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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 17:49:47 2007" /> 9 <meta name="created" content="Sat Dec 8 15:27:35 2007" />
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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
… …
766 <dt>bool ev_is_pending (ev_TYPE *watcher)</dt> 769 <dt>bool ev_is_pending (ev_TYPE *watcher)</dt>
767 <dd> 770 <dd>
768 <p>Returns a true value iff the watcher is pending, (i.e. it has outstanding 771 <p>Returns a true value iff the watcher is pending, (i.e. it has outstanding
769events but its callback has not yet been invoked). As long as a watcher 772events but its callback has not yet been invoked). As long as a watcher
770is pending (but not active) you must not call an init function on it (but 773is pending (but not active) you must not call an init function on it (but
771<code>ev_TYPE_set</code> is safe) and you must make sure the watcher is available to 774<code>ev_TYPE_set</code> is safe), you must not change its priority, and you must
772libev (e.g. you cnanot <code>free ()</code> it).</p> 775make sure the watcher is available to libev (e.g. you cannot <code>free ()</code>
776it).</p>
773 </dd> 777 </dd>
774 <dt>callback ev_cb (ev_TYPE *watcher)</dt> 778 <dt>callback ev_cb (ev_TYPE *watcher)</dt>
775 <dd> 779 <dd>
776 <p>Returns the callback currently set on the watcher.</p> 780 <p>Returns the callback currently set on the watcher.</p>
777 </dd> 781 </dd>
… …
792invocation after new events have been received. This is useful, for 796invocation after new events have been received. This is useful, for
793example, to reduce latency after idling, or more often, to bind two 797example, to reduce latency after idling, or more often, to bind two
794watchers on the same event and make sure one is called first.</p> 798watchers on the same event and make sure one is called first.</p>
795 <p>If you need to suppress invocation when higher priority events are pending 799 <p>If you need to suppress invocation when higher priority events are pending
796you need to look at <code>ev_idle</code> watchers, which provide this functionality.</p> 800you need to look at <code>ev_idle</code> watchers, which provide this functionality.</p>
801 <p>You <i>must not</i> change the priority of a watcher as long as it is active or
802pending.</p>
797 <p>The default priority used by watchers when no priority has been set is 803 <p>The default priority used by watchers when no priority has been set is
798always <code>0</code>, which is supposed to not be too high and not be too low :).</p> 804always <code>0</code>, which is supposed to not be too high and not be too low :).</p>
799 <p>Setting a priority outside the range of <code>EV_MINPRI</code> to <code>EV_MAXPRI</code> is 805 <p>Setting a priority outside the range of <code>EV_MINPRI</code> to <code>EV_MAXPRI</code> is
800fine, as long as you do not mind that the priority value you query might 806fine, as long as you do not mind that the priority value you query might
801or might not have been adjusted to be within valid range.</p> 807or might not have been adjusted to be within valid range.</p>
808 </dd>
809 <dt>ev_invoke (loop, ev_TYPE *watcher, int revents)</dt>
810 <dd>
811 <p>Invoke the <code>watcher</code> with the given <code>loop</code> and <code>revents</code>. Neither
812<code>loop</code> nor <code>revents</code> need to be valid as long as the watcher callback
813can deal with that fact.</p>
814 </dd>
815 <dt>int ev_clear_pending (loop, ev_TYPE *watcher)</dt>
816 <dd>
817 <p>If the watcher is pending, this function returns clears its pending status
818and returns its <code>revents</code> bitset (as if its callback was invoked). If the
819watcher isn't pending it does nothing and returns <code>0</code>.</p>
802 </dd> 820 </dd>
803</dl> 821</dl>
804 822
805 823
806 824
… …
917this situation even with a relatively standard program structure. Thus 935this situation even with a relatively standard program structure. Thus
918it is best to always use non-blocking I/O: An extra <code>read</code>(2) returning 936it is best to always use non-blocking I/O: An extra <code>read</code>(2) returning
919<code>EAGAIN</code> is far preferable to a program hanging until some data arrives.</p> 937<code>EAGAIN</code> is far preferable to a program hanging until some data arrives.</p>
920<p>If you cannot run the fd in non-blocking mode (for example you should not 938<p>If you cannot run the fd in non-blocking mode (for example you should not
921play around with an Xlib connection), then you have to seperately re-test 939play around with an Xlib connection), then you have to seperately re-test
922wether a file descriptor is really ready with a known-to-be good interface 940whether a file descriptor is really ready with a known-to-be good interface
923such as poll (fortunately in our Xlib example, Xlib already does this on 941such as poll (fortunately in our Xlib example, Xlib already does this on
924its own, so its quite safe to use).</p> 942its own, so its quite safe to use).</p>
925<dl> 943<dl>
926 <dt>ev_io_init (ev_io *, callback, int fd, int events)</dt> 944 <dt>ev_io_init (ev_io *, callback, int fd, int events)</dt>
927 <dt>ev_io_set (ev_io *, int fd, int events)</dt> 945 <dt>ev_io_set (ev_io *, int fd, int events)</dt>
… …
1733the callback model to a model using method callbacks on objects.</p> 1751the callback model to a model using method callbacks on objects.</p>
1734<p>To use it,</p> 1752<p>To use it,</p>
1735<pre> #include &lt;ev++.h&gt; 1753<pre> #include &lt;ev++.h&gt;
1736 1754
1737</pre> 1755</pre>
1738<p>(it is not installed by default). This automatically includes <cite>ev.h</cite> 1756<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 1757of 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> 1758put 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 1759options as <cite>ev.h</cite>, most notably <code>EV_MULTIPLICITY</code>.</p>
1742<code>EV_MULTIPLICITY</code>.</p> 1760<p>Care has been taken to keep the overhead low. The only data member the C++
1761classes add (compared to plain C-style watchers) is the event loop pointer
1762that the watcher is associated with (or no additional members at all if
1763you disable <code>EV_MULTIPLICITY</code> when embedding libev).</p>
1764<p>Currently, functions, and static and non-static member functions can be
1765used as callbacks. Other types should be easy to add as long as they only
1766need one additional pointer for context. If you need support for other
1767types of functors please contact the author (preferably after implementing
1768it).</p>
1743<p>Here is a list of things available in the <code>ev</code> namespace:</p> 1769<p>Here is a list of things available in the <code>ev</code> namespace:</p>
1744<dl> 1770<dl>
1745 <dt><code>ev::READ</code>, <code>ev::WRITE</code> etc.</dt> 1771 <dt><code>ev::READ</code>, <code>ev::WRITE</code> etc.</dt>
1746 <dd> 1772 <dd>
1747 <p>These are just enum values with the same values as the <code>EV_READ</code> etc. 1773 <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 1784which is called <code>ev::sig</code> to avoid clashes with the <code>signal</code> macro
1759defines by many implementations.</p> 1785defines by many implementations.</p>
1760 <p>All of those classes have these methods:</p> 1786 <p>All of those classes have these methods:</p>
1761 <p> 1787 <p>
1762 <dl> 1788 <dl>
1763 <dt>ev::TYPE::TYPE (object *, object::method *)</dt> 1789 <dt>ev::TYPE::TYPE ()</dt>
1764 <dt>ev::TYPE::TYPE (object *, object::method *, struct ev_loop *)</dt> 1790 <dt>ev::TYPE::TYPE (struct ev_loop *)</dt>
1765 <dt>ev::TYPE::~TYPE</dt> 1791 <dt>ev::TYPE::~TYPE</dt>
1766 <dd> 1792 <dd>
1767 <p>The constructor takes a pointer to an object and a method pointer to 1793 <p>The constructor (optionally) takes an event loop to associate the watcher
1768the event handler callback to call in this class. The constructor calls 1794with. 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 1795 <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 1796<code>set</code> method before starting it.</p>
1771automatically associates the default loop with this watcher.</p> 1797 <p>It will not set a callback, however: You have to call the templated <code>set</code>
1798method to set a callback before you can start the watcher.</p>
1799 <p>(The reason why you have to use a method is a limitation in C++ which does
1800not allow explicit template arguments for constructors).</p>
1772 <p>The destructor automatically stops the watcher if it is active.</p> 1801 <p>The destructor automatically stops the watcher if it is active.</p>
1802 </dd>
1803 <dt>w-&gt;set&lt;class, &amp;class::method&gt; (object *)</dt>
1804 <dd>
1805 <p>This method sets the callback method to call. The method has to have a
1806signature of <code>void (*)(ev_TYPE &amp;, int)</code>, it receives the watcher as
1807first argument and the <code>revents</code> as second. The object must be given as
1808parameter and is stored in the <code>data</code> member of the watcher.</p>
1809 <p>This method synthesizes efficient thunking code to call your method from
1810the C callback that libev requires. If your compiler can inline your
1811callback (i.e. it is visible to it at the place of the <code>set</code> call and
1812your compiler is good :), then the method will be fully inlined into the
1813thunking function, making it as fast as a direct C callback.</p>
1814 <p>Example: simple class declaration and watcher initialisation</p>
1815<pre> struct myclass
1816 {
1817 void io_cb (ev::io &amp;w, int revents) { }
1818 }
1819
1820 myclass obj;
1821 ev::io iow;
1822 iow.set &lt;myclass, &amp;myclass::io_cb&gt; (&amp;obj);
1823
1824</pre>
1825 </dd>
1826 <dt>w-&gt;set&lt;function&gt; (void *data = 0)</dt>
1827 <dd>
1828 <p>Also sets a callback, but uses a static method or plain function as
1829callback. The optional <code>data</code> argument will be stored in the watcher's
1830<code>data</code> member and is free for you to use.</p>
1831 <p>The prototype of the <code>function</code> must be <code>void (*)(ev::TYPE &amp;w, int)</code>.</p>
1832 <p>See the method-<code>set</code> above for more details.</p>
1833 <p>Example:</p>
1834<pre> static void io_cb (ev::io &amp;w, int revents) { }
1835 iow.set &lt;io_cb&gt; ();
1836
1837</pre>
1773 </dd> 1838 </dd>
1774 <dt>w-&gt;set (struct ev_loop *)</dt> 1839 <dt>w-&gt;set (struct ev_loop *)</dt>
1775 <dd> 1840 <dd>
1776 <p>Associates a different <code>struct ev_loop</code> with this watcher. You can only 1841 <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> 1842do this when the watcher is inactive (and not pending either).</p>
1778 </dd> 1843 </dd>
1779 <dt>w-&gt;set ([args])</dt> 1844 <dt>w-&gt;set ([args])</dt>
1780 <dd> 1845 <dd>
1781 <p>Basically the same as <code>ev_TYPE_set</code>, with the same args. Must be 1846 <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 1847called at least once. Unlike the C counterpart, an active watcher gets
1783automatically stopped and restarted.</p> 1848automatically stopped and restarted when reconfiguring it with this
1849method.</p>
1784 </dd> 1850 </dd>
1785 <dt>w-&gt;start ()</dt> 1851 <dt>w-&gt;start ()</dt>
1786 <dd> 1852 <dd>
1787 <p>Starts the watcher. Note that there is no <code>loop</code> argument as the 1853 <p>Starts the watcher. Note that there is no <code>loop</code> argument, as the
1788constructor already takes the loop.</p> 1854constructor already stores the event loop.</p>
1789 </dd> 1855 </dd>
1790 <dt>w-&gt;stop ()</dt> 1856 <dt>w-&gt;stop ()</dt>
1791 <dd> 1857 <dd>
1792 <p>Stops the watcher if it is active. Again, no <code>loop</code> argument.</p> 1858 <p>Stops the watcher if it is active. Again, no <code>loop</code> argument.</p>
1793 </dd> 1859 </dd>
… …
1817 1883
1818 myclass (); 1884 myclass ();
1819 } 1885 }
1820 1886
1821 myclass::myclass (int fd) 1887 myclass::myclass (int fd)
1822 : io (this, &amp;myclass::io_cb),
1823 idle (this, &amp;myclass::idle_cb)
1824 { 1888 {
1889 io .set &lt;myclass, &amp;myclass::io_cb &gt; (this);
1890 idle.set &lt;myclass, &amp;myclass::idle_cb&gt; (this);
1891
1825 io.start (fd, ev::READ); 1892 io.start (fd, ev::READ);
1826 } 1893 }
1827 1894
1828 1895
1829 1896
… …
1832 1899
1833</div> 1900</div>
1834<h1 id="MACRO_MAGIC">MACRO MAGIC</h1> 1901<h1 id="MACRO_MAGIC">MACRO MAGIC</h1>
1835<div id="MACRO_MAGIC_CONTENT"> 1902<div id="MACRO_MAGIC_CONTENT">
1836<p>Libev can be compiled with a variety of options, the most fundemantal is 1903<p>Libev can be compiled with a variety of options, the most fundemantal is
1837<code>EV_MULTIPLICITY</code>. This option determines wether (most) functions and 1904<code>EV_MULTIPLICITY</code>. This option determines whether (most) functions and
1838callbacks have an initial <code>struct ev_loop *</code> argument.</p> 1905callbacks have an initial <code>struct ev_loop *</code> argument.</p>
1839<p>To make it easier to write programs that cope with either variant, the 1906<p>To make it easier to write programs that cope with either variant, the
1840following macros are defined:</p> 1907following macros are defined:</p>
1841<dl> 1908<dl>
1842 <dt><code>EV_A</code>, <code>EV_A_</code></dt> 1909 <dt><code>EV_A</code>, <code>EV_A_</code></dt>
… …
1872 <p>Similar to the other two macros, this gives you the value of the default 1939 <p>Similar to the other two macros, this gives you the value of the default
1873loop, if multiple loops are supported (&quot;ev loop default&quot;).</p> 1940loop, if multiple loops are supported (&quot;ev loop default&quot;).</p>
1874 </dd> 1941 </dd>
1875</dl> 1942</dl>
1876<p>Example: Declare and initialise a check watcher, utilising the above 1943<p>Example: Declare and initialise a check watcher, utilising the above
1877macros so it will work regardless of wether multiple loops are supported 1944macros so it will work regardless of whether multiple loops are supported
1878or not.</p> 1945or not.</p>
1879<pre> static void 1946<pre> static void
1880 check_cb (EV_P_ ev_timer *w, int revents) 1947 check_cb (EV_P_ ev_timer *w, int revents)
1881 { 1948 {
1882 ev_check_stop (EV_A_ w); 1949 ev_check_stop (EV_A_ w);
… …
2109 <p>If undefined or defined to <code>1</code>, then all event-loop-specific functions 2176 <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 2177will have the <code>struct ev_loop *</code> as first argument, and you can create
2111additional independent event loops. Otherwise there will be no support 2178additional independent event loops. Otherwise there will be no support
2112for multiple event loops and there is no first event loop pointer 2179for multiple event loops and there is no first event loop pointer
2113argument. Instead, all functions act on the single default loop.</p> 2180argument. Instead, all functions act on the single default loop.</p>
2181 </dd>
2182 <dt>EV_MINPRI</dt>
2183 <dt>EV_MAXPRI</dt>
2184 <dd>
2185 <p>The range of allowed priorities. <code>EV_MINPRI</code> must be smaller or equal to
2186<code>EV_MAXPRI</code>, but otherwise there are no non-obvious limitations. You can
2187provide for more priorities by overriding those symbols (usually defined
2188to be <code>-2</code> and <code>2</code>, respectively).</p>
2189 <p>When doing priority-based operations, libev usually has to linearly search
2190all the priorities, so having many of them (hundreds) uses a lot of space
2191and time, so using the defaults of five priorities (-2 .. +2) is usually
2192fine.</p>
2193 <p>If your embedding app does not need any priorities, defining these both to
2194<code>0</code> will save some memory and cpu.</p>
2114 </dd> 2195 </dd>
2115 <dt>EV_PERIODIC_ENABLE</dt> 2196 <dt>EV_PERIODIC_ENABLE</dt>
2116 <dd> 2197 <dd>
2117 <p>If undefined or defined to be <code>1</code>, then periodic timers are supported. If 2198 <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 2199defined to be <code>0</code>, then they are not. Disabling them saves a few kB of
… …
2222<h1 id="COMPLEXITIES">COMPLEXITIES</h1> 2303<h1 id="COMPLEXITIES">COMPLEXITIES</h1>
2223<div id="COMPLEXITIES_CONTENT"> 2304<div id="COMPLEXITIES_CONTENT">
2224 <p>In this section the complexities of (many of) the algorithms used inside 2305 <p>In this section the complexities of (many of) the algorithms used inside
2225libev will be explained. For complexity discussions about backends see the 2306libev will be explained. For complexity discussions about backends see the
2226documentation for <code>ev_default_init</code>.</p> 2307documentation for <code>ev_default_init</code>.</p>
2308 <p>All of the following are about amortised time: If an array needs to be
2309extended, libev needs to realloc and move the whole array, but this
2310happens asymptotically never with higher number of elements, so O(1) might
2311mean it might do a lengthy realloc operation in rare cases, but on average
2312it is much faster and asymptotically approaches constant time.</p>
2227 <p> 2313 <p>
2228 <dl> 2314 <dl>
2229 <dt>Starting and stopping timer/periodic watchers: O(log skipped_other_timers)</dt> 2315 <dt>Starting and stopping timer/periodic watchers: O(log skipped_other_timers)</dt>
2316 <dd>
2317 <p>This means that, when you have a watcher that triggers in one hour and
2318there are 100 watchers that would trigger before that then inserting will
2319have to skip those 100 watchers.</p>
2320 </dd>
2230 <dt>Changing timer/periodic watchers (by autorepeat, again): O(log skipped_other_timers)</dt> 2321 <dt>Changing timer/periodic watchers (by autorepeat, again): O(log skipped_other_timers)</dt>
2322 <dd>
2323 <p>That means that for changing a timer costs less than removing/adding them
2324as only the relative motion in the event queue has to be paid for.</p>
2325 </dd>
2231 <dt>Starting io/check/prepare/idle/signal/child watchers: O(1)</dt> 2326 <dt>Starting io/check/prepare/idle/signal/child watchers: O(1)</dt>
2327 <dd>
2328 <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> 2329=item Stopping check/prepare/idle watchers: O(1)</p>
2330 </dd>
2233 <dt>Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))</dt> 2331 <dt>Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))</dt>
2332 <dd>
2333 <p>These watchers are stored in lists then need to be walked to find the
2334correct watcher to remove. The lists are usually short (you don't usually
2335have many watchers waiting for the same fd or signal).</p>
2336 </dd>
2234 <dt>Finding the next timer per loop iteration: O(1)</dt> 2337 <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> 2338 <dt>Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)</dt>
2339 <dd>
2340 <p>A change means an I/O watcher gets started or stopped, which requires
2341libev to recalculate its status (and possibly tell the kernel).</p>
2342 </dd>
2236 <dt>Activating one watcher: O(1)</dt> 2343 <dt>Activating one watcher: O(1)</dt>
2344 <dt>Priority handling: O(number_of_priorities)</dt>
2345 <dd>
2346 <p>Priorities are implemented by allocating some space for each
2347priority. When doing priority-based operations, libev usually has to
2348linearly search all the priorities.</p>
2349 </dd>
2237 </dl> 2350 </dl>
2238 </p> 2351 </p>
2239 2352
2240 2353
2241 2354

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