'\fR).
+.IP "event library" 4
+.IX Item "event library"
+A software package implementing an event model and loop.
+.IP "event loop" 4
+.IX Item "event loop"
+An entity that handles and processes external events and converts them
+into callback invocations.
+.IP "event model" 4
+.IX Item "event model"
+The model used to describe how an event loop handles and processes
+watchers and events.
+.IP "pending" 4
+.IX Item "pending"
+A watcher is pending as soon as the corresponding event has been detected,
+and stops being pending as soon as the watcher will be invoked or its
+pending status is explicitly cleared by the application.
+.Sp
+A watcher can be pending, but not active. Stopping a watcher also clears
+its pending status.
+.IP "real time" 4
+.IX Item "real time"
+The physical time that is observed. It is apparently strictly monotonic :)
+.IP "wall-clock time" 4
+.IX Item "wall-clock time"
+The time and date as shown on clocks. Unlike real time, it can actually
+be wrong and jump forwards and backwards, e.g. when the you adjust your
+clock.
+.IP "watcher" 4
+.IX Item "watcher"
+A data structure that describes interest in certain events. Watchers need
+to be started (attached to an event loop) before they can receive events.
+.IP "watcher invocation" 4
+.IX Item "watcher invocation"
+The act of calling the callback associated with a watcher.
 .SH "AUTHOR"
 .IX Header "AUTHOR"
 Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael Magnusson.

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Revision 1.79 by root, Fri Jul 17 14:43:38 2009 UTC