<meta name="description" content="Pod documentation for libev" />
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<meta name="outputfile" content="<standard output>" />
- <meta name="created" content="Sat Nov 24 11:19:13 2007" />
+ <meta name="created" content="Mon Nov 26 11:20:35 2007" />
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<body>
<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="#SUMMARY_OF_GENERIC_WATCHER_FUNCTIONS">SUMMARY OF GENERIC WATCHER FUNCTIONS</a></li>
+<ul><li><a href="#GENERIC_WATCHER_FUNCTIONS">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>
-<ul><li><a href="#code_ev_io_code_is_this_file_descrip"><code>ev_io</code> - is this file descriptor readable or writable</a></li>
-<li><a href="#code_ev_timer_code_relative_and_opti"><code>ev_timer</code> - relative and optionally recurring timeouts</a></li>
-<li><a href="#code_ev_periodic_code_to_cron_or_not"><code>ev_periodic</code> - to cron or not to cron</a></li>
-<li><a href="#code_ev_signal_code_signal_me_when_a"><code>ev_signal</code> - signal me when a signal gets signalled</a></li>
-<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><a href="#code_ev_io_code_is_this_file_descrip"><code>ev_io</code> - is this file descriptor readable or writable?</a></li>
+<li><a href="#code_ev_timer_code_relative_and_opti"><code>ev_timer</code> - relative and optionally repeating timeouts</a></li>
+<li><a href="#code_ev_periodic_code_to_cron_or_not"><code>ev_periodic</code> - to cron or not to cron?</a></li>
+<li><a href="#code_ev_signal_code_signal_me_when_a"><code>ev_signal</code> - signal me when a signal gets signalled!</a></li>
+<li><a href="#code_ev_child_code_watch_out_for_pro"><code>ev_child</code> - watch out for process 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>
<li><a href="#EXAMPLES">EXAMPLES</a></li>
</ul>
</li>
+<li><a href="#COMPLEXITIES">COMPLEXITIES</a></li>
<li><a href="#AUTHOR">AUTHOR</a>
</li>
</ul><hr />
</dd>
</dl>
+
+
+
+
</div>
<h1 id="ANATOMY_OF_A_WATCHER">ANATOMY OF A WATCHER</h1><p><a href="#TOP" class="toplink">Top</a></p>
<div id="ANATOMY_OF_A_WATCHER_CONTENT">
</dl>
</div>
-<h2 id="SUMMARY_OF_GENERIC_WATCHER_FUNCTIONS">SUMMARY OF GENERIC WATCHER FUNCTIONS</h2>
-<div id="SUMMARY_OF_GENERIC_WATCHER_FUNCTIONS-2">
+<h2 id="GENERIC_WATCHER_FUNCTIONS">GENERIC WATCHER FUNCTIONS</h2>
+<div id="GENERIC_WATCHER_FUNCTIONS_CONTENT">
<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>
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,
+ <p>The callback 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>
</div>
-<h2 id="code_ev_io_code_is_this_file_descrip"><code>ev_io</code> - is this file descriptor readable or writable</h2>
+<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>I/O watchers check whether a file descriptor is readable or writable
-in each iteration of the event loop (This behaviour is called
-level-triggering because you keep receiving events as long as the
-condition persists. Remember you can stop the watcher if you don't want to
-act on the event and neither want to receive future events).</p>
+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.</p>
<p>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
<p>You have to be careful with dup'ed file descriptors, though. Some backends
(the linux epoll backend is a notable example) cannot handle dup'ed file
descriptors correctly if you register interest in two or more fds pointing
-to the same underlying file/socket etc. description (that is, they share
+to the same underlying file/socket/etc. description (that is, they share
the same underlying "file open").</p>
<p>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 <code>EVBACKEND_SELECT</code> and
<code>EVBACKEND_POLL</code>).</p>
+<p>Another thing you have to watch out for is that it is quite easy to
+receive "spurious" readyness notifications, that is your callback might
+be called with <code>EV_READ</code> but a subsequent <code>read</code>(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 <code>read</code>(2) returning
+<code>EAGAIN</code> is far preferable to a program hanging until some data arrives.</p>
+<p>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
+wether 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).</p>
<dl>
<dt>ev_io_init (ev_io *, callback, int fd, int events)</dt>
<dt>ev_io_set (ev_io *, int fd, int events)</dt>
<dd>
- <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>
+ <p>Configures an <code>ev_io</code> watcher. The <code>fd</code> 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>
</dd>
</dl>
<p>Example: call <code>stdin_readable_cb</code> when STDIN_FILENO has become, well
</pre>
</div>
-<h2 id="code_ev_timer_code_relative_and_opti"><code>ev_timer</code> - relative and optionally recurring timeouts</h2>
+<h2 id="code_ev_timer_code_relative_and_opti"><code>ev_timer</code> - relative and optionally repeating timeouts</h2>
<div id="code_ev_timer_code_relative_and_opti-2">
<p>Timer watchers are simple relative timers that generate an event after a
given time, and optionally repeating in regular intervals after that.</p>
</pre>
</div>
-<h2 id="code_ev_periodic_code_to_cron_or_not"><code>ev_periodic</code> - to cron or not to cron</h2>
+<h2 id="code_ev_periodic_code_to_cron_or_not"><code>ev_periodic</code> - to cron or not to cron?</h2>
<div id="code_ev_periodic_code_to_cron_or_not-2">
<p>Periodic watchers are also timers of a kind, but they are very versatile
(and unfortunately a bit complex).</p>
</pre>
</div>
-<h2 id="code_ev_signal_code_signal_me_when_a"><code>ev_signal</code> - signal me when a signal gets signalled</h2>
+<h2 id="code_ev_signal_code_signal_me_when_a"><code>ev_signal</code> - signal me when a signal gets signalled!</h2>
<div id="code_ev_signal_code_signal_me_when_a-2">
<p>Signal watchers will trigger an event when the process receives a specific
signal one or more times. Even though signals are very asynchronous, libev
</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">
+<h2 id="code_ev_child_code_watch_out_for_pro"><code>ev_child</code> - watch out for process status changes</h2>
+<div id="code_ev_child_code_watch_out_for_pro-2">
<p>Child watchers trigger when your process receives a SIGCHLD in response to
some child status changes (most typically when a child of yours dies).</p>
<dl>
</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>
+<h2 id="code_ev_idle_code_when_you_ve_got_no"><code>ev_idle</code> - when you've got nothing better to do...</h2>
<div id="code_ev_idle_code_when_you_ve_got_no-2">
<p>Idle watchers trigger events when there are no other events are pending
(prepare, check and other idle watchers do not count). That is, as long
</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>
+<h2 id="code_ev_prepare_code_and_code_ev_che"><code>ev_prepare</code> and <code>ev_check</code> - customise your event loop!</h2>
<div id="code_ev_prepare_code_and_code_ev_che-2">
<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>You <i>must not</i> call <code>ev_loop</code> or similar functions that enter
+the current event loop from either <code>ev_prepare</code> or <code>ev_check</code>
+watchers. Other loops than the current one are fine, however. The
+rationale behind this is that you do not need to check for recursion in
+those watchers, i.e. the sequence will always be <code>ev_prepare</code>, blocking,
+<code>ev_check</code> so if you have one watcher of each kind they will always be
+called in pairs bracketing the blocking call.</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>
+coroutine library and lots more. They are also occasionally useful if
+you cache some data and want to flush it before blocking (for example,
+in X programs you might want to do an <code>XFlush ()</code> in an <code>ev_prepare</code>
+watcher).</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>
+<p>Example: To include a library such as adns, you would add IO watchers
+and a timeout watcher in a prepare handler, as required by libadns, and
+in a check watcher, destroy them and call into libadns. What follows is
+pseudo-code only of course:</p>
+<pre> static ev_io iow [nfd];
+ static ev_timer tw;
+
+ static void
+ io_cb (ev_loop *loop, ev_io *w, int revents)
+ {
+ // set the relevant poll flags
+ // could also call adns_processreadable etc. here
+ struct pollfd *fd = (struct pollfd *)w->data;
+ if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;
+ if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;
+ }
+
+ // create io watchers for each fd and a timer before blocking
+ static void
+ adns_prepare_cb (ev_loop *loop, ev_prepare *w, int revents)
+ {
+ int timeout = 3600000;truct pollfd fds [nfd];
+ // actual code will need to loop here and realloc etc.
+ adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
+
+ /* the callback is illegal, but won't be called as we stop during check */
+ ev_timer_init (&tw, 0, timeout * 1e-3);
+ ev_timer_start (loop, &tw);
+
+ // create on ev_io per pollfd
+ for (int i = 0; i < nfd; ++i)
+ {
+ ev_io_init (iow + i, io_cb, fds [i].fd,
+ ((fds [i].events & POLLIN ? EV_READ : 0)
+ | (fds [i].events & POLLOUT ? EV_WRITE : 0)));
+
+ fds [i].revents = 0;
+ iow [i].data = fds + i;
+ ev_io_start (loop, iow + i);
+ }
+ }
+
+ // stop all watchers after blocking
+ static void
+ adns_check_cb (ev_loop *loop, ev_check *w, int revents)
+ {
+ ev_timer_stop (loop, &tw);
+
+ for (int i = 0; i < nfd; ++i)
+ ev_io_stop (loop, iow + i);
+
+ adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
+ }
+</pre>
</div>
-<h2 id="code_ev_embed_code_when_one_backend_"><code>ev_embed</code> - when one backend isn't enough</h2>
+<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
ev_win32.c required on win32 platforms only
- ev_select.c only when select backend is enabled (which is is by default)
+ ev_select.c only when select backend is enabled (which is by default)
ev_poll.c only when poll backend is enabled (disabled by default)
ev_epoll.c only when the epoll backend is enabled (disabled by default)
ev_kqueue.c only when the kqueue backend is enabled (disabled by default)
</pre>
<p><cite>ev.c</cite> includes the backend files directly when enabled, so you only need
-to compile a single file.</p>
+to compile this single file.</p>
</div>
<h3 id="LIBEVENT_COMPATIBILITY_API">LIBEVENT COMPATIBILITY API</h3>
<div id="AUTOCONF_SUPPORT_CONTENT">
<p>Instead of using <code>EV_STANDALONE=1</code> and providing your config in
whatever way you want, you can also <code>m4_include([libev.m4])</code> in your
-<cite>configure.ac</cite> and leave <code>EV_STANDALONE</code> off. <cite>ev.c</cite> will then include
-<cite>config.h</cite> and configure itself accordingly.</p>
+<cite>configure.ac</cite> and leave <code>EV_STANDALONE</code> undefined. <cite>ev.c</cite> will then
+include <cite>config.h</cite> and configure itself accordingly.</p>
<p>For this of course you need the m4 file:</p>
<pre> libev.m4
</pre>
</dd>
- <dt>EV_CB_DECLARE(type)</dt>
- <dt>EV_CB_INVOKE(watcher,revents)</dt>
- <dt>ev_set_cb(ev,cb)</dt>
+ <dt>EV_CB_DECLARE (type)</dt>
+ <dt>EV_CB_INVOKE (watcher, revents)</dt>
+ <dt>ev_set_cb (ev, cb)</dt>
<dd>
<p>Can be used to change the callback member declaration in each watcher,
and the way callbacks are invoked and set. Must expand to a struct member
definition and a statement, respectively. See the <cite>ev.v</cite> header file for
their default definitions. One possible use for overriding these is to
-avoid the ev_loop pointer as first argument in all cases, or to use method
-calls instead of plain function calls in C++.</p>
+avoid the <code>struct ev_loop *</code> as first argument in all cases, or to use
+method calls instead of plain function calls in C++.</p>
</div>
<h2 id="EXAMPLES">EXAMPLES</h2>
<pre> #include "ev_cpp.h"
#include "ev.c"
+
+
+
</pre>
+</div>
+<h1 id="COMPLEXITIES">COMPLEXITIES</h1><p><a href="#TOP" class="toplink">Top</a></p>
+<div id="COMPLEXITIES_CONTENT">
+ <p>In this section the complexities of (many of) the algorithms used inside
+libev will be explained. For complexity discussions about backends see the
+documentation for <code>ev_default_init</code>.</p>
+ <p>
+ <dl>
+ <dt>Starting and stopping timer/periodic watchers: O(log skipped_other_timers)</dt>
+ <dt>Changing timer/periodic watchers (by autorepeat, again): O(log skipped_other_timers)</dt>
+ <dt>Starting io/check/prepare/idle/signal/child watchers: O(1)</dt>
+ <dt>Stopping check/prepare/idle watchers: O(1)</dt>
+ <dt>Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % 16))</dt>
+ <dt>Finding the next timer per loop iteration: O(1)</dt>
+ <dt>Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)</dt>
+ <dt>Activating one watcher: O(1)</dt>
+ </dl>
+ </p>
+
+
+
+
+
</div>
<h1 id="AUTHOR">AUTHOR</h1><p><a href="#TOP" class="toplink">Top</a></p>
<div id="AUTHOR_CONTENT">
projects / software / libev.git / blobdiff