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@ -6,7 +6,7 @@
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<meta name="description" content="Pod documentation for libev" />
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<meta name="inputfile" content="<standard input>" />
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<meta name="outputfile" content="<standard output>" />
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<meta name="created" content="Sat Dec 8 15:31:35 2007" />
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<meta name="created" content="Sat Dec 8 16:30:24 2007" />
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<meta name="generator" content="Pod::Xhtml 1.57" />
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<link rel="stylesheet" href="http://res.tst.eu/pod.css"/></head>
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<body>
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@ -1494,21 +1494,23 @@ parameters of any kind. There are <code>ev_prepare_set</code> and <code>ev_check
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macros, but using them is utterly, utterly and completely pointless.</p>
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</dd>
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</dl>
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<p>Example: To include a library such as adns, you would add IO watchers
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and a timeout watcher in a prepare handler, as required by libadns, and
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in a check watcher, destroy them and call into libadns. What follows is
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pseudo-code only of course:</p>
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<p>There are a number of principal ways to embed other event loops or modules
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into libev. Here are some ideas on how to include libadns into libev
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(there is a Perl module named <code>EV::ADNS</code> that does this, which you could
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use for an actually working example. Another Perl module named <code>EV::Glib</code>
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embeds a Glib main context into libev, and finally, <code>Glib::EV</code> embeds EV
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into the Glib event loop).</p>
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<p>Method 1: Add IO watchers and a timeout watcher in a prepare handler,
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and in a check watcher, destroy them and call into libadns. What follows
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is pseudo-code only of course. This requires you to either use a low
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priority for the check watcher or use <code>ev_clear_pending</code> explicitly, as
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the callbacks for the IO/timeout watchers might not have been called yet.</p>
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<pre> static ev_io iow [nfd];
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static ev_timer tw;
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static void
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io_cb (ev_loop *loop, ev_io *w, int revents)
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{
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// set the relevant poll flags
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// could also call adns_processreadable etc. here
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struct pollfd *fd = (struct pollfd *)w->data;
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if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;
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if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;
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}
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// create io watchers for each fd and a timer before blocking
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@ -1524,7 +1526,7 @@ pseudo-code only of course:</p>
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ev_timer_init (&tw, 0, timeout * 1e-3);
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ev_timer_start (loop, &tw);
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// create on ev_io per pollfd
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// create one ev_io per pollfd
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for (int i = 0; i < nfd; ++i)
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{
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ev_io_init (iow + i, io_cb, fds [i].fd,
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@ -1532,7 +1534,6 @@ pseudo-code only of course:</p>
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| (fds [i].events & POLLOUT ? EV_WRITE : 0)));
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fds [i].revents = 0;
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iow [i].data = fds + i;
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ev_io_start (loop, iow + i);
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}
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}
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@ -1544,11 +1545,79 @@ pseudo-code only of course:</p>
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ev_timer_stop (loop, &tw);
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for (int i = 0; i < nfd; ++i)
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ev_io_stop (loop, iow + i);
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{
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// set the relevant poll flags
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// could also call adns_processreadable etc. here
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struct pollfd *fd = fds + i;
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int revents = ev_clear_pending (iow + i);
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if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;
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if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;
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// now stop the watcher
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ev_io_stop (loop, iow + i);
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}
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adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
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}
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</pre>
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<p>Method 2: This would be just like method 1, but you run <code>adns_afterpoll</code>
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in the prepare watcher and would dispose of the check watcher.</p>
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<p>Method 3: If the module to be embedded supports explicit event
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notification (adns does), you can also make use of the actual watcher
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callbacks, and only destroy/create the watchers in the prepare watcher.</p>
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<pre> static void
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timer_cb (EV_P_ ev_timer *w, int revents)
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{
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adns_state ads = (adns_state)w->data;
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update_now (EV_A);
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adns_processtimeouts (ads, &tv_now);
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}
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static void
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io_cb (EV_P_ ev_io *w, int revents)
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{
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adns_state ads = (adns_state)w->data;
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update_now (EV_A);
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if (revents & EV_READ ) adns_processreadable (ads, w->fd, &tv_now);
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if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now);
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}
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// do not ever call adns_afterpoll
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</pre>
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<p>Method 4: Do not use a prepare or check watcher because the module you
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want to embed is too inflexible to support it. Instead, youc na override
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their poll function. The drawback with this solution is that the main
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loop is now no longer controllable by EV. The <code>Glib::EV</code> module does
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this.</p>
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<pre> static gint
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event_poll_func (GPollFD *fds, guint nfds, gint timeout)
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{
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int got_events = 0;
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for (n = 0; n < nfds; ++n)
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// create/start io watcher that sets the relevant bits in fds[n] and increment got_events
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if (timeout >= 0)
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// create/start timer
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// poll
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ev_loop (EV_A_ 0);
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// stop timer again
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if (timeout >= 0)
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ev_timer_stop (EV_A_ &to);
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// stop io watchers again - their callbacks should have set
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for (n = 0; n < nfds; ++n)
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ev_io_stop (EV_A_ iow [n]);
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return got_events;
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}
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Marc Alexander Lehmann
16 years ago