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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 |
|
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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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|
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=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 |
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|
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 |
40 |
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 *>) |
42 |
will not have this argument. |
43 |
|
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=head1 TIME REPRESENTATION |
45 |
|
46 |
Libev represents time as a single floating point number, representing the |
47 |
(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 |
49 |
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 |
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|
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=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 |
86 |
destructive action. The default is your system realloc function. |
87 |
|
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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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|
110 |
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 |
112 |
create, you also create another event loop. Libev itself does no locking |
113 |
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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|
150 |
=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). |
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|
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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 :). |
180 |
|
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=item ev_loop_destroy (loop) |
182 |
|
183 |
Like C<ev_default_destroy>, but destroys an event loop created by an |
184 |
earlier call to C<ev_loop_new>. |
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|
186 |
=item ev_default_fork () |
187 |
|
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). |
192 |
|
193 |
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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|
197 |
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 |
199 |
quite nicely into a call to C<pthread_atfork>: |
200 |
|
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pthread_atfork (0, 0, ev_default_fork); |
202 |
|
203 |
=item ev_loop_fork (loop) |
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|
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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. |
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|
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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|
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=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 |
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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). |
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|
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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 |
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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 |
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no event watchers are active anymore or C<ev_unloop> was called. |
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|
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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 |
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case there are no events and will return after one iteration of the loop. |
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|
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A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if |
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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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|
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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 |
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more generic mechanism. |
243 |
|
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=item ev_unloop (loop, how) |
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|
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Can be used to make a call to C<ev_loop> return early (but only after it |
247 |
has processed all outstanding events). The C<how> argument must be either |
248 |
C<EVUNLOOP_ONE>, which will make the innermost C<ev_loop> call return, or |
249 |
C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return. |
250 |
|
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=item ev_ref (loop) |
252 |
|
253 |
=item ev_unref (loop) |
254 |
|
255 |
Ref/unref can be used to add or remove a reference count on the event |
256 |
loop: Every watcher keeps one reference, and as long as the reference |
257 |
count is nonzero, C<ev_loop> will not return on its own. If you have |
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a watcher you never unregister that should not keep C<ev_loop> from |
259 |
returning, ev_unref() after starting, and ev_ref() before stopping it. For |
260 |
example, libev itself uses this for its internal signal pipe: It is not |
261 |
visible to the libev user and should not keep C<ev_loop> from exiting if |
262 |
no event watchers registered by it are active. It is also an excellent |
263 |
way to do this for generic recurring timers or from within third-party |
264 |
libraries. Just remember to I<unref after start> and I<ref before stop>. |
265 |
|
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=back |
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|
268 |
=head1 ANATOMY OF A WATCHER |
269 |
|
270 |
A watcher is a structure that you create and register to record your |
271 |
interest in some event. For instance, if you want to wait for STDIN to |
272 |
become readable, you would create an C<ev_io> watcher for that: |
273 |
|
274 |
static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents) |
275 |
{ |
276 |
ev_io_stop (w); |
277 |
ev_unloop (loop, EVUNLOOP_ALL); |
278 |
} |
279 |
|
280 |
struct ev_loop *loop = ev_default_loop (0); |
281 |
struct ev_io stdin_watcher; |
282 |
ev_init (&stdin_watcher, my_cb); |
283 |
ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ); |
284 |
ev_io_start (loop, &stdin_watcher); |
285 |
ev_loop (loop, 0); |
286 |
|
287 |
As you can see, you are responsible for allocating the memory for your |
288 |
watcher structures (and it is usually a bad idea to do this on the stack, |
289 |
although this can sometimes be quite valid). |
290 |
|
291 |
Each watcher structure must be initialised by a call to C<ev_init |
292 |
(watcher *, callback)>, which expects a callback to be provided. This |
293 |
callback gets invoked each time the event occurs (or, in the case of io |
294 |
watchers, each time the event loop detects that the file descriptor given |
295 |
is readable and/or writable). |
296 |
|
297 |
Each watcher type has its own C<< ev_<type>_set (watcher *, ...) >> macro |
298 |
with arguments specific to this watcher type. There is also a macro |
299 |
to combine initialisation and setting in one call: C<< ev_<type>_init |
300 |
(watcher *, callback, ...) >>. |
301 |
|
302 |
To make the watcher actually watch out for events, you have to start it |
303 |
with a watcher-specific start function (C<< ev_<type>_start (loop, watcher |
304 |
*) >>), and you can stop watching for events at any time by calling the |
305 |
corresponding stop function (C<< ev_<type>_stop (loop, watcher *) >>. |
306 |
|
307 |
As long as your watcher is active (has been started but not stopped) you |
308 |
must not touch the values stored in it. Most specifically you must never |
309 |
reinitialise it or call its set method. |
310 |
|
311 |
You can check whether an event is active by calling the C<ev_is_active |
312 |
(watcher *)> macro. To see whether an event is outstanding (but the |
313 |
callback for it has not been called yet) you can use the C<ev_is_pending |
314 |
(watcher *)> macro. |
315 |
|
316 |
Each and every callback receives the event loop pointer as first, the |
317 |
registered watcher structure as second, and a bitset of received events as |
318 |
third argument. |
319 |
|
320 |
The received events usually include a single bit per event type received |
321 |
(you can receive multiple events at the same time). The possible bit masks |
322 |
are: |
323 |
|
324 |
=over 4 |
325 |
|
326 |
=item C<EV_READ> |
327 |
|
328 |
=item C<EV_WRITE> |
329 |
|
330 |
The file descriptor in the C<ev_io> watcher has become readable and/or |
331 |
writable. |
332 |
|
333 |
=item C<EV_TIMEOUT> |
334 |
|
335 |
The C<ev_timer> watcher has timed out. |
336 |
|
337 |
=item C<EV_PERIODIC> |
338 |
|
339 |
The C<ev_periodic> watcher has timed out. |
340 |
|
341 |
=item C<EV_SIGNAL> |
342 |
|
343 |
The signal specified in the C<ev_signal> watcher has been received by a thread. |
344 |
|
345 |
=item C<EV_CHILD> |
346 |
|
347 |
The pid specified in the C<ev_child> watcher has received a status change. |
348 |
|
349 |
=item C<EV_IDLE> |
350 |
|
351 |
The C<ev_idle> watcher has determined that you have nothing better to do. |
352 |
|
353 |
=item C<EV_PREPARE> |
354 |
|
355 |
=item C<EV_CHECK> |
356 |
|
357 |
All C<ev_prepare> watchers are invoked just I<before> C<ev_loop> starts |
358 |
to gather new events, and all C<ev_check> watchers are invoked just after |
359 |
C<ev_loop> has gathered them, but before it invokes any callbacks for any |
360 |
received events. Callbacks of both watcher types can start and stop as |
361 |
many watchers as they want, and all of them will be taken into account |
362 |
(for example, a C<ev_prepare> watcher might start an idle watcher to keep |
363 |
C<ev_loop> from blocking). |
364 |
|
365 |
=item C<EV_ERROR> |
366 |
|
367 |
An unspecified error has occured, the watcher has been stopped. This might |
368 |
happen because the watcher could not be properly started because libev |
369 |
ran out of memory, a file descriptor was found to be closed or any other |
370 |
problem. You best act on it by reporting the problem and somehow coping |
371 |
with the watcher being stopped. |
372 |
|
373 |
Libev will usually signal a few "dummy" events together with an error, |
374 |
for example it might indicate that a fd is readable or writable, and if |
375 |
your callbacks is well-written it can just attempt the operation and cope |
376 |
with the error from read() or write(). This will not work in multithreaded |
377 |
programs, though, so beware. |
378 |
|
379 |
=back |
380 |
|
381 |
=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER |
382 |
|
383 |
Each watcher has, by default, a member C<void *data> that you can change |
384 |
and read at any time, libev will completely ignore it. This can be used |
385 |
to associate arbitrary data with your watcher. If you need more data and |
386 |
don't want to allocate memory and store a pointer to it in that data |
387 |
member, you can also "subclass" the watcher type and provide your own |
388 |
data: |
389 |
|
390 |
struct my_io |
391 |
{ |
392 |
struct ev_io io; |
393 |
int otherfd; |
394 |
void *somedata; |
395 |
struct whatever *mostinteresting; |
396 |
} |
397 |
|
398 |
And since your callback will be called with a pointer to the watcher, you |
399 |
can cast it back to your own type: |
400 |
|
401 |
static void my_cb (struct ev_loop *loop, struct ev_io *w_, int revents) |
402 |
{ |
403 |
struct my_io *w = (struct my_io *)w_; |
404 |
... |
405 |
} |
406 |
|
407 |
More interesting and less C-conformant ways of catsing your callback type |
408 |
have been omitted.... |
409 |
|
410 |
|
411 |
=head1 WATCHER TYPES |
412 |
|
413 |
This section describes each watcher in detail, but will not repeat |
414 |
information given in the last section. |
415 |
|
416 |
=head2 C<ev_io> - is this file descriptor readable or writable |
417 |
|
418 |
I/O watchers check whether a file descriptor is readable or writable |
419 |
in each iteration of the event loop (This behaviour is called |
420 |
level-triggering because you keep receiving events as long as the |
421 |
condition persists. Remember you can stop the watcher if you don't want to |
422 |
act on the event and neither want to receive future events). |
423 |
|
424 |
In general you can register as many read and/or write event watchers per |
425 |
fd as you want (as long as you don't confuse yourself). Setting all file |
426 |
descriptors to non-blocking mode is also usually a good idea (but not |
427 |
required if you know what you are doing). |
428 |
|
429 |
You have to be careful with dup'ed file descriptors, though. Some backends |
430 |
(the linux epoll backend is a notable example) cannot handle dup'ed file |
431 |
descriptors correctly if you register interest in two or more fds pointing |
432 |
to the same underlying file/socket etc. description (that is, they share |
433 |
the same underlying "file open"). |
434 |
|
435 |
If you must do this, then force the use of a known-to-be-good backend |
436 |
(at the time of this writing, this includes only EVMETHOD_SELECT and |
437 |
EVMETHOD_POLL). |
438 |
|
439 |
=over 4 |
440 |
|
441 |
=item ev_io_init (ev_io *, callback, int fd, int events) |
442 |
|
443 |
=item ev_io_set (ev_io *, int fd, int events) |
444 |
|
445 |
Configures an C<ev_io> watcher. The fd is the file descriptor to rceeive |
446 |
events for and events is either C<EV_READ>, C<EV_WRITE> or C<EV_READ | |
447 |
EV_WRITE> to receive the given events. |
448 |
|
449 |
=back |
450 |
|
451 |
=head2 C<ev_timer> - relative and optionally recurring timeouts |
452 |
|
453 |
Timer watchers are simple relative timers that generate an event after a |
454 |
given time, and optionally repeating in regular intervals after that. |
455 |
|
456 |
The timers are based on real time, that is, if you register an event that |
457 |
times out after an hour and you reset your system clock to last years |
458 |
time, it will still time out after (roughly) and hour. "Roughly" because |
459 |
detecting time jumps is hard, and soem inaccuracies are unavoidable (the |
460 |
monotonic clock option helps a lot here). |
461 |
|
462 |
The relative timeouts are calculated relative to the C<ev_now ()> |
463 |
time. This is usually the right thing as this timestamp refers to the time |
464 |
of the event triggering whatever timeout you are modifying/starting. If |
465 |
you suspect event processing to be delayed and you *need* to base the timeout |
466 |
on the current time, use something like this to adjust for this: |
467 |
|
468 |
ev_timer_set (&timer, after + ev_now () - ev_time (), 0.); |
469 |
|
470 |
=over 4 |
471 |
|
472 |
=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat) |
473 |
|
474 |
=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat) |
475 |
|
476 |
Configure the timer to trigger after C<after> seconds. If C<repeat> is |
477 |
C<0.>, then it will automatically be stopped. If it is positive, then the |
478 |
timer will automatically be configured to trigger again C<repeat> seconds |
479 |
later, again, and again, until stopped manually. |
480 |
|
481 |
The timer itself will do a best-effort at avoiding drift, that is, if you |
482 |
configure a timer to trigger every 10 seconds, then it will trigger at |
483 |
exactly 10 second intervals. If, however, your program cannot keep up with |
484 |
the timer (because it takes longer than those 10 seconds to do stuff) the |
485 |
timer will not fire more than once per event loop iteration. |
486 |
|
487 |
=item ev_timer_again (loop) |
488 |
|
489 |
This will act as if the timer timed out and restart it again if it is |
490 |
repeating. The exact semantics are: |
491 |
|
492 |
If the timer is started but nonrepeating, stop it. |
493 |
|
494 |
If the timer is repeating, either start it if necessary (with the repeat |
495 |
value), or reset the running timer to the repeat value. |
496 |
|
497 |
This sounds a bit complicated, but here is a useful and typical |
498 |
example: Imagine you have a tcp connection and you want a so-called idle |
499 |
timeout, that is, you want to be called when there have been, say, 60 |
500 |
seconds of inactivity on the socket. The easiest way to do this is to |
501 |
configure an C<ev_timer> with after=repeat=60 and calling ev_timer_again each |
502 |
time you successfully read or write some data. If you go into an idle |
503 |
state where you do not expect data to travel on the socket, you can stop |
504 |
the timer, and again will automatically restart it if need be. |
505 |
|
506 |
=back |
507 |
|
508 |
=head2 C<ev_periodic> - to cron or not to cron |
509 |
|
510 |
Periodic watchers are also timers of a kind, but they are very versatile |
511 |
(and unfortunately a bit complex). |
512 |
|
513 |
Unlike C<ev_timer>'s, they are not based on real time (or relative time) |
514 |
but on wallclock time (absolute time). You can tell a periodic watcher |
515 |
to trigger "at" some specific point in time. For example, if you tell a |
516 |
periodic watcher to trigger in 10 seconds (by specifiying e.g. c<ev_now () |
517 |
+ 10.>) and then reset your system clock to the last year, then it will |
518 |
take a year to trigger the event (unlike an C<ev_timer>, which would trigger |
519 |
roughly 10 seconds later and of course not if you reset your system time |
520 |
again). |
521 |
|
522 |
They can also be used to implement vastly more complex timers, such as |
523 |
triggering an event on eahc midnight, local time. |
524 |
|
525 |
=over 4 |
526 |
|
527 |
=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb) |
528 |
|
529 |
=item ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb) |
530 |
|
531 |
Lots of arguments, lets sort it out... There are basically three modes of |
532 |
operation, and we will explain them from simplest to complex: |
533 |
|
534 |
|
535 |
=over 4 |
536 |
|
537 |
=item * absolute timer (interval = reschedule_cb = 0) |
538 |
|
539 |
In this configuration the watcher triggers an event at the wallclock time |
540 |
C<at> and doesn't repeat. It will not adjust when a time jump occurs, |
541 |
that is, if it is to be run at January 1st 2011 then it will run when the |
542 |
system time reaches or surpasses this time. |
543 |
|
544 |
=item * non-repeating interval timer (interval > 0, reschedule_cb = 0) |
545 |
|
546 |
In this mode the watcher will always be scheduled to time out at the next |
547 |
C<at + N * interval> time (for some integer N) and then repeat, regardless |
548 |
of any time jumps. |
549 |
|
550 |
This can be used to create timers that do not drift with respect to system |
551 |
time: |
552 |
|
553 |
ev_periodic_set (&periodic, 0., 3600., 0); |
554 |
|
555 |
This doesn't mean there will always be 3600 seconds in between triggers, |
556 |
but only that the the callback will be called when the system time shows a |
557 |
full hour (UTC), or more correctly, when the system time is evenly divisible |
558 |
by 3600. |
559 |
|
560 |
Another way to think about it (for the mathematically inclined) is that |
561 |
C<ev_periodic> will try to run the callback in this mode at the next possible |
562 |
time where C<time = at (mod interval)>, regardless of any time jumps. |
563 |
|
564 |
=item * manual reschedule mode (reschedule_cb = callback) |
565 |
|
566 |
In this mode the values for C<interval> and C<at> are both being |
567 |
ignored. Instead, each time the periodic watcher gets scheduled, the |
568 |
reschedule callback will be called with the watcher as first, and the |
569 |
current time as second argument. |
570 |
|
571 |
NOTE: I<This callback MUST NOT stop or destroy any periodic watcher, |
572 |
ever, or make any event loop modifications>. If you need to stop it, |
573 |
return C<now + 1e30> (or so, fudge fudge) and stop it afterwards (e.g. by |
574 |
starting a prepare watcher). |
575 |
|
576 |
Its prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic *w, |
577 |
ev_tstamp now)>, e.g.: |
578 |
|
579 |
static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now) |
580 |
{ |
581 |
return now + 60.; |
582 |
} |
583 |
|
584 |
It must return the next time to trigger, based on the passed time value |
585 |
(that is, the lowest time value larger than to the second argument). It |
586 |
will usually be called just before the callback will be triggered, but |
587 |
might be called at other times, too. |
588 |
|
589 |
NOTE: I<< This callback must always return a time that is later than the |
590 |
passed C<now> value >>. Not even C<now> itself will do, it I<must> be larger. |
591 |
|
592 |
This can be used to create very complex timers, such as a timer that |
593 |
triggers on each midnight, local time. To do this, you would calculate the |
594 |
next midnight after C<now> and return the timestamp value for this. How |
595 |
you do this is, again, up to you (but it is not trivial, which is the main |
596 |
reason I omitted it as an example). |
597 |
|
598 |
=back |
599 |
|
600 |
=item ev_periodic_again (loop, ev_periodic *) |
601 |
|
602 |
Simply stops and restarts the periodic watcher again. This is only useful |
603 |
when you changed some parameters or the reschedule callback would return |
604 |
a different time than the last time it was called (e.g. in a crond like |
605 |
program when the crontabs have changed). |
606 |
|
607 |
=back |
608 |
|
609 |
=head2 C<ev_signal> - signal me when a signal gets signalled |
610 |
|
611 |
Signal watchers will trigger an event when the process receives a specific |
612 |
signal one or more times. Even though signals are very asynchronous, libev |
613 |
will try it's best to deliver signals synchronously, i.e. as part of the |
614 |
normal event processing, like any other event. |
615 |
|
616 |
You can configure as many watchers as you like per signal. Only when the |
617 |
first watcher gets started will libev actually register a signal watcher |
618 |
with the kernel (thus it coexists with your own signal handlers as long |
619 |
as you don't register any with libev). Similarly, when the last signal |
620 |
watcher for a signal is stopped libev will reset the signal handler to |
621 |
SIG_DFL (regardless of what it was set to before). |
622 |
|
623 |
=over 4 |
624 |
|
625 |
=item ev_signal_init (ev_signal *, callback, int signum) |
626 |
|
627 |
=item ev_signal_set (ev_signal *, int signum) |
628 |
|
629 |
Configures the watcher to trigger on the given signal number (usually one |
630 |
of the C<SIGxxx> constants). |
631 |
|
632 |
=back |
633 |
|
634 |
=head2 C<ev_child> - wait for pid status changes |
635 |
|
636 |
Child watchers trigger when your process receives a SIGCHLD in response to |
637 |
some child status changes (most typically when a child of yours dies). |
638 |
|
639 |
=over 4 |
640 |
|
641 |
=item ev_child_init (ev_child *, callback, int pid) |
642 |
|
643 |
=item ev_child_set (ev_child *, int pid) |
644 |
|
645 |
Configures the watcher to wait for status changes of process C<pid> (or |
646 |
I<any> process if C<pid> is specified as C<0>). The callback can look |
647 |
at the C<rstatus> member of the C<ev_child> watcher structure to see |
648 |
the status word (use the macros from C<sys/wait.h> and see your systems |
649 |
C<waitpid> documentation). The C<rpid> member contains the pid of the |
650 |
process causing the status change. |
651 |
|
652 |
=back |
653 |
|
654 |
=head2 C<ev_idle> - when you've got nothing better to do |
655 |
|
656 |
Idle watchers trigger events when there are no other events are pending |
657 |
(prepare, check and other idle watchers do not count). That is, as long |
658 |
as your process is busy handling sockets or timeouts (or even signals, |
659 |
imagine) it will not be triggered. But when your process is idle all idle |
660 |
watchers are being called again and again, once per event loop iteration - |
661 |
until stopped, that is, or your process receives more events and becomes |
662 |
busy. |
663 |
|
664 |
The most noteworthy effect is that as long as any idle watchers are |
665 |
active, the process will not block when waiting for new events. |
666 |
|
667 |
Apart from keeping your process non-blocking (which is a useful |
668 |
effect on its own sometimes), idle watchers are a good place to do |
669 |
"pseudo-background processing", or delay processing stuff to after the |
670 |
event loop has handled all outstanding events. |
671 |
|
672 |
=over 4 |
673 |
|
674 |
=item ev_idle_init (ev_signal *, callback) |
675 |
|
676 |
Initialises and configures the idle watcher - it has no parameters of any |
677 |
kind. There is a C<ev_idle_set> macro, but using it is utterly pointless, |
678 |
believe me. |
679 |
|
680 |
=back |
681 |
|
682 |
=head2 C<ev_prepare> and C<ev_check> - customise your event loop |
683 |
|
684 |
Prepare and check watchers are usually (but not always) used in tandem: |
685 |
prepare watchers get invoked before the process blocks and check watchers |
686 |
afterwards. |
687 |
|
688 |
Their main purpose is to integrate other event mechanisms into libev. This |
689 |
could be used, for example, to track variable changes, implement your own |
690 |
watchers, integrate net-snmp or a coroutine library and lots more. |
691 |
|
692 |
This is done by examining in each prepare call which file descriptors need |
693 |
to be watched by the other library, registering C<ev_io> watchers for |
694 |
them and starting an C<ev_timer> watcher for any timeouts (many libraries |
695 |
provide just this functionality). Then, in the check watcher you check for |
696 |
any events that occured (by checking the pending status of all watchers |
697 |
and stopping them) and call back into the library. The I/O and timer |
698 |
callbacks will never actually be called (but must be valid nevertheless, |
699 |
because you never know, you know?). |
700 |
|
701 |
As another example, the Perl Coro module uses these hooks to integrate |
702 |
coroutines into libev programs, by yielding to other active coroutines |
703 |
during each prepare and only letting the process block if no coroutines |
704 |
are ready to run (it's actually more complicated: it only runs coroutines |
705 |
with priority higher than or equal to the event loop and one coroutine |
706 |
of lower priority, but only once, using idle watchers to keep the event |
707 |
loop from blocking if lower-priority coroutines are active, thus mapping |
708 |
low-priority coroutines to idle/background tasks). |
709 |
|
710 |
=over 4 |
711 |
|
712 |
=item ev_prepare_init (ev_prepare *, callback) |
713 |
|
714 |
=item ev_check_init (ev_check *, callback) |
715 |
|
716 |
Initialises and configures the prepare or check watcher - they have no |
717 |
parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set> |
718 |
macros, but using them is utterly, utterly and completely pointless. |
719 |
|
720 |
=back |
721 |
|
722 |
=head1 OTHER FUNCTIONS |
723 |
|
724 |
There are some other functions of possible interest. Described. Here. Now. |
725 |
|
726 |
=over 4 |
727 |
|
728 |
=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback) |
729 |
|
730 |
This function combines a simple timer and an I/O watcher, calls your |
731 |
callback on whichever event happens first and automatically stop both |
732 |
watchers. This is useful if you want to wait for a single event on an fd |
733 |
or timeout without having to allocate/configure/start/stop/free one or |
734 |
more watchers yourself. |
735 |
|
736 |
If C<fd> is less than 0, then no I/O watcher will be started and events |
737 |
is being ignored. Otherwise, an C<ev_io> watcher for the given C<fd> and |
738 |
C<events> set will be craeted and started. |
739 |
|
740 |
If C<timeout> is less than 0, then no timeout watcher will be |
741 |
started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and |
742 |
repeat = 0) will be started. While C<0> is a valid timeout, it is of |
743 |
dubious value. |
744 |
|
745 |
The callback has the type C<void (*cb)(int revents, void *arg)> and gets |
746 |
passed an C<revents> set like normal event callbacks (a combination of |
747 |
C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg> |
748 |
value passed to C<ev_once>: |
749 |
|
750 |
static void stdin_ready (int revents, void *arg) |
751 |
{ |
752 |
if (revents & EV_TIMEOUT) |
753 |
/* doh, nothing entered */; |
754 |
else if (revents & EV_READ) |
755 |
/* stdin might have data for us, joy! */; |
756 |
} |
757 |
|
758 |
ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0); |
759 |
|
760 |
=item ev_feed_event (loop, watcher, int events) |
761 |
|
762 |
Feeds the given event set into the event loop, as if the specified event |
763 |
had happened for the specified watcher (which must be a pointer to an |
764 |
initialised but not necessarily started event watcher). |
765 |
|
766 |
=item ev_feed_fd_event (loop, int fd, int revents) |
767 |
|
768 |
Feed an event on the given fd, as if a file descriptor backend detected |
769 |
the given events it. |
770 |
|
771 |
=item ev_feed_signal_event (loop, int signum) |
772 |
|
773 |
Feed an event as if the given signal occured (loop must be the default loop!). |
774 |
|
775 |
=back |
776 |
|
777 |
=head1 LIBEVENT EMULATION |
778 |
|
779 |
Libev offers a compatibility emulation layer for libevent. It cannot |
780 |
emulate the internals of libevent, so here are some usage hints: |
781 |
|
782 |
=over 4 |
783 |
|
784 |
=item * Use it by including <event.h>, as usual. |
785 |
|
786 |
=item * The following members are fully supported: ev_base, ev_callback, |
787 |
ev_arg, ev_fd, ev_res, ev_events. |
788 |
|
789 |
=item * Avoid using ev_flags and the EVLIST_*-macros, while it is |
790 |
maintained by libev, it does not work exactly the same way as in libevent (consider |
791 |
it a private API). |
792 |
|
793 |
=item * Priorities are not currently supported. Initialising priorities |
794 |
will fail and all watchers will have the same priority, even though there |
795 |
is an ev_pri field. |
796 |
|
797 |
=item * Other members are not supported. |
798 |
|
799 |
=item * The libev emulation is I<not> ABI compatible to libevent, you need |
800 |
to use the libev header file and library. |
801 |
|
802 |
=back |
803 |
|
804 |
=head1 C++ SUPPORT |
805 |
|
806 |
TBD. |
807 |
|
808 |
=head1 AUTHOR |
809 |
|
810 |
Marc Lehmann <libev@schmorp.de>. |
811 |
|