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+ <meta name="created" content="Sat Dec 8 15:31:35 2007" />
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<h1 id="DESCRIPTION">DESCRIPTION</h1>
<div id="DESCRIPTION_CONTENT">
+<p>The newest version of this document is also available as a html-formatted
+web page you might find easier to navigate when reading it for the first
+time: <a href="http://cvs.schmorp.de/libev/ev.html">http://cvs.schmorp.de/libev/ev.html</a>.</p>
<p>Libev is an event loop: you register interest in certain events (such as a
file descriptor being readable or a timeout occuring), and it will manage
these event sources and provide your program with events.</p>
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>EVFLAG_FORKCHECK</code></dt>
+ <dd>
+ <p>Instead of calling <code>ev_default_fork</code> or <code>ev_loop_fork</code> manually after
+a fork, you can also make libev check for a fork in each iteration by
+enabling this flag.</p>
+ <p>This works by calling <code>getpid ()</code> on every iteration of the loop,
+and thus this might slow down your event loop if you do a lot of loop
+iterations and little real work, but is usually not noticeable (on my
+Linux system for example, <code>getpid</code> is actually a simple 5-insn sequence
+without a syscall and thus <i>very</i> fast, but my Linux system also has
+<code>pthread_atfork</code> which is even faster).</p>
+ <p>The big advantage of this flag is that you can forget about fork (and
+forget about forgetting to tell libev about forking) when you use this
+flag.</p>
+ <p>This flag setting cannot be overriden or specified in the <code>LIBEV_FLAGS</code>
+environment variable.</p>
</dd>
<dt><code>EVBACKEND_SELECT</code> (value 1, portable select backend)</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_loop_count (loop)</dt>
+ <dd>
+ <p>Returns the count of loop iterations for the loop, which is identical to
+the number of times libev did poll for new events. It starts at <code>0</code> and
+happily wraps around with enough iterations.</p>
+ <p>This value can sometimes be useful as a generation counter of sorts (it
+"ticks" the number of loop iterations), as it roughly corresponds with
+<code>ev_prepare</code> and <code>ev_check</code> calls.</p>
</dd>
<dt>unsigned int ev_backend (loop)</dt>
<dd>
<p>Returns a true value iff the watcher is pending, (i.e. it has outstanding
events but its callback has not yet been invoked). As long as a watcher
is pending (but not active) you must not call an init function on it (but
-<code>ev_TYPE_set</code> is safe) and you must make sure the watcher is available to
-libev (e.g. you cnanot <code>free ()</code> it).</p>
+<code>ev_TYPE_set</code> is safe), you must not change its priority, and you must
+make sure the watcher is available to libev (e.g. you cannot <code>free ()</code>
+it).</p>
</dd>
<dt>callback ev_cb (ev_TYPE *watcher)</dt>
<dd>
<p>Change the callback. You can change the callback at virtually any time
(modulo threads).</p>
</dd>
+ <dt>ev_set_priority (ev_TYPE *watcher, priority)</dt>
+ <dt>int ev_priority (ev_TYPE *watcher)</dt>
+ <dd>
+ <p>Set and query the priority of the watcher. The priority is a small
+integer between <code>EV_MAXPRI</code> (default: <code>2</code>) and <code>EV_MINPRI</code>
+(default: <code>-2</code>). Pending watchers with higher priority will be invoked
+before watchers with lower priority, but priority will not keep watchers
+from being executed (except for <code>ev_idle</code> watchers).</p>
+ <p>This means that priorities are <i>only</i> used for ordering callback
+invocation after new events have been received. This is useful, for
+example, to reduce latency after idling, or more often, to bind two
+watchers on the same event and make sure one is called first.</p>
+ <p>If you need to suppress invocation when higher priority events are pending
+you need to look at <code>ev_idle</code> watchers, which provide this functionality.</p>
+ <p>You <i>must not</i> change the priority of a watcher as long as it is active or
+pending.</p>
+ <p>The default priority used by watchers when no priority has been set is
+always <code>0</code>, which is supposed to not be too high and not be too low :).</p>
+ <p>Setting a priority outside the range of <code>EV_MINPRI</code> to <code>EV_MAXPRI</code> is
+fine, as long as you do not mind that the priority value you query might
+or might not have been adjusted to be within valid range.</p>
+ </dd>
+ <dt>ev_invoke (loop, ev_TYPE *watcher, int revents)</dt>
+ <dd>
+ <p>Invoke the <code>watcher</code> with the given <code>loop</code> and <code>revents</code>. Neither
+<code>loop</code> nor <code>revents</code> need to be valid as long as the watcher callback
+can deal with that fact.</p>
+ </dd>
+ <dt>int ev_clear_pending (loop, ev_TYPE *watcher)</dt>
+ <dd>
+ <p>If the watcher is pending, this function returns clears its pending status
+and returns its <code>revents</code> bitset (as if its callback was invoked). If the
+watcher isn't pending it does nothing and returns <code>0</code>.</p>
+ </dd>
</dl>
<code>EAGAIN</code> is far preferable to a program hanging until some data arrives.</p>
<p>If you cannot run the fd in non-blocking mode (for example you should not
play around with an Xlib connection), then you have to seperately re-test
-wether a file descriptor is really ready with a known-to-be good interface
+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>
<dl>
</div>
<h2 id="code_ev_idle_code_when_you_ve_got_no"><code>ev_idle</code> - when you've got nothing better to do...</h2>
<div id="code_ev_idle_code_when_you_ve_got_no-2">
-<p>Idle watchers trigger events when there are no other events are pending
-(prepare, check and other idle watchers do not count). That is, as long
-as your process is busy handling sockets or timeouts (or even signals,
-imagine) it will not be triggered. But when your process is idle all idle
-watchers are being called again and again, once per event loop iteration -
-until stopped, that is, or your process receives more events and becomes
-busy.</p>
+<p>Idle watchers trigger events when no other events of the same or higher
+priority are pending (prepare, check and other idle watchers do not
+count).</p>
+<p>That is, as long as your process is busy handling sockets or timeouts
+(or even signals, imagine) of the same or higher priority it will not be
+triggered. But when your process is idle (or only lower-priority watchers
+are pending), the idle watchers are being called once per event loop
+iteration - until stopped, that is, or your process receives more events
+and becomes busy again with higher priority stuff.</p>
<p>The most noteworthy effect is that as long as any idle watchers are
active, the process will not block when waiting for new events.</p>
<p>Apart from keeping your process non-blocking (which is a useful
static void
adns_prepare_cb (ev_loop *loop, ev_prepare *w, int revents)
{
- int timeout = 3600000;truct pollfd fds [nfd];
+ int timeout = 3600000;
+ struct pollfd fds [nfd];
// actual code will need to loop here and realloc etc.
adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
<pre> #include <ev++.h>
</pre>
-<p>(it is not installed by default). This automatically includes <cite>ev.h</cite>
-and puts all of its definitions (many of them macros) into the global
-namespace. All C++ specific things are put into the <code>ev</code> namespace.</p>
-<p>It should support all the same embedding options as <cite>ev.h</cite>, most notably
-<code>EV_MULTIPLICITY</code>.</p>
+<p>This automatically includes <cite>ev.h</cite> and puts all of its definitions (many
+of them macros) into the global namespace. All C++ specific things are
+put into the <code>ev</code> namespace. It should support all the same embedding
+options as <cite>ev.h</cite>, most notably <code>EV_MULTIPLICITY</code>.</p>
+<p>Care has been taken to keep the overhead low. The only data member the C++
+classes add (compared to plain C-style watchers) is the event loop pointer
+that the watcher is associated with (or no additional members at all if
+you disable <code>EV_MULTIPLICITY</code> when embedding libev).</p>
+<p>Currently, functions, and static and non-static member functions can be
+used as callbacks. Other types should be easy to add as long as they only
+need one additional pointer for context. If you need support for other
+types of functors please contact the author (preferably after implementing
+it).</p>
<p>Here is a list of things available in the <code>ev</code> namespace:</p>
<dl>
<dt><code>ev::READ</code>, <code>ev::WRITE</code> etc.</dt>
<p>All of those classes have these methods:</p>
<p>
<dl>
- <dt>ev::TYPE::TYPE (object *, object::method *)</dt>
- <dt>ev::TYPE::TYPE (object *, object::method *, struct ev_loop *)</dt>
+ <dt>ev::TYPE::TYPE ()</dt>
+ <dt>ev::TYPE::TYPE (struct ev_loop *)</dt>
<dt>ev::TYPE::~TYPE</dt>
<dd>
- <p>The constructor takes a pointer to an object and a method pointer to
-the event handler callback to call in this class. The constructor calls
-<code>ev_init</code> for you, which means you have to call the <code>set</code> method
-before starting it. If you do not specify a loop then the constructor
-automatically associates the default loop with this watcher.</p>
+ <p>The constructor (optionally) takes an event loop to associate the watcher
+with. If it is omitted, it will use <code>EV_DEFAULT</code>.</p>
+ <p>The constructor calls <code>ev_init</code> for you, which means you have to call the
+<code>set</code> method before starting it.</p>
+ <p>It will not set a callback, however: You have to call the templated <code>set</code>
+method to set a callback before you can start the watcher.</p>
+ <p>(The reason why you have to use a method is a limitation in C++ which does
+not allow explicit template arguments for constructors).</p>
<p>The destructor automatically stops the watcher if it is active.</p>
</dd>
+ <dt>w->set<class, &class::method> (object *)</dt>
+ <dd>
+ <p>This method sets the callback method to call. The method has to have a
+signature of <code>void (*)(ev_TYPE &, int)</code>, it receives the watcher as
+first argument and the <code>revents</code> as second. The object must be given as
+parameter and is stored in the <code>data</code> member of the watcher.</p>
+ <p>This method synthesizes efficient thunking code to call your method from
+the C callback that libev requires. If your compiler can inline your
+callback (i.e. it is visible to it at the place of the <code>set</code> call and
+your compiler is good :), then the method will be fully inlined into the
+thunking function, making it as fast as a direct C callback.</p>
+ <p>Example: simple class declaration and watcher initialisation</p>
+<pre> struct myclass
+ {
+ void io_cb (ev::io &w, int revents) { }
+ }
+
+ myclass obj;
+ ev::io iow;
+ iow.set <myclass, &myclass::io_cb> (&obj);
+
+</pre>
+ </dd>
+ <dt>w->set<function> (void *data = 0)</dt>
+ <dd>
+ <p>Also sets a callback, but uses a static method or plain function as
+callback. The optional <code>data</code> argument will be stored in the watcher's
+<code>data</code> member and is free for you to use.</p>
+ <p>The prototype of the <code>function</code> must be <code>void (*)(ev::TYPE &w, int)</code>.</p>
+ <p>See the method-<code>set</code> above for more details.</p>
+ <p>Example:</p>
+<pre> static void io_cb (ev::io &w, int revents) { }
+ iow.set <io_cb> ();
+
+</pre>
+ </dd>
<dt>w->set (struct ev_loop *)</dt>
<dd>
<p>Associates a different <code>struct ev_loop</code> with this watcher. You can only
<dt>w->set ([args])</dt>
<dd>
<p>Basically the same as <code>ev_TYPE_set</code>, with the same args. Must be
-called at least once. Unlike the C counterpart, an active watcher gets
-automatically stopped and restarted.</p>
+called at least once. Unlike the C counterpart, an active watcher gets
+automatically stopped and restarted when reconfiguring it with this
+method.</p>
</dd>
<dt>w->start ()</dt>
<dd>
- <p>Starts the watcher. Note that there is no <code>loop</code> argument as the
-constructor already takes the loop.</p>
+ <p>Starts the watcher. Note that there is no <code>loop</code> argument, as the
+constructor already stores the event loop.</p>
</dd>
<dt>w->stop ()</dt>
<dd>
}
myclass::myclass (int fd)
- : io (this, &myclass::io_cb),
- idle (this, &myclass::idle_cb)
{
+ io .set <myclass, &myclass::io_cb > (this);
+ idle.set <myclass, &myclass::idle_cb> (this);
+
io.start (fd, ev::READ);
}
<h1 id="MACRO_MAGIC">MACRO MAGIC</h1>
<div id="MACRO_MAGIC_CONTENT">
<p>Libev can be compiled with a variety of options, the most fundemantal is
-<code>EV_MULTIPLICITY</code>. This option determines wether (most) functions and
+<code>EV_MULTIPLICITY</code>. This option determines whether (most) functions and
callbacks have an initial <code>struct ev_loop *</code> argument.</p>
<p>To make it easier to write programs that cope with either variant, the
following macros are defined:</p>
loop, if multiple loops are supported ("ev loop default").</p>
</dd>
</dl>
-<p>Example: Declare and initialise a check watcher, working regardless of
-wether multiple loops are supported or not.</p>
+<p>Example: Declare and initialise a check watcher, utilising the above
+macros so it will work regardless of whether multiple loops are supported
+or not.</p>
<pre> static void
check_cb (EV_P_ ev_timer *w, int revents)
{
ev_check_start (EV_DEFAULT_ &check);
ev_loop (EV_DEFAULT_ 0);
-
-
-
</pre>
</div>
ev_win32.c required on win32 platforms only
- ev_select.c only when select backend is enabled (which is by default)
+ ev_select.c only when select backend is enabled (which is enabled by default)
ev_poll.c only when poll backend is enabled (disabled by default)
ev_epoll.c only when the epoll backend is enabled (disabled by default)
ev_kqueue.c only when the kqueue backend is enabled (disabled by default)
additional independent event loops. Otherwise there will be no support
for multiple event loops and there is no first event loop pointer
argument. Instead, all functions act on the single default loop.</p>
+ </dd>
+ <dt>EV_MINPRI</dt>
+ <dt>EV_MAXPRI</dt>
+ <dd>
+ <p>The range of allowed priorities. <code>EV_MINPRI</code> must be smaller or equal to
+<code>EV_MAXPRI</code>, but otherwise there are no non-obvious limitations. You can
+provide for more priorities by overriding those symbols (usually defined
+to be <code>-2</code> and <code>2</code>, respectively).</p>
+ <p>When doing priority-based operations, libev usually has to linearly search
+all the priorities, so having many of them (hundreds) uses a lot of space
+and time, so using the defaults of five priorities (-2 .. +2) is usually
+fine.</p>
+ <p>If your embedding app does not need any priorities, defining these both to
+<code>0</code> will save some memory and cpu.</p>
</dd>
<dt>EV_PERIODIC_ENABLE</dt>
<dd>
<p>If undefined or defined to be <code>1</code>, then periodic timers are supported. If
defined to be <code>0</code>, then they are not. Disabling them saves a few kB of
+code.</p>
+ </dd>
+ <dt>EV_IDLE_ENABLE</dt>
+ <dd>
+ <p>If undefined or defined to be <code>1</code>, then idle watchers are supported. If
+defined to be <code>0</code>, then they are not. Disabling them saves a few kB of
code.</p>
</dd>
<dt>EV_EMBED_ENABLE</dt>
will be compiled. It is pretty complex because it provides its own header
file.</p>
<p>The usage in rxvt-unicode is simpler. It has a <cite>ev_cpp.h</cite> header file
-that everybody includes and which overrides some autoconf choices:</p>
-<pre> #define EV_USE_POLL 0
+that everybody includes and which overrides some configure choices:</p>
+<pre> #define EV_MINIMAL 1
+ #define EV_USE_POLL 0
#define EV_MULTIPLICITY 0
- #define EV_PERIODICS 0
+ #define EV_PERIODIC_ENABLE 0
+ #define EV_STAT_ENABLE 0
+ #define EV_FORK_ENABLE 0
#define EV_CONFIG_H <config.h>
+ #define EV_MINPRI 0
+ #define EV_MAXPRI 0
#include "ev++.h"
<p>In this section the complexities of (many of) the algorithms used inside
libev will be explained. For complexity discussions about backends see the
documentation for <code>ev_default_init</code>.</p>
+ <p>All of the following are about amortised time: If an array needs to be
+extended, libev needs to realloc and move the whole array, but this
+happens asymptotically never with higher number of elements, so O(1) might
+mean it might do a lengthy realloc operation in rare cases, but on average
+it is much faster and asymptotically approaches constant time.</p>
<p>
<dl>
<dt>Starting and stopping timer/periodic watchers: O(log skipped_other_timers)</dt>
+ <dd>
+ <p>This means that, when you have a watcher that triggers in one hour and
+there are 100 watchers that would trigger before that then inserting will
+have to skip those 100 watchers.</p>
+ </dd>
<dt>Changing timer/periodic watchers (by autorepeat, again): O(log skipped_other_timers)</dt>
+ <dd>
+ <p>That means that for changing a timer costs less than removing/adding them
+as only the relative motion in the event queue has to be paid for.</p>
+ </dd>
<dt>Starting io/check/prepare/idle/signal/child watchers: O(1)</dt>
- <dt>Stopping check/prepare/idle watchers: O(1)</dt>
+ <dd>
+ <p>These just add the watcher into an array or at the head of a list.
+=item Stopping check/prepare/idle watchers: O(1)</p>
+ </dd>
<dt>Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))</dt>
+ <dd>
+ <p>These watchers are stored in lists then need to be walked to find the
+correct watcher to remove. The lists are usually short (you don't usually
+have many watchers waiting for the same fd or signal).</p>
+ </dd>
<dt>Finding the next timer per loop iteration: O(1)</dt>
<dt>Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)</dt>
+ <dd>
+ <p>A change means an I/O watcher gets started or stopped, which requires
+libev to recalculate its status (and possibly tell the kernel).</p>
+ </dd>
<dt>Activating one watcher: O(1)</dt>
+ <dt>Priority handling: O(number_of_priorities)</dt>
+ <dd>
+ <p>Priorities are implemented by allocating some space for each
+priority. When doing priority-based operations, libev usually has to
+linearly search all the priorities.</p>
+ </dd>
</dl>
</p>
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