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+ <meta name="created" content="Sat Nov 24 08:13:46 2007" />
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<li><a href="#GLOBAL_FUNCTIONS">GLOBAL FUNCTIONS</a></li>
<li><a href="#FUNCTIONS_CONTROLLING_THE_EVENT_LOOP">FUNCTIONS CONTROLLING THE EVENT LOOP</a></li>
<li><a href="#ANATOMY_OF_A_WATCHER">ANATOMY OF A WATCHER</a>
-<ul><li><a href="#ASSOCIATING_CUSTOM_DATA_WITH_A_WATCH">ASSOCIATING CUSTOM DATA WITH A WATCHER</a></li>
+<ul><li><a href="#SUMMARY_OF_GENERIC_WATCHER_FUNCTIONS">SUMMARY OF GENERIC WATCHER FUNCTIONS</a></li>
+<li><a href="#ASSOCIATING_CUSTOM_DATA_WITH_A_WATCH">ASSOCIATING CUSTOM DATA WITH A WATCHER</a></li>
</ul>
</li>
<li><a href="#WATCHER_TYPES">WATCHER TYPES</a>
<li><a href="#code_ev_child_code_wait_for_pid_stat"><code>ev_child</code> - wait for pid status changes</a></li>
<li><a href="#code_ev_idle_code_when_you_ve_got_no"><code>ev_idle</code> - when you've got nothing better to do</a></li>
<li><a href="#code_ev_prepare_code_and_code_ev_che"><code>ev_prepare</code> and <code>ev_check</code> - customise your event loop</a></li>
+<li><a href="#code_ev_embed_code_when_one_backend_"><code>ev_embed</code> - when one backend isn't enough</a></li>
</ul>
</li>
<li><a href="#OTHER_FUNCTIONS">OTHER FUNCTIONS</a></li>
(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>
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 (("libev version mismatch",
+ ev_version_major () == EV_VERSION_MAJOR
+ && ev_version_minor () >= EV_VERSION_MINOR));
+
+</pre>
</dd>
<dt>unsigned int ev_supported_backends ()</dt>
<dd>
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 (("sorry, no epoll, no sex",
+ ev_supported_backends () & EVBACKEND_EPOLL));
+
+</pre>
</dd>
<dt>unsigned int ev_recommended_backends ()</dt>
<dd>
returned by <code>ev_supported_backends</code>, 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
-<code>EVFLAG_AUTO</code> will probe for.</p>
+libev will probe for if you specify no backends explicitly.</p>
+ </dd>
+ <dt>unsigned int ev_embeddable_backends ()</dt>
+ <dd>
+ <p>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
+<code>ev_embeddable_backends () & ev_supported_backends ()</code>, likewise for
+recommended ones.</p>
+ <p>See the description of <code>ev_embed</code> watchers for more info.</p>
</dd>
<dt>ev_set_allocator (void *(*cb)(void *ptr, long size))</dt>
<dd>
<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>
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>
<p>If you don't know what event loop to use, use the one returned from this
function.</p>
<p>The flags argument can be used to specify special behaviour or specific
-backends to use, and is usually specified as <code>0</code> (or EVFLAG_AUTO).</p>
- <p>It supports the following flags:</p>
+backends to use, and is usually specified as <code>0</code> (or <code>EVFLAG_AUTO</code>).</p>
+ <p>The following flags are supported:</p>
<p>
<dl>
<dt><code>EVFLAG_AUTO</code></dt>
(because the fd could point to a different file description now), so its
best to avoid that. Also, dup()ed file descriptors might not work very
well if you register events for both fds.</p>
+ <p>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.</p>
</dd>
<dt><code>EVBACKEND_KQUEUE</code> (value 8, most BSD clones)</dt>
<dd>
<p>Kqueue deserves special mention, as at the time of this writing, it
was broken on all BSDs except NetBSD (usually it doesn't work with
anything but sockets and pipes, except on Darwin, where of course its
-completely useless). For this reason its not being "autodetected" unless
-you explicitly specify the flags (i.e. you don't use EVFLAG_AUTO).</p>
+completely useless). For this reason its not being "autodetected"
+unless you explicitly specify it explicitly in the flags (i.e. using
+<code>EVBACKEND_KQUEUE</code>).</p>
<p>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 starting and stopping an I/O watcher does not cause an
<dd>
<p>This uses the Solaris 10 port mechanism. As with everything on Solaris,
it's really slow, but it still scales very well (O(active_fds)).</p>
+ <p>Please note that solaris ports can result in 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.</p>
</dd>
<dt><code>EVBACKEND_ALL</code></dt>
<dd>
backends will be tried (in the reverse order as given here). If none are
specified, most compiled-in backend will be tried, usually in reverse
order of their flag values :)</p>
+ <p>The most typical usage is like this:</p>
+<pre> if (!ev_default_loop (0))
+ fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
+
+</pre>
+ <p>Restrict libev to the select and poll backends, and do not allow
+environment settings to be taken into account:</p>
+<pre> ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
+
+</pre>
+ <p>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 OS supports your types of fds):</p>
+<pre> ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);
+
+</pre>
</dd>
<dt>struct ev_loop *ev_loop_new (unsigned int flags)</dt>
<dd>
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 ("no epoll found here, maybe it hides under your chair");
+
+</pre>
</dd>
<dt>ev_default_destroy ()</dt>
<dd>
<dt>ev_tstamp ev_now (loop)</dt>
<dd>
<p>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).</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>
<p>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.</p>
- <p>If the flags argument is specified as 0, it will not return until either
-no event watchers are active anymore or <code>ev_unloop</code> was called.</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>
<p>A flags value of <code>EVLOOP_ONESHOT</code> 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.</p>
- <p>This flags value could be used to implement alternative looping
-constructs, but the <code>prepare</code> and <code>check</code> watchers provide a better and
-more generic mechanism.</p>
- <p>Here are the gory details of what ev_loop does:</p>
-<pre> 1. If there are no active watchers (reference count is zero), return.
- 2. Queue and immediately call all prepare watchers.
- 3. If we have been forked, recreate the kernel state.
- 4. Update the kernel state with all outstanding changes.
- 5. Update the "event loop time".
- 6. Calculate for how long to block.
- 7. Block the process, waiting for events.
- 8. Update the "event loop time" and do time jump handling.
- 9. Queue all outstanding timers.
- 10. Queue all outstanding periodics.
- 11. If no events are pending now, queue all idle watchers.
- 12. Queue all check watchers.
- 13. Call all queued watchers in reverse order (i.e. check watchers first).
- 14. If ev_unloop has been called or EVLOOP_ONESHOT or EVLOOP_NONBLOCK
- was used, return, otherwise continue with step #1.
+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 <code>ev_prepare</code>/<code>ev_check</code> watchers is
+usually a better approach for this kind of thing.</p>
+ <p>Here are the gory details of what <code>ev_loop</code> does:</p>
+<pre> * If there are no active watchers (reference count is zero), return.
+ - Queue prepare watchers and then call all outstanding watchers.
+ - If we have been forked, recreate the kernel state.
+ - Update the kernel state with all outstanding changes.
+ - Update the "event loop time".
+ - Calculate for how long to block.
+ - 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, 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>
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 (&exitsig, sig_cb, SIGINT);
+ ev_signal_start (myloop, &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, &exitsig);
+
+</pre>
</dd>
</dl>
corresponding stop function (<code>ev_<type>_stop (loop, watcher *)</code>.</p>
<p>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 set macro.</p>
-<p>You can check whether an event is active by calling the <code>ev_is_active
-(watcher *)</code> macro. To see whether an event is outstanding (but the
-callback for it has not been called yet) you can use the <code>ev_is_pending
-(watcher *)</code> macro.</p>
+reinitialise it or call its <code>set</code> macro.</p>
<p>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.</p>
</dd>
</dl>
+</div>
+<h2 id="SUMMARY_OF_GENERIC_WATCHER_FUNCTIONS">SUMMARY OF GENERIC WATCHER FUNCTIONS</h2>
+<div id="SUMMARY_OF_GENERIC_WATCHER_FUNCTIONS-2">
+<p>In the following description, <code>TYPE</code> stands for the watcher type,
+e.g. <code>timer</code> for <code>ev_timer</code> watchers and <code>io</code> for <code>ev_io</code> watchers.</p>
+<dl>
+ <dt><code>ev_init</code> (ev_TYPE *watcher, callback)</dt>
+ <dd>
+ <p>This macro initialises the generic portion of a watcher. The contents
+of the watcher object can be arbitrary (so <code>malloc</code> will do). Only
+the generic parts of the watcher are initialised, you <i>need</i> to call
+the type-specific <code>ev_TYPE_set</code> macro afterwards to initialise the
+type-specific parts. For each type there is also a <code>ev_TYPE_init</code> macro
+which rolls both calls into one.</p>
+ <p>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.</p>
+ <p>The callbakc is always of type <code>void (*)(ev_loop *loop, ev_TYPE *watcher,
+int revents)</code>.</p>
+ </dd>
+ <dt><code>ev_TYPE_set</code> (ev_TYPE *, [args])</dt>
+ <dd>
+ <p>This macro initialises the type-specific parts of a watcher. You need to
+call <code>ev_init</code> at least once before you call this macro, but you can
+call <code>ev_TYPE_set</code> 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 <code>ev_init</code> macro).</p>
+ <p>Although some watcher types do not have type-specific arguments
+(e.g. <code>ev_prepare</code>) you still need to call its <code>set</code> macro.</p>
+ </dd>
+ <dt><code>ev_TYPE_init</code> (ev_TYPE *watcher, callback, [args])</dt>
+ <dd>
+ <p>This convinience macro rolls both <code>ev_init</code> and <code>ev_TYPE_set</code> macro
+calls into a single call. This is the most convinient method to initialise
+a watcher. The same limitations apply, of course.</p>
+ </dd>
+ <dt><code>ev_TYPE_start</code> (loop *, ev_TYPE *watcher)</dt>
+ <dd>
+ <p>Starts (activates) the given watcher. Only active watchers will receive
+events. If the watcher is already active nothing will happen.</p>
+ </dd>
+ <dt><code>ev_TYPE_stop</code> (loop *, ev_TYPE *watcher)</dt>
+ <dd>
+ <p>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
+<code>ev_TYPE_stop</code> 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 <code>ev_TYPE_stop</code> function.</p>
+ </dd>
+ <dt>bool ev_is_active (ev_TYPE *watcher)</dt>
+ <dd>
+ <p>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.</p>
+ </dd>
+ <dt>bool ev_is_pending (ev_TYPE *watcher)</dt>
+ <dd>
+ <p>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
+<code>ev_TYPE_set</code> is safe) and you must make sure the watcher is available to
+libev (e.g. you cnanot <code>free ()</code> it).</p>
+ </dd>
+ <dt>callback = ev_cb (ev_TYPE *watcher)</dt>
+ <dd>
+ <p>Returns the callback currently set on the watcher.</p>
+ </dd>
+ <dt>ev_cb_set (ev_TYPE *watcher, callback)</dt>
+ <dd>
+ <p>Change the callback. You can change the callback at virtually any time
+(modulo threads).</p>
+ </dd>
+</dl>
+
+
+
+
+
</div>
<h2 id="ASSOCIATING_CUSTOM_DATA_WITH_A_WATCH">ASSOCIATING CUSTOM DATA WITH A WATCHER</h2>
<div id="ASSOCIATING_CUSTOM_DATA_WITH_A_WATCH-2">
<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">
<p>Configures an <code>ev_io</code> watcher. The fd is the file descriptor to rceeive
events for and events is either <code>EV_READ</code>, <code>EV_WRITE</code> or <code>EV_READ |
EV_WRITE</code> to receive the given events.</p>
+ <p>Please note that most of the more scalable backend mechanisms (for example
+epoll and solaris ports) can result in spurious readyness notifications
+for file descriptors, so you practically need to use non-blocking I/O (and
+treat callback invocation as hint only), or retest separately with a safe
+interface before doing I/O (XLib can do this), or force the use of either
+<code>EVBACKEND_SELECT</code> or <code>EVBACKEND_POLL</code>, which don't suffer from this
+problem. Also note that it is quite easy to have your callback invoked
+when the readyness condition is no longer valid even when employing
+typical ways of handling events, so its a good idea to use non-blocking
+I/O unconditionally.</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->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);
+
+
+
+
+</pre>
</div>
<h2 id="code_ev_timer_code_relative_and_opti"><code>ev_timer</code> - relative and optionally recurring timeouts</h2>
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 (&mytimer, one_minute_cb, 60., 0.);
+ ev_timer_start (loop, &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 (&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);
+
+
+
+
+</pre>
</div>
<h2 id="code_ev_periodic_code_to_cron_or_not"><code>ev_periodic</code> - to cron or not to cron</h2>
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 (&hourly_tick, clock_cb, 0., 3600., 0);
+ ev_periodic_start (loop, &hourly_tick);
+
+</pre>
+<p>Example: the same as above, but use a reschedule callback to do it:</p>
+<pre> #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);
+
+</pre>
+<p>Example: call a callback every hour, starting now:</p>
+<pre> 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);
+
+
+
+
+</pre>
</div>
<h2 id="code_ev_signal_code_signal_me_when_a"><code>ev_signal</code> - signal me when a signal gets signalled</h2>
</dd>
</dl>
+
+
+
+
</div>
<h2 id="code_ev_child_code_wait_for_pid_stat"><code>ev_child</code> - wait for pid status changes</h2>
<div id="code_ev_child_code_wait_for_pid_stat-2">
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 (&signal_watcher, sigint_cb, SIGINT);
+ ev_signal_start (loop, &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>
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>
<p>Prepare and check watchers are usually (but not always) used in tandem:
prepare watchers get invoked before the process blocks and check watchers
afterwards.</p>
-<p>Their main purpose is to integrate other event mechanisms into libev. This
-could be used, for example, to track variable changes, implement your own
-watchers, integrate net-snmp or a coroutine library and lots more.</p>
+<p>Their main purpose is to integrate other event mechanisms into libev and
+their use is somewhat advanced. This could be used, for example, to track
+variable changes, implement your own watchers, integrate net-snmp or a
+coroutine library and lots more.</p>
<p>This is done by examining in each prepare call which file descriptors need
to be watched by the other library, registering <code>ev_io</code> watchers for
them and starting an <code>ev_timer</code> watcher for any timeouts (many libraries
macros, but using them is utterly, utterly and completely pointless.</p>
</dd>
</dl>
+<p>Example: *TODO*.</p>
+
+
+
+
+
+</div>
+<h2 id="code_ev_embed_code_when_one_backend_"><code>ev_embed</code> - when one backend isn't enough</h2>
+<div id="code_ev_embed_code_when_one_backend_-2">
+<p>This is a rather advanced watcher type that lets you embed one event loop
+into another (currently only <code>ev_io</code> events are supported in the embedded
+loop, other types of watchers might be handled in a delayed or incorrect
+fashion and must not be used).</p>
+<p>There are primarily two reasons you would want that: work around bugs and
+prioritise I/O.</p>
+<p>As an example for a bug workaround, the kqueue backend might only support
+sockets on some platform, so it is unusable as generic backend, but you
+still want to make use of it because you have many sockets and it scales
+so nicely. In this case, you would create a kqueue-based loop and embed it
+into your default loop (which might use e.g. poll). Overall operation will
+be a bit slower because first libev has to poll and then call kevent, but
+at least you can use both at what they are best.</p>
+<p>As for prioritising I/O: rarely you have the case where some fds have
+to be watched and handled very quickly (with low latency), and even
+priorities and idle watchers might have too much overhead. In this case
+you would put all the high priority stuff in one loop and all the rest in
+a second one, and embed the second one in the first.</p>
+<p>As long as the watcher is active, the callback will be invoked every time
+there might be events pending in the embedded loop. The callback must then
+call <code>ev_embed_sweep (mainloop, watcher)</code> to make a single sweep and invoke
+their callbacks (you could also start an idle watcher to give the embedded
+loop strictly lower priority for example). You can also set the callback
+to <code>0</code>, in which case the embed watcher will automatically execute the
+embedded loop sweep.</p>
+<p>As long as the watcher is started it will automatically handle events. The
+callback will be invoked whenever some events have been handled. You can
+set the callback to <code>0</code> to avoid having to specify one if you are not
+interested in that.</p>
+<p>Also, there have not currently been made special provisions for forking:
+when you fork, you not only have to call <code>ev_loop_fork</code> on both loops,
+but you will also have to stop and restart any <code>ev_embed</code> watchers
+yourself.</p>
+<p>Unfortunately, not all backends are embeddable, only the ones returned by
+<code>ev_embeddable_backends</code> are, which, unfortunately, does not include any
+portable one.</p>
+<p>So when you want to use this feature you will always have to be prepared
+that you cannot get an embeddable loop. The recommended way to get around
+this is to have a separate variables for your embeddable loop, try to
+create it, and if that fails, use the normal loop for everything:</p>
+<pre> struct ev_loop *loop_hi = ev_default_init (0);
+ struct ev_loop *loop_lo = 0;
+ struct ev_embed embed;
+
+ // see if there is a chance of getting one that works
+ // (remember that a flags value of 0 means autodetection)
+ loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
+ ? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
+ : 0;
+
+ // if we got one, then embed it, otherwise default to loop_hi
+ if (loop_lo)
+ {
+ ev_embed_init (&embed, 0, loop_lo);
+ ev_embed_start (loop_hi, &embed);
+ }
+ else
+ loop_lo = loop_hi;
+
+</pre>
+<dl>
+ <dt>ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)</dt>
+ <dt>ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)</dt>
+ <dd>
+ <p>Configures the watcher to embed the given loop, which must be
+embeddable. If the callback is <code>0</code>, then <code>ev_embed_sweep</code> will be
+invoked automatically, otherwise it is the responsibility of the callback
+to invoke it (it will continue to be called until the sweep has been done,
+if you do not want thta, you need to temporarily stop the embed watcher).</p>
+ </dd>
+ <dt>ev_embed_sweep (loop, ev_embed *)</dt>
+ <dd>
+ <p>Make a single, non-blocking sweep over the embedded loop. This works
+similarly to <code>ev_loop (embedded_loop, EVLOOP_NONBLOCK)</code>, but in the most
+apropriate way for embedded loops.</p>
+ </dd>
+</dl>
+
+
+
+
</div>
<h1 id="OTHER_FUNCTIONS">OTHER FUNCTIONS</h1><p><a href="#TOP" class="toplink">Top</a></p>
</pre>
</dd>
- <dt>ev_feed_event (loop, watcher, int events)</dt>
+ <dt>ev_feed_event (ev_loop *, watcher *, int revents)</dt>
<dd>
<p>Feeds the given event set into the event loop, as if the specified event
had happened for the specified watcher (which must be a pointer to an
initialised but not necessarily started event watcher).</p>
</dd>
- <dt>ev_feed_fd_event (loop, int fd, int revents)</dt>
+ <dt>ev_feed_fd_event (ev_loop *, int fd, int revents)</dt>
<dd>
<p>Feed an event on the given fd, as if a file descriptor backend detected
the given events it.</p>
</dd>
- <dt>ev_feed_signal_event (loop, int signum)</dt>
+ <dt>ev_feed_signal_event (ev_loop *loop, int signum)</dt>
<dd>
- <p>Feed an event as if the given signal occured (loop must be the default loop!).</p>
+ <p>Feed an event as if the given signal occured (<code>loop</code> must be the default
+loop!).</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">
projects / software / libev.git / blobdiff