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

Comparing libev/ev.3 (file contents):
Revision 1.55 by root, Fri Dec 21 05:10:38 2007 UTC vs.
Revision 1.57 by root, Sat Dec 22 11:49:17 2007 UTC

 .\}
 .rm #[ #] #H #V #F C
 .\" ========================================================================
 .\"
 .IX Title "EV 1"
-.TH EV 1 "2007-12-21" "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
 .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 ()"
 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 O(total_fds) where n is the total number of fds (or the highest fd),
 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 rewuiring a syscall per fd change, no fork support and bad
+cases and rewiring a syscall per fd change, no fork support and bad
 support for dup:
 .Sp
 While stopping, setting and starting an I/O watcher in the same iteration
 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
 (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 \fIall\fR BSDs (usually it doesn't work with anything but
+was broken on all BSDs except NetBSD (usually it doesn't work reliably
-sockets and pipes, except on Darwin, where of course it's completely
+with anything but sockets and pipes, except on Darwin, where of course
-useless. On NetBSD, it seems to work for all the \s-1FD\s0 types I tested, so it
-is used by default there). For this reason it's 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) 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,
+kernel is more efficient (which says nothing about its actual speed, of
-of course). While stopping, setting and starting an I/O watcher does
+course). While stopping, setting and starting an I/O watcher does never
-never cause an extra syscall as with epoll, it still adds up to two event
+cause an extra syscall as with \f(CW\*(C`EVBACKEND_EPOLL\*(C'\fR, it still adds up to
-changes per incident, support for \f(CW\*(C`fork ()\*(C'\fR is very bad and it drops fds
+two event changes per incident, support for \f(CW\*(C`fork ()\*(C'\fR is very bad and it
-silently in similarly hard-to-detetc cases.
+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
 .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:
 .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
+supports this, they will be called before other \f(CW\*(C`ev_check\*(C'\fR watchers
-their job. As \f(CW\*(C`ev_check\*(C'\fR watchers are often used to embed other event
+did their job. As \f(CW\*(C`ev_check\*(C'\fR watchers are often used to embed other
-loops those other event loops might be in an unusable state until their
+(non\-libev) event loops those other event loops might be in an unusable
-\&\f(CW\*(C`ev_check\*(C'\fR watcher ran (always remind yourself to coexist peacefully with
+state until their \f(CW\*(C`ev_check\*(C'\fR watcher ran (always remind yourself to
-others).
+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)"
 .el .Sh "\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). (See portability notes, below).
+fashion and must not be used).
 .PP
 There are primarily two reasons you would want that: work around bugs and
 prioritise I/O.
 .PP
 As an example for a bug workaround, the kqueue backend might only support
 \&      ev_embed_start (loop_hi, &embed);
 \&    }
 \&  else
 \&    loop_lo = loop_hi;
 .Ve
-.Sh "Portability notes"
-.IX Subsection "Portability notes"
-Kqueue is nominally embeddable, but this is broken on all BSDs that I
-tried, in various ways. Usually the embedded event loop will simply never
-receive events, sometimes it will only trigger a few times, sometimes in a
-loop. Epoll is also nominally embeddable, but many Linux kernel versions
-will always eport the epoll fd as ready, even when no events are pending.
-.PP
-While libev allows embedding these backends (they are contained in
-\&\f(CW\*(C`ev_embeddable_backends ()\*(C'\fR), take extreme care that it will actually
-work.
-.PP
-When in doubt, create a dynamic event loop forced to use sockets (this
-usually works) and possibly another thread and a pipe or so to report to
-your main event loop.
 .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)"
 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 the
 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

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Comparing libev/ev.3 (file contents): Revision 1.55 by root, Fri Dec 21 05:10:38 2007 UTC vs. Revision 1.57 by root, Sat Dec 22 11:49:17 2007 UTC

Diff Legend

Comparing libev/ev.3 (file contents):
Revision 1.55 by root, Fri Dec 21 05:10:38 2007 UTC vs.
Revision 1.57 by root, Sat Dec 22 11:49:17 2007 UTC