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

Comparing libev/ev.html (file contents):
Revision 1.28 by root, Sun Nov 18 03:43:24 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="Sun Nov 18 04:43:20 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>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
 and free memory (no surprises here). If it returns zero when memory
 	<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
 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
 (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 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>

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Comparing libev/ev.html (file contents): Revision 1.28 by root, Sun Nov 18 03:43:24 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 1.28 by root, Sun Nov 18 03:43:24 2007 UTC vs.
Revision 1.33 by root, Fri Nov 23 08:36:35 2007 UTC