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4<head> 4<head>
5 <title>libev</title> 5 <title>libev</title>
6 <meta name="description" content="Pod documentation for libev" /> 6 <meta name="description" content="Pod documentation for libev" />
7 <meta name="inputfile" content="&lt;standard input&gt;" /> 7 <meta name="inputfile" content="&lt;standard input&gt;" />
8 <meta name="outputfile" content="&lt;standard output&gt;" /> 8 <meta name="outputfile" content="&lt;standard output&gt;" />
9 <meta name="created" content="Fri Dec 7 19:03:06 2007" /> 9 <meta name="created" content="Fri Dec 7 21:19:14 2007" />
10 <meta name="generator" content="Pod::Xhtml 1.57" /> 10 <meta name="generator" content="Pod::Xhtml 1.57" />
11<link rel="stylesheet" href="http://res.tst.eu/pod.css"/></head> 11<link rel="stylesheet" href="http://res.tst.eu/pod.css"/></head>
12<body> 12<body>
13<div class="pod"> 13<div class="pod">
14<!-- INDEX START --> 14<!-- INDEX START -->
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119</pre> 119</pre>
120 120
121</div> 121</div>
122<h1 id="DESCRIPTION">DESCRIPTION</h1> 122<h1 id="DESCRIPTION">DESCRIPTION</h1>
123<div id="DESCRIPTION_CONTENT"> 123<div id="DESCRIPTION_CONTENT">
124<p>The newest version of this document is also available as a html-formatted
125web page you might find easier to navigate when reading it for the first
126time: <a href="http://cvs.schmorp.de/libev/ev.html">http://cvs.schmorp.de/libev/ev.html</a>.</p>
124<p>Libev is an event loop: you register interest in certain events (such as a 127<p>Libev is an event loop: you register interest in certain events (such as a
125file descriptor being readable or a timeout occuring), and it will manage 128file descriptor being readable or a timeout occuring), and it will manage
126these event sources and provide your program with events.</p> 129these event sources and provide your program with events.</p>
127<p>To do this, it must take more or less complete control over your process 130<p>To do this, it must take more or less complete control over your process
128(or thread) by executing the <i>event loop</i> handler, and will then 131(or thread) by executing the <i>event loop</i> handler, and will then
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1733the callback model to a model using method callbacks on objects.</p> 1736the callback model to a model using method callbacks on objects.</p>
1734<p>To use it,</p> 1737<p>To use it,</p>
1735<pre> #include &lt;ev++.h&gt; 1738<pre> #include &lt;ev++.h&gt;
1736 1739
1737</pre> 1740</pre>
1738<p>(it is not installed by default). This automatically includes <cite>ev.h</cite> 1741<p>This automatically includes <cite>ev.h</cite> and puts all of its definitions (many
1739and puts all of its definitions (many of them macros) into the global 1742of them macros) into the global namespace. All C++ specific things are
1740namespace. All C++ specific things are put into the <code>ev</code> namespace.</p> 1743put into the <code>ev</code> namespace. It should support all the same embedding
1741<p>It should support all the same embedding options as <cite>ev.h</cite>, most notably 1744options as <cite>ev.h</cite>, most notably <code>EV_MULTIPLICITY</code>.</p>
1742<code>EV_MULTIPLICITY</code>.</p> 1745<p>Care has been taken to keep the overhead low. The only data member the C++
1746classes add (compared to plain C-style watchers) is the event loop pointer
1747that the watcher is associated with (or no additional members at all if
1748you disable <code>EV_MULTIPLICITY</code> when embedding libev).</p>
1749<p>Currently, functions, and static and non-static member functions can be
1750used as callbacks. Other types should be easy to add as long as they only
1751need one additional pointer for context. If you need support for other
1752types of functors please contact the author (preferably after implementing
1753it).</p>
1743<p>Here is a list of things available in the <code>ev</code> namespace:</p> 1754<p>Here is a list of things available in the <code>ev</code> namespace:</p>
1744<dl> 1755<dl>
1745 <dt><code>ev::READ</code>, <code>ev::WRITE</code> etc.</dt> 1756 <dt><code>ev::READ</code>, <code>ev::WRITE</code> etc.</dt>
1746 <dd> 1757 <dd>
1747 <p>These are just enum values with the same values as the <code>EV_READ</code> etc. 1758 <p>These are just enum values with the same values as the <code>EV_READ</code> etc.
… …
1758which is called <code>ev::sig</code> to avoid clashes with the <code>signal</code> macro 1769which is called <code>ev::sig</code> to avoid clashes with the <code>signal</code> macro
1759defines by many implementations.</p> 1770defines by many implementations.</p>
1760 <p>All of those classes have these methods:</p> 1771 <p>All of those classes have these methods:</p>
1761 <p> 1772 <p>
1762 <dl> 1773 <dl>
1763 <dt>ev::TYPE::TYPE (object *, object::method *)</dt> 1774 <dt>ev::TYPE::TYPE ()</dt>
1764 <dt>ev::TYPE::TYPE (object *, object::method *, struct ev_loop *)</dt> 1775 <dt>ev::TYPE::TYPE (struct ev_loop *)</dt>
1765 <dt>ev::TYPE::~TYPE</dt> 1776 <dt>ev::TYPE::~TYPE</dt>
1766 <dd> 1777 <dd>
1767 <p>The constructor takes a pointer to an object and a method pointer to 1778 <p>The constructor (optionally) takes an event loop to associate the watcher
1768the event handler callback to call in this class. The constructor calls 1779with. If it is omitted, it will use <code>EV_DEFAULT</code>.</p>
1769<code>ev_init</code> for you, which means you have to call the <code>set</code> method 1780 <p>The constructor calls <code>ev_init</code> for you, which means you have to call the
1770before starting it. If you do not specify a loop then the constructor 1781<code>set</code> method before starting it.</p>
1771automatically associates the default loop with this watcher.</p> 1782 <p>It will not set a callback, however: You have to call the templated <code>set</code>
1783method to set a callback before you can start the watcher.</p>
1784 <p>(The reason why you have to use a method is a limitation in C++ which does
1785not allow explicit template arguments for constructors).</p>
1772 <p>The destructor automatically stops the watcher if it is active.</p> 1786 <p>The destructor automatically stops the watcher if it is active.</p>
1787 </dd>
1788 <dt>w-&gt;set&lt;class, &amp;class::method&gt; (object *)</dt>
1789 <dd>
1790 <p>This method sets the callback method to call. The method has to have a
1791signature of <code>void (*)(ev_TYPE &amp;, int)</code>, it receives the watcher as
1792first argument and the <code>revents</code> as second. The object must be given as
1793parameter and is stored in the <code>data</code> member of the watcher.</p>
1794 <p>This method synthesizes efficient thunking code to call your method from
1795the C callback that libev requires. If your compiler can inline your
1796callback (i.e. it is visible to it at the place of the <code>set</code> call and
1797your compiler is good :), then the method will be fully inlined into the
1798thunking function, making it as fast as a direct C callback.</p>
1799 <p>Example: simple class declaration and watcher initialisation</p>
1800<pre> struct myclass
1801 {
1802 void io_cb (ev::io &amp;w, int revents) { }
1803 }
1804
1805 myclass obj;
1806 ev::io iow;
1807 iow.set &lt;myclass, &amp;myclass::io_cb&gt; (&amp;obj);
1808
1809</pre>
1810 </dd>
1811 <dt>w-&gt;set (void (*function)(watcher &amp;w, int), void *data = 0)</dt>
1812 <dd>
1813 <p>Also sets a callback, but uses a static method or plain function as
1814callback. The optional <code>data</code> argument will be stored in the watcher's
1815<code>data</code> member and is free for you to use.</p>
1816 <p>See the method-<code>set</code> above for more details.</p>
1773 </dd> 1817 </dd>
1774 <dt>w-&gt;set (struct ev_loop *)</dt> 1818 <dt>w-&gt;set (struct ev_loop *)</dt>
1775 <dd> 1819 <dd>
1776 <p>Associates a different <code>struct ev_loop</code> with this watcher. You can only 1820 <p>Associates a different <code>struct ev_loop</code> with this watcher. You can only
1777do this when the watcher is inactive (and not pending either).</p> 1821do this when the watcher is inactive (and not pending either).</p>
1778 </dd> 1822 </dd>
1779 <dt>w-&gt;set ([args])</dt> 1823 <dt>w-&gt;set ([args])</dt>
1780 <dd> 1824 <dd>
1781 <p>Basically the same as <code>ev_TYPE_set</code>, with the same args. Must be 1825 <p>Basically the same as <code>ev_TYPE_set</code>, with the same args. Must be
1782called at least once. Unlike the C counterpart, an active watcher gets 1826called at least once. Unlike the C counterpart, an active watcher gets
1783automatically stopped and restarted.</p> 1827automatically stopped and restarted when reconfiguring it with this
1828method.</p>
1784 </dd> 1829 </dd>
1785 <dt>w-&gt;start ()</dt> 1830 <dt>w-&gt;start ()</dt>
1786 <dd> 1831 <dd>
1787 <p>Starts the watcher. Note that there is no <code>loop</code> argument as the 1832 <p>Starts the watcher. Note that there is no <code>loop</code> argument, as the
1788constructor already takes the loop.</p> 1833constructor already stores the event loop.</p>
1789 </dd> 1834 </dd>
1790 <dt>w-&gt;stop ()</dt> 1835 <dt>w-&gt;stop ()</dt>
1791 <dd> 1836 <dd>
1792 <p>Stops the watcher if it is active. Again, no <code>loop</code> argument.</p> 1837 <p>Stops the watcher if it is active. Again, no <code>loop</code> argument.</p>
1793 </dd> 1838 </dd>
… …
1817 1862
1818 myclass (); 1863 myclass ();
1819 } 1864 }
1820 1865
1821 myclass::myclass (int fd) 1866 myclass::myclass (int fd)
1822 : io (this, &amp;myclass::io_cb),
1823 idle (this, &amp;myclass::idle_cb)
1824 { 1867 {
1868 io .set &lt;myclass, &amp;myclass::io_cb &gt; (this);
1869 idle.set &lt;myclass, &amp;myclass::idle_cb&gt; (this);
1870
1825 io.start (fd, ev::READ); 1871 io.start (fd, ev::READ);
1826 } 1872 }
1827 1873
1828 1874
1829 1875
… …
2109 <p>If undefined or defined to <code>1</code>, then all event-loop-specific functions 2155 <p>If undefined or defined to <code>1</code>, then all event-loop-specific functions
2110will have the <code>struct ev_loop *</code> as first argument, and you can create 2156will have the <code>struct ev_loop *</code> as first argument, and you can create
2111additional independent event loops. Otherwise there will be no support 2157additional independent event loops. Otherwise there will be no support
2112for multiple event loops and there is no first event loop pointer 2158for multiple event loops and there is no first event loop pointer
2113argument. Instead, all functions act on the single default loop.</p> 2159argument. Instead, all functions act on the single default loop.</p>
2160 </dd>
2161 <dt>EV_MINPRI</dt>
2162 <dt>EV_MAXPRI</dt>
2163 <dd>
2164 <p>The range of allowed priorities. <code>EV_MINPRI</code> must be smaller or equal to
2165<code>EV_MAXPRI</code>, but otherwise there are no non-obvious limitations. You can
2166provide for more priorities by overriding those symbols (usually defined
2167to be <code>-2</code> and <code>2</code>, respectively).</p>
2168 <p>When doing priority-based operations, libev usually has to linearly search
2169all the priorities, so having many of them (hundreds) uses a lot of space
2170and time, so using the defaults of five priorities (-2 .. +2) is usually
2171fine.</p>
2172 <p>If your embedding app does not need any priorities, defining these both to
2173<code>0</code> will save some memory and cpu.</p>
2114 </dd> 2174 </dd>
2115 <dt>EV_PERIODIC_ENABLE</dt> 2175 <dt>EV_PERIODIC_ENABLE</dt>
2116 <dd> 2176 <dd>
2117 <p>If undefined or defined to be <code>1</code>, then periodic timers are supported. If 2177 <p>If undefined or defined to be <code>1</code>, then periodic timers are supported. If
2118defined to be <code>0</code>, then they are not. Disabling them saves a few kB of 2178defined to be <code>0</code>, then they are not. Disabling them saves a few kB of
… …
2222<h1 id="COMPLEXITIES">COMPLEXITIES</h1> 2282<h1 id="COMPLEXITIES">COMPLEXITIES</h1>
2223<div id="COMPLEXITIES_CONTENT"> 2283<div id="COMPLEXITIES_CONTENT">
2224 <p>In this section the complexities of (many of) the algorithms used inside 2284 <p>In this section the complexities of (many of) the algorithms used inside
2225libev will be explained. For complexity discussions about backends see the 2285libev will be explained. For complexity discussions about backends see the
2226documentation for <code>ev_default_init</code>.</p> 2286documentation for <code>ev_default_init</code>.</p>
2287 <p>All of the following are about amortised time: If an array needs to be
2288extended, libev needs to realloc and move the whole array, but this
2289happens asymptotically never with higher number of elements, so O(1) might
2290mean it might do a lengthy realloc operation in rare cases, but on average
2291it is much faster and asymptotically approaches constant time.</p>
2227 <p> 2292 <p>
2228 <dl> 2293 <dl>
2229 <dt>Starting and stopping timer/periodic watchers: O(log skipped_other_timers)</dt> 2294 <dt>Starting and stopping timer/periodic watchers: O(log skipped_other_timers)</dt>
2295 <dd>
2296 <p>This means that, when you have a watcher that triggers in one hour and
2297there are 100 watchers that would trigger before that then inserting will
2298have to skip those 100 watchers.</p>
2299 </dd>
2230 <dt>Changing timer/periodic watchers (by autorepeat, again): O(log skipped_other_timers)</dt> 2300 <dt>Changing timer/periodic watchers (by autorepeat, again): O(log skipped_other_timers)</dt>
2301 <dd>
2302 <p>That means that for changing a timer costs less than removing/adding them
2303as only the relative motion in the event queue has to be paid for.</p>
2304 </dd>
2231 <dt>Starting io/check/prepare/idle/signal/child watchers: O(1)</dt> 2305 <dt>Starting io/check/prepare/idle/signal/child watchers: O(1)</dt>
2306 <dd>
2307 <p>These just add the watcher into an array or at the head of a list.
2232 <dt>Stopping check/prepare/idle watchers: O(1)</dt> 2308=item Stopping check/prepare/idle watchers: O(1)</p>
2309 </dd>
2233 <dt>Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))</dt> 2310 <dt>Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))</dt>
2311 <dd>
2312 <p>These watchers are stored in lists then need to be walked to find the
2313correct watcher to remove. The lists are usually short (you don't usually
2314have many watchers waiting for the same fd or signal).</p>
2315 </dd>
2234 <dt>Finding the next timer per loop iteration: O(1)</dt> 2316 <dt>Finding the next timer per loop iteration: O(1)</dt>
2235 <dt>Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)</dt> 2317 <dt>Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)</dt>
2318 <dd>
2319 <p>A change means an I/O watcher gets started or stopped, which requires
2320libev to recalculate its status (and possibly tell the kernel).</p>
2321 </dd>
2236 <dt>Activating one watcher: O(1)</dt> 2322 <dt>Activating one watcher: O(1)</dt>
2323 <dt>Priority handling: O(number_of_priorities)</dt>
2324 <dd>
2325 <p>Priorities are implemented by allocating some space for each
2326priority. When doing priority-based operations, libev usually has to
2327linearly search all the priorities.</p>
2328 </dd>
2237 </dl> 2329 </dl>
2238 </p> 2330 </p>
2239 2331
2240 2332
2241 2333

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