diff options
Diffstat (limited to 'ev.pod')
| -rw-r--r-- | ev.pod | 49 |
1 files changed, 18 insertions, 31 deletions
@@ -341,20 +341,23 @@ 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 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" +was broken on all BSDs except NetBSD (usually it doesn't work reliably +with anything but sockets and pipes, except on Darwin, where of course +it's completely useless). For this reason it's not being "autodetected" unless you explicitly specify it explicitly in the flags (i.e. using C<EVBACKEND_KQUEUE>) or libev was compiled on a known-to-be-good (-enough) system like NetBSD. +You still can embed kqueue into a normal poll or select backend and use it +only for sockets (after having made sure that sockets work with kqueue on +the target platform). See C<ev_embed> watchers for more info. + It scales in the same way as the epoll backend, but the interface to the -kernel is more efficient (which says nothing about its actual speed, -of course). While 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. +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 C<EVBACKEND_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-detect cases. =item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8) @@ -1625,11 +1628,11 @@ It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>) priority, to ensure that they are being run before any other watchers after the poll. Also, C<ev_check> watchers (and C<ev_prepare> watchers, too) should not activate ("feed") events into libev. While libev fully -supports this, they will be called before other C<ev_check> watchers did -their job. As C<ev_check> watchers are often used to embed other event -loops those other event loops might be in an unusable state until their -C<ev_check> watcher ran (always remind yourself to coexist peacefully with -others). +supports this, they will be called before other C<ev_check> watchers +did their job. As C<ev_check> watchers are often used to embed other +(non-libev) event loops those other event loops might be in an unusable +state until their C<ev_check> watcher ran (always remind yourself to +coexist peacefully with others). =head3 Watcher-Specific Functions and Data Members @@ -1778,7 +1781,7 @@ this. 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). (See portability notes, below). +fashion and must not be used). There are primarily two reasons you would want that: work around bugs and prioritise I/O. @@ -1843,22 +1846,6 @@ create it, and if that fails, use the normal loop for everything: 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 |