xref: /netbsd-src/external/bsd/libevent/dist/evutil_time.c (revision 657871a79c9a2060a6255a242fa1a1ef76b56ec6)
1 /*	$NetBSD: evutil_time.c,v 1.1.1.2 2021/04/07 02:43:13 christos Exp $	*/
2 /*
3  * Copyright (c) 2007-2012 Niels Provos and Nick Mathewson
4  *
5  * Redistribution and use in source and binary forms, with or without
6  * modification, are permitted provided that the following conditions
7  * are met:
8  * 1. Redistributions of source code must retain the above copyright
9  *    notice, this list of conditions and the following disclaimer.
10  * 2. Redistributions in binary form must reproduce the above copyright
11  *    notice, this list of conditions and the following disclaimer in the
12  *    documentation and/or other materials provided with the distribution.
13  * 3. The name of the author may not be used to endorse or promote products
14  *    derived from this software without specific prior written permission.
15  *
16  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
17  * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
18  * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
19  * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
20  * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
21  * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
22  * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
23  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
24  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
25  * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
26  */
27 
28 #include "event2/event-config.h"
29 #include <sys/cdefs.h>
30 __RCSID("$NetBSD: evutil_time.c,v 1.1.1.2 2021/04/07 02:43:13 christos Exp $");
31 #include "evconfig-private.h"
32 
33 #ifdef _WIN32
34 #include <winsock2.h>
35 #define WIN32_LEAN_AND_MEAN
36 #include <windows.h>
37 #undef WIN32_LEAN_AND_MEAN
38 #endif
39 
40 #include <sys/types.h>
41 #ifdef EVENT__HAVE_STDLIB_H
42 #include <stdlib.h>
43 #endif
44 #include <errno.h>
45 #include <limits.h>
46 #ifndef EVENT__HAVE_GETTIMEOFDAY
47 #include <sys/timeb.h>
48 #endif
49 #if !defined(EVENT__HAVE_NANOSLEEP) && !defined(EVENT__HAVE_USLEEP) && \
50 	!defined(_WIN32)
51 #include <sys/select.h>
52 #endif
53 #include <time.h>
54 #include <sys/stat.h>
55 #include <string.h>
56 
57 /** evutil_usleep_() */
58 #if defined(_WIN32)
59 #elif defined(EVENT__HAVE_NANOSLEEP)
60 #elif defined(EVENT__HAVE_USLEEP)
61 #include <unistd.h>
62 #endif
63 
64 #include "event2/util.h"
65 #include "util-internal.h"
66 #include "log-internal.h"
67 #include "mm-internal.h"
68 
69 #ifndef EVENT__HAVE_GETTIMEOFDAY
70 /* No gettimeofday; this must be windows. */
71 
72 typedef void (WINAPI *GetSystemTimePreciseAsFileTime_fn_t) (LPFILETIME);
73 
74 int
evutil_gettimeofday(struct timeval * tv,struct timezone * tz)75 evutil_gettimeofday(struct timeval *tv, struct timezone *tz)
76 {
77 #ifdef _MSC_VER
78 #define U64_LITERAL(n) n##ui64
79 #else
80 #define U64_LITERAL(n) n##llu
81 #endif
82 
83 	/* Conversion logic taken from Tor, which in turn took it
84 	 * from Perl.  GetSystemTimeAsFileTime returns its value as
85 	 * an unaligned (!) 64-bit value containing the number of
86 	 * 100-nanosecond intervals since 1 January 1601 UTC. */
87 #define EPOCH_BIAS U64_LITERAL(116444736000000000)
88 #define UNITS_PER_SEC U64_LITERAL(10000000)
89 #define USEC_PER_SEC U64_LITERAL(1000000)
90 #define UNITS_PER_USEC U64_LITERAL(10)
91 	union {
92 		FILETIME ft_ft;
93 		ev_uint64_t ft_64;
94 	} ft;
95 
96 	if (tv == NULL)
97 		return -1;
98 
99 	static GetSystemTimePreciseAsFileTime_fn_t GetSystemTimePreciseAsFileTime_fn = NULL;
100 	static int check_precise = 1;
101 
102 	if (EVUTIL_UNLIKELY(check_precise)) {
103 		HMODULE h = evutil_load_windows_system_library_(TEXT("kernel32.dll"));
104 		if (h != NULL)
105 			GetSystemTimePreciseAsFileTime_fn =
106 				(GetSystemTimePreciseAsFileTime_fn_t)
107 					GetProcAddress(h, "GetSystemTimePreciseAsFileTime");
108 		check_precise = 0;
109 	}
110 
111 	if (GetSystemTimePreciseAsFileTime_fn != NULL)
112 		GetSystemTimePreciseAsFileTime_fn(&ft.ft_ft);
113 	else
114 		GetSystemTimeAsFileTime(&ft.ft_ft);
115 
116 	if (EVUTIL_UNLIKELY(ft.ft_64 < EPOCH_BIAS)) {
117 		/* Time before the unix epoch. */
118 		return -1;
119 	}
120 	ft.ft_64 -= EPOCH_BIAS;
121 	tv->tv_sec = (long) (ft.ft_64 / UNITS_PER_SEC);
122 	tv->tv_usec = (long) ((ft.ft_64 / UNITS_PER_USEC) % USEC_PER_SEC);
123 	return 0;
124 }
125 #endif
126 
127 #define MAX_SECONDS_IN_MSEC_LONG \
128 	(((LONG_MAX) - 999) / 1000)
129 
130 long
evutil_tv_to_msec_(const struct timeval * tv)131 evutil_tv_to_msec_(const struct timeval *tv)
132 {
133 	if (tv->tv_usec > 1000000 || tv->tv_sec > MAX_SECONDS_IN_MSEC_LONG)
134 		return -1;
135 
136 	return (tv->tv_sec * 1000) + ((tv->tv_usec + 999) / 1000);
137 }
138 
139 /*
140   Replacement for usleep on platforms that don't have one.  Not guaranteed to
141   be any more finegrained than 1 msec.
142  */
143 void
evutil_usleep_(const struct timeval * tv)144 evutil_usleep_(const struct timeval *tv)
145 {
146 	if (!tv)
147 		return;
148 #if defined(_WIN32)
149 	{
150 		__int64 usec;
151 		LARGE_INTEGER li;
152 		HANDLE timer;
153 
154 		usec = tv->tv_sec * 1000000LL + tv->tv_usec;
155 		if (!usec)
156 			return;
157 
158 		li.QuadPart = -10LL * usec;
159 		timer = CreateWaitableTimer(NULL, TRUE, NULL);
160 		if (!timer)
161 			return;
162 
163 		SetWaitableTimer(timer, &li, 0, NULL, NULL, 0);
164 		WaitForSingleObject(timer, INFINITE);
165 		CloseHandle(timer);
166 	}
167 #elif defined(EVENT__HAVE_NANOSLEEP)
168 	{
169 		struct timespec ts;
170 		ts.tv_sec = tv->tv_sec;
171 		ts.tv_nsec = tv->tv_usec*1000;
172 		nanosleep(&ts, NULL);
173 	}
174 #elif defined(EVENT__HAVE_USLEEP)
175 	/* Some systems don't like to usleep more than 999999 usec */
176 	sleep(tv->tv_sec);
177 	usleep(tv->tv_usec);
178 #else
179 	{
180 		struct timeval tv2 = *tv;
181 		select(0, NULL, NULL, NULL, &tv2);
182 	}
183 #endif
184 }
185 
186 int
evutil_date_rfc1123(char * date,const size_t datelen,const struct tm * tm)187 evutil_date_rfc1123(char *date, const size_t datelen, const struct tm *tm)
188 {
189 	static const char *DAYS[] =
190 		{ "Sun", "Mon", "Tue", "Wed", "Thu", "Fri", "Sat" };
191 	static const char *MONTHS[] =
192 		{ "Jan", "Feb", "Mar", "Apr", "May", "Jun", "Jul", "Aug", "Sep", "Oct", "Nov", "Dec" };
193 
194 	time_t t = time(NULL);
195 
196 #if defined(EVENT__HAVE__GMTIME64_S) || !defined(_WIN32)
197 	struct tm sys;
198 #endif
199 
200 	/* If `tm` is null, set system's current time. */
201 	if (tm == NULL) {
202 #if !defined(_WIN32)
203 		gmtime_r(&t, &sys);
204 		tm = &sys;
205 		/** detect _gmtime64()/_gmtime64_s() */
206 #elif defined(EVENT__HAVE__GMTIME64_S)
207 		errno_t err;
208 		err = _gmtime64_s(&sys, &t);
209 		if (err) {
210 			event_errx(1, "Invalid argument to _gmtime64_s");
211 		} else {
212 			tm = &sys;
213 		}
214 #elif defined(EVENT__HAVE__GMTIME64)
215 		tm = _gmtime64(&t);
216 #else
217 		tm = gmtime(&t);
218 #endif
219 	}
220 
221 	return evutil_snprintf(
222 		date, datelen, "%s, %02d %s %4d %02d:%02d:%02d GMT",
223 		DAYS[tm->tm_wday], tm->tm_mday, MONTHS[tm->tm_mon],
224 		1900 + tm->tm_year, tm->tm_hour, tm->tm_min, tm->tm_sec);
225 }
226 
227 /*
228    This function assumes it's called repeatedly with a
229    not-actually-so-monotonic time source whose outputs are in 'tv'. It
230    implements a trivial ratcheting mechanism so that the values never go
231    backwards.
232  */
233 static void
adjust_monotonic_time(struct evutil_monotonic_timer * base,struct timeval * tv)234 adjust_monotonic_time(struct evutil_monotonic_timer *base,
235     struct timeval *tv)
236 {
237 	evutil_timeradd(tv, &base->adjust_monotonic_clock, tv);
238 
239 	if (evutil_timercmp(tv, &base->last_time, <)) {
240 		/* Guess it wasn't monotonic after all. */
241 		struct timeval adjust;
242 		evutil_timersub(&base->last_time, tv, &adjust);
243 		evutil_timeradd(&adjust, &base->adjust_monotonic_clock,
244 		    &base->adjust_monotonic_clock);
245 		*tv = base->last_time;
246 	}
247 	base->last_time = *tv;
248 }
249 
250 /*
251    Allocate a new struct evutil_monotonic_timer
252  */
253 struct evutil_monotonic_timer *
evutil_monotonic_timer_new(void)254 evutil_monotonic_timer_new(void)
255 {
256   struct evutil_monotonic_timer *p = NULL;
257 
258   p = mm_malloc(sizeof(*p));
259   if (!p) goto done;
260 
261   memset(p, 0, sizeof(*p));
262 
263  done:
264   return p;
265 }
266 
267 /*
268    Free a struct evutil_monotonic_timer
269  */
270 void
evutil_monotonic_timer_free(struct evutil_monotonic_timer * timer)271 evutil_monotonic_timer_free(struct evutil_monotonic_timer *timer)
272 {
273   if (timer) {
274     mm_free(timer);
275   }
276 }
277 
278 /*
279    Set up a struct evutil_monotonic_timer for initial use
280  */
281 int
evutil_configure_monotonic_time(struct evutil_monotonic_timer * timer,int flags)282 evutil_configure_monotonic_time(struct evutil_monotonic_timer *timer,
283                                 int flags)
284 {
285   return evutil_configure_monotonic_time_(timer, flags);
286 }
287 
288 /*
289    Query the current monotonic time
290  */
291 int
evutil_gettime_monotonic(struct evutil_monotonic_timer * timer,struct timeval * tp)292 evutil_gettime_monotonic(struct evutil_monotonic_timer *timer,
293                          struct timeval *tp)
294 {
295   return evutil_gettime_monotonic_(timer, tp);
296 }
297 
298 
299 #if defined(HAVE_POSIX_MONOTONIC)
300 /* =====
301    The POSIX clock_gettime() interface provides a few ways to get at a
302    monotonic clock.  CLOCK_MONOTONIC is most widely supported.  Linux also
303    provides a CLOCK_MONOTONIC_COARSE with accuracy of about 1-4 msec.
304 
305    On all platforms I'm aware of, CLOCK_MONOTONIC really is monotonic.
306    Platforms don't agree about whether it should jump on a sleep/resume.
307  */
308 
309 int
evutil_configure_monotonic_time_(struct evutil_monotonic_timer * base,int flags)310 evutil_configure_monotonic_time_(struct evutil_monotonic_timer *base,
311     int flags)
312 {
313 	/* CLOCK_MONOTONIC exists on FreeBSD, Linux, and Solaris.  You need to
314 	 * check for it at runtime, because some older kernel versions won't
315 	 * have it working. */
316 #ifdef CLOCK_MONOTONIC_COARSE
317 	const int precise = flags & EV_MONOT_PRECISE;
318 #endif
319 	const int fallback = flags & EV_MONOT_FALLBACK;
320 	struct timespec	ts;
321 
322 #ifdef CLOCK_MONOTONIC_COARSE
323 	if (CLOCK_MONOTONIC_COARSE < 0) {
324 		/* Technically speaking, nothing keeps CLOCK_* from being
325 		 * negative (as far as I know). This check and the one below
326 		 * make sure that it's safe for us to use -1 as an "unset"
327 		 * value. */
328 		event_errx(1,"I didn't expect CLOCK_MONOTONIC_COARSE to be < 0");
329 	}
330 	if (! precise && ! fallback) {
331 		if (clock_gettime(CLOCK_MONOTONIC_COARSE, &ts) == 0) {
332 			base->monotonic_clock = CLOCK_MONOTONIC_COARSE;
333 			return 0;
334 		}
335 	}
336 #endif
337 	if (!fallback && clock_gettime(CLOCK_MONOTONIC, &ts) == 0) {
338 		base->monotonic_clock = CLOCK_MONOTONIC;
339 		return 0;
340 	}
341 
342 	if (CLOCK_MONOTONIC < 0) {
343 		event_errx(1,"I didn't expect CLOCK_MONOTONIC to be < 0");
344 	}
345 
346 	base->monotonic_clock = -1;
347 	return 0;
348 }
349 
350 int
evutil_gettime_monotonic_(struct evutil_monotonic_timer * base,struct timeval * tp)351 evutil_gettime_monotonic_(struct evutil_monotonic_timer *base,
352     struct timeval *tp)
353 {
354 	struct timespec ts;
355 
356 	if (base->monotonic_clock < 0) {
357 		if (evutil_gettimeofday(tp, NULL) < 0)
358 			return -1;
359 		adjust_monotonic_time(base, tp);
360 		return 0;
361 	}
362 
363 	if (clock_gettime(base->monotonic_clock, &ts) == -1)
364 		return -1;
365 	tp->tv_sec = ts.tv_sec;
366 	tp->tv_usec = ts.tv_nsec / 1000;
367 
368 	return 0;
369 }
370 #endif
371 
372 #if defined(HAVE_MACH_MONOTONIC)
373 /* ======
374    Apple is a little late to the POSIX party.  And why not?  Instead of
375    clock_gettime(), they provide mach_absolute_time().  Its units are not
376    fixed; we need to use mach_timebase_info() to get the right functions to
377    convert its units into nanoseconds.
378 
379    To all appearances, mach_absolute_time() seems to be honest-to-goodness
380    monotonic.  Whether it stops during sleep or not is unspecified in
381    principle, and dependent on CPU architecture in practice.
382  */
383 
384 int
evutil_configure_monotonic_time_(struct evutil_monotonic_timer * base,int flags)385 evutil_configure_monotonic_time_(struct evutil_monotonic_timer *base,
386     int flags)
387 {
388 	const int fallback = flags & EV_MONOT_FALLBACK;
389 	struct mach_timebase_info mi;
390 	memset(base, 0, sizeof(*base));
391 	/* OSX has mach_absolute_time() */
392 	if (!fallback &&
393 	    mach_timebase_info(&mi) == 0 &&
394 	    mach_absolute_time() != 0) {
395 		/* mach_timebase_info tells us how to convert
396 		 * mach_absolute_time() into nanoseconds, but we
397 		 * want to use microseconds instead. */
398 		mi.denom *= 1000;
399 		memcpy(&base->mach_timebase_units, &mi, sizeof(mi));
400 	} else {
401 		base->mach_timebase_units.numer = 0;
402 	}
403 	return 0;
404 }
405 
406 int
evutil_gettime_monotonic_(struct evutil_monotonic_timer * base,struct timeval * tp)407 evutil_gettime_monotonic_(struct evutil_monotonic_timer *base,
408     struct timeval *tp)
409 {
410 	ev_uint64_t abstime, usec;
411 	if (base->mach_timebase_units.numer == 0) {
412 		if (evutil_gettimeofday(tp, NULL) < 0)
413 			return -1;
414 		adjust_monotonic_time(base, tp);
415 		return 0;
416 	}
417 
418 	abstime = mach_absolute_time();
419 	usec = (abstime * base->mach_timebase_units.numer)
420 	    / (base->mach_timebase_units.denom);
421 	tp->tv_sec = usec / 1000000;
422 	tp->tv_usec = usec % 1000000;
423 
424 	return 0;
425 }
426 #endif
427 
428 #if defined(HAVE_WIN32_MONOTONIC)
429 /* =====
430    Turn we now to Windows.  Want monontonic time on Windows?
431 
432    Windows has QueryPerformanceCounter(), which gives time most high-
433    resolution time.  It's a pity it's not so monotonic in practice; it's
434    also got some fun bugs, especially: with older Windowses, under
435    virtualizations, with funny hardware, on multiprocessor systems, and so
436    on.  PEP418 [1] has a nice roundup of the issues here.
437 
438    There's GetTickCount64() on Vista and later, which gives a number of 1-msec
439    ticks since startup.  The accuracy here might be as bad as 10-20 msec, I
440    hear.  There's an undocumented function (NtSetTimerResolution) that
441    allegedly increases the accuracy. Good luck!
442 
443    There's also GetTickCount(), which is only 32 bits, but seems to be
444    supported on pre-Vista versions of Windows.  Apparently, you can coax
445    another 14 bits out of it, giving you 2231 years before rollover.
446 
447    The less said about timeGetTime() the better.
448 
449    "We don't care.  We don't have to.  We're the Phone Company."
450             -- Lily Tomlin, SNL
451 
452    Our strategy, if precise timers are turned off, is to just use the best
453    GetTickCount equivalent available.  If we've been asked for precise timing,
454    then we mostly[2] assume that GetTickCount is monotonic, and correct
455    GetPerformanceCounter to approximate it.
456 
457    [1] http://www.python.org/dev/peps/pep-0418
458    [2] Of course, we feed the Windows stuff into adjust_monotonic_time()
459        anyway, just in case it isn't.
460 
461  */
462 /*
463     Parts of our logic in the win32 timer code here are closely based on
464     BitTorrent's libUTP library.  That code is subject to the following
465     license:
466 
467       Copyright (c) 2010 BitTorrent, Inc.
468 
469       Permission is hereby granted, free of charge, to any person obtaining a
470       copy of this software and associated documentation files (the
471       "Software"), to deal in the Software without restriction, including
472       without limitation the rights to use, copy, modify, merge, publish,
473       distribute, sublicense, and/or sell copies of the Software, and to
474       permit persons to whom the Software is furnished to do so, subject to
475       the following conditions:
476 
477       The above copyright notice and this permission notice shall be included
478       in all copies or substantial portions of the Software.
479 
480       THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
481       OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
482       MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
483       NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
484       LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
485       OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
486       WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
487 */
488 
489 static ev_uint64_t
evutil_GetTickCount_(struct evutil_monotonic_timer * base)490 evutil_GetTickCount_(struct evutil_monotonic_timer *base)
491 {
492 	if (base->GetTickCount64_fn) {
493 		/* Let's just use GetTickCount64 if we can. */
494 		return base->GetTickCount64_fn();
495 	} else if (base->GetTickCount_fn) {
496 		/* Greg Hazel assures me that this works, that BitTorrent has
497 		 * done it for years, and this it won't turn around and
498 		 * bite us.  He says they found it on some game programmers'
499 		 * forum some time around 2007.
500 		 */
501 		ev_uint64_t v = base->GetTickCount_fn();
502 		return (DWORD)v | ((v >> 18) & 0xFFFFFFFF00000000);
503 	} else {
504 		/* Here's the fallback implementation. We have to use
505 		 * GetTickCount() with its given signature, so we only get
506 		 * 32 bits worth of milliseconds, which will roll ove every
507 		 * 49 days or so.  */
508 		DWORD ticks = GetTickCount();
509 		if (ticks < base->last_tick_count) {
510 			base->adjust_tick_count += ((ev_uint64_t)1) << 32;
511 		}
512 		base->last_tick_count = ticks;
513 		return ticks + base->adjust_tick_count;
514 	}
515 }
516 
517 int
evutil_configure_monotonic_time_(struct evutil_monotonic_timer * base,int flags)518 evutil_configure_monotonic_time_(struct evutil_monotonic_timer *base,
519     int flags)
520 {
521 	const int precise = flags & EV_MONOT_PRECISE;
522 	const int fallback = flags & EV_MONOT_FALLBACK;
523 	HANDLE h;
524 	memset(base, 0, sizeof(*base));
525 
526 	h = evutil_load_windows_system_library_(TEXT("kernel32.dll"));
527 	if (h != NULL && !fallback) {
528 		base->GetTickCount64_fn = (ev_GetTickCount_func)GetProcAddress(h, "GetTickCount64");
529 		base->GetTickCount_fn = (ev_GetTickCount_func)GetProcAddress(h, "GetTickCount");
530 	}
531 
532 	base->first_tick = base->last_tick_count = evutil_GetTickCount_(base);
533 	if (precise && !fallback) {
534 		LARGE_INTEGER freq;
535 		if (QueryPerformanceFrequency(&freq)) {
536 			LARGE_INTEGER counter;
537 			QueryPerformanceCounter(&counter);
538 			base->first_counter = counter.QuadPart;
539 			base->usec_per_count = 1.0e6 / freq.QuadPart;
540 			base->use_performance_counter = 1;
541 		}
542 	}
543 
544 	return 0;
545 }
546 
547 static inline ev_int64_t
abs64(ev_int64_t i)548 abs64(ev_int64_t i)
549 {
550 	return i < 0 ? -i : i;
551 }
552 
553 
554 int
evutil_gettime_monotonic_(struct evutil_monotonic_timer * base,struct timeval * tp)555 evutil_gettime_monotonic_(struct evutil_monotonic_timer *base,
556     struct timeval *tp)
557 {
558 	ev_uint64_t ticks = evutil_GetTickCount_(base);
559 	if (base->use_performance_counter) {
560 		/* Here's a trick we took from BitTorrent's libutp, at Greg
561 		 * Hazel's recommendation.  We use QueryPerformanceCounter for
562 		 * our high-resolution timer, but use GetTickCount*() to keep
563 		 * it sane, and adjust_monotonic_time() to keep it monotonic.
564 		 */
565 		LARGE_INTEGER counter;
566 		ev_int64_t counter_elapsed, counter_usec_elapsed, ticks_elapsed;
567 		QueryPerformanceCounter(&counter);
568 		counter_elapsed = (ev_int64_t)
569 		    (counter.QuadPart - base->first_counter);
570 		ticks_elapsed = ticks - base->first_tick;
571 		/* TODO: This may upset VC6. If you need this to work with
572 		 * VC6, please supply an appropriate patch. */
573 		counter_usec_elapsed = (ev_int64_t)
574 		    (counter_elapsed * base->usec_per_count);
575 
576 		if (abs64(ticks_elapsed*1000 - counter_usec_elapsed) > 1000000) {
577 			/* It appears that the QueryPerformanceCounter()
578 			 * result is more than 1 second away from
579 			 * GetTickCount() result. Let's adjust it to be as
580 			 * accurate as we can; adjust_monotnonic_time() below
581 			 * will keep it monotonic. */
582 			counter_usec_elapsed = ticks_elapsed * 1000;
583 			base->first_counter = (ev_uint64_t) (counter.QuadPart - counter_usec_elapsed / base->usec_per_count);
584 		}
585 		tp->tv_sec = (time_t) (counter_usec_elapsed / 1000000);
586 		tp->tv_usec = counter_usec_elapsed % 1000000;
587 
588 	} else {
589 		/* We're just using GetTickCount(). */
590 		tp->tv_sec = (time_t) (ticks / 1000);
591 		tp->tv_usec = (ticks % 1000) * 1000;
592 	}
593 	adjust_monotonic_time(base, tp);
594 
595 	return 0;
596 }
597 #endif
598 
599 #if defined(HAVE_FALLBACK_MONOTONIC)
600 /* =====
601    And if none of the other options work, let's just use gettimeofday(), and
602    ratchet it forward so that it acts like a monotonic timer, whether it
603    wants to or not.
604  */
605 
606 int
evutil_configure_monotonic_time_(struct evutil_monotonic_timer * base,int precise)607 evutil_configure_monotonic_time_(struct evutil_monotonic_timer *base,
608     int precise)
609 {
610 	memset(base, 0, sizeof(*base));
611 	return 0;
612 }
613 
614 int
evutil_gettime_monotonic_(struct evutil_monotonic_timer * base,struct timeval * tp)615 evutil_gettime_monotonic_(struct evutil_monotonic_timer *base,
616     struct timeval *tp)
617 {
618 	if (evutil_gettimeofday(tp, NULL) < 0)
619 		return -1;
620 	adjust_monotonic_time(base, tp);
621 	return 0;
622 
623 }
624 #endif
625