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

Comparing libev/ev.pod (file contents):
Revision 1.449 by root, Sun Jun 23 02:02:30 2019 UTC vs.
Revision 1.455 by root, Wed Jun 26 00:01:46 2019 UTC

 When libev detects a usage error such as a negative timer interval, then
 it will print a diagnostic message and abort (via the C<assert> mechanism,
 so C<NDEBUG> will disable this checking): these are programming errors in
 the libev caller and need to be fixed there.
+Via the C<EV_FREQUENT> macro you can compile in and/or enable extensive
+consistency checking code inside libev that can be used to check for
+internal inconsistencies, suually caused by application bugs.
-Libev also has a few internal error-checking C<assert>ions, and also has
+Libev also has a few internal error-checking C<assert>ions. These do not
-extensive consistency checking code. These do not trigger under normal
-circumstances, as they indicate either a bug in libev or worse.
+trigger under normal circumstances, as they indicate either a bug in libev
+or worse.
 =head1 GLOBAL FUNCTIONS
 These functions can be called anytime, even before initialising the
 This backend maps C<EV_READ> to C<POLLIN | POLLERR | POLLHUP>, and
 C<EV_WRITE> to C<POLLOUT | POLLERR | POLLHUP>.
 =item C<EVBACKEND_EPOLL>   (value 4, Linux)
-Use the linux-specific epoll(7) interface (for both pre- and post-2.6.9
+Use the Linux-specific epoll(7) interface (for both pre- and post-2.6.9
 kernels).
 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 total_fds is the total number of fds (or the highest
 This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
 C<EVBACKEND_POLL>.
 =item C<EVBACKEND_LINUXAIO>   (value 64, Linux)
-Use the linux-specific linux aio (I<not> C<< aio(7) >> but C<<
+Use the Linux-specific Linux AIO (I<not> C<< aio(7) >> but C<<
-io_submit(2) >>) event interface available in post-4.18 kernels.
+io_submit(2) >>) event interface available in post-4.18 kernels (but libev
+only tries to use it in 4.19+).
+This is another Linux train wreck of an event interface.
 If this backend works for you (as of this writing, it was very
-experimental), it is the best event interface available on linux and might
+experimental), it is the best event interface available on Linux and might
 be well worth enabling it - if it isn't available in your kernel this will
 be detected and this backend will be skipped.
 This backend can batch oneshot requests and supports a user-space ring
 buffer to receive events. It also doesn't suffer from most of the design
 problems of epoll (such as not being able to remove event sources from
 the epoll set), and generally sounds too good to be true. Because, this
-being the linux kernel, of course it suffers from a whole new set of
+being the Linux kernel, of course it suffers from a whole new set of
-limitations.
+limitations, forcing you to fall back to epoll, inheriting all its design
+issues.
 For one, it is not easily embeddable (but probably could be done using
 an event fd at some extra overhead). It also is subject to a system wide
-limit that can be configured in F</proc/sys/fs/aio-max-nr> - each loop
+limit that can be configured in F</proc/sys/fs/aio-max-nr>. If no AIO
-currently requires C<61> of this number. If no aio requests are left, this
-backend will be skipped during initialisation.
+requests are left, this backend will be skipped during initialisation, and
+will switch to epoll when the loop is active.
-Most problematic in practise, however, is that not all file descriptors
+Most problematic in practice, however, is that not all file descriptors
-work with it. For example, in linux 5.1, tcp sockets, pipes, event fds,
+work with it. For example, in Linux 5.1, TCP sockets, pipes, event fds,
-files, F</dev/null> and a few others are supported, but ttys do not work
+files, F</dev/null> and many others are supported, but ttys do not work
-(probably because of a bug), so this is not (yet?) a generic event polling
+properly (a known bug that the kernel developers don't care about, see
-interface.
+L<https://lore.kernel.org/patchwork/patch/1047453/>), so this is not
+(yet?) a generic event polling interface.
+Overall, it seems the Linux developers just don't want it to have a
+generic event handling mechanism other than C<select> or C<poll>.
-To work around this latter problem, the current version of libev uses
+To work around all these problem, the current version of libev uses its
-epoll as a fallback for file deescriptor types that do not work. Epoll
+epoll backend as a fallback for file descriptor types that do not work. Or
-is used in, kind of, slow mode that hopefully avoids most of its design
+falls back completely to epoll if the kernel acts up.
-problems and requires 1-3 extra syscalls per active fd every iteration.
 This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
 C<EVBACKEND_POLL>.
 =item C<EVBACKEND_KQUEUE>  (value 8, most BSD clones)
-Kqueue deserves special mention, as at the time of this writing, it
+Kqueue deserves special mention, as at the time this backend was
-was broken on all BSDs except NetBSD (usually it doesn't work reliably
+implemented, it was broken on all BSDs except NetBSD (usually it doesn't
-with anything but sockets and pipes, except on Darwin, where of course
+work reliably with anything but sockets and pipes, except on Darwin,
-it's completely useless). Unlike epoll, however, whose brokenness
+where of course it's completely useless). Unlike epoll, however, whose
-is by design, these kqueue bugs can (and eventually will) be fixed
+brokenness is by design, these kqueue bugs can be (and mostly have been)
-without API changes to existing programs. For this reason it's not being
+fixed without API changes to existing programs. For this reason it's not
-"auto-detected" unless you explicitly specify it in the flags (i.e. using
+being "auto-detected" on all platforms unless you explicitly specify it
-C<EVBACKEND_KQUEUE>) or libev was compiled on a known-to-be-good (-enough)
+in the flags (i.e. using C<EVBACKEND_KQUEUE>) or libev was compiled on a
-system like NetBSD.
+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 system call as with C<EVBACKEND_EPOLL>, it still adds up to
 two event changes per incident. Support for C<fork ()> is very bad (you
-might have to leak fd's on fork, but it's more sane than epoll) and it
+might have to leak fds on fork, but it's more sane than epoll) and it
 drops fds silently in similarly hard-to-detect cases.
 This backend usually performs well under most conditions.
 While nominally embeddable in other event loops, this doesn't work
 called. If set to C<2>, then the internal verification code will be
 called once per loop, which can slow down libev. If set to C<3>, then the
 verification code will be called very frequently, which will slow down
 libev considerably.
+Verification errors are reported via C's C<assert> mechanism, so if you
+disable that (e.g. by defining C<NDEBUG>) then no errors will be reported.
 The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
 will be C<0>.
 =item EV_COMMON

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Comparing libev/ev.pod (file contents): Revision 1.449 by root, Sun Jun 23 02:02:30 2019 UTC vs. Revision 1.455 by root, Wed Jun 26 00:01:46 2019 UTC

Diff Legend

Comparing libev/ev.pod (file contents):
Revision 1.449 by root, Sun Jun 23 02:02:30 2019 UTC vs.
Revision 1.455 by root, Wed Jun 26 00:01:46 2019 UTC