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4.11

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Marc Alexander Lehmann 9 years ago
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4 changed files with 319 additions and 114 deletions
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  1. 4
      Changes
  2. 2
      configure.ac
  3. 423
      ev.3
  4. 4
      ev.h

4
Changes
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@ -1,9 +1,9 @@
Revision history for libev, a high-performance and full-featured event loop.
TODO: ev_loop_wakeup
TODO: EV_STANDALONE == NO_HASSEL (do not use clock_gettime in ev_standalone)
4.11
4.11 Sat Feb 4 19:52:39 CET 2012
- INCOMPATIBLE CHANGE: ev_timer_again now clears the pending status, as
was documented already, but not implemented in the repeating case.
- new compiletime symbols: EV_NO_SMP and EV_NO_THREADS.

2
configure.ac
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@ -1,7 +1,7 @@
AC_INIT
AC_CONFIG_SRCDIR([ev_epoll.c])
AM_INIT_AUTOMAKE(libev,4.09) dnl also update ev.h!
AM_INIT_AUTOMAKE(libev,4.11) dnl also update ev.h!
AC_CONFIG_HEADERS([config.h])
AM_MAINTAINER_MODE

423
ev.3
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@ -1,4 +1,4 @@
.\" Automatically generated by Pod::Man 2.22 (Pod::Simple 3.07)
.\" Automatically generated by Pod::Man 2.23 (Pod::Simple 3.14)
.\"
.\" Standard preamble:
.\" ========================================================================
@ -124,7 +124,7 @@
.\" ========================================================================
.\"
.IX Title "LIBEV 3"
.TH LIBEV 3 "2011-02-16" "libev-4.04" "libev - high performance full featured event loop"
.TH LIBEV 3 "2012-02-04" "libev-4.11" "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
@ -246,7 +246,7 @@ loop mechanism itself (\f(CW\*(C`ev_idle\*(C'\fR, \f(CW\*(C`ev_embed\*(C'\fR, \f
limited support for fork events (\f(CW\*(C`ev_fork\*(C'\fR).
.PP
It also is quite fast (see this
<benchmark> comparing it to libevent
benchmark <http://libev.schmorp.de/bench.html> comparing it to libevent
for example).
.SS "\s-1CONVENTIONS\s0"
.IX Subsection "CONVENTIONS"
@ -296,12 +296,18 @@ library in any way.
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. Also interesting is the combination of
\&\f(CW\*(C`ev_update_now\*(C'\fR and \f(CW\*(C`ev_now\*(C'\fR.
\&\f(CW\*(C`ev_now_update\*(C'\fR and \f(CW\*(C`ev_now\*(C'\fR.
.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 sub-second-resolution \f(CW\*(C`sleep ()\*(C'\fR.
Sleep for the given interval: The current thread will be blocked
until either it is interrupted or the given time interval has
passed (approximately \- it might return a bit earlier even if not
interrupted). Returns immediately if \f(CW\*(C`interval <= 0\*(C'\fR.
.Sp
Basically this is a sub-second-resolution \f(CW\*(C`sleep ()\*(C'\fR.
.Sp
The range of the \f(CW\*(C`interval\*(C'\fR is limited \- libev only guarantees to work
with sleep times of up to one day (\f(CW\*(C`interval <= 86400\*(C'\fR).
.IP "int ev_version_major ()" 4
.IX Item "int ev_version_major ()"
.PD 0
@ -555,7 +561,7 @@ example) that can't properly initialise their signal masks.
.el .IP "\f(CWEVFLAG_NOSIGMASK\fR" 4
.IX Item "EVFLAG_NOSIGMASK"
When this flag is specified, then libev will avoid to modify the signal
mask. Specifically, this means you ahve to make sure signals are unblocked
mask. Specifically, this means you have to make sure signals are unblocked
when you want to receive them.
.Sp
This behaviour is useful when you want to do your own signal handling, or
@ -603,10 +609,10 @@ This backend maps \f(CW\*(C`EV_READ\*(C'\fR to \f(CW\*(C`POLLIN | POLLERR | POLL
Use the linux-specific \fIepoll\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 n is the total number of fds (or the highest fd),
epoll scales either O(1) or O(active_fds).
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
fd), epoll scales either O(1) or O(active_fds).
.Sp
The epoll mechanism deserves honorable mention as the most misdesigned
of the more advanced event mechanisms: mere annoyances include silently
@ -619,19 +625,22 @@ forks then \fIboth\fR parent and child process have to recreate the epoll
set, which can take considerable time (one syscall per file descriptor)
and is of course hard to detect.
.Sp
Epoll is also notoriously buggy \- embedding epoll fds \fIshould\fR work, but
of course \fIdoesn't\fR, and epoll just loves to report events for totally
\&\fIdifferent\fR file descriptors (even already closed ones, so one cannot
even remove them from the set) than registered in the set (especially
on \s-1SMP\s0 systems). Libev tries to counter these spurious notifications by
employing an additional generation counter and comparing that against the
events to filter out spurious ones, recreating the set when required. Last
Epoll is also notoriously buggy \- embedding epoll fds \fIshould\fR work,
but of course \fIdoesn't\fR, and epoll just loves to report events for
totally \fIdifferent\fR file descriptors (even already closed ones, so
one cannot even remove them from the set) than registered in the set
(especially on \s-1SMP\s0 systems). Libev tries to counter these spurious
notifications by employing an additional generation counter and comparing
that against the events to filter out spurious ones, recreating the set
when required. Epoll also erroneously rounds down timeouts, but gives you
no way to know when and by how much, so sometimes you have to busy-wait
because epoll returns immediately despite a nonzero timeout. And last
not least, it also refuses to work with some file descriptors which work
perfectly fine with \f(CW\*(C`select\*(C'\fR (files, many character devices...).
.Sp
Epoll is truly the train wreck analog among event poll mechanisms,
a frankenpoll, cobbled together in a hurry, no thought to design or
interaction with others.
Epoll is truly the train wreck among event poll mechanisms, a frankenpoll,
cobbled together in a hurry, no thought to design or interaction with
others. Oh, the pain, will it ever stop...
.Sp
While stopping, setting and starting an I/O watcher in the same iteration
will result in some caching, there is still a system call per such
@ -719,11 +728,11 @@ hacks).
.Sp
On the negative side, the interface is \fIbizarre\fR \- so bizarre that
even sun itself gets it wrong in their code examples: The event polling
function sometimes returning events to the caller even though an error
function sometimes returns events to the caller even though an error
occurred, but with no indication whether it has done so or not (yes, it's
even documented that way) \- deadly for edge-triggered interfaces where
you absolutely have to know whether an event occurred or not because you
have to re-arm the watcher.
even documented that way) \- deadly for edge-triggered interfaces where you
absolutely have to know whether an event occurred or not because you have
to re-arm the watcher.
.Sp
Fortunately libev seems to be able to work around these idiocies.
.Sp
@ -944,7 +953,9 @@ with something not expressible using other libev watchers (i.e. "roll your
own \f(CW\*(C`ev_run\*(C'\fR"). However, a pair of \f(CW\*(C`ev_prepare\*(C'\fR/\f(CW\*(C`ev_check\*(C'\fR watchers is
usually a better approach for this kind of thing.
.Sp
Here are the gory details of what \f(CW\*(C`ev_run\*(C'\fR does:
Here are the gory details of what \f(CW\*(C`ev_run\*(C'\fR does (this is for your
understanding, not a guarantee that things will work exactly like this in
future versions):
.Sp
.Vb 10
\& \- Increment loop depth.
@ -1069,10 +1080,11 @@ overhead for the actual polling but can deliver many events at once.
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 value will
\&\f(CW\*(C`ev_timer\*(C'\fR) will not be affected. Setting this to a non-null value will
introduce an additional \f(CW\*(C`ev_sleep ()\*(C'\fR call into most loop iterations. The
sleep time ensures that libev will not poll for I/O events more often then
once per this interval, on average.
once per this interval, on average (as long as the host time resolution is
good enough).
.Sp
Likewise, by setting a higher \fItimeout collect interval\fR you allow libev
to spend more time collecting timeouts, at the expense of increased
@ -1134,7 +1146,7 @@ each call to a libev function.
.Sp
However, \f(CW\*(C`ev_run\*(C'\fR can run an indefinite time, so it is not feasible
to wait for it to return. One way around this is to wake up the event
loop via \f(CW\*(C`ev_break\*(C'\fR and \f(CW\*(C`av_async_send\*(C'\fR, another way is to set these
loop via \f(CW\*(C`ev_break\*(C'\fR and \f(CW\*(C`ev_async_send\*(C'\fR, another way is to set these
\&\fIrelease\fR and \fIacquire\fR callbacks on the loop.
.Sp
When set, then \f(CW\*(C`release\*(C'\fR will be called just before the thread is
@ -1491,7 +1503,7 @@ transition between them will be described in more detail \- and while these
rules might look complicated, they usually do \*(L"the right thing\*(R".
.IP "initialiased" 4
.IX Item "initialiased"
Before a watcher can be registered with the event looop it has to be
Before a watcher can be registered with the event loop it has to be
initialised. This can be done with a call to \f(CW\*(C`ev_TYPE_init\*(C'\fR, or calls to
\&\f(CW\*(C`ev_init\*(C'\fR followed by the watcher-specific \f(CW\*(C`ev_TYPE_set\*(C'\fR function.
.Sp
@ -1873,10 +1885,11 @@ monotonic clock option helps a lot here).
.PP
The callback is guaranteed to be invoked only \fIafter\fR its timeout has
passed (not \fIat\fR, so on systems with very low-resolution clocks this
might introduce a small delay). If multiple timers become ready during the
same loop iteration then the ones with earlier time-out values are invoked
before ones of the same priority with later time-out values (but this is
no longer true when a callback calls \f(CW\*(C`ev_run\*(C'\fR recursively).
might introduce a small delay, see \*(L"the special problem of being too
early\*(R", below). If multiple timers become ready during the same loop
iteration then the ones with earlier time-out values are invoked before
ones of the same priority with later time-out values (but this is no
longer true when a callback calls \f(CW\*(C`ev_run\*(C'\fR recursively).
.PP
\fIBe smart about timeouts\fR
.IX Subsection "Be smart about timeouts"
@ -1968,68 +1981,84 @@ In this case, it would be more efficient to leave the \f(CW\*(C`ev_timer\*(C'\fR
but remember the time of last activity, and check for a real timeout only
within the callback:
.Sp
.Vb 1
.Vb 3
\& ev_tstamp timeout = 60.;
\& ev_tstamp last_activity; // time of last activity
\& ev_timer timer;
\&
\& static void
\& callback (EV_P_ ev_timer *w, int revents)
\& {
\& ev_tstamp now = ev_now (EV_A);
\& ev_tstamp timeout = last_activity + 60.;
\& // calculate when the timeout would happen
\& ev_tstamp after = last_activity \- ev_now (EV_A) + timeout;
\&
\& // if last_activity + 60. is older than now, we did time out
\& if (timeout < now)
\& // if negative, it means we the timeout already occured
\& if (after < 0.)
\& {
\& // timeout occurred, take action
\& }
\& else
\& {
\& // callback was invoked, but there was some activity, re\-arm
\& // the watcher to fire in last_activity + 60, which is
\& // guaranteed to be in the future, so "again" is positive:
\& w\->repeat = timeout \- now;
\& ev_timer_again (EV_A_ w);
\& // callback was invoked, but there was some recent
\& // activity. simply restart the timer to time out
\& // after "after" seconds, which is the earliest time
\& // the timeout can occur.
\& ev_timer_set (w, after, 0.);
\& ev_timer_start (EV_A_ w);
\& }
\& }
.Ve
.Sp
To summarise the callback: first calculate the real timeout (defined
as \*(L"60 seconds after the last activity\*(R"), then check if that time has
been reached, which means something \fIdid\fR, in fact, time out. Otherwise
the callback was invoked too early (\f(CW\*(C`timeout\*(C'\fR is in the future), so
re-schedule the timer to fire at that future time, to see if maybe we have
a timeout then.
To summarise the callback: first calculate in how many seconds the
timeout will occur (by calculating the absolute time when it would occur,
\&\f(CW\*(C`last_activity + timeout\*(C'\fR, and subtracting the current time, \f(CW\*(C`ev_now
(EV_A)\*(C'\fR from that).
.Sp
Note how \f(CW\*(C`ev_timer_again\*(C'\fR is used, taking advantage of the
\&\f(CW\*(C`ev_timer_again\*(C'\fR optimisation when the timer is already running.
If this value is negative, then we are already past the timeout, i.e. we
timed out, and need to do whatever is needed in this case.
.Sp
Otherwise, we now the earliest time at which the timeout would trigger,
and simply start the timer with this timeout value.
.Sp
In other words, each time the callback is invoked it will check whether
the timeout cocured. If not, it will simply reschedule itself to check
again at the earliest time it could time out. Rinse. Repeat.
.Sp
This scheme causes more callback invocations (about one every 60 seconds
minus half the average time between activity), but virtually no calls to
libev to change the timeout.
.Sp
To start the timer, simply initialise the watcher and set \f(CW\*(C`last_activity\*(C'\fR
to the current time (meaning we just have some activity :), then call the
callback, which will \*(L"do the right thing\*(R" and start the timer:
To start the machinery, simply initialise the watcher and set
\&\f(CW\*(C`last_activity\*(C'\fR to the current time (meaning there was some activity just
now), then call the callback, which will \*(L"do the right thing\*(R" and start
the timer:
.Sp
.Vb 3
\& ev_init (timer, callback);
\& last_activity = ev_now (loop);
\& callback (loop, timer, EV_TIMER);
\& last_activity = ev_now (EV_A);
\& ev_init (&timer, callback);
\& callback (EV_A_ &timer, 0);
.Ve
.Sp
And when there is some activity, simply store the current time in
When there is some activity, simply store the current time in
\&\f(CW\*(C`last_activity\*(C'\fR, no libev calls at all:
.Sp
.Vb 1
\& last_activity = ev_now (loop);
.Vb 2
\& if (activity detected)
\& last_activity = ev_now (EV_A);
.Ve
.Sp
When your timeout value changes, then the timeout can be changed by simply
providing a new value, stopping the timer and calling the callback, which
will agaion do the right thing (for example, time out immediately :).
.Sp
.Vb 3
\& timeout = new_value;
\& ev_timer_stop (EV_A_ &timer);
\& callback (EV_A_ &timer, 0);
.Ve
.Sp
This technique is slightly more complex, but in most cases where the
time-out is unlikely to be triggered, much more efficient.
.Sp
Changing the timeout is trivial as well (if it isn't hard-coded in the
callback :) \- just change the timeout and invoke the callback, which will
fix things for you.
.IP "4. Wee, just use a double-linked list for your timeouts." 4
.IX Item "4. Wee, just use a double-linked list for your timeouts."
If there is not one request, but many thousands (millions...), all
@ -2063,11 +2092,49 @@ rather complicated, but extremely efficient, something that really pays
off after the first million or so of active timers, i.e. it's usually
overkill :)
.PP
\fIThe special problem of being too early\fR
.IX Subsection "The special problem of being too early"
.PP
If you ask a timer to call your callback after three seconds, then
you expect it to be invoked after three seconds \- but of course, this
cannot be guaranteed to infinite precision. Less obviously, it cannot be
guaranteed to any precision by libev \- imagine somebody suspending the
process with a \s-1STOP\s0 signal for a few hours for example.
.PP
So, libev tries to invoke your callback as soon as possible \fIafter\fR the
delay has occurred, but cannot guarantee this.
.PP
A less obvious failure mode is calling your callback too early: many event
loops compare timestamps with a \*(L"elapsed delay >= requested delay\*(R", but
this can cause your callback to be invoked much earlier than you would
expect.
.PP
To see why, imagine a system with a clock that only offers full second
resolution (think windows if you can't come up with a broken enough \s-1OS\s0
yourself). If you schedule a one-second timer at the time 500.9, then the
event loop will schedule your timeout to elapse at a system time of 500
(500.9 truncated to the resolution) + 1, or 501.
.PP
If an event library looks at the timeout 0.1s later, it will see \*(L"501 >=
501\*(R" and invoke the callback 0.1s after it was started, even though a
one-second delay was requested \- this is being \*(L"too early\*(R", despite best
intentions.
.PP
This is the reason why libev will never invoke the callback if the elapsed
delay equals the requested delay, but only when the elapsed delay is
larger than the requested delay. In the example above, libev would only invoke
the callback at system time 502, or 1.1s after the timer was started.
.PP
So, while libev cannot guarantee that your callback will be invoked
exactly when requested, it \fIcan\fR and \fIdoes\fR guarantee that the requested
delay has actually elapsed, or in other words, it always errs on the \*(L"too
late\*(R" side of things.
.PP
\fIThe special problem of time updates\fR
.IX Subsection "The special problem of time updates"
.PP
Establishing the current time is a costly operation (it usually takes at
least two system calls): \s-1EV\s0 therefore updates its idea of the current
Establishing the current time is a costly operation (it usually takes
at least one system call): \s-1EV\s0 therefore updates its idea of the current
time only before and after \f(CW\*(C`ev_run\*(C'\fR collects new events, which causes a
growing difference between \f(CW\*(C`ev_now ()\*(C'\fR and \f(CW\*(C`ev_time ()\*(C'\fR when handling
lots of events in one iteration.
@ -2086,6 +2153,40 @@ If the event loop is suspended for a long time, you can also force an
update of the time returned by \f(CW\*(C`ev_now ()\*(C'\fR by calling \f(CW\*(C`ev_now_update
()\*(C'\fR.
.PP
\fIThe special problem of unsynchronised clocks\fR
.IX Subsection "The special problem of unsynchronised clocks"
.PP
Modern systems have a variety of clocks \- libev itself uses the normal
\&\*(L"wall clock\*(R" clock and, if available, the monotonic clock (to avoid time
jumps).
.PP
Neither of these clocks is synchronised with each other or any other clock
on the system, so \f(CW\*(C`ev_time ()\*(C'\fR might return a considerably different time
than \f(CW\*(C`gettimeofday ()\*(C'\fR or \f(CW\*(C`time ()\*(C'\fR. On a GNU/Linux system, for example,
a call to \f(CW\*(C`gettimeofday\*(C'\fR might return a second count that is one higher
than a directly following call to \f(CW\*(C`time\*(C'\fR.
.PP
The moral of this is to only compare libev-related timestamps with
\&\f(CW\*(C`ev_time ()\*(C'\fR and \f(CW\*(C`ev_now ()\*(C'\fR, at least if you want better precision than
a second or so.
.PP
One more problem arises due to this lack of synchronisation: if libev uses
the system monotonic clock and you compare timestamps from \f(CW\*(C`ev_time\*(C'\fR
or \f(CW\*(C`ev_now\*(C'\fR from when you started your timer and when your callback is
invoked, you will find that sometimes the callback is a bit \*(L"early\*(R".
.PP
This is because \f(CW\*(C`ev_timer\*(C'\fRs work in real time, not wall clock time, so
libev makes sure your callback is not invoked before the delay happened,
\&\fImeasured according to the real time\fR, not the system clock.
.PP
If your timeouts are based on a physical timescale (e.g. \*(L"time out this
connection after 100 seconds\*(R") then this shouldn't bother you as it is
exactly the right behaviour.
.PP
If you want to compare wall clock/system timestamps to your timers, then
you need to use \f(CW\*(C`ev_periodic\*(C'\fRs, as these are based on the wall clock
time, where your comparisons will always generate correct results.
.PP
\fIThe special problems of suspended animation\fR
.IX Subsection "The special problems of suspended animation"
.PP
@ -2138,18 +2239,28 @@ keep up with the timer (because it takes longer than those 10 seconds to
do stuff) the timer will not fire more than once per event loop iteration.
.IP "ev_timer_again (loop, ev_timer *)" 4
.IX Item "ev_timer_again (loop, ev_timer *)"
This will act as if the timer timed out and restart it again if it is
repeating. The exact semantics are:
.Sp
If the timer is pending, its pending status is cleared.
.Sp
If the timer is started but non-repeating, stop it (as if it timed out).
This will act as if the timer timed out, and restarts it again if it is
repeating. It basically works like calling \f(CW\*(C`ev_timer_stop\*(C'\fR, updating the
timeout to the \f(CW\*(C`repeat\*(C'\fR value and calling \f(CW\*(C`ev_timer_start\*(C'\fR.
.Sp
If the timer is repeating, either start it if necessary (with the
\&\f(CW\*(C`repeat\*(C'\fR value), or reset the running timer to the \f(CW\*(C`repeat\*(C'\fR value.
The exact semantics are as in the following rules, all of which will be
applied to the watcher:
.RS 4
.IP "If the timer is pending, the pending status is always cleared." 4
.IX Item "If the timer is pending, the pending status is always cleared."
.PD 0
.IP "If the timer is started but non-repeating, stop it (as if it timed out, without invoking it)." 4
.IX Item "If the timer is started but non-repeating, stop it (as if it timed out, without invoking it)."
.ie n .IP "If the timer is repeating, make the ""repeat"" value the new timeout and start the timer, if necessary." 4
.el .IP "If the timer is repeating, make the \f(CWrepeat\fR value the new timeout and start the timer, if necessary." 4
.IX Item "If the timer is repeating, make the repeat value the new timeout and start the timer, if necessary."
.RE
.RS 4
.PD
.Sp
This sounds a bit complicated, see \*(L"Be smart about timeouts\*(R", above, for a
usage example.
.RE
.IP "ev_tstamp ev_timer_remaining (loop, ev_timer *)" 4
.IX Item "ev_tstamp ev_timer_remaining (loop, ev_timer *)"
Returns the remaining time until a timer fires. If the timer is active,
@ -2279,9 +2390,12 @@ Another way to think about it (for the mathematically inclined) is that
\&\f(CW\*(C`ev_periodic\*(C'\fR will try to run the callback in this mode at the next possible
time where \f(CW\*(C`time = offset (mod interval)\*(C'\fR, regardless of any time jumps.
.Sp
For numerical stability it is preferable that the \f(CW\*(C`offset\*(C'\fR value is near
\&\f(CW\*(C`ev_now ()\*(C'\fR (the current time), but there is no range requirement for
this value, and in fact is often specified as zero.
The \f(CW\*(C`interval\*(C'\fR \fI\s-1MUST\s0\fR be positive, and for numerical stability, the
interval value should be higher than \f(CW\*(C`1/8192\*(C'\fR (which is around 100
microseconds) and \f(CW\*(C`offset\*(C'\fR should be higher than \f(CW0\fR and should have
at most a similar magnitude as the current time (say, within a factor of
ten). Typical values for offset are, in fact, \f(CW0\fR or something between
\&\f(CW0\fR and \f(CW\*(C`interval\*(C'\fR, which is also the recommended range.
.Sp
Note also that there is an upper limit to how often a timer can fire (\s-1CPU\s0
speed for example), so if \f(CW\*(C`interval\*(C'\fR is very small then timing stability
@ -3333,9 +3447,6 @@ of \*(L"global async watchers\*(R" by using a watcher on an otherwise unused
signal, and \f(CW\*(C`ev_feed_signal\*(C'\fR to signal this watcher from another thread,
even without knowing which loop owns the signal.
.PP
Unlike \f(CW\*(C`ev_signal\*(C'\fR watchers, \f(CW\*(C`ev_async\*(C'\fR works with any event loop, not
just the default loop.
.PP
\fIQueueing\fR
.IX Subsection "Queueing"
.PP
@ -3439,13 +3550,16 @@ signal or similar contexts (see the discussion of \f(CW\*(C`EV_ATOMIC_T\*(C'\fR
embedding section below on what exactly this means).
.Sp
Note that, as with other watchers in libev, multiple events might get
compressed into a single callback invocation (another way to look at this
is that \f(CW\*(C`ev_async\*(C'\fR watchers are level-triggered, set on \f(CW\*(C`ev_async_send\*(C'\fR,
reset when the event loop detects that).
.Sp
This call incurs the overhead of a system call only once per event loop
iteration, so while the overhead might be noticeable, it doesn't apply to
repeated calls to \f(CW\*(C`ev_async_send\*(C'\fR for the same event loop.
compressed into a single callback invocation (another way to look at
this is that \f(CW\*(C`ev_async\*(C'\fR watchers are level-triggered: they are set on
\&\f(CW\*(C`ev_async_send\*(C'\fR, reset when the event loop detects that).
.Sp
This call incurs the overhead of at most one extra system call per event
loop iteration, if the event loop is blocked, and no syscall at all if
the event loop (or your program) is processing events. That means that
repeated calls are basically free (there is no need to avoid calls for
performance reasons) and that the overhead becomes smaller (typically
zero) under load.
.IP "bool = ev_async_pending (ev_async *)" 4
.IX Item "bool = ev_async_pending (ev_async *)"
Returns a non-zero value when \f(CW\*(C`ev_async_send\*(C'\fR has been called on the
@ -3503,7 +3617,7 @@ Example: wait up to ten seconds for data to appear on \s-1STDIN_FILENO\s0.
.IP "ev_feed_fd_event (loop, int fd, int revents)" 4
.IX Item "ev_feed_fd_event (loop, int fd, int revents)"
Feed an event on the given fd, as if a file descriptor backend detected
the given events it.
the given events.
.IP "ev_feed_signal_event (loop, int signum)" 4
.IX Item "ev_feed_signal_event (loop, int signum)"
Feed an event as if the given signal occurred. See also \f(CW\*(C`ev_feed_signal\*(C'\fR,
@ -3587,6 +3701,49 @@ real programmers):
\& (((char *)w) \- offsetof (struct my_biggy, t2));
\& }
.Ve
.SS "\s-1AVOIDING\s0 \s-1FINISHING\s0 \s-1BEFORE\s0 \s-1RETURNING\s0"
.IX Subsection "AVOIDING FINISHING BEFORE RETURNING"
Often you have structures like this in event-based programs:
.PP
.Vb 4
\& callback ()
\& {
\& free (request);
\& }
\&
\& request = start_new_request (..., callback);
.Ve
.PP
The intent is to start some \*(L"lengthy\*(R" operation. The \f(CW\*(C`request\*(C'\fR could be
used to cancel the operation, or do other things with it.
.PP
It's not uncommon to have code paths in \f(CW\*(C`start_new_request\*(C'\fR that
immediately invoke the callback, for example, to report errors. Or you add
some caching layer that finds that it can skip the lengthy aspects of the
operation and simply invoke the callback with the result.
.PP
The problem here is that this will happen \fIbefore\fR \f(CW\*(C`start_new_request\*(C'\fR
has returned, so \f(CW\*(C`request\*(C'\fR is not set.
.PP
Even if you pass the request by some safer means to the callback, you
might want to do something to the request after starting it, such as
canceling it, which probably isn't working so well when the callback has
already been invoked.
.PP
A common way around all these issues is to make sure that
\&\f(CW\*(C`start_new_request\*(C'\fR \fIalways\fR returns before the callback is invoked. If
\&\f(CW\*(C`start_new_request\*(C'\fR immediately knows the result, it can artificially
delay invoking the callback by e.g. using a \f(CW\*(C`prepare\*(C'\fR or \f(CW\*(C`idle\*(C'\fR watcher
for example, or more sneakily, by reusing an existing (stopped) watcher
and pushing it into the pending queue:
.PP
.Vb 2
\& ev_set_cb (watcher, callback);
\& ev_feed_event (EV_A_ watcher, 0);
.Ve
.PP
This way, \f(CW\*(C`start_new_request\*(C'\fR can safely return before the callback is
invoked, while not delaying callback invocation too much.
.SS "\s-1MODEL/NESTED\s0 \s-1EVENT\s0 \s-1LOOP\s0 \s-1INVOCATIONS\s0 \s-1AND\s0 \s-1EXIT\s0 \s-1CONDITIONS\s0"
.IX Subsection "MODEL/NESTED EVENT LOOP INVOCATIONS AND EXIT CONDITIONS"
Often (especially in \s-1GUI\s0 toolkits) there are places where you have
@ -3610,7 +3767,7 @@ triggered, using \f(CW\*(C`EVRUN_ONCE\*(C'\fR:
\& while (!exit_main_loop)
\& ev_run (EV_DEFAULT_ EVRUN_ONCE);
\&
\& // in a model watcher
\& // in a modal watcher
\& int exit_nested_loop = 0;
\&
\& while (!exit_nested_loop)
@ -3819,7 +3976,7 @@ called):
.PP
That basically suspends the coroutine inside \f(CW\*(C`wait_for_event\*(C'\fR and
continues the libev coroutine, which, when appropriate, switches back to
this or any other coroutine. I am sure if you sue this your own :)
this or any other coroutine.
.PP
You can do similar tricks if you have, say, threads with an event queue \-
instead of storing a coroutine, you store the queue object and instead of
@ -3917,7 +4074,7 @@ Aliases to the same types/functions as with the \f(CW\*(C`ev_\*(C'\fR prefix.
For each \f(CW\*(C`ev_TYPE\*(C'\fR watcher in \fIev.h\fR there is a corresponding class of
the same name in the \f(CW\*(C`ev\*(C'\fR namespace, with the exception of \f(CW\*(C`ev_signal\*(C'\fR
which is called \f(CW\*(C`ev::sig\*(C'\fR to avoid clashes with the \f(CW\*(C`signal\*(C'\fR macro
defines by many implementations.
defined by many implementations.
.Sp
All of those classes have these methods:
.RS 4
@ -4058,7 +4215,7 @@ watchers in the constructor.
\& class myclass
\& {
\& ev::io io ; void io_cb (ev::io &w, int revents);
\& ev::io2 io2 ; void io2_cb (ev::io &w, int revents);
\& ev::io io2 ; void io2_cb (ev::io &w, int revents);
\& ev::idle idle; void idle_cb (ev::idle &w, int revents);
\&
\& myclass (int fd)
@ -4107,20 +4264,20 @@ makes rev work even on mingw.
.IP "Haskell" 4
.IX Item "Haskell"
A haskell binding to libev is available at
<http://hackage.haskell.org/cgi\-bin/hackage\-scripts/package/hlibev>.
http://hackage.haskell.org/cgi\-bin/hackage\-scripts/package/hlibev <http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.
.IP "D" 4
.IX Item "D"
Leandro Lucarella has written a D language binding (\fIev.d\fR) for libev, to
be found at <http://proj.llucax.com.ar/wiki/evd>.
be found at <http://www.llucax.com.ar/proj/ev.d/index.html>.
.IP "Ocaml" 4
.IX Item "Ocaml"
Erkki Seppala has written Ocaml bindings for libev, to be found at
<http://modeemi.cs.tut.fi/~flux/software/ocaml\-ev/>.
http://modeemi.cs.tut.fi/~flux/software/ocaml\-ev/ <http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.
.IP "Lua" 4
.IX Item "Lua"
Brian Maher has written a partial interface to libev for lua (at the
time of this writing, only \f(CW\*(C`ev_io\*(C'\fR and \f(CW\*(C`ev_timer\*(C'\fR), to be found at
<http://github.com/brimworks/lua\-ev>.
http://github.com/brimworks/lua\-ev <http://github.com/brimworks/lua-ev>.
.SH "MACRO MAGIC"
.IX Header "MACRO MAGIC"
Libev can be compiled with a variety of options, the most fundamental
@ -4165,7 +4322,11 @@ suitable for use with \f(CW\*(C`EV_A\*(C'\fR.
.el .IP "\f(CWEV_DEFAULT\fR, \f(CWEV_DEFAULT_\fR" 4
.IX Item "EV_DEFAULT, EV_DEFAULT_"
Similar to the other two macros, this gives you the value of the default
loop, if multiple loops are supported (\*(L"ev loop default\*(R").
loop, if multiple loops are supported (\*(L"ev loop default\*(R"). The default loop
will be initialised if it isn't already initialised.
.Sp
For non-multiplicity builds, these macros do nothing, so you always have
to initialise the loop somewhere.
.ie n .IP """EV_DEFAULT_UC"", ""EV_DEFAULT_UC_""" 4
.el .IP "\f(CWEV_DEFAULT_UC\fR, \f(CWEV_DEFAULT_UC_\fR" 4
.IX Item "EV_DEFAULT_UC, EV_DEFAULT_UC_"
@ -4330,6 +4491,14 @@ supported). It will also not define any of the structs usually found in
.Sp
In standalone mode, libev will still try to automatically deduce the
configuration, but has to be more conservative.
.IP "\s-1EV_USE_FLOOR\s0" 4
.IX Item "EV_USE_FLOOR"
If defined to be \f(CW1\fR, libev will use the \f(CW\*(C`floor ()\*(C'\fR function for its
periodic reschedule calculations, otherwise libev will fall back on a
portable (slower) implementation. If you enable this, you usually have to
link against libm or something equivalent. Enabling this when the \f(CW\*(C`floor\*(C'\fR
function is not available will fail, so the safe default is to not enable
this.
.IP "\s-1EV_USE_MONOTONIC\s0" 4
.IX Item "EV_USE_MONOTONIC"
If defined to be \f(CW1\fR, libev will try to detect the availability of the
@ -4451,16 +4620,30 @@ If defined to be \f(CW1\fR, libev will compile in support for the Linux inotify
interface to speed up \f(CW\*(C`ev_stat\*(C'\fR watchers. Its actual availability will
be detected at runtime. If undefined, it will be enabled if the headers
indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
.IP "\s-1EV_NO_SMP\s0" 4
.IX Item "EV_NO_SMP"
If defined to be \f(CW1\fR, libev will assume that memory is always coherent
between threads, that is, threads can be used, but threads never run on
different cpus (or different cpu cores). This reduces dependencies
and makes libev faster.
.IP "\s-1EV_NO_THREADS\s0" 4
.IX Item "EV_NO_THREADS"
If defined to be \f(CW1\fR, libev will assume that it will never be called
from different threads, which is a stronger assumption than \f(CW\*(C`EV_NO_SMP\*(C'\fR,
above. This reduces dependencies and makes libev faster.
.IP "\s-1EV_ATOMIC_T\s0" 4
.IX Item "EV_ATOMIC_T"
Libev requires an integer type (suitable for storing \f(CW0\fR or \f(CW1\fR) whose
access is atomic with respect to other threads or signal contexts. No such
type is easily found in the C language, so you can provide your own type
that you know is safe for your purposes. It is used both for signal handler \*(L"locking\*(R"
as well as for signal and thread safety in \f(CW\*(C`ev_async\*(C'\fR watchers.
access is atomic and serialised with respect to other threads or signal
contexts. No such type is easily found in the C language, so you can
provide your own type that you know is safe for your purposes. It is used
both for signal handler \*(L"locking\*(R" as well as for signal and thread safety
in \f(CW\*(C`ev_async\*(C'\fR watchers.
.Sp
In the absence of this define, libev will use \f(CW\*(C`sig_atomic_t volatile\*(C'\fR
(from \fIsignal.h\fR), which is usually good enough on most platforms.
(from \fIsignal.h\fR), which is usually good enough on most platforms,
although strictly speaking using a type that also implies a memory fence
is required.
.IP "\s-1EV_H\s0 (h)" 4
.IX Item "EV_H (h)"
The name of the \fIev.h\fR header file used to include it. The default if
@ -4488,6 +4671,10 @@ will have the \f(CW\*(C`struct ev_loop *\*(C'\fR as first argument, and you can
additional independent event loops. Otherwise there will be no support
for multiple event loops and there is no first event loop pointer
argument. Instead, all functions act on the single default loop.
.Sp
Note that \f(CW\*(C`EV_DEFAULT\*(C'\fR and \f(CW\*(C`EV_DEFAULT_\*(C'\fR will no longer provide a
default loop when multiplicity is switched off \- you always have to
initialise the loop manually in this case.
.IP "\s-1EV_MINPRI\s0" 4
.IX Item "EV_MINPRI"
.PD 0
@ -4594,6 +4781,19 @@ when you use \f(CW\*(C`\-Wl,\-\-gc\-sections \-ffunction\-sections\*(C'\fR) func
your program might be left out as well \- a binary starting a timer and an
I/O watcher then might come out at only 5Kb.
.RE
.IP "\s-1EV_API_STATIC\s0" 4
.IX Item "EV_API_STATIC"
If this symbol is defined (by default it is not), then all identifiers
will have static linkage. This means that libev will not export any
identifiers, and you cannot link against libev anymore. This can be useful
when you embed libev, only want to use libev functions in a single file,
and do not want its identifiers to be visible.
.Sp
To use this, define \f(CW\*(C`EV_API_STATIC\*(C'\fR and include \fIev.c\fR in the file that
wants to use libev.
.Sp
This option only works when libev is compiled with a C compiler, as \*(C+
doesn't support the required declaration syntax.
.IP "\s-1EV_AVOID_STDIO\s0" 4
.IX Item "EV_AVOID_STDIO"
If this is set to \f(CW1\fR at compiletime, then libev will avoid using stdio
@ -4980,7 +5180,7 @@ model. Libev still offers limited functionality on this platform in
the form of the \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR backend, and only supports socket
descriptors. This only applies when using Win32 natively, not when using
e.g. cygwin. Actually, it only applies to the microsofts own compilers,
as every compielr comes with a slightly differently broken/incompatible
as every compiler comes with a slightly differently broken/incompatible
environment.
.PP
Lifting these limitations would basically require the full
@ -5126,8 +5326,12 @@ The type \f(CW\*(C`double\*(C'\fR is used to represent timestamps. It is require
have at least 51 bits of mantissa (and 9 bits of exponent), which is
good enough for at least into the year 4000 with millisecond accuracy
(the design goal for libev). This requirement is overfulfilled by
implementations using \s-1IEEE\s0 754, which is basically all existing ones. With
\&\s-1IEEE\s0 754 doubles, you get microsecond accuracy until at least 2200.
implementations using \s-1IEEE\s0 754, which is basically all existing ones.
.Sp
With \s-1IEEE\s0 754 doubles, you get microsecond accuracy until at least the
year 2255 (and millisecond accuracy till the year 287396 \- by then, libev
is either obsolete or somebody patched it to use \f(CW\*(C`long double\*(C'\fR or
something like that, just kidding).
.PP
If you know of other additional requirements drop me a note.
.SH "ALGORITHMIC COMPLEXITIES"
@ -5191,8 +5395,9 @@ watchers becomes O(1) with respect to priority handling.
.IX Item "Processing signals: O(max_signal_number)"
.PD
Sending involves a system call \fIiff\fR there were no other \f(CW\*(C`ev_async_send\*(C'\fR
calls in the current loop iteration. Checking for async and signal events
involves iterating over all running async watchers or all signal numbers.
calls in the current loop iteration and the loop is currently
blocked. Checking for async and signal events involves iterating over all
running async watchers or all signal numbers.
.SH "PORTING FROM LIBEV 3.X TO 4.X"
.IX Header "PORTING FROM LIBEV 3.X TO 4.X"
The major version 4 introduced some incompatible changes to the \s-1API\s0.

4
ev.h
View File

@ -1,7 +1,7 @@
/*
* libev native API header
*
* Copyright (c) 2007,2008,2009,2010,2011 Marc Alexander Lehmann <libev@schmorp.de>
* Copyright (c) 2007,2008,2009,2010,2011,2012 Marc Alexander Lehmann <libev@schmorp.de>
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without modifica-
@ -199,7 +199,7 @@ struct ev_loop;
/*****************************************************************************/
#define EV_VERSION_MAJOR 4
#define EV_VERSION_MINOR 4
#define EV_VERSION_MINOR 11
/* eventmask, revents, events... */
enum {

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