time: L<http://cvs.schmorp.de/libev/ev.html>.
Libev is an event loop: you register interest in certain events (such as a
-file descriptor being readable or a timeout occuring), and it will manage
+file descriptor being readable or a timeout occurring), and it will manage
these event sources and provide your program with events.
To do this, it must take more or less complete control over your process
=item C<EVBACKEND_EPOLL> (value 4, Linux)
For few fds, this backend is a bit little slower than poll and select,
-but it scales phenomenally better. While poll and select usually scale like
-O(total_fds) where n is the total number of fds (or the highest fd), epoll scales
-either O(1) or O(active_fds).
-
-While stopping and starting an I/O watcher in the same iteration will
-result in some caching, there is still a syscall per such incident
+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
+support for dup:
+
+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
-best to avoid that. Also, dup()ed file descriptors might not work very
-well if you register events for both fds.
+best to avoid that. Also, C<dup ()>'ed file descriptors might not work
+very well if you register events for both fds.
Please note that epoll sometimes generates spurious notifications, so you
need to use non-blocking I/O or other means to avoid blocking when no data
=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)
Kqueue deserves special mention, as at the time of this writing, it
-was broken on all BSDs except NetBSD (usually it doesn't work with
-anything but sockets and pipes, except on Darwin, where of course its
-completely useless). For this reason its not being "autodetected"
+was broken on I<all> BSDs (usually it doesn't work with anything but
+sockets and pipes, except on Darwin, where of course it's completely
+useless. On NetBSD, it seems to work for all the FD types I tested, so it
+is used by default there). For this reason it's not being "autodetected"
unless you explicitly specify it explicitly in the flags (i.e. using
-C<EVBACKEND_KQUEUE>).
+C<EVBACKEND_KQUEUE>) or libev was compiled on a known-to-be-good (-enough)
+system like NetBSD.
It scales in the same way as the epoll backend, but the interface to the
-kernel is more efficient (which says nothing about its actual speed, of
-course). While starting and stopping an I/O watcher does not cause an
-extra syscall as with epoll, it still adds up to four event changes per
-incident, so its best to avoid that.
+kernel is more efficient (which says nothing about its actual speed,
+of course). While stopping, setting and starting an I/O watcher does
+never cause an extra syscall as with epoll, it still adds up to two event
+changes per incident, support for C<fork ()> is very bad and it drops fds
+silently in similarly hard-to-detetc cases.
=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)
=item C<EVBACKEND_PORT> (value 32, Solaris 10)
-This uses the Solaris 10 port mechanism. As with everything on Solaris,
+This uses the Solaris 10 event port mechanism. As with everything on Solaris,
it's really slow, but it still scales very well (O(active_fds)).
-Please note that solaris ports can result in a lot of spurious
+Please note that solaris event ports can deliver a lot of spurious
notifications, so you need to use non-blocking I/O or other means to avoid
blocking when no data (or space) is available.
received events and started processing them. This timestamp does not
change as long as callbacks are being processed, and this is also the base
time used for relative timers. You can treat it as the timestamp of the
-event occuring (or more correctly, libev finding out about it).
+event occurring (or more correctly, libev finding out about it).
=item ev_loop (loop, int flags)
=head3 The special problem of disappearing file descriptors
-Some backends (e.g kqueue, epoll) need to be told about closing a file
+Some backends (e.g. kqueue, epoll) need to be told about closing a file
descriptor (either by calling C<close> explicitly or by any other means,
such as C<dup>). The reason is that you register interest in some file
descriptor, but when it goes away, the operating system will silently drop
the libev application should not optimise around libev but should leave
optimisations to libev.
+=head3 The special problem of dup'ed file descriptors
+
+Some backends (e.g. epoll), cannot register events for file descriptors,
+but only events for the underlying file descriptions. That menas when you
+have C<dup ()>'ed file descriptors and register events for them, only one
+file descriptor might actually receive events.
+
+There is no workaorund possible except not registering events
+for potentially C<dup ()>'ed file descriptors or to resort to
+C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
+
+=head3 The special problem of fork
+
+Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit
+useless behaviour. Libev fully supports fork, but needs to be told about
+it in the child.
+
+To support fork in your programs, you either have to call
+C<ev_default_fork ()> or C<ev_loop_fork ()> after a fork in the child,
+enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or
+C<EVBACKEND_POLL>.
+
=head3 Watcher-Specific Functions
This is a rather advanced watcher type that lets you embed one event loop
into another (currently only C<ev_io> 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).
+fashion and must not be used). (See portability notes, below).
There are primarily two reasons you would want that: work around bugs and
prioritise I/O.
else
loop_lo = loop_hi;
+=head2 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.
+
+While libev allows embedding these backends (they are contained in
+C<ev_embeddable_backends ()>), take extreme care that it will actually
+work.
+
+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.
+
=head3 Watcher-Specific Functions and Data Members
=over 4
similarly to C<ev_loop (embedded_loop, EVLOOP_NONBLOCK)>, but in the most
apropriate way for embedded loops.
-=item struct ev_loop *loop [read-only]
+=item struct ev_loop *other [read-only]
The embedded event loop.
Game Server, the EV perl module, the GNU Virtual Private Ethernet (gvpe)
and rxvt-unicode.
-The goal is to enable you to just copy the neecssary files into your
+The goal is to enable you to just copy the necessary files into your
source directory without having to change even a single line in them, so
you can easily upgrade by simply copying (or having a checked-out copy of
libev somewhere in your source tree).
monotonic clock option at both compiletime and runtime. Otherwise no use
of the monotonic clock option will be attempted. If you enable this, you
usually have to link against librt or something similar. Enabling it when
-the functionality isn't available is safe, though, althoguh you have
+the functionality isn't available is safe, though, although you have
to make sure you link against any libraries where the C<clock_gettime>
function is hiding in (often F<-lrt>).
realtime clock option at compiletime (and assume its availability at
runtime if successful). Otherwise no use of the realtime clock option will
be attempted. This effectively replaces C<gettimeofday> by C<clock_get
-(CLOCK_REALTIME, ...)> and will not normally affect correctness. See tzhe note about libraries
-in the description of C<EV_USE_MONOTONIC>, though.
+(CLOCK_REALTIME, ...)> and will not normally affect correctness. See the
+note about libraries in the description of C<EV_USE_MONOTONIC>, though.
=item EV_USE_SELECT
Can be used to change the callback member declaration in each watcher,
and the way callbacks are invoked and set. Must expand to a struct member
-definition and a statement, respectively. See the F<ev.v> header file for
+definition and a statement, respectively. See the F<ev.h> header file for
their default definitions. One possible use for overriding these is to
avoid the C<struct ev_loop *> as first argument in all cases, or to use
method calls instead of plain function calls in C++.
+=head2 EXPORTED API SYMBOLS
+
+If you need to re-export the API (e.g. via a dll) and you need a list of
+exported symbols, you can use the provided F<Symbol.*> files which list
+all public symbols, one per line:
+
+ Symbols.ev for libev proper
+ Symbols.event for the libevent emulation
+
+This can also be used to rename all public symbols to avoid clashes with
+multiple versions of libev linked together (which is obviously bad in
+itself, but sometimes it is inconvinient to avoid this).
+
+A sed command like this will create wrapper C<#define>'s that you need to
+include before including F<ev.h>:
+
+ <Symbols.ev sed -e "s/.*/#define & myprefix_&/" >wrap.h
+
+This would create a file F<wrap.h> which essentially looks like this:
+
+ #define ev_backend myprefix_ev_backend
+ #define ev_check_start myprefix_ev_check_start
+ #define ev_check_stop myprefix_ev_check_stop
+ ...
+
=head2 EXAMPLES
For a real-world example of a program the includes libev
projects / software / libev.git / blobdiff