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

Comparing libev/ev.3 (file contents):
Revision 1.111 by root, Sun Jun 23 02:02:24 2019 UTC vs.
Revision 1.115 by root, Wed Jun 26 00:01:46 2019 UTC

 .\}
 .rm #[ #] #H #V #F C
 .\" ========================================================================
 .\"
 .IX Title "LIBEV 3"
-.TH LIBEV 3 "2019-06-22" "libev-4.25" "libev - high performance full featured event loop"
+.TH LIBEV 3 "2019-06-25" "libev-4.25" "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"
 When libev detects a usage error such as a negative timer interval, then
 it will print a diagnostic message and abort (via the \f(CW\*(C`assert\*(C'\fR mechanism,
 so \f(CW\*(C`NDEBUG\*(C'\fR will disable this checking): these are programming errors in
 the libev caller and need to be fixed there.
 .PP
+Via the \f(CW\*(C`EV_FREQUENT\*(C'\fR 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.
+.PP
-Libev also has a few internal error-checking \f(CW\*(C`assert\*(C'\fRions, and also has
+Libev also has a few internal error-checking \f(CW\*(C`assert\*(C'\fRions. 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.
 .SH "GLOBAL FUNCTIONS"
 .IX Header "GLOBAL FUNCTIONS"
 These functions can be called anytime, even before initialising the
 library in any way.
 .IP "ev_tstamp ev_time ()" 4
 This backend maps \f(CW\*(C`EV_READ\*(C'\fR to \f(CW\*(C`POLLIN | POLLERR | POLLHUP\*(C'\fR, and
 \&\f(CW\*(C`EV_WRITE\*(C'\fR to \f(CW\*(C`POLLOUT | POLLERR | POLLHUP\*(C'\fR.
 .ie n .IP """EVBACKEND_EPOLL""   (value 4, Linux)" 4
 .el .IP "\f(CWEVBACKEND_EPOLL\fR   (value 4, Linux)" 4
 .IX Item "EVBACKEND_EPOLL (value 4, Linux)"
-Use the linux-specific \fBepoll\fR\|(7) interface (for both pre\- and post\-2.6.9
+Use the Linux-specific \fBepoll\fR\|(7) interface (for both pre\- and post\-2.6.9
 kernels).
 .Sp
 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 \f(CW\*(C`EV_READ\*(C'\fR and \f(CW\*(C`EV_WRITE\*(C'\fR in the same way as
 \&\f(CW\*(C`EVBACKEND_POLL\*(C'\fR.
 .ie n .IP """EVBACKEND_LINUXAIO""   (value 64, Linux)" 4
 .el .IP "\f(CWEVBACKEND_LINUXAIO\fR   (value 64, Linux)" 4
 .IX Item "EVBACKEND_LINUXAIO (value 64, Linux)"
-Use the linux-specific linux aio (\fInot\fR \f(CWaio(7)\fR) event interface
+Use the Linux-specific Linux \s-1AIO\s0 (\fInot\fR \f(CWaio(7)\fR but \f(CWio_submit(2)\fR) event interface available in post\-4.18 kernels (but libev
-available in post\-4.18 kernels.
+only tries to use it in 4.19+).
+.Sp
+This is another Linux train wreck of an event interface.
 .Sp
 If this backend works for you (as of this writing, it was very
-experimental and only supports a subset of file types), it is the best
+experimental), it is the best event interface available on Linux and might
-event interface available on linux and might be well worth it enabling it
+be well worth enabling it \- if it isn't available in your kernel this will
-\&\- if it isn't available in your kernel this will be detected and another
+be detected and this backend will be skipped.
-backend will be chosen.
 .Sp
-This backend can batch oneshot requests and uses a user-space ring buffer
+This backend can batch oneshot requests and supports a user-space ring
-to receive events. It also doesn't suffer from most of the design problems
+buffer to receive events. It also doesn't suffer from most of the design
-of epoll (such as not being able to remove event sources from the epoll
+problems of epoll (such as not being able to remove event sources from
-set), and generally sounds too good to be true. Because, this being the
+the epoll set), and generally sounds too good to be true. Because, this
-linux kernel, of course it suffers from a whole new set of limitations.
+being the Linux kernel, of course it suffers from a whole new set of
+limitations, forcing you to fall back to epoll, inheriting all its design
+issues.
 .Sp
 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 various
+an event fd at some extra overhead). It also is subject to a system wide
-arbitrary limits that can be configured in \fI/proc/sys/fs/aio\-max\-nr\fR
+limit that can be configured in \fI/proc/sys/fs/aio\-max\-nr\fR. If no \s-1AIO\s0
-and \fI/proc/sys/fs/aio\-nr\fR), which could lead to it being skipped during
+requests are left, this backend will be skipped during initialisation, and
-initialisation.
+will switch to epoll when the loop is active.
 .Sp
-Most problematic in practise, however, is that, like kqueue, it requires
+Most problematic in practice, however, is that not all file descriptors
-special support from drivers, and, not surprisingly, not all drivers
-implement it. For example, in linux 4.19, tcp sockets, pipes, event fds,
+work with it. For example, in Linux 5.1, \s-1TCP\s0 sockets, pipes, event fds,
-files, \fI/dev/null\fR and a few others are supported, but ttys are not, so
+files, \fI/dev/null\fR and many others are supported, but ttys do not work
-this is not (yet?) a generic event polling interface but is probably still
+properly (a known bug that the kernel developers don't care about, see
-be very useful in a web server or similar program.
+<https://lore.kernel.org/patchwork/patch/1047453/>), so this is not
+(yet?) a generic event polling interface.
+.Sp
+Overall, it seems the Linux developers just don't want it to have a
+generic event handling mechanism other than \f(CW\*(C`select\*(C'\fR or \f(CW\*(C`poll\*(C'\fR.
+.Sp
+To work around all these problem, the current version of libev uses its
+epoll backend as a fallback for file descriptor types that do not work. Or
+falls back completely to epoll if the kernel acts up.
 .Sp
 This backend maps \f(CW\*(C`EV_READ\*(C'\fR and \f(CW\*(C`EV_WRITE\*(C'\fR in the same way as
 \&\f(CW\*(C`EVBACKEND_POLL\*(C'\fR.
 .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
+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 \s-1API\s0 changes to existing programs. For this reason it's not being
+fixed without \s-1API\s0 changes to existing programs. For this reason it's not
-\&\*(L"auto-detected\*(R" unless you explicitly specify it in the flags (i.e. using
+being \*(L"auto-detected\*(R" on all platforms unless you explicitly specify it
-\&\f(CW\*(C`EVBACKEND_KQUEUE\*(C'\fR) or libev was compiled on a known-to-be-good (\-enough)
+in the flags (i.e. using \f(CW\*(C`EVBACKEND_KQUEUE\*(C'\fR) or libev was compiled on a
-system like NetBSD.
+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, of
 course). While stopping, setting and starting an I/O watcher does never
 cause an extra system call as with \f(CW\*(C`EVBACKEND_EPOLL\*(C'\fR, it still adds up to
 two event changes per incident. Support for \f(CW\*(C`fork ()\*(C'\fR 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.
 .Sp
 This backend usually performs well under most conditions.
 .Sp
 While nominally embeddable in other event loops, this doesn't work
 called. If set to \f(CW2\fR, then the internal verification code will be
 called once per loop, which can slow down libev. If set to \f(CW3\fR, then the
 verification code will be called very frequently, which will slow down
 libev considerably.
 .Sp
+Verification errors are reported via C's \f(CW\*(C`assert\*(C'\fR mechanism, so if you
+disable that (e.g. by defining \f(CW\*(C`NDEBUG\*(C'\fR) then no errors will be reported.
+.Sp
 The default is \f(CW1\fR, unless \f(CW\*(C`EV_FEATURES\*(C'\fR overrides it, in which case it
 will be \f(CW0\fR.
 .IP "\s-1EV_COMMON\s0" 4
 .IX Item "EV_COMMON"
 By default, all watchers have a \f(CW\*(C`void *data\*(C'\fR member. By redefining

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Comparing libev/ev.3 (file contents): Revision 1.111 by root, Sun Jun 23 02:02:24 2019 UTC vs. Revision 1.115 by root, Wed Jun 26 00:01:46 2019 UTC

Diff Legend

Comparing libev/ev.3 (file contents):
Revision 1.111 by root, Sun Jun 23 02:02:24 2019 UTC vs.
Revision 1.115 by root, Wed Jun 26 00:01:46 2019 UTC