Annotation of embedaddon/libevent/event.3, revision 1.1.1.1
1.1 misho 1: .\" $OpenBSD: event.3,v 1.4 2002/07/12 18:50:48 provos Exp $
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3: .\" Copyright (c) 2000 Artur Grabowski <art@openbsd.org>
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29: .Dd August 8, 2000
30: .Dt EVENT 3
31: .Os
32: .Sh NAME
33: .Nm event_init ,
34: .Nm event_dispatch ,
35: .Nm event_loop ,
36: .Nm event_loopexit ,
37: .Nm event_loopbreak ,
38: .Nm event_set ,
39: .Nm event_base_dispatch ,
40: .Nm event_base_loop ,
41: .Nm event_base_loopexit ,
42: .Nm event_base_loopbreak ,
43: .Nm event_base_set ,
44: .Nm event_base_free ,
45: .Nm event_add ,
46: .Nm event_del ,
47: .Nm event_once ,
48: .Nm event_base_once ,
49: .Nm event_pending ,
50: .Nm event_initialized ,
51: .Nm event_priority_init ,
52: .Nm event_priority_set ,
53: .Nm evtimer_set ,
54: .Nm evtimer_add ,
55: .Nm evtimer_del ,
56: .Nm evtimer_pending ,
57: .Nm evtimer_initialized ,
58: .Nm signal_set ,
59: .Nm signal_add ,
60: .Nm signal_del ,
61: .Nm signal_pending ,
62: .Nm signal_initialized ,
63: .Nm bufferevent_new ,
64: .Nm bufferevent_free ,
65: .Nm bufferevent_write ,
66: .Nm bufferevent_write_buffer ,
67: .Nm bufferevent_read ,
68: .Nm bufferevent_enable ,
69: .Nm bufferevent_disable ,
70: .Nm bufferevent_settimeout ,
71: .Nm bufferevent_base_set ,
72: .Nm evbuffer_new ,
73: .Nm evbuffer_free ,
74: .Nm evbuffer_add ,
75: .Nm evbuffer_add_buffer ,
76: .Nm evbuffer_add_printf ,
77: .Nm evbuffer_add_vprintf ,
78: .Nm evbuffer_drain ,
79: .Nm evbuffer_write ,
80: .Nm evbuffer_read ,
81: .Nm evbuffer_find ,
82: .Nm evbuffer_readline ,
83: .Nm evhttp_new ,
84: .Nm evhttp_bind_socket ,
85: .Nm evhttp_free
86: .Nd execute a function when a specific event occurs
87: .Sh SYNOPSIS
88: .Fd #include <sys/time.h>
89: .Fd #include <event.h>
90: .Ft "struct event_base *"
91: .Fn "event_init" "void"
92: .Ft int
93: .Fn "event_dispatch" "void"
94: .Ft int
95: .Fn "event_loop" "int flags"
96: .Ft int
97: .Fn "event_loopexit" "struct timeval *tv"
98: .Ft int
99: .Fn "event_loopbreak" "void"
100: .Ft void
101: .Fn "event_set" "struct event *ev" "int fd" "short event" "void (*fn)(int, short, void *)" "void *arg"
102: .Ft int
103: .Fn "event_base_dispatch" "struct event_base *base"
104: .Ft int
105: .Fn "event_base_loop" "struct event_base *base" "int flags"
106: .Ft int
107: .Fn "event_base_loopexit" "struct event_base *base" "struct timeval *tv"
108: .Ft int
109: .Fn "event_base_loopbreak" "struct event_base *base"
110: .Ft int
111: .Fn "event_base_set" "struct event_base *base" "struct event *"
112: .Ft void
113: .Fn "event_base_free" "struct event_base *base"
114: .Ft int
115: .Fn "event_add" "struct event *ev" "struct timeval *tv"
116: .Ft int
117: .Fn "event_del" "struct event *ev"
118: .Ft int
119: .Fn "event_once" "int fd" "short event" "void (*fn)(int, short, void *)" "void *arg" "struct timeval *tv"
120: .Ft int
121: .Fn "event_base_once" "struct event_base *base" "int fd" "short event" "void (*fn)(int, short, void *)" "void *arg" "struct timeval *tv"
122: .Ft int
123: .Fn "event_pending" "struct event *ev" "short event" "struct timeval *tv"
124: .Ft int
125: .Fn "event_initialized" "struct event *ev"
126: .Ft int
127: .Fn "event_priority_init" "int npriorities"
128: .Ft int
129: .Fn "event_priority_set" "struct event *ev" "int priority"
130: .Ft void
131: .Fn "evtimer_set" "struct event *ev" "void (*fn)(int, short, void *)" "void *arg"
132: .Ft void
133: .Fn "evtimer_add" "struct event *ev" "struct timeval *"
134: .Ft void
135: .Fn "evtimer_del" "struct event *ev"
136: .Ft int
137: .Fn "evtimer_pending" "struct event *ev" "struct timeval *tv"
138: .Ft int
139: .Fn "evtimer_initialized" "struct event *ev"
140: .Ft void
141: .Fn "signal_set" "struct event *ev" "int signal" "void (*fn)(int, short, void *)" "void *arg"
142: .Ft void
143: .Fn "signal_add" "struct event *ev" "struct timeval *"
144: .Ft void
145: .Fn "signal_del" "struct event *ev"
146: .Ft int
147: .Fn "signal_pending" "struct event *ev" "struct timeval *tv"
148: .Ft int
149: .Fn "signal_initialized" "struct event *ev"
150: .Ft "struct bufferevent *"
151: .Fn "bufferevent_new" "int fd" "evbuffercb readcb" "evbuffercb writecb" "everrorcb" "void *cbarg"
152: .Ft void
153: .Fn "bufferevent_free" "struct bufferevent *bufev"
154: .Ft int
155: .Fn "bufferevent_write" "struct bufferevent *bufev" "void *data" "size_t size"
156: .Ft int
157: .Fn "bufferevent_write_buffer" "struct bufferevent *bufev" "struct evbuffer *buf"
158: .Ft size_t
159: .Fn "bufferevent_read" "struct bufferevent *bufev" "void *data" "size_t size"
160: .Ft int
161: .Fn "bufferevent_enable" "struct bufferevent *bufev" "short event"
162: .Ft int
163: .Fn "bufferevent_disable" "struct bufferevent *bufev" "short event"
164: .Ft void
165: .Fn "bufferevent_settimeout" "struct bufferevent *bufev" "int timeout_read" "int timeout_write"
166: .Ft int
167: .Fn "bufferevent_base_set" "struct event_base *base" "struct bufferevent *bufev"
168: .Ft "struct evbuffer *"
169: .Fn "evbuffer_new" "void"
170: .Ft void
171: .Fn "evbuffer_free" "struct evbuffer *buf"
172: .Ft int
173: .Fn "evbuffer_add" "struct evbuffer *buf" "const void *data" "size_t size"
174: .Ft int
175: .Fn "evbuffer_add_buffer" "struct evbuffer *dst" "struct evbuffer *src"
176: .Ft int
177: .Fn "evbuffer_add_printf" "struct evbuffer *buf" "const char *fmt" "..."
178: .Ft int
179: .Fn "evbuffer_add_vprintf" "struct evbuffer *buf" "const char *fmt" "va_list ap"
180: .Ft void
181: .Fn "evbuffer_drain" "struct evbuffer *buf" "size_t size"
182: .Ft int
183: .Fn "evbuffer_write" "struct evbuffer *buf" "int fd"
184: .Ft int
185: .Fn "evbuffer_read" "struct evbuffer *buf" "int fd" "int size"
186: .Ft "u_char *"
187: .Fn "evbuffer_find" "struct evbuffer *buf" "const u_char *data" "size_t size"
188: .Ft "char *"
189: .Fn "evbuffer_readline" "struct evbuffer *buf"
190: .Ft "struct evhttp *"
191: .Fn "evhttp_new" "struct event_base *base"
192: .Ft int
193: .Fn "evhttp_bind_socket" "struct evhttp *http" "const char *address" "u_short port"
194: .Ft "void"
195: .Fn "evhttp_free" "struct evhttp *http"
196: .Ft int
197: .Fa (*event_sigcb)(void) ;
198: .Ft volatile sig_atomic_t
199: .Fa event_gotsig ;
200: .Sh DESCRIPTION
201: The
202: .Nm event
203: API provides a mechanism to execute a function when a specific event
204: on a file descriptor occurs or after a given time has passed.
205: .Pp
206: The
207: .Nm event
208: API needs to be initialized with
209: .Fn event_init
210: before it can be used.
211: .Pp
212: In order to process events, an application needs to call
213: .Fn event_dispatch .
214: This function only returns on error, and should replace the event core
215: of the application program.
216: .Pp
217: The function
218: .Fn event_set
219: prepares the event structure
220: .Fa ev
221: to be used in future calls to
222: .Fn event_add
223: and
224: .Fn event_del .
225: The event will be prepared to call the function specified by the
226: .Fa fn
227: argument with an
228: .Fa int
229: argument indicating the file descriptor, a
230: .Fa short
231: argument indicating the type of event, and a
232: .Fa void *
233: argument given in the
234: .Fa arg
235: argument.
236: The
237: .Fa fd
238: indicates the file descriptor that should be monitored for events.
239: The events can be either
240: .Va EV_READ ,
241: .Va EV_WRITE ,
242: or both,
243: indicating that an application can read or write from the file descriptor
244: respectively without blocking.
245: .Pp
246: The function
247: .Fa fn
248: will be called with the file descriptor that triggered the event and
249: the type of event which will be either
250: .Va EV_TIMEOUT ,
251: .Va EV_SIGNAL ,
252: .Va EV_READ ,
253: or
254: .Va EV_WRITE .
255: Additionally, an event which has registered interest in more than one of the
256: preceeding events, via bitwise-OR to
257: .Fn event_set ,
258: can provide its callback function with a bitwise-OR of more than one triggered
259: event.
260: The additional flag
261: .Va EV_PERSIST
262: makes an
263: .Fn event_add
264: persistent until
265: .Fn event_del
266: has been called.
267: .Pp
268: Once initialized, the
269: .Fa ev
270: structure can be used repeatedly with
271: .Fn event_add
272: and
273: .Fn event_del
274: and does not need to be reinitialized unless the function called and/or
275: the argument to it are to be changed.
276: However, when an
277: .Fa ev
278: structure has been added to libevent using
279: .Fn event_add
280: the structure must persist until the event occurs (assuming
281: .Fa EV_PERSIST
282: is not set) or is removed
283: using
284: .Fn event_del .
285: You may not reuse the same
286: .Fa ev
287: structure for multiple monitored descriptors; each descriptor
288: needs its own
289: .Fa ev .
290: .Pp
291: The function
292: .Fn event_add
293: schedules the execution of the
294: .Fa ev
295: event when the event specified in
296: .Fn event_set
297: occurs or in at least the time specified in the
298: .Fa tv .
299: If
300: .Fa tv
301: is
302: .Dv NULL ,
303: no timeout occurs and the function will only be called
304: if a matching event occurs on the file descriptor.
305: The event in the
306: .Fa ev
307: argument must be already initialized by
308: .Fn event_set
309: and may not be used in calls to
310: .Fn event_set
311: until it has timed out or been removed with
312: .Fn event_del .
313: If the event in the
314: .Fa ev
315: argument already has a scheduled timeout, the old timeout will be
316: replaced by the new one.
317: .Pp
318: The function
319: .Fn event_del
320: will cancel the event in the argument
321: .Fa ev .
322: If the event has already executed or has never been added
323: the call will have no effect.
324: .Pp
325: The functions
326: .Fn evtimer_set ,
327: .Fn evtimer_add ,
328: .Fn evtimer_del ,
329: .Fn evtimer_initialized ,
330: and
331: .Fn evtimer_pending
332: are abbreviations for common situations where only a timeout is required.
333: The file descriptor passed will be \-1, and the event type will be
334: .Va EV_TIMEOUT .
335: .Pp
336: The functions
337: .Fn signal_set ,
338: .Fn signal_add ,
339: .Fn signal_del ,
340: .Fn signal_initialized ,
341: and
342: .Fn signal_pending
343: are abbreviations.
344: The event type will be a persistent
345: .Va EV_SIGNAL .
346: That means
347: .Fn signal_set
348: adds
349: .Va EV_PERSIST .
350: .Pp
351: In order to avoid races in signal handlers, the
352: .Nm event
353: API provides two variables:
354: .Va event_sigcb
355: and
356: .Va event_gotsig .
357: A signal handler
358: sets
359: .Va event_gotsig
360: to indicate that a signal has been received.
361: The application sets
362: .Va event_sigcb
363: to a callback function.
364: After the signal handler sets
365: .Va event_gotsig ,
366: .Nm event_dispatch
367: will execute the callback function to process received signals.
368: The callback returns 1 when no events are registered any more.
369: It can return \-1 to indicate an error to the
370: .Nm event
371: library, causing
372: .Fn event_dispatch
373: to terminate with
374: .Va errno
375: set to
376: .Er EINTR .
377: .Pp
378: The function
379: .Fn event_once
380: is similar to
381: .Fn event_set .
382: However, it schedules a callback to be called exactly once and does not
383: require the caller to prepare an
384: .Fa event
385: structure.
386: This function supports
387: .Fa EV_TIMEOUT ,
388: .Fa EV_READ ,
389: and
390: .Fa EV_WRITE .
391: .Pp
392: The
393: .Fn event_pending
394: function can be used to check if the event specified by
395: .Fa event
396: is pending to run.
397: If
398: .Va EV_TIMEOUT
399: was specified and
400: .Fa tv
401: is not
402: .Dv NULL ,
403: the expiration time of the event will be returned in
404: .Fa tv .
405: .Pp
406: The
407: .Fn event_initialized
408: macro can be used to check if an event has been initialized.
409: .Pp
410: The
411: .Nm event_loop
412: function provides an interface for single pass execution of pending
413: events.
414: The flags
415: .Va EVLOOP_ONCE
416: and
417: .Va EVLOOP_NONBLOCK
418: are recognized.
419: The
420: .Nm event_loopexit
421: function exits from the event loop. The next
422: .Fn event_loop
423: iteration after the
424: given timer expires will complete normally (handling all queued events) then
425: exit without blocking for events again. Subsequent invocations of
426: .Fn event_loop
427: will proceed normally.
428: The
429: .Nm event_loopbreak
430: function exits from the event loop immediately.
431: .Fn event_loop
432: will abort after the next event is completed;
433: .Fn event_loopbreak
434: is typically invoked from this event's callback. This behavior is analogous
435: to the "break;" statement. Subsequent invocations of
436: .Fn event_loop
437: will proceed normally.
438: .Pp
439: It is the responsibility of the caller to provide these functions with
440: pre-allocated event structures.
441: .Pp
442: .Sh EVENT PRIORITIES
443: By default
444: .Nm libevent
445: schedules all active events with the same priority.
446: However, sometimes it is desirable to process some events with a higher
447: priority than others.
448: For that reason,
449: .Nm libevent
450: supports strict priority queues.
451: Active events with a lower priority are always processed before events
452: with a higher priority.
453: .Pp
454: The number of different priorities can be set initially with the
455: .Fn event_priority_init
456: function.
457: This function should be called before the first call to
458: .Fn event_dispatch .
459: The
460: .Fn event_priority_set
461: function can be used to assign a priority to an event.
462: By default,
463: .Nm libevent
464: assigns the middle priority to all events unless their priority
465: is explicitly set.
466: .Sh THREAD SAFE EVENTS
467: .Nm Libevent
468: has experimental support for thread-safe events.
469: When initializing the library via
470: .Fn event_init ,
471: an event base is returned.
472: This event base can be used in conjunction with calls to
473: .Fn event_base_set ,
474: .Fn event_base_dispatch ,
475: .Fn event_base_loop ,
476: .Fn event_base_loopexit ,
477: .Fn bufferevent_base_set
478: and
479: .Fn event_base_free .
480: .Fn event_base_set
481: should be called after preparing an event with
482: .Fn event_set ,
483: as
484: .Fn event_set
485: assigns the provided event to the most recently created event base.
486: .Fn bufferevent_base_set
487: should be called after preparing a bufferevent with
488: .Fn bufferevent_new .
489: .Fn event_base_free
490: should be used to free memory associated with the event base
491: when it is no longer needed.
492: .Sh BUFFERED EVENTS
493: .Nm libevent
494: provides an abstraction on top of the regular event callbacks.
495: This abstraction is called a
496: .Va "buffered event" .
497: A buffered event provides input and output buffers that get filled
498: and drained automatically.
499: The user of a buffered event no longer deals directly with the IO,
500: but instead is reading from input and writing to output buffers.
501: .Pp
502: A new bufferevent is created by
503: .Fn bufferevent_new .
504: The parameter
505: .Fa fd
506: specifies the file descriptor from which data is read and written to.
507: This file descriptor is not allowed to be a
508: .Xr pipe 2 .
509: The next three parameters are callbacks.
510: The read and write callback have the following form:
511: .Ft void
512: .Fn "(*cb)" "struct bufferevent *bufev" "void *arg" .
513: The error callback has the following form:
514: .Ft void
515: .Fn "(*cb)" "struct bufferevent *bufev" "short what" "void *arg" .
516: The argument is specified by the fourth parameter
517: .Fa "cbarg" .
518: A
519: .Fa bufferevent struct
520: pointer is returned on success, NULL on error.
521: Both the read and the write callback may be NULL.
522: The error callback has to be always provided.
523: .Pp
524: Once initialized, the bufferevent structure can be used repeatedly with
525: bufferevent_enable() and bufferevent_disable().
526: The flags parameter can be a combination of
527: .Va EV_READ
528: and
529: .Va EV_WRITE .
530: When read enabled the bufferevent will try to read from the file
531: descriptor and call the read callback.
532: The write callback is executed
533: whenever the output buffer is drained below the write low watermark,
534: which is
535: .Va 0
536: by default.
537: .Pp
538: The
539: .Fn bufferevent_write
540: function can be used to write data to the file descriptor.
541: The data is appended to the output buffer and written to the descriptor
542: automatically as it becomes available for writing.
543: .Fn bufferevent_write
544: returns 0 on success or \-1 on failure.
545: The
546: .Fn bufferevent_read
547: function is used to read data from the input buffer,
548: returning the amount of data read.
549: .Pp
550: If multiple bases are in use, bufferevent_base_set() must be called before
551: enabling the bufferevent for the first time.
552: .Sh NON-BLOCKING HTTP SUPPORT
553: .Nm libevent
554: provides a very thin HTTP layer that can be used both to host an HTTP
555: server and also to make HTTP requests.
556: An HTTP server can be created by calling
557: .Fn evhttp_new .
558: It can be bound to any port and address with the
559: .Fn evhttp_bind_socket
560: function.
561: When the HTTP server is no longer used, it can be freed via
562: .Fn evhttp_free .
563: .Pp
564: To be notified of HTTP requests, a user needs to register callbacks with the
565: HTTP server.
566: This can be done by calling
567: .Fn evhttp_set_cb .
568: The second argument is the URI for which a callback is being registered.
569: The corresponding callback will receive an
570: .Va struct evhttp_request
571: object that contains all information about the request.
572: .Pp
573: This section does not document all the possible function calls; please
574: check
575: .Va event.h
576: for the public interfaces.
577: .Sh ADDITIONAL NOTES
578: It is possible to disable support for
579: .Va epoll , kqueue , devpoll , poll
580: or
581: .Va select
582: by setting the environment variable
583: .Va EVENT_NOEPOLL , EVENT_NOKQUEUE , EVENT_NODEVPOLL , EVENT_NOPOLL
584: or
585: .Va EVENT_NOSELECT ,
586: respectively.
587: By setting the environment variable
588: .Va EVENT_SHOW_METHOD ,
589: .Nm libevent
590: displays the kernel notification method that it uses.
591: .Sh RETURN VALUES
592: Upon successful completion
593: .Fn event_add
594: and
595: .Fn event_del
596: return 0.
597: Otherwise, \-1 is returned and the global variable errno is
598: set to indicate the error.
599: .Sh SEE ALSO
600: .Xr kqueue 2 ,
601: .Xr poll 2 ,
602: .Xr select 2 ,
603: .Xr evdns 3 ,
604: .Xr timeout 9
605: .Sh HISTORY
606: The
607: .Nm event
608: API manpage is based on the
609: .Xr timeout 9
610: manpage by Artur Grabowski.
611: The port of
612: .Nm libevent
613: to Windows is due to Michael A. Davis.
614: Support for real-time signals is due to Taral.
615: .Sh AUTHORS
616: The
617: .Nm event
618: library was written by Niels Provos.
619: .Sh BUGS
620: This documentation is neither complete nor authoritative.
621: If you are in doubt about the usage of this API then
622: check the source code to find out how it works, write
623: up the missing piece of documentation and send it to
624: me for inclusion in this man page.
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