<meta name="description" content="Pod documentation for libev" />
<meta name="inputfile" content="<standard input>" />
<meta name="outputfile" content="<standard output>" />
- <meta name="created" content="Mon Nov 12 19:49:15 2007" />
+ <meta name="created" content="Thu Nov 22 13:26:17 2007" />
<meta name="generator" content="Pod::Xhtml 1.57" />
<link rel="stylesheet" href="http://res.tst.eu/pod.css"/></head>
<body>
<dl>
<dt>ev_tstamp ev_time ()</dt>
<dd>
- <p>Returns the current time as libev would use it.</p>
+ <p>Returns the current time as libev would use it. Please note that the
+<code>ev_now</code> function is usually faster and also often returns the timestamp
+you actually want to know.</p>
</dd>
<dt>int ev_version_major ()</dt>
<dt>int ev_version_minor ()</dt>
useful to try out specific backends to test their performance, or to work
around bugs.</p>
</dd>
- <dt><code>EVMETHOD_SELECT</code> (portable select backend)</dt>
- <dt><code>EVMETHOD_POLL</code> (poll backend, available everywhere except on windows)</dt>
- <dt><code>EVMETHOD_EPOLL</code> (linux only)</dt>
- <dt><code>EVMETHOD_KQUEUE</code> (some bsds only)</dt>
- <dt><code>EVMETHOD_DEVPOLL</code> (solaris 8 only)</dt>
- <dt><code>EVMETHOD_PORT</code> (solaris 10 only)</dt>
+ <dt><code>EVMETHOD_SELECT</code> (value 1, portable select backend)</dt>
<dd>
- <p>If one or more of these are ored into the flags value, then only these
-backends will be tried (in the reverse order as given here). If one are
-specified, any backend will do.</p>
+ <p>This is your standard select(2) backend. Not <i>completely</i> standard, as
+libev tries to roll its own fd_set with no limits on the number of fds,
+but if that fails, expect a fairly low limit on the number of fds when
+using this backend. It doesn't scale too well (O(highest_fd)), but its usually
+the fastest backend for a low number of fds.</p>
+ </dd>
+ <dt><code>EVMETHOD_POLL</code> (value 2, poll backend, available everywhere except on windows)</dt>
+ <dd>
+ <p>And this is your standard poll(2) backend. It's more complicated than
+select, but handles sparse fds better and has no artificial limit on the
+number of fds you can use (except it will slow down considerably with a
+lot of inactive fds). It scales similarly to select, i.e. O(total_fds).</p>
+ </dd>
+ <dt><code>EVMETHOD_EPOLL</code> (value 4, Linux)</dt>
+ <dd>
+ <p>For few fds, this backend is a bit little slower than poll and select,
+but it scales phenomenally better. While poll and select usually scale like
+O(total_fds) where n is the total number of fds (or the highest fd), epoll scales
+either O(1) or O(active_fds).</p>
+ <p>While stopping and starting an I/O watcher in the same iteration will
+result in some caching, there is still a syscall per such incident
+(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>
+ </dd>
+ <dt><code>EVMETHOD_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>
+ <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
+extra syscall as with epoll, it still adds up to four event changes per
+incident, so its best to avoid that.</p>
+ </dd>
+ <dt><code>EVMETHOD_DEVPOLL</code> (value 16, Solaris 8)</dt>
+ <dd>
+ <p>This is not implemented yet (and might never be).</p>
+ </dd>
+ <dt><code>EVMETHOD_PORT</code> (value 32, Solaris 10)</dt>
+ <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>
+ </dd>
+ <dt><code>EVMETHOD_ALL</code></dt>
+ <dd>
+ <p>Try all backends (even potentially broken ones). Since this is a mask, you
+can do stuff like <code>EVMETHOD_ALL & ~EVMETHOD_KQUEUE</code>.</p>
</dd>
</dl>
</p>
+ <p>If one or more of these are ored into the flags value, then only these
+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>
</dd>
<dt>struct ev_loop *ev_loop_new (unsigned int flags)</dt>
<dd>
<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.
+
+</pre>
</dd>
<dt>ev_unloop (loop, how)</dt>
<dd>
<p>Can be used to make a call to <code>ev_loop</code> return early (but only after it
has processed all outstanding events). The <code>how</code> argument must be either
-<code>EVUNLOOP_ONCE</code>, which will make the innermost <code>ev_loop</code> call return, or
+<code>EVUNLOOP_ONE</code>, which will make the innermost <code>ev_loop</code> call return, or
<code>EVUNLOOP_ALL</code>, which will make all nested <code>ev_loop</code> calls return.</p>
</dd>
<dt>ev_ref (loop)</dt>
<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 file/socket etc. description (that is, they share the same
-underlying "file open").</p>
+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 EVMETHOD_SELECT and
EVMETHOD_POLL).</p>
<p>The timers are based on real time, that is, if you register an event that
times out after an hour and you reset your system clock to last years
time, it will still time out after (roughly) and hour. "Roughly" because
-detecting time jumps is hard, and soem inaccuracies are unavoidable (the
+detecting time jumps is hard, and some inaccuracies are unavoidable (the
monotonic clock option helps a lot here).</p>
<p>The relative timeouts are calculated relative to the <code>ev_now ()</code>
time. This is usually the right thing as this timestamp refers to the time
-of the event triggering whatever timeout you are modifying/starting. If
-you suspect event processing to be delayed and you *need* to base the timeout
+of the event triggering whatever timeout you are modifying/starting. If
+you suspect event processing to be delayed and you <i>need</i> to base the timeout
on the current time, use something like this to adjust for this:</p>
<pre> ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);
</pre>
+<p>The callback is guarenteed to be invoked only when its timeout has passed,
+but if multiple timers become ready during the same loop iteration then
+order of execution is undefined.</p>
<dl>
<dt>ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)</dt>
<dt>ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)</dt>
again).</p>
<p>They can also be used to implement vastly more complex timers, such as
triggering an event on eahc midnight, local time.</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>
<dl>
<dt>ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)</dt>
<dt>ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)</dt>
<dd>
<p>Lots of arguments, lets sort it out... There are basically three modes of
operation, and we will explain them from simplest to complex:</p>
-
-
-
-
<p>
<dl>
<dt>* absolute timer (interval = reschedule_cb = 0)</dt>
</div>
<h1 id="LIBEVENT_EMULATION">LIBEVENT EMULATION</h1><p><a href="#TOP" class="toplink">Top</a></p>
<div id="LIBEVENT_EMULATION_CONTENT">
-<p>TBD.</p>
+<p>Libev offers a compatibility emulation layer for libevent. It cannot
+emulate the internals of libevent, so here are some usage hints:</p>
+<dl>
+ <dt>* Use it by including <event.h>, as usual.</dt>
+ <dt>* The following members are fully supported: ev_base, ev_callback,
+ev_arg, ev_fd, ev_res, ev_events.</dt>
+ <dt>* Avoid using ev_flags and the EVLIST_*-macros, while it is
+maintained by libev, it does not work exactly the same way as in libevent (consider
+it a private API).</dt>
+ <dt>* Priorities are not currently supported. Initialising priorities
+will fail and all watchers will have the same priority, even though there
+is an ev_pri field.</dt>
+ <dt>* Other members are not supported.</dt>
+ <dt>* The libev emulation is <i>not</i> ABI compatible to libevent, you need
+to use the libev header file and library.</dt>
+</dl>
</div>
<h1 id="C_SUPPORT">C++ SUPPORT</h1><p><a href="#TOP" class="toplink">Top</a></p>
projects / software / libev.git / blobdiff