[ViewVC] Diff of: cvs/libev/ev.html

Comparing libev/ev.html (file contents):
Revision 1.69 by root, Fri Dec 7 20:19:16 2007 UTC vs.
Revision 1.73 by root, Sat Dec 8 22:11:14 2007 UTC

 <head>
 	<title>libev</title>
 	<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 Dec  7 21:19:14 2007" />
+	<meta name="created" content="Sat Dec  8 23:11:11 2007" />
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 <body>
 <div class="pod">
 <!-- INDEX START -->
 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>   - Before the first iteration, call any pending watchers.
-<pre>   * If there are no active watchers (reference count is zero), return.
+   * If there are no active watchers (reference count is zero), return.
-   - Queue prepare watchers and then call all outstanding watchers.
+   - Queue all prepare watchers and then call all outstanding watchers.
    - If we have been forked, recreate the kernel state.
    - Update the kernel state with all outstanding changes.
    - Update the &quot;event loop time&quot;.
    - Calculate for how long to block.
    - Block the process, waiting for any events.
 	<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
+<code>ev_TYPE_set</code> is safe), you must not change its priority, and you must
-libev (e.g. you cnanot <code>free ()</code> it).</p>
+make sure the watcher is available to libev (e.g. you cannot <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>
 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.</p>
 		<p>If you need to suppress invocation when higher priority events are pending
 you need to look at <code>ev_idle</code> watchers, which provide this functionality.</p>
+		<p>You <i>must not</i> change the priority of a watcher as long as it is active or
+pending.</p>
 		<p>The default priority used by watchers when no priority has been set is
 always <code>0</code>, which is supposed to not be too high and not be too low :).</p>
 		<p>Setting a priority outside the range of <code>EV_MINPRI</code> to <code>EV_MAXPRI</code> 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.</p>
+	</dd>
+	<dt>ev_invoke (loop, ev_TYPE *watcher, int revents)</dt>
+	<dd>
+		<p>Invoke the <code>watcher</code> with the given <code>loop</code> and <code>revents</code>. Neither
+<code>loop</code> nor <code>revents</code> need to be valid as long as the watcher callback
+can deal with that fact.</p>
+	</dd>
+	<dt>int ev_clear_pending (loop, ev_TYPE *watcher)</dt>
+	<dd>
+		<p>If the watcher is pending, this function returns clears its pending status
+and returns its <code>revents</code> bitset (as if its callback was invoked). If the
+watcher isn't pending it does nothing and returns <code>0</code>.</p>
 	</dd>
 </dl>
 are ready to run (it's actually more complicated: it only runs coroutines
 with priority higher than or equal to the event loop and one coroutine
 of lower priority, but only once, using idle watchers to keep the event
 loop from blocking if lower-priority coroutines are active, thus mapping
 low-priority coroutines to idle/background tasks).</p>
+<p>It is recommended to give <code>ev_check</code> watchers highest (<code>EV_MAXPRI</code>)
+priority, to ensure that they are being run before any other watchers
+after the poll. Also, <code>ev_check</code> watchers (and <code>ev_prepare</code> watchers,
+too) should not activate (&quot;feed&quot;) events into libev. While libev fully
+supports this, they will be called before other <code>ev_check</code> watchers did
+their job. As <code>ev_check</code> watchers are often used to embed other event
+loops those other event loops might be in an unusable state until their
+<code>ev_check</code> watcher ran (always remind yourself to coexist peacefully with
+others).</p>
 <dl>
 	<dt>ev_prepare_init (ev_prepare *, callback)</dt>
 	<dt>ev_check_init (ev_check *, callback)</dt>
 	<dd>
 		<p>Initialises and configures the prepare or check watcher - they have no
 parameters of any kind. There are <code>ev_prepare_set</code> and <code>ev_check_set</code>
 macros, but using them is utterly, utterly and completely pointless.</p>
 	</dd>
 </dl>
-<p>Example: To include a library such as adns, you would add IO watchers
+<p>There are a number of principal ways to embed other event loops or modules
-and a timeout watcher in a prepare handler, as required by libadns, and
+into libev. Here are some ideas on how to include libadns into libev
+(there is a Perl module named <code>EV::ADNS</code> that does this, which you could
+use for an actually working example. Another Perl module named <code>EV::Glib</code>
+embeds a Glib main context into libev, and finally, <code>Glib::EV</code> embeds EV
+into the Glib event loop).</p>
+<p>Method 1: Add IO watchers and a timeout watcher in a prepare handler,
-in a check watcher, destroy them and call into libadns. What follows is
+and in a check watcher, destroy them and call into libadns. What follows
-pseudo-code only of course:</p>
+is pseudo-code only of course. This requires you to either use a low
+priority for the check watcher or use <code>ev_clear_pending</code> explicitly, as
+the callbacks for the IO/timeout watchers might not have been called yet.</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-&gt;data;
-    if (revents &amp; EV_READ ) fd-&gt;revents |= fd-&gt;events &amp; POLLIN;
-    if (revents &amp; EV_WRITE) fd-&gt;revents |= fd-&gt;events &amp; 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)
     /* the callback is illegal, but won't be called as we stop during check */
     ev_timer_init (&amp;tw, 0, timeout * 1e-3);
     ev_timer_start (loop, &amp;tw);
-    // create on ev_io per pollfd
+    // create one ev_io per pollfd
     for (int i = 0; i &lt; nfd; ++i)
       {
         ev_io_init (iow + i, io_cb, fds [i].fd,
           ((fds [i].events &amp; POLLIN ? EV_READ : 0)
            | (fds [i].events &amp; POLLOUT ? EV_WRITE : 0)));
         fds [i].revents = 0;
-        iow [i].data = fds + i;
         ev_io_start (loop, iow + i);
       }
   }
   // stop all watchers after blocking
   adns_check_cb (ev_loop *loop, ev_check *w, int revents)
   {
     ev_timer_stop (loop, &amp;tw);
     for (int i = 0; i &lt; nfd; ++i)
+      {
+        // set the relevant poll flags
+        // could also call adns_processreadable etc. here
+        struct pollfd *fd = fds + i;
+        int revents = ev_clear_pending (iow + i);
+        if (revents &amp; EV_READ ) fd-&gt;revents |= fd-&gt;events &amp; POLLIN;
+        if (revents &amp; EV_WRITE) fd-&gt;revents |= fd-&gt;events &amp; POLLOUT;
+        // now stop the watcher
-      ev_io_stop (loop, iow + i);
+        ev_io_stop (loop, iow + i);
+      }
     adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
+  }
+</pre>
+<p>Method 2: This would be just like method 1, but you run <code>adns_afterpoll</code>
+in the prepare watcher and would dispose of the check watcher.</p>
+<p>Method 3: If the module to be embedded supports explicit event
+notification (adns does), you can also make use of the actual watcher
+callbacks, and only destroy/create the watchers in the prepare watcher.</p>
+<pre>  static void
+  timer_cb (EV_P_ ev_timer *w, int revents)
+  {
+    adns_state ads = (adns_state)w-&gt;data;
+    update_now (EV_A);
+    adns_processtimeouts (ads, &amp;tv_now);
+  }
+  static void
+  io_cb (EV_P_ ev_io *w, int revents)
+  {
+    adns_state ads = (adns_state)w-&gt;data;
+    update_now (EV_A);
+    if (revents &amp; EV_READ ) adns_processreadable  (ads, w-&gt;fd, &amp;tv_now);
+    if (revents &amp; EV_WRITE) adns_processwriteable (ads, w-&gt;fd, &amp;tv_now);
+  }
+  // do not ever call adns_afterpoll
+</pre>
+<p>Method 4: Do not use a prepare or check watcher because the module you
+want to embed is too inflexible to support it. Instead, youc na override
+their poll function.  The drawback with this solution is that the main
+loop is now no longer controllable by EV. The <code>Glib::EV</code> module does
+this.</p>
+<pre>  static gint
+  event_poll_func (GPollFD *fds, guint nfds, gint timeout)
+  {
+    int got_events = 0;
+    for (n = 0; n &lt; nfds; ++n)
+      // create/start io watcher that sets the relevant bits in fds[n] and increment got_events
+    if (timeout &gt;= 0)
+      // create/start timer
+    // poll
+    ev_loop (EV_A_ 0);
+    // stop timer again
+    if (timeout &gt;= 0)
+      ev_timer_stop (EV_A_ &amp;to);
+    // stop io watchers again - their callbacks should have set
+    for (n = 0; n &lt; nfds; ++n)
+      ev_io_stop (EV_A_ iow [n]);
+    return got_events;
   }
   ev::io iow;
   iow.set &lt;myclass, &amp;myclass::io_cb&gt; (&amp;obj);
 </pre>
 				</dd>
-				<dt>w-&gt;set (void (*function)(watcher &amp;w, int), void *data = 0)</dt>
+				<dt>w-&gt;set&lt;function&gt; (void *data = 0)</dt>
 				<dd>
 					<p>Also sets a callback, but uses a static method or plain function as
 callback. The optional <code>data</code> argument will be stored in the watcher's
 <code>data</code> member and is free for you to use.</p>
+					<p>The prototype of the <code>function</code> must be <code>void (*)(ev::TYPE &amp;w, int)</code>.</p>
 					<p>See the method-<code>set</code> above for more details.</p>
+					<p>Example:</p>
+<pre>  static void io_cb (ev::io &amp;w, int revents) { }
+  iow.set &lt;io_cb&gt; ();
+</pre>
 				</dd>
 				<dt>w-&gt;set (struct ev_loop *)</dt>
 				<dd>
 					<p>Associates a different <code>struct ev_loop</code> with this watcher. You can only
 do this when the watcher is inactive (and not pending either).</p>

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Comparing libev/ev.html (file contents): Revision 1.69 by root, Fri Dec 7 20:19:16 2007 UTC vs. Revision 1.73 by root, Sat Dec 8 22:11:14 2007 UTC

Diff Legend

Comparing libev/ev.html (file contents):
Revision 1.69 by root, Fri Dec 7 20:19:16 2007 UTC vs.
Revision 1.73 by root, Sat Dec 8 22:11:14 2007 UTC