<meta name="description" content="Pod documentation for libev" />
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- <meta name="created" content="Mon Nov 12 09:46:59 2007" />
+ <meta name="created" content="Fri Nov 23 05:35:59 2007" />
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<body>
<li><a href="#DESCRIPTION">DESCRIPTION</a></li>
<li><a href="#FEATURES">FEATURES</a></li>
<li><a href="#CONVENTIONS">CONVENTIONS</a></li>
-<li><a href="#TIME_AND_OTHER_GLOBAL_FUNCTIONS">TIME AND OTHER GLOBAL FUNCTIONS</a></li>
+<li><a href="#TIME_REPRESENTATION">TIME REPRESENTATION</a></li>
+<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="#ASSOCIATING_CUSTOM_DATA_WITH_A_WATCH">ASSOCIATING CUSTOM DATA WITH A WATCHER</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> - your hooks into the event loop</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>
</ul>
</li>
<li><a href="#OTHER_FUNCTIONS">OTHER FUNCTIONS</a></li>
+<li><a href="#LIBEVENT_EMULATION">LIBEVENT EMULATION</a></li>
+<li><a href="#C_SUPPORT">C++ SUPPORT</a></li>
<li><a href="#AUTHOR">AUTHOR</a>
</li>
</ul><hr />
will not have this argument.</p>
</div>
-<h1 id="TIME_
AND_OTHER_GLOBAL_FUNCTIONS">TIME AND OTHER GLOBAL FUNCTIONS</h1><p><a href="#TOP" class="toplink">Top</a></p>
-<div id="TIME_AND_OTHER_GLOBAL_FUNCTIONS_CONT">
+<h1 id="TIME_
REPRESENTATION">TIME REPRESENTATION</h1><p><a href="#TOP" class="toplink">Top</a></p>
+<div id="TIME_REPRESENTATION_CONTENT">
<p>Libev represents time as a single floating point number, representing the
(fractional) number of seconds since the (POSIX) epoch (somewhere near
the beginning of 1970, details are complicated, don't ask). This type is
called <code>ev_tstamp</code>, which is what you should use too. It usually aliases
to the double type in C.</p>
+
+</div>
+<h1 id="GLOBAL_FUNCTIONS">GLOBAL FUNCTIONS</h1><p><a href="#TOP" class="toplink">Top</a></p>
+<div id="GLOBAL_FUNCTIONS_CONTENT">
+<p>These functions can be called anytime, even before initialising the
+library in any way.</p>
<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>
types of such loops, the <i>default</i> loop, which supports signals and child
events, and dynamically created loops which do not.</p>
<p>If you use threads, a common model is to run the default event loop
-in your main thread (or in a separate thrad) and for each thread you
+in your main thread (or in a separate thread) and for each thread you
create, you also create another event loop. Libev itself does no locking
whatsoever, so if you mix calls to the same event loop in different
threads, make sure you lock (this is usually a bad idea, though, even if
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>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>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>Try all backends (even potentially broken ones that wouldn't be tried
+with <code>EVFLAG_AUTO</code>). Since this is a mask, you can do stuff such as
+<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>
one. Despite the name, you can call it anytime, but it makes most sense
after forking, in either the parent or child process (or both, but that
again makes little sense).</p>
- <p>You <i>must</i> call this function after forking if and only if you want to
-use the event library in both processes. If you just fork+exec, you don't
-have to call it.</p>
+ <p>You <i>must</i> call this function in the child process after forking if and
+only if you want to use the event library in both processes. If you just
+fork+exec, you don't have to call it.</p>
<p>The function itself is quite fast and it's usually not a problem to call
it just in case after a fork. To make this easy, the function will fit in
quite nicely into a call to <code>pthread_atfork</code>:</p>
<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>
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 oer
+<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
required if you know what you are doing).</p>
<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.</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>Timer watchers are simple relative timers that generate an event after a
given time, and optionally repeating in regular intervals after that.</p>
<p>The timers are based on real time, that is, if you register an event that
-times out after an hour and youreset your system clock to last years
+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
-ion the current time, use something like this to adjust for this:</p>
+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>
<p>The timer itself will do a best-effort at avoiding drift, that is, if you
configure a timer to trigger every 10 seconds, then it will trigger at
exactly 10 second intervals. If, however, your program cannot keep up with
-the timer (ecause it takes longer than those 10 seconds to do stuff) the
+the timer (because it takes longer than those 10 seconds to do stuff) the
timer will not fire more than once per event loop iteration.</p>
</dd>
<dt>ev_timer_again (loop)</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>
ignored. Instead, each time the periodic watcher gets scheduled, the
reschedule callback will be called with the watcher as first, and the
current time as second argument.</p>
- <p>NOTE: <i>This callback MUST NOT stop or destroy the periodic or any other
-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.</p>
- <p>Also, <i>this callback must always return a time that is later than the
-passed <code>now</code> value</i>. Not even <code>now</code> itself will be ok.</p>
+ <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>
<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)
(that is, the lowest time value larger than to the second argument). It
will usually be called just before the callback will be triggered, but
might be called at other times, too.</p>
+ <p>NOTE: <i>This callback must always return a time that is later than the
+passed <code>now</code> value</i>. Not even <code>now</code> itself will do, it <i>must</i> be larger.</p>
<p>This can be used to create very complex timers, such as a timer that
triggers on each midnight, local time. To do this, you would calculate the
-next midnight after <code>now</code> and return the timestamp value for this. How you do this
-is, again, up to you (but it is not trivial).</p>
+next midnight after <code>now</code> and return the timestamp value for this. How
+you do this is, again, up to you (but it is not trivial, which is the main
+reason I omitted it as an example).</p>
</dd>
</dl>
</p>
</dl>
</div>
-<h2 id="code_ev_prepare_code_and_code_ev_che"><code>ev_prepare</code> and <code>ev_check</code> - your hooks into the 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
+prepare watchers get invoked before the process blocks and check watchers
afterwards.</p>
<p>Their main purpose is to integrate other event mechanisms into libev. This
could be used, for example, to track variable changes, implement your own
provide just this functionality). Then, in the check watcher you check for
any events that occured (by checking the pending status of all watchers
and stopping them) and call back into the library. The I/O and timer
-callbacks will never actually be called (but must be valid neverthelles,
+callbacks will never actually be called (but must be valid nevertheless,
because you never know, you know?).</p>
<p>As another example, the Perl Coro module uses these hooks to integrate
coroutines into libev programs, by yielding to other active coroutines
during each prepare and only letting the process block if no coroutines
-are ready to run (its actually more complicated, it only runs coroutines
-with priority higher than the event loop and one lower priority once,
-using idle watchers to keep the event loop from blocking if lower-priority
-coroutines exist, thus mapping low-priority coroutines to idle/background
-tasks).</p>
+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>
<dl>
<dt>ev_prepare_init (ev_prepare *, callback)</dt>
<dt>ev_check_init (ev_check *, callback)</dt>
<p>This function combines a simple timer and an I/O watcher, calls your
callback on whichever event happens first and automatically stop both
watchers. This is useful if you want to wait for a single event on an fd
-or timeout without havign to allocate/configure/start/stop/free one or
+or timeout without having to allocate/configure/start/stop/free one or
more watchers yourself.</p>
<p>If <code>fd</code> is less than 0, then no I/O watcher will be started and events
is being ignored. Otherwise, an <code>ev_io</code> watcher for the given <code>fd</code> and
repeat = 0) will be started. While <code>0</code> is a valid timeout, it is of
dubious value.</p>
<p>The callback has the type <code>void (*cb)(int revents, void *arg)</code> and gets
-passed an events set like normal event callbacks (with a combination of
+passed an <code>revents</code> set like normal event callbacks (a combination of
<code>EV_ERROR</code>, <code>EV_READ</code>, <code>EV_WRITE</code> or <code>EV_TIMEOUT</code>) and the <code>arg</code>
value passed to <code>ev_once</code>:</p>
<pre> static void stdin_ready (int revents, void *arg)
</dd>
</dl>
+</div>
+<h1 id="LIBEVENT_EMULATION">LIBEVENT EMULATION</h1><p><a href="#TOP" class="toplink">Top</a></p>
+<div id="LIBEVENT_EMULATION_CONTENT">
+<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>
+<div id="C_SUPPORT_CONTENT">
+<p>TBD.</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