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1 | .\" Copyright (C) 2008 Michael Kerrisk <mtk.manpages@gmail.com> |
2 | .\" | |
f0008367 | 3 | .\" %%%LICENSE_START(GPLv2+_SW_3_PARA) |
45b81c9c MK |
4 | .\" This program is free software; you can redistribute it and/or modify |
5 | .\" it under the terms of the GNU General Public License as published by | |
6 | .\" the Free Software Foundation; either version 2 of the License, or | |
7 | .\" (at your option) any later version. | |
8 | .\" | |
9 | .\" This program is distributed in the hope that it will be useful, | |
10 | .\" but WITHOUT ANY WARRANTY; without even the implied warranty of | |
11 | .\" MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the | |
12 | .\" GNU General Public License for more details. | |
13 | .\" | |
68fa4398 MK |
14 | .\" You should have received a copy of the GNU General Public |
15 | .\" License along with this manual; if not, see | |
16 | .\" <http://www.gnu.org/licenses/>. | |
8ff7380d | 17 | .\" %%%LICENSE_END |
45b81c9c | 18 | .\" |
e8426ca2 | 19 | .TH TIMERFD_CREATE 2 2020-04-11 Linux "Linux Programmer's Manual" |
45b81c9c MK |
20 | .SH NAME |
21 | timerfd_create, timerfd_settime, timerfd_gettime \- | |
22 | timers that notify via file descriptors | |
23 | .SH SYNOPSIS | |
45b81c9c MK |
24 | .nf |
25 | .B #include <sys/timerfd.h> | |
68e4db0a | 26 | .PP |
45b81c9c | 27 | .BI "int timerfd_create(int " clockid ", int " flags ); |
68e4db0a | 28 | .PP |
45b81c9c MK |
29 | .BI "int timerfd_settime(int " fd ", int " flags , |
30 | .BI " const struct itimerspec *" new_value , | |
5c902597 | 31 | .BI " struct itimerspec *" old_value ); |
68e4db0a | 32 | .PP |
45b81c9c MK |
33 | .BI "int timerfd_gettime(int " fd ", struct itimerspec *" curr_value ); |
34 | .fi | |
35 | .SH DESCRIPTION | |
36 | These system calls create and operate on a timer | |
37 | that delivers timer expiration notifications via a file descriptor. | |
38 | They provide an alternative to the use of | |
39 | .BR setitimer (2) | |
40 | or | |
804f03e6 | 41 | .BR timer_create (2), |
45b81c9c MK |
42 | with the advantage that the file descriptor may be monitored by |
43 | .BR select (2), | |
44 | .BR poll (2), | |
45 | and | |
46 | .BR epoll (7). | |
efeece04 | 47 | .PP |
45b81c9c | 48 | The use of these three system calls is analogous to the use of |
804f03e6 MK |
49 | .BR timer_create (2), |
50 | .BR timer_settime (2), | |
45b81c9c | 51 | and |
804f03e6 | 52 | .BR timer_gettime (2). |
45b81c9c | 53 | (There is no analog of |
804f03e6 | 54 | .BR timer_getoverrun (2), |
45b81c9c MK |
55 | since that functionality is provided by |
56 | .BR read (2), | |
57 | as described below.) | |
58 | .\" | |
59 | .SS timerfd_create() | |
60 | .BR timerfd_create () | |
61 | creates a new timer object, | |
62 | and returns a file descriptor that refers to that timer. | |
63 | The | |
64 | .I clockid | |
65 | argument specifies the clock that is used to mark the progress | |
205b1bce | 66 | of the timer, and must be one of the following: |
4b76fffb | 67 | .TP |
45b81c9c | 68 | .B CLOCK_REALTIME |
4b76fffb MK |
69 | A settable system-wide real-time clock. |
70 | .TP | |
45b81c9c | 71 | .B CLOCK_MONOTONIC |
4b76fffb MK |
72 | A nonsettable monotonically increasing clock that measures time |
73 | from some unspecified point in the past that does not change | |
74 | after system startup. | |
4c747119 MK |
75 | .TP |
76 | .BR CLOCK_BOOTTIME " (Since Linux 3.15)" | |
77 | .\" commit 4a2378a943f09907fb1ae35c15de917f60289c14 | |
78 | Like | |
79 | .BR CLOCK_MONOTONIC , | |
80 | this is a monotonically increasing clock. | |
81 | However, whereas the | |
82 | .BR CLOCK_MONOTONIC | |
83 | clock does not measure the time while a system is suspended, the | |
84 | .BR CLOCK_BOOTTIME | |
85 | clock does include the time during which the system is suspended. | |
86 | This is useful for applications that need to be suspend-aware. | |
87 | .BR CLOCK_REALTIME | |
88 | is not suitable for such applications, since that clock is affected | |
89 | by discontinuous changes to the system clock. | |
90 | .TP | |
91 | .BR CLOCK_REALTIME_ALARM " (since Linux 3.11)" | |
92 | .\" commit 11ffa9d6065f344a9bd769a2452f26f2f671e5f8 | |
93 | This clock is like | |
94 | .BR CLOCK_REALTIME , | |
95 | but will wake the system if it is suspended. | |
96 | The caller must have the | |
97 | .B CAP_WAKE_ALARM | |
98 | capability in order to set a timer against this clock. | |
99 | .TP | |
100 | .BR CLOCK_BOOTTIME_ALARM " (since Linux 3.11)" | |
101 | .\" commit 11ffa9d6065f344a9bd769a2452f26f2f671e5f8 | |
102 | This clock is like | |
103 | .BR CLOCK_BOOTTIME , | |
104 | but will wake the system if it is suspended. | |
105 | The caller must have the | |
106 | .B CAP_WAKE_ALARM | |
107 | capability in order to set a timer against this clock. | |
4b76fffb | 108 | .PP |
ff5de6ec MK |
109 | See |
110 | .BR clock_getres (2) | |
111 | for some further details on the above clocks. | |
112 | .PP | |
45b81c9c | 113 | The current value of each of these clocks can be retrieved using |
0eb44391 | 114 | .BR clock_gettime (2). |
efeece04 | 115 | .PP |
3df1b973 MK |
116 | Starting with Linux 2.6.27, the following values may be bitwise ORed in |
117 | .IR flags | |
118 | to change the behavior of | |
119 | .BR timerfd_create (): | |
120 | .TP 14 | |
121 | .B TFD_NONBLOCK | |
122 | Set the | |
123 | .BR O_NONBLOCK | |
7f11e32c MK |
124 | file status flag on the open file description (see |
125 | .BR open (2)) | |
126 | referred to by the new file descriptor. | |
3df1b973 | 127 | Using this flag saves extra calls to |
ef7db4f5 | 128 | .BR fcntl (2) |
3df1b973 MK |
129 | to achieve the same result. |
130 | .TP | |
131 | .B TFD_CLOEXEC | |
132 | Set the close-on-exec | |
133 | .RB ( FD_CLOEXEC ) | |
134 | flag on the new file descriptor. | |
c5571b61 | 135 | See the description of the |
3df1b973 MK |
136 | .B O_CLOEXEC |
137 | flag in | |
138 | .BR open (2) | |
139 | for reasons why this may be useful. | |
140 | .PP | |
141 | In Linux versions up to and including 2.6.26, | |
45b81c9c | 142 | .I flags |
3df1b973 | 143 | must be specified as zero. |
45b81c9c MK |
144 | .SS timerfd_settime() |
145 | .BR timerfd_settime () | |
146 | arms (starts) or disarms (stops) | |
147 | the timer referred to by the file descriptor | |
148 | .IR fd . | |
efeece04 | 149 | .PP |
45b81c9c MK |
150 | The |
151 | .I new_value | |
152 | argument specifies the initial expiration and interval for the timer. | |
153 | The | |
251ebc1e | 154 | .I itimerspec |
45b81c9c MK |
155 | structure used for this argument contains two fields, |
156 | each of which is in turn a structure of type | |
157 | .IR timespec : | |
e646a1ba | 158 | .PP |
45b81c9c | 159 | .in +4n |
e646a1ba | 160 | .EX |
45b81c9c MK |
161 | struct timespec { |
162 | time_t tv_sec; /* Seconds */ | |
163 | long tv_nsec; /* Nanoseconds */ | |
164 | }; | |
165 | ||
166 | struct itimerspec { | |
167 | struct timespec it_interval; /* Interval for periodic timer */ | |
168 | struct timespec it_value; /* Initial expiration */ | |
169 | }; | |
b8302363 | 170 | .EE |
45b81c9c MK |
171 | .in |
172 | .PP | |
173 | .I new_value.it_value | |
174 | specifies the initial expiration of the timer, | |
175 | in seconds and nanoseconds. | |
176 | Setting either field of | |
177 | .I new_value.it_value | |
c7094399 | 178 | to a nonzero value arms the timer. |
45b81c9c MK |
179 | Setting both fields of |
180 | .I new_value.it_value | |
181 | to zero disarms the timer. | |
efeece04 | 182 | .PP |
45b81c9c MK |
183 | Setting one or both fields of |
184 | .I new_value.it_interval | |
c7094399 | 185 | to nonzero values specifies the period, in seconds and nanoseconds, |
45b81c9c MK |
186 | for repeated timer expirations after the initial expiration. |
187 | If both fields of | |
188 | .I new_value.it_interval | |
189 | are zero, the timer expires just once, at the time specified by | |
190 | .IR new_value.it_value . | |
efeece04 | 191 | .PP |
51062576 MK |
192 | By default, |
193 | the initial expiration time specified in | |
194 | .I new_value | |
195 | is interpreted relative to the current time | |
196 | on the timer's clock at the time of the call (i.e., | |
197 | .I new_value.it_value | |
198 | specifies a time relative to the current value of the clock specified by | |
199 | .IR clockid ). | |
200 | An absolute timeout can be selected via the | |
201 | .I flags | |
202 | argument. | |
efeece04 | 203 | .PP |
45b81c9c MK |
204 | The |
205 | .I flags | |
51062576 MK |
206 | argument is a bit mask that can include the following values: |
207 | .TP | |
208 | .B TFD_TIMER_ABSTIME | |
209 | Interpret | |
210 | .I new_value.it_value | |
211 | as an absolute value on the timer's clock. | |
212 | The timer will expire when the value of the timer's | |
45b81c9c | 213 | clock reaches the value specified in |
51062576 | 214 | .IR new_value.it_value . |
e9477548 MK |
215 | .TP |
216 | .BR TFD_TIMER_CANCEL_ON_SET | |
217 | If this flag is specified along with | |
218 | .B TFD_TIMER_ABSTIME | |
219 | and the clock for this timer is | |
220 | .BR CLOCK_REALTIME | |
221 | or | |
222 | .BR CLOCK_REALTIME_ALARM , | |
223 | then mark this timer as cancelable if the real-time clock | |
224 | undergoes a discontinuous change | |
225 | .RB ( settimeofday (2), | |
226 | .BR clock_settime (2), | |
227 | or similar). | |
228 | When such changes occur, a current or future | |
229 | .BR read (2) | |
230 | from the file descriptor will fail with the error | |
231 | .BR ECANCELED . | |
51062576 | 232 | .PP |
009cdc22 | 233 | If the |
5c902597 | 234 | .I old_value |
009cdc22 MK |
235 | argument is not NULL, then the |
236 | .I itimerspec | |
237 | structure that it points to is used to return the setting of the timer | |
238 | that was current at the time of the call; | |
239 | see the description of | |
45b81c9c MK |
240 | .BR timerfd_gettime () |
241 | following. | |
242 | .\" | |
243 | .SS timerfd_gettime() | |
244 | .BR timerfd_gettime () | |
245 | returns, in | |
246 | .IR curr_value , | |
247 | an | |
248 | .IR itimerspec | |
dc55661b | 249 | structure that contains the current setting of the timer |
45b81c9c MK |
250 | referred to by the file descriptor |
251 | .IR fd . | |
efeece04 | 252 | .PP |
45b81c9c MK |
253 | The |
254 | .I it_value | |
255 | field returns the amount of time | |
256 | until the timer will next expire. | |
257 | If both fields of this structure are zero, | |
258 | then the timer is currently disarmed. | |
259 | This field always contains a relative value, regardless of whether the | |
260 | .BR TFD_TIMER_ABSTIME | |
261 | flag was specified when setting the timer. | |
efeece04 | 262 | .PP |
45b81c9c MK |
263 | The |
264 | .I it_interval | |
265 | field returns the interval of the timer. | |
266 | If both fields of this structure are zero, | |
267 | then the timer is set to expire just once, at the time specified by | |
268 | .IR curr_value.it_value . | |
269 | .SS Operating on a timer file descriptor | |
270 | The file descriptor returned by | |
271 | .BR timerfd_create () | |
066dcd09 | 272 | supports the following additional operations: |
45b81c9c MK |
273 | .TP |
274 | .BR read (2) | |
275 | If the timer has already expired one or more times since | |
276 | its settings were last modified using | |
277 | .BR timerfd_settime (), | |
278 | or since the last successful | |
279 | .BR read (2), | |
280 | then the buffer given to | |
281 | .BR read (2) | |
282 | returns an unsigned 8-byte integer | |
283 | .RI ( uint64_t ) | |
284 | containing the number of expirations that have occurred. | |
88879aeb MK |
285 | (The returned value is in host byte order\(emthat is, |
286 | the native byte order for integers on the host machine.) | |
45b81c9c MK |
287 | .IP |
288 | If no timer expirations have occurred at the time of the | |
289 | .BR read (2), | |
290 | then the call either blocks until the next timer expiration, | |
291 | or fails with the error | |
292 | .B EAGAIN | |
ff40dbb3 | 293 | if the file descriptor has been made nonblocking |
45b81c9c MK |
294 | (via the use of the |
295 | .BR fcntl (2) | |
296 | .B F_SETFL | |
297 | operation to set the | |
298 | .B O_NONBLOCK | |
299 | flag). | |
300 | .IP | |
301 | A | |
302 | .BR read (2) | |
26cd31fd | 303 | fails with the error |
45b81c9c MK |
304 | .B EINVAL |
305 | if the size of the supplied buffer is less than 8 bytes. | |
efeece04 | 306 | .IP |
e9477548 MK |
307 | If the associated clock is either |
308 | .BR CLOCK_REALTIME | |
309 | or | |
310 | .BR CLOCK_REALTIME_ALARM , | |
311 | the timer is absolute | |
312 | .RB ( TFD_TIMER_ABSTIME ), | |
313 | and the flag | |
314 | .BR TFD_TIMER_CANCEL_ON_SET | |
315 | was specified when calling | |
316 | .BR timerfd_settime (), | |
317 | then | |
318 | .BR read (2) | |
26cd31fd | 319 | fails with the error |
e9477548 MK |
320 | .BR ECANCELED |
321 | if the real-time clock undergoes a discontinuous change. | |
322 | (This allows the reading application to discover | |
323 | such discontinuous changes to the clock.) | |
1ae24555 MK |
324 | .IP |
325 | If the associated clock is either | |
326 | .BR CLOCK_REALTIME | |
327 | or | |
328 | .BR CLOCK_REALTIME_ALARM , | |
329 | the timer is absolute | |
330 | .RB ( TFD_TIMER_ABSTIME ), | |
331 | and the flag | |
332 | .BR TFD_TIMER_CANCEL_ON_SET | |
333 | was | |
334 | .I not | |
335 | specified when calling | |
336 | .BR timerfd_settime (), | |
337 | then a discontinuous negative change to the clock (e.g., | |
338 | .BR clock_settime (2)) | |
339 | may cause | |
340 | .BR read (2) | |
341 | to unblock, but return a value of 0 (i.e., no bytes read), | |
342 | if the clock change occurs after the time expired, | |
343 | but before the | |
344 | .BR read (2) | |
345 | on the file descriptor. | |
45b81c9c MK |
346 | .TP |
347 | .BR poll "(2), " select "(2) (and similar)" | |
348 | The file descriptor is readable | |
349 | (the | |
350 | .BR select (2) | |
351 | .I readfds | |
352 | argument; the | |
353 | .BR poll (2) | |
354 | .B POLLIN | |
355 | flag) | |
356 | if one or more timer expirations have occurred. | |
357 | .IP | |
358 | The file descriptor also supports the other file-descriptor | |
359 | multiplexing APIs: | |
360 | .BR pselect (2), | |
361 | .BR ppoll (2), | |
362 | and | |
363 | .BR epoll (7). | |
364 | .TP | |
6614e292 | 365 | .BR ioctl (2) |
80d27367 MK |
366 | The following timerfd-specific command is supported: |
367 | .RS | |
368 | .TP | |
40f6b649 MK |
369 | .BR TFD_IOC_SET_TICKS " (since Linux 3.17)" |
370 | .\" commit 5442e9fbd7c23172a1c9bc736629cd123a9923f0 | |
80d27367 MK |
371 | Adjust the number of timer expirations that have occurred. |
372 | The argument is a pointer to a nonzero 8-byte integer | |
5a3eb9cd CG |
373 | .RI ( uint64_t *) |
374 | containing the new number of expirations. | |
80d27367 | 375 | Once the number is set, any waiter on the timer is woken up. |
5a3eb9cd | 376 | The only purpose of this command is to restore the expirations |
80d27367 MK |
377 | for the purpose of checkpoint/restore. |
378 | This operation is available only if the kernel was configured with the | |
5a3eb9cd | 379 | .BR CONFIG_CHECKPOINT_RESTORE |
80d27367 MK |
380 | option. |
381 | .RE | |
5a3eb9cd | 382 | .TP |
45b81c9c MK |
383 | .BR close (2) |
384 | When the file descriptor is no longer required it should be closed. | |
385 | When all file descriptors associated with the same timer object | |
386 | have been closed, | |
387 | the timer is disarmed and its resources are freed by the kernel. | |
388 | .\" | |
389 | .SS fork(2) semantics | |
390 | After a | |
391 | .BR fork (2), | |
392 | the child inherits a copy of the file descriptor created by | |
393 | .BR timerfd_create (). | |
394 | The file descriptor refers to the same underlying | |
395 | timer object as the corresponding file descriptor in the parent, | |
396 | and | |
397 | .BR read (2)s | |
398 | in the child will return information about | |
399 | expirations of the timer. | |
400 | .\" | |
401 | .SS execve(2) semantics | |
402 | A file descriptor created by | |
403 | .BR timerfd_create () | |
404 | is preserved across | |
405 | .BR execve (2), | |
406 | and continues to generate timer expirations if the timer was armed. | |
47297adb | 407 | .SH RETURN VALUE |
45b81c9c MK |
408 | On success, |
409 | .BR timerfd_create () | |
410 | returns a new file descriptor. | |
411 | On error, \-1 is returned and | |
412 | .I errno | |
413 | is set to indicate the error. | |
efeece04 | 414 | .PP |
45b81c9c MK |
415 | .BR timerfd_settime () |
416 | and | |
417 | .BR timerfd_gettime () | |
418 | return 0 on success; | |
419 | on error they return \-1, and set | |
420 | .I errno | |
421 | to indicate the error. | |
422 | .SH ERRORS | |
423 | .BR timerfd_create () | |
424 | can fail with the following errors: | |
425 | .TP | |
426 | .B EINVAL | |
427 | The | |
428 | .I clockid | |
04e2e313 | 429 | is not valid. |
3df1b973 MK |
430 | .TP |
431 | .B EINVAL | |
432 | .I flags | |
433 | is invalid; | |
434 | or, in Linux 2.6.26 or earlier, | |
45b81c9c | 435 | .I flags |
c7094399 | 436 | is nonzero. |
45b81c9c MK |
437 | .TP |
438 | .B EMFILE | |
26c32fab | 439 | The per-process limit on the number of open file descriptors has been reached. |
45b81c9c MK |
440 | .TP |
441 | .B ENFILE | |
442 | The system-wide limit on the total number of open files has been | |
443 | reached. | |
444 | .TP | |
445 | .B ENODEV | |
446 | Could not mount (internal) anonymous inode device. | |
447 | .TP | |
448 | .B ENOMEM | |
449 | There was insufficient kernel memory to create the timer. | |
96d951a4 MK |
450 | .TP |
451 | .B EPERM | |
452 | .I clockid | |
453 | was | |
454 | .BR CLOCK_REALTIME_ALARM | |
455 | or | |
456 | ,BR CLOCK_BOOTTIME_ALARM | |
457 | but the caller did not have the | |
458 | .BR CAP_WAKE_ALARM | |
459 | capability. | |
45b81c9c MK |
460 | .PP |
461 | .BR timerfd_settime () | |
462 | and | |
463 | .BR timerfd_gettime () | |
464 | can fail with the following errors: | |
465 | .TP | |
466 | .B EBADF | |
467 | .I fd | |
468 | is not a valid file descriptor. | |
469 | .TP | |
2bbb3907 MK |
470 | .B EFAULT |
471 | .IR new_value , | |
472 | .IR old_value , | |
473 | or | |
474 | .I curr_value | |
475 | is not valid a pointer. | |
476 | .TP | |
45b81c9c MK |
477 | .B EINVAL |
478 | .I fd | |
479 | is not a valid timerfd file descriptor. | |
c71b054d MK |
480 | .PP |
481 | .BR timerfd_settime () | |
482 | can also fail with the following errors: | |
483 | .TP | |
0f1553b5 MK |
484 | .B ECANCELED |
485 | See NOTES. | |
486 | .TP | |
c71b054d | 487 | .B EINVAL |
45b81c9c MK |
488 | .I new_value |
489 | is not properly initialized (one of the | |
490 | .I tv_nsec | |
491 | falls outside the range zero to 999,999,999). | |
86d95cf2 MK |
492 | .TP |
493 | .B EINVAL | |
494 | .\" This case only checked since 2.6.29, and 2.2.2[78].some-stable-version. | |
495 | .\" In older kernel versions, no check was made for invalid flags. | |
496 | .I flags | |
497 | is invalid. | |
45b81c9c MK |
498 | .SH VERSIONS |
499 | These system calls are available on Linux since kernel 2.6.25. | |
d6a54d42 | 500 | Library support is provided by glibc since version 2.8. |
45b81c9c MK |
501 | .SH CONFORMING TO |
502 | These system calls are Linux-specific. | |
0f1553b5 MK |
503 | .SH NOTES |
504 | Suppose the following scenario for | |
505 | .BR CLOCK_REALTIME | |
506 | or | |
507 | .BR CLOCK_REALTIME_ALARM | |
508 | timer that was created with | |
509 | .BR timerfd_create (): | |
510 | .IP (a) 4 | |
511 | The timer has been started | |
512 | .RB ( timerfd_settime ()) | |
513 | with the | |
514 | .BR TFD_TIMER_ABSTIME | |
515 | and | |
516 | .BR TFD_TIMER_CANCEL_ON_SET | |
517 | flags; | |
518 | .IP (b) | |
519 | A discontinuous change (e.g. | |
520 | .BR settimeofday (2)) | |
521 | is subsequently made to the | |
522 | .BR CLOCK_REALTIME | |
523 | clock; and | |
524 | .IP (c) | |
525 | the caller once more calls | |
526 | .BR timerfd_settime () | |
527 | to rearm the timer (without first doing a | |
528 | .BR read (2) | |
529 | on the file descriptor). | |
530 | .PP | |
531 | In this case the following occurs: | |
532 | .IP \(bu 2 | |
533 | The | |
534 | .BR timerfd_settime () | |
535 | returns \-1 with | |
536 | .I errno | |
537 | set to | |
538 | .BR ECANCELED . | |
539 | (This enables the caller to know that the previous timer was affected | |
540 | by a discontinuous change to the clock.) | |
541 | .IP \(bu | |
542 | The timer | |
543 | .I "is successfully rearmed" | |
544 | with the settings provided in the second | |
545 | .BR timerfd_settime () | |
546 | call. | |
547 | (This was probably an implementation accident, but won't be fixed now, | |
548 | in case there are applications that depend on this behaviour.) | |
7484d5a7 MK |
549 | .SH BUGS |
550 | Currently, | |
551 | .\" 2.6.29 | |
552 | .BR timerfd_create () | |
553 | supports fewer types of clock IDs than | |
554 | .BR timer_create (2). | |
45b81c9c MK |
555 | .SH EXAMPLE |
556 | The following program creates a timer and then monitors its progress. | |
557 | The program accepts up to three command-line arguments. | |
558 | The first argument specifies the number of seconds for | |
559 | the initial expiration of the timer. | |
560 | The second argument specifies the interval for the timer, in seconds. | |
561 | The third argument specifies the number of times the program should | |
562 | allow the timer to expire before terminating. | |
563 | The second and third command-line arguments are optional. | |
efeece04 | 564 | .PP |
45b81c9c | 565 | The following shell session demonstrates the use of the program: |
e646a1ba | 566 | .PP |
45b81c9c | 567 | .in +4n |
e646a1ba | 568 | .EX |
b43a3b30 | 569 | .RB "$" " a.out 3 1 100" |
45b81c9c MK |
570 | 0.000: timer started |
571 | 3.000: read: 1; total=1 | |
572 | 4.000: read: 1; total=2 | |
b43a3b30 | 573 | .BR "^Z " " # type control-Z to suspend the program" |
45b81c9c | 574 | [1]+ Stopped ./timerfd3_demo 3 1 100 |
b43a3b30 | 575 | .RB "$ " "fg" " # Resume execution after a few seconds" |
45b81c9c MK |
576 | a.out 3 1 100 |
577 | 9.660: read: 5; total=7 | |
578 | 10.000: read: 1; total=8 | |
579 | 11.000: read: 1; total=9 | |
b43a3b30 | 580 | .BR "^C " " # type control-C to suspend the program" |
b8302363 | 581 | .EE |
45b81c9c | 582 | .in |
9c330504 | 583 | .SS Program source |
d84d0300 | 584 | \& |
e7d0bb47 | 585 | .EX |
45b81c9c MK |
586 | .\" The commented out code here is what we currently need until |
587 | .\" the required stuff is in glibc | |
588 | .\" | |
589 | .\" | |
590 | .\"/* Link with -lrt */ | |
591 | .\"#define _GNU_SOURCE | |
592 | .\"#include <sys/syscall.h> | |
593 | .\"#include <unistd.h> | |
594 | .\"#include <time.h> | |
595 | .\"#if defined(__i386__) | |
596 | .\"#define __NR_timerfd_create 322 | |
597 | .\"#define __NR_timerfd_settime 325 | |
598 | .\"#define __NR_timerfd_gettime 326 | |
599 | .\"#endif | |
600 | .\" | |
601 | .\"static int | |
602 | .\"timerfd_create(int clockid, int flags) | |
603 | .\"{ | |
604 | .\" return syscall(__NR_timerfd_create, clockid, flags); | |
605 | .\"} | |
606 | .\" | |
607 | .\"static int | |
608 | .\"timerfd_settime(int fd, int flags, struct itimerspec *new_value, | |
609 | .\" struct itimerspec *curr_value) | |
610 | .\"{ | |
611 | .\" return syscall(__NR_timerfd_settime, fd, flags, new_value, | |
612 | .\" curr_value); | |
613 | .\"} | |
614 | .\" | |
615 | .\"static int | |
616 | .\"timerfd_gettime(int fd, struct itimerspec *curr_value) | |
617 | .\"{ | |
618 | .\" return syscall(__NR_timerfd_gettime, fd, curr_value); | |
619 | .\"} | |
620 | .\" | |
621 | .\"#define TFD_TIMER_ABSTIME (1 << 0) | |
622 | .\" | |
623 | .\"//////////////////////////////////////////////////////////// | |
45b81c9c MK |
624 | #include <sys/timerfd.h> |
625 | #include <time.h> | |
626 | #include <unistd.h> | |
627 | #include <stdlib.h> | |
628 | #include <stdio.h> | |
629 | #include <stdint.h> /* Definition of uint64_t */ | |
630 | ||
d1a71985 | 631 | #define handle_error(msg) \e |
45b81c9c MK |
632 | do { perror(msg); exit(EXIT_FAILURE); } while (0) |
633 | ||
634 | static void | |
635 | print_elapsed_time(void) | |
636 | { | |
637 | static struct timespec start; | |
638 | struct timespec curr; | |
639 | static int first_call = 1; | |
640 | int secs, nsecs; | |
641 | ||
642 | if (first_call) { | |
643 | first_call = 0; | |
644 | if (clock_gettime(CLOCK_MONOTONIC, &start) == \-1) | |
645 | handle_error("clock_gettime"); | |
646 | } | |
647 | ||
648 | if (clock_gettime(CLOCK_MONOTONIC, &curr) == \-1) | |
649 | handle_error("clock_gettime"); | |
650 | ||
651 | secs = curr.tv_sec \- start.tv_sec; | |
652 | nsecs = curr.tv_nsec \- start.tv_nsec; | |
653 | if (nsecs < 0) { | |
654 | secs\-\-; | |
655 | nsecs += 1000000000; | |
656 | } | |
657 | printf("%d.%03d: ", secs, (nsecs + 500000) / 1000000); | |
658 | } | |
659 | ||
660 | int | |
661 | main(int argc, char *argv[]) | |
662 | { | |
663 | struct itimerspec new_value; | |
664 | int max_exp, fd; | |
665 | struct timespec now; | |
666 | uint64_t exp, tot_exp; | |
667 | ssize_t s; | |
668 | ||
669 | if ((argc != 2) && (argc != 4)) { | |
d1a71985 | 670 | fprintf(stderr, "%s init\-secs [interval\-secs max\-exp]\en", |
45b81c9c MK |
671 | argv[0]); |
672 | exit(EXIT_FAILURE); | |
673 | } | |
674 | ||
675 | if (clock_gettime(CLOCK_REALTIME, &now) == \-1) | |
676 | handle_error("clock_gettime"); | |
677 | ||
678 | /* Create a CLOCK_REALTIME absolute timer with initial | |
679 | expiration and interval as specified in command line */ | |
680 | ||
681 | new_value.it_value.tv_sec = now.tv_sec + atoi(argv[1]); | |
682 | new_value.it_value.tv_nsec = now.tv_nsec; | |
683 | if (argc == 2) { | |
684 | new_value.it_interval.tv_sec = 0; | |
685 | max_exp = 1; | |
686 | } else { | |
687 | new_value.it_interval.tv_sec = atoi(argv[2]); | |
688 | max_exp = atoi(argv[3]); | |
689 | } | |
690 | new_value.it_interval.tv_nsec = 0; | |
691 | ||
692 | fd = timerfd_create(CLOCK_REALTIME, 0); | |
693 | if (fd == \-1) | |
694 | handle_error("timerfd_create"); | |
695 | ||
a279595b | 696 | if (timerfd_settime(fd, TFD_TIMER_ABSTIME, &new_value, NULL) == \-1) |
45b81c9c MK |
697 | handle_error("timerfd_settime"); |
698 | ||
699 | print_elapsed_time(); | |
d1a71985 | 700 | printf("timer started\en"); |
45b81c9c MK |
701 | |
702 | for (tot_exp = 0; tot_exp < max_exp;) { | |
703 | s = read(fd, &exp, sizeof(uint64_t)); | |
704 | if (s != sizeof(uint64_t)) | |
705 | handle_error("read"); | |
706 | ||
707 | tot_exp += exp; | |
708 | print_elapsed_time(); | |
d1a71985 | 709 | printf("read: %llu; total=%llu\en", |
45b81c9c MK |
710 | (unsigned long long) exp, |
711 | (unsigned long long) tot_exp); | |
712 | } | |
713 | ||
714 | exit(EXIT_SUCCESS); | |
715 | } | |
e7d0bb47 | 716 | .EE |
47297adb | 717 | .SH SEE ALSO |
45b81c9c MK |
718 | .BR eventfd (2), |
719 | .BR poll (2), | |
720 | .BR read (2), | |
721 | .BR select (2), | |
722 | .BR setitimer (2), | |
723 | .BR signalfd (2), | |
804f03e6 MK |
724 | .BR timer_create (2), |
725 | .BR timer_gettime (2), | |
726 | .BR timer_settime (2), | |
45b81c9c MK |
727 | .BR epoll (7), |
728 | .BR time (7) |