ev_io - is this file descriptor readable or writableev_timer - relative and optionally recurring timeoutsev_periodic - to cron or not to cronev_signal - signal me when a signal gets signalledev_child - wait for pid status changesev_idle - when you've got nothing better to doev_prepare and ev_check - customise your event loopev_embed - when one backend isn't enoughev_io - is this file descriptor readable or writable?
+
+ev_timer - relative and optionally repeating timeoutsev_periodic - to cron or not to cron?ev_signal - signal me when a signal gets signalled!ev_child - watch out for process status changesev_stat - did the file attributes just change?ev_idle - when you've got nothing better to do...ev_prepare and ev_check - customise your event loop!ev_embed - when one backend isn't enough...ev_fork - the audacity to resume the event loop after a forklibev - a high performance full-featured event loop written in C
#include <ev.h>
#include <ev.h>
+
+ ev_io stdin_watcher;
+ ev_timer timeout_watcher;
+
+ /* called when data readable on stdin */
+ static void
+ stdin_cb (EV_P_ struct ev_io *w, int revents)
+ {
+ /* puts ("stdin ready"); */
+ ev_io_stop (EV_A_ w); /* just a syntax example */
+ ev_unloop (EV_A_ EVUNLOOP_ALL); /* leave all loop calls */
+ }
+
+ static void
+ timeout_cb (EV_P_ struct ev_timer *w, int revents)
+ {
+ /* puts ("timeout"); */
+ ev_unloop (EV_A_ EVUNLOOP_ONE); /* leave one loop call */
+ }
+
+ int
+ main (void)
+ {
+ struct ev_loop *loop = ev_default_loop (0);
+
+ /* initialise an io watcher, then start it */
+ ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ);
+ ev_io_start (loop, &stdin_watcher);
+
+ /* simple non-repeating 5.5 second timeout */
+ ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
+ ev_timer_start (loop, &timeout_watcher);
+
+ /* loop till timeout or data ready */
+ ev_loop (loop, 0);
+
+ return 0;
+ }
+
+
+
+The newest version of this document is also available as a html-formatted +web page you might find easier to navigate when reading it for the first +time: 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 these event sources and provide your program with events.
@@ -83,29 +139,34 @@ details of the event, and then hand it over to libev by starting the watcher.Libev supports select, poll, the linux-specific epoll and the bsd-specific -kqueue mechanisms for file descriptor events, relative timers, absolute -timers with customised rescheduling, signal events, process status change -events (related to SIGCHLD), and event watchers dealing with the event -loop mechanism itself (idle, prepare and check watchers). It also is quite -fast (see this benchmark comparing -it to libevent for example).
+Libev supports select, poll, the Linux-specific epoll, the
+BSD-specific kqueue and the Solaris-specific event port mechanisms
+for file descriptor events (ev_io), the Linux inotify interface
+(for ev_stat), relative timers (ev_timer), absolute timers
+with customised rescheduling (ev_periodic), synchronous signals
+(ev_signal), process status change events (ev_child), and event
+watchers dealing with the event loop mechanism itself (ev_idle,
+ev_embed, ev_prepare and ev_check watchers) as well as
+file watchers (ev_stat) and even limited support for fork events
+(ev_fork).
It also is quite fast (see this +benchmark comparing it to libevent +for example).
Libev is very configurable. In this manual the default configuration
-will be described, which supports multiple event loops. For more info
-about various configuration options please have a look at the file
-README.embed in the libev distribution. If libev was configured without
-support for multiple event loops, then all functions taking an initial
-argument of name loop (which is always of type struct ev_loop *)
-will not have this argument.
Libev is very configurable. In this manual the default configuration will
+be described, which supports multiple event loops. For more info about
+various configuration options please have a look at EMBED section in
+this manual. If libev was configured without support for multiple event
+loops, then all functions taking an initial argument of name loop
+(which is always of type struct ev_loop *) will not have this argument.
Libev represents time as a single floating point number, representing the
(fractional) number of seconds since the (POSIX) epoch (somewhere near
@@ -114,12 +175,8 @@ called ev_tstamp, which is what you should use too. It usually alia
to the double type in C, and when you need to do any calculations on
it, you should treat it as such.
These functions can be called anytime, even before initialising the library in any way.
@@ -133,17 +190,19 @@ you actually want to know.You can find out the major and minor version numbers of the library +
You can find out the major and minor ABI version numbers of the library
you linked against by calling the functions ev_version_major and
ev_version_minor. If you want, you can compare against the global
symbols EV_VERSION_MAJOR and EV_VERSION_MINOR, which specify the
version of the library your program was compiled against.
These version numbers refer to the ABI version of the library, not the +release version.
Usually, it's a good idea to terminate if the major versions mismatch, -as this indicates an incompatible change. Minor versions are usually +as this indicates an incompatible change. Minor versions are usually compatible to older versions, so a larger minor version alone is usually not a problem.
-Example: make sure we haven't accidentally been linked against the wrong -version:
+Example: Make sure we haven't accidentally been linked against the wrong +version.
assert (("libev version mismatch",
ev_version_major () == EV_VERSION_MAJOR
&& ev_version_minor () >= EV_VERSION_MINOR));
@@ -183,18 +242,19 @@ recommended ones.
Sets the allocation function to use (the prototype is similar to the -realloc C function, the semantics are identical). It is used to allocate -and free memory (no surprises here). If it returns zero when memory -needs to be allocated, the library might abort or take some potentially -destructive action. The default is your system realloc function.
+Sets the allocation function to use (the prototype is similar - the +semantics is identical - to the realloc C function). It is used to +allocate and free memory (no surprises here). If it returns zero when +memory needs to be allocated, the library might abort or take some +potentially destructive action. The default is your system realloc +function.
You could override this function in high-availability programs to, say, free some memory if it cannot allocate memory, to use a special allocator, or even to sleep a while and retry until some memory is available.
-Example: replace the libev allocator with one that waits a bit and then -retries: better than mine).
+Example: Replace the libev allocator with one that waits a bit and then +retries).
static void *
- persistent_realloc (void *ptr, long size)
+ persistent_realloc (void *ptr, size_t size)
{
for (;;)
{
@@ -221,7 +281,7 @@ callback is set, then libev will expect it to remedy the sitution, no
matter what, when it returns. That is, libev will generally retry the
requested operation, or, if the condition doesn't go away, do bad stuff
(such as abort).
- Example: do the same thing as libev does internally:
+ Example: This is basically the same thing that libev does internally, too.
static void
fatal_error (const char *msg)
{
@@ -237,7 +297,7 @@ requested operation, or, if the condition doesn't go away, do bad stuff
An event loop is described by a struct ev_loop *. The library knows two
types of such loops, the default loop, which supports signals and child
@@ -275,6 +335,23 @@ or setgid) then libev will not look at the environment variable
override the flags completely if it is found in the environment. This is
useful to try out specific backends to test their performance, or to work
around bugs.
EVFLAG_FORKCHECKInstead of calling ev_default_fork or ev_loop_fork manually after
+a fork, you can also make libev check for a fork in each iteration by
+enabling this flag.
This works by calling getpid () on every iteration of the loop,
+and thus this might slow down your event loop if you do a lot of loop
+iterations and little real work, but is usually not noticeable (on my
+Linux system for example, getpid is actually a simple 5-insn sequence
+without a syscall and thus very fast, but my Linux system also has
+pthread_atfork which is even faster).
The big advantage of this flag is that you can forget about fork (and +forget about forgetting to tell libev about forking) when you use this +flag.
+This flag setting cannot be overriden or specified in the LIBEV_FLAGS
+environment variable.
EVBACKEND_SELECT (value 1, portable select backend)Example: try to create a event loop that uses epoll and nothing else.
+Example: Try to create a event loop that uses epoll and nothing else.
struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
if (!epoller)
fatal ("no epoll found here, maybe it hides under your chair");
@@ -413,6 +490,15 @@ do not need to care.
Like ev_default_fork, but acts on an event loop created by
ev_loop_new. Yes, you have to call this on every allocated event loop
after fork, and how you do this is entirely your own problem.
+ Returns the count of loop iterations for the loop, which is identical to
+the number of times libev did poll for new events. It starts at 0 and
+happily wraps around with enough iterations.
This value can sometimes be useful as a generation counter of sorts (it
+"ticks" the number of loop iterations), as it roughly corresponds with
+ev_prepare and ev_check calls.
ev_prepare/ev_check watchers is
usually a better approach for this kind of thing.
Here are the gory details of what ev_loop does:
* If there are no active watchers (reference count is zero), return. - - Queue prepare watchers and then call all outstanding watchers. +- Before the first iteration, call any pending watchers. + * If there are no active watchers (reference count is zero), return. + - Queue all prepare watchers and then call all outstanding watchers. - If we have been forked, recreate the kernel state. - Update the kernel state with all outstanding changes. - Update the "event loop time". @@ -470,7 +557,7 @@ usually a better approach for this kind of thing. were used, return, otherwise continue with step *.-Example: queue some jobs and then loop until no events are outsanding +
Example: Queue some jobs and then loop until no events are outsanding anymore.
... queue jobs here, make sure they register event watchers as long ... as they still have work to do (even an idle watcher will do..) @@ -499,24 +586,28 @@ visible to the libev user and should not keepev_loopfrom exiting no event watchers registered by it are active. It is also an excellent way to do this for generic recurring timers or from within third-party libraries. Just remember to unref after start and ref before stop. -Example: create a signal watcher, but keep it from keeping
ev_loop+Example: Create a signal watcher, but keep it from keeping
-ev_looprunning when nothing else is active.struct dv_signal exitsig; +struct ev_signal exitsig; ev_signal_init (&exitsig, sig_cb, SIGINT); - ev_signal_start (myloop, &exitsig); - evf_unref (myloop); + ev_signal_start (loop, &exitsig); + evf_unref (loop);-Example: for some weird reason, unregister the above signal handler again.
-ev_ref (myloop); - ev_signal_stop (myloop, &exitsig); +Example: For some weird reason, unregister the above signal handler again.
+ev_ref (loop); + ev_signal_stop (loop, &exitsig);
A watcher is a structure that you create and register to record your interest in some event. For instance, if you want to wait for STDIN to @@ -583,6 +674,10 @@ writable.
The pid specified in the ev_child watcher has received a status change.
EV_STATThe path specified in the ev_stat watcher changed its attributes somehow.
EV_IDLEThe ev_idle watcher has determined that you have nothing better to do.
ev_prepare watcher might start an idle watcher to keep
ev_loop from blocking).
+ EV_EMBEDThe embedded event loop specified in the ev_embed watcher needs attention.
EV_FORKThe event loop has been resumed in the child process after fork (see
+ev_fork).
EV_ERRORIn the following description, TYPE stands for the watcher type,
e.g. timer for ev_timer watchers and io for ev_io watchers.
ev_TYPE_init mac
which rolls both calls into one.
You can reinitialise a watcher at any time as long as it has been stopped (or never started) and there are no pending events outstanding.
-The callbakc is always of type The callback is always of type void (*)(ev_loop *loop, ev_TYPE *watcher,
+ void (*)(ev_loop *loop, ev_TYPE *watcher,
int revents).ev_TYPE_set (ev_TYPE *, [args])
Returns a true value iff the watcher is pending, (i.e. it has outstanding
events but its callback has not yet been invoked). As long as a watcher
is pending (but not active) you must not call an init function on it (but
-ev_TYPE_set is safe) and you must make sure the watcher is available to
-libev (e.g. you cnanot free () it).
ev_TYPE_set is safe), you must not change its priority, and you must
+make sure the watcher is available to libev (e.g. you cannot free ()
+it).
- Returns the callback currently set on the watcher.
free () it).
Change the callback. You can change the callback at virtually any time (modulo threads).
+Set and query the priority of the watcher. The priority is a small
+integer between EV_MAXPRI (default: 2) and EV_MINPRI
+(default: -2). Pending watchers with higher priority will be invoked
+before watchers with lower priority, but priority will not keep watchers
+from being executed (except for ev_idle watchers).
This means that priorities are only used for ordering callback +invocation after new events have been received. This is useful, for +example, to reduce latency after idling, or more often, to bind two +watchers on the same event and make sure one is called first.
+If you need to suppress invocation when higher priority events are pending
+you need to look at ev_idle watchers, which provide this functionality.
You must not change the priority of a watcher as long as it is active or +pending.
+The default priority used by watchers when no priority has been set is
+always 0, which is supposed to not be too high and not be too low :).
Setting a priority outside the range of EV_MINPRI to EV_MAXPRI is
+fine, as long as you do not mind that the priority value you query might
+or might not have been adjusted to be within valid range.
Invoke the watcher with the given loop and revents. Neither
+loop nor revents need to be valid as long as the watcher callback
+can deal with that fact.
If the watcher is pending, this function returns clears its pending status
+and returns its revents bitset (as if its callback was invoked). If the
+watcher isn't pending it does nothing and returns 0.
More interesting and less C-conformant ways of catsing your callback type -have been omitted....
+More interesting and less C-conformant ways of casting your callback type +instead have been omitted.
+Another common scenario is having some data structure with multiple +watchers:
+ struct my_biggy
+ {
+ int some_data;
+ ev_timer t1;
+ ev_timer t2;
+ }
+
+
+In this case getting the pointer to my_biggy is a bit more complicated,
+you need to use offsetof:
#include <stddef.h>
+
+ static void
+ t1_cb (EV_P_ struct ev_timer *w, int revents)
+ {
+ struct my_biggy big = (struct my_biggy *
+ (((char *)w) - offsetof (struct my_biggy, t1));
+ }
+
+ static void
+ t2_cb (EV_P_ struct ev_timer *w, int revents)
+ {
+ struct my_biggy big = (struct my_biggy *
+ (((char *)w) - offsetof (struct my_biggy, t2));
+ }
+
This section describes each watcher in detail, but will not repeat -information given in the last section.
+information given in the last section. Any initialisation/set macros, +functions and members specific to the watcher type are explained. +Members are additionally marked with either [read-only], meaning that, +while the watcher is active, you can look at the member and expect some +sensible content, but you must not modify it (you can modify it while the +watcher is stopped to your hearts content), or [read-write], which +means you can expect it to have some sensible content while the watcher +is active, but you can also modify it. Modifying it may not do something +sensible or take immediate effect (or do anything at all), but libev will +not crash or malfunction in any way.
ev_io - is this file descriptor readable or writableev_io - is this file descriptor readable or writable?I/O watchers check whether a file descriptor is readable or writable -in each iteration of the event loop (This behaviour is called -level-triggering because you keep receiving events as long as the -condition persists. Remember you can stop the watcher if you don't want to -act on the event and neither want to receive future events).
+in each iteration of the event loop, or, more precisely, when reading +would not block the process and writing would at least be able to write +some data. This behaviour is called level-triggering because you keep +receiving events as long as the condition persists. Remember you can stop +the watcher if you don't want to act on the event and neither want to +receive future events.In general you can register as many read and/or write event watchers per fd as you want (as long as you don't confuse yourself). Setting all file descriptors to non-blocking mode is also usually a good idea (but not @@ -750,33 +928,68 @@ required if you know what you are doing).
You have to be careful with dup'ed file descriptors, though. Some backends (the linux epoll backend is a notable example) cannot handle dup'ed file descriptors correctly if you register interest in two or more fds pointing -to the same underlying file/socket etc. description (that is, they share +to the same underlying file/socket/etc. description (that is, they share the same underlying "file open").
If you must do this, then force the use of a known-to-be-good backend
(at the time of this writing, this includes only EVBACKEND_SELECT and
EVBACKEND_POLL).
Another thing you have to watch out for is that it is quite easy to
+receive "spurious" readyness notifications, that is your callback might
+be called with EV_READ but a subsequent read(2) will actually block
+because there is no data. Not only are some backends known to create a
+lot of those (for example solaris ports), it is very easy to get into
+this situation even with a relatively standard program structure. Thus
+it is best to always use non-blocking I/O: An extra read(2) returning
+EAGAIN is far preferable to a program hanging until some data arrives.
If you cannot run the fd in non-blocking mode (for example you should not +play around with an Xlib connection), then you have to seperately re-test +whether a file descriptor is really ready with a known-to-be good interface +such as poll (fortunately in our Xlib example, Xlib already does this on +its own, so its quite safe to use).
+ +Some backends (e.g kqueue, epoll) need to be told about closing a file
+descriptor (either by calling close explicitly or by any other means,
+such as dup). The reason is that you register interest in some file
+descriptor, but when it goes away, the operating system will silently drop
+this interest. If another file descriptor with the same number then is
+registered with libev, there is no efficient way to see that this is, in
+fact, a different file descriptor.
To avoid having to explicitly tell libev about such cases, libev follows
+the following policy: Each time ev_io_set is being called, libev
+will assume that this is potentially a new file descriptor, otherwise
+it is assumed that the file descriptor stays the same. That means that
+you have to call ev_io_set (or ev_io_init) when you change the
+descriptor even if the file descriptor number itself did not change.
This is how one would do it normally anyway, the important point is that +the libev application should not optimise around libev but should leave +optimisations to libev.
+ + + +Configures an ev_io watcher. The fd is the file descriptor to rceeive
-events for and events is either EV_READ, EV_WRITE or EV_READ |
-EV_WRITE to receive the given events.
Please note that most of the more scalable backend mechanisms (for example
-epoll and solaris ports) can result in spurious readyness notifications
-for file descriptors, so you practically need to use non-blocking I/O (and
-treat callback invocation as hint only), or retest separately with a safe
-interface before doing I/O (XLib can do this), or force the use of either
-EVBACKEND_SELECT or EVBACKEND_POLL, which don't suffer from this
-problem. Also note that it is quite easy to have your callback invoked
-when the readyness condition is no longer valid even when employing
-typical ways of handling events, so its a good idea to use non-blocking
-I/O unconditionally.
Configures an ev_io watcher. The fd is the file descriptor to
+rceeive events for and events is either EV_READ, EV_WRITE or
+EV_READ | EV_WRITE to receive the given events.
The file descriptor being watched.
+The events being watched.
Example: call stdin_readable_cb when STDIN_FILENO has become, well
+
Example: Call stdin_readable_cb when STDIN_FILENO has become, well
readable, but only once. Since it is likely line-buffered, you could
-attempt to read a whole line in the callback:
static void
stdin_readable_cb (struct ev_loop *loop, struct ev_io *w, int revents)
{
@@ -797,7 +1010,7 @@ attempt to read a whole line in the callback:
ev_timer - relative and optionally recurring timeoutsev_timer - relative and optionally repeating timeoutsTimer watchers are simple relative timers that generate an event after a given time, and optionally repeating in regular intervals after that.
@@ -835,20 +1048,42 @@ timer will not fire more than once per event loop iteration.This will act as if the timer timed out and restart it again if it is repeating. The exact semantics are:
-If the timer is started but nonrepeating, stop it.
-If the timer is repeating, either start it if necessary (with the repeat -value), or reset the running timer to the repeat value.
+If the timer is pending, its pending status is cleared.
+If the timer is started but nonrepeating, stop it (as if it timed out).
+If the timer is repeating, either start it if necessary (with the
+repeat value), or reset the running timer to the repeat value.
This sounds a bit complicated, but here is a useful and typical
example: Imagine you have a tcp connection and you want a so-called idle
timeout, that is, you want to be called when there have been, say, 60
seconds of inactivity on the socket. The easiest way to do this is to
-configure an ev_timer with after=repeat=60 and calling ev_timer_again each
-time you successfully read or write some data. If you go into an idle
-state where you do not expect data to travel on the socket, you can stop
-the timer, and again will automatically restart it if need be.
ev_timer with a repeat value of 60 and then call
+ev_timer_again each time you successfully read or write some data. If
+you go into an idle state where you do not expect data to travel on the
+socket, you can ev_timer_stop the timer, and ev_timer_again will
+automatically restart it if need be.
+ That means you can ignore the after value and ev_timer_start
+altogether and only ever use the repeat value and ev_timer_again:
ev_timer_init (timer, callback, 0., 5.); + ev_timer_again (loop, timer); + ... + timer->again = 17.; + ev_timer_again (loop, timer); + ... + timer->again = 10.; + ev_timer_again (loop, timer); + ++
This is more slightly efficient then stopping/starting the timer each time +you want to modify its timeout value.
+The current repeat value. Will be used each time the watcher times out
+or ev_timer_again is called and determines the next timeout (if any),
+which is also when any modifications are taken into account.
Example: create a timer that fires after 60 seconds.
+Example: Create a timer that fires after 60 seconds.
static void
one_minute_cb (struct ev_loop *loop, struct ev_timer *w, int revents)
{
@@ -860,7 +1095,7 @@ the timer, and again will automatically restart it if need be.
ev_timer_start (loop, &mytimer);
-Example: create a timeout timer that times out after 10 seconds of +
Example: Create a timeout timer that times out after 10 seconds of inactivity.
static void timeout_cb (struct ev_loop *loop, struct ev_timer *w, int revents) @@ -883,7 +1118,7 @@ inactivity.
ev_periodic - to cron or not to cronev_periodic - to cron or not to cron?Periodic watchers are also timers of a kind, but they are very versatile (and unfortunately a bit complex).
@@ -893,10 +1128,10 @@ to trigger "at" some specific point in time. For example, if you tell periodic watcher to trigger in 10 seconds (by specifiying e.g.ev_now ()
+ 10.) and then reset your system clock to the last year, then it will
take a year to trigger the event (unlike an ev_timer, which would trigger
-roughly 10 seconds later and of course not if you reset your system time
-again).
+roughly 10 seconds later).
They can also be used to implement vastly more complex timers, such as -triggering an event on eahc midnight, local time.
+triggering an event on each midnight, local time or other, complicated, +rules.As with timers, the callback is guarenteed to be invoked only when the
time (at) has been passed, but if multiple periodic timers become ready
during the same loop iteration then order of execution is undefined.
In this configuration the watcher triggers an event at the wallclock time
at and doesn't repeat. It will not adjust when a time jump occurs,
that is, if it is to be run at January 1st 2011 then it will run when the
system time reaches or surpasses this time.
In this mode the watcher will always be scheduled to time out at the next
-at + N * interval time (for some integer N) and then repeat, regardless
-of any time jumps.
at + N * interval time (for some integer N, which can also be negative)
+and then repeat, regardless of any time jumps.
This can be used to create timers that do not drift with respect to system time:
ev_periodic_set (&periodic, 0., 3600., 0); @@ -932,8 +1167,11 @@ by 3600.Another way to think about it (for the mathematically inclined) is that
+ev_periodicwill try to run the callback in this mode at the next possible time wheretime = at (mod interval), regardless of any time jumps.For numerical stability it is preferable that the
atvalue is near +ev_now ()(the current time), but there is no range requirement for +this value.
In this mode the values for interval and at are both being
ignored. Instead, each time the periodic watcher gets scheduled, the
@@ -942,7 +1180,7 @@ current time as second argument.
NOTE: This callback MUST NOT stop or destroy any periodic watcher,
ever, or make any event loop modifications. If you need to stop it,
return now + 1e30 (or so, fudge fudge) and stop it afterwards (e.g. by
-starting a prepare watcher).
ev_prepare watcher, which is legal).
Its prototype is ev_tstamp (*reschedule_cb)(struct ev_periodic *w,
ev_tstamp now), e.g.:
static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now) @@ -973,8 +1211,27 @@ when you changed some parameters or the reschedule callback would return a different time than the last time it was called (e.g. in a crond like program when the crontabs have changed).
When repeating, this contains the offset value, otherwise this is the
+absolute point in time (the at value passed to ev_periodic_set).
Can be modified any time, but changes only take effect when the periodic
+timer fires or ev_periodic_again is being called.
The current interval value. Can be modified any time, but changes only
+take effect when the periodic timer fires or ev_periodic_again is being
+called.
The current reschedule callback, or 0, if this functionality is
+switched off. Can be changed any time, but changes only take effect when
+the periodic timer fires or ev_periodic_again is being called.
Example: call a callback every hour, or, more precisely, whenever the +
Example: Call a callback every hour, or, more precisely, whenever the system clock is divisible by 3600. The callback invocation times have potentially a lot of jittering, but good long-term stability.
static void @@ -988,7 +1245,7 @@ potentially a lot of jittering, but good long-term stability. ev_periodic_start (loop, &hourly_tick);-
Example: the same as above, but use a reschedule callback to do it:
+Example: The same as above, but use a reschedule callback to do it:
#include <math.h> static ev_tstamp @@ -1000,7 +1257,7 @@ potentially a lot of jittering, but good long-term stability. ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);-
Example: call a callback every hour, starting now:
+Example: Call a callback every hour, starting now:
struct ev_periodic hourly_tick;
ev_periodic_init (&hourly_tick, clock_cb,
fmod (ev_now (loop), 3600.), 3600., 0);
@@ -1012,7 +1269,7 @@ potentially a lot of jittering, but good long-term stability.
ev_signal - signal me when a signal gets signalledev_signal - signal me when a signal gets signalled!Signal watchers will trigger an event when the process receives a specific signal one or more times. Even though signals are very asynchronous, libev @@ -1031,6 +1288,10 @@ SIG_DFL (regardless of what it was set to before).
Configures the watcher to trigger on the given signal number (usually one
of the SIGxxx constants).
The signal the watcher watches out for.
+SIGxxx constants).
ev_child - wait for pid status changesev_child - watch out for process status changesChild watchers trigger when your process receives a SIGCHLD in response to some child status changes (most typically when a child of yours dies).
sys/wait.h and see your system
waitpid documentation). The rpid member contains the pid of the
process causing the status change.
+ The process id this watcher watches out for, or 0, meaning any process id.
The process id that detected a status change.
+The process exit/trace status caused by rpid (see your systems
+waitpid and sys/wait.h documentation for details).
Example: try to exit cleanly on SIGINT and SIGTERM.
+Example: Try to exit cleanly on SIGINT and SIGTERM.
static void
sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents)
{
@@ -1071,15 +1345,117 @@ process causing the status change.
ev_idle - when you've got nothing better to doev_stat - did the file attributes just change?This watches a filesystem path for attribute changes. That is, it calls
+stat regularly (or when the OS says it changed) and sees if it changed
+compared to the last time, invoking the callback if it did.
The path does not need to exist: changing from "path exists" to "path does
+not exist" is a status change like any other. The condition "path does
+not exist" is signified by the st_nlink field being zero (which is
+otherwise always forced to be at least one) and all the other fields of
+the stat buffer having unspecified contents.
The path should be absolute and must not end in a slash. If it is +relative and your working directory changes, the behaviour is undefined.
+Since there is no standard to do this, the portable implementation simply
+calls stat (2) regularly on the path to see if it changed somehow. You
+can specify a recommended polling interval for this case. If you specify
+a polling interval of 0 (highly recommended!) then a suitable,
+unspecified default value will be used (which you can expect to be around
+five seconds, although this might change dynamically). Libev will also
+impose a minimum interval which is currently around 0.1, but thats
+usually overkill.
This watcher type is not meant for massive numbers of stat watchers, +as even with OS-supported change notifications, this can be +resource-intensive.
+At the time of this writing, only the Linux inotify interface is
+implemented (implementing kqueue support is left as an exercise for the
+reader). Inotify will be used to give hints only and should not change the
+semantics of ev_stat watchers, which means that libev sometimes needs
+to fall back to regular polling again even with inotify, but changes are
+usually detected immediately, and if the file exists there will be no
+polling.
Configures the watcher to wait for status changes of the given
+path. The interval is a hint on how quickly a change is expected to
+be detected and should normally be specified as 0 to let libev choose
+a suitable value. The memory pointed to by path must point to the same
+path for as long as the watcher is active.
The callback will be receive EV_STAT when a change was detected,
+relative to the attributes at the time the watcher was started (or the
+last change was detected).
Updates the stat buffer immediately with new values. If you change the +watched path in your callback, you could call this fucntion to avoid +detecting this change (while introducing a race condition). Can also be +useful simply to find out the new values.
+The most-recently detected attributes of the file. Although the type is of
+ev_statdata, this is usually the (or one of the) struct stat types
+suitable for your system. If the st_nlink member is 0, then there
+was some error while stating the file.
The previous attributes of the file. The callback gets invoked whenever
+prev != attr.
The specified interval.
+The filesystem path that is being watched.
+Example: Watch /etc/passwd for attribute changes.
static void
+ passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)
+ {
+ /* /etc/passwd changed in some way */
+ if (w->attr.st_nlink)
+ {
+ printf ("passwd current size %ld\n", (long)w->attr.st_size);
+ printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);
+ printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);
+ }
+ else
+ /* you shalt not abuse printf for puts */
+ puts ("wow, /etc/passwd is not there, expect problems. "
+ "if this is windows, they already arrived\n");
+ }
+
+ ...
+ ev_stat passwd;
+
+ ev_stat_init (&passwd, passwd_cb, "/etc/passwd");
+ ev_stat_start (loop, &passwd);
+
+
+
+
+
+
+ev_idle - when you've got nothing better to do...Idle watchers trigger events when there are no other events are pending -(prepare, check and other idle watchers do not count). That is, as long -as your process is busy handling sockets or timeouts (or even signals, -imagine) it will not be triggered. But when your process is idle all idle -watchers are being called again and again, once per event loop iteration - -until stopped, that is, or your process receives more events and becomes -busy.
+Idle watchers trigger events when no other events of the same or higher +priority are pending (prepare, check and other idle watchers do not +count).
+That is, as long as your process is busy handling sockets or timeouts +(or even signals, imagine) of the same or higher priority it will not be +triggered. But when your process is idle (or only lower-priority watchers +are pending), the idle watchers are being called once per event loop +iteration - until stopped, that is, or your process receives more events +and becomes busy again with higher priority stuff.
The most noteworthy effect is that as long as any idle watchers are active, the process will not block when waiting for new events.
Apart from keeping your process non-blocking (which is a useful
@@ -1094,8 +1470,8 @@ kind. There is a ev_idle_set macro, but using it is utterly pointle
believe me.
Example: dynamically allocate an ev_idle, start it, and in the
-callback, free it. Alos, use no error checking, as usual.
Example: Dynamically allocate an ev_idle watcher, start it, and in the
+callback, free it. Also, use no error checking, as usual.
static void
idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents)
{
@@ -1114,15 +1490,25 @@ callback, free it. Alos, use no error checking, as usual.
ev_prepare and ev_check - customise your event loopev_prepare and ev_check - customise your event loop!Prepare and check watchers are usually (but not always) used in tandem: prepare watchers get invoked before the process blocks and check watchers afterwards.
+You must not call ev_loop or similar functions that enter
+the current event loop from either ev_prepare or ev_check
+watchers. Other loops than the current one are fine, however. The
+rationale behind this is that you do not need to check for recursion in
+those watchers, i.e. the sequence will always be ev_prepare, blocking,
+ev_check so if you have one watcher of each kind they will always be
+called in pairs bracketing the blocking call.
Their main purpose is to integrate other event mechanisms into libev and their use is somewhat advanced. This could be used, for example, to track variable changes, implement your own watchers, integrate net-snmp or a -coroutine library and lots more.
+coroutine library and lots more. They are also occasionally useful if +you cache some data and want to flush it before blocking (for example, +in X programs you might want to do anXFlush () in an ev_prepare
+watcher).
This is done by examining in each prepare call which file descriptors need
to be watched by the other library, registering ev_io watchers for
them and starting an ev_timer watcher for any timeouts (many libraries
@@ -1139,6 +1525,15 @@ with priority higher than or equal to the event loop and one coroutine
of lower priority, but only once, using idle watchers to keep the event
loop from blocking if lower-priority coroutines are active, thus mapping
low-priority coroutines to idle/background tasks).
It is recommended to give ev_check watchers highest (EV_MAXPRI)
+priority, to ensure that they are being run before any other watchers
+after the poll. Also, ev_check watchers (and ev_prepare watchers,
+too) should not activate ("feed") events into libev. While libev fully
+supports this, they will be called before other ev_check watchers did
+their job. As ev_check watchers are often used to embed other event
+loops those other event loops might be in an unusable state until their
+ev_check watcher ran (always remind yourself to coexist peacefully with
+others).
ev_prepare_set and ev_check
macros, but using them is utterly, utterly and completely pointless.
Example: *TODO*.
+There are a number of principal ways to embed other event loops or modules
+into libev. Here are some ideas on how to include libadns into libev
+(there is a Perl module named EV::ADNS that does this, which you could
+use for an actually working example. Another Perl module named EV::Glib
+embeds a Glib main context into libev, and finally, Glib::EV embeds EV
+into the Glib event loop).
Method 1: Add IO watchers and a timeout watcher in a prepare handler,
+and in a check watcher, destroy them and call into libadns. What follows
+is pseudo-code only of course. This requires you to either use a low
+priority for the check watcher or use ev_clear_pending explicitly, as
+the callbacks for the IO/timeout watchers might not have been called yet.
static ev_io iow [nfd];
+ static ev_timer tw;
+
+ static void
+ io_cb (ev_loop *loop, ev_io *w, int revents)
+ {
+ }
+
+ // create io watchers for each fd and a timer before blocking
+ static void
+ adns_prepare_cb (ev_loop *loop, ev_prepare *w, int revents)
+ {
+ int timeout = 3600000;
+ struct pollfd fds [nfd];
+ // actual code will need to loop here and realloc etc.
+ adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
+
+ /* the callback is illegal, but won't be called as we stop during check */
+ ev_timer_init (&tw, 0, timeout * 1e-3);
+ ev_timer_start (loop, &tw);
+
+ // create one ev_io per pollfd
+ for (int i = 0; i < nfd; ++i)
+ {
+ ev_io_init (iow + i, io_cb, fds [i].fd,
+ ((fds [i].events & POLLIN ? EV_READ : 0)
+ | (fds [i].events & POLLOUT ? EV_WRITE : 0)));
+
+ fds [i].revents = 0;
+ ev_io_start (loop, iow + i);
+ }
+ }
+
+ // stop all watchers after blocking
+ static void
+ adns_check_cb (ev_loop *loop, ev_check *w, int revents)
+ {
+ ev_timer_stop (loop, &tw);
+
+ for (int i = 0; i < nfd; ++i)
+ {
+ // set the relevant poll flags
+ // could also call adns_processreadable etc. here
+ struct pollfd *fd = fds + i;
+ int revents = ev_clear_pending (iow + i);
+ if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;
+ if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;
+
+ // now stop the watcher
+ ev_io_stop (loop, iow + i);
+ }
+
+ adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
+ }
+
+
+Method 2: This would be just like method 1, but you run adns_afterpoll
+in the prepare watcher and would dispose of the check watcher.
Method 3: If the module to be embedded supports explicit event +notification (adns does), you can also make use of the actual watcher +callbacks, and only destroy/create the watchers in the prepare watcher.
+ static void
+ timer_cb (EV_P_ ev_timer *w, int revents)
+ {
+ adns_state ads = (adns_state)w->data;
+ update_now (EV_A);
+
+ adns_processtimeouts (ads, &tv_now);
+ }
+
+ static void
+ io_cb (EV_P_ ev_io *w, int revents)
+ {
+ adns_state ads = (adns_state)w->data;
+ update_now (EV_A);
+
+ if (revents & EV_READ ) adns_processreadable (ads, w->fd, &tv_now);
+ if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now);
+ }
+
+ // do not ever call adns_afterpoll
+
+
+Method 4: Do not use a prepare or check watcher because the module you
+want to embed is too inflexible to support it. Instead, youc na override
+their poll function. The drawback with this solution is that the main
+loop is now no longer controllable by EV. The Glib::EV module does
+this.
static gint
+ event_poll_func (GPollFD *fds, guint nfds, gint timeout)
+ {
+ int got_events = 0;
+ for (n = 0; n < nfds; ++n)
+ // create/start io watcher that sets the relevant bits in fds[n] and increment got_events
+ if (timeout >= 0)
+ // create/start timer
+ // poll
+ ev_loop (EV_A_ 0);
+ // stop timer again
+ if (timeout >= 0)
+ ev_timer_stop (EV_A_ &to);
+
+ // stop io watchers again - their callbacks should have set
+ for (n = 0; n < nfds; ++n)
+ ev_io_stop (EV_A_ iow [n]);
+
+ return got_events;
+ }
+
+
+
+
+
ev_embed - when one backend isn't enoughev_embed - when one backend isn't enough...This is a rather advanced watcher type that lets you embed one event loop
into another (currently only ev_io events are supported in the embedded
@@ -1233,6 +1751,10 @@ if you do not want thta, you need to temporarily stop the embed watcher).
ev_loop (embedded_loop, EVLOOP_NONBLOCK), but in the most
apropriate way for embedded loops.
+ The embedded event loop.
+ev_fork - the audacity to resume the event loop after a forkFork watchers are called when a fork () was detected (usually because
+whoever is a good citizen cared to tell libev about it by calling
+ev_default_fork or ev_loop_fork). The invocation is done before the
+event loop blocks next and before ev_check watchers are being called,
+and only in the child after the fork. If whoever good citizen calling
+ev_default_fork cheats and calls it in the wrong process, the fork
+handlers will be invoked, too, of course.
Initialises and configures the fork watcher - it has no parameters of any
+kind. There is a ev_fork_set macro, but using it is utterly pointless,
+believe me.
There are some other functions of possible interest. Described. Here. Now.
Libev offers a compatibility emulation layer for libevent. It cannot emulate the internals of libevent, so here are some usage hints:
@@ -1317,7 +1862,7 @@ to use the libev header file and library.Libev comes with some simplistic wrapper classes for C++ that mainly allow you to use some convinience methods to start/stop watchers and also change @@ -1326,11 +1871,19 @@ the callback model to a model using method callbacks on objects.
#include <ev++.h>-
(it is not installed by default). This automatically includes ev.h
-and puts all of its definitions (many of them macros) into the global
-namespace. All C++ specific things are put into the ev namespace.
It should support all the same embedding options as ev.h, most notably
-EV_MULTIPLICITY.
This automatically includes ev.h and puts all of its definitions (many
+of them macros) into the global namespace. All C++ specific things are
+put into the ev namespace. It should support all the same embedding
+options as ev.h, most notably EV_MULTIPLICITY.
Care has been taken to keep the overhead low. The only data member the C++
+classes add (compared to plain C-style watchers) is the event loop pointer
+that the watcher is associated with (or no additional members at all if
+you disable EV_MULTIPLICITY when embedding libev).
Currently, functions, and static and non-static member functions can be +used as callbacks. Other types should be easy to add as long as they only +need one additional pointer for context. If you need support for other +types of functors please contact the author (preferably after implementing +it).
Here is a list of things available in the ev namespace:
ev::READ, ev::WRITE etc.All of those classes have these methods:
The constructor takes a pointer to an object and a method pointer to
-the event handler callback to call in this class. The constructor calls
-ev_init for you, which means you have to call the set method
-before starting it. If you do not specify a loop then the constructor
-automatically associates the default loop with this watcher.
The constructor (optionally) takes an event loop to associate the watcher
+with. If it is omitted, it will use EV_DEFAULT.
The constructor calls ev_init for you, which means you have to call the
+set method before starting it.
It will not set a callback, however: You have to call the templated set
+method to set a callback before you can start the watcher.
(The reason why you have to use a method is a limitation in C++ which does +not allow explicit template arguments for constructors).
The destructor automatically stops the watcher if it is active.
This method sets the callback method to call. The method has to have a
+signature of void (*)(ev_TYPE &, int), it receives the watcher as
+first argument and the revents as second. The object must be given as
+parameter and is stored in the data member of the watcher.
This method synthesizes efficient thunking code to call your method from
+the C callback that libev requires. If your compiler can inline your
+callback (i.e. it is visible to it at the place of the set call and
+your compiler is good :), then the method will be fully inlined into the
+thunking function, making it as fast as a direct C callback.
Example: simple class declaration and watcher initialisation
+ struct myclass
+ {
+ void io_cb (ev::io &w, int revents) { }
+ }
+
+ myclass obj;
+ ev::io iow;
+ iow.set <myclass, &myclass::io_cb> (&obj);
+
+
+ Also sets a callback, but uses a static method or plain function as
+callback. The optional data argument will be stored in the watcher's
+data member and is free for you to use.
The prototype of the function must be void (*)(ev::TYPE &w, int).
See the method-set above for more details.
Example:
+ static void io_cb (ev::io &w, int revents) { }
+ iow.set <io_cb> ();
+
+
+ Associates a different struct ev_loop with this watcher. You can only
@@ -1370,13 +1962,14 @@ do this when the watcher is inactive (and not pending either).
Basically the same as ev_TYPE_set, with the same args. Must be
-called at least once. Unlike the C counterpart, an active watcher gets
-automatically stopped and restarted.
Starts the watcher. Note that there is no loop argument as the
-constructor already takes the loop.
Starts the watcher. Note that there is no loop argument, as the
+constructor already stores the event loop.
Invokes ev_embed_sweep.
ev::stat onlyInvokes ev_stat_stat.
Libev can be compiled with a variety of options, the most fundemantal is
+EV_MULTIPLICITY. This option determines whether (most) functions and
+callbacks have an initial struct ev_loop * argument.
To make it easier to write programs that cope with either variant, the +following macros are defined:
+EV_A, EV_A_This provides the loop argument for functions, if one is required ("ev
+loop argument"). The EV_A form is used when this is the sole argument,
+EV_A_ is used when other arguments are following. Example:
ev_unref (EV_A); + ev_timer_add (EV_A_ watcher); + ev_loop (EV_A_ 0); + ++
It assumes the variable loop of type struct ev_loop * is in scope,
+which is often provided by the following macro.
EV_P, EV_P_This provides the loop parameter for functions, if one is required ("ev
+loop parameter"). The EV_P form is used when this is the sole parameter,
+EV_P_ is used when other parameters are following. Example:
// this is how ev_unref is being declared + static void ev_unref (EV_P); + + // this is how you can declare your typical callback + static void cb (EV_P_ ev_timer *w, int revents) + ++
It declares a parameter loop of type struct ev_loop *, quite
+suitable for use with EV_A.
EV_DEFAULT, EV_DEFAULT_Similar to the other two macros, this gives you the value of the default +loop, if multiple loops are supported ("ev loop default").
+Example: Declare and initialise a check watcher, utilising the above +macros so it will work regardless of whether multiple loops are supported +or not.
+ static void
+ check_cb (EV_P_ ev_timer *w, int revents)
+ {
+ ev_check_stop (EV_A_ w);
+ }
+
+ ev_check check;
+ ev_check_init (&check, check_cb);
+ ev_check_start (EV_DEFAULT_ &check);
+ ev_loop (EV_DEFAULT_ 0);
+
+
+
+Libev can (and often is) directly embedded into host applications. Examples of applications that embed it include the Deliantra @@ -1462,7 +2122,7 @@ in your include path (e.g. in libev/ when using -Ilibev):
ev_win32.c required on win32 platforms only - ev_select.c only when select backend is enabled (which is is by default) + ev_select.c only when select backend is enabled (which is enabled by default) ev_poll.c only when poll backend is enabled (disabled by default) ev_epoll.c only when the epoll backend is enabled (disabled by default) ev_kqueue.c only when the kqueue backend is enabled (disabled by default) @@ -1470,7 +2130,7 @@ in your include path (e.g. in libev/ when using -Ilibev):ev.c includes the backend files directly when enabled, so you only need -to compile a single file.
+to compile this single file.Instead of using EV_STANDALONE=1 and providing your config in
whatever way you want, you can also m4_include([libev.m4]) in your
-configure.ac and leave EV_STANDALONE off. ev.c will then include
-config.h and configure itself accordingly.
EV_STANDALONE undefined. ev.c will then
+include config.h and configure itself accordingly.
For this of course you need the m4 file:
libev.m4 @@ -1585,7 +2245,7 @@ backend for BSD and BSD-like systems, although on most BSDs kqueue only supports some types of fds correctly (the only platform we found that supports ptys for example was NetBSD), so kqueue might be compiled in, but not be used unless explicitly requested. The best way to use it is to find -out wether kqueue supports your type of fd properly and use an embedded +out whether kqueue supports your type of fd properly and use an embedded kqueue loop.
reserved for future expansion, works like the USE symbols above.
If defined to be 1, libev will compile in support for the Linux inotify
+interface to speed up ev_stat watchers. Its actual availability will
+be detected at runtime.
The name of the ev.h header file used to include it. The default if @@ -1631,10 +2297,67 @@ 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.
The range of allowed priorities. EV_MINPRI must be smaller or equal to
+EV_MAXPRI, but otherwise there are no non-obvious limitations. You can
+provide for more priorities by overriding those symbols (usually defined
+to be -2 and 2, respectively).
When doing priority-based operations, libev usually has to linearly search +all the priorities, so having many of them (hundreds) uses a lot of space +and time, so using the defaults of five priorities (-2 .. +2) is usually +fine.
+If your embedding app does not need any priorities, defining these both to
+0 will save some memory and cpu.
If undefined or defined to be 1, then periodic timers are supported. If
+defined to be 0, then they are not. Disabling them saves a few kB of
+code.
If undefined or defined to be 1, then idle watchers are supported. If
+defined to be 0, then they are not. Disabling them saves a few kB of
+code.
If undefined or defined to be 1, then embed watchers are supported. If
+defined to be 0, then they are not.
If undefined or defined to be 1, then stat watchers are supported. If
+defined to be 0, then they are not.
If undefined or defined to be 1, then fork watchers are supported. If
+defined to be 0, then they are not.
If undefined or defined to be 1, then periodic timers are supported,
-otherwise not. This saves a few kb of code.
If you need to shave off some kilobytes of code at the expense of some
+speed, define this symbol to 1. Currently only used for gcc to override
+some inlining decisions, saves roughly 30% codesize of amd64.
ev_child watchers use a small hash table to distribute workload by
+pid. The default size is 16 (or 1 with EV_MINIMAL), usually more
+than enough. If you need to manage thousands of children you might want to
+increase this value (must be a power of two).
ev_staz watchers use a small hash table to distribute workload by
+inotify watch id. The default size is 16 (or 1 with EV_MINIMAL),
+usually more than enough. If you need to manage thousands of ev_stat
+watchers you might want to increase this value (must be a power of
+two).
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 ev.v header file for their default definitions. One possible use for overriding these is to -avoid the ev_loop pointer as first argument in all cases, or to use method -calls instead of plain function calls in C++.
+avoid thestruct ev_loop * as first argument in all cases, or to use
+method calls instead of plain function calls in C++.
The usage in rxvt-unicode is simpler. It has a ev_cpp.h header file -that everybody includes and which overrides some autoconf choices:
-#define EV_USE_POLL 0 +that everybody includes and which overrides some configure choices: +#define EV_MINIMAL 1 + #define EV_USE_POLL 0 #define EV_MULTIPLICITY 0 - #define EV_PERIODICS 0 + #define EV_PERIODIC_ENABLE 0 + #define EV_STAT_ENABLE 0 + #define EV_FORK_ENABLE 0 #define EV_CONFIG_H <config.h> + #define EV_MINPRI 0 + #define EV_MAXPRI 0 #include "ev++.h" @@ -1684,10 +2412,68 @@ that everybody includes and which overrides some autoconf choices:#include "ev_cpp.h" #include "ev.c" + + +
In this section the complexities of (many of) the algorithms used inside
+libev will be explained. For complexity discussions about backends see the
+documentation for ev_default_init.
All of the following are about amortised time: If an array needs to be +extended, libev needs to realloc and move the whole array, but this +happens asymptotically never with higher number of elements, so O(1) might +mean it might do a lengthy realloc operation in rare cases, but on average +it is much faster and asymptotically approaches constant time.
++
This means that, when you have a watcher that triggers in one hour and +there are 100 watchers that would trigger before that then inserting will +have to skip those 100 watchers.
+That means that for changing a timer costs less than removing/adding them +as only the relative motion in the event queue has to be paid for.
+These just add the watcher into an array or at the head of a list. +=item Stopping check/prepare/idle watchers: O(1)
+These watchers are stored in lists then need to be walked to find the +correct watcher to remove. The lists are usually short (you don't usually +have many watchers waiting for the same fd or signal).
+A change means an I/O watcher gets started or stopped, which requires +libev to recalculate its status (and possibly tell the kernel).
+Priorities are implemented by allocating some space for each +priority. When doing priority-based operations, libev usually has to +linearly search all the priorities.
+Marc Lehmann <libev@schmorp.de>.