1EVENT(3) BSD Library Functions Manual EVENT(3)
2
4 event_init, event_dispatch, event_loop, event_loopexit, event_loopbreak,
5 event_set, event_base_dispatch, event_base_loop, event_base_loopexit,
6 event_base_loopbreak, event_base_set, event_base_free, event_add,
7 event_del, event_once, event_base_once, event_pending, event_initialized,
8 event_priority_init, event_priority_set, evtimer_set, evtimer_add,
9 evtimer_del, evtimer_pending, evtimer_initialized, signal_set,
10 signal_add, signal_del, signal_pending, signal_initialized,
11 bufferevent_new, bufferevent_free, bufferevent_write,
12 bufferevent_write_buffer, bufferevent_read, bufferevent_enable,
13 bufferevent_disable, bufferevent_settimeout, bufferevent_base_set,
14 evbuffer_new, evbuffer_free, evbuffer_add, evbuffer_add_buffer,
15 evbuffer_add_printf, evbuffer_add_vprintf, evbuffer_drain,
16 evbuffer_write, evbuffer_read, evbuffer_find, evbuffer_readline,
17 evhttp_new, evhttp_bind_socket, evhttp_free — execute a function when a
18 specific event occurs
19
21 #include <sys/time.h>
22 #include <event.h>
23 struct event_base *
25 event_init(void);
26 int
28 event_dispatch(void);
29 int
31 event_loop(int flags);
32 int
34 event_loopexit(struct timeval *tv);
35 int
37 event_loopbreak(void);
38 void
40 event_set(struct event *ev, int fd, short event,
41 void (*fn)(int, short, void *), void *arg);
42 int
44 event_base_dispatch(struct event_base *base);
45 int
47 event_base_loop(struct event_base *base, int flags);
48 int
50 event_base_loopexit(struct event_base *base, struct timeval *tv);
51 int
53 event_base_loopbreak(struct event_base *base);
54 int
56 event_base_set(struct event_base *base, struct event *);
57 void
59 event_base_free(struct event_base *base);
60 int
62 event_add(struct event *ev, struct timeval *tv);
63 int
65 event_del(struct event *ev);
66 int
68 event_once(int fd, short event, void (*fn)(int, short, void *),
69 void *arg, struct timeval *tv);
70 int
72 event_base_once(struct event_base *base, int fd, short event,
73 void (*fn)(int, short, void *), void *arg, struct timeval *tv);
74 int
76 event_pending(struct event *ev, short event, struct timeval *tv);
77 int
79 event_initialized(struct event *ev);
80 int
82 event_priority_init(int npriorities);
83 int
85 event_priority_set(struct event *ev, int priority);
86 void
88 evtimer_set(struct event *ev, void (*fn)(int, short, void *), void *arg);
89 void
91 evtimer_add(struct event *ev, struct timeval *);
92 void
94 evtimer_del(struct event *ev);
95 int
97 evtimer_pending(struct event *ev, struct timeval *tv);
98 int
100 evtimer_initialized(struct event *ev);
101 void
103 signal_set(struct event *ev, int signal, void (*fn)(int, short, void *),
104 void *arg);
105 void
107 signal_add(struct event *ev, struct timeval *);
108 void
110 signal_del(struct event *ev);
111 int
113 signal_pending(struct event *ev, struct timeval *tv);
114 int
116 signal_initialized(struct event *ev);
117 struct bufferevent *
119 bufferevent_new(int fd, evbuffercb readcb, evbuffercb writecb, everrorcb,
120 void *cbarg);
121 void
123 bufferevent_free(struct bufferevent *bufev);
124 int
126 bufferevent_write(struct bufferevent *bufev, void *data, size_t size);
127 int
129 bufferevent_write_buffer(struct bufferevent *bufev,
130 struct evbuffer *buf);
131 size_t
133 bufferevent_read(struct bufferevent *bufev, void *data, size_t size);
134 int
136 bufferevent_enable(struct bufferevent *bufev, short event);
137 int
139 bufferevent_disable(struct bufferevent *bufev, short event);
140 void
142 bufferevent_settimeout(struct bufferevent *bufev, int timeout_read,
143 int timeout_write);
144 int
146 bufferevent_base_set(struct event_base *base, struct bufferevent *bufev);
147 struct evbuffer *
149 evbuffer_new(void);
150 void
152 evbuffer_free(struct evbuffer *buf);
153 int
155 evbuffer_add(struct evbuffer *buf, const void *data, size_t size);
156 int
158 evbuffer_add_buffer(struct evbuffer *dst, struct evbuffer *src);
159 int
161 evbuffer_add_printf(struct evbuffer *buf, const char *fmt, ...);
162 int
164 evbuffer_add_vprintf(struct evbuffer *buf, const char *fmt, va_list ap);
165 void
167 evbuffer_drain(struct evbuffer *buf, size_t size);
168 int
170 evbuffer_write(struct evbuffer *buf, int fd);
171 int
173 evbuffer_read(struct evbuffer *buf, int fd, int size);
174 u_char *
176 evbuffer_find(struct evbuffer *buf, const u_char *data, size_t size);
177 char *
179 evbuffer_readline(struct evbuffer *buf);
180 struct evhttp *
182 evhttp_new(struct event_base *base);
183 int
185 evhttp_bind_socket(struct evhttp *http, const char *address,
186 u_short port);
187 void
189 evhttp_free(struct evhttp *http);
190 int (*event_sigcb)(void);
192 volatile sig_atomic_t event_gotsig;
194
196 The event API provides a mechanism to execute a function when a specific
197 event on a file descriptor occurs or after a given time has passed.
198 The event API needs to be initialized with event_init() before it can be
200 used.
201 In order to process events, an application needs to call
203 event_dispatch(). This function only returns on error, and should
204 replace the event core of the application program.
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. Additionally, an event which has regis‐
218 tered interest in more than one of the preceeding events, via bitwise-OR
219 to event_set(), can provide its callback function with a bitwise-OR of
220 more than one triggered event. The additional flag EV_PERSIST makes an
221 event_add() persistent until event_del() has been called.
222 Once initialized, the ev structure can be used repeatedly with
224 event_add() and event_del() and does not need to be reinitialized unless
225 the function called and/or the argument to it are to be changed. How‐
226 ever, when an ev structure has been added to libevent using event_add()
227 the structure must persist until the event occurs (assuming EV_PERSIST is
228 not set) or is removed using event_del(). You may not reuse the same ev
229 structure for multiple monitored descriptors; each descriptor needs its
230 own ev.
231 The function event_add() schedules the execution of the ev event when the
233 event specified in event_set() occurs or in at least the time specified
234 in the tv. If tv is NULL, no timeout occurs and the function will only
235 be called if a matching event occurs on the file descriptor. The event
236 in the ev argument must be already initialized by event_set() and may not
237 be used in calls to event_set() until it has timed out or been removed
238 with event_del(). If the event in the ev argument already has a sched‐
239 uled timeout, the old timeout will be replaced by the new one.
240 The function event_del() will cancel the event in the argument ev. If
242 the event has already executed or has never been added the call will have
243 no effect.
244 The functions evtimer_set(), evtimer_add(), evtimer_del(),
246 evtimer_initialized(), and evtimer_pending() are abbreviations for common
247 situations where only a timeout is required. The file descriptor passed
248 will be -1, and the event type will be EV_TIMEOUT.
249 The functions signal_set(), signal_add(), signal_del(),
251 signal_initialized(), and signal_pending() are abbreviations. The event
252 type will be a persistent EV_SIGNAL. That means signal_set() adds
253 EV_PERSIST.
254 In order to avoid races in signal handlers, the event API provides two
256 variables: event_sigcb and event_gotsig. A signal handler sets
257 event_gotsig to indicate that a signal has been received. The applica‐
258 tion sets event_sigcb to a callback function. After the signal handler
259 sets event_gotsig, event_dispatch will execute the callback function to
260 process received signals. The callback returns 1 when no events are reg‐
261 istered any more. It can return -1 to indicate an error to the event
262 library, causing event_dispatch() to terminate with errno set to EINTR.
263 The function event_once() is similar to event_set(). However, it sched‐
265 ules a callback to be called exactly once and does not require the caller
266 to prepare an event structure. This function supports EV_TIMEOUT,
267 EV_READ, and EV_WRITE.
268 The event_pending() function can be used to check if the event specified
270 by event is pending to run. If EV_TIMEOUT was specified and tv is not
271 NULL, the expiration time of the event will be returned in tv.
272 The event_initialized() macro can be used to check if an event has been
274 initialized.
275 The event_loop function provides an interface for single pass execution
277 of pending events. The flags EVLOOP_ONCE and EVLOOP_NONBLOCK are recog‐
278 nized. The event_loopexit function exits from the event loop. The next
279 event_loop() iteration after the given timer expires will complete nor‐
280 mally (handling all queued events) then exit without blocking for events
281 again. Subsequent invocations of event_loop() will proceed normally. The
282 event_loopbreak function exits from the event loop immediately.
283 event_loop() will abort after the next event is completed;
284 event_loopbreak() is typically invoked from this event's callback. This
285 behavior is analogous to the "break;" statement. Subsequent invocations
286 of event_loop() will proceed normally.
287 It is the responsibility of the caller to provide these functions with
289 pre-allocated event structures.
290
292 By default libevent schedules all active events with the same priority.
293 However, sometimes it is desirable to process some events with a higher
294 priority than others. For that reason, libevent supports strict priority
295 queues. Active events with a lower priority are always processed before
296 events with a higher priority.
297 The number of different priorities can be set initially with the
299 event_priority_init() function. This function should be called before
300 the first call to event_dispatch(). The event_priority_set() function
301 can be used to assign a priority to an event. By default, libevent
302 assigns the middle priority to all events unless their priority is
303 explicitly set.
304
306 Libevent has experimental support for thread-safe events. When initial‐
307 izing the library via event_init(), an event base is returned. This
308 event base can be used in conjunction with calls to event_base_set(),
309 event_base_dispatch(), event_base_loop(), event_base_loopexit(),
310 bufferevent_base_set() and event_base_free(). event_base_set() should be
311 called after preparing an event with event_set(), as event_set() assigns
312 the provided event to the most recently created event base.
313 bufferevent_base_set() should be called after preparing a bufferevent
314 with bufferevent_new(). event_base_free() should be used to free memory
315 associated with the event base when it is no longer needed.
316
318 libevent provides an abstraction on top of the regular event callbacks.
319 This abstraction is called a buffered event. A buffered event provides
320 input and output buffers that get filled and drained automatically. The
321 user of a buffered event no longer deals directly with the IO, but
322 instead is reading from input and writing to output buffers.
323 A new bufferevent is created by bufferevent_new(). The parameter fd
325 specifies the file descriptor from which data is read and written to.
326 This file descriptor is not allowed to be a pipe(2). The next three
327 parameters are callbacks. The read and write callback have the following
328 form: void (*cb)(struct bufferevent *bufev, void *arg). The error call‐
329 back has the following form: void (*cb)(struct bufferevent *bufev, short
330 what, void *arg). The argument is specified by the fourth parameter
331 cbarg. A bufferevent struct pointer is returned on success, NULL on
332 error. Both the read and the write callback may be NULL. The error
333 callback has to be always provided.
334 Once initialized, the bufferevent structure can be used repeatedly with
336 bufferevent_enable() and bufferevent_disable(). The flags parameter can
337 be a combination of EV_READ and EV_WRITE. When read enabled the buffer‐
338 event will try to read from the file descriptor and call the read call‐
339 back. The write callback is executed whenever the output buffer is
340 drained below the write low watermark, which is 0 by default.
341 The bufferevent_write() function can be used to write data to the file
343 descriptor. The data is appended to the output buffer and written to the
344 descriptor automatically as it becomes available for writing.
345 bufferevent_write() returns 0 on success or -1 on failure. The
346 bufferevent_read() function is used to read data from the input buffer,
347 returning the amount of data read.
348 If multiple bases are in use, bufferevent_base_set() must be called
350 before enabling the bufferevent for the first time.
351
353 libevent provides a very thin HTTP layer that can be used both to host an
354 HTTP server and also to make HTTP requests. An HTTP server can be cre‐
355 ated by calling evhttp_new(). It can be bound to any port and address
356 with the evhttp_bind_socket() function. When the HTTP server is no
357 longer used, it can be freed via evhttp_free().
358 To be notified of HTTP requests, a user needs to register callbacks with
360 the HTTP server. This can be done by calling evhttp_set_cb(). The sec‐
361 ond argument is the URI for which a callback is being registered. The
362 corresponding callback will receive an struct evhttp_request object that
363 contains all information about the request.
364 This section does not document all the possible function calls; please
366 check event.h for the public interfaces.
367
369 It is possible to disable support for epoll, kqueue, devpoll, poll or
370 select by setting the environment variable EVENT_NOEPOLL, EVENT_NOKQUEUE,
371 EVENT_NODEVPOLL, EVENT_NOPOLL or EVENT_NOSELECT, respectively. By set‐
372 ting the environment variable EVENT_SHOW_METHOD, libevent displays the
373 kernel notification method that it uses.
374
376 Upon successful completion event_add() and event_del() return 0. Other‐
377 wise, -1 is returned and the global variable errno is set to indicate the
378 error.
379
381 kqueue(2), poll(2), select(2), evdns(3), timeout(9)
382
384 The event API manpage is based on the timeout(9) manpage by Artur
385 Grabowski. The port of libevent to Windows is due to Michael A. Davis.
386 Support for real-time signals is due to Taral.
387
389 The event library was written by Niels Provos.
390
392 This documentation is neither complete nor authoritative. If you are in
393 doubt about the usage of this API then check the source code to find out
394 how it works, write up the missing piece of documentation and send it to
395 me for inclusion in this man page.
396BSD August 8, 2000 BSD