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

Comparing libev/ev.html (file contents):
Revision 1.24 by root, Mon Nov 12 09:07:10 2007 UTC vs.
Revision 1.33 by root, Fri Nov 23 08:36:35 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="Mon Nov 12 10:07:10 2007" />
+	<meta name="created" content="Fri Nov 23 09:26:40 2007" />
 	<meta name="generator" content="Pod::Xhtml 1.57" />
 <link rel="stylesheet" href="http://res.tst.eu/pod.css"/></head>
 <body>
 <div class="pod">
 <!-- INDEX START -->
 <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>
 	<dd>
 		<p>You can find out the major and minor version numbers of the library
 version of the library your program was compiled against.</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
 compatible to older versions, so a larger minor version alone is usually
 not a problem.</p>
+	</dd>
+	<dt>unsigned int ev_supported_backends ()</dt>
+	<dd>
+		<p>Return the set of all backends (i.e. their corresponding <code>EV_BACKEND_*</code>
+value) compiled into this binary of libev (independent of their
+availability on the system you are running on). See <code>ev_default_loop</code> for
+a description of the set values.</p>
+	</dd>
+	<dt>unsigned int ev_recommended_backends ()</dt>
+	<dd>
+		<p>Return the set of all backends compiled into this binary of libev and also
+recommended for this platform. This set is often smaller than the one
+returned by <code>ev_supported_backends</code>, as for example kqueue is broken on
+most BSDs and will not be autodetected unless you explicitly request it
+(assuming you know what you are doing). This is the set of backends that
+<code>EVFLAG_AUTO</code> will probe for.</p>
 	</dd>
 	<dt>ev_set_allocator (void *(*cb)(void *ptr, long size))</dt>
 	<dd>
 		<p>Sets the allocation function to use (the prototype is similar to the
 realloc C function, the semantics are identical). It is used to allocate
 	<dt>struct ev_loop *ev_default_loop (unsigned int flags)</dt>
 	<dd>
 		<p>This will initialise the default event loop if it hasn't been initialised
 yet and return it. If the default loop could not be initialised, returns
 false. If it already was initialised it simply returns it (and ignores the
-flags).</p>
+flags. If that is troubling you, check <code>ev_backend ()</code> afterwards).</p>
 		<p>If you don't know what event loop to use, use the one returned from this
 function.</p>
 		<p>The flags argument can be used to specify special behaviour or specific
-backends to use, and is usually specified as 0 (or EVFLAG_AUTO).</p>
+backends to use, and is usually specified as <code>0</code> (or EVFLAG_AUTO).</p>
 		<p>It supports the following flags:</p>
 		<p>
 			<dl>
 				<dt><code>EVFLAG_AUTO</code></dt>
 				<dd>
 <code>LIBEV_FLAGS</code>. Otherwise (the default), this environment variable will
 override the flags completely if it is found in the environment. This is
 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>EVBACKEND_SELECT</code>  (value 1, portable select backend)</dt>
-				<dt><code>EVMETHOD_POLL</code>    (poll backend, available everywhere except on windows)</dt>
+				<dd>
-				<dt><code>EVMETHOD_EPOLL</code>   (linux only)</dt>
+					<p>This is your standard select(2) backend. Not <i>completely</i> standard, as
-				<dt><code>EVMETHOD_KQUEUE</code>  (some bsds only)</dt>
+libev tries to roll its own fd_set with no limits on the number of fds,
-				<dt><code>EVMETHOD_DEVPOLL</code> (solaris 8 only)</dt>
+but if that fails, expect a fairly low limit on the number of fds when
-				<dt><code>EVMETHOD_PORT</code>    (solaris 10 only)</dt>
+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>
+				</dd>
-					<p>If one or more of these are ored into the flags value, then only these
+				<dt><code>EVBACKEND_POLL</code>    (value 2, poll backend, available everywhere except on windows)</dt>
-backends will be tried (in the reverse order as given here). If one are
+				<dd>
-specified, any backend will do.</p>
+					<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>EVBACKEND_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>
+					<p>Please note that epoll sometimes generates spurious notifications, so you
+need to use non-blocking I/O or other means to avoid blocking when no data
+(or space) is available.</p>
+				</dd>
+				<dt><code>EVBACKEND_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 &quot;autodetected&quot; 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>EVBACKEND_DEVPOLL</code> (value 16, Solaris 8)</dt>
+				<dd>
+					<p>This is not implemented yet (and might never be).</p>
+				</dd>
+				<dt><code>EVBACKEND_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>
+					<p>Please note that solaris ports can result in a lot of spurious
+notifications, so you need to use non-blocking I/O or other means to avoid
+blocking when no data (or space) is available.</p>
+				</dd>
+				<dt><code>EVBACKEND_ALL</code></dt>
+				<dd>
+					<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>EVBACKEND_ALL &amp; ~EVBACKEND_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>Similar to <code>ev_default_loop</code>, but always creates a new event loop that is
 always distinct from the default loop. Unlike the default loop, it cannot
 	<dd>
 		<p>This function reinitialises the kernel state for backends that have
 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
+		<p>You <i>must</i> call this function in the child process after forking if and
-use the event library in both processes. If you just fork+exec, you don't
+only if you want to use the event library in both processes. If you just
-have to call it.</p>
+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>
 <pre>    pthread_atfork (0, 0, ev_default_fork);
 </pre>
+		<p>At the moment, <code>EVBACKEND_SELECT</code> and <code>EVBACKEND_POLL</code> are safe to use
+without calling this function, so if you force one of those backends you
+do not need to care.</p>
 	</dd>
 	<dt>ev_loop_fork (loop)</dt>
 	<dd>
 		<p>Like <code>ev_default_fork</code>, but acts on an event loop created by
 <code>ev_loop_new</code>. Yes, you have to call this on every allocated event loop
 after fork, and how you do this is entirely your own problem.</p>
 	</dd>
-	<dt>unsigned int ev_method (loop)</dt>
+	<dt>unsigned int ev_backend (loop)</dt>
 	<dd>
-		<p>Returns one of the <code>EVMETHOD_*</code> flags indicating the event backend in
+		<p>Returns one of the <code>EVBACKEND_*</code> flags indicating the event backend in
 use.</p>
 	</dd>
 	<dt>ev_tstamp ev_now (loop)</dt>
 	<dd>
 		<p>Returns the current &quot;event loop time&quot;, which is the time the event loop
 your process until at least one new event arrives, and will return after
 one iteration of the loop.</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 &quot;event loop time&quot;.
+   6. Calculate for how long to block.
+   7. Block the process, waiting for events.
+   8. Update the &quot;event loop time&quot; 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>
 	<dt>ev_unref (loop)</dt>
 	<dd>
 with a watcher-specific start function (<code>ev_&lt;type&gt;_start (loop, watcher
 *)</code>), and you can stop watching for events at any time by calling the
 corresponding stop function (<code>ev_&lt;type&gt;_stop (loop, watcher *)</code>.</p>
 <p>As long as your watcher is active (has been started but not stopped) you
 must not touch the values stored in it. Most specifically you must never
-reinitialise it or call its set method.</p>
+reinitialise it or call its set macro.</p>
 <p>You can check whether an event is active by calling the <code>ev_is_active
 (watcher *)</code> macro. To see whether an event is outstanding (but the
 callback for it has not been called yet) you can use the <code>ev_is_pending
 (watcher *)</code> macro.</p>
 <p>Each and every callback receives the event loop pointer as first, the
 <p>I/O watchers check whether a file descriptor is readable or writable
 in each iteration of the event loop (This behaviour is called
 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 &quot;file open&quot;).</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
+(at the time of this writing, this includes only <code>EVBACKEND_SELECT</code> and
-EVMETHOD_POLL).</p>
+<code>EVBACKEND_POLL</code>).</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>
 	<dd>
 		<p>Configures an <code>ev_io</code> watcher. The fd is the file descriptor to rceeive
 events for and events is either <code>EV_READ</code>, <code>EV_WRITE</code> or <code>EV_READ |
 EV_WRITE</code> to receive the given events.</p>
+		<p>Please note that most of the more scalable backend mechanisms (for example
+epoll and solaris ports) can result in spurious readyness notifications
+for file descriptors, so you practically need to use non-blocking I/O (and
+treat callback invocation as hint only), or retest separately with a safe
+interface before doing I/O (XLib can do this), or force the use of either
+<code>EVBACKEND_SELECT</code> or <code>EVBACKEND_POLL</code>, which don't suffer from this
+problem. Also note that it is quite easy to have your callback invoked
+when the readyness condition is no longer valid even when employing
+typical ways of handling events, so its a good idea to use non-blocking
+I/O unconditionally.</p>
 	</dd>
 </dl>
 </div>
 <h2 id="code_ev_timer_code_relative_and_opti"><code>ev_timer</code> - relative and optionally recurring timeouts</h2>
 <div id="code_ev_timer_code_relative_and_opti-2">
 <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. &quot;Roughly&quot; 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
+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
+you suspect event processing to be delayed and you <i>need</i> to base the timeout
-ion the current time, use something like this to adjust for this:</p>
+on the current time, use something like this to adjust for this:</p>
 <pre>   ev_timer_set (&amp;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>
 	<dd>
 		<p>Configure the timer to trigger after <code>after</code> seconds. If <code>repeat</code> is
 timer will automatically be configured to trigger again <code>repeat</code> seconds
 later, again, and again, until stopped manually.</p>
 		<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>
 	<dd>
 		<p>This will act as if the timer timed out and restart it again if it is
 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>
 <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>
 				<dd>
 					<p>In this configuration the watcher triggers an event at the wallclock time
 	<dt>ev_once (loop, int fd, int events, ev_tstamp timeout, callback)</dt>
 	<dd>
 		<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
 <code>events</code> set will be craeted and started.</p>
 		<p>If <code>timeout</code> is less than 0, then no timeout watcher will be
 </dl>
 </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 &lt;event.h&gt;, 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>

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Comparing libev/ev.html (file contents): Revision 1.24 by root, Mon Nov 12 09:07:10 2007 UTC vs. Revision 1.33 by root, Fri Nov 23 08:36:35 2007 UTC

Diff Legend

Comparing libev/ev.html (file contents):
Revision 1.24 by root, Mon Nov 12 09:07:10 2007 UTC vs.
Revision 1.33 by root, Fri Nov 23 08:36:35 2007 UTC