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=head1 NAME |
2 |
|
3 |
libev - a high performance full-featured event loop written in C |
4 |
|
5 |
=head1 SYNOPSIS |
6 |
|
7 |
#include <ev.h> |
8 |
|
9 |
=head1 DESCRIPTION |
10 |
|
11 |
Libev is an event loop: you register interest in certain events (such as a |
12 |
file descriptor being readable or a timeout occuring), and it will manage |
13 |
these event sources and provide your program with events. |
14 |
|
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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> handler, and will then |
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communicate events via a callback mechanism. |
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|
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You register interest in certain events by registering so-called I<event |
20 |
watchers>, 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> the |
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watcher. |
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|
24 |
=head1 FEATURES |
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|
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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 |
28 |
timers with customised rescheduling, signal events, process status change |
29 |
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 L<benchmark|http://libev.schmorp.de/bench.html> comparing |
32 |
it to libevent for example). |
33 |
|
34 |
=head1 CONVENTIONS |
35 |
|
36 |
Libev is very configurable. In this manual the default configuration |
37 |
will be described, which supports multiple event loops. For more info |
38 |
about various configuration options please have a look at the file |
39 |
F<README.embed> 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 C<loop> (which is always of type C<struct ev_loop *>) |
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will not have this argument. |
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|
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=head1 TIME REPRESENTATION |
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|
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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 C<ev_tstamp>, which is what you should use too. It usually aliases |
50 |
to the double type in C. |
51 |
|
52 |
=head1 GLOBAL FUNCTIONS |
53 |
|
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These functions can be called anytime, even before initialising the |
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library in any way. |
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|
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=over 4 |
58 |
|
59 |
=item ev_tstamp ev_time () |
60 |
|
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Returns the current time as libev would use it. Please note that the |
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C<ev_now> function is usually faster and also often returns the timestamp |
63 |
you actually want to know. |
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|
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=item int ev_version_major () |
66 |
|
67 |
=item int ev_version_minor () |
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|
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You can find out the major and minor version numbers of the library |
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you linked against by calling the functions C<ev_version_major> and |
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C<ev_version_minor>. If you want, you can compare against the global |
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symbols C<EV_VERSION_MAJOR> and C<EV_VERSION_MINOR>, which specify the |
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version of the library your program was compiled against. |
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|
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Usually, it's a good idea to terminate if the major versions mismatch, |
76 |
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. |
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|
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=item ev_set_allocator (void *(*cb)(void *ptr, long size)) |
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|
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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. |
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|
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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. |
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|
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=item ev_set_syserr_cb (void (*cb)(const char *msg)); |
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|
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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). |
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|
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=back |
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|
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=head1 FUNCTIONS CONTROLLING THE EVENT LOOP |
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|
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An event loop is described by a C<struct ev_loop *>. The library knows two |
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types of such loops, the I<default> loop, which supports signals and child |
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events, and dynamically created loops which do not. |
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|
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If you use threads, a common model is to run the default event loop |
111 |
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). |
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|
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=over 4 |
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|
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=item struct ev_loop *ev_default_loop (unsigned int flags) |
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|
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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). |
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|
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If you don't know what event loop to use, use the one returned from this |
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function. |
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|
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The flags argument can be used to specify special behaviour or specific |
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backends to use, and is usually specified as 0 (or EVFLAG_AUTO). |
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|
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It supports the following flags: |
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|
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=over 4 |
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|
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=item C<EVFLAG_AUTO> |
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|
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The default flags value. Use this if you have no clue (it's the right |
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thing, believe me). |
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|
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=item C<EVFLAG_NOENV> |
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|
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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> look at the environment variable |
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C<LIBEV_FLAGS>. 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 |
148 |
around bugs. |
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|
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=item C<EVMETHOD_SELECT> (portable select backend) |
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|
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=item C<EVMETHOD_POLL> (poll backend, available everywhere except on windows) |
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|
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=item C<EVMETHOD_EPOLL> (linux only) |
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|
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=item C<EVMETHOD_KQUEUE> (some bsds only) |
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|
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=item C<EVMETHOD_DEVPOLL> (solaris 8 only) |
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|
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=item C<EVMETHOD_PORT> (solaris 10 only) |
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|
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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 one are |
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specified, any backend will do. |
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|
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=back |
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|
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=item struct ev_loop *ev_loop_new (unsigned int flags) |
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|
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Similar to C<ev_default_loop>, but always creates a new event loop that is |
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always distinct from the default loop. Unlike the default loop, it cannot |
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handle signal and child watchers, and attempts to do so will be greeted by |
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undefined behaviour (or a failed assertion if assertions are enabled). |
174 |
|
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=item ev_default_destroy () |
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|
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Destroys the default loop again (frees all memory and kernel state |
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etc.). This stops all registered event watchers (by not touching them in |
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any way whatsoever, although you cannot rely on this :). |
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|
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=item ev_loop_destroy (loop) |
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|
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Like C<ev_default_destroy>, but destroys an event loop created by an |
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earlier call to C<ev_loop_new>. |
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|
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=item ev_default_fork () |
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|
188 |
This function reinitialises the kernel state for backends that have |
189 |
one. Despite the name, you can call it anytime, but it makes most sense |
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after forking, in either the parent or child process (or both, but that |
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again makes little sense). |
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|
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You I<must> call this function after forking if and only if you want to |
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use the event library in both processes. If you just fork+exec, you don't |
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have to call it. |
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|
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The function itself is quite fast and it's usually not a problem to call |
198 |
it just in case after a fork. To make this easy, the function will fit in |
199 |
quite nicely into a call to C<pthread_atfork>: |
200 |
|
201 |
pthread_atfork (0, 0, ev_default_fork); |
202 |
|
203 |
=item ev_loop_fork (loop) |
204 |
|
205 |
Like C<ev_default_fork>, but acts on an event loop created by |
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C<ev_loop_new>. Yes, you have to call this on every allocated event loop |
207 |
after fork, and how you do this is entirely your own problem. |
208 |
|
209 |
=item unsigned int ev_method (loop) |
210 |
|
211 |
Returns one of the C<EVMETHOD_*> flags indicating the event backend in |
212 |
use. |
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|
214 |
=item ev_tstamp ev_now (loop) |
215 |
|
216 |
Returns the current "event loop time", which is the time the event loop |
217 |
got events and started processing them. This timestamp does not change |
218 |
as long as callbacks are being processed, and this is also the base time |
219 |
used for relative timers. You can treat it as the timestamp of the event |
220 |
occuring (or more correctly, the mainloop finding out about it). |
221 |
|
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=item ev_loop (loop, int flags) |
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|
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Finally, this is it, the event handler. This function usually is called |
225 |
after you initialised all your watchers and you want to start handling |
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events. |
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|
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If the flags argument is specified as 0, it will not return until either |
229 |
no event watchers are active anymore or C<ev_unloop> was called. |
230 |
|
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A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle |
232 |
those events and any outstanding ones, but will not block your process in |
233 |
case there are no events and will return after one iteration of the loop. |
234 |
|
235 |
A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if |
236 |
neccessary) and will handle those and any outstanding ones. It will block |
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your process until at least one new event arrives, and will return after |
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one iteration of the loop. |
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|
240 |
This flags value could be used to implement alternative looping |
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constructs, but the C<prepare> and C<check> watchers provide a better and |
242 |
more generic mechanism. |
243 |
|
244 |
Here are the gory details of what ev_loop does: |
245 |
|
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1. If there are no active watchers (reference count is zero), return. |
247 |
2. Queue and immediately call all prepare watchers. |
248 |
3. If we have been forked, recreate the kernel state. |
249 |
4. Update the kernel state with all outstanding changes. |
250 |
5. Update the "event loop time". |
251 |
6. Calculate for how long to block. |
252 |
7. Block the process, waiting for events. |
253 |
8. Update the "event loop time" and do time jump handling. |
254 |
9. Queue all outstanding timers. |
255 |
10. Queue all outstanding periodics. |
256 |
11. If no events are pending now, queue all idle watchers. |
257 |
12. Queue all check watchers. |
258 |
13. Call all queued watchers in reverse order (i.e. check watchers first). |
259 |
14. If ev_unloop has been called or EVLOOP_ONESHOT or EVLOOP_NONBLOCK |
260 |
was used, return, otherwise continue with step #1. |
261 |
|
262 |
=item ev_unloop (loop, how) |
263 |
|
264 |
Can be used to make a call to C<ev_loop> return early (but only after it |
265 |
has processed all outstanding events). The C<how> argument must be either |
266 |
C<EVUNLOOP_ONE>, which will make the innermost C<ev_loop> call return, or |
267 |
C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return. |
268 |
|
269 |
=item ev_ref (loop) |
270 |
|
271 |
=item ev_unref (loop) |
272 |
|
273 |
Ref/unref can be used to add or remove a reference count on the event |
274 |
loop: Every watcher keeps one reference, and as long as the reference |
275 |
count is nonzero, C<ev_loop> will not return on its own. If you have |
276 |
a watcher you never unregister that should not keep C<ev_loop> from |
277 |
returning, ev_unref() after starting, and ev_ref() before stopping it. For |
278 |
example, libev itself uses this for its internal signal pipe: It is not |
279 |
visible to the libev user and should not keep C<ev_loop> from exiting if |
280 |
no event watchers registered by it are active. It is also an excellent |
281 |
way to do this for generic recurring timers or from within third-party |
282 |
libraries. Just remember to I<unref after start> and I<ref before stop>. |
283 |
|
284 |
=back |
285 |
|
286 |
=head1 ANATOMY OF A WATCHER |
287 |
|
288 |
A watcher is a structure that you create and register to record your |
289 |
interest in some event. For instance, if you want to wait for STDIN to |
290 |
become readable, you would create an C<ev_io> watcher for that: |
291 |
|
292 |
static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents) |
293 |
{ |
294 |
ev_io_stop (w); |
295 |
ev_unloop (loop, EVUNLOOP_ALL); |
296 |
} |
297 |
|
298 |
struct ev_loop *loop = ev_default_loop (0); |
299 |
struct ev_io stdin_watcher; |
300 |
ev_init (&stdin_watcher, my_cb); |
301 |
ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ); |
302 |
ev_io_start (loop, &stdin_watcher); |
303 |
ev_loop (loop, 0); |
304 |
|
305 |
As you can see, you are responsible for allocating the memory for your |
306 |
watcher structures (and it is usually a bad idea to do this on the stack, |
307 |
although this can sometimes be quite valid). |
308 |
|
309 |
Each watcher structure must be initialised by a call to C<ev_init |
310 |
(watcher *, callback)>, which expects a callback to be provided. This |
311 |
callback gets invoked each time the event occurs (or, in the case of io |
312 |
watchers, each time the event loop detects that the file descriptor given |
313 |
is readable and/or writable). |
314 |
|
315 |
Each watcher type has its own C<< ev_<type>_set (watcher *, ...) >> macro |
316 |
with arguments specific to this watcher type. There is also a macro |
317 |
to combine initialisation and setting in one call: C<< ev_<type>_init |
318 |
(watcher *, callback, ...) >>. |
319 |
|
320 |
To make the watcher actually watch out for events, you have to start it |
321 |
with a watcher-specific start function (C<< ev_<type>_start (loop, watcher |
322 |
*) >>), and you can stop watching for events at any time by calling the |
323 |
corresponding stop function (C<< ev_<type>_stop (loop, watcher *) >>. |
324 |
|
325 |
As long as your watcher is active (has been started but not stopped) you |
326 |
must not touch the values stored in it. Most specifically you must never |
327 |
reinitialise it or call its set method. |
328 |
|
329 |
You can check whether an event is active by calling the C<ev_is_active |
330 |
(watcher *)> macro. To see whether an event is outstanding (but the |
331 |
callback for it has not been called yet) you can use the C<ev_is_pending |
332 |
(watcher *)> macro. |
333 |
|
334 |
Each and every callback receives the event loop pointer as first, the |
335 |
registered watcher structure as second, and a bitset of received events as |
336 |
third argument. |
337 |
|
338 |
The received events usually include a single bit per event type received |
339 |
(you can receive multiple events at the same time). The possible bit masks |
340 |
are: |
341 |
|
342 |
=over 4 |
343 |
|
344 |
=item C<EV_READ> |
345 |
|
346 |
=item C<EV_WRITE> |
347 |
|
348 |
The file descriptor in the C<ev_io> watcher has become readable and/or |
349 |
writable. |
350 |
|
351 |
=item C<EV_TIMEOUT> |
352 |
|
353 |
The C<ev_timer> watcher has timed out. |
354 |
|
355 |
=item C<EV_PERIODIC> |
356 |
|
357 |
The C<ev_periodic> watcher has timed out. |
358 |
|
359 |
=item C<EV_SIGNAL> |
360 |
|
361 |
The signal specified in the C<ev_signal> watcher has been received by a thread. |
362 |
|
363 |
=item C<EV_CHILD> |
364 |
|
365 |
The pid specified in the C<ev_child> watcher has received a status change. |
366 |
|
367 |
=item C<EV_IDLE> |
368 |
|
369 |
The C<ev_idle> watcher has determined that you have nothing better to do. |
370 |
|
371 |
=item C<EV_PREPARE> |
372 |
|
373 |
=item C<EV_CHECK> |
374 |
|
375 |
All C<ev_prepare> watchers are invoked just I<before> C<ev_loop> starts |
376 |
to gather new events, and all C<ev_check> watchers are invoked just after |
377 |
C<ev_loop> has gathered them, but before it invokes any callbacks for any |
378 |
received events. Callbacks of both watcher types can start and stop as |
379 |
many watchers as they want, and all of them will be taken into account |
380 |
(for example, a C<ev_prepare> watcher might start an idle watcher to keep |
381 |
C<ev_loop> from blocking). |
382 |
|
383 |
=item C<EV_ERROR> |
384 |
|
385 |
An unspecified error has occured, the watcher has been stopped. This might |
386 |
happen because the watcher could not be properly started because libev |
387 |
ran out of memory, a file descriptor was found to be closed or any other |
388 |
problem. You best act on it by reporting the problem and somehow coping |
389 |
with the watcher being stopped. |
390 |
|
391 |
Libev will usually signal a few "dummy" events together with an error, |
392 |
for example it might indicate that a fd is readable or writable, and if |
393 |
your callbacks is well-written it can just attempt the operation and cope |
394 |
with the error from read() or write(). This will not work in multithreaded |
395 |
programs, though, so beware. |
396 |
|
397 |
=back |
398 |
|
399 |
=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER |
400 |
|
401 |
Each watcher has, by default, a member C<void *data> that you can change |
402 |
and read at any time, libev will completely ignore it. This can be used |
403 |
to associate arbitrary data with your watcher. If you need more data and |
404 |
don't want to allocate memory and store a pointer to it in that data |
405 |
member, you can also "subclass" the watcher type and provide your own |
406 |
data: |
407 |
|
408 |
struct my_io |
409 |
{ |
410 |
struct ev_io io; |
411 |
int otherfd; |
412 |
void *somedata; |
413 |
struct whatever *mostinteresting; |
414 |
} |
415 |
|
416 |
And since your callback will be called with a pointer to the watcher, you |
417 |
can cast it back to your own type: |
418 |
|
419 |
static void my_cb (struct ev_loop *loop, struct ev_io *w_, int revents) |
420 |
{ |
421 |
struct my_io *w = (struct my_io *)w_; |
422 |
... |
423 |
} |
424 |
|
425 |
More interesting and less C-conformant ways of catsing your callback type |
426 |
have been omitted.... |
427 |
|
428 |
|
429 |
=head1 WATCHER TYPES |
430 |
|
431 |
This section describes each watcher in detail, but will not repeat |
432 |
information given in the last section. |
433 |
|
434 |
=head2 C<ev_io> - is this file descriptor readable or writable |
435 |
|
436 |
I/O watchers check whether a file descriptor is readable or writable |
437 |
in each iteration of the event loop (This behaviour is called |
438 |
level-triggering because you keep receiving events as long as the |
439 |
condition persists. Remember you can stop the watcher if you don't want to |
440 |
act on the event and neither want to receive future events). |
441 |
|
442 |
In general you can register as many read and/or write event watchers per |
443 |
fd as you want (as long as you don't confuse yourself). Setting all file |
444 |
descriptors to non-blocking mode is also usually a good idea (but not |
445 |
required if you know what you are doing). |
446 |
|
447 |
You have to be careful with dup'ed file descriptors, though. Some backends |
448 |
(the linux epoll backend is a notable example) cannot handle dup'ed file |
449 |
descriptors correctly if you register interest in two or more fds pointing |
450 |
to the same underlying file/socket etc. description (that is, they share |
451 |
the same underlying "file open"). |
452 |
|
453 |
If you must do this, then force the use of a known-to-be-good backend |
454 |
(at the time of this writing, this includes only EVMETHOD_SELECT and |
455 |
EVMETHOD_POLL). |
456 |
|
457 |
=over 4 |
458 |
|
459 |
=item ev_io_init (ev_io *, callback, int fd, int events) |
460 |
|
461 |
=item ev_io_set (ev_io *, int fd, int events) |
462 |
|
463 |
Configures an C<ev_io> watcher. The fd is the file descriptor to rceeive |
464 |
events for and events is either C<EV_READ>, C<EV_WRITE> or C<EV_READ | |
465 |
EV_WRITE> to receive the given events. |
466 |
|
467 |
=back |
468 |
|
469 |
=head2 C<ev_timer> - relative and optionally recurring timeouts |
470 |
|
471 |
Timer watchers are simple relative timers that generate an event after a |
472 |
given time, and optionally repeating in regular intervals after that. |
473 |
|
474 |
The timers are based on real time, that is, if you register an event that |
475 |
times out after an hour and you reset your system clock to last years |
476 |
time, it will still time out after (roughly) and hour. "Roughly" because |
477 |
detecting time jumps is hard, and some inaccuracies are unavoidable (the |
478 |
monotonic clock option helps a lot here). |
479 |
|
480 |
The relative timeouts are calculated relative to the C<ev_now ()> |
481 |
time. This is usually the right thing as this timestamp refers to the time |
482 |
of the event triggering whatever timeout you are modifying/starting. If |
483 |
you suspect event processing to be delayed and you I<need> to base the timeout |
484 |
on the current time, use something like this to adjust for this: |
485 |
|
486 |
ev_timer_set (&timer, after + ev_now () - ev_time (), 0.); |
487 |
|
488 |
The callback is guarenteed to be invoked only when its timeout has passed, |
489 |
but if multiple timers become ready during the same loop iteration then |
490 |
order of execution is undefined. |
491 |
|
492 |
=over 4 |
493 |
|
494 |
=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat) |
495 |
|
496 |
=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat) |
497 |
|
498 |
Configure the timer to trigger after C<after> seconds. If C<repeat> is |
499 |
C<0.>, then it will automatically be stopped. If it is positive, then the |
500 |
timer will automatically be configured to trigger again C<repeat> seconds |
501 |
later, again, and again, until stopped manually. |
502 |
|
503 |
The timer itself will do a best-effort at avoiding drift, that is, if you |
504 |
configure a timer to trigger every 10 seconds, then it will trigger at |
505 |
exactly 10 second intervals. If, however, your program cannot keep up with |
506 |
the timer (because it takes longer than those 10 seconds to do stuff) the |
507 |
timer will not fire more than once per event loop iteration. |
508 |
|
509 |
=item ev_timer_again (loop) |
510 |
|
511 |
This will act as if the timer timed out and restart it again if it is |
512 |
repeating. The exact semantics are: |
513 |
|
514 |
If the timer is started but nonrepeating, stop it. |
515 |
|
516 |
If the timer is repeating, either start it if necessary (with the repeat |
517 |
value), or reset the running timer to the repeat value. |
518 |
|
519 |
This sounds a bit complicated, but here is a useful and typical |
520 |
example: Imagine you have a tcp connection and you want a so-called idle |
521 |
timeout, that is, you want to be called when there have been, say, 60 |
522 |
seconds of inactivity on the socket. The easiest way to do this is to |
523 |
configure an C<ev_timer> with after=repeat=60 and calling ev_timer_again each |
524 |
time you successfully read or write some data. If you go into an idle |
525 |
state where you do not expect data to travel on the socket, you can stop |
526 |
the timer, and again will automatically restart it if need be. |
527 |
|
528 |
=back |
529 |
|
530 |
=head2 C<ev_periodic> - to cron or not to cron |
531 |
|
532 |
Periodic watchers are also timers of a kind, but they are very versatile |
533 |
(and unfortunately a bit complex). |
534 |
|
535 |
Unlike C<ev_timer>'s, they are not based on real time (or relative time) |
536 |
but on wallclock time (absolute time). You can tell a periodic watcher |
537 |
to trigger "at" some specific point in time. For example, if you tell a |
538 |
periodic watcher to trigger in 10 seconds (by specifiying e.g. c<ev_now () |
539 |
+ 10.>) and then reset your system clock to the last year, then it will |
540 |
take a year to trigger the event (unlike an C<ev_timer>, which would trigger |
541 |
roughly 10 seconds later and of course not if you reset your system time |
542 |
again). |
543 |
|
544 |
They can also be used to implement vastly more complex timers, such as |
545 |
triggering an event on eahc midnight, local time. |
546 |
|
547 |
As with timers, the callback is guarenteed to be invoked only when the |
548 |
time (C<at>) has been passed, but if multiple periodic timers become ready |
549 |
during the same loop iteration then order of execution is undefined. |
550 |
|
551 |
=over 4 |
552 |
|
553 |
=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb) |
554 |
|
555 |
=item ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb) |
556 |
|
557 |
Lots of arguments, lets sort it out... There are basically three modes of |
558 |
operation, and we will explain them from simplest to complex: |
559 |
|
560 |
=over 4 |
561 |
|
562 |
=item * absolute timer (interval = reschedule_cb = 0) |
563 |
|
564 |
In this configuration the watcher triggers an event at the wallclock time |
565 |
C<at> and doesn't repeat. It will not adjust when a time jump occurs, |
566 |
that is, if it is to be run at January 1st 2011 then it will run when the |
567 |
system time reaches or surpasses this time. |
568 |
|
569 |
=item * non-repeating interval timer (interval > 0, reschedule_cb = 0) |
570 |
|
571 |
In this mode the watcher will always be scheduled to time out at the next |
572 |
C<at + N * interval> time (for some integer N) and then repeat, regardless |
573 |
of any time jumps. |
574 |
|
575 |
This can be used to create timers that do not drift with respect to system |
576 |
time: |
577 |
|
578 |
ev_periodic_set (&periodic, 0., 3600., 0); |
579 |
|
580 |
This doesn't mean there will always be 3600 seconds in between triggers, |
581 |
but only that the the callback will be called when the system time shows a |
582 |
full hour (UTC), or more correctly, when the system time is evenly divisible |
583 |
by 3600. |
584 |
|
585 |
Another way to think about it (for the mathematically inclined) is that |
586 |
C<ev_periodic> will try to run the callback in this mode at the next possible |
587 |
time where C<time = at (mod interval)>, regardless of any time jumps. |
588 |
|
589 |
=item * manual reschedule mode (reschedule_cb = callback) |
590 |
|
591 |
In this mode the values for C<interval> and C<at> are both being |
592 |
ignored. Instead, each time the periodic watcher gets scheduled, the |
593 |
reschedule callback will be called with the watcher as first, and the |
594 |
current time as second argument. |
595 |
|
596 |
NOTE: I<This callback MUST NOT stop or destroy any periodic watcher, |
597 |
ever, or make any event loop modifications>. If you need to stop it, |
598 |
return C<now + 1e30> (or so, fudge fudge) and stop it afterwards (e.g. by |
599 |
starting a prepare watcher). |
600 |
|
601 |
Its prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic *w, |
602 |
ev_tstamp now)>, e.g.: |
603 |
|
604 |
static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now) |
605 |
{ |
606 |
return now + 60.; |
607 |
} |
608 |
|
609 |
It must return the next time to trigger, based on the passed time value |
610 |
(that is, the lowest time value larger than to the second argument). It |
611 |
will usually be called just before the callback will be triggered, but |
612 |
might be called at other times, too. |
613 |
|
614 |
NOTE: I<< This callback must always return a time that is later than the |
615 |
passed C<now> value >>. Not even C<now> itself will do, it I<must> be larger. |
616 |
|
617 |
This can be used to create very complex timers, such as a timer that |
618 |
triggers on each midnight, local time. To do this, you would calculate the |
619 |
next midnight after C<now> and return the timestamp value for this. How |
620 |
you do this is, again, up to you (but it is not trivial, which is the main |
621 |
reason I omitted it as an example). |
622 |
|
623 |
=back |
624 |
|
625 |
=item ev_periodic_again (loop, ev_periodic *) |
626 |
|
627 |
Simply stops and restarts the periodic watcher again. This is only useful |
628 |
when you changed some parameters or the reschedule callback would return |
629 |
a different time than the last time it was called (e.g. in a crond like |
630 |
program when the crontabs have changed). |
631 |
|
632 |
=back |
633 |
|
634 |
=head2 C<ev_signal> - signal me when a signal gets signalled |
635 |
|
636 |
Signal watchers will trigger an event when the process receives a specific |
637 |
signal one or more times. Even though signals are very asynchronous, libev |
638 |
will try it's best to deliver signals synchronously, i.e. as part of the |
639 |
normal event processing, like any other event. |
640 |
|
641 |
You can configure as many watchers as you like per signal. Only when the |
642 |
first watcher gets started will libev actually register a signal watcher |
643 |
with the kernel (thus it coexists with your own signal handlers as long |
644 |
as you don't register any with libev). Similarly, when the last signal |
645 |
watcher for a signal is stopped libev will reset the signal handler to |
646 |
SIG_DFL (regardless of what it was set to before). |
647 |
|
648 |
=over 4 |
649 |
|
650 |
=item ev_signal_init (ev_signal *, callback, int signum) |
651 |
|
652 |
=item ev_signal_set (ev_signal *, int signum) |
653 |
|
654 |
Configures the watcher to trigger on the given signal number (usually one |
655 |
of the C<SIGxxx> constants). |
656 |
|
657 |
=back |
658 |
|
659 |
=head2 C<ev_child> - wait for pid status changes |
660 |
|
661 |
Child watchers trigger when your process receives a SIGCHLD in response to |
662 |
some child status changes (most typically when a child of yours dies). |
663 |
|
664 |
=over 4 |
665 |
|
666 |
=item ev_child_init (ev_child *, callback, int pid) |
667 |
|
668 |
=item ev_child_set (ev_child *, int pid) |
669 |
|
670 |
Configures the watcher to wait for status changes of process C<pid> (or |
671 |
I<any> process if C<pid> is specified as C<0>). The callback can look |
672 |
at the C<rstatus> member of the C<ev_child> watcher structure to see |
673 |
the status word (use the macros from C<sys/wait.h> and see your systems |
674 |
C<waitpid> documentation). The C<rpid> member contains the pid of the |
675 |
process causing the status change. |
676 |
|
677 |
=back |
678 |
|
679 |
=head2 C<ev_idle> - when you've got nothing better to do |
680 |
|
681 |
Idle watchers trigger events when there are no other events are pending |
682 |
(prepare, check and other idle watchers do not count). That is, as long |
683 |
as your process is busy handling sockets or timeouts (or even signals, |
684 |
imagine) it will not be triggered. But when your process is idle all idle |
685 |
watchers are being called again and again, once per event loop iteration - |
686 |
until stopped, that is, or your process receives more events and becomes |
687 |
busy. |
688 |
|
689 |
The most noteworthy effect is that as long as any idle watchers are |
690 |
active, the process will not block when waiting for new events. |
691 |
|
692 |
Apart from keeping your process non-blocking (which is a useful |
693 |
effect on its own sometimes), idle watchers are a good place to do |
694 |
"pseudo-background processing", or delay processing stuff to after the |
695 |
event loop has handled all outstanding events. |
696 |
|
697 |
=over 4 |
698 |
|
699 |
=item ev_idle_init (ev_signal *, callback) |
700 |
|
701 |
Initialises and configures the idle watcher - it has no parameters of any |
702 |
kind. There is a C<ev_idle_set> macro, but using it is utterly pointless, |
703 |
believe me. |
704 |
|
705 |
=back |
706 |
|
707 |
=head2 C<ev_prepare> and C<ev_check> - customise your event loop |
708 |
|
709 |
Prepare and check watchers are usually (but not always) used in tandem: |
710 |
prepare watchers get invoked before the process blocks and check watchers |
711 |
afterwards. |
712 |
|
713 |
Their main purpose is to integrate other event mechanisms into libev. This |
714 |
could be used, for example, to track variable changes, implement your own |
715 |
watchers, integrate net-snmp or a coroutine library and lots more. |
716 |
|
717 |
This is done by examining in each prepare call which file descriptors need |
718 |
to be watched by the other library, registering C<ev_io> watchers for |
719 |
them and starting an C<ev_timer> watcher for any timeouts (many libraries |
720 |
provide just this functionality). Then, in the check watcher you check for |
721 |
any events that occured (by checking the pending status of all watchers |
722 |
and stopping them) and call back into the library. The I/O and timer |
723 |
callbacks will never actually be called (but must be valid nevertheless, |
724 |
because you never know, you know?). |
725 |
|
726 |
As another example, the Perl Coro module uses these hooks to integrate |
727 |
coroutines into libev programs, by yielding to other active coroutines |
728 |
during each prepare and only letting the process block if no coroutines |
729 |
are ready to run (it's actually more complicated: it only runs coroutines |
730 |
with priority higher than or equal to the event loop and one coroutine |
731 |
of lower priority, but only once, using idle watchers to keep the event |
732 |
loop from blocking if lower-priority coroutines are active, thus mapping |
733 |
low-priority coroutines to idle/background tasks). |
734 |
|
735 |
=over 4 |
736 |
|
737 |
=item ev_prepare_init (ev_prepare *, callback) |
738 |
|
739 |
=item ev_check_init (ev_check *, callback) |
740 |
|
741 |
Initialises and configures the prepare or check watcher - they have no |
742 |
parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set> |
743 |
macros, but using them is utterly, utterly and completely pointless. |
744 |
|
745 |
=back |
746 |
|
747 |
=head1 OTHER FUNCTIONS |
748 |
|
749 |
There are some other functions of possible interest. Described. Here. Now. |
750 |
|
751 |
=over 4 |
752 |
|
753 |
=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback) |
754 |
|
755 |
This function combines a simple timer and an I/O watcher, calls your |
756 |
callback on whichever event happens first and automatically stop both |
757 |
watchers. This is useful if you want to wait for a single event on an fd |
758 |
or timeout without having to allocate/configure/start/stop/free one or |
759 |
more watchers yourself. |
760 |
|
761 |
If C<fd> is less than 0, then no I/O watcher will be started and events |
762 |
is being ignored. Otherwise, an C<ev_io> watcher for the given C<fd> and |
763 |
C<events> set will be craeted and started. |
764 |
|
765 |
If C<timeout> is less than 0, then no timeout watcher will be |
766 |
started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and |
767 |
repeat = 0) will be started. While C<0> is a valid timeout, it is of |
768 |
dubious value. |
769 |
|
770 |
The callback has the type C<void (*cb)(int revents, void *arg)> and gets |
771 |
passed an C<revents> set like normal event callbacks (a combination of |
772 |
C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg> |
773 |
value passed to C<ev_once>: |
774 |
|
775 |
static void stdin_ready (int revents, void *arg) |
776 |
{ |
777 |
if (revents & EV_TIMEOUT) |
778 |
/* doh, nothing entered */; |
779 |
else if (revents & EV_READ) |
780 |
/* stdin might have data for us, joy! */; |
781 |
} |
782 |
|
783 |
ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0); |
784 |
|
785 |
=item ev_feed_event (loop, watcher, int events) |
786 |
|
787 |
Feeds the given event set into the event loop, as if the specified event |
788 |
had happened for the specified watcher (which must be a pointer to an |
789 |
initialised but not necessarily started event watcher). |
790 |
|
791 |
=item ev_feed_fd_event (loop, int fd, int revents) |
792 |
|
793 |
Feed an event on the given fd, as if a file descriptor backend detected |
794 |
the given events it. |
795 |
|
796 |
=item ev_feed_signal_event (loop, int signum) |
797 |
|
798 |
Feed an event as if the given signal occured (loop must be the default loop!). |
799 |
|
800 |
=back |
801 |
|
802 |
=head1 LIBEVENT EMULATION |
803 |
|
804 |
Libev offers a compatibility emulation layer for libevent. It cannot |
805 |
emulate the internals of libevent, so here are some usage hints: |
806 |
|
807 |
=over 4 |
808 |
|
809 |
=item * Use it by including <event.h>, as usual. |
810 |
|
811 |
=item * The following members are fully supported: ev_base, ev_callback, |
812 |
ev_arg, ev_fd, ev_res, ev_events. |
813 |
|
814 |
=item * Avoid using ev_flags and the EVLIST_*-macros, while it is |
815 |
maintained by libev, it does not work exactly the same way as in libevent (consider |
816 |
it a private API). |
817 |
|
818 |
=item * Priorities are not currently supported. Initialising priorities |
819 |
will fail and all watchers will have the same priority, even though there |
820 |
is an ev_pri field. |
821 |
|
822 |
=item * Other members are not supported. |
823 |
|
824 |
=item * The libev emulation is I<not> ABI compatible to libevent, you need |
825 |
to use the libev header file and library. |
826 |
|
827 |
=back |
828 |
|
829 |
=head1 C++ SUPPORT |
830 |
|
831 |
TBD. |
832 |
|
833 |
=head1 AUTHOR |
834 |
|
835 |
Marc Lehmann <libev@schmorp.de>. |
836 |
|