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<!-- INDEX START --> |
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<h3 id="TOP">Index</h3> |
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|
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<ul><li><a href="#NAME">NAME</a></li> |
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<li><a href="#SYNOPSIS">SYNOPSIS</a></li> |
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<li><a href="#DESCRIPTION">DESCRIPTION</a></li> |
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<li><a href="#FEATURES">FEATURES</a></li> |
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<li><a href="#CONVENTIONS">CONVENTIONS</a></li> |
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<li><a href="#TIME_REPRESENTATION">TIME REPRESENTATION</a></li> |
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<li><a href="#GLOBAL_FUNCTIONS">GLOBAL FUNCTIONS</a></li> |
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<li><a href="#FUNCTIONS_CONTROLLING_THE_EVENT_LOOP">FUNCTIONS CONTROLLING THE EVENT LOOP</a></li> |
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<li><a href="#ANATOMY_OF_A_WATCHER">ANATOMY OF A WATCHER</a> |
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<ul><li><a href="#ASSOCIATING_CUSTOM_DATA_WITH_A_WATCH">ASSOCIATING CUSTOM DATA WITH A WATCHER</a></li> |
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</ul> |
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</li> |
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<li><a href="#WATCHER_TYPES">WATCHER TYPES</a> |
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<ul><li><a href="#code_ev_io_code_is_this_file_descrip"><code>ev_io</code> - is this file descriptor readable or writable</a></li> |
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<li><a href="#code_ev_timer_code_relative_and_opti"><code>ev_timer</code> - relative and optionally recurring timeouts</a></li> |
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<li><a href="#code_ev_periodic_code_to_cron_or_not"><code>ev_periodic</code> - to cron or not to cron</a></li> |
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<li><a href="#code_ev_signal_code_signal_me_when_a"><code>ev_signal</code> - signal me when a signal gets signalled</a></li> |
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<li><a href="#code_ev_child_code_wait_for_pid_stat"><code>ev_child</code> - wait for pid status changes</a></li> |
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<li><a href="#code_ev_idle_code_when_you_ve_got_no"><code>ev_idle</code> - when you've got nothing better to do</a></li> |
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<li><a href="#code_ev_prepare_code_and_code_ev_che"><code>ev_prepare</code> and <code>ev_check</code> - customise your event loop</a></li> |
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</ul> |
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</li> |
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<li><a href="#OTHER_FUNCTIONS">OTHER FUNCTIONS</a></li> |
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<li><a href="#LIBEVENT_EMULATION">LIBEVENT EMULATION</a></li> |
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<li><a href="#C_SUPPORT">C++ SUPPORT</a></li> |
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<li><a href="#AUTHOR">AUTHOR</a> |
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</li> |
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</ul><hr /> |
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<!-- INDEX END --> |
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|
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<h1 id="NAME">NAME</h1><p><a href="#TOP" class="toplink">Top</a></p> |
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<div id="NAME_CONTENT"> |
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<p>libev - a high performance full-featured event loop written in C</p> |
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|
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</div> |
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<h1 id="SYNOPSIS">SYNOPSIS</h1><p><a href="#TOP" class="toplink">Top</a></p> |
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<div id="SYNOPSIS_CONTENT"> |
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<pre> #include <ev.h> |
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|
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</pre> |
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|
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</div> |
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<h1 id="DESCRIPTION">DESCRIPTION</h1><p><a href="#TOP" class="toplink">Top</a></p> |
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<div id="DESCRIPTION_CONTENT"> |
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<p>Libev is an event loop: you register interest in certain events (such as a |
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file descriptor being readable or a timeout occuring), and it will manage |
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these event sources and provide your program with events.</p> |
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<p>To do this, it must take more or less complete control over your process |
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(or thread) by executing the <i>event loop</i> handler, and will then |
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communicate events via a callback mechanism.</p> |
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<p>You register interest in certain events by registering so-called <i>event |
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watchers</i>, which are relatively small C structures you initialise with the |
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details of the event, and then hand it over to libev by <i>starting</i> the |
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watcher.</p> |
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|
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</div> |
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<h1 id="FEATURES">FEATURES</h1><p><a href="#TOP" class="toplink">Top</a></p> |
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<div id="FEATURES_CONTENT"> |
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<p>Libev supports select, poll, the linux-specific epoll and the bsd-specific |
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kqueue mechanisms for file descriptor events, relative timers, absolute |
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timers with customised rescheduling, signal events, process status change |
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events (related to SIGCHLD), and event watchers dealing with the event |
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loop mechanism itself (idle, prepare and check watchers). It also is quite |
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fast (see this <a href="http://libev.schmorp.de/bench.html">benchmark</a> comparing |
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it to libevent for example).</p> |
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|
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</div> |
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<h1 id="CONVENTIONS">CONVENTIONS</h1><p><a href="#TOP" class="toplink">Top</a></p> |
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<div id="CONVENTIONS_CONTENT"> |
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<p>Libev is very configurable. In this manual the default configuration |
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will be described, which supports multiple event loops. For more info |
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about various configuration options please have a look at the file |
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<cite>README.embed</cite> in the libev distribution. If libev was configured without |
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support for multiple event loops, then all functions taking an initial |
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argument of name <code>loop</code> (which is always of type <code>struct ev_loop *</code>) |
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will not have this argument.</p> |
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|
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</div> |
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<h1 id="TIME_REPRESENTATION">TIME REPRESENTATION</h1><p><a href="#TOP" class="toplink">Top</a></p> |
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<div id="TIME_REPRESENTATION_CONTENT"> |
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<p>Libev represents time as a single floating point number, representing the |
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(fractional) number of seconds since the (POSIX) epoch (somewhere near |
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the beginning of 1970, details are complicated, don't ask). This type is |
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called <code>ev_tstamp</code>, which is what you should use too. It usually aliases |
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to the <code>double</code> type in C, and when you need to do any calculations on |
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it, you should treat it as such.</p> |
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|
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|
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|
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|
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|
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</div> |
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<h1 id="GLOBAL_FUNCTIONS">GLOBAL FUNCTIONS</h1><p><a href="#TOP" class="toplink">Top</a></p> |
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<div id="GLOBAL_FUNCTIONS_CONTENT"> |
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<p>These functions can be called anytime, even before initialising the |
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library in any way.</p> |
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<dl> |
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<dt>ev_tstamp ev_time ()</dt> |
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<dd> |
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<p>Returns the current time as libev would use it. Please note that the |
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<code>ev_now</code> function is usually faster and also often returns the timestamp |
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you actually want to know.</p> |
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</dd> |
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<dt>int ev_version_major ()</dt> |
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<dt>int ev_version_minor ()</dt> |
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<dd> |
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<p>You can find out the major and minor version numbers of the library |
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you linked against by calling the functions <code>ev_version_major</code> and |
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<code>ev_version_minor</code>. If you want, you can compare against the global |
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symbols <code>EV_VERSION_MAJOR</code> and <code>EV_VERSION_MINOR</code>, which specify the |
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version of the library your program was compiled against.</p> |
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<p>Usually, it's a good idea to terminate if the major versions mismatch, |
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as this indicates an incompatible change. Minor versions are usually |
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compatible to older versions, so a larger minor version alone is usually |
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not a problem.</p> |
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<p>Example: make sure we haven't accidentally been linked against the wrong |
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version:</p> |
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<pre> assert (("libev version mismatch", |
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ev_version_major () == EV_VERSION_MAJOR |
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&& ev_version_minor () >= EV_VERSION_MINOR)); |
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|
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</pre> |
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</dd> |
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<dt>unsigned int ev_supported_backends ()</dt> |
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<dd> |
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<p>Return the set of all backends (i.e. their corresponding <code>EV_BACKEND_*</code> |
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value) compiled into this binary of libev (independent of their |
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availability on the system you are running on). See <code>ev_default_loop</code> for |
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a description of the set values.</p> |
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<p>Example: make sure we have the epoll method, because yeah this is cool and |
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a must have and can we have a torrent of it please!!!11</p> |
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<pre> assert (("sorry, no epoll, no sex", |
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ev_supported_backends () & EVBACKEND_EPOLL)); |
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|
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</pre> |
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</dd> |
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<dt>unsigned int ev_recommended_backends ()</dt> |
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<dd> |
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<p>Return the set of all backends compiled into this binary of libev and also |
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recommended for this platform. This set is often smaller than the one |
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returned by <code>ev_supported_backends</code>, as for example kqueue is broken on |
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most BSDs and will not be autodetected unless you explicitly request it |
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(assuming you know what you are doing). This is the set of backends that |
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libev will probe for if you specify no backends explicitly.</p> |
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</dd> |
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<dt>ev_set_allocator (void *(*cb)(void *ptr, long size))</dt> |
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<dd> |
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<p>Sets the allocation function to use (the prototype is similar to the |
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realloc C function, the semantics are identical). It is used to allocate |
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and free memory (no surprises here). If it returns zero when memory |
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needs to be allocated, the library might abort or take some potentially |
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destructive action. The default is your system realloc function.</p> |
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<p>You could override this function in high-availability programs to, say, |
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free some memory if it cannot allocate memory, to use a special allocator, |
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or even to sleep a while and retry until some memory is available.</p> |
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<p>Example: replace the libev allocator with one that waits a bit and then |
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retries: better than mine).</p> |
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<pre> static void * |
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persistent_realloc (void *ptr, long size) |
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{ |
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for (;;) |
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{ |
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void *newptr = realloc (ptr, size); |
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|
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if (newptr) |
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return newptr; |
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|
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sleep (60); |
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} |
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} |
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|
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... |
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ev_set_allocator (persistent_realloc); |
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|
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</pre> |
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</dd> |
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<dt>ev_set_syserr_cb (void (*cb)(const char *msg));</dt> |
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<dd> |
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<p>Set the callback function to call on a retryable syscall error (such |
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as failed select, poll, epoll_wait). The message is a printable string |
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indicating the system call or subsystem causing the problem. If this |
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callback is set, then libev will expect it to remedy the sitution, no |
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matter what, when it returns. That is, libev will generally retry the |
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requested operation, or, if the condition doesn't go away, do bad stuff |
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(such as abort).</p> |
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<p>Example: do the same thing as libev does internally:</p> |
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<pre> static void |
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fatal_error (const char *msg) |
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{ |
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perror (msg); |
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abort (); |
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} |
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|
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... |
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ev_set_syserr_cb (fatal_error); |
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|
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</pre> |
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</dd> |
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</dl> |
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|
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</div> |
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<h1 id="FUNCTIONS_CONTROLLING_THE_EVENT_LOOP">FUNCTIONS CONTROLLING THE EVENT LOOP</h1><p><a href="#TOP" class="toplink">Top</a></p> |
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<div id="FUNCTIONS_CONTROLLING_THE_EVENT_LOOP-2"> |
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<p>An event loop is described by a <code>struct ev_loop *</code>. The library knows two |
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types of such loops, the <i>default</i> loop, which supports signals and child |
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events, and dynamically created loops which do not.</p> |
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<p>If you use threads, a common model is to run the default event loop |
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in your main thread (or in a separate thread) and for each thread you |
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create, you also create another event loop. Libev itself does no locking |
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whatsoever, so if you mix calls to the same event loop in different |
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threads, make sure you lock (this is usually a bad idea, though, even if |
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done correctly, because it's hideous and inefficient).</p> |
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<dl> |
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<dt>struct ev_loop *ev_default_loop (unsigned int flags)</dt> |
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<dd> |
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<p>This will initialise the default event loop if it hasn't been initialised |
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yet and return it. If the default loop could not be initialised, returns |
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false. If it already was initialised it simply returns it (and ignores the |
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flags. If that is troubling you, check <code>ev_backend ()</code> afterwards).</p> |
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<p>If you don't know what event loop to use, use the one returned from this |
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function.</p> |
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<p>The flags argument can be used to specify special behaviour or specific |
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backends to use, and is usually specified as <code>0</code> (or <code>EVFLAG_AUTO</code>).</p> |
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<p>The following flags are supported:</p> |
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<p> |
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<dl> |
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<dt><code>EVFLAG_AUTO</code></dt> |
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<dd> |
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<p>The default flags value. Use this if you have no clue (it's the right |
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thing, believe me).</p> |
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</dd> |
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<dt><code>EVFLAG_NOENV</code></dt> |
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<dd> |
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<p>If this flag bit is ored into the flag value (or the program runs setuid |
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or setgid) then libev will <i>not</i> look at the environment variable |
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<code>LIBEV_FLAGS</code>. Otherwise (the default), this environment variable will |
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override the flags completely if it is found in the environment. This is |
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useful to try out specific backends to test their performance, or to work |
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around bugs.</p> |
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</dd> |
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<dt><code>EVBACKEND_SELECT</code> (value 1, portable select backend)</dt> |
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<dd> |
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<p>This is your standard select(2) backend. Not <i>completely</i> standard, as |
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libev tries to roll its own fd_set with no limits on the number of fds, |
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but if that fails, expect a fairly low limit on the number of fds when |
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using this backend. It doesn't scale too well (O(highest_fd)), but its usually |
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the fastest backend for a low number of fds.</p> |
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</dd> |
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<dt><code>EVBACKEND_POLL</code> (value 2, poll backend, available everywhere except on windows)</dt> |
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<dd> |
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<p>And this is your standard poll(2) backend. It's more complicated than |
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select, but handles sparse fds better and has no artificial limit on the |
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number of fds you can use (except it will slow down considerably with a |
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lot of inactive fds). It scales similarly to select, i.e. O(total_fds).</p> |
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</dd> |
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<dt><code>EVBACKEND_EPOLL</code> (value 4, Linux)</dt> |
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<dd> |
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<p>For few fds, this backend is a bit little slower than poll and select, |
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but it scales phenomenally better. While poll and select usually scale like |
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O(total_fds) where n is the total number of fds (or the highest fd), epoll scales |
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either O(1) or O(active_fds).</p> |
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<p>While stopping and starting an I/O watcher in the same iteration will |
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result in some caching, there is still a syscall per such incident |
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(because the fd could point to a different file description now), so its |
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best to avoid that. Also, dup()ed file descriptors might not work very |
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well if you register events for both fds.</p> |
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<p>Please note that epoll sometimes generates spurious notifications, so you |
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need to use non-blocking I/O or other means to avoid blocking when no data |
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(or space) is available.</p> |
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</dd> |
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<dt><code>EVBACKEND_KQUEUE</code> (value 8, most BSD clones)</dt> |
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<dd> |
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<p>Kqueue deserves special mention, as at the time of this writing, it |
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was broken on all BSDs except NetBSD (usually it doesn't work with |
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anything but sockets and pipes, except on Darwin, where of course its |
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completely useless). For this reason its not being "autodetected" |
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unless you explicitly specify it explicitly in the flags (i.e. using |
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<code>EVBACKEND_KQUEUE</code>).</p> |
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<p>It scales in the same way as the epoll backend, but the interface to the |
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kernel is more efficient (which says nothing about its actual speed, of |
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course). While starting and stopping an I/O watcher does not cause an |
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extra syscall as with epoll, it still adds up to four event changes per |
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incident, so its best to avoid that.</p> |
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</dd> |
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<dt><code>EVBACKEND_DEVPOLL</code> (value 16, Solaris 8)</dt> |
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<dd> |
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<p>This is not implemented yet (and might never be).</p> |
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</dd> |
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<dt><code>EVBACKEND_PORT</code> (value 32, Solaris 10)</dt> |
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<dd> |
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<p>This uses the Solaris 10 port mechanism. As with everything on Solaris, |
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it's really slow, but it still scales very well (O(active_fds)).</p> |
309 |
<p>Please note that solaris ports can result in a lot of spurious |
310 |
notifications, so you need to use non-blocking I/O or other means to avoid |
311 |
blocking when no data (or space) is available.</p> |
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</dd> |
313 |
<dt><code>EVBACKEND_ALL</code></dt> |
314 |
<dd> |
315 |
<p>Try all backends (even potentially broken ones that wouldn't be tried |
316 |
with <code>EVFLAG_AUTO</code>). Since this is a mask, you can do stuff such as |
317 |
<code>EVBACKEND_ALL & ~EVBACKEND_KQUEUE</code>.</p> |
318 |
</dd> |
319 |
</dl> |
320 |
</p> |
321 |
<p>If one or more of these are ored into the flags value, then only these |
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backends will be tried (in the reverse order as given here). If none are |
323 |
specified, most compiled-in backend will be tried, usually in reverse |
324 |
order of their flag values :)</p> |
325 |
<p>The most typical usage is like this:</p> |
326 |
<pre> if (!ev_default_loop (0)) |
327 |
fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?"); |
328 |
|
329 |
</pre> |
330 |
<p>Restrict libev to the select and poll backends, and do not allow |
331 |
environment settings to be taken into account:</p> |
332 |
<pre> ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV); |
333 |
|
334 |
</pre> |
335 |
<p>Use whatever libev has to offer, but make sure that kqueue is used if |
336 |
available (warning, breaks stuff, best use only with your own private |
337 |
event loop and only if you know the OS supports your types of fds):</p> |
338 |
<pre> ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE); |
339 |
|
340 |
</pre> |
341 |
</dd> |
342 |
<dt>struct ev_loop *ev_loop_new (unsigned int flags)</dt> |
343 |
<dd> |
344 |
<p>Similar to <code>ev_default_loop</code>, but always creates a new event loop that is |
345 |
always distinct from the default loop. Unlike the default loop, it cannot |
346 |
handle signal and child watchers, and attempts to do so will be greeted by |
347 |
undefined behaviour (or a failed assertion if assertions are enabled).</p> |
348 |
<p>Example: try to create a event loop that uses epoll and nothing else.</p> |
349 |
<pre> struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV); |
350 |
if (!epoller) |
351 |
fatal ("no epoll found here, maybe it hides under your chair"); |
352 |
|
353 |
</pre> |
354 |
</dd> |
355 |
<dt>ev_default_destroy ()</dt> |
356 |
<dd> |
357 |
<p>Destroys the default loop again (frees all memory and kernel state |
358 |
etc.). This stops all registered event watchers (by not touching them in |
359 |
any way whatsoever, although you cannot rely on this :).</p> |
360 |
</dd> |
361 |
<dt>ev_loop_destroy (loop)</dt> |
362 |
<dd> |
363 |
<p>Like <code>ev_default_destroy</code>, but destroys an event loop created by an |
364 |
earlier call to <code>ev_loop_new</code>.</p> |
365 |
</dd> |
366 |
<dt>ev_default_fork ()</dt> |
367 |
<dd> |
368 |
<p>This function reinitialises the kernel state for backends that have |
369 |
one. Despite the name, you can call it anytime, but it makes most sense |
370 |
after forking, in either the parent or child process (or both, but that |
371 |
again makes little sense).</p> |
372 |
<p>You <i>must</i> call this function in the child process after forking if and |
373 |
only if you want to use the event library in both processes. If you just |
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fork+exec, you don't have to call it.</p> |
375 |
<p>The function itself is quite fast and it's usually not a problem to call |
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it just in case after a fork. To make this easy, the function will fit in |
377 |
quite nicely into a call to <code>pthread_atfork</code>:</p> |
378 |
<pre> pthread_atfork (0, 0, ev_default_fork); |
379 |
|
380 |
</pre> |
381 |
<p>At the moment, <code>EVBACKEND_SELECT</code> and <code>EVBACKEND_POLL</code> are safe to use |
382 |
without calling this function, so if you force one of those backends you |
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do not need to care.</p> |
384 |
</dd> |
385 |
<dt>ev_loop_fork (loop)</dt> |
386 |
<dd> |
387 |
<p>Like <code>ev_default_fork</code>, but acts on an event loop created by |
388 |
<code>ev_loop_new</code>. Yes, you have to call this on every allocated event loop |
389 |
after fork, and how you do this is entirely your own problem.</p> |
390 |
</dd> |
391 |
<dt>unsigned int ev_backend (loop)</dt> |
392 |
<dd> |
393 |
<p>Returns one of the <code>EVBACKEND_*</code> flags indicating the event backend in |
394 |
use.</p> |
395 |
</dd> |
396 |
<dt>ev_tstamp ev_now (loop)</dt> |
397 |
<dd> |
398 |
<p>Returns the current "event loop time", which is the time the event loop |
399 |
received events and started processing them. This timestamp does not |
400 |
change as long as callbacks are being processed, and this is also the base |
401 |
time used for relative timers. You can treat it as the timestamp of the |
402 |
event occuring (or more correctly, libev finding out about it).</p> |
403 |
</dd> |
404 |
<dt>ev_loop (loop, int flags)</dt> |
405 |
<dd> |
406 |
<p>Finally, this is it, the event handler. This function usually is called |
407 |
after you initialised all your watchers and you want to start handling |
408 |
events.</p> |
409 |
<p>If the flags argument is specified as <code>0</code>, it will not return until |
410 |
either no event watchers are active anymore or <code>ev_unloop</code> was called.</p> |
411 |
<p>Please note that an explicit <code>ev_unloop</code> is usually better than |
412 |
relying on all watchers to be stopped when deciding when a program has |
413 |
finished (especially in interactive programs), but having a program that |
414 |
automatically loops as long as it has to and no longer by virtue of |
415 |
relying on its watchers stopping correctly is a thing of beauty.</p> |
416 |
<p>A flags value of <code>EVLOOP_NONBLOCK</code> will look for new events, will handle |
417 |
those events and any outstanding ones, but will not block your process in |
418 |
case there are no events and will return after one iteration of the loop.</p> |
419 |
<p>A flags value of <code>EVLOOP_ONESHOT</code> will look for new events (waiting if |
420 |
neccessary) and will handle those and any outstanding ones. It will block |
421 |
your process until at least one new event arrives, and will return after |
422 |
one iteration of the loop. This is useful if you are waiting for some |
423 |
external event in conjunction with something not expressible using other |
424 |
libev watchers. However, a pair of <code>ev_prepare</code>/<code>ev_check</code> watchers is |
425 |
usually a better approach for this kind of thing.</p> |
426 |
<p>Here are the gory details of what <code>ev_loop</code> does:</p> |
427 |
<pre> * If there are no active watchers (reference count is zero), return. |
428 |
- Queue prepare watchers and then call all outstanding watchers. |
429 |
- If we have been forked, recreate the kernel state. |
430 |
- Update the kernel state with all outstanding changes. |
431 |
- Update the "event loop time". |
432 |
- Calculate for how long to block. |
433 |
- Block the process, waiting for any events. |
434 |
- Queue all outstanding I/O (fd) events. |
435 |
- Update the "event loop time" and do time jump handling. |
436 |
- Queue all outstanding timers. |
437 |
- Queue all outstanding periodics. |
438 |
- If no events are pending now, queue all idle watchers. |
439 |
- Queue all check watchers. |
440 |
- Call all queued watchers in reverse order (i.e. check watchers first). |
441 |
Signals and child watchers are implemented as I/O watchers, and will |
442 |
be handled here by queueing them when their watcher gets executed. |
443 |
- If ev_unloop has been called or EVLOOP_ONESHOT or EVLOOP_NONBLOCK |
444 |
were used, return, otherwise continue with step *. |
445 |
|
446 |
</pre> |
447 |
<p>Example: queue some jobs and then loop until no events are outsanding |
448 |
anymore.</p> |
449 |
<pre> ... queue jobs here, make sure they register event watchers as long |
450 |
... as they still have work to do (even an idle watcher will do..) |
451 |
ev_loop (my_loop, 0); |
452 |
... jobs done. yeah! |
453 |
|
454 |
</pre> |
455 |
</dd> |
456 |
<dt>ev_unloop (loop, how)</dt> |
457 |
<dd> |
458 |
<p>Can be used to make a call to <code>ev_loop</code> return early (but only after it |
459 |
has processed all outstanding events). The <code>how</code> argument must be either |
460 |
<code>EVUNLOOP_ONE</code>, which will make the innermost <code>ev_loop</code> call return, or |
461 |
<code>EVUNLOOP_ALL</code>, which will make all nested <code>ev_loop</code> calls return.</p> |
462 |
</dd> |
463 |
<dt>ev_ref (loop)</dt> |
464 |
<dt>ev_unref (loop)</dt> |
465 |
<dd> |
466 |
<p>Ref/unref can be used to add or remove a reference count on the event |
467 |
loop: Every watcher keeps one reference, and as long as the reference |
468 |
count is nonzero, <code>ev_loop</code> will not return on its own. If you have |
469 |
a watcher you never unregister that should not keep <code>ev_loop</code> from |
470 |
returning, ev_unref() after starting, and ev_ref() before stopping it. For |
471 |
example, libev itself uses this for its internal signal pipe: It is not |
472 |
visible to the libev user and should not keep <code>ev_loop</code> from exiting if |
473 |
no event watchers registered by it are active. It is also an excellent |
474 |
way to do this for generic recurring timers or from within third-party |
475 |
libraries. Just remember to <i>unref after start</i> and <i>ref before stop</i>.</p> |
476 |
<p>Example: create a signal watcher, but keep it from keeping <code>ev_loop</code> |
477 |
running when nothing else is active.</p> |
478 |
<pre> struct dv_signal exitsig; |
479 |
ev_signal_init (&exitsig, sig_cb, SIGINT); |
480 |
ev_signal_start (myloop, &exitsig); |
481 |
evf_unref (myloop); |
482 |
|
483 |
</pre> |
484 |
<p>Example: for some weird reason, unregister the above signal handler again.</p> |
485 |
<pre> ev_ref (myloop); |
486 |
ev_signal_stop (myloop, &exitsig); |
487 |
|
488 |
</pre> |
489 |
</dd> |
490 |
</dl> |
491 |
|
492 |
</div> |
493 |
<h1 id="ANATOMY_OF_A_WATCHER">ANATOMY OF A WATCHER</h1><p><a href="#TOP" class="toplink">Top</a></p> |
494 |
<div id="ANATOMY_OF_A_WATCHER_CONTENT"> |
495 |
<p>A watcher is a structure that you create and register to record your |
496 |
interest in some event. For instance, if you want to wait for STDIN to |
497 |
become readable, you would create an <code>ev_io</code> watcher for that:</p> |
498 |
<pre> static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents) |
499 |
{ |
500 |
ev_io_stop (w); |
501 |
ev_unloop (loop, EVUNLOOP_ALL); |
502 |
} |
503 |
|
504 |
struct ev_loop *loop = ev_default_loop (0); |
505 |
struct ev_io stdin_watcher; |
506 |
ev_init (&stdin_watcher, my_cb); |
507 |
ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ); |
508 |
ev_io_start (loop, &stdin_watcher); |
509 |
ev_loop (loop, 0); |
510 |
|
511 |
</pre> |
512 |
<p>As you can see, you are responsible for allocating the memory for your |
513 |
watcher structures (and it is usually a bad idea to do this on the stack, |
514 |
although this can sometimes be quite valid).</p> |
515 |
<p>Each watcher structure must be initialised by a call to <code>ev_init |
516 |
(watcher *, callback)</code>, which expects a callback to be provided. This |
517 |
callback gets invoked each time the event occurs (or, in the case of io |
518 |
watchers, each time the event loop detects that the file descriptor given |
519 |
is readable and/or writable).</p> |
520 |
<p>Each watcher type has its own <code>ev_<type>_set (watcher *, ...)</code> macro |
521 |
with arguments specific to this watcher type. There is also a macro |
522 |
to combine initialisation and setting in one call: <code>ev_<type>_init |
523 |
(watcher *, callback, ...)</code>.</p> |
524 |
<p>To make the watcher actually watch out for events, you have to start it |
525 |
with a watcher-specific start function (<code>ev_<type>_start (loop, watcher |
526 |
*)</code>), and you can stop watching for events at any time by calling the |
527 |
corresponding stop function (<code>ev_<type>_stop (loop, watcher *)</code>.</p> |
528 |
<p>As long as your watcher is active (has been started but not stopped) you |
529 |
must not touch the values stored in it. Most specifically you must never |
530 |
reinitialise it or call its set macro.</p> |
531 |
<p>You can check whether an event is active by calling the <code>ev_is_active |
532 |
(watcher *)</code> macro. To see whether an event is outstanding (but the |
533 |
callback for it has not been called yet) you can use the <code>ev_is_pending |
534 |
(watcher *)</code> macro.</p> |
535 |
<p>Each and every callback receives the event loop pointer as first, the |
536 |
registered watcher structure as second, and a bitset of received events as |
537 |
third argument.</p> |
538 |
<p>The received events usually include a single bit per event type received |
539 |
(you can receive multiple events at the same time). The possible bit masks |
540 |
are:</p> |
541 |
<dl> |
542 |
<dt><code>EV_READ</code></dt> |
543 |
<dt><code>EV_WRITE</code></dt> |
544 |
<dd> |
545 |
<p>The file descriptor in the <code>ev_io</code> watcher has become readable and/or |
546 |
writable.</p> |
547 |
</dd> |
548 |
<dt><code>EV_TIMEOUT</code></dt> |
549 |
<dd> |
550 |
<p>The <code>ev_timer</code> watcher has timed out.</p> |
551 |
</dd> |
552 |
<dt><code>EV_PERIODIC</code></dt> |
553 |
<dd> |
554 |
<p>The <code>ev_periodic</code> watcher has timed out.</p> |
555 |
</dd> |
556 |
<dt><code>EV_SIGNAL</code></dt> |
557 |
<dd> |
558 |
<p>The signal specified in the <code>ev_signal</code> watcher has been received by a thread.</p> |
559 |
</dd> |
560 |
<dt><code>EV_CHILD</code></dt> |
561 |
<dd> |
562 |
<p>The pid specified in the <code>ev_child</code> watcher has received a status change.</p> |
563 |
</dd> |
564 |
<dt><code>EV_IDLE</code></dt> |
565 |
<dd> |
566 |
<p>The <code>ev_idle</code> watcher has determined that you have nothing better to do.</p> |
567 |
</dd> |
568 |
<dt><code>EV_PREPARE</code></dt> |
569 |
<dt><code>EV_CHECK</code></dt> |
570 |
<dd> |
571 |
<p>All <code>ev_prepare</code> watchers are invoked just <i>before</i> <code>ev_loop</code> starts |
572 |
to gather new events, and all <code>ev_check</code> watchers are invoked just after |
573 |
<code>ev_loop</code> has gathered them, but before it invokes any callbacks for any |
574 |
received events. Callbacks of both watcher types can start and stop as |
575 |
many watchers as they want, and all of them will be taken into account |
576 |
(for example, a <code>ev_prepare</code> watcher might start an idle watcher to keep |
577 |
<code>ev_loop</code> from blocking).</p> |
578 |
</dd> |
579 |
<dt><code>EV_ERROR</code></dt> |
580 |
<dd> |
581 |
<p>An unspecified error has occured, the watcher has been stopped. This might |
582 |
happen because the watcher could not be properly started because libev |
583 |
ran out of memory, a file descriptor was found to be closed or any other |
584 |
problem. You best act on it by reporting the problem and somehow coping |
585 |
with the watcher being stopped.</p> |
586 |
<p>Libev will usually signal a few "dummy" events together with an error, |
587 |
for example it might indicate that a fd is readable or writable, and if |
588 |
your callbacks is well-written it can just attempt the operation and cope |
589 |
with the error from read() or write(). This will not work in multithreaded |
590 |
programs, though, so beware.</p> |
591 |
</dd> |
592 |
</dl> |
593 |
|
594 |
</div> |
595 |
<h2 id="ASSOCIATING_CUSTOM_DATA_WITH_A_WATCH">ASSOCIATING CUSTOM DATA WITH A WATCHER</h2> |
596 |
<div id="ASSOCIATING_CUSTOM_DATA_WITH_A_WATCH-2"> |
597 |
<p>Each watcher has, by default, a member <code>void *data</code> that you can change |
598 |
and read at any time, libev will completely ignore it. This can be used |
599 |
to associate arbitrary data with your watcher. If you need more data and |
600 |
don't want to allocate memory and store a pointer to it in that data |
601 |
member, you can also "subclass" the watcher type and provide your own |
602 |
data:</p> |
603 |
<pre> struct my_io |
604 |
{ |
605 |
struct ev_io io; |
606 |
int otherfd; |
607 |
void *somedata; |
608 |
struct whatever *mostinteresting; |
609 |
} |
610 |
|
611 |
</pre> |
612 |
<p>And since your callback will be called with a pointer to the watcher, you |
613 |
can cast it back to your own type:</p> |
614 |
<pre> static void my_cb (struct ev_loop *loop, struct ev_io *w_, int revents) |
615 |
{ |
616 |
struct my_io *w = (struct my_io *)w_; |
617 |
... |
618 |
} |
619 |
|
620 |
</pre> |
621 |
<p>More interesting and less C-conformant ways of catsing your callback type |
622 |
have been omitted....</p> |
623 |
|
624 |
|
625 |
|
626 |
|
627 |
|
628 |
</div> |
629 |
<h1 id="WATCHER_TYPES">WATCHER TYPES</h1><p><a href="#TOP" class="toplink">Top</a></p> |
630 |
<div id="WATCHER_TYPES_CONTENT"> |
631 |
<p>This section describes each watcher in detail, but will not repeat |
632 |
information given in the last section.</p> |
633 |
|
634 |
|
635 |
|
636 |
|
637 |
|
638 |
</div> |
639 |
<h2 id="code_ev_io_code_is_this_file_descrip"><code>ev_io</code> - is this file descriptor readable or writable</h2> |
640 |
<div id="code_ev_io_code_is_this_file_descrip-2"> |
641 |
<p>I/O watchers check whether a file descriptor is readable or writable |
642 |
in each iteration of the event loop (This behaviour is called |
643 |
level-triggering because you keep receiving events as long as the |
644 |
condition persists. Remember you can stop the watcher if you don't want to |
645 |
act on the event and neither want to receive future events).</p> |
646 |
<p>In general you can register as many read and/or write event watchers per |
647 |
fd as you want (as long as you don't confuse yourself). Setting all file |
648 |
descriptors to non-blocking mode is also usually a good idea (but not |
649 |
required if you know what you are doing).</p> |
650 |
<p>You have to be careful with dup'ed file descriptors, though. Some backends |
651 |
(the linux epoll backend is a notable example) cannot handle dup'ed file |
652 |
descriptors correctly if you register interest in two or more fds pointing |
653 |
to the same underlying file/socket etc. description (that is, they share |
654 |
the same underlying "file open").</p> |
655 |
<p>If you must do this, then force the use of a known-to-be-good backend |
656 |
(at the time of this writing, this includes only <code>EVBACKEND_SELECT</code> and |
657 |
<code>EVBACKEND_POLL</code>).</p> |
658 |
<dl> |
659 |
<dt>ev_io_init (ev_io *, callback, int fd, int events)</dt> |
660 |
<dt>ev_io_set (ev_io *, int fd, int events)</dt> |
661 |
<dd> |
662 |
<p>Configures an <code>ev_io</code> watcher. The fd is the file descriptor to rceeive |
663 |
events for and events is either <code>EV_READ</code>, <code>EV_WRITE</code> or <code>EV_READ | |
664 |
EV_WRITE</code> to receive the given events.</p> |
665 |
<p>Please note that most of the more scalable backend mechanisms (for example |
666 |
epoll and solaris ports) can result in spurious readyness notifications |
667 |
for file descriptors, so you practically need to use non-blocking I/O (and |
668 |
treat callback invocation as hint only), or retest separately with a safe |
669 |
interface before doing I/O (XLib can do this), or force the use of either |
670 |
<code>EVBACKEND_SELECT</code> or <code>EVBACKEND_POLL</code>, which don't suffer from this |
671 |
problem. Also note that it is quite easy to have your callback invoked |
672 |
when the readyness condition is no longer valid even when employing |
673 |
typical ways of handling events, so its a good idea to use non-blocking |
674 |
I/O unconditionally.</p> |
675 |
</dd> |
676 |
</dl> |
677 |
<p>Example: call <code>stdin_readable_cb</code> when STDIN_FILENO has become, well |
678 |
readable, but only once. Since it is likely line-buffered, you could |
679 |
attempt to read a whole line in the callback:</p> |
680 |
<pre> static void |
681 |
stdin_readable_cb (struct ev_loop *loop, struct ev_io *w, int revents) |
682 |
{ |
683 |
ev_io_stop (loop, w); |
684 |
.. read from stdin here (or from w->fd) and haqndle any I/O errors |
685 |
} |
686 |
|
687 |
... |
688 |
struct ev_loop *loop = ev_default_init (0); |
689 |
struct ev_io stdin_readable; |
690 |
ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ); |
691 |
ev_io_start (loop, &stdin_readable); |
692 |
ev_loop (loop, 0); |
693 |
|
694 |
|
695 |
|
696 |
|
697 |
</pre> |
698 |
|
699 |
</div> |
700 |
<h2 id="code_ev_timer_code_relative_and_opti"><code>ev_timer</code> - relative and optionally recurring timeouts</h2> |
701 |
<div id="code_ev_timer_code_relative_and_opti-2"> |
702 |
<p>Timer watchers are simple relative timers that generate an event after a |
703 |
given time, and optionally repeating in regular intervals after that.</p> |
704 |
<p>The timers are based on real time, that is, if you register an event that |
705 |
times out after an hour and you reset your system clock to last years |
706 |
time, it will still time out after (roughly) and hour. "Roughly" because |
707 |
detecting time jumps is hard, and some inaccuracies are unavoidable (the |
708 |
monotonic clock option helps a lot here).</p> |
709 |
<p>The relative timeouts are calculated relative to the <code>ev_now ()</code> |
710 |
time. This is usually the right thing as this timestamp refers to the time |
711 |
of the event triggering whatever timeout you are modifying/starting. If |
712 |
you suspect event processing to be delayed and you <i>need</i> to base the timeout |
713 |
on the current time, use something like this to adjust for this:</p> |
714 |
<pre> ev_timer_set (&timer, after + ev_now () - ev_time (), 0.); |
715 |
|
716 |
</pre> |
717 |
<p>The callback is guarenteed to be invoked only when its timeout has passed, |
718 |
but if multiple timers become ready during the same loop iteration then |
719 |
order of execution is undefined.</p> |
720 |
<dl> |
721 |
<dt>ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)</dt> |
722 |
<dt>ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)</dt> |
723 |
<dd> |
724 |
<p>Configure the timer to trigger after <code>after</code> seconds. If <code>repeat</code> is |
725 |
<code>0.</code>, then it will automatically be stopped. If it is positive, then the |
726 |
timer will automatically be configured to trigger again <code>repeat</code> seconds |
727 |
later, again, and again, until stopped manually.</p> |
728 |
<p>The timer itself will do a best-effort at avoiding drift, that is, if you |
729 |
configure a timer to trigger every 10 seconds, then it will trigger at |
730 |
exactly 10 second intervals. If, however, your program cannot keep up with |
731 |
the timer (because it takes longer than those 10 seconds to do stuff) the |
732 |
timer will not fire more than once per event loop iteration.</p> |
733 |
</dd> |
734 |
<dt>ev_timer_again (loop)</dt> |
735 |
<dd> |
736 |
<p>This will act as if the timer timed out and restart it again if it is |
737 |
repeating. The exact semantics are:</p> |
738 |
<p>If the timer is started but nonrepeating, stop it.</p> |
739 |
<p>If the timer is repeating, either start it if necessary (with the repeat |
740 |
value), or reset the running timer to the repeat value.</p> |
741 |
<p>This sounds a bit complicated, but here is a useful and typical |
742 |
example: Imagine you have a tcp connection and you want a so-called idle |
743 |
timeout, that is, you want to be called when there have been, say, 60 |
744 |
seconds of inactivity on the socket. The easiest way to do this is to |
745 |
configure an <code>ev_timer</code> with after=repeat=60 and calling ev_timer_again each |
746 |
time you successfully read or write some data. If you go into an idle |
747 |
state where you do not expect data to travel on the socket, you can stop |
748 |
the timer, and again will automatically restart it if need be.</p> |
749 |
</dd> |
750 |
</dl> |
751 |
<p>Example: create a timer that fires after 60 seconds.</p> |
752 |
<pre> static void |
753 |
one_minute_cb (struct ev_loop *loop, struct ev_timer *w, int revents) |
754 |
{ |
755 |
.. one minute over, w is actually stopped right here |
756 |
} |
757 |
|
758 |
struct ev_timer mytimer; |
759 |
ev_timer_init (&mytimer, one_minute_cb, 60., 0.); |
760 |
ev_timer_start (loop, &mytimer); |
761 |
|
762 |
</pre> |
763 |
<p>Example: create a timeout timer that times out after 10 seconds of |
764 |
inactivity.</p> |
765 |
<pre> static void |
766 |
timeout_cb (struct ev_loop *loop, struct ev_timer *w, int revents) |
767 |
{ |
768 |
.. ten seconds without any activity |
769 |
} |
770 |
|
771 |
struct ev_timer mytimer; |
772 |
ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */ |
773 |
ev_timer_again (&mytimer); /* start timer */ |
774 |
ev_loop (loop, 0); |
775 |
|
776 |
// and in some piece of code that gets executed on any "activity": |
777 |
// reset the timeout to start ticking again at 10 seconds |
778 |
ev_timer_again (&mytimer); |
779 |
|
780 |
|
781 |
|
782 |
|
783 |
</pre> |
784 |
|
785 |
</div> |
786 |
<h2 id="code_ev_periodic_code_to_cron_or_not"><code>ev_periodic</code> - to cron or not to cron</h2> |
787 |
<div id="code_ev_periodic_code_to_cron_or_not-2"> |
788 |
<p>Periodic watchers are also timers of a kind, but they are very versatile |
789 |
(and unfortunately a bit complex).</p> |
790 |
<p>Unlike <code>ev_timer</code>'s, they are not based on real time (or relative time) |
791 |
but on wallclock time (absolute time). You can tell a periodic watcher |
792 |
to trigger "at" some specific point in time. For example, if you tell a |
793 |
periodic watcher to trigger in 10 seconds (by specifiying e.g. c<ev_now () |
794 |
+ 10.>) and then reset your system clock to the last year, then it will |
795 |
take a year to trigger the event (unlike an <code>ev_timer</code>, which would trigger |
796 |
roughly 10 seconds later and of course not if you reset your system time |
797 |
again).</p> |
798 |
<p>They can also be used to implement vastly more complex timers, such as |
799 |
triggering an event on eahc midnight, local time.</p> |
800 |
<p>As with timers, the callback is guarenteed to be invoked only when the |
801 |
time (<code>at</code>) has been passed, but if multiple periodic timers become ready |
802 |
during the same loop iteration then order of execution is undefined.</p> |
803 |
<dl> |
804 |
<dt>ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)</dt> |
805 |
<dt>ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)</dt> |
806 |
<dd> |
807 |
<p>Lots of arguments, lets sort it out... There are basically three modes of |
808 |
operation, and we will explain them from simplest to complex:</p> |
809 |
<p> |
810 |
<dl> |
811 |
<dt>* absolute timer (interval = reschedule_cb = 0)</dt> |
812 |
<dd> |
813 |
<p>In this configuration the watcher triggers an event at the wallclock time |
814 |
<code>at</code> and doesn't repeat. It will not adjust when a time jump occurs, |
815 |
that is, if it is to be run at January 1st 2011 then it will run when the |
816 |
system time reaches or surpasses this time.</p> |
817 |
</dd> |
818 |
<dt>* non-repeating interval timer (interval > 0, reschedule_cb = 0)</dt> |
819 |
<dd> |
820 |
<p>In this mode the watcher will always be scheduled to time out at the next |
821 |
<code>at + N * interval</code> time (for some integer N) and then repeat, regardless |
822 |
of any time jumps.</p> |
823 |
<p>This can be used to create timers that do not drift with respect to system |
824 |
time:</p> |
825 |
<pre> ev_periodic_set (&periodic, 0., 3600., 0); |
826 |
|
827 |
</pre> |
828 |
<p>This doesn't mean there will always be 3600 seconds in between triggers, |
829 |
but only that the the callback will be called when the system time shows a |
830 |
full hour (UTC), or more correctly, when the system time is evenly divisible |
831 |
by 3600.</p> |
832 |
<p>Another way to think about it (for the mathematically inclined) is that |
833 |
<code>ev_periodic</code> will try to run the callback in this mode at the next possible |
834 |
time where <code>time = at (mod interval)</code>, regardless of any time jumps.</p> |
835 |
</dd> |
836 |
<dt>* manual reschedule mode (reschedule_cb = callback)</dt> |
837 |
<dd> |
838 |
<p>In this mode the values for <code>interval</code> and <code>at</code> are both being |
839 |
ignored. Instead, each time the periodic watcher gets scheduled, the |
840 |
reschedule callback will be called with the watcher as first, and the |
841 |
current time as second argument.</p> |
842 |
<p>NOTE: <i>This callback MUST NOT stop or destroy any periodic watcher, |
843 |
ever, or make any event loop modifications</i>. If you need to stop it, |
844 |
return <code>now + 1e30</code> (or so, fudge fudge) and stop it afterwards (e.g. by |
845 |
starting a prepare watcher).</p> |
846 |
<p>Its prototype is <code>ev_tstamp (*reschedule_cb)(struct ev_periodic *w, |
847 |
ev_tstamp now)</code>, e.g.:</p> |
848 |
<pre> static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now) |
849 |
{ |
850 |
return now + 60.; |
851 |
} |
852 |
|
853 |
</pre> |
854 |
<p>It must return the next time to trigger, based on the passed time value |
855 |
(that is, the lowest time value larger than to the second argument). It |
856 |
will usually be called just before the callback will be triggered, but |
857 |
might be called at other times, too.</p> |
858 |
<p>NOTE: <i>This callback must always return a time that is later than the |
859 |
passed <code>now</code> value</i>. Not even <code>now</code> itself will do, it <i>must</i> be larger.</p> |
860 |
<p>This can be used to create very complex timers, such as a timer that |
861 |
triggers on each midnight, local time. To do this, you would calculate the |
862 |
next midnight after <code>now</code> and return the timestamp value for this. How |
863 |
you do this is, again, up to you (but it is not trivial, which is the main |
864 |
reason I omitted it as an example).</p> |
865 |
</dd> |
866 |
</dl> |
867 |
</p> |
868 |
</dd> |
869 |
<dt>ev_periodic_again (loop, ev_periodic *)</dt> |
870 |
<dd> |
871 |
<p>Simply stops and restarts the periodic watcher again. This is only useful |
872 |
when you changed some parameters or the reschedule callback would return |
873 |
a different time than the last time it was called (e.g. in a crond like |
874 |
program when the crontabs have changed).</p> |
875 |
</dd> |
876 |
</dl> |
877 |
<p>Example: call a callback every hour, or, more precisely, whenever the |
878 |
system clock is divisible by 3600. The callback invocation times have |
879 |
potentially a lot of jittering, but good long-term stability.</p> |
880 |
<pre> static void |
881 |
clock_cb (struct ev_loop *loop, struct ev_io *w, int revents) |
882 |
{ |
883 |
... its now a full hour (UTC, or TAI or whatever your clock follows) |
884 |
} |
885 |
|
886 |
struct ev_periodic hourly_tick; |
887 |
ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0); |
888 |
ev_periodic_start (loop, &hourly_tick); |
889 |
|
890 |
</pre> |
891 |
<p>Example: the same as above, but use a reschedule callback to do it:</p> |
892 |
<pre> #include <math.h> |
893 |
|
894 |
static ev_tstamp |
895 |
my_scheduler_cb (struct ev_periodic *w, ev_tstamp now) |
896 |
{ |
897 |
return fmod (now, 3600.) + 3600.; |
898 |
} |
899 |
|
900 |
ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb); |
901 |
|
902 |
</pre> |
903 |
<p>Example: call a callback every hour, starting now:</p> |
904 |
<pre> struct ev_periodic hourly_tick; |
905 |
ev_periodic_init (&hourly_tick, clock_cb, |
906 |
fmod (ev_now (loop), 3600.), 3600., 0); |
907 |
ev_periodic_start (loop, &hourly_tick); |
908 |
|
909 |
|
910 |
|
911 |
|
912 |
</pre> |
913 |
|
914 |
</div> |
915 |
<h2 id="code_ev_signal_code_signal_me_when_a"><code>ev_signal</code> - signal me when a signal gets signalled</h2> |
916 |
<div id="code_ev_signal_code_signal_me_when_a-2"> |
917 |
<p>Signal watchers will trigger an event when the process receives a specific |
918 |
signal one or more times. Even though signals are very asynchronous, libev |
919 |
will try it's best to deliver signals synchronously, i.e. as part of the |
920 |
normal event processing, like any other event.</p> |
921 |
<p>You can configure as many watchers as you like per signal. Only when the |
922 |
first watcher gets started will libev actually register a signal watcher |
923 |
with the kernel (thus it coexists with your own signal handlers as long |
924 |
as you don't register any with libev). Similarly, when the last signal |
925 |
watcher for a signal is stopped libev will reset the signal handler to |
926 |
SIG_DFL (regardless of what it was set to before).</p> |
927 |
<dl> |
928 |
<dt>ev_signal_init (ev_signal *, callback, int signum)</dt> |
929 |
<dt>ev_signal_set (ev_signal *, int signum)</dt> |
930 |
<dd> |
931 |
<p>Configures the watcher to trigger on the given signal number (usually one |
932 |
of the <code>SIGxxx</code> constants).</p> |
933 |
</dd> |
934 |
</dl> |
935 |
|
936 |
</div> |
937 |
<h2 id="code_ev_child_code_wait_for_pid_stat"><code>ev_child</code> - wait for pid status changes</h2> |
938 |
<div id="code_ev_child_code_wait_for_pid_stat-2"> |
939 |
<p>Child watchers trigger when your process receives a SIGCHLD in response to |
940 |
some child status changes (most typically when a child of yours dies).</p> |
941 |
<dl> |
942 |
<dt>ev_child_init (ev_child *, callback, int pid)</dt> |
943 |
<dt>ev_child_set (ev_child *, int pid)</dt> |
944 |
<dd> |
945 |
<p>Configures the watcher to wait for status changes of process <code>pid</code> (or |
946 |
<i>any</i> process if <code>pid</code> is specified as <code>0</code>). The callback can look |
947 |
at the <code>rstatus</code> member of the <code>ev_child</code> watcher structure to see |
948 |
the status word (use the macros from <code>sys/wait.h</code> and see your systems |
949 |
<code>waitpid</code> documentation). The <code>rpid</code> member contains the pid of the |
950 |
process causing the status change.</p> |
951 |
</dd> |
952 |
</dl> |
953 |
<p>Example: try to exit cleanly on SIGINT and SIGTERM.</p> |
954 |
<pre> static void |
955 |
sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents) |
956 |
{ |
957 |
ev_unloop (loop, EVUNLOOP_ALL); |
958 |
} |
959 |
|
960 |
struct ev_signal signal_watcher; |
961 |
ev_signal_init (&signal_watcher, sigint_cb, SIGINT); |
962 |
ev_signal_start (loop, &sigint_cb); |
963 |
|
964 |
|
965 |
|
966 |
|
967 |
</pre> |
968 |
|
969 |
</div> |
970 |
<h2 id="code_ev_idle_code_when_you_ve_got_no"><code>ev_idle</code> - when you've got nothing better to do</h2> |
971 |
<div id="code_ev_idle_code_when_you_ve_got_no-2"> |
972 |
<p>Idle watchers trigger events when there are no other events are pending |
973 |
(prepare, check and other idle watchers do not count). That is, as long |
974 |
as your process is busy handling sockets or timeouts (or even signals, |
975 |
imagine) it will not be triggered. But when your process is idle all idle |
976 |
watchers are being called again and again, once per event loop iteration - |
977 |
until stopped, that is, or your process receives more events and becomes |
978 |
busy.</p> |
979 |
<p>The most noteworthy effect is that as long as any idle watchers are |
980 |
active, the process will not block when waiting for new events.</p> |
981 |
<p>Apart from keeping your process non-blocking (which is a useful |
982 |
effect on its own sometimes), idle watchers are a good place to do |
983 |
"pseudo-background processing", or delay processing stuff to after the |
984 |
event loop has handled all outstanding events.</p> |
985 |
<dl> |
986 |
<dt>ev_idle_init (ev_signal *, callback)</dt> |
987 |
<dd> |
988 |
<p>Initialises and configures the idle watcher - it has no parameters of any |
989 |
kind. There is a <code>ev_idle_set</code> macro, but using it is utterly pointless, |
990 |
believe me.</p> |
991 |
</dd> |
992 |
</dl> |
993 |
<p>Example: dynamically allocate an <code>ev_idle</code>, start it, and in the |
994 |
callback, free it. Alos, use no error checking, as usual.</p> |
995 |
<pre> static void |
996 |
idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents) |
997 |
{ |
998 |
free (w); |
999 |
// now do something you wanted to do when the program has |
1000 |
// no longer asnything immediate to do. |
1001 |
} |
1002 |
|
1003 |
struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle)); |
1004 |
ev_idle_init (idle_watcher, idle_cb); |
1005 |
ev_idle_start (loop, idle_cb); |
1006 |
|
1007 |
|
1008 |
|
1009 |
|
1010 |
</pre> |
1011 |
|
1012 |
</div> |
1013 |
<h2 id="code_ev_prepare_code_and_code_ev_che"><code>ev_prepare</code> and <code>ev_check</code> - customise your event loop</h2> |
1014 |
<div id="code_ev_prepare_code_and_code_ev_che-2"> |
1015 |
<p>Prepare and check watchers are usually (but not always) used in tandem: |
1016 |
prepare watchers get invoked before the process blocks and check watchers |
1017 |
afterwards.</p> |
1018 |
<p>Their main purpose is to integrate other event mechanisms into libev. This |
1019 |
could be used, for example, to track variable changes, implement your own |
1020 |
watchers, integrate net-snmp or a coroutine library and lots more.</p> |
1021 |
<p>This is done by examining in each prepare call which file descriptors need |
1022 |
to be watched by the other library, registering <code>ev_io</code> watchers for |
1023 |
them and starting an <code>ev_timer</code> watcher for any timeouts (many libraries |
1024 |
provide just this functionality). Then, in the check watcher you check for |
1025 |
any events that occured (by checking the pending status of all watchers |
1026 |
and stopping them) and call back into the library. The I/O and timer |
1027 |
callbacks will never actually be called (but must be valid nevertheless, |
1028 |
because you never know, you know?).</p> |
1029 |
<p>As another example, the Perl Coro module uses these hooks to integrate |
1030 |
coroutines into libev programs, by yielding to other active coroutines |
1031 |
during each prepare and only letting the process block if no coroutines |
1032 |
are ready to run (it's actually more complicated: it only runs coroutines |
1033 |
with priority higher than or equal to the event loop and one coroutine |
1034 |
of lower priority, but only once, using idle watchers to keep the event |
1035 |
loop from blocking if lower-priority coroutines are active, thus mapping |
1036 |
low-priority coroutines to idle/background tasks).</p> |
1037 |
<dl> |
1038 |
<dt>ev_prepare_init (ev_prepare *, callback)</dt> |
1039 |
<dt>ev_check_init (ev_check *, callback)</dt> |
1040 |
<dd> |
1041 |
<p>Initialises and configures the prepare or check watcher - they have no |
1042 |
parameters of any kind. There are <code>ev_prepare_set</code> and <code>ev_check_set</code> |
1043 |
macros, but using them is utterly, utterly and completely pointless.</p> |
1044 |
</dd> |
1045 |
</dl> |
1046 |
<p>Example: *TODO*.</p> |
1047 |
|
1048 |
|
1049 |
|
1050 |
|
1051 |
|
1052 |
</div> |
1053 |
<h1 id="OTHER_FUNCTIONS">OTHER FUNCTIONS</h1><p><a href="#TOP" class="toplink">Top</a></p> |
1054 |
<div id="OTHER_FUNCTIONS_CONTENT"> |
1055 |
<p>There are some other functions of possible interest. Described. Here. Now.</p> |
1056 |
<dl> |
1057 |
<dt>ev_once (loop, int fd, int events, ev_tstamp timeout, callback)</dt> |
1058 |
<dd> |
1059 |
<p>This function combines a simple timer and an I/O watcher, calls your |
1060 |
callback on whichever event happens first and automatically stop both |
1061 |
watchers. This is useful if you want to wait for a single event on an fd |
1062 |
or timeout without having to allocate/configure/start/stop/free one or |
1063 |
more watchers yourself.</p> |
1064 |
<p>If <code>fd</code> is less than 0, then no I/O watcher will be started and events |
1065 |
is being ignored. Otherwise, an <code>ev_io</code> watcher for the given <code>fd</code> and |
1066 |
<code>events</code> set will be craeted and started.</p> |
1067 |
<p>If <code>timeout</code> is less than 0, then no timeout watcher will be |
1068 |
started. Otherwise an <code>ev_timer</code> watcher with after = <code>timeout</code> (and |
1069 |
repeat = 0) will be started. While <code>0</code> is a valid timeout, it is of |
1070 |
dubious value.</p> |
1071 |
<p>The callback has the type <code>void (*cb)(int revents, void *arg)</code> and gets |
1072 |
passed an <code>revents</code> set like normal event callbacks (a combination of |
1073 |
<code>EV_ERROR</code>, <code>EV_READ</code>, <code>EV_WRITE</code> or <code>EV_TIMEOUT</code>) and the <code>arg</code> |
1074 |
value passed to <code>ev_once</code>:</p> |
1075 |
<pre> static void stdin_ready (int revents, void *arg) |
1076 |
{ |
1077 |
if (revents & EV_TIMEOUT) |
1078 |
/* doh, nothing entered */; |
1079 |
else if (revents & EV_READ) |
1080 |
/* stdin might have data for us, joy! */; |
1081 |
} |
1082 |
|
1083 |
ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0); |
1084 |
|
1085 |
</pre> |
1086 |
</dd> |
1087 |
<dt>ev_feed_event (loop, watcher, int events)</dt> |
1088 |
<dd> |
1089 |
<p>Feeds the given event set into the event loop, as if the specified event |
1090 |
had happened for the specified watcher (which must be a pointer to an |
1091 |
initialised but not necessarily started event watcher).</p> |
1092 |
</dd> |
1093 |
<dt>ev_feed_fd_event (loop, int fd, int revents)</dt> |
1094 |
<dd> |
1095 |
<p>Feed an event on the given fd, as if a file descriptor backend detected |
1096 |
the given events it.</p> |
1097 |
</dd> |
1098 |
<dt>ev_feed_signal_event (loop, int signum)</dt> |
1099 |
<dd> |
1100 |
<p>Feed an event as if the given signal occured (loop must be the default loop!).</p> |
1101 |
</dd> |
1102 |
</dl> |
1103 |
|
1104 |
|
1105 |
|
1106 |
|
1107 |
|
1108 |
</div> |
1109 |
<h1 id="LIBEVENT_EMULATION">LIBEVENT EMULATION</h1><p><a href="#TOP" class="toplink">Top</a></p> |
1110 |
<div id="LIBEVENT_EMULATION_CONTENT"> |
1111 |
<p>Libev offers a compatibility emulation layer for libevent. It cannot |
1112 |
emulate the internals of libevent, so here are some usage hints:</p> |
1113 |
<dl> |
1114 |
<dt>* Use it by including <event.h>, as usual.</dt> |
1115 |
<dt>* The following members are fully supported: ev_base, ev_callback, |
1116 |
ev_arg, ev_fd, ev_res, ev_events.</dt> |
1117 |
<dt>* Avoid using ev_flags and the EVLIST_*-macros, while it is |
1118 |
maintained by libev, it does not work exactly the same way as in libevent (consider |
1119 |
it a private API).</dt> |
1120 |
<dt>* Priorities are not currently supported. Initialising priorities |
1121 |
will fail and all watchers will have the same priority, even though there |
1122 |
is an ev_pri field.</dt> |
1123 |
<dt>* Other members are not supported.</dt> |
1124 |
<dt>* The libev emulation is <i>not</i> ABI compatible to libevent, you need |
1125 |
to use the libev header file and library.</dt> |
1126 |
</dl> |
1127 |
|
1128 |
</div> |
1129 |
<h1 id="C_SUPPORT">C++ SUPPORT</h1><p><a href="#TOP" class="toplink">Top</a></p> |
1130 |
<div id="C_SUPPORT_CONTENT"> |
1131 |
<p>TBD.</p> |
1132 |
|
1133 |
</div> |
1134 |
<h1 id="AUTHOR">AUTHOR</h1><p><a href="#TOP" class="toplink">Top</a></p> |
1135 |
<div id="AUTHOR_CONTENT"> |
1136 |
<p>Marc Lehmann <libev@schmorp.de>.</p> |
1137 |
|
1138 |
</div> |
1139 |
</div></body> |
1140 |
</html> |