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+ <meta name="created" content="Mon Nov 12 09:32:26 2007" />
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</ul>
</li>
<li><a href="#WATCHER_TYPES">WATCHER TYPES</a>
-<ul><li><a href="#struct_ev_io_is_my_file_descriptor_r">struct ev_io - is my file descriptor readable or writable</a></li>
-<li><a href="#struct_ev_timer_relative_and_optiona">struct ev_timer - relative and optionally recurring timeouts</a></li>
-<li><a href="#ev_periodic_to_cron_or_not_to_cron_i">ev_periodic - to cron or not to cron it</a></li>
-<li><a href="#ev_signal_signal_me_when_a_signal_ge">ev_signal - signal me when a signal gets signalled</a></li>
-<li><a href="#ev_child_wait_for_pid_status_changes">ev_child - wait for pid status changes</a></li>
-<li><a href="#ev_idle_when_you_ve_got_nothing_bett">ev_idle - when you've got nothing better to do</a></li>
+<ul><li><a href="#code_ev_io_code_is_my_file_descripto"><code>ev_io</code> - is my file descriptor readable or writable</a></li>
+<li><a href="#code_ev_timer_code_relative_and_opti"><code>ev_timer</code> - relative and optionally recurring timeouts</a></li>
+<li><a href="#code_ev_periodic_code_to_cron_or_not"><code>ev_periodic</code> - to cron or not to cron it</a></li>
+<li><a href="#code_ev_signal_code_signal_me_when_a"><code>ev_signal</code> - signal me when a signal gets signalled</a></li>
+<li><a href="#code_ev_child_code_wait_for_pid_stat"><code>ev_child</code> - wait for pid status changes</a></li>
+<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>
<li><a href="#prepare_and_check_your_hooks_into_th">prepare and check - your hooks into the event loop</a></li>
</ul>
</li>
timers with customised rescheduling, signal events, process status change
events (related to SIGCHLD), and event watchers dealing with the event
loop mechanism itself (idle, prepare and check watchers). It also is quite
-fast (see a <b>http://libev.schmorp.de/bench.html</b> (<cite>benchmark</cite>) comparing it
-to libevent).</p>
+fast (see this <a href="http://libev.schmorp.de/bench.html">benchmark</a> comparing
+it to libevent for example).</p>
</div>
<h1 id="CONVENTIONS">CONVENTIONS</h1><p><a href="#TOP" class="toplink">Top</a></p>
<div id="CONVENTIONS_CONTENT">
<p>Libev is very configurable. In this manual the default configuration
will be described, which supports multiple event loops. For more info
-about various configuraiton options please have a look at the file
+about various configuration options please have a look at the file
<cite>README.embed</cite> in the libev distribution. If libev was configured without
support for multiple event loops, then all functions taking an initial
argument of name <code>loop</code> (which is always of type <code>struct ev_loop *</code>)
<code>ev_version_minor</code>. If you want, you can compare against the global
symbols <code>EV_VERSION_MAJOR</code> and <code>EV_VERSION_MINOR</code>, which specify the
version of the library your program was compiled against.</p>
- <p>Usually, its a good idea to terminate if the major versions mismatch,
+ <p>Usually, it's a good idea to terminate if the major versions mismatch,
as this indicates an incompatible change. Minor versions are usually
compatible to older versions, so a larger minor version alone is usually
not a problem.</p>
<dt>ev_set_allocator (void *(*cb)(void *ptr, long size))</dt>
<dd>
<p>Sets the allocation function to use (the prototype is similar to the
-realloc function). It is used to allocate and free memory (no surprises
-here). If it returns zero when memory needs to be allocated, the library
-might abort or take some potentially destructive action. The default is
-your system realloc function.</p>
+realloc C function, the semantics are identical). It is used to allocate
+and free memory (no surprises here). If it returns zero when memory
+needs to be allocated, the library might abort or take some potentially
+destructive action. The default is your system realloc function.</p>
<p>You could override this function in high-availability programs to, say,
free some memory if it cannot allocate memory, to use a special allocator,
or even to sleep a while and retry until some memory is available.</p>
as failed select, poll, epoll_wait). The message is a printable string
indicating the system call or subsystem causing the problem. If this
callback is set, then libev will expect it to remedy the sitution, no
-matter what, when it returns. That is, libev will geenrally retry the
+matter what, when it returns. That is, libev will generally retry the
requested operation, or, if the condition doesn't go away, do bad stuff
(such as abort).</p>
</dd>
events, and dynamically created loops which do not.</p>
<p>If you use threads, a common model is to run the default event loop
in your main thread (or in a separate thrad) and for each thread you
-create, you also create another event loop. Libev itself does no lockign
-whatsoever, so if you mix calls to different event loops, make sure you
-lock (this is usually a bad idea, though, even if done right).</p>
+create, you also create another event loop. Libev itself does no locking
+whatsoever, so if you mix calls to the same event loop in different
+threads, make sure you lock (this is usually a bad idea, though, even if
+done correctly, because it's hideous and inefficient).</p>
<dl>
<dt>struct ev_loop *ev_default_loop (unsigned int flags)</dt>
<dd>
<p>If you don't know what event loop to use, use the one returned from this
function.</p>
<p>The flags argument can be used to specify special behaviour or specific
-backends to use, and is usually specified as 0 (or EVFLAG_AUTO)</p>
+backends to use, and is usually specified as 0 (or EVFLAG_AUTO).</p>
<p>It supports the following flags:</p>
<p>
<dl>
- <dt>EVFLAG_AUTO</dt>
+ <dt><code>EVFLAG_AUTO</code></dt>
<dd>
- <p>The default flags value. Use this if you have no clue (its the right
+ <p>The default flags value. Use this if you have no clue (it's the right
thing, believe me).</p>
</dd>
- <dt>EVFLAG_NOENV</dt>
+ <dt><code>EVFLAG_NOENV</code></dt>
<dd>
- <p>If this flag bit is ored into the flag value then libev will <i>not</i> look
-at the environment variable <code>LIBEV_FLAGS</code>. Otherwise (the default), this
-environment variable will override the flags completely. This is useful
-to try out specific backends to tets their performance, or to work around
-bugs.</p>
+ <p>If this flag bit is ored into the flag value (or the program runs setuid
+or setgid) then libev will <i>not</i> look at the environment variable
+<code>LIBEV_FLAGS</code>. Otherwise (the default), this environment variable will
+override the flags completely if it is found in the environment. This is
+useful to try out specific backends to test their performance, or to work
+around bugs.</p>
</dd>
- <dt>EVMETHOD_SELECT portable select backend</dt>
- <dt>EVMETHOD_POLL poll backend (everywhere except windows)</dt>
- <dt>EVMETHOD_EPOLL linux only</dt>
- <dt>EVMETHOD_KQUEUE some bsds only</dt>
- <dt>EVMETHOD_DEVPOLL solaris 8 only</dt>
- <dt>EVMETHOD_PORT solaris 10 only</dt>
+ <dt><code>EVMETHOD_SELECT</code> (portable select backend)</dt>
+ <dt><code>EVMETHOD_POLL</code> (poll backend, available everywhere except on windows)</dt>
+ <dt><code>EVMETHOD_EPOLL</code> (linux only)</dt>
+ <dt><code>EVMETHOD_KQUEUE</code> (some bsds only)</dt>
+ <dt><code>EVMETHOD_DEVPOLL</code> (solaris 8 only)</dt>
+ <dt><code>EVMETHOD_PORT</code> (solaris 10 only)</dt>
<dd>
<p>If one or more of these are ored into the flags value, then only these
backends will be tried (in the reverse order as given here). If one are
<dd>
<p>Destroys the default loop again (frees all memory and kernel state
etc.). This stops all registered event watchers (by not touching them in
-any way whatsoever, although you cnanot rely on this :).</p>
+any way whatsoever, although you cannot rely on this :).</p>
</dd>
<dt>ev_loop_destroy (loop)</dt>
<dd>
<p>You <i>must</i> call this function after forking if and only if you want to
use the event library in both processes. If you just fork+exec, you don't
have to call it.</p>
- <p>The function itself is quite fast and its usually not a problem to call
+ <p>The function itself is quite fast and it's usually not a problem to call
it just in case after a fork. To make this easy, the function will fit in
quite nicely into a call to <code>pthread_atfork</code>:</p>
<pre> pthread_atfork (0, 0, ev_default_fork);
<p>Returns one of the <code>EVMETHOD_*</code> flags indicating the event backend in
use.</p>
</dd>
- <dt>ev_tstamp = ev_now (loop)</dt>
+ <dt>ev_tstamp ev_now (loop)</dt>
<dd>
<p>Returns the current "event loop time", which is the time the event loop
got events and started processing them. This timestamp does not change
no event watchers are active anymore or <code>ev_unloop</code> was called.</p>
<p>A flags value of <code>EVLOOP_NONBLOCK</code> will look for new events, will handle
those events and any outstanding ones, but will not block your process in
-case there are no events.</p>
+case there are no events and will return after one iteration of the loop.</p>
<p>A flags value of <code>EVLOOP_ONESHOT</code> will look for new events (waiting if
neccessary) and will handle those and any outstanding ones. It will block
-your process until at least one new event arrives.</p>
+your process until at least one new event arrives, and will return after
+one iteration of the loop.</p>
<p>This flags value could be used to implement alternative looping
constructs, but the <code>prepare</code> and <code>check</code> watchers provide a better and
more generic mechanism.</p>
</dd>
<dt>ev_unloop (loop, how)</dt>
<dd>
- <p>Can be used to make a call to <code>ev_loop</code> return early. The <code>how</code> argument
-must be either <code>EVUNLOOP_ONCE</code>, which will make the innermost <code>ev_loop</code>
-call return, or <code>EVUNLOOP_ALL</code>, which will make all nested <code>ev_loop</code>
-calls return.</p>
+ <p>Can be used to make a call to <code>ev_loop</code> return early (but only after it
+has processed all outstanding events). The <code>how</code> argument must be either
+<code>EVUNLOOP_ONCE</code>, which will make the innermost <code>ev_loop</code> call return, or
+<code>EVUNLOOP_ALL</code>, which will make all nested <code>ev_loop</code> calls return.</p>
</dd>
<dt>ev_ref (loop)</dt>
<dt>ev_unref (loop)</dt>
<dd>
- <p>Ref/unref can be used to add or remove a refcount on the event loop: Every
-watcher keeps one reference. If you have a long-runing watcher you never
-unregister that should not keep ev_loop from running, ev_unref() after
-starting, and ev_ref() before stopping it. Libev itself uses this for
-example for its internal signal pipe: It is not visible to you as a user
-and should not keep <code>ev_loop</code> from exiting if the work is done. It is
-also an excellent way to do this for generic recurring timers or from
-within third-party libraries. Just remember to unref after start and ref
-before stop.</p>
+ <p>Ref/unref can be used to add or remove a reference count on the event
+loop: Every watcher keeps one reference, and as long as the reference
+count is nonzero, <code>ev_loop</code> will not return on its own. If you have
+a watcher you never unregister that should not keep <code>ev_loop</code> from
+returning, ev_unref() after starting, and ev_ref() before stopping it. For
+example, libev itself uses this for its internal signal pipe: It is not
+visible to the libev user and should not keep <code>ev_loop</code> from exiting if
+no event watchers registered by it are active. It is also an excellent
+way to do this for generic recurring timers or from within third-party
+libraries. Just remember to <i>unref after start</i> and <i>ref before stop</i>.</p>
</dd>
</dl>
<div id="ANATOMY_OF_A_WATCHER_CONTENT">
<p>A watcher is a structure that you create and register to record your
interest in some event. For instance, if you want to wait for STDIN to
-become readable, you would create an ev_io watcher for that:</p>
+become readable, you would create an <code>ev_io</code> watcher for that:</p>
<pre> static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents)
{
ev_io_stop (w);
(you can receive multiple events at the same time). The possible bit masks
are:</p>
<dl>
- <dt>EV_READ</dt>
- <dt>EV_WRITE</dt>
+ <dt><code>EV_READ</code></dt>
+ <dt><code>EV_WRITE</code></dt>
<dd>
- <p>The file descriptor in the ev_io watcher has become readable and/or
+ <p>The file descriptor in the <code>ev_io</code> watcher has become readable and/or
writable.</p>
</dd>
- <dt>EV_TIMEOUT</dt>
+ <dt><code>EV_TIMEOUT</code></dt>
<dd>
- <p>The ev_timer watcher has timed out.</p>
+ <p>The <code>ev_timer</code> watcher has timed out.</p>
</dd>
- <dt>EV_PERIODIC</dt>
+ <dt><code>EV_PERIODIC</code></dt>
<dd>
- <p>The ev_periodic watcher has timed out.</p>
+ <p>The <code>ev_periodic</code> watcher has timed out.</p>
</dd>
- <dt>EV_SIGNAL</dt>
+ <dt><code>EV_SIGNAL</code></dt>
<dd>
- <p>The signal specified in the ev_signal watcher has been received by a thread.</p>
+ <p>The signal specified in the <code>ev_signal</code> watcher has been received by a thread.</p>
</dd>
- <dt>EV_CHILD</dt>
+ <dt><code>EV_CHILD</code></dt>
<dd>
- <p>The pid specified in the ev_child watcher has received a status change.</p>
+ <p>The pid specified in the <code>ev_child</code> watcher has received a status change.</p>
</dd>
- <dt>EV_IDLE</dt>
+ <dt><code>EV_IDLE</code></dt>
<dd>
- <p>The ev_idle watcher has determined that you have nothing better to do.</p>
+ <p>The <code>ev_idle</code> watcher has determined that you have nothing better to do.</p>
</dd>
- <dt>EV_PREPARE</dt>
- <dt>EV_CHECK</dt>
+ <dt><code>EV_PREPARE</code></dt>
+ <dt><code>EV_CHECK</code></dt>
<dd>
- <p>All ev_prepare watchers are invoked just <i>before</i> <code>ev_loop</code> starts
-to gather new events, and all ev_check watchers are invoked just after
+ <p>All <code>ev_prepare</code> watchers are invoked just <i>before</i> <code>ev_loop</code> starts
+to gather new events, and all <code>ev_check</code> watchers are invoked just after
<code>ev_loop</code> has gathered them, but before it invokes any callbacks for any
received events. Callbacks of both watcher types can start and stop as
many watchers as they want, and all of them will be taken into account
-(for example, a ev_prepare watcher might start an idle watcher to keep
+(for example, a <code>ev_prepare</code> watcher might start an idle watcher to keep
<code>ev_loop</code> from blocking).</p>
</dd>
- <dt>EV_ERROR</dt>
+ <dt><code>EV_ERROR</code></dt>
<dd>
<p>An unspecified error has occured, the watcher has been stopped. This might
happen because the watcher could not be properly started because libev
information given in the last section.</p>
</div>
-<h2 id="struct_ev_io_is_my_file_descriptor_r">struct ev_io - is my file descriptor readable or writable</h2>
-<div id="struct_ev_io_is_my_file_descriptor_r-2">
+<h2 id="code_ev_io_code_is_my_file_descripto"><code>ev_io</code> - is my file descriptor readable or writable</h2>
+<div id="code_ev_io_code_is_my_file_descripto-2">
<p>I/O watchers check whether a file descriptor is readable or writable
in each iteration of the event loop (This behaviour is called
level-triggering because you keep receiving events as long as the
condition persists. Remember you cna stop the watcher if you don't want to
act on the event and neither want to receive future events).</p>
+<p>In general you can register as many read and/or write event watchers oer
+fd as you want (as long as you don't confuse yourself). Setting all file
+descriptors to non-blocking mode is also usually a good idea (but not
+required if you know what you are doing).</p>
+<p>You have to be careful with dup'ed file descriptors, though. Some backends
+(the linux epoll backend is a notable example) cannot handle dup'ed file
+descriptors correctly if you register interest in two or more fds pointing
+to the same file/socket etc. description.</p>
+<p>If you must do this, then force the use of a known-to-be-good backend
+(at the time of this writing, this includes only EVMETHOD_SELECT and
+EVMETHOD_POLL).</p>
<dl>
<dt>ev_io_init (ev_io *, callback, int fd, int events)</dt>
<dt>ev_io_set (ev_io *, int fd, int events)</dt>
<dd>
- <p>Configures an ev_io watcher. The fd is the file descriptor to rceeive
+ <p>Configures an <code>ev_io</code> watcher. The fd is the file descriptor to rceeive
events for and events is either <code>EV_READ</code>, <code>EV_WRITE</code> or <code>EV_READ |
EV_WRITE</code> to receive the given events.</p>
</dd>
</dl>
</div>
-<h2 id="struct_ev_timer_relative_and_optiona">struct ev_timer - relative and optionally recurring timeouts</h2>
-<div id="struct_ev_timer_relative_and_optiona-2">
+<h2 id="code_ev_timer_code_relative_and_opti"><code>ev_timer</code> - relative and optionally recurring timeouts</h2>
+<div id="code_ev_timer_code_relative_and_opti-2">
<p>Timer watchers are simple relative timers that generate an event after a
given time, and optionally repeating in regular intervals after that.</p>
<p>The timers are based on real time, that is, if you register an event that
time, it will still time out after (roughly) and hour. "Roughly" because
detecting time jumps is hard, and soem inaccuracies are unavoidable (the
monotonic clock option helps a lot here).</p>
+<p>The relative timeouts are calculated relative to the <code>ev_now ()</code>
+time. This is usually the right thing as this timestamp refers to the time
+of the event triggering whatever timeout you are modifying/starting. If
+you suspect event processing to be delayed and you *need* to base the timeout
+ion the current time, use something like this to adjust for this:</p>
+<pre> ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);
+
+</pre>
<dl>
<dt>ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)</dt>
<dt>ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)</dt>
example: Imagine you have a tcp connection and you want a so-called idle
timeout, that is, you want to be called when there have been, say, 60
seconds of inactivity on the socket. The easiest way to do this is to
-configure an ev_timer with after=repeat=60 and calling ev_timer_again each
+configure an <code>ev_timer</code> with after=repeat=60 and calling ev_timer_again each
time you successfully read or write some data. If you go into an idle
state where you do not expect data to travel on the socket, you can stop
the timer, and again will automatically restart it if need be.</p>
</dl>
</div>
-<h2 id="ev_periodic_to_cron_or_not_to_cron_i">ev_periodic - to cron or not to cron it</h2>
-<div id="ev_periodic_to_cron_or_not_to_cron_i-2">
+<h2 id="code_ev_periodic_code_to_cron_or_not"><code>ev_periodic</code> - to cron or not to cron it</h2>
+<div id="code_ev_periodic_code_to_cron_or_not-2">
<p>Periodic watchers are also timers of a kind, but they are very versatile
(and unfortunately a bit complex).</p>
-<p>Unlike ev_timer's, they are not based on real time (or relative time)
+<p>Unlike <code>ev_timer</code>'s, they are not based on real time (or relative time)
but on wallclock time (absolute time). You can tell a periodic watcher
to trigger "at" some specific point in time. For example, if you tell a
periodic watcher to trigger in 10 seconds (by specifiying e.g. c<ev_now ()
+ 10.>) and then reset your system clock to the last year, then it will
-take a year to trigger the event (unlike an ev_timer, which would trigger
+take a year to trigger the event (unlike an <code>ev_timer</code>, which would trigger
roughly 10 seconds later and of course not if you reset your system time
again).</p>
<p>They can also be used to implement vastly more complex timers, such as
full hour (UTC), or more correct, when the system time is evenly divisible
by 3600.</p>
<p>Another way to think about it (for the mathematically inclined) is that
-ev_periodic will try to run the callback in this mode at the next possible
+<code>ev_periodic</code> will try to run the callback in this mode at the next possible
time where <code>time = at (mod interval)</code>, regardless of any time jumps.</p>
</dd>
<dt>* manual reschedule mode (reschedule_cb = callback)</dt>
</dl>
</div>
-<h2 id="ev_signal_signal_me_when_a_signal_ge">ev_signal - signal me when a signal gets signalled</h2>
-<div id="ev_signal_signal_me_when_a_signal_ge-2">
+<h2 id="code_ev_signal_code_signal_me_when_a"><code>ev_signal</code> - signal me when a signal gets signalled</h2>
+<div id="code_ev_signal_code_signal_me_when_a-2">
<p>Signal watchers will trigger an event when the process receives a specific
signal one or more times. Even though signals are very asynchronous, libev
-will try its best to deliver signals synchronously, i.e. as part of the
+will try it's best to deliver signals synchronously, i.e. as part of the
normal event processing, like any other event.</p>
<p>You cna configure as many watchers as you like per signal. Only when the
first watcher gets started will libev actually register a signal watcher
</dl>
</div>
-<h2 id="ev_child_wait_for_pid_status_changes">ev_child - wait for pid status changes</h2>
-<div id="ev_child_wait_for_pid_status_changes-2">
+<h2 id="code_ev_child_code_wait_for_pid_stat"><code>ev_child</code> - wait for pid status changes</h2>
+<div id="code_ev_child_code_wait_for_pid_stat-2">
<p>Child watchers trigger when your process receives a SIGCHLD in response to
some child status changes (most typically when a child of yours dies).</p>
<dl>
</dl>
</div>
-<h2 id="ev_idle_when_you_ve_got_nothing_bett">ev_idle - when you've got nothing better to do</h2>
-<div id="ev_idle_when_you_ve_got_nothing_bett-2">
+<h2 id="code_ev_idle_code_when_you_ve_got_no"><code>ev_idle</code> - when you've got nothing better to do</h2>
+<div id="code_ev_idle_code_when_you_ve_got_no-2">
<p>Idle watchers trigger events when there are no other I/O or timer (or
periodic) events pending. That is, as long as your process is busy
handling sockets or timeouts it will not be called. But when your process
could be used, for example, to track variable changes, implement your own
watchers, integrate net-snmp or a coroutine library and lots more.</p>
<p>This is done by examining in each prepare call which file descriptors need
-to be watched by the other library, registering ev_io watchers for them
-and starting an ev_timer watcher for any timeouts (many libraries provide
+to be watched by the other library, registering <code>ev_io</code> watchers for them
+and starting an <code>ev_timer</code> watcher for any timeouts (many libraries provide
just this functionality). Then, in the check watcher you check for any
events that occured (by making your callbacks set soem flags for example)
and call back into the library.</p>
or timeout without havign to allocate/configure/start/stop/free one or
more watchers yourself.</p>
<p>If <code>fd</code> is less than 0, then no I/O watcher will be started and events is
-ignored. Otherwise, an ev_io watcher for the given <code>fd</code> and <code>events</code> set
+ignored. Otherwise, an <code>ev_io</code> watcher for the given <code>fd</code> and <code>events</code> set
will be craeted and started.</p>
<p>If <code>timeout</code> is less than 0, then no timeout watcher will be
-started. Otherwise an ev_timer watcher with after = <code>timeout</code> (and repeat
+started. Otherwise an <code>ev_timer</code> watcher with after = <code>timeout</code> (and repeat
= 0) will be started.</p>
<p>The callback has the type <code>void (*cb)(int revents, void *arg)</code> and
-gets passed an events set (normally a combination of EV_ERROR, EV_READ,
-EV_WRITE or EV_TIMEOUT) and the <code>arg</code> value passed to <code>ev_once</code>:</p>
+gets passed an events set (normally a combination of <code>EV_ERROR</code>, <code>EV_READ</code>,
+<code>EV_WRITE</code> or <code>EV_TIMEOUT</code>) and the <code>arg</code> value passed to <code>ev_once</code>:</p>
<pre> static void stdin_ready (int revents, void *arg)
{
if (revents & EV_TIMEOUT)
projects / software / libev.git / blobdiff