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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="<standard input>" /> |
7 | <meta name="inputfile" content="<standard input>" /> |
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8 | <meta name="outputfile" content="<standard output>" /> |
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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"> |
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124 | <p>The newest version of this document is also available as a html-formatted |
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125 | web page you might find easier to navigate when reading it for the first |
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126 | time: <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 |
125 | file descriptor being readable or a timeout occuring), and it will manage |
128 | file descriptor being readable or a timeout occuring), and it will manage |
126 | these event sources and provide your program with events.</p> |
129 | these 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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333 | <p>Instead of calling <code>ev_default_fork</code> or <code>ev_loop_fork</code> manually after |
336 | <p>Instead of calling <code>ev_default_fork</code> or <code>ev_loop_fork</code> manually after |
334 | a fork, you can also make libev check for a fork in each iteration by |
337 | a fork, you can also make libev check for a fork in each iteration by |
335 | enabling this flag.</p> |
338 | enabling this flag.</p> |
336 | <p>This works by calling <code>getpid ()</code> on every iteration of the loop, |
339 | <p>This works by calling <code>getpid ()</code> on every iteration of the loop, |
337 | and thus this might slow down your event loop if you do a lot of loop |
340 | and thus this might slow down your event loop if you do a lot of loop |
338 | iterations and little real work, but is usually not noticable (on my |
341 | iterations and little real work, but is usually not noticeable (on my |
339 | Linux system for example, <code>getpid</code> is actually a simple 5-insn sequence |
342 | Linux system for example, <code>getpid</code> is actually a simple 5-insn sequence |
340 | without a syscall and thus <i>very</i> fast, but my Linux system also has |
343 | without a syscall and thus <i>very</i> fast, but my Linux system also has |
341 | <code>pthread_atfork</code> which is even faster).</p> |
344 | <code>pthread_atfork</code> which is even faster).</p> |
342 | <p>The big advantage of this flag is that you can forget about fork (and |
345 | <p>The big advantage of this flag is that you can forget about fork (and |
343 | forget about forgetting to tell libev about forking) when you use this |
346 | forget about forgetting to tell libev about forking) when you use this |
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480 | <dt>ev_loop_fork (loop)</dt> |
483 | <dt>ev_loop_fork (loop)</dt> |
481 | <dd> |
484 | <dd> |
482 | <p>Like <code>ev_default_fork</code>, but acts on an event loop created by |
485 | <p>Like <code>ev_default_fork</code>, but acts on an event loop created by |
483 | <code>ev_loop_new</code>. Yes, you have to call this on every allocated event loop |
486 | <code>ev_loop_new</code>. Yes, you have to call this on every allocated event loop |
484 | after fork, and how you do this is entirely your own problem.</p> |
487 | after fork, and how you do this is entirely your own problem.</p> |
|
|
488 | </dd> |
|
|
489 | <dt>unsigned int ev_loop_count (loop)</dt> |
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|
490 | <dd> |
|
|
491 | <p>Returns the count of loop iterations for the loop, which is identical to |
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|
492 | the number of times libev did poll for new events. It starts at <code>0</code> and |
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493 | happily wraps around with enough iterations.</p> |
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494 | <p>This value can sometimes be useful as a generation counter of sorts (it |
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495 | "ticks" the number of loop iterations), as it roughly corresponds with |
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496 | <code>ev_prepare</code> and <code>ev_check</code> calls.</p> |
485 | </dd> |
497 | </dd> |
486 | <dt>unsigned int ev_backend (loop)</dt> |
498 | <dt>unsigned int ev_backend (loop)</dt> |
487 | <dd> |
499 | <dd> |
488 | <p>Returns one of the <code>EVBACKEND_*</code> flags indicating the event backend in |
500 | <p>Returns one of the <code>EVBACKEND_*</code> flags indicating the event backend in |
489 | use.</p> |
501 | use.</p> |
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769 | <dt>ev_cb_set (ev_TYPE *watcher, callback)</dt> |
781 | <dt>ev_cb_set (ev_TYPE *watcher, callback)</dt> |
770 | <dd> |
782 | <dd> |
771 | <p>Change the callback. You can change the callback at virtually any time |
783 | <p>Change the callback. You can change the callback at virtually any time |
772 | (modulo threads).</p> |
784 | (modulo threads).</p> |
773 | </dd> |
785 | </dd> |
|
|
786 | <dt>ev_set_priority (ev_TYPE *watcher, priority)</dt> |
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|
787 | <dt>int ev_priority (ev_TYPE *watcher)</dt> |
|
|
788 | <dd> |
|
|
789 | <p>Set and query the priority of the watcher. The priority is a small |
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790 | integer between <code>EV_MAXPRI</code> (default: <code>2</code>) and <code>EV_MINPRI</code> |
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791 | (default: <code>-2</code>). Pending watchers with higher priority will be invoked |
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792 | before watchers with lower priority, but priority will not keep watchers |
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793 | from being executed (except for <code>ev_idle</code> watchers).</p> |
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794 | <p>This means that priorities are <i>only</i> used for ordering callback |
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795 | invocation after new events have been received. This is useful, for |
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796 | example, to reduce latency after idling, or more often, to bind two |
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797 | watchers on the same event and make sure one is called first.</p> |
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798 | <p>If you need to suppress invocation when higher priority events are pending |
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799 | you need to look at <code>ev_idle</code> watchers, which provide this functionality.</p> |
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800 | <p>The default priority used by watchers when no priority has been set is |
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801 | always <code>0</code>, which is supposed to not be too high and not be too low :).</p> |
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802 | <p>Setting a priority outside the range of <code>EV_MINPRI</code> to <code>EV_MAXPRI</code> is |
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803 | fine, as long as you do not mind that the priority value you query might |
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804 | or might not have been adjusted to be within valid range.</p> |
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805 | </dd> |
774 | </dl> |
806 | </dl> |
775 | |
807 | |
776 | |
808 | |
777 | |
809 | |
778 | |
810 | |
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888 | this situation even with a relatively standard program structure. Thus |
920 | this situation even with a relatively standard program structure. Thus |
889 | it is best to always use non-blocking I/O: An extra <code>read</code>(2) returning |
921 | it is best to always use non-blocking I/O: An extra <code>read</code>(2) returning |
890 | <code>EAGAIN</code> is far preferable to a program hanging until some data arrives.</p> |
922 | <code>EAGAIN</code> is far preferable to a program hanging until some data arrives.</p> |
891 | <p>If you cannot run the fd in non-blocking mode (for example you should not |
923 | <p>If you cannot run the fd in non-blocking mode (for example you should not |
892 | play around with an Xlib connection), then you have to seperately re-test |
924 | play around with an Xlib connection), then you have to seperately re-test |
893 | wether a file descriptor is really ready with a known-to-be good interface |
925 | whether a file descriptor is really ready with a known-to-be good interface |
894 | such as poll (fortunately in our Xlib example, Xlib already does this on |
926 | such as poll (fortunately in our Xlib example, Xlib already does this on |
895 | its own, so its quite safe to use).</p> |
927 | its own, so its quite safe to use).</p> |
896 | <dl> |
928 | <dl> |
897 | <dt>ev_io_init (ev_io *, callback, int fd, int events)</dt> |
929 | <dt>ev_io_init (ev_io *, callback, int fd, int events)</dt> |
898 | <dt>ev_io_set (ev_io *, int fd, int events)</dt> |
930 | <dt>ev_io_set (ev_io *, int fd, int events)</dt> |
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1358 | </pre> |
1390 | </pre> |
1359 | |
1391 | |
1360 | </div> |
1392 | </div> |
1361 | <h2 id="code_ev_idle_code_when_you_ve_got_no"><code>ev_idle</code> - when you've got nothing better to do...</h2> |
1393 | <h2 id="code_ev_idle_code_when_you_ve_got_no"><code>ev_idle</code> - when you've got nothing better to do...</h2> |
1362 | <div id="code_ev_idle_code_when_you_ve_got_no-2"> |
1394 | <div id="code_ev_idle_code_when_you_ve_got_no-2"> |
1363 | <p>Idle watchers trigger events when there are no other events are pending |
1395 | <p>Idle watchers trigger events when no other events of the same or higher |
1364 | (prepare, check and other idle watchers do not count). That is, as long |
1396 | priority are pending (prepare, check and other idle watchers do not |
1365 | as your process is busy handling sockets or timeouts (or even signals, |
1397 | count).</p> |
1366 | imagine) it will not be triggered. But when your process is idle all idle |
1398 | <p>That is, as long as your process is busy handling sockets or timeouts |
1367 | watchers are being called again and again, once per event loop iteration - |
1399 | (or even signals, imagine) of the same or higher priority it will not be |
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1400 | triggered. But when your process is idle (or only lower-priority watchers |
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1401 | are pending), the idle watchers are being called once per event loop |
1368 | until stopped, that is, or your process receives more events and becomes |
1402 | iteration - until stopped, that is, or your process receives more events |
1369 | busy.</p> |
1403 | and becomes busy again with higher priority stuff.</p> |
1370 | <p>The most noteworthy effect is that as long as any idle watchers are |
1404 | <p>The most noteworthy effect is that as long as any idle watchers are |
1371 | active, the process will not block when waiting for new events.</p> |
1405 | active, the process will not block when waiting for new events.</p> |
1372 | <p>Apart from keeping your process non-blocking (which is a useful |
1406 | <p>Apart from keeping your process non-blocking (which is a useful |
1373 | effect on its own sometimes), idle watchers are a good place to do |
1407 | effect on its own sometimes), idle watchers are a good place to do |
1374 | "pseudo-background processing", or delay processing stuff to after the |
1408 | "pseudo-background processing", or delay processing stuff to after the |
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1464 | |
1498 | |
1465 | // create io watchers for each fd and a timer before blocking |
1499 | // create io watchers for each fd and a timer before blocking |
1466 | static void |
1500 | static void |
1467 | adns_prepare_cb (ev_loop *loop, ev_prepare *w, int revents) |
1501 | adns_prepare_cb (ev_loop *loop, ev_prepare *w, int revents) |
1468 | { |
1502 | { |
1469 | int timeout = 3600000;truct pollfd fds [nfd]; |
1503 | int timeout = 3600000; |
|
|
1504 | struct pollfd fds [nfd]; |
1470 | // actual code will need to loop here and realloc etc. |
1505 | // actual code will need to loop here and realloc etc. |
1471 | adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ())); |
1506 | adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ())); |
1472 | |
1507 | |
1473 | /* the callback is illegal, but won't be called as we stop during check */ |
1508 | /* the callback is illegal, but won't be called as we stop during check */ |
1474 | ev_timer_init (&tw, 0, timeout * 1e-3); |
1509 | ev_timer_init (&tw, 0, timeout * 1e-3); |
… | |
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1800 | |
1835 | |
1801 | </div> |
1836 | </div> |
1802 | <h1 id="MACRO_MAGIC">MACRO MAGIC</h1> |
1837 | <h1 id="MACRO_MAGIC">MACRO MAGIC</h1> |
1803 | <div id="MACRO_MAGIC_CONTENT"> |
1838 | <div id="MACRO_MAGIC_CONTENT"> |
1804 | <p>Libev can be compiled with a variety of options, the most fundemantal is |
1839 | <p>Libev can be compiled with a variety of options, the most fundemantal is |
1805 | <code>EV_MULTIPLICITY</code>. This option determines wether (most) functions and |
1840 | <code>EV_MULTIPLICITY</code>. This option determines whether (most) functions and |
1806 | callbacks have an initial <code>struct ev_loop *</code> argument.</p> |
1841 | callbacks have an initial <code>struct ev_loop *</code> argument.</p> |
1807 | <p>To make it easier to write programs that cope with either variant, the |
1842 | <p>To make it easier to write programs that cope with either variant, the |
1808 | following macros are defined:</p> |
1843 | following macros are defined:</p> |
1809 | <dl> |
1844 | <dl> |
1810 | <dt><code>EV_A</code>, <code>EV_A_</code></dt> |
1845 | <dt><code>EV_A</code>, <code>EV_A_</code></dt> |
… | |
… | |
1840 | <p>Similar to the other two macros, this gives you the value of the default |
1875 | <p>Similar to the other two macros, this gives you the value of the default |
1841 | loop, if multiple loops are supported ("ev loop default").</p> |
1876 | loop, if multiple loops are supported ("ev loop default").</p> |
1842 | </dd> |
1877 | </dd> |
1843 | </dl> |
1878 | </dl> |
1844 | <p>Example: Declare and initialise a check watcher, utilising the above |
1879 | <p>Example: Declare and initialise a check watcher, utilising the above |
1845 | macros so it will work regardless of wether multiple loops are supported |
1880 | macros so it will work regardless of whether multiple loops are supported |
1846 | or not.</p> |
1881 | or not.</p> |
1847 | <pre> static void |
1882 | <pre> static void |
1848 | check_cb (EV_P_ ev_timer *w, int revents) |
1883 | check_cb (EV_P_ ev_timer *w, int revents) |
1849 | { |
1884 | { |
1850 | ev_check_stop (EV_A_ w); |
1885 | ev_check_stop (EV_A_ w); |
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… | |
2078 | will have the <code>struct ev_loop *</code> as first argument, and you can create |
2113 | will have the <code>struct ev_loop *</code> as first argument, and you can create |
2079 | additional independent event loops. Otherwise there will be no support |
2114 | additional independent event loops. Otherwise there will be no support |
2080 | for multiple event loops and there is no first event loop pointer |
2115 | for multiple event loops and there is no first event loop pointer |
2081 | argument. Instead, all functions act on the single default loop.</p> |
2116 | argument. Instead, all functions act on the single default loop.</p> |
2082 | </dd> |
2117 | </dd> |
|
|
2118 | <dt>EV_MINPRI</dt> |
|
|
2119 | <dt>EV_MAXPRI</dt> |
|
|
2120 | <dd> |
|
|
2121 | <p>The range of allowed priorities. <code>EV_MINPRI</code> must be smaller or equal to |
|
|
2122 | <code>EV_MAXPRI</code>, but otherwise there are no non-obvious limitations. You can |
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2123 | provide for more priorities by overriding those symbols (usually defined |
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2124 | to be <code>-2</code> and <code>2</code>, respectively).</p> |
|
|
2125 | <p>When doing priority-based operations, libev usually has to linearly search |
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2126 | all the priorities, so having many of them (hundreds) uses a lot of space |
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|
2127 | and time, so using the defaults of five priorities (-2 .. +2) is usually |
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2128 | fine.</p> |
|
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2129 | <p>If your embedding app does not need any priorities, defining these both to |
|
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2130 | <code>0</code> will save some memory and cpu.</p> |
|
|
2131 | </dd> |
2083 | <dt>EV_PERIODIC_ENABLE</dt> |
2132 | <dt>EV_PERIODIC_ENABLE</dt> |
2084 | <dd> |
2133 | <dd> |
2085 | <p>If undefined or defined to be <code>1</code>, then periodic timers are supported. If |
2134 | <p>If undefined or defined to be <code>1</code>, then periodic timers are supported. If |
|
|
2135 | defined to be <code>0</code>, then they are not. Disabling them saves a few kB of |
|
|
2136 | code.</p> |
|
|
2137 | </dd> |
|
|
2138 | <dt>EV_IDLE_ENABLE</dt> |
|
|
2139 | <dd> |
|
|
2140 | <p>If undefined or defined to be <code>1</code>, then idle watchers are supported. If |
2086 | defined to be <code>0</code>, then they are not. Disabling them saves a few kB of |
2141 | defined to be <code>0</code>, then they are not. Disabling them saves a few kB of |
2087 | code.</p> |
2142 | code.</p> |
2088 | </dd> |
2143 | </dd> |
2089 | <dt>EV_EMBED_ENABLE</dt> |
2144 | <dt>EV_EMBED_ENABLE</dt> |
2090 | <dd> |
2145 | <dd> |
… | |
… | |
2184 | <h1 id="COMPLEXITIES">COMPLEXITIES</h1> |
2239 | <h1 id="COMPLEXITIES">COMPLEXITIES</h1> |
2185 | <div id="COMPLEXITIES_CONTENT"> |
2240 | <div id="COMPLEXITIES_CONTENT"> |
2186 | <p>In this section the complexities of (many of) the algorithms used inside |
2241 | <p>In this section the complexities of (many of) the algorithms used inside |
2187 | libev will be explained. For complexity discussions about backends see the |
2242 | libev will be explained. For complexity discussions about backends see the |
2188 | documentation for <code>ev_default_init</code>.</p> |
2243 | documentation for <code>ev_default_init</code>.</p> |
|
|
2244 | <p>All of the following are about amortised time: If an array needs to be |
|
|
2245 | extended, libev needs to realloc and move the whole array, but this |
|
|
2246 | happens asymptotically never with higher number of elements, so O(1) might |
|
|
2247 | mean it might do a lengthy realloc operation in rare cases, but on average |
|
|
2248 | it is much faster and asymptotically approaches constant time.</p> |
2189 | <p> |
2249 | <p> |
2190 | <dl> |
2250 | <dl> |
2191 | <dt>Starting and stopping timer/periodic watchers: O(log skipped_other_timers)</dt> |
2251 | <dt>Starting and stopping timer/periodic watchers: O(log skipped_other_timers)</dt> |
|
|
2252 | <dd> |
|
|
2253 | <p>This means that, when you have a watcher that triggers in one hour and |
|
|
2254 | there are 100 watchers that would trigger before that then inserting will |
|
|
2255 | have to skip those 100 watchers.</p> |
|
|
2256 | </dd> |
2192 | <dt>Changing timer/periodic watchers (by autorepeat, again): O(log skipped_other_timers)</dt> |
2257 | <dt>Changing timer/periodic watchers (by autorepeat, again): O(log skipped_other_timers)</dt> |
|
|
2258 | <dd> |
|
|
2259 | <p>That means that for changing a timer costs less than removing/adding them |
|
|
2260 | as only the relative motion in the event queue has to be paid for.</p> |
|
|
2261 | </dd> |
2193 | <dt>Starting io/check/prepare/idle/signal/child watchers: O(1)</dt> |
2262 | <dt>Starting io/check/prepare/idle/signal/child watchers: O(1)</dt> |
|
|
2263 | <dd> |
|
|
2264 | <p>These just add the watcher into an array or at the head of a list. |
2194 | <dt>Stopping check/prepare/idle watchers: O(1)</dt> |
2265 | =item Stopping check/prepare/idle watchers: O(1)</p> |
|
|
2266 | </dd> |
2195 | <dt>Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))</dt> |
2267 | <dt>Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))</dt> |
|
|
2268 | <dd> |
|
|
2269 | <p>These watchers are stored in lists then need to be walked to find the |
|
|
2270 | correct watcher to remove. The lists are usually short (you don't usually |
|
|
2271 | have many watchers waiting for the same fd or signal).</p> |
|
|
2272 | </dd> |
2196 | <dt>Finding the next timer per loop iteration: O(1)</dt> |
2273 | <dt>Finding the next timer per loop iteration: O(1)</dt> |
2197 | <dt>Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)</dt> |
2274 | <dt>Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)</dt> |
|
|
2275 | <dd> |
|
|
2276 | <p>A change means an I/O watcher gets started or stopped, which requires |
|
|
2277 | libev to recalculate its status (and possibly tell the kernel).</p> |
|
|
2278 | </dd> |
2198 | <dt>Activating one watcher: O(1)</dt> |
2279 | <dt>Activating one watcher: O(1)</dt> |
|
|
2280 | <dt>Priority handling: O(number_of_priorities)</dt> |
|
|
2281 | <dd> |
|
|
2282 | <p>Priorities are implemented by allocating some space for each |
|
|
2283 | priority. When doing priority-based operations, libev usually has to |
|
|
2284 | linearly search all the priorities.</p> |
|
|
2285 | </dd> |
2199 | </dl> |
2286 | </dl> |
2200 | </p> |
2287 | </p> |
2201 | |
2288 | |
2202 | |
2289 | |
2203 | |
2290 | |