CSE2410 Fall 2014 Bounce

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.\" ========================================================================

.\"

.IX Title "LIBEIO 3"

.TH LIBEIO 3 "2008-05-11" "libeio-1.0" "libeio - truly asynchronous POSIX I/O"

.\" For nroff, turn off justification.  Always turn off hyphenation; it makes

.\" way too many mistakes in technical documents.

.if n .ad l

.nh

.SH "NAME"

libev \- a high performance full\-featured event loop written in C

.SH "SYNOPSIS"

.IX Header "SYNOPSIS"

.Vb 1

\&  #include <ev.h>

.Ve

.Sh "\s-1EXAMPLE\s0 \s-1PROGRAM\s0"

.IX Subsection "EXAMPLE PROGRAM"

.Vb 2

\&  // a single header file is required

\&  #include <ev.h>

\&

\&  // every watcher type has its own typedef\*(Aqd struct

\&  // with the name ev_<type>

\&  ev_io stdin_watcher;

\&  ev_timer timeout_watcher;

\&

\&  // all watcher callbacks have a similar signature

\&  // this callback is called when data is readable on stdin

\&  static void

\&  stdin_cb (EV_P_ struct ev_io *w, int revents)

\&  {

\&    puts ("stdin ready");

\&    // for one\-shot events, one must manually stop the watcher

\&    // with its corresponding stop function.

\&    ev_io_stop (EV_A_ w);

\&

\&    // this causes all nested ev_loop\*(Aqs to stop iterating

\&    ev_unloop (EV_A_ EVUNLOOP_ALL);

\&  }

\&

\&  // another callback, this time for a time\-out

\&  static void

\&  timeout_cb (EV_P_ struct ev_timer *w, int revents)

\&  {

\&    puts ("timeout");

\&    // this causes the innermost ev_loop to stop iterating

\&    ev_unloop (EV_A_ EVUNLOOP_ONE);

\&  }

\&

\&  int

\&  main (void)

\&  {

\&    // use the default event loop unless you have special needs

\&    struct ev_loop *loop = ev_default_loop (0);

\&

\&    // initialise an io watcher, then start it

\&    // this one will watch for stdin to become readable

\&    ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ);

\&    ev_io_start (loop, &stdin_watcher);

\&

\&    // initialise a timer watcher, then start it

\&    // simple non\-repeating 5.5 second timeout

\&    ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);

\&    ev_timer_start (loop, &timeout_watcher);

\&

\&    // now wait for events to arrive

\&    ev_loop (loop, 0);

\&

\&    // unloop was called, so exit

\&    return 0;

\&  }

.Ve

.SH "DESCRIPTION"

.IX Header "DESCRIPTION"

The newest version of this document is also available as an html-formatted

web page you might find easier to navigate when reading it for the first

time: <http://cvs.schmorp.de/libev/ev.html>.

.PP

Libev is an event loop: you register interest in certain events (such as a

file descriptor being readable or a timeout occurring), and it will manage

these event sources and provide your program with events.

.PP

To do this, it must take more or less complete control over your process

(or thread) by executing the \fIevent loop\fR handler, and will then

communicate events via a callback mechanism.

.PP

You register interest in certain events by registering so-called \fIevent

watchers\fR, which are relatively small C structures you initialise with the

details of the event, and then hand it over to libev by \fIstarting\fR the

watcher.

.Sh "\s-1FEATURES\s0"

.IX Subsection "FEATURES"

Libev supports \f(CW\*(C`select\*(C'\fR, \f(CW\*(C`poll\*(C'\fR, the Linux-specific \f(CW\*(C`epoll\*(C'\fR, the

BSD-specific \f(CW\*(C`kqueue\*(C'\fR and the Solaris-specific event port mechanisms

for file descriptor events (\f(CW\*(C`ev_io\*(C'\fR), the Linux \f(CW\*(C`inotify\*(C'\fR interface

(for \f(CW\*(C`ev_stat\*(C'\fR), relative timers (\f(CW\*(C`ev_timer\*(C'\fR), absolute timers

with customised rescheduling (\f(CW\*(C`ev_periodic\*(C'\fR), synchronous signals

(\f(CW\*(C`ev_signal\*(C'\fR), process status change events (\f(CW\*(C`ev_child\*(C'\fR), and event

watchers dealing with the event loop mechanism itself (\f(CW\*(C`ev_idle\*(C'\fR,

\&\f(CW\*(C`ev_embed\*(C'\fR, \f(CW\*(C`ev_prepare\*(C'\fR and \f(CW\*(C`ev_check\*(C'\fR watchers) as well as

file watchers (\f(CW\*(C`ev_stat\*(C'\fR) and even 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

for example).

.Sh "\s-1CONVENTIONS\s0"

.IX Subsection "CONVENTIONS"

Libev is very configurable. In this manual the default (and most common)

configuration will be described, which supports multiple event loops. For

more info about various configuration options please have a look at

\&\fB\s-1EMBED\s0\fR section in this manual. If libev was configured without support

for multiple event loops, then all functions taking an initial argument of

name \f(CW\*(C`loop\*(C'\fR (which is always of type \f(CW\*(C`struct ev_loop *\*(C'\fR) will not have

this argument.

.Sh "\s-1TIME\s0 \s-1REPRESENTATION\s0"

.IX Subsection "TIME REPRESENTATION"

Libev represents time as a single floating point number, representing the

(fractional) number of seconds since the (\s-1POSIX\s0) epoch (somewhere near

the beginning of 1970, details are complicated, don't ask). This type is

called \f(CW\*(C`ev_tstamp\*(C'\fR, which is what you should use too. It usually aliases

to the \f(CW\*(C`double\*(C'\fR type in C, and when you need to do any calculations on

it, you should treat it as some floatingpoint value. Unlike the name

component \f(CW\*(C`stamp\*(C'\fR might indicate, it is also used for time differences

throughout libev.

.SH "GLOBAL FUNCTIONS"

.IX Header "GLOBAL FUNCTIONS"

These functions can be called anytime, even before initialising the

library in any way.

.IP "ev_tstamp ev_time ()" 4

.IX Item "ev_tstamp ev_time ()"

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.

.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 subsecond-resolution \f(CW\*(C`sleep ()\*(C'\fR.

.IP "int ev_version_major ()" 4

.IX Item "int ev_version_major ()"

.PD 0

.IP "int ev_version_minor ()" 4

.IX Item "int ev_version_minor ()"

.PD

You can find out the major and minor \s-1ABI\s0 version numbers of the library

you linked against by calling the functions \f(CW\*(C`ev_version_major\*(C'\fR and

\&\f(CW\*(C`ev_version_minor\*(C'\fR. If you want, you can compare against the global

symbols \f(CW\*(C`EV_VERSION_MAJOR\*(C'\fR and \f(CW\*(C`EV_VERSION_MINOR\*(C'\fR, which specify the

version of the library your program was compiled against.

.Sp

These version numbers refer to the \s-1ABI\s0 version of the library, not the

release version.

.Sp

Usually, it's a good idea to terminate if the major versions mismatch,

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.

.Sp

Example: Make sure we haven't accidentally been linked against the wrong

version.

.Sp

.Vb 3

\&  assert (("libev version mismatch",

\&           ev_version_major () == EV_VERSION_MAJOR

\&           && ev_version_minor () >= EV_VERSION_MINOR));

.Ve

.IP "unsigned int ev_supported_backends ()" 4

.IX Item "unsigned int ev_supported_backends ()"

Return the set of all backends (i.e. their corresponding \f(CW\*(C`EV_BACKEND_*\*(C'\fR

value) compiled into this binary of libev (independent of their

availability on the system you are running on). See \f(CW\*(C`ev_default_loop\*(C'\fR for

a description of the set values.

.Sp

Example: make sure we have the epoll method, because yeah this is cool and

a must have and can we have a torrent of it please!!!11

.Sp

.Vb 2

\&  assert (("sorry, no epoll, no sex",

\&           ev_supported_backends () & EVBACKEND_EPOLL));

.Ve

.IP "unsigned int ev_recommended_backends ()" 4

.IX Item "unsigned int ev_recommended_backends ()"

Return the set of all backends compiled into this binary of libev and also

recommended for this platform. This set is often smaller than the one

returned by \f(CW\*(C`ev_supported_backends\*(C'\fR, as for example kqueue is broken on

most BSDs and will not be autodetected unless you explicitly request it

(assuming you know what you are doing). This is the set of backends that

libev will probe for if you specify no backends explicitly.

.IP "unsigned int ev_embeddable_backends ()" 4

.IX Item "unsigned int ev_embeddable_backends ()"

Returns the set of backends that are embeddable in other event loops. This

is the theoretical, all-platform, value. To find which backends

might be supported on the current system, you would need to look at

\&\f(CW\*(C`ev_embeddable_backends () & ev_supported_backends ()\*(C'\fR, likewise for

recommended ones.

.Sp

See the description of \f(CW\*(C`ev_embed\*(C'\fR watchers for more info.

.IP "ev_set_allocator (void *(*cb)(void *ptr, long size))" 4

.IX Item "ev_set_allocator (void *(*cb)(void *ptr, long size))"

Sets the allocation function to use (the prototype is similar \- the

semantics are identical to the \f(CW\*(C`realloc\*(C'\fR C89/SuS/POSIX function). It is

used to allocate and free memory (no surprises here). If it returns zero

when memory needs to be allocated (\f(CW\*(C`size != 0\*(C'\fR), the library might abort

or take some potentially destructive action.

.Sp

Since some systems (at least OpenBSD and Darwin) fail to implement

correct \f(CW\*(C`realloc\*(C'\fR semantics, libev will use a wrapper around the system

\&\f(CW\*(C`realloc\*(C'\fR and \f(CW\*(C`free\*(C'\fR functions by default.

.Sp

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.

.Sp

Example: Replace the libev allocator with one that waits a bit and then

retries (example requires a standards-compliant \f(CW\*(C`realloc\*(C'\fR).

.Sp

.Vb 6

\&   static void *

\&   persistent_realloc (void *ptr, size_t size)

\&   {

\&     for (;;)

\&       {

\&         void *newptr = realloc (ptr, size);

\&

\&         if (newptr)

\&           return newptr;

\&

\&         sleep (60);

\&       }

\&   }

\&

\&   ...

\&   ev_set_allocator (persistent_realloc);

.Ve

.IP "ev_set_syserr_cb (void (*cb)(const char *msg));" 4

.IX Item "ev_set_syserr_cb (void (*cb)(const char *msg));"

Set the callback function to call on a retryable syscall error (such

as failed select, poll, epoll_wait). The message is a printable string

indicating the system call or subsystem causing the problem. If this

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).

.Sp

Example: This is basically the same thing that libev does internally, too.

.Sp

.Vb 6

\&   static void

\&   fatal_error (const char *msg)

\&   {

\&     perror (msg);

\&     abort ();

\&   }

\&

\&   ...

\&   ev_set_syserr_cb (fatal_error);

.Ve

.SH "FUNCTIONS CONTROLLING THE EVENT LOOP"

.IX Header "FUNCTIONS CONTROLLING THE EVENT LOOP"

An event loop is described by a \f(CW\*(C`struct ev_loop *\*(C'\fR. The library knows two

types of such loops, the \fIdefault\fR loop, which supports signals and child

events, and dynamically created loops which do not.

.IP "struct ev_loop *ev_default_loop (unsigned int flags)" 4

.IX Item "struct ev_loop *ev_default_loop (unsigned int flags)"

This will initialise the default event loop if it hasn't been initialised

yet and return it. If the default loop could not be initialised, returns

false. If it already was initialised it simply returns it (and ignores the

flags. If that is troubling you, check \f(CW\*(C`ev_backend ()\*(C'\fR afterwards).

.Sp

If you don't know what event loop to use, use the one returned from this

function.

.Sp

Note that this function is \fInot\fR thread-safe, so if you want to use it

from multiple threads, you have to lock (note also that this is unlikely,

as loops cannot bes hared easily between threads anyway).

.Sp

The default loop is the only loop that can handle \f(CW\*(C`ev_signal\*(C'\fR and

\&\f(CW\*(C`ev_child\*(C'\fR watchers, and to do this, it always registers a handler

for \f(CW\*(C`SIGCHLD\*(C'\fR. If this is a problem for your app you can either

create a dynamic loop with \f(CW\*(C`ev_loop_new\*(C'\fR that doesn't do that, or you

can simply overwrite the \f(CW\*(C`SIGCHLD\*(C'\fR signal handler \fIafter\fR calling

\&\f(CW\*(C`ev_default_init\*(C'\fR.

.Sp

The flags argument can be used to specify special behaviour or specific

backends to use, and is usually specified as \f(CW0\fR (or \f(CW\*(C`EVFLAG_AUTO\*(C'\fR).

.Sp

The following flags are supported:

.RS 4

.ie n .IP """EVFLAG_AUTO""" 4

.el .IP "\f(CWEVFLAG_AUTO\fR" 4

.IX Item "EVFLAG_AUTO"

The default flags value. Use this if you have no clue (it's the right

thing, believe me).

.ie n .IP """EVFLAG_NOENV""" 4

.el .IP "\f(CWEVFLAG_NOENV\fR" 4

.IX Item "EVFLAG_NOENV"

If this flag bit is ored into the flag value (or the program runs setuid

or setgid) then libev will \fInot\fR look at the environment variable

\&\f(CW\*(C`LIBEV_FLAGS\*(C'\fR. Otherwise (the default), this environment variable will

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.

.ie n .IP """EVFLAG_FORKCHECK""" 4

.el .IP "\f(CWEVFLAG_FORKCHECK\fR" 4

.IX Item "EVFLAG_FORKCHECK"

Instead of calling \f(CW\*(C`ev_default_fork\*(C'\fR or \f(CW\*(C`ev_loop_fork\*(C'\fR manually after

a fork, you can also make libev check for a fork in each iteration by

enabling this flag.

.Sp

This works by calling \f(CW\*(C`getpid ()\*(C'\fR 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

GNU/Linux system for example, \f(CW\*(C`getpid\*(C'\fR is actually a simple 5\-insn sequence

without a syscall and thus \fIvery\fR fast, but my GNU/Linux system also has

\&\f(CW\*(C`pthread_atfork\*(C'\fR which is even faster).

.Sp

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.

.Sp

This flag setting cannot be overriden or specified in the \f(CW\*(C`LIBEV_FLAGS\*(C'\fR

environment variable.

.ie n .IP """EVBACKEND_SELECT""  (value 1, portable select backend)" 4

.el .IP "\f(CWEVBACKEND_SELECT\fR  (value 1, portable select backend)" 4

.IX Item "EVBACKEND_SELECT  (value 1, portable select backend)"

This is your standard \fIselect\fR\|(2) backend. Not \fIcompletely\fR standard, as

libev tries to roll its own fd_set with no limits on the number of fds,

but if that fails, expect a fairly low limit on the number of fds when

using this backend. It doesn't scale too well (O(highest_fd)), but its

usually the fastest backend for a low number of (low-numbered :) fds.

.Sp

To get good performance out of this backend you need a high amount of

parallelity (most of the file descriptors should be busy). If you are

writing a server, you should \f(CW\*(C`accept ()\*(C'\fR in a loop to accept as many

connections as possible during one iteration. You might also want to have

a look at \f(CW\*(C`ev_set_io_collect_interval ()\*(C'\fR to increase the amount of

readyness notifications you get per iteration.

.ie n .IP """EVBACKEND_POLL""    (value 2, poll backend, available everywhere except on windows)" 4

.el .IP "\f(CWEVBACKEND_POLL\fR    (value 2, poll backend, available everywhere except on windows)" 4

.IX Item "EVBACKEND_POLL    (value 2, poll backend, available everywhere except on windows)"

And this is your standard \fIpoll\fR\|(2) backend. It's more complicated

than select, but handles sparse fds better and has no artificial

limit on the number of fds you can use (except it will slow down

considerably with a lot of inactive fds). It scales similarly to select,

i.e. O(total_fds). See the entry for \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR, above, for

performance tips.

.ie n .IP """EVBACKEND_EPOLL""   (value 4, Linux)" 4

.el .IP "\f(CWEVBACKEND_EPOLL\fR   (value 4, Linux)" 4

.IX Item "EVBACKEND_EPOLL   (value 4, Linux)"

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). The epoll design has a number

of shortcomings, such as silently dropping events in some hard-to-detect

cases and requiring a syscall per fd change, no fork support and bad

support for dup.

.Sp

While stopping, setting and starting an I/O watcher in the same iteration

will result in some caching, there is still a syscall per such incident

(because the fd could point to a different file description now), so its

best to avoid that. Also, \f(CW\*(C`dup ()\*(C'\fR'ed file descriptors might not work

very well if you register events for both fds.

.Sp

Please note that epoll sometimes generates spurious notifications, so you

need to use non-blocking I/O or other means to avoid blocking when no data

(or space) is available.

.Sp

Best performance from this backend is achieved by not unregistering all

watchers for a file descriptor until it has been closed, if possible, i.e.

keep at least one watcher active per fd at all times.

.Sp

While nominally embeddeble in other event loops, this feature is broken in

all kernel versions tested so far.

.ie n .IP """EVBACKEND_KQUEUE""  (value 8, most \s-1BSD\s0 clones)" 4

.el .IP "\f(CWEVBACKEND_KQUEUE\fR  (value 8, most \s-1BSD\s0 clones)" 4

.IX Item "EVBACKEND_KQUEUE  (value 8, most BSD clones)"

Kqueue deserves special mention, as at the time of this writing, it

was broken on all BSDs except NetBSD (usually it doesn't work reliably

with anything but sockets and pipes, except on Darwin, where of course

it's completely useless). For this reason it's not being \*(L"autodetected\*(R"

unless you explicitly specify it explicitly in the flags (i.e. using

\&\f(CW\*(C`EVBACKEND_KQUEUE\*(C'\fR) or libev was compiled on a known-to-be-good (\-enough)

system like NetBSD.

.Sp

You still can embed kqueue into a normal poll or select backend and use it

only for sockets (after having made sure that sockets work with kqueue on

the target platform). See \f(CW\*(C`ev_embed\*(C'\fR watchers for more info.

.Sp

It scales in the same way as the epoll backend, but the interface to the

kernel is more efficient (which says nothing about its actual speed, of

course). While stopping, setting and starting an I/O watcher does never

cause an extra syscall as with \f(CW\*(C`EVBACKEND_EPOLL\*(C'\fR, it still adds up to

two event changes per incident, support for \f(CW\*(C`fork ()\*(C'\fR is very bad and it

drops fds silently in similarly hard-to-detect cases.

.Sp

This backend usually performs well under most conditions.

.Sp

While nominally embeddable in other event loops, this doesn't work

everywhere, so you might need to test for this. And since it is broken

almost everywhere, you should only use it when you have a lot of sockets

(for which it usually works), by embedding it into another event loop

(e.g. \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR or \f(CW\*(C`EVBACKEND_POLL\*(C'\fR) and using it only for

sockets.

.ie n .IP """EVBACKEND_DEVPOLL"" (value 16, Solaris 8)" 4

.el .IP "\f(CWEVBACKEND_DEVPOLL\fR (value 16, Solaris 8)" 4

.IX Item "EVBACKEND_DEVPOLL (value 16, Solaris 8)"

This is not implemented yet (and might never be, unless you send me an

implementation). According to reports, \f(CW\*(C`/dev/poll\*(C'\fR only supports sockets

and is not embeddable, which would limit the usefulness of this backend

immensely.

.ie n .IP """EVBACKEND_PORT""    (value 32, Solaris 10)" 4

.el .IP "\f(CWEVBACKEND_PORT\fR    (value 32, Solaris 10)" 4

.IX Item "EVBACKEND_PORT    (value 32, Solaris 10)"

This uses the Solaris 10 event port mechanism. As with everything on Solaris,

it's really slow, but it still scales very well (O(active_fds)).

.Sp

Please note that solaris event ports can deliver a lot of spurious

notifications, so you need to use non-blocking I/O or other means to avoid

blocking when no data (or space) is available.

.Sp

While this backend scales well, it requires one system call per active

file descriptor per loop iteration. For small and medium numbers of file

descriptors a \*(L"slow\*(R" \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR or \f(CW\*(C`EVBACKEND_POLL\*(C'\fR backend

might perform better.

.Sp

On the positive side, ignoring the spurious readyness notifications, this

backend actually performed to specification in all tests and is fully

embeddable, which is a rare feat among the OS-specific backends.

.ie n .IP """EVBACKEND_ALL""" 4

.el .IP "\f(CWEVBACKEND_ALL\fR" 4

.IX Item "EVBACKEND_ALL"

Try all backends (even potentially broken ones that wouldn't be tried

with \f(CW\*(C`EVFLAG_AUTO\*(C'\fR). Since this is a mask, you can do stuff such as

\&\f(CW\*(C`EVBACKEND_ALL & ~EVBACKEND_KQUEUE\*(C'\fR.

.Sp

It is definitely not recommended to use this flag.

.RE

.RS 4

.Sp

If one or more of these are ored into the flags value, then only these

backends will be tried (in the reverse order as listed here). If none are

specified, all backends in \f(CW\*(C`ev_recommended_backends ()\*(C'\fR will be tried.

.Sp

The most typical usage is like this:

.Sp

.Vb 2

\&  if (!ev_default_loop (0))

\&    fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");

.Ve

.Sp

Restrict libev to the select and poll backends, and do not allow

environment settings to be taken into account:

.Sp

.Vb 1

\&  ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);

.Ve

.Sp

Use whatever libev has to offer, but make sure that kqueue is used if

available (warning, breaks stuff, best use only with your own private

event loop and only if you know the \s-1OS\s0 supports your types of fds):

.Sp

.Vb 1

\&  ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);

.Ve

.RE

.IP "struct ev_loop *ev_loop_new (unsigned int flags)" 4

.IX Item "struct ev_loop *ev_loop_new (unsigned int flags)"

Similar to \f(CW\*(C`ev_default_loop\*(C'\fR, but always creates a new event loop that is

always distinct from the default loop. Unlike the default loop, it cannot

handle signal and child watchers, and attempts to do so will be greeted by

undefined behaviour (or a failed assertion if assertions are enabled).

.Sp

Note that this function \fIis\fR thread-safe, and the recommended way to use

libev with threads is indeed to create one loop per thread, and using the

default loop in the \*(L"main\*(R" or \*(L"initial\*(R" thread.

.Sp

Example: Try to create a event loop that uses epoll and nothing else.

.Sp

.Vb 3

\&  struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);

\&  if (!epoller)

\&    fatal ("no epoll found here, maybe it hides under your chair");

.Ve

.IP "ev_default_destroy ()" 4

.IX Item "ev_default_destroy ()"

Destroys the default loop again (frees all memory and kernel state

etc.). None of the active event watchers will be stopped in the normal

sense, so e.g. \f(CW\*(C`ev_is_active\*(C'\fR might still return true. It is your

responsibility to either stop all watchers cleanly yoursef \fIbefore\fR

calling this function, or cope with the fact afterwards (which is usually

the easiest thing, you can just ignore the watchers and/or \f(CW\*(C`free ()\*(C'\fR them

for example).

.Sp

Note that certain global state, such as signal state, will not be freed by

this function, and related watchers (such as signal and child watchers)

would need to be stopped manually.

.Sp

In general it is not advisable to call this function except in the

rare occasion where you really need to free e.g. the signal handling

pipe fds. If you need dynamically allocated loops it is better to use

\&\f(CW\*(C`ev_loop_new\*(C'\fR and \f(CW\*(C`ev_loop_destroy\*(C'\fR).

.IP "ev_loop_destroy (loop)" 4

.IX Item "ev_loop_destroy (loop)"

Like \f(CW\*(C`ev_default_destroy\*(C'\fR, but destroys an event loop created by an

earlier call to \f(CW\*(C`ev_loop_new\*(C'\fR.

.IP "ev_default_fork ()" 4

.IX Item "ev_default_fork ()"

This function sets a flag that causes subsequent \f(CW\*(C`ev_loop\*(C'\fR iterations

to reinitialise the kernel state for backends that have one. Despite the

name, you can call it anytime, but it makes most sense after forking, in

the child process (or both child and parent, but that again makes little

sense). You \fImust\fR call it in the child before using any of the libev

functions, and it will only take effect at the next \f(CW\*(C`ev_loop\*(C'\fR iteration.

.Sp

On the other hand, you only need to call this function in the child

process if and only if you want to use the event library in the child. If

you just fork+exec, you don't have to call it at all.

.Sp

The function itself is quite fast and it's usually not a problem to call

it just in case after a fork. To make this easy, the function will fit in

quite nicely into a call to \f(CW\*(C`pthread_atfork\*(C'\fR:

.Sp

.Vb 1

\&    pthread_atfork (0, 0, ev_default_fork);

.Ve

.IP "ev_loop_fork (loop)" 4

.IX Item "ev_loop_fork (loop)"

Like \f(CW\*(C`ev_default_fork\*(C'\fR, but acts on an event loop created by

\&\f(CW\*(C`ev_loop_new\*(C'\fR. Yes, you have to call this on every allocated event loop

after fork, and how you do this is entirely your own problem.

.IP "int ev_is_default_loop (loop)" 4

.IX Item "int ev_is_default_loop (loop)"

Returns true when the given loop actually is the default loop, false otherwise.

.IP "unsigned int ev_loop_count (loop)" 4

.IX Item "unsigned int ev_loop_count (loop)"

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 \f(CW0\fR and

happily wraps around with enough iterations.

.Sp

This value can sometimes be useful as a generation counter of sorts (it

\&\*(L"ticks\*(R" the number of loop iterations), as it roughly corresponds with

\&\f(CW\*(C`ev_prepare\*(C'\fR and \f(CW\*(C`ev_check\*(C'\fR calls.

.IP "unsigned int ev_backend (loop)" 4

.IX Item "unsigned int ev_backend (loop)"

Returns one of the \f(CW\*(C`EVBACKEND_*\*(C'\fR flags indicating the event backend in

use.

.IP "ev_tstamp ev_now (loop)" 4

.IX Item "ev_tstamp ev_now (loop)"

Returns the current \*(L"event loop time\*(R", which is the time the event loop

received events and started processing them. This timestamp does not

change as long as callbacks are being processed, and this is also the base

time used for relative timers. You can treat it as the timestamp of the

event occurring (or more correctly, libev finding out about it).

.IP "ev_loop (loop, int flags)" 4

.IX Item "ev_loop (loop, int flags)"

Finally, this is it, the event handler. This function usually is called

after you initialised all your watchers and you want to start handling

events.

.Sp

If the flags argument is specified as \f(CW0\fR, it will not return until

either no event watchers are active anymore or \f(CW\*(C`ev_unloop\*(C'\fR was called.

.Sp

Please note that an explicit \f(CW\*(C`ev_unloop\*(C'\fR is usually better than

relying on all watchers to be stopped when deciding when a program has

finished (especially in interactive programs), but having a program that

automatically loops as long as it has to and no longer by virtue of

relying on its watchers stopping correctly is a thing of beauty.

.Sp

A flags value of \f(CW\*(C`EVLOOP_NONBLOCK\*(C'\fR will look for new events, will handle

those events and any outstanding ones, but will not block your process in

case there are no events and will return after one iteration of the loop.

.Sp

A flags value of \f(CW\*(C`EVLOOP_ONESHOT\*(C'\fR will look for new events (waiting if

neccessary) and will handle those and any outstanding ones. It will block

your process until at least one new event arrives, and will return after

one iteration of the loop. This is useful if you are waiting for some

external event in conjunction with something not expressible using other

libev watchers. 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_loop\*(C'\fR does:

.Sp

.Vb 10

\&   \- Before the first iteration, call any pending watchers.

\&   * If EVFLAG_FORKCHECK was used, check for a fork.

\&   \- If a fork was detected, queue and call all fork watchers.

\&   \- Queue and call all prepare watchers.

\&   \- If we have been forked, recreate the kernel state.

\&   \- Update the kernel state with all outstanding changes.

\&   \- Update the "event loop time".

\&   \- Calculate for how long to sleep or block, if at all

\&     (active idle watchers, EVLOOP_NONBLOCK or not having

\&     any active watchers at all will result in not sleeping).

\&   \- Sleep if the I/O and timer collect interval say so.

\&   \- Block the process, waiting for any events.

\&   \- Queue all outstanding I/O (fd) events.

\&   \- Update the "event loop time" and do time jump handling.

\&   \- Queue all outstanding timers.

\&   \- Queue all outstanding periodics.

\&   \- If no events are pending now, queue all idle watchers.

\&   \- Queue all check watchers.

\&   \- Call all queued watchers in reverse order (i.e. check watchers first).

\&     Signals and child watchers are implemented as I/O watchers, and will

\&     be handled here by queueing them when their watcher gets executed.

\&   \- If ev_unloop has been called, or EVLOOP_ONESHOT or EVLOOP_NONBLOCK

\&     were used, or there are no active watchers, return, otherwise

\&     continue with step *.

.Ve

.Sp

Example: Queue some jobs and then loop until no events are outstanding

anymore.

.Sp

.Vb 4

\&   ... queue jobs here, make sure they register event watchers as long

\&   ... as they still have work to do (even an idle watcher will do..)

\&   ev_loop (my_loop, 0);

\&   ... jobs done. yeah!

.Ve

.IP "ev_unloop (loop, how)" 4

.IX Item "ev_unloop (loop, how)"

Can be used to make a call to \f(CW\*(C`ev_loop\*(C'\fR return early (but only after it

has processed all outstanding events). The \f(CW\*(C`how\*(C'\fR argument must be either

\&\f(CW\*(C`EVUNLOOP_ONE\*(C'\fR, which will make the innermost \f(CW\*(C`ev_loop\*(C'\fR call return, or

\&\f(CW\*(C`EVUNLOOP_ALL\*(C'\fR, which will make all nested \f(CW\*(C`ev_loop\*(C'\fR calls return.

.Sp

This \*(L"unloop state\*(R" will be cleared when entering \f(CW\*(C`ev_loop\*(C'\fR again.

.IP "ev_ref (loop)" 4

.IX Item "ev_ref (loop)"

.PD 0

.IP "ev_unref (loop)" 4

.IX Item "ev_unref (loop)"

.PD

Ref/unref can be used to add or remove a reference count on the event

loop: Every watcher keeps one reference, and as long as the reference

count is nonzero, \f(CW\*(C`ev_loop\*(C'\fR will not return on its own. If you have

a watcher you never unregister that should not keep \f(CW\*(C`ev_loop\*(C'\fR from

returning, \fIev_unref()\fR after starting, and \fIev_ref()\fR before stopping it. For

example, libev itself uses this for its internal signal pipe: It is not

visible to the libev user and should not keep \f(CW\*(C`ev_loop\*(C'\fR from exiting if

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 \fIunref after start\fR and \fIref before stop\fR

(but only if the watcher wasn't active before, or was active before,

respectively).

.Sp

Example: Create a signal watcher, but keep it from keeping \f(CW\*(C`ev_loop\*(C'\fR

running when nothing else is active.

.Sp

.Vb 4

\&  struct ev_signal exitsig;

\&  ev_signal_init (&exitsig, sig_cb, SIGINT);

\&  ev_signal_start (loop, &exitsig);

\&  evf_unref (loop);

.Ve

.Sp

Example: For some weird reason, unregister the above signal handler again.

.Sp

.Vb 2

\&  ev_ref (loop);

\&  ev_signal_stop (loop, &exitsig);

.Ve

.IP "ev_set_io_collect_interval (loop, ev_tstamp interval)" 4

.IX Item "ev_set_io_collect_interval (loop, ev_tstamp interval)"

.PD 0

.IP "ev_set_timeout_collect_interval (loop, ev_tstamp interval)" 4

.IX Item "ev_set_timeout_collect_interval (loop, ev_tstamp interval)"

.PD

These advanced functions influence the time that libev will spend waiting

for events. Both are by default \f(CW0\fR, meaning that libev will try to

invoke timer/periodic callbacks and I/O callbacks with minimum latency.

.Sp

Setting these to a higher value (the \f(CW\*(C`interval\*(C'\fR \fImust\fR be >= \f(CW0\fR)

allows libev to delay invocation of I/O and timer/periodic callbacks to

increase efficiency of loop iterations.

.Sp

The background is that sometimes your program runs just fast enough to

handle one (or very few) event(s) per loop iteration. While this makes

the program responsive, it also wastes a lot of \s-1CPU\s0 time to poll for new

events, especially with backends like \f(CW\*(C`select ()\*(C'\fR which have a high

overhead for the actual polling but can deliver many events at once.

.Sp

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

introduce an additional \f(CW\*(C`ev_sleep ()\*(C'\fR call into most loop iterations.

.Sp

Likewise, by setting a higher \fItimeout collect interval\fR you allow libev

to spend more time collecting timeouts, at the expense of increased

latency (the watcher callback will be called later). \f(CW\*(C`ev_io\*(C'\fR watchers

will not be affected. Setting this to a non-null value will not introduce

any overhead in libev.

.Sp

Many (busy) programs can usually benefit by setting the io collect

interval to a value near \f(CW0.1\fR or so, which is often enough for

interactive servers (of course not for games), likewise for timeouts. It

usually doesn't make much sense to set it to a lower value than \f(CW0.01\fR,

as this approsaches the timing granularity of most systems.

.SH "ANATOMY OF A WATCHER"

.IX Header "ANATOMY OF A WATCHER"

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 \s-1STDIN\s0 to

become readable, you would create an \f(CW\*(C`ev_io\*(C'\fR watcher for that:

.PP

.Vb 5

\&  static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents)

\&  {

\&    ev_io_stop (w);

\&    ev_unloop (loop, EVUNLOOP_ALL);

\&  }

\&

\&  struct ev_loop *loop = ev_default_loop (0);

\&  struct ev_io stdin_watcher;

\&  ev_init (&stdin_watcher, my_cb);

\&  ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);

\&  ev_io_start (loop, &stdin_watcher);

\&  ev_loop (loop, 0);

.Ve

.PP

As you can see, you are responsible for allocating the memory for your

watcher structures (and it is usually a bad idea to do this on the stack,

although this can sometimes be quite valid).

.PP

Each watcher structure must be initialised by a call to \f(CW\*(C`ev_init

(watcher *, callback)\*(C'\fR, which expects a callback to be provided. This

callback gets invoked each time the event occurs (or, in the case of io

watchers, each time the event loop detects that the file descriptor given

is readable and/or writable).

.PP

Each watcher type has its own \f(CW\*(C`ev_<type>_set (watcher *, ...)\*(C'\fR macro

with arguments specific to this watcher type. There is also a macro

to combine initialisation and setting in one call: \f(CW\*(C`ev_<type>_init

(watcher *, callback, ...)\*(C'\fR.

.PP

To make the watcher actually watch out for events, you have to start it

with a watcher-specific start function (\f(CW\*(C`ev_<type>_start (loop, watcher

*)\*(C'\fR), and you can stop watching for events at any time by calling the

corresponding stop function (\f(CW\*(C`ev_<type>_stop (loop, watcher *)\*(C'\fR.

.PP

As long as your watcher is active (has been started but not stopped) you

must not touch the values stored in it. Most specifically you must never

reinitialise it or call its \f(CW\*(C`set\*(C'\fR macro.

.PP

Each and every callback receives the event loop pointer as first, the

registered watcher structure as second, and a bitset of received events as

third argument.

.PP

The received events usually include a single bit per event type received

(you can receive multiple events at the same time). The possible bit masks

are:

.ie n .IP """EV_READ""" 4

.el .IP "\f(CWEV_READ\fR" 4

.IX Item "EV_READ"

.PD 0

.ie n .IP """EV_WRITE""" 4

.el .IP "\f(CWEV_WRITE\fR" 4

.IX Item "EV_WRITE"

.PD

The file descriptor in the \f(CW\*(C`ev_io\*(C'\fR watcher has become readable and/or

writable.

.ie n .IP """EV_TIMEOUT""" 4

.el .IP "\f(CWEV_TIMEOUT\fR" 4

.IX Item "EV_TIMEOUT"

The \f(CW\*(C`ev_timer\*(C'\fR watcher has timed out.

.ie n .IP """EV_PERIODIC""" 4

.el .IP "\f(CWEV_PERIODIC\fR" 4

.IX Item "EV_PERIODIC"

The \f(CW\*(C`ev_periodic\*(C'\fR watcher has timed out.

.ie n .IP """EV_SIGNAL""" 4

.el .IP "\f(CWEV_SIGNAL\fR" 4

.IX Item "EV_SIGNAL"

The signal specified in the \f(CW\*(C`ev_signal\*(C'\fR watcher has been received by a thread.

.ie n .IP """EV_CHILD""" 4

.el .IP "\f(CWEV_CHILD\fR" 4

.IX Item "EV_CHILD"

The pid specified in the \f(CW\*(C`ev_child\*(C'\fR watcher has received a status change.

.ie n .IP """EV_STAT""" 4

.el .IP "\f(CWEV_STAT\fR" 4

.IX Item "EV_STAT"

The path specified in the \f(CW\*(C`ev_stat\*(C'\fR watcher changed its attributes somehow.

.ie n .IP """EV_IDLE""" 4

.el .IP "\f(CWEV_IDLE\fR" 4

.IX Item "EV_IDLE"

The \f(CW\*(C`ev_idle\*(C'\fR watcher has determined that you have nothing better to do.

.ie n .IP """EV_PREPARE""" 4

.el .IP "\f(CWEV_PREPARE\fR" 4

.IX Item "EV_PREPARE"

.PD 0

.ie n .IP """EV_CHECK""" 4

.el .IP "\f(CWEV_CHECK\fR" 4

.IX Item "EV_CHECK"

.PD

All \f(CW\*(C`ev_prepare\*(C'\fR watchers are invoked just \fIbefore\fR \f(CW\*(C`ev_loop\*(C'\fR starts

to gather new events, and all \f(CW\*(C`ev_check\*(C'\fR watchers are invoked just after

\&\f(CW\*(C`ev_loop\*(C'\fR has gathered them, but before it invokes any callbacks for any

received events. Callbacks of both watcher types can start and stop as

many watchers as they want, and all of them will be taken into account

(for example, a \f(CW\*(C`ev_prepare\*(C'\fR watcher might start an idle watcher to keep

\&\f(CW\*(C`ev_loop\*(C'\fR from blocking).

.ie n .IP """EV_EMBED""" 4

.el .IP "\f(CWEV_EMBED\fR" 4

.IX Item "EV_EMBED"

The embedded event loop specified in the \f(CW\*(C`ev_embed\*(C'\fR watcher needs attention.

.ie n .IP """EV_FORK""" 4

.el .IP "\f(CWEV_FORK\fR" 4

.IX Item "EV_FORK"

The event loop has been resumed in the child process after fork (see

\&\f(CW\*(C`ev_fork\*(C'\fR).

.ie n .IP """EV_ASYNC""" 4

.el .IP "\f(CWEV_ASYNC\fR" 4

.IX Item "EV_ASYNC"

The given async watcher has been asynchronously notified (see \f(CW\*(C`ev_async\*(C'\fR).

.ie n .IP """EV_ERROR""" 4

.el .IP "\f(CWEV_ERROR\fR" 4

.IX Item "EV_ERROR"

An unspecified error has occured, the watcher has been stopped. This might

happen because the watcher could not be properly started because libev

ran out of memory, a file descriptor was found to be closed or any other

problem. You best act on it by reporting the problem and somehow coping

with the watcher being stopped.

.Sp

Libev will usually signal a few \*(L"dummy\*(R" events together with an error,

for example it might indicate that a fd is readable or writable, and if

your callbacks is well-written it can just attempt the operation and cope

with the error from \fIread()\fR or \fIwrite()\fR. This will not work in multithreaded

programs, though, so beware.

.Sh "\s-1GENERIC\s0 \s-1WATCHER\s0 \s-1FUNCTIONS\s0"

.IX Subsection "GENERIC WATCHER FUNCTIONS"

In the following description, \f(CW\*(C`TYPE\*(C'\fR stands for the watcher type,

e.g. \f(CW\*(C`timer\*(C'\fR for \f(CW\*(C`ev_timer\*(C'\fR watchers and \f(CW\*(C`io\*(C'\fR for \f(CW\*(C`ev_io\*(C'\fR watchers.

.ie n .IP """ev_init"" (ev_TYPE *watcher, callback)" 4

.el .IP "\f(CWev_init\fR (ev_TYPE *watcher, callback)" 4

.IX Item "ev_init (ev_TYPE *watcher, callback)"

This macro initialises the generic portion of a watcher. The contents

of the watcher object can be arbitrary (so \f(CW\*(C`malloc\*(C'\fR will do). Only

the generic parts of the watcher are initialised, you \fIneed\fR to call

the type-specific \f(CW\*(C`ev_TYPE_set\*(C'\fR macro afterwards to initialise the

type-specific parts. For each type there is also a \f(CW\*(C`ev_TYPE_init\*(C'\fR macro

which rolls both calls into one.

.Sp

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.

.Sp

The callback is always of type \f(CW\*(C`void (*)(ev_loop *loop, ev_TYPE *watcher,

int revents)\*(C'\fR.

.ie n .IP """ev_TYPE_set"" (ev_TYPE *, [args])" 4

.el .IP "\f(CWev_TYPE_set\fR (ev_TYPE *, [args])" 4

.IX Item "ev_TYPE_set (ev_TYPE *, [args])"

This macro initialises the type-specific parts of a watcher. You need to

call \f(CW\*(C`ev_init\*(C'\fR at least once before you call this macro, but you can

call \f(CW\*(C`ev_TYPE_set\*(C'\fR any number of times. You must not, however, call this

macro on a watcher that is active (it can be pending, however, which is a

difference to the \f(CW\*(C`ev_init\*(C'\fR macro).

.Sp

Although some watcher types do not have type-specific arguments

(e.g. \f(CW\*(C`ev_prepare\*(C'\fR) you still need to call its \f(CW\*(C`set\*(C'\fR macro.

.ie n .IP """ev_TYPE_init"" (ev_TYPE *watcher, callback, [args])" 4

.el .IP "\f(CWev_TYPE_init\fR (ev_TYPE *watcher, callback, [args])" 4

.IX Item "ev_TYPE_init (ev_TYPE *watcher, callback, [args])"

This convinience macro rolls both \f(CW\*(C`ev_init\*(C'\fR and \f(CW\*(C`ev_TYPE_set\*(C'\fR macro

calls into a single call. This is the most convinient method to initialise

a watcher. The same limitations apply, of course.

.ie n .IP """ev_TYPE_start"" (loop *, ev_TYPE *watcher)" 4

.el .IP "\f(CWev_TYPE_start\fR (loop *, ev_TYPE *watcher)" 4

.IX Item "ev_TYPE_start (loop *, ev_TYPE *watcher)"

Starts (activates) the given watcher. Only active watchers will receive

events. If the watcher is already active nothing will happen.

.ie n .IP """ev_TYPE_stop"" (loop *, ev_TYPE *watcher)" 4

.el .IP "\f(CWev_TYPE_stop\fR (loop *, ev_TYPE *watcher)" 4

.IX Item "ev_TYPE_stop (loop *, ev_TYPE *watcher)"

Stops the given watcher again (if active) and clears the pending

status. It is possible that stopped watchers are pending (for example,

non-repeating timers are being stopped when they become pending), but

\&\f(CW\*(C`ev_TYPE_stop\*(C'\fR ensures that the watcher is neither active nor pending. If

you want to free or reuse the memory used by the watcher it is therefore a

good idea to always call its \f(CW\*(C`ev_TYPE_stop\*(C'\fR function.

.IP "bool ev_is_active (ev_TYPE *watcher)" 4

.IX Item "bool ev_is_active (ev_TYPE *watcher)"

Returns a true value iff the watcher is active (i.e. it has been started

and not yet been stopped). As long as a watcher is active you must not modify

it.

.IP "bool ev_is_pending (ev_TYPE *watcher)" 4

.IX Item "bool ev_is_pending (ev_TYPE *watcher)"

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

\&\f(CW\*(C`ev_TYPE_set\*(C'\fR is safe), you must not change its priority, and you must

make sure the watcher is available to libev (e.g. you cannot \f(CW\*(C`free ()\*(C'\fR

it).

.IP "callback ev_cb (ev_TYPE *watcher)" 4

.IX Item "callback ev_cb (ev_TYPE *watcher)"

Returns the callback currently set on the watcher.

.IP "ev_cb_set (ev_TYPE *watcher, callback)" 4

.IX Item "ev_cb_set (ev_TYPE *watcher, callback)"

Change the callback. You can change the callback at virtually any time

(modulo threads).

.IP "ev_set_priority (ev_TYPE *watcher, priority)" 4

.IX Item "ev_set_priority (ev_TYPE *watcher, priority)"

.PD 0

.IP "int ev_priority (ev_TYPE *watcher)" 4

.IX Item "int ev_priority (ev_TYPE *watcher)"

.PD

Set and query the priority of the watcher. The priority is a small

integer between \f(CW\*(C`EV_MAXPRI\*(C'\fR (default: \f(CW2\fR) and \f(CW\*(C`EV_MINPRI\*(C'\fR

(default: \f(CW\*(C`\-2\*(C'\fR). Pending watchers with higher priority will be invoked

before watchers with lower priority, but priority will not keep watchers

from being executed (except for \f(CW\*(C`ev_idle\*(C'\fR watchers).

.Sp

This means that priorities are \fIonly\fR 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.

.Sp

If you need to suppress invocation when higher priority events are pending

you need to look at \f(CW\*(C`ev_idle\*(C'\fR watchers, which provide this functionality.

.Sp

You \fImust not\fR change the priority of a watcher as long as it is active or

pending.

.Sp

The default priority used by watchers when no priority has been set is

always \f(CW0\fR, which is supposed to not be too high and not be too low :).

.Sp

Setting a priority outside the range of \f(CW\*(C`EV_MINPRI\*(C'\fR to \f(CW\*(C`EV_MAXPRI\*(C'\fR 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.

.IP "ev_invoke (loop, ev_TYPE *watcher, int revents)" 4

.IX Item "ev_invoke (loop, ev_TYPE *watcher, int revents)"

Invoke the \f(CW\*(C`watcher\*(C'\fR with the given \f(CW\*(C`loop\*(C'\fR and \f(CW\*(C`revents\*(C'\fR. Neither

\&\f(CW\*(C`loop\*(C'\fR nor \f(CW\*(C`revents\*(C'\fR need to be valid as long as the watcher callback

can deal with that fact.

.IP "int ev_clear_pending (loop, ev_TYPE *watcher)" 4

.IX Item "int ev_clear_pending (loop, ev_TYPE *watcher)"

If the watcher is pending, this function returns clears its pending status

and returns its \f(CW\*(C`revents\*(C'\fR bitset (as if its callback was invoked). If the

watcher isn't pending it does nothing and returns \f(CW0\fR.

.Sh "\s-1ASSOCIATING\s0 \s-1CUSTOM\s0 \s-1DATA\s0 \s-1WITH\s0 A \s-1WATCHER\s0"

.IX Subsection "ASSOCIATING CUSTOM DATA WITH A WATCHER"

Each watcher has, by default, a member \f(CW\*(C`void *data\*(C'\fR that you can change

and read at any time, libev will completely ignore it. This can be used

to associate arbitrary data with your watcher. If you need more data and

don't want to allocate memory and store a pointer to it in that data

member, you can also \*(L"subclass\*(R" the watcher type and provide your own

data:

.PP

.Vb 7

\&  struct my_io

\&  {

\&    struct ev_io io;

\&    int otherfd;

\&    void *somedata;

\&    struct whatever *mostinteresting;

\&  }

.Ve

.PP

And since your callback will be called with a pointer to the watcher, you

can cast it back to your own type:

.PP

.Vb 5

\&  static void my_cb (struct ev_loop *loop, struct ev_io *w_, int revents)

\&  {

\&    struct my_io *w = (struct my_io *)w_;

\&    ...

\&  }

.Ve

.PP

More interesting and less C\-conformant ways of casting your callback type

instead have been omitted.

.PP

Another common scenario is having some data structure with multiple

watchers:

.PP

.Vb 6

\&  struct my_biggy

\&  {

\&    int some_data;

\&    ev_timer t1;

\&    ev_timer t2;

\&  }

.Ve

.PP

In this case getting the pointer to \f(CW\*(C`my_biggy\*(C'\fR is a bit more complicated,

you need to use \f(CW\*(C`offsetof\*(C'\fR:

.PP

.Vb 1

\&  #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));

\&  }

.Ve

.SH "WATCHER TYPES"

.IX Header "WATCHER TYPES"

This section describes each watcher in detail, but will not repeat

information given in the last section. Any initialisation/set macros,

functions and members specific to the watcher type are explained.

.PP

Members are additionally marked with either \fI[read\-only]\fR, 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 \fI[read\-write]\fR, 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.

.ie n .Sh """ev_io"" \- is this file descriptor readable or writable?"

.el .Sh "\f(CWev_io\fP \- is this file descriptor readable or writable?"

.IX Subsection "ev_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, 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.

.PP

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

required if you know what you are doing).

.PP

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 \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR and

\&\f(CW\*(C`EVBACKEND_POLL\*(C'\fR).

.PP

Another thing you have to watch out for is that it is quite easy to

receive \*(L"spurious\*(R" readyness notifications, that is your callback might

be called with \f(CW\*(C`EV_READ\*(C'\fR but a subsequent \f(CW\*(C`read\*(C'\fR(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 \f(CW\*(C`read\*(C'\fR(2) returning

\&\f(CW\*(C`EAGAIN\*(C'\fR is far preferable to a program hanging until some data arrives.

.PP

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).

.PP

\fIThe special problem of disappearing file descriptors\fR

.IX Subsection "The special problem of disappearing file descriptors"

.PP

Some backends (e.g. kqueue, epoll) need to be told about closing a file

descriptor (either by calling \f(CW\*(C`close\*(C'\fR explicitly or by any other means,

such as \f(CW\*(C`dup\*(C'\fR). 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.

.PP

To avoid having to explicitly tell libev about such cases, libev follows

the following policy:  Each time \f(CW\*(C`ev_io_set\*(C'\fR 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 \fIhave\fR to call \f(CW\*(C`ev_io_set\*(C'\fR (or \f(CW\*(C`ev_io_init\*(C'\fR) when you change the

descriptor even if the file descriptor number itself did not change.

.PP

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.

.PP

\fIThe special problem of dup'ed file descriptors\fR

.IX Subsection "The special problem of dup'ed file descriptors"

.PP

Some backends (e.g. epoll), cannot register events for file descriptors,

but only events for the underlying file descriptions. That means when you

have \f(CW\*(C`dup ()\*(C'\fR'ed file descriptors or weirder constellations, and register

events for them, only one file descriptor might actually receive events.

.PP

There is no workaround possible except not registering events

for potentially \f(CW\*(C`dup ()\*(C'\fR'ed file descriptors, or to resort to

\&\f(CW\*(C`EVBACKEND_SELECT\*(C'\fR or \f(CW\*(C`EVBACKEND_POLL\*(C'\fR.

.PP

\fIThe special problem of fork\fR

.IX Subsection "The special problem of fork"

.PP

Some backends (epoll, kqueue) do not support \f(CW\*(C`fork ()\*(C'\fR at all or exhibit

useless behaviour. Libev fully supports fork, but needs to be told about

it in the child.

.PP

To support fork in your programs, you either have to call

\&\f(CW\*(C`ev_default_fork ()\*(C'\fR or \f(CW\*(C`ev_loop_fork ()\*(C'\fR after a fork in the child,

enable \f(CW\*(C`EVFLAG_FORKCHECK\*(C'\fR, or resort to \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR or

\&\f(CW\*(C`EVBACKEND_POLL\*(C'\fR.

.PP

\fIThe special problem of \s-1SIGPIPE\s0\fR

.IX Subsection "The special problem of SIGPIPE"

.PP

While not really specific to libev, it is easy to forget about \s-1SIGPIPE:\s0

when reading from a pipe whose other end has been closed, your program

gets send a \s-1SIGPIPE\s0, which, by default, aborts your program. For most

programs this is sensible behaviour, for daemons, this is usually

undesirable.

.PP

So when you encounter spurious, unexplained daemon exits, make sure you

ignore \s-1SIGPIPE\s0 (and maybe make sure you log the exit status of your daemon

somewhere, as that would have given you a big clue).

.PP

\fIWatcher-Specific Functions\fR

.IX Subsection "Watcher-Specific Functions"

.IP "ev_io_init (ev_io *, callback, int fd, int events)" 4

.IX Item "ev_io_init (ev_io *, callback, int fd, int events)"

.PD 0

.IP "ev_io_set (ev_io *, int fd, int events)" 4

.IX Item "ev_io_set (ev_io *, int fd, int events)"

.PD

Configures an \f(CW\*(C`ev_io\*(C'\fR watcher. The \f(CW\*(C`fd\*(C'\fR is the file descriptor to

rceeive events for and events is either \f(CW\*(C`EV_READ\*(C'\fR, \f(CW\*(C`EV_WRITE\*(C'\fR or

\&\f(CW\*(C`EV_READ | EV_WRITE\*(C'\fR to receive the given events.

.IP "int fd [read\-only]" 4

.IX Item "int fd [read-only]"

The file descriptor being watched.

.IP "int events [read\-only]" 4

.IX Item "int events [read-only]"

The events being watched.

.PP

\fIExamples\fR

.IX Subsection "Examples"

.PP

Example: Call \f(CW\*(C`stdin_readable_cb\*(C'\fR when \s-1STDIN_FILENO\s0 has become, well

readable, but only once. Since it is likely line-buffered, you could

attempt to read a whole line in the callback.

.PP

.Vb 6

\&  static void

\&  stdin_readable_cb (struct ev_loop *loop, struct ev_io *w, int revents)

\&  {

\&     ev_io_stop (loop, w);

\&    .. read from stdin here (or from w\->fd) and haqndle any I/O errors

\&  }

\&

\&  ...

\&  struct ev_loop *loop = ev_default_init (0);

\&  struct ev_io stdin_readable;

\&  ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);

\&  ev_io_start (loop, &stdin_readable);

\&  ev_loop (loop, 0);

.Ve

.ie n .Sh """ev_timer"" \- relative and optionally repeating timeouts"

.el .Sh "\f(CWev_timer\fP \- relative and optionally repeating timeouts"

.IX Subsection "ev_timer - relative and optionally repeating timeouts"

Timer watchers are simple relative timers that generate an event after a

given time, and optionally repeating in regular intervals after that.

.PP

The timers are based on real time, that is, if you register an event that

times out after an hour and you reset your system clock to last years

time, it will still time out after (roughly) and hour. \*(L"Roughly\*(R" because

detecting time jumps is hard, and some inaccuracies are unavoidable (the

monotonic clock option helps a lot here).

.PP

The relative timeouts are calculated relative to the \f(CW\*(C`ev_now ()\*(C'\fR

time. This is usually the right thing as this timestamp refers to the time

of the event triggering whatever timeout you are modifying/starting. If

you suspect event processing to be delayed and you \fIneed\fR to base the timeout

on the current time, use something like this to adjust for this:

.PP

.Vb 1

\&   ev_timer_set (&timer, after + ev_now () \- ev_time (), 0.);

.Ve

.PP

The callback is guarenteed to be invoked only when its timeout has passed,

but if multiple timers become ready during the same loop iteration then

order of execution is undefined.

.PP

\fIWatcher-Specific Functions and Data Members\fR

.IX Subsection "Watcher-Specific Functions and Data Members"

.IP "ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)" 4

.IX Item "ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)"

.PD 0

.IP "ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)" 4

.IX Item "ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)"

.PD

Configure the timer to trigger after \f(CW\*(C`after\*(C'\fR seconds. If \f(CW\*(C`repeat\*(C'\fR is

\&\f(CW0.\fR, then it will automatically be stopped. If it is positive, then the

timer will automatically be configured to trigger again \f(CW\*(C`repeat\*(C'\fR seconds

later, again, and again, until stopped manually.

.Sp

The timer itself will do a best-effort at avoiding drift, that is, if you

configure a timer to trigger every 10 seconds, then it will trigger at

exactly 10 second intervals. If, however, your program cannot 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 nonrepeating, stop it (as if it timed out).

.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.

.Sp

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 \f(CW\*(C`ev_timer\*(C'\fR with a \f(CW\*(C`repeat\*(C'\fR value of \f(CW60\fR and then call

\&\f(CW\*(C`ev_timer_again\*(C'\fR 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 \f(CW\*(C`ev_timer_stop\*(C'\fR the timer, and \f(CW\*(C`ev_timer_again\*(C'\fR will

automatically restart it if need be.

.Sp

That means you can ignore the \f(CW\*(C`after\*(C'\fR value and \f(CW\*(C`ev_timer_start\*(C'\fR

altogether and only ever use the \f(CW\*(C`repeat\*(C'\fR value and \f(CW\*(C`ev_timer_again\*(C'\fR:

.Sp

.Vb 8

\&   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);

.Ve

.Sp

This is more slightly efficient then stopping/starting the timer each time

you want to modify its timeout value.

.IP "ev_tstamp repeat [read\-write]" 4

.IX Item "ev_tstamp repeat [read-write]"

The current \f(CW\*(C`repeat\*(C'\fR value. Will be used each time the watcher times out

or \f(CW\*(C`ev_timer_again\*(C'\fR is called and determines the next timeout (if any),

which is also when any modifications are taken into account.

.PP

\fIExamples\fR

.IX Subsection "Examples"

.PP

Example: Create a timer that fires after 60 seconds.

.PP

.Vb 5

\&  static void

\&  one_minute_cb (struct ev_loop *loop, struct ev_timer *w, int revents)

\&  {

\&    .. one minute over, w is actually stopped right here

\&  }

\&

\&  struct ev_timer mytimer;

\&  ev_timer_init (&mytimer, one_minute_cb, 60., 0.);

\&  ev_timer_start (loop, &mytimer);

.Ve

.PP

Example: Create a timeout timer that times out after 10 seconds of

inactivity.

.PP

.Vb 5

\&  static void

\&  timeout_cb (struct ev_loop *loop, struct ev_timer *w, int revents)

\&  {

\&    .. ten seconds without any activity

\&  }

\&

\&  struct ev_timer mytimer;

\&  ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */

\&  ev_timer_again (&mytimer); /* start timer */

\&  ev_loop (loop, 0);

\&

\&  // and in some piece of code that gets executed on any "activity":

\&  // reset the timeout to start ticking again at 10 seconds

\&  ev_timer_again (&mytimer);

.Ve

.ie n .Sh """ev_periodic"" \- to cron or not to cron?"

.el .Sh "\f(CWev_periodic\fP \- to cron or not to cron?"

.IX Subsection "ev_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).

.PP

Unlike \f(CW\*(C`ev_timer\*(C'\fR's, they are not based on real time (or relative time)

but on wallclock time (absolute time). You can tell a periodic watcher

to trigger \*(L"at\*(R" some specific point in time. For example, if you tell a

periodic watcher to trigger in 10 seconds (by specifiying e.g. \f(CW\*(C`ev_now ()

+ 10.\*(C'\fR) and then reset your system clock to the last year, then it will

take a year to trigger the event (unlike an \f(CW\*(C`ev_timer\*(C'\fR, which would trigger

roughly 10 seconds later).

.PP

They can also be used to implement vastly more complex timers, such as

triggering an event on each midnight, local time or other, complicated,

rules.

.PP

As with timers, the callback is guarenteed to be invoked only when the

time (\f(CW\*(C`at\*(C'\fR) has been passed, but if multiple periodic timers become ready

during the same loop iteration then order of execution is undefined.

.PP

\fIWatcher-Specific Functions and Data Members\fR

.IX Subsection "Watcher-Specific Functions and Data Members"

.IP "ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)" 4

.IX Item "ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)"

.PD 0

.IP "ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)" 4

.IX Item "ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)"

.PD

Lots of arguments, lets sort it out... There are basically three modes of

operation, and we will explain them from simplest to complex:

.RS 4

.IP "\(bu" 4

absolute timer (at = time, interval = reschedule_cb = 0)

.Sp

In this configuration the watcher triggers an event at the wallclock time

\&\f(CW\*(C`at\*(C'\fR 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.

.IP "\(bu" 4

repeating interval timer (at = offset, interval > 0, reschedule_cb = 0)

.Sp

In this mode the watcher will always be scheduled to time out at the next

\&\f(CW\*(C`at + N * interval\*(C'\fR time (for some integer N, which can also be negative)

and then repeat, regardless of any time jumps.

.Sp

This can be used to create timers that do not drift with respect to system

time:

.Sp

.Vb 1

\&   ev_periodic_set (&periodic, 0., 3600., 0);

.Ve

.Sp

This doesn't mean there will always be 3600 seconds in between triggers,

but only that the the callback will be called when the system time shows a

full hour (\s-1UTC\s0), or more correctly, when the system time is evenly divisible

by 3600.

.Sp

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 = at (mod interval)\*(C'\fR, regardless of any time jumps.

.Sp

For numerical stability it is preferable that the \f(CW\*(C`at\*(C'\fR value is near

\&\f(CW\*(C`ev_now ()\*(C'\fR (the current time), but there is no range requirement for

this value.

.IP "\(bu" 4

manual reschedule mode (at and interval ignored, reschedule_cb = callback)

.Sp

In this mode the values for \f(CW\*(C`interval\*(C'\fR and \f(CW\*(C`at\*(C'\fR are both being

ignored. Instead, each time the periodic watcher gets scheduled, the

reschedule callback will be called with the watcher as first, and the

current time as second argument.

.Sp

\&\s-1NOTE:\s0 \fIThis callback \s-1MUST\s0 \s-1NOT\s0 stop or destroy any periodic watcher,

ever, or make any event loop modifications\fR. If you need to stop it,

return \f(CW\*(C`now + 1e30\*(C'\fR (or so, fudge fudge) and stop it afterwards (e.g. by

starting an \f(CW\*(C`ev_prepare\*(C'\fR watcher, which is legal).

.Sp

Its prototype is \f(CW\*(C`ev_tstamp (*reschedule_cb)(struct ev_periodic *w,

ev_tstamp now)\*(C'\fR, e.g.:

.Sp

.Vb 4

\&   static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)

\&   {

\&     return now + 60.;

\&   }

.Ve

.Sp

It must return the next time to trigger, based on the passed time value

(that is, the lowest time value larger than to the second argument). It

will usually be called just before the callback will be triggered, but

might be called at other times, too.

.Sp

\&\s-1NOTE:\s0 \fIThis callback must always return a time that is later than the

passed \f(CI\*(C`now\*(C'\fI value\fR. Not even \f(CW\*(C`now\*(C'\fR itself will do, it \fImust\fR be larger.

.Sp

This can be used to create very complex timers, such as a timer that

triggers on each midnight, local time. To do this, you would calculate the

next midnight after \f(CW\*(C`now\*(C'\fR and return the timestamp value for this. How

you do this is, again, up to you (but it is not trivial, which is the main

reason I omitted it as an example).

.RE

.RS 4

.RE

.IP "ev_periodic_again (loop, ev_periodic *)" 4

.IX Item "ev_periodic_again (loop, ev_periodic *)"

Simply stops and restarts the periodic watcher again. This is only useful

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).

.IP "ev_tstamp ev_periodic_at (ev_periodic *)" 4

.IX Item "ev_tstamp ev_periodic_at (ev_periodic *)"

When active, returns the absolute time that the watcher is supposed to

trigger next.

.IP "ev_tstamp offset [read\-write]" 4

.IX Item "ev_tstamp offset [read-write]"

When repeating, this contains the offset value, otherwise this is the

absolute point in time (the \f(CW\*(C`at\*(C'\fR value passed to \f(CW\*(C`ev_periodic_set\*(C'\fR).

.Sp

Can be modified any time, but changes only take effect when the periodic

timer fires or \f(CW\*(C`ev_periodic_again\*(C'\fR is being called.

.IP "ev_tstamp interval [read\-write]" 4

.IX Item "ev_tstamp interval [read-write]"

The current interval value. Can be modified any time, but changes only

take effect when the periodic timer fires or \f(CW\*(C`ev_periodic_again\*(C'\fR is being

called.

.IP "ev_tstamp (*reschedule_cb)(struct ev_periodic *w, ev_tstamp now) [read\-write]" 4

.IX Item "ev_tstamp (*reschedule_cb)(struct ev_periodic *w, ev_tstamp now) [read-write]"

The current reschedule callback, or \f(CW0\fR, if this functionality is

switched off. Can be changed any time, but changes only take effect when

the periodic timer fires or \f(CW\*(C`ev_periodic_again\*(C'\fR is being called.

.PP

\fIExamples\fR

.IX Subsection "Examples"

.PP

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.

.PP

.Vb 5

\&  static void

\&  clock_cb (struct ev_loop *loop, struct ev_io *w, int revents)

\&  {

\&    ... its now a full hour (UTC, or TAI or whatever your clock follows)

\&  }

\&

\&  struct ev_periodic hourly_tick;

\&  ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);

\&  ev_periodic_start (loop, &hourly_tick);

.Ve

.PP

Example: The same as above, but use a reschedule callback to do it:

.PP

.Vb 1

\&  #include <math.h>

\&

\&  static ev_tstamp

\&  my_scheduler_cb (struct ev_periodic *w, ev_tstamp now)

\&  {

\&    return fmod (now, 3600.) + 3600.;

\&  }

\&

\&  ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);

.Ve

.PP

Example: Call a callback every hour, starting now:

.PP

.Vb 4

\&  struct ev_periodic hourly_tick;

\&  ev_periodic_init (&hourly_tick, clock_cb,

\&                    fmod (ev_now (loop), 3600.), 3600., 0);

\&  ev_periodic_start (loop, &hourly_tick);

.Ve

.ie n .Sh """ev_signal"" \- signal me when a signal gets signalled!"

.el .Sh "\f(CWev_signal\fP \- signal me when a signal gets signalled!"

.IX Subsection "ev_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

will try it's best to deliver signals synchronously, i.e. as part of the