1EVENT(3) BSD Library Functions Manual EVENT(3)
2
4 event_init, event_dispatch, event_loop, event_loopexit, event_set,
5 event_base_dispatch, event_base_loop, event_base_loopexit,
6 event_base_set, event_add, event_del, event_once, event_pending,
7 event_initialized, event_priority_init, event_priority_set, evtimer_set,
8 evtimer_add, evtimer_del, evtimer_pending, evtimer_initialized,
9 signal_set, signal_add, signal_del, signal_pending, signal_initialized,
10 bufferevent_new, bufferevent_free, bufferevent_write,
11 bufferevent_write_buffer, bufferevent_read, bufferevent_enable,
12 bufferevent_disable, bufferevent_settimeout, bufferevent_base_set,
13 evbuffer_new, evbuffer_free, evbuffer_add, evbuffer_add_buffer,
14 evbuffer_add_printf, evbuffer_add_vprintf, evbuffer_drain,
15 evbuffer_write, evbuffer_read, evbuffer_find, evbuffer_readline,
16 evhttp_start, evhttp_free — execute a function when a specific event
17 occurs
18
20 #include <sys/time.h>
21 #include <event.h>
22 struct event_base *
24 event_init();
25 int
27 event_dispatch();
28 int
30 event_loop(int flags);
31 int
33 event_loopexit(struct timeval *tv);
34 void
36 event_set(struct event *ev, int fd, short event,
37 void (*fn)(int, short, void *), void *arg);
38 int
40 event_base_dispatch(struct event_base *base);
41 int
43 event_base_loop(struct event_base *base, int flags);
44 int
46 event_base_loopexit(struct event_base *base, struct timeval *tv);
47 int
49 event_base_set(struct event_base *base, struct event *);
50 int
52 event_add(struct event *ev, struct timeval *tv);
53 int
55 event_del(struct event *ev);
56 int
58 event_once(int fd, short event, void (*fn)(int, short, void *),
59 void *arg, struct timeval *tv);
60 int
62 event_pending(struct event *ev, short event, struct timeval *tv);
63 int
65 event_initialized(struct event *ev);
66 int
68 event_priority_init(int npriorities);
69 int
71 event_priority_set(struct event *ev, int priority);
72 void
74 evtimer_set(struct event *ev, void (*fn)(int, short, void *), void *arg);
75 void
77 evtimer_add(struct event *ev, struct timeval *);
78 void
80 evtimer_del(struct event *ev);
81 int
83 evtimer_pending(struct event *ev, struct timeval *tv);
84 int
86 evtimer_initialized(struct event *ev);
87 void
89 signal_set(struct event *ev, int signal, void (*fn)(int, short, void *),
90 void *arg);
91 void
93 signal_add(struct event *ev, struct timeval *);
94 void
96 signal_del(struct event *ev);
97 int
99 signal_pending(struct event *ev, struct timeval *tv);
100 int
102 signal_initialized(struct event *ev);
103 struct bufferevent *
105 bufferevent_new(int fd, evbuffercb readcb, evbuffercb writecb, everrorcb,
106 void *cbarg);
107 void
109 bufferevent_free(struct bufferevent *bufev);
110 int
112 bufferevent_write(struct bufferevent *bufev, void *data, size_t size);
113 int
115 bufferevent_write_buffer(struct bufferevent *bufev,
116 struct evbuffer *buf);
117 size_t
119 bufferevent_read(struct bufferevent *bufev, void *data, size_t size);
120 int
122 bufferevent_enable(struct bufferevent *bufev, short event);
123 int
125 bufferevent_disable(struct bufferevent *bufev, short event);
126 void
128 bufferevent_settimeout(struct bufferevent *bufev, int timeout_read,
129 int timeout_write);
130 int
132 bufferevent_base_set(struct event_base *base, struct bufferevent *bufev);
133 struct evbuffer *
135 evbuffer_new(void);
136 void
138 evbuffer_free(struct evbuffer *buf);
139 int
141 evbuffer_add(struct evbuffer *buf, u_char *data, size_t size);
142 int
144 evbuffer_add_buffer(struct evbuffer *dst, struct evbuffer *src);
145 int
147 evbuffer_add_printf(struct evbuffer *buf, char *fmt, ...);
148 int
150 evbuffer_add_vprintf(struct evbuffer *buf, const char *fmt, va_list ap);
151 void
153 evbuffer_drain(struct evbuffer *buf, size_t size);
154 int
156 evbuffer_write(struct evbuffer *buf, int fd);
157 int
159 evbuffer_read(struct evbuffer *buf, int fd, int size);
160 u_char *
162 evbuffer_find(struct evbuffer *buf, u_char *data, size_t size);
163 char *
165 evbuffer_readline(struct evbuffer *buf);
166 struct evhttp *
168 evhttp_start(const char *address, u_short port);
169 void
171 evhttp_free(struct evhttp* http);
172 int (*event_sigcb)(void);
174 int event_gotsig;
176
178 The event API provides a mechanism to execute a function when a specific
179 event on a file descriptor occurs or after a given time has passed.
180 The event API needs to be initialized with event_init() before it can be
182 used.
183 In order to process events, an application needs to call
185 event_dispatch(). This function only returns on error, and should
186 replace the event core of the application program.
187 In order to avoid races in signal handlers, the event API provides two
189 variables: event_sigcb and event_gotsig. A signal handler sets
190 event_gotsig to indicate that a signal has been received. The applica‐
191 tion sets event_sigcb to a callback function. After the signal handler
192 sets event_gotsig, event_dispatch will execute the callback function to
193 process received signals. The callback returns 1 when no events are reg‐
194 istered any more. It can return -1 to indicate an error to the event
195 library, causing event_dispatch() to terminate with errno set to EINTR.
196 The event_loop function provides an interface for single pass execution
198 of pending events. The flags EVLOOP_ONCE and EVLOOP_NONBLOCK are recog‐
199 nized. The event_loopexit function allows the loop to be terminated
200 after some amount of time has passed. The parameter indicates the time
201 after which the loop should terminate.
202 It is the responsibility of the caller to provide these functions with
204 pre-allocated event structures.
205 The function event_set() prepares the event structure ev to be used in
207 future calls to event_add() and event_del(). The event will be prepared
208 to call the function specified by the fn argument with an int argument
209 indicating the file descriptor, a short argument indicating the type of
210 event, and a void * argument given in the arg argument. The fd indicates
211 the file descriptor that should be monitored for events. The events can
212 be either EV_READ, EV_WRITE, or both, indicating that an application can
213 read or write from the file descriptor respectively without blocking.
214 The function fn will be called with the file descriptor that triggered
216 the event and the type of event which will be either EV_TIMEOUT,
217 EV_SIGNAL, EV_READ, or EV_WRITE. The additional flag EV_PERSIST makes an
218 event_add() persistent until event_del() has been called.
219 Once initialized, the ev structure can be used repeatedly with
221 event_add() and event_del() and does not need to be reinitialized unless
222 the function called and/or the argument to it are to be changed. How‐
223 ever, when an ev structure has been added to libevent using event_add()
224 the structure must persist until the event occurs (assuming EV_PERSIST is
225 not set) or is removed using event_del(). You may not reuse the same ev
226 structure for multiple monitored descriptors; each descriptor needs its
227 own ev.
228 The function event_add() schedules the execution of the ev event when the
230 event specified in event_set() occurs or in at least the time specified
231 in the tv. If tv is NULL, no timeout occurs and the function will only
232 be called if a matching event occurs on the file descriptor. The event
233 in the ev argument must be already initialized by event_set() and may not
234 be used in calls to event_set() until it has timed out or been removed
235 with event_del(). If the event in the ev argument already has a sched‐
236 uled timeout, the old timeout will be replaced by the new one.
237 The function event_del() will cancel the event in the argument ev. If
239 the event has already executed or has never been added the call will have
240 no effect.
241 The function event_once() is similar to event_set(). However, it sched‐
243 ules a callback to be called exactly once and does not require the caller
244 to prepare an event structure. This function supports EV_TIMEOUT,
245 EV_READ, and EV_WRITE.
246 The event_pending() function can be used to check if the event specified
248 by event is pending to run. If EV_TIMEOUT was specified and tv is not
249 NULL, the expiration time of the event will be returned in tv.
250 The event_initialized() macro can be used to check if an event has been
252 initialized.
253 The functions evtimer_set(), evtimer_add(), evtimer_del(),
255 evtimer_initialized(), and evtimer_pending() are abbreviations for common
256 situations where only a timeout is required. The file descriptor passed
257 will be -1, and the event type will be EV_TIMEOUT.
258 The functions signal_set(), signal_add(), signal_del(),
260 signal_initialized(), and signal_pending() are abbreviations. The event
261 type will be a persistent EV_SIGNAL. That means signal_set() adds
262 EV_PERSIST.
263 It is possible to disable support for epoll, kqueue, devpoll, poll or
265 select by setting the environment variable EVENT_NOEPOLL, EVENT_NOKQUEUE,
266 EVENT_NODEVPOLL, EVENT_NOPOLL or EVENT_NOSELECT, respectively. By set‐
267 ting the environment variable EVENT_SHOW_METHOD, libevent displays the
268 kernel notification method that it uses.
269
271 By default libevent schedules all active events with the same priority.
272 However, sometimes it is desirable to process some events with a higher
273 priority than others. For that reason, libevent supports strict priority
274 queues. Active events with a lower priority are always processed before
275 events with a higher priority.
276 The number of different priorities can be set initially with the
278 event_priority_init() function. This function should be called before
279 the first call to event_dispatch(). The event_priority_set() function
280 can be used to assign a priority to an event. By default, libevent
281 assigns the middle priority to all events unless their priority is
282 explicitly set.
283
285 Libevent has experimental support for thread-safe events. When initial‐
286 izing the library via event_init(), an event base is returned. This
287 event base can be used in conjunction with calls to event_base_set(),
288 event_base_dispatch(), event_base_loop(), event_base_loopexit(), and
289 bufferevent_base_set(). event_base_set() should be called after prepar‐
290 ing an event with event_set(), as event_set() assigns the provided event
291 to the most recently created event base. bufferevent_base_set() should
292 be called after preparing a bufferevent with bufferevent_new().
293
295 libevent provides an abstraction on top of the regular event callbacks.
296 This abstraction is called a buffered event. A buffered event provides
297 input and output buffers that get filled and drained automatically. The
298 user of a buffered event no longer deals directly with the IO, but
299 instead is reading from input and writing to output buffers.
300 A new bufferevent is created by bufferevent_new(). The parameter fd
302 specifies the file descriptor from which data is read and written to.
303 This file descriptor is not allowed to be a pipe(2). The next three
304 parameters are callbacks. The read and write callback have the following
305 form: void (*cb)(struct bufferevent *bufev, void *arg). The error call‐
306 back has the following form: void (*cb)(struct bufferevent *bufev, short
307 what, void *arg). The argument is specified by the fourth parameter
308 cbarg. A bufferevent struct pointer is returned on success, NULL on
309 error. Both the read and the write callback may be NULL. The error
310 callback has to be always provided.
311 Once initialized, the bufferevent structure can be used repeatedly with
313 bufferevent_enable() and bufferevent_disable(). The flags parameter can
314 be a combination of EV_READ and EV_WRITE. When read enabled the buffer‐
315 event will try to read from the file descriptor and call the read call‐
316 back. The write callback is executed whenever the output buffer is
317 drained below the write low watermark, which is 0 by default.
318 The bufferevent_write() function can be used to write data to the file
320 descriptor. The data is appended to the output buffer and written to the
321 descriptor automatically as it becomes available for writing. The
322 bufferevent_read() function is used to read data from the input buffer.
323 Both functions return the amount of data written or read.
324 If multiple bases are in use, bufferevent_base_set() must be called
326 before enabling the bufferevent for the first time.
327
329 libevent provides a very thin HTTP layer that can be used both to host an
330 HTTP server and also to make HTTP requests. An HTTP server can be cre‐
331 ated by calling evhttp_start(). When the HTTP server is no longer used,
332 it can be freed via evhttp_free().
333 To be notified of HTTP requests, a user needs to register callbacks with
335 the HTTP server. This can be done by calling evhttp_set_cb(). The sec‐
336 ond argument is the URI for which a callback is being registered. The
337 corresponding callback will receive an struct evhttp_request object that
338 contains all information about the request.
339 This section does not document all the possible function calls, please
341 check event.h for the public interfaces.
342
344 Upon successful completion event_add() and event_del() return 0. Other‐
345 wise, -1 is returned and the global variable errno is set to indicate the
346 error.
347
349 kqueue(2), poll(2), select(2), timeout(9)
350
352 The event API manpage is based on the timeout(9) manpage by Artur
353 Grabowski. The port of libevent to Windows is due to Michael A. Davis.
354 Support for real-time signals is due to Taral.
355
357 The event library was written by Niels Provos.
358
360 This documentation is neither complete nor authoritative. If you are in
361 doubt about the usage of this API then check the source code to find out
362 how it works, write up the missing piece of documentation and send it to
363 me for inclusion in this man page.
364BSD August 8, 2000 BSD