1 /* Portable timers.
2 Copyright (C) 2005-2011, 2015, 2018-2021 Free Software Foundation,
3 Inc.
4
5 This file is part of GNU Wget.
6
7 GNU Wget is free software; you can redistribute it and/or modify
8 it under the terms of the GNU General Public License as published by
9 the Free Software Foundation; either version 3 of the License, or
10 (at your option) any later version.
11
12 GNU Wget is distributed in the hope that it will be useful,
13 but WITHOUT ANY WARRANTY; without even the implied warranty of
14 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
15 GNU General Public License for more details.
16
17 You should have received a copy of the GNU General Public License
18 along with Wget. If not, see <http://www.gnu.org/licenses/>.
19
20 Additional permission under GNU GPL version 3 section 7
21
22 If you modify this program, or any covered work, by linking or
23 combining it with the OpenSSL project's OpenSSL library (or a
24 modified version of that library), containing parts covered by the
25 terms of the OpenSSL or SSLeay licenses, the Free Software Foundation
26 grants you additional permission to convey the resulting work.
27 Corresponding Source for a non-source form of such a combination
28 shall include the source code for the parts of OpenSSL used as well
29 as that of the covered work. */
30
31 /* This file implements "portable timers" (ptimers), objects that
32 measure elapsed time using the primitives most appropriate for the
33 underlying operating system. The entry points are:
34
35 ptimer_new -- creates a timer.
36 ptimer_reset -- resets the timer's elapsed time to zero.
37 ptimer_measure -- measure and return the time elapsed since
38 creation or last reset.
39 ptimer_read -- reads the last measured elapsed value.
40 ptimer_destroy -- destroy the timer.
41 ptimer_granularity -- returns the approximate granularity of the timers.
42
43 Timers measure time in seconds, returning the timings as floating
44 point numbers, so they can carry as much precision as the
45 underlying system timer supports. For example, to measure the time
46 it takes to run a loop, you can use something like:
47
48 ptimer *tmr = ptimer_new ();
49 while (...)
50 ... loop ...
51 double secs = ptimer_measure ();
52 printf ("The loop took %.2fs\n", secs); */
53
54 #include "wget.h"
55
56 #include <stdio.h>
57 #include <stdlib.h>
58 #include <string.h>
59 #include <errno.h>
60 #include <unistd.h>
61 #include <time.h>
62 #include <sys/time.h>
63
64 /* Cygwin currently (as of 2005-04-08, Cygwin 1.5.14) lacks clock_getres,
65 but still defines _POSIX_TIMERS! Because of that we simply use the
66 Windows timers under Cygwin. */
67 #ifdef __CYGWIN__
68 # include <windows.h>
69 #endif
70
71 #include "utils.h"
72 #include "ptimer.h"
73
74 /* Depending on the OS, one and only one of PTIMER_POSIX,
75 PTIMER_GETTIMEOFDAY, or PTIMER_WINDOWS will be defined. */
76
77 #undef PTIMER_POSIX
78 #undef PTIMER_GETTIMEOFDAY
79 #undef PTIMER_WINDOWS
80
81 #if defined(WINDOWS) || defined(__CYGWIN__)
82 # define PTIMER_WINDOWS /* use Windows timers */
83 #elif _POSIX_TIMERS - 0 > 0
84 # define PTIMER_POSIX /* use POSIX timers (clock_gettime) */
85 #else
86 # define PTIMER_GETTIMEOFDAY /* use gettimeofday */
87 #endif
88
89 #ifdef PTIMER_POSIX
90 /* Elapsed time measurement using POSIX timers: system time is held in
91 struct timespec, time is retrieved using clock_gettime, and
92 resolution using clock_getres.
93
94 This method is used on Unix systems that implement POSIX
95 timers. */
96
97 typedef struct timespec ptimer_system_time;
98
99 #define IMPL_init posix_init
100 #define IMPL_measure posix_measure
101 #define IMPL_diff posix_diff
102 #define IMPL_resolution posix_resolution
103
104 /* clock_id to use for POSIX clocks. This tries to use
105 CLOCK_MONOTONIC where available, CLOCK_REALTIME otherwise. */
106 static int posix_clock_id;
107
108 /* Resolution of the clock, initialized in posix_init. */
109 static double posix_clock_resolution;
110
111 /* Decide which clock_id to use. */
112
113 static void
posix_init(void)114 posix_init (void)
115 {
116 /* List of clocks we want to support: some systems support monotonic
117 clocks, Solaris has "high resolution" clock (sometimes
118 unavailable except to superuser), and all should support the
119 real-time clock. */
120 #define NO_SYSCONF_CHECK -1
121 static const struct {
122 int id;
123 int sysconf_name;
124 } clocks[] = {
125 #if defined(_POSIX_MONOTONIC_CLOCK) && _POSIX_MONOTONIC_CLOCK - 0 >= 0
126 { CLOCK_MONOTONIC, _SC_MONOTONIC_CLOCK },
127 #endif
128 #ifdef CLOCK_HIGHRES
129 { CLOCK_HIGHRES, NO_SYSCONF_CHECK },
130 #endif
131 { CLOCK_REALTIME, NO_SYSCONF_CHECK },
132 };
133 size_t i;
134
135 /* Determine the clock we can use. For a clock to be usable, it
136 must be confirmed with sysconf (where applicable) and with
137 clock_getres. If no clock is found, CLOCK_REALTIME is used. */
138
139 for (i = 0; i < countof (clocks); i++)
140 {
141 struct timespec r;
142 if (clocks[i].sysconf_name != NO_SYSCONF_CHECK)
143 if (sysconf (clocks[i].sysconf_name) < 0)
144 continue; /* sysconf claims this clock is unavailable */
145 if (clock_getres (clocks[i].id, &r) < 0)
146 continue; /* clock_getres doesn't work for this clock */
147 posix_clock_id = clocks[i].id;
148 posix_clock_resolution = (double) r.tv_sec + r.tv_nsec / 1e9;
149 /* Guard against nonsense returned by a broken clock_getres. */
150 if (posix_clock_resolution == 0)
151 posix_clock_resolution = 1e-3;
152 break;
153 }
154 if (i == countof (clocks))
155 {
156 /* If no clock was found, it means that clock_getres failed for
157 the realtime clock. */
158 logprintf (LOG_NOTQUIET, _("Cannot get REALTIME clock frequency: %s\n"),
159 strerror (errno));
160 /* Use CLOCK_REALTIME, but invent a plausible resolution. */
161 posix_clock_id = CLOCK_REALTIME;
162 posix_clock_resolution = 1e-3;
163 }
164 }
165
166 static inline void
posix_measure(ptimer_system_time * pst)167 posix_measure (ptimer_system_time *pst)
168 {
169 clock_gettime (posix_clock_id, pst);
170 }
171
172 static inline double
posix_diff(ptimer_system_time * pst1,ptimer_system_time * pst2)173 posix_diff (ptimer_system_time *pst1, ptimer_system_time *pst2)
174 {
175 return ((pst1->tv_sec - pst2->tv_sec)
176 + (pst1->tv_nsec - pst2->tv_nsec) / 1e9);
177 }
178
179 static inline double
posix_resolution(void)180 posix_resolution (void)
181 {
182 return posix_clock_resolution;
183 }
184 #endif /* PTIMER_POSIX */
185
186 #ifdef PTIMER_GETTIMEOFDAY
187 /* Elapsed time measurement using gettimeofday: system time is held in
188 struct timeval, retrieved using gettimeofday, and resolution is
189 unknown.
190
191 This method is used Unix systems without POSIX timers. */
192
193 typedef struct timeval ptimer_system_time;
194
195 #define IMPL_measure gettimeofday_measure
196 #define IMPL_diff gettimeofday_diff
197 #define IMPL_resolution gettimeofday_resolution
198
199 static inline void
gettimeofday_measure(ptimer_system_time * pst)200 gettimeofday_measure (ptimer_system_time *pst)
201 {
202 gettimeofday (pst, NULL);
203 }
204
205 static inline double
gettimeofday_diff(ptimer_system_time * pst1,ptimer_system_time * pst2)206 gettimeofday_diff (ptimer_system_time *pst1, ptimer_system_time *pst2)
207 {
208 return ((pst1->tv_sec - pst2->tv_sec)
209 + (pst1->tv_usec - pst2->tv_usec) / 1e6);
210 }
211
212 static inline double
gettimeofday_resolution(void)213 gettimeofday_resolution (void)
214 {
215 /* Granularity of gettimeofday varies wildly between architectures.
216 However, it appears that on modern machines it tends to be better
217 than 1ms. Assume 100 usecs. */
218 return 0.1;
219 }
220 #endif /* PTIMER_GETTIMEOFDAY */
221
222 #ifdef PTIMER_WINDOWS
223 /* Elapsed time measurement on Windows: where high-resolution timers
224 are available, time is stored in a LARGE_INTEGER and retrieved
225 using QueryPerformanceCounter. Otherwise, it is stored in a DWORD
226 and retrieved using GetTickCount.
227
228 This method is used on Windows. */
229
230 typedef union {
231 DWORD lores; /* In case GetTickCount is used */
232 LARGE_INTEGER hires; /* In case high-resolution timer is used */
233 } ptimer_system_time;
234
235 #define IMPL_init windows_init
236 #define IMPL_measure windows_measure
237 #define IMPL_diff windows_diff
238 #define IMPL_resolution windows_resolution
239
240 /* Whether high-resolution timers are used. Set by ptimer_initialize_once
241 the first time ptimer_new is called. */
242 static bool windows_hires_timers;
243
244 /* Frequency of high-resolution timers -- number of updates per
245 second. Calculated the first time ptimer_new is called provided
246 that high-resolution timers are available. */
247 static double windows_hires_freq;
248
249 static void
windows_init(void)250 windows_init (void)
251 {
252 LARGE_INTEGER freq;
253 freq.QuadPart = 0;
254 QueryPerformanceFrequency (&freq);
255 if (freq.QuadPart != 0)
256 {
257 windows_hires_timers = true;
258 windows_hires_freq = (double) freq.QuadPart;
259 }
260 }
261
262 static inline void
windows_measure(ptimer_system_time * pst)263 windows_measure (ptimer_system_time *pst)
264 {
265 if (windows_hires_timers)
266 QueryPerformanceCounter (&pst->hires);
267 else
268 /* Where hires counters are not available, use GetTickCount rather
269 GetSystemTime, because it is unaffected by clock skew and
270 simpler to use. Note that overflows don't affect us because we
271 never use absolute values of the ticker, only the
272 differences. */
273 pst->lores = GetTickCount ();
274 }
275
276 static inline double
windows_diff(ptimer_system_time * pst1,ptimer_system_time * pst2)277 windows_diff (ptimer_system_time *pst1, ptimer_system_time *pst2)
278 {
279 if (windows_hires_timers)
280 return (pst1->hires.QuadPart - pst2->hires.QuadPart) / windows_hires_freq;
281 else
282 return pst1->lores - pst2->lores;
283 }
284
285 static double
windows_resolution(void)286 windows_resolution (void)
287 {
288 if (windows_hires_timers)
289 return 1.0 / windows_hires_freq;
290 else
291 return 10; /* according to MSDN */
292 }
293 #endif /* PTIMER_WINDOWS */
294
295 /* The code below this point is independent of timer implementation. */
296
297 struct ptimer {
298 /* The starting point in time which, subtracted from the current
299 time, yields elapsed time. */
300 ptimer_system_time start;
301
302 /* The most recent elapsed time, calculated by ptimer_measure(). */
303 double elapsed_last;
304
305 /* Approximately, the time elapsed between the true start of the
306 measurement and the time represented by START. This is used for
307 adjustment when clock skew is detected. */
308 double elapsed_pre_start;
309 };
310
311 /* Allocate a new timer and reset it. Return the new timer. */
312
313 struct ptimer *
ptimer_new(void)314 ptimer_new (void)
315 {
316 struct ptimer *pt = xnew0 (struct ptimer);
317 #ifdef IMPL_init
318 static bool init_done;
319 if (!init_done)
320 {
321 init_done = true;
322 IMPL_init ();
323 }
324 #endif
325 ptimer_reset (pt);
326 return pt;
327 }
328
329 /* Free the resources associated with the timer. Its further use is
330 prohibited. */
331
332 void
ptimer_destroy(struct ptimer * pt)333 ptimer_destroy (struct ptimer *pt)
334 {
335 xfree (pt);
336 }
337
338 /* Reset timer PT. This establishes the starting point from which
339 ptimer_measure() will return the elapsed time in seconds. It is
340 allowed to reset a previously used timer. */
341
342 void
ptimer_reset(struct ptimer * pt)343 ptimer_reset (struct ptimer *pt)
344 {
345 /* Set the start time to the current time. */
346 IMPL_measure (&pt->start);
347 pt->elapsed_last = 0;
348 pt->elapsed_pre_start = 0;
349 }
350
351 /* Measure the elapsed time since timer creation/reset. This causes
352 the timer to internally call clock_gettime (or gettimeofday, etc.)
353 to update its idea of current time. The time is returned, but is
354 also stored for later access through ptimer_read().
355
356 This function handles clock skew, i.e. time that moves backwards is
357 ignored. */
358
359 double
ptimer_measure(struct ptimer * pt)360 ptimer_measure (struct ptimer *pt)
361 {
362 ptimer_system_time now;
363 double elapsed;
364
365 IMPL_measure (&now);
366 elapsed = pt->elapsed_pre_start + IMPL_diff (&now, &pt->start);
367
368 /* Ideally we'd just return the difference between NOW and
369 pt->start. However, the system timer can be set back, and we
370 could return a value smaller than when we were last called, even
371 a negative value. Both of these would confuse the callers, which
372 expect us to return monotonically nondecreasing values.
373
374 Therefore: if ELAPSED is smaller than its previous known value,
375 we reset pt->start to the current time and effectively start
376 measuring from this point. But since we don't want the elapsed
377 value to start from zero, we set elapsed_pre_start to the last
378 elapsed time and increment all future calculations by that
379 amount.
380
381 This cannot happen with Windows and POSIX monotonic/highres
382 timers, but the check is not expensive. */
383
384 if (elapsed < pt->elapsed_last)
385 {
386 pt->start = now;
387 pt->elapsed_pre_start = pt->elapsed_last;
388 elapsed = pt->elapsed_last;
389 }
390
391 pt->elapsed_last = elapsed;
392 return elapsed;
393 }
394
395 /* Return the most recent elapsed time measured with ptimer_measure.
396 If ptimer_measure has not yet been called since the timer was
397 created or reset, this returns 0. */
398
399 double
ptimer_read(const struct ptimer * pt)400 ptimer_read (const struct ptimer *pt)
401 {
402 return pt->elapsed_last;
403 }
404
405 /* Return the assessed resolution of the timer implementation, in
406 seconds. This is used by code that tries to substitute a better
407 value for timers that have returned zero. */
408
409 double
ptimer_resolution(void)410 ptimer_resolution (void)
411 {
412 return IMPL_resolution ();
413 }
414