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- <meta name="created" content="Sat Dec 8 16:30:24 2007" />
+ <meta name="created" content="Wed Dec 12 05:53:55 2007" />
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</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>
+<ul><li><a href="#code_ev_io_code_is_this_file_descrip"><code>ev_io</code> - is this file descriptor readable or writable?</a>
+<ul><li><a href="#The_special_problem_of_disappearing_">The special problem of disappearing file descriptors</a></li>
+</ul>
+</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>
<dt>int ev_version_major ()</dt>
<dt>int ev_version_minor ()</dt>
<dd>
- <p>You can find out the major and minor version numbers of the library
+ <p>You can find out the major and minor ABI version numbers of the library
you linked against by calling the functions <code>ev_version_major</code> and
<code>ev_version_minor</code>. If you want, you can compare against the global
symbols <code>EV_VERSION_MAJOR</code> and <code>EV_VERSION_MINOR</code>, which specify the
version of the library your program was compiled against.</p>
+ <p>These version numbers refer to the ABI version of the library, not the
+release version.</p>
<p>Usually, it's a good idea to terminate if the major versions mismatch,
-as this indicates an incompatible change. Minor versions are usually
+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
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.
+<pre> - Before the first iteration, call any pending watchers.
+ * If there are no active watchers (reference count is zero), return.
+ - 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 "event loop time".
whether 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>
+
+</div>
+<h3 id="The_special_problem_of_disappearing_">The special problem of disappearing file descriptors</h3>
+<div id="The_special_problem_of_disappearing_-2">
+<p>Some backends (e.g kqueue, epoll) need to be told about closing a file
+descriptor (either by calling <code>close</code> explicitly or by any other means,
+such as <code>dup</code>). The reason is that you register interest in some file
+descriptor, but when it goes away, the operating system will silently drop
+this interest. If another file descriptor with the same number then is
+registered with libev, there is no efficient way to see that this is, in
+fact, a different file descriptor.</p>
+<p>To avoid having to explicitly tell libev about such cases, libev follows
+the following policy: Each time <code>ev_io_set</code> is being called, libev
+will assume that this is potentially a new file descriptor, otherwise
+it is assumed that the file descriptor stays the same. That means that
+you <i>have</i> to call <code>ev_io_set</code> (or <code>ev_io_init</code>) when you change the
+descriptor even if the file descriptor number itself did not change.</p>
+<p>This is how one would do it normally anyway, the important point is that
+the libev application should not optimise around libev but should leave
+optimisations to libev.</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>
periodic watcher to trigger in 10 seconds (by specifiying e.g. <code>ev_now ()
+ 10.</code>) and then reset your system clock to the last year, then it will
take a year to trigger the event (unlike an <code>ev_timer</code>, which would trigger
-roughly 10 seconds later and of course not if you reset your system time
-again).</p>
+roughly 10 seconds later).</p>
<p>They can also be used to implement vastly more complex timers, such as
-triggering an event on eahc midnight, local time.</p>
+triggering an event on each midnight, local time or other, complicated,
+rules.</p>
<p>As with timers, the callback is guarenteed to be invoked only when the
time (<code>at</code>) has been passed, but if multiple periodic timers become ready
during the same loop iteration then order of execution is undefined.</p>
operation, and we will explain them from simplest to complex:</p>
<p>
<dl>
- <dt>* absolute timer (interval = reschedule_cb = 0)</dt>
+ <dt>* absolute timer (at = time, interval = reschedule_cb = 0)</dt>
<dd>
<p>In this configuration the watcher triggers an event at the wallclock time
<code>at</code> and doesn't repeat. It will not adjust when a time jump occurs,
that is, if it is to be run at January 1st 2011 then it will run when the
system time reaches or surpasses this time.</p>
</dd>
- <dt>* non-repeating interval timer (interval > 0, reschedule_cb = 0)</dt>
+ <dt>* non-repeating interval timer (at = offset, interval > 0, reschedule_cb = 0)</dt>
<dd>
<p>In this mode the watcher will always be scheduled to time out at the next
-<code>at + N * interval</code> time (for some integer N) and then repeat, regardless
-of any time jumps.</p>
+<code>at + N * interval</code> time (for some integer N, which can also be negative)
+and then repeat, regardless of any time jumps.</p>
<p>This can be used to create timers that do not drift with respect to system
time:</p>
<pre> ev_periodic_set (&periodic, 0., 3600., 0);
<p>Another way to think about it (for the mathematically inclined) is that
<code>ev_periodic</code> will try to run the callback in this mode at the next possible
time where <code>time = at (mod interval)</code>, regardless of any time jumps.</p>
+ <p>For numerical stability it is preferable that the <code>at</code> value is near
+<code>ev_now ()</code> (the current time), but there is no range requirement for
+this value.</p>
</dd>
- <dt>* manual reschedule mode (reschedule_cb = callback)</dt>
+ <dt>* manual reschedule mode (at and interval ignored, reschedule_cb = callback)</dt>
<dd>
<p>In this mode the values for <code>interval</code> and <code>at</code> are both being
ignored. Instead, each time the periodic watcher gets scheduled, the
<p>NOTE: <i>This callback MUST NOT stop or destroy any periodic watcher,
ever, or make any event loop modifications</i>. If you need to stop it,
return <code>now + 1e30</code> (or so, fudge fudge) and stop it afterwards (e.g. by
-starting a prepare watcher).</p>
+starting an <code>ev_prepare</code> watcher, which is legal).</p>
<p>Its prototype is <code>ev_tstamp (*reschedule_cb)(struct ev_periodic *w,
ev_tstamp now)</code>, e.g.:</p>
<pre> static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)
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).</p>
+ </dd>
+ <dt>ev_tstamp offset [read-write]</dt>
+ <dd>
+ <p>When repeating, this contains the offset value, otherwise this is the
+absolute point in time (the <code>at</code> value passed to <code>ev_periodic_set</code>).</p>
+ <p>Can be modified any time, but changes only take effect when the periodic
+timer fires or <code>ev_periodic_again</code> is being called.</p>
</dd>
<dt>ev_tstamp interval [read-write]</dt>
<dd>
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 ("feed") 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>
projects / software / libev.git / blobdiff