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add lots of theoretical examples

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Marc Alexander Lehmann 14 years ago
parent
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0162f178a9
  1. 257
      ev.3
  2. 230
      ev.html
  3. 208
      ev.pod

257
ev.3

@ -175,7 +175,8 @@ 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 double type in C.
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 such.
.SH "GLOBAL FUNCTIONS"
.IX Header "GLOBAL FUNCTIONS"
These functions can be called anytime, even before initialising the
@ -201,12 +202,29 @@ 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
@ -226,6 +244,34 @@ 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.
.Sp
Example: replace the libev allocator with one that waits a bit and then
retries: better than mine).
.Sp
.Vb 6
\& static void *
\& persistent_realloc (void *ptr, long size)
\& {
\& for (;;)
\& {
\& void *newptr = realloc (ptr, size);
.Ve
.Sp
.Vb 2
\& if (newptr)
\& return newptr;
.Ve
.Sp
.Vb 3
\& sleep (60);
\& }
\& }
.Ve
.Sp
.Vb 2
\& ...
\& 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
@ -235,6 +281,22 @@ 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: do the same thing as libev does internally:
.Sp
.Vb 6
\& static void
\& fatal_error (const char *msg)
\& {
\& perror (msg);
\& abort ();
\& }
.Ve
.Sp
.Vb 2
\& ...
\& 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
@ -378,6 +440,14 @@ Similar to \f(CW\*(C`ev_default_loop\*(C'\fR, but always creates a new event loo
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
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
@ -421,10 +491,10 @@ 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
got 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
occuring (or more correctly, the mainloop finding out about it).
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 occuring (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
@ -434,6 +504,12 @@ events.
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.
@ -468,6 +544,16 @@ Here are the gory details of what \f(CW\*(C`ev_loop\*(C'\fR does:
\& - If ev_unloop has been called or EVLOOP_ONESHOT or EVLOOP_NONBLOCK
\& were used, return, otherwise continue with step *.
.Ve
.Sp
Example: queue some jobs and then loop until no events are outsanding
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
@ -490,6 +576,23 @@ visible to the libev user and should not keep \f(CW\*(C`ev_loop\*(C'\fR from exi
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.
.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 dv_signal exitsig;
\& ev_signal_init (&exitsig, sig_cb, SIGINT);
\& ev_signal_start (myloop, &exitsig);
\& evf_unref (myloop);
.Ve
.Sp
Example: for some weird reason, unregister the above signal handler again.
.Sp
.Vb 2
\& ev_ref (myloop);
\& ev_signal_stop (myloop, &exitsig);
.Ve
.SH "ANATOMY OF A WATCHER"
.IX Header "ANATOMY OF A WATCHER"
A watcher is a structure that you create and register to record your
@ -687,6 +790,28 @@ 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.
.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
\& }
.Ve
.PP
.Vb 6
\& ...
\& 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 recurring timeouts"
.el .Sh "\f(CWev_timer\fP \- relative and optionally recurring timeouts"
.IX Subsection "ev_timer - relative and optionally recurring timeouts"
@ -746,6 +871,46 @@ configure an \f(CW\*(C`ev_timer\*(C'\fR with after=repeat=60 and calling ev_time
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.
.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
\& }
.Ve
.PP
.Vb 3
\& 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
\& }
.Ve
.PP
.Vb 4
\& 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);
.Ve
.PP
.Vb 3
\& // 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"
@ -847,6 +1012,51 @@ 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).
.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)
\& }
.Ve
.PP
.Vb 3
\& 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>
.Ve
.PP
.Vb 5
\& static ev_tstamp
\& my_scheduler_cb (struct ev_periodic *w, ev_tstamp now)
\& {
\& return fmod (now, 3600.) + 3600.;
\& }
.Ve
.PP
.Vb 1
\& 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"
@ -886,6 +1096,22 @@ at the \f(CW\*(C`rstatus\*(C'\fR member of the \f(CW\*(C`ev_child\*(C'\fR watche
the status word (use the macros from \f(CW\*(C`sys/wait.h\*(C'\fR and see your systems
\&\f(CW\*(C`waitpid\*(C'\fR documentation). The \f(CW\*(C`rpid\*(C'\fR member contains the pid of the
process causing the status change.
.PP
Example: try to exit cleanly on \s-1SIGINT\s0 and \s-1SIGTERM\s0.
.PP
.Vb 5
\& static void
\& sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents)
\& {
\& ev_unloop (loop, EVUNLOOP_ALL);
\& }
.Ve
.PP
.Vb 3
\& struct ev_signal signal_watcher;
\& ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
\& ev_signal_start (loop, &sigint_cb);
.Ve
.ie n .Sh """ev_idle"" \- when you've got nothing better to do"
.el .Sh "\f(CWev_idle\fP \- when you've got nothing better to do"
.IX Subsection "ev_idle - when you've got nothing better to do"
@ -909,6 +1135,25 @@ event loop has handled all outstanding events.
Initialises and configures the idle watcher \- it has no parameters of any
kind. There is a \f(CW\*(C`ev_idle_set\*(C'\fR macro, but using it is utterly pointless,
believe me.
.PP
Example: dynamically allocate an \f(CW\*(C`ev_idle\*(C'\fR, start it, and in the
callback, free it. Alos, use no error checking, as usual.
.PP
.Vb 7
\& static void
\& idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents)
\& {
\& free (w);
\& // now do something you wanted to do when the program has
\& // no longer asnything immediate to do.
\& }
.Ve
.PP
.Vb 3
\& struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle));
\& ev_idle_init (idle_watcher, idle_cb);
\& ev_idle_start (loop, idle_cb);
.Ve
.ie n .Sh """ev_prepare""\fP and \f(CW""ev_check"" \- customise your event loop"
.el .Sh "\f(CWev_prepare\fP and \f(CWev_check\fP \- customise your event loop"
.IX Subsection "ev_prepare and ev_check - customise your event loop"
@ -946,6 +1191,8 @@ low-priority coroutines to idle/background tasks).
Initialises and configures the prepare or check watcher \- they have no
parameters of any kind. There are \f(CW\*(C`ev_prepare_set\*(C'\fR and \f(CW\*(C`ev_check_set\*(C'\fR
macros, but using them is utterly, utterly and completely pointless.
.PP
Example: *TODO*.
.SH "OTHER FUNCTIONS"
.IX Header "OTHER FUNCTIONS"
There are some other functions of possible interest. Described. Here. Now.

230
ev.html

@ -6,7 +6,7 @@
<meta name="description" content="Pod documentation for libev" />
<meta name="inputfile" content="&lt;standard input&gt;" />
<meta name="outputfile" content="&lt;standard output&gt;" />
<meta name="created" content="Fri Nov 23 16:26:06 2007" />
<meta name="created" content="Fri Nov 23 17:17:04 2007" />
<meta name="generator" content="Pod::Xhtml 1.57" />
<link rel="stylesheet" href="http://res.tst.eu/pod.css"/></head>
<body>
@ -98,7 +98,12 @@ will not have this argument.</p>
(fractional) number of seconds since the (POSIX) epoch (somewhere near
the beginning of 1970, details are complicated, don't ask). This type is
called <code>ev_tstamp</code>, which is what you should use too. It usually aliases
to the double type in C.</p>
to the <code>double</code> type in C, and when you need to do any calculations on
it, you should treat it as such.</p>
</div>
<h1 id="GLOBAL_FUNCTIONS">GLOBAL FUNCTIONS</h1><p><a href="#TOP" class="toplink">Top</a></p>
@ -124,6 +129,13 @@ version of the library your program was compiled against.</p>
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.</p>
<p>Example: make sure we haven't accidentally been linked against the wrong
version:</p>
<pre> assert ((&quot;libev version mismatch&quot;,
ev_version_major () == EV_VERSION_MAJOR
&amp;&amp; ev_version_minor () &gt;= EV_VERSION_MINOR));
</pre>
</dd>
<dt>unsigned int ev_supported_backends ()</dt>
<dd>
@ -131,6 +143,12 @@ not a problem.</p>
value) compiled into this binary of libev (independent of their
availability on the system you are running on). See <code>ev_default_loop</code> for
a description of the set values.</p>
<p>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</p>
<pre> assert ((&quot;sorry, no epoll, no sex&quot;,
ev_supported_backends () &amp; EVBACKEND_EPOLL));
</pre>
</dd>
<dt>unsigned int ev_recommended_backends ()</dt>
<dd>
@ -151,6 +169,26 @@ destructive action. The default is your system realloc function.</p>
<p>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.</p>
<p>Example: replace the libev allocator with one that waits a bit and then
retries: better than mine).</p>
<pre> static void *
persistent_realloc (void *ptr, long size)
{
for (;;)
{
void *newptr = realloc (ptr, size);
if (newptr)
return newptr;
sleep (60);
}
}
...
ev_set_allocator (persistent_realloc);
</pre>
</dd>
<dt>ev_set_syserr_cb (void (*cb)(const char *msg));</dt>
<dd>
@ -161,6 +199,18 @@ 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).</p>
<p>Example: do the same thing as libev does internally:</p>
<pre> static void
fatal_error (const char *msg)
{
perror (msg);
abort ();
}
...
ev_set_syserr_cb (fatal_error);
</pre>
</dd>
</dl>
@ -295,6 +345,12 @@ event loop and only if you know the OS supports your types of fds):</p>
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).</p>
<p>Example: try to create a event loop that uses epoll and nothing else.</p>
<pre> struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
if (!epoller)
fatal (&quot;no epoll found here, maybe it hides under your chair&quot;);
</pre>
</dd>
<dt>ev_default_destroy ()</dt>
<dd>
@ -340,10 +396,10 @@ use.</p>
<dt>ev_tstamp ev_now (loop)</dt>
<dd>
<p>Returns the current &quot;event loop time&quot;, which is the time the event loop
got 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
occuring (or more correctly, the mainloop finding out about it).</p>
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 occuring (or more correctly, libev finding out about it).</p>
</dd>
<dt>ev_loop (loop, int flags)</dt>
<dd>
@ -352,6 +408,11 @@ after you initialised all your watchers and you want to start handling
events.</p>
<p>If the flags argument is specified as <code>0</code>, it will not return until
either no event watchers are active anymore or <code>ev_unloop</code> was called.</p>
<p>Please note that an explicit <code>ev_unloop</code> 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.</p>
<p>A flags value of <code>EVLOOP_NONBLOCK</code> 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.</p>
@ -382,6 +443,14 @@ usually a better approach for this kind of thing.</p>
- If ev_unloop has been called or EVLOOP_ONESHOT or EVLOOP_NONBLOCK
were used, return, otherwise continue with step *.
</pre>
<p>Example: queue some jobs and then loop until no events are outsanding
anymore.</p>
<pre> ... 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!
</pre>
</dd>
<dt>ev_unloop (loop, how)</dt>
@ -404,6 +473,19 @@ visible to the libev user and should not keep <code>ev_loop</code> from 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 <i>unref after start</i> and <i>ref before stop</i>.</p>
<p>Example: create a signal watcher, but keep it from keeping <code>ev_loop</code>
running when nothing else is active.</p>
<pre> struct dv_signal exitsig;
ev_signal_init (&amp;exitsig, sig_cb, SIGINT);
ev_signal_start (myloop, &amp;exitsig);
evf_unref (myloop);
</pre>
<p>Example: for some weird reason, unregister the above signal handler again.</p>
<pre> ev_ref (myloop);
ev_signal_stop (myloop, &amp;exitsig);
</pre>
</dd>
</dl>
@ -549,6 +631,10 @@ have been omitted....</p>
<p>This section describes each watcher in detail, but will not repeat
information given in the last section.</p>
</div>
<h2 id="code_ev_io_code_is_this_file_descrip"><code>ev_io</code> - is this file descriptor readable or writable</h2>
<div id="code_ev_io_code_is_this_file_descrip-2">
@ -588,6 +674,27 @@ typical ways of handling events, so its a good idea to use non-blocking
I/O unconditionally.</p>
</dd>
</dl>
<p>Example: call <code>stdin_readable_cb</code> 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:</p>
<pre> 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-&gt;fd) and haqndle any I/O errors
}
...
struct ev_loop *loop = ev_default_init (0);
struct ev_io stdin_readable;
ev_io_init (&amp;stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
ev_io_start (loop, &amp;stdin_readable);
ev_loop (loop, 0);
</pre>
</div>
<h2 id="code_ev_timer_code_relative_and_opti"><code>ev_timer</code> - relative and optionally recurring timeouts</h2>
@ -641,6 +748,39 @@ 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.</p>
</dd>
</dl>
<p>Example: create a timer that fires after 60 seconds.</p>
<pre> 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 (&amp;mytimer, one_minute_cb, 60., 0.);
ev_timer_start (loop, &amp;mytimer);
</pre>
<p>Example: create a timeout timer that times out after 10 seconds of
inactivity.</p>
<pre> 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 (&amp;mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
ev_timer_again (&amp;mytimer); /* start timer */
ev_loop (loop, 0);
// and in some piece of code that gets executed on any &quot;activity&quot;:
// reset the timeout to start ticking again at 10 seconds
ev_timer_again (&amp;mytimer);
</pre>
</div>
<h2 id="code_ev_periodic_code_to_cron_or_not"><code>ev_periodic</code> - to cron or not to cron</h2>
@ -734,6 +874,42 @@ a different time than the last time it was called (e.g. in a crond like
program when the crontabs have changed).</p>
</dd>
</dl>
<p>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.</p>
<pre> 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 (&amp;hourly_tick, clock_cb, 0., 3600., 0);
ev_periodic_start (loop, &amp;hourly_tick);
</pre>
<p>Example: the same as above, but use a reschedule callback to do it:</p>
<pre> #include &lt;math.h&gt;
static ev_tstamp
my_scheduler_cb (struct ev_periodic *w, ev_tstamp now)
{
return fmod (now, 3600.) + 3600.;
}
ev_periodic_init (&amp;hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
</pre>
<p>Example: call a callback every hour, starting now:</p>
<pre> struct ev_periodic hourly_tick;
ev_periodic_init (&amp;hourly_tick, clock_cb,
fmod (ev_now (loop), 3600.), 3600., 0);
ev_periodic_start (loop, &amp;hourly_tick);
</pre>
</div>
<h2 id="code_ev_signal_code_signal_me_when_a"><code>ev_signal</code> - signal me when a signal gets signalled</h2>
@ -774,6 +950,21 @@ the status word (use the macros from <code>sys/wait.h</code> and see your system
process causing the status change.</p>
</dd>
</dl>
<p>Example: try to exit cleanly on SIGINT and SIGTERM.</p>
<pre> static void
sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents)
{
ev_unloop (loop, EVUNLOOP_ALL);
}
struct ev_signal signal_watcher;
ev_signal_init (&amp;signal_watcher, sigint_cb, SIGINT);
ev_signal_start (loop, &amp;sigint_cb);
</pre>
</div>
<h2 id="code_ev_idle_code_when_you_ve_got_no"><code>ev_idle</code> - when you've got nothing better to do</h2>
@ -799,6 +990,24 @@ kind. There is a <code>ev_idle_set</code> macro, but using it is utterly pointle
believe me.</p>
</dd>
</dl>
<p>Example: dynamically allocate an <code>ev_idle</code>, start it, and in the
callback, free it. Alos, use no error checking, as usual.</p>
<pre> static void
idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents)
{
free (w);
// now do something you wanted to do when the program has
// no longer asnything immediate to do.
}
struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle));
ev_idle_init (idle_watcher, idle_cb);
ev_idle_start (loop, idle_cb);
</pre>
</div>
<h2 id="code_ev_prepare_code_and_code_ev_che"><code>ev_prepare</code> and <code>ev_check</code> - customise your event loop</h2>
@ -834,6 +1043,11 @@ parameters of any kind. There are <code>ev_prepare_set</code> and <code>ev_check
macros, but using them is utterly, utterly and completely pointless.</p>
</dd>
</dl>
<p>Example: *TODO*.</p>
</div>
<h1 id="OTHER_FUNCTIONS">OTHER FUNCTIONS</h1><p><a href="#TOP" class="toplink">Top</a></p>
@ -887,6 +1101,10 @@ the given events it.</p>
</dd>
</dl>
</div>
<h1 id="LIBEVENT_EMULATION">LIBEVENT EMULATION</h1><p><a href="#TOP" class="toplink">Top</a></p>
<div id="LIBEVENT_EMULATION_CONTENT">

208
ev.pod

@ -47,7 +47,9 @@ Libev represents time as a single floating point number, representing the
(fractional) number of seconds since the (POSIX) epoch (somewhere near
the beginning of 1970, details are complicated, don't ask). This type is
called C<ev_tstamp>, which is what you should use too. It usually aliases
to the double type in C.
to the C<double> type in C, and when you need to do any calculations on
it, you should treat it as such.
=head1 GLOBAL FUNCTIONS
@ -77,6 +79,13 @@ 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:
assert (("libev version mismatch",
ev_version_major () == EV_VERSION_MAJOR
&& ev_version_minor () >= EV_VERSION_MINOR));
=item unsigned int ev_supported_backends ()
Return the set of all backends (i.e. their corresponding C<EV_BACKEND_*>
@ -84,6 +93,12 @@ value) compiled into this binary of libev (independent of their
availability on the system you are running on). See C<ev_default_loop> for
a description of the set values.
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
assert (("sorry, no epoll, no sex",
ev_supported_backends () & EVBACKEND_EPOLL));
=item unsigned int ev_recommended_backends ()
Return the set of all backends compiled into this binary of libev and also
@ -105,6 +120,26 @@ 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).
static void *
persistent_realloc (void *ptr, long size)
{
for (;;)
{
void *newptr = realloc (ptr, size);
if (newptr)
return newptr;
sleep (60);
}
}
...
ev_set_allocator (persistent_realloc);
=item ev_set_syserr_cb (void (*cb)(const char *msg));
Set the callback function to call on a retryable syscall error (such
@ -115,6 +150,18 @@ 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:
static void
fatal_error (const char *msg)
{
perror (msg);
abort ();
}
...
ev_set_syserr_cb (fatal_error);
=back
=head1 FUNCTIONS CONTROLLING THE EVENT LOOP
@ -259,6 +306,12 @@ 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).
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");
=item ev_default_destroy ()
Destroys the default loop again (frees all memory and kernel state
@ -305,10 +358,10 @@ use.
=item ev_tstamp ev_now (loop)
Returns the current "event loop time", which is the time the event loop
got 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
occuring (or more correctly, the mainloop finding out about it).
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 occuring (or more correctly, libev finding out about it).
=item ev_loop (loop, int flags)
@ -319,6 +372,12 @@ events.
If the flags argument is specified as C<0>, it will not return until
either no event watchers are active anymore or C<ev_unloop> was called.
Please note that an explicit C<ev_unloop> 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.
A flags value of C<EVLOOP_NONBLOCK> 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.
@ -352,6 +411,14 @@ Here are the gory details of what C<ev_loop> does:
- If ev_unloop has been called or EVLOOP_ONESHOT or EVLOOP_NONBLOCK
were used, return, otherwise continue with step *.
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..)
ev_loop (my_loop, 0);
... jobs done. yeah!
=item ev_unloop (loop, how)
Can be used to make a call to C<ev_loop> return early (but only after it
@ -374,6 +441,19 @@ 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 I<unref after start> and I<ref before stop>.
Example: create a signal watcher, but keep it from keeping C<ev_loop>
running when nothing else is active.
struct dv_signal exitsig;
ev_signal_init (&exitsig, sig_cb, SIGINT);
ev_signal_start (myloop, &exitsig);
evf_unref (myloop);
Example: for some weird reason, unregister the above signal handler again.
ev_ref (myloop);
ev_signal_stop (myloop, &exitsig);
=back
=head1 ANATOMY OF A WATCHER
@ -524,6 +604,7 @@ have been omitted....
This section describes each watcher in detail, but will not repeat
information given in the last section.
=head2 C<ev_io> - is this file descriptor readable or writable
I/O watchers check whether a file descriptor is readable or writable
@ -570,6 +651,25 @@ I/O unconditionally.
=back
Example: call C<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)
{
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);
=head2 C<ev_timer> - relative and optionally recurring timeouts
Timer watchers are simple relative timers that generate an event after a
@ -631,6 +731,37 @@ the timer, and again will automatically restart it if need be.
=back
Example: create a timer that fires after 60 seconds.
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);
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)
{
.. 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);
=head2 C<ev_periodic> - to cron or not to cron
Periodic watchers are also timers of a kind, but they are very versatile
@ -735,6 +866,40 @@ program when the crontabs have changed).
=back
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
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);
Example: the same as above, but use a reschedule callback to do it:
#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);
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);
ev_periodic_start (loop, &hourly_tick);
=head2 C<ev_signal> - signal me when a signal gets signalled
Signal watchers will trigger an event when the process receives a specific
@ -780,6 +945,19 @@ process causing the status change.
=back
Example: try to exit cleanly on SIGINT and SIGTERM.
static void
sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents)
{
ev_unloop (loop, EVUNLOOP_ALL);
}
struct ev_signal signal_watcher;
ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
ev_signal_start (loop, &sigint_cb);
=head2 C<ev_idle> - when you've got nothing better to do
Idle watchers trigger events when there are no other events are pending
@ -808,6 +986,22 @@ believe me.
=back
Example: dynamically allocate an C<ev_idle>, start it, and in the
callback, free it. Alos, use no error checking, as usual.
static void
idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents)
{
free (w);
// now do something you wanted to do when the program has
// no longer asnything immediate to do.
}
struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle));
ev_idle_init (idle_watcher, idle_cb);
ev_idle_start (loop, idle_cb);
=head2 C<ev_prepare> and C<ev_check> - customise your event loop
Prepare and check watchers are usually (but not always) used in tandem:
@ -848,6 +1042,9 @@ macros, but using them is utterly, utterly and completely pointless.
=back
Example: *TODO*.
=head1 OTHER FUNCTIONS
There are some other functions of possible interest. Described. Here. Now.
@ -903,6 +1100,7 @@ Feed an event as if the given signal occured (loop must be the default loop!).
=back
=head1 LIBEVENT EMULATION
Libev offers a compatibility emulation layer for libevent. It cannot

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