1 // Copyright 2013 the V8 project authors. All rights reserved.
2 // Use of this source code is governed by a BSD-style license that can be
3 // found in the LICENSE file.
4
5 #include "src/base/platform/time.h"
6
7 #if V8_OS_POSIX
8 #include <fcntl.h> // for O_RDONLY
9 #include <sys/time.h>
10 #include <unistd.h>
11 #endif
12 #if V8_OS_MACOSX
13 #include <mach/mach.h>
14 #include <mach/mach_time.h>
15 #include <pthread.h>
16 #endif
17
18 #include <cstring>
19 #include <ostream>
20
21 #if V8_OS_WIN
22 #include "src/base/atomicops.h"
23 #include "src/base/lazy-instance.h"
24 #include "src/base/win32-headers.h"
25 #endif
26 #include "src/base/cpu.h"
27 #include "src/base/logging.h"
28 #include "src/base/platform/platform.h"
29
30 namespace {
31
32 #if V8_OS_MACOSX
ComputeThreadTicks()33 int64_t ComputeThreadTicks() {
34 mach_msg_type_number_t thread_info_count = THREAD_BASIC_INFO_COUNT;
35 thread_basic_info_data_t thread_info_data;
36 kern_return_t kr = thread_info(
37 pthread_mach_thread_np(pthread_self()),
38 THREAD_BASIC_INFO,
39 reinterpret_cast<thread_info_t>(&thread_info_data),
40 &thread_info_count);
41 CHECK_EQ(kr, KERN_SUCCESS);
42
43 v8::base::CheckedNumeric<int64_t> absolute_micros(
44 thread_info_data.user_time.seconds +
45 thread_info_data.system_time.seconds);
46 absolute_micros *= v8::base::Time::kMicrosecondsPerSecond;
47 absolute_micros += (thread_info_data.user_time.microseconds +
48 thread_info_data.system_time.microseconds);
49 return absolute_micros.ValueOrDie();
50 }
51 #elif V8_OS_POSIX
52 // Helper function to get results from clock_gettime() and convert to a
53 // microsecond timebase. Minimum requirement is MONOTONIC_CLOCK to be supported
54 // on the system. FreeBSD 6 has CLOCK_MONOTONIC but defines
55 // _POSIX_MONOTONIC_CLOCK to -1.
56 V8_INLINE int64_t ClockNow(clockid_t clk_id) {
57 #if (defined(_POSIX_MONOTONIC_CLOCK) && _POSIX_MONOTONIC_CLOCK >= 0) || \
58 defined(V8_OS_BSD) || defined(V8_OS_ANDROID)
59 // On AIX clock_gettime for CLOCK_THREAD_CPUTIME_ID outputs time with
60 // resolution of 10ms. thread_cputime API provides the time in ns
61 #if defined(V8_OS_AIX)
62 thread_cputime_t tc;
63 if (clk_id == CLOCK_THREAD_CPUTIME_ID) {
64 if (thread_cputime(-1, &tc) != 0) {
65 UNREACHABLE();
66 }
67 }
68 #endif
69 struct timespec ts;
70 if (clock_gettime(clk_id, &ts) != 0) {
71 UNREACHABLE();
72 }
73 v8::base::internal::CheckedNumeric<int64_t> result(ts.tv_sec);
74 result *= v8::base::Time::kMicrosecondsPerSecond;
75 #if defined(V8_OS_AIX)
76 if (clk_id == CLOCK_THREAD_CPUTIME_ID) {
77 result += (tc.stime / v8::base::Time::kNanosecondsPerMicrosecond);
78 } else {
79 result += (ts.tv_nsec / v8::base::Time::kNanosecondsPerMicrosecond);
80 }
81 #else
82 result += (ts.tv_nsec / v8::base::Time::kNanosecondsPerMicrosecond);
83 #endif
84 return result.ValueOrDie();
85 #else // Monotonic clock not supported.
86 return 0;
87 #endif
88 }
89 #elif V8_OS_WIN
90 V8_INLINE bool IsQPCReliable() {
91 v8::base::CPU cpu;
92 // On Athlon X2 CPUs (e.g. model 15) QueryPerformanceCounter is unreliable.
93 return strcmp(cpu.vendor(), "AuthenticAMD") == 0 && cpu.family() == 15;
94 }
95
96 // Returns the current value of the performance counter.
97 V8_INLINE uint64_t QPCNowRaw() {
98 LARGE_INTEGER perf_counter_now = {};
99 // According to the MSDN documentation for QueryPerformanceCounter(), this
100 // will never fail on systems that run XP or later.
101 // https://msdn.microsoft.com/library/windows/desktop/ms644904.aspx
102 BOOL result = ::QueryPerformanceCounter(&perf_counter_now);
103 DCHECK(result);
104 USE(result);
105 return perf_counter_now.QuadPart;
106 }
107 #endif // V8_OS_MACOSX
108
109
110 } // namespace
111
112 namespace v8 {
113 namespace base {
114
FromDays(int days)115 TimeDelta TimeDelta::FromDays(int days) {
116 return TimeDelta(days * Time::kMicrosecondsPerDay);
117 }
118
119
FromHours(int hours)120 TimeDelta TimeDelta::FromHours(int hours) {
121 return TimeDelta(hours * Time::kMicrosecondsPerHour);
122 }
123
124
FromMinutes(int minutes)125 TimeDelta TimeDelta::FromMinutes(int minutes) {
126 return TimeDelta(minutes * Time::kMicrosecondsPerMinute);
127 }
128
129
FromSeconds(int64_t seconds)130 TimeDelta TimeDelta::FromSeconds(int64_t seconds) {
131 return TimeDelta(seconds * Time::kMicrosecondsPerSecond);
132 }
133
134
FromMilliseconds(int64_t milliseconds)135 TimeDelta TimeDelta::FromMilliseconds(int64_t milliseconds) {
136 return TimeDelta(milliseconds * Time::kMicrosecondsPerMillisecond);
137 }
138
139
FromNanoseconds(int64_t nanoseconds)140 TimeDelta TimeDelta::FromNanoseconds(int64_t nanoseconds) {
141 return TimeDelta(nanoseconds / Time::kNanosecondsPerMicrosecond);
142 }
143
144
InDays() const145 int TimeDelta::InDays() const {
146 if (IsMax()) {
147 // Preserve max to prevent overflow.
148 return std::numeric_limits<int>::max();
149 }
150 return static_cast<int>(delta_ / Time::kMicrosecondsPerDay);
151 }
152
InHours() const153 int TimeDelta::InHours() const {
154 if (IsMax()) {
155 // Preserve max to prevent overflow.
156 return std::numeric_limits<int>::max();
157 }
158 return static_cast<int>(delta_ / Time::kMicrosecondsPerHour);
159 }
160
InMinutes() const161 int TimeDelta::InMinutes() const {
162 if (IsMax()) {
163 // Preserve max to prevent overflow.
164 return std::numeric_limits<int>::max();
165 }
166 return static_cast<int>(delta_ / Time::kMicrosecondsPerMinute);
167 }
168
InSecondsF() const169 double TimeDelta::InSecondsF() const {
170 if (IsMax()) {
171 // Preserve max to prevent overflow.
172 return std::numeric_limits<double>::infinity();
173 }
174 return static_cast<double>(delta_) / Time::kMicrosecondsPerSecond;
175 }
176
InSeconds() const177 int64_t TimeDelta::InSeconds() const {
178 if (IsMax()) {
179 // Preserve max to prevent overflow.
180 return std::numeric_limits<int64_t>::max();
181 }
182 return delta_ / Time::kMicrosecondsPerSecond;
183 }
184
InMillisecondsF() const185 double TimeDelta::InMillisecondsF() const {
186 if (IsMax()) {
187 // Preserve max to prevent overflow.
188 return std::numeric_limits<double>::infinity();
189 }
190 return static_cast<double>(delta_) / Time::kMicrosecondsPerMillisecond;
191 }
192
InMilliseconds() const193 int64_t TimeDelta::InMilliseconds() const {
194 if (IsMax()) {
195 // Preserve max to prevent overflow.
196 return std::numeric_limits<int64_t>::max();
197 }
198 return delta_ / Time::kMicrosecondsPerMillisecond;
199 }
200
InMillisecondsRoundedUp() const201 int64_t TimeDelta::InMillisecondsRoundedUp() const {
202 if (IsMax()) {
203 // Preserve max to prevent overflow.
204 return std::numeric_limits<int64_t>::max();
205 }
206 return (delta_ + Time::kMicrosecondsPerMillisecond - 1) /
207 Time::kMicrosecondsPerMillisecond;
208 }
209
InMicroseconds() const210 int64_t TimeDelta::InMicroseconds() const {
211 if (IsMax()) {
212 // Preserve max to prevent overflow.
213 return std::numeric_limits<int64_t>::max();
214 }
215 return delta_;
216 }
217
InNanoseconds() const218 int64_t TimeDelta::InNanoseconds() const {
219 if (IsMax()) {
220 // Preserve max to prevent overflow.
221 return std::numeric_limits<int64_t>::max();
222 }
223 return delta_ * Time::kNanosecondsPerMicrosecond;
224 }
225
226
227 #if V8_OS_MACOSX
228
FromMachTimespec(struct mach_timespec ts)229 TimeDelta TimeDelta::FromMachTimespec(struct mach_timespec ts) {
230 DCHECK_GE(ts.tv_nsec, 0);
231 DCHECK_LT(ts.tv_nsec,
232 static_cast<long>(Time::kNanosecondsPerSecond)); // NOLINT
233 return TimeDelta(ts.tv_sec * Time::kMicrosecondsPerSecond +
234 ts.tv_nsec / Time::kNanosecondsPerMicrosecond);
235 }
236
237
ToMachTimespec() const238 struct mach_timespec TimeDelta::ToMachTimespec() const {
239 struct mach_timespec ts;
240 DCHECK_GE(delta_, 0);
241 ts.tv_sec = static_cast<unsigned>(delta_ / Time::kMicrosecondsPerSecond);
242 ts.tv_nsec = (delta_ % Time::kMicrosecondsPerSecond) *
243 Time::kNanosecondsPerMicrosecond;
244 return ts;
245 }
246
247 #endif // V8_OS_MACOSX
248
249
250 #if V8_OS_POSIX
251
FromTimespec(struct timespec ts)252 TimeDelta TimeDelta::FromTimespec(struct timespec ts) {
253 DCHECK_GE(ts.tv_nsec, 0);
254 DCHECK_LT(ts.tv_nsec,
255 static_cast<long>(Time::kNanosecondsPerSecond)); // NOLINT
256 return TimeDelta(ts.tv_sec * Time::kMicrosecondsPerSecond +
257 ts.tv_nsec / Time::kNanosecondsPerMicrosecond);
258 }
259
260
ToTimespec() const261 struct timespec TimeDelta::ToTimespec() const {
262 struct timespec ts;
263 ts.tv_sec = static_cast<time_t>(delta_ / Time::kMicrosecondsPerSecond);
264 ts.tv_nsec = (delta_ % Time::kMicrosecondsPerSecond) *
265 Time::kNanosecondsPerMicrosecond;
266 return ts;
267 }
268
269 #endif // V8_OS_POSIX
270
271
272 #if V8_OS_WIN
273
274 // We implement time using the high-resolution timers so that we can get
275 // timeouts which are smaller than 10-15ms. To avoid any drift, we
276 // periodically resync the internal clock to the system clock.
277 class Clock final {
278 public:
Clock()279 Clock() : initial_ticks_(GetSystemTicks()), initial_time_(GetSystemTime()) {}
280
Now()281 Time Now() {
282 // Time between resampling the un-granular clock for this API (1 minute).
283 const TimeDelta kMaxElapsedTime = TimeDelta::FromMinutes(1);
284
285 LockGuard<Mutex> lock_guard(&mutex_);
286
287 // Determine current time and ticks.
288 TimeTicks ticks = GetSystemTicks();
289 Time time = GetSystemTime();
290
291 // Check if we need to synchronize with the system clock due to a backwards
292 // time change or the amount of time elapsed.
293 TimeDelta elapsed = ticks - initial_ticks_;
294 if (time < initial_time_ || elapsed > kMaxElapsedTime) {
295 initial_ticks_ = ticks;
296 initial_time_ = time;
297 return time;
298 }
299
300 return initial_time_ + elapsed;
301 }
302
NowFromSystemTime()303 Time NowFromSystemTime() {
304 LockGuard<Mutex> lock_guard(&mutex_);
305 initial_ticks_ = GetSystemTicks();
306 initial_time_ = GetSystemTime();
307 return initial_time_;
308 }
309
310 private:
GetSystemTicks()311 static TimeTicks GetSystemTicks() {
312 return TimeTicks::Now();
313 }
314
GetSystemTime()315 static Time GetSystemTime() {
316 FILETIME ft;
317 ::GetSystemTimeAsFileTime(&ft);
318 return Time::FromFiletime(ft);
319 }
320
321 TimeTicks initial_ticks_;
322 Time initial_time_;
323 Mutex mutex_;
324 };
325
326
327 static LazyStaticInstance<Clock, DefaultConstructTrait<Clock>,
328 ThreadSafeInitOnceTrait>::type clock =
329 LAZY_STATIC_INSTANCE_INITIALIZER;
330
331
Now()332 Time Time::Now() {
333 return clock.Pointer()->Now();
334 }
335
336
NowFromSystemTime()337 Time Time::NowFromSystemTime() {
338 return clock.Pointer()->NowFromSystemTime();
339 }
340
341
342 // Time between windows epoch and standard epoch.
343 static const int64_t kTimeToEpochInMicroseconds = int64_t{11644473600000000};
344
FromFiletime(FILETIME ft)345 Time Time::FromFiletime(FILETIME ft) {
346 if (ft.dwLowDateTime == 0 && ft.dwHighDateTime == 0) {
347 return Time();
348 }
349 if (ft.dwLowDateTime == std::numeric_limits<DWORD>::max() &&
350 ft.dwHighDateTime == std::numeric_limits<DWORD>::max()) {
351 return Max();
352 }
353 int64_t us = (static_cast<uint64_t>(ft.dwLowDateTime) +
354 (static_cast<uint64_t>(ft.dwHighDateTime) << 32)) / 10;
355 return Time(us - kTimeToEpochInMicroseconds);
356 }
357
358
ToFiletime() const359 FILETIME Time::ToFiletime() const {
360 DCHECK_GE(us_, 0);
361 FILETIME ft;
362 if (IsNull()) {
363 ft.dwLowDateTime = 0;
364 ft.dwHighDateTime = 0;
365 return ft;
366 }
367 if (IsMax()) {
368 ft.dwLowDateTime = std::numeric_limits<DWORD>::max();
369 ft.dwHighDateTime = std::numeric_limits<DWORD>::max();
370 return ft;
371 }
372 uint64_t us = static_cast<uint64_t>(us_ + kTimeToEpochInMicroseconds) * 10;
373 ft.dwLowDateTime = static_cast<DWORD>(us);
374 ft.dwHighDateTime = static_cast<DWORD>(us >> 32);
375 return ft;
376 }
377
378 #elif V8_OS_POSIX
379
Now()380 Time Time::Now() {
381 struct timeval tv;
382 int result = gettimeofday(&tv, nullptr);
383 DCHECK_EQ(0, result);
384 USE(result);
385 return FromTimeval(tv);
386 }
387
388
NowFromSystemTime()389 Time Time::NowFromSystemTime() {
390 return Now();
391 }
392
393
FromTimespec(struct timespec ts)394 Time Time::FromTimespec(struct timespec ts) {
395 DCHECK_GE(ts.tv_nsec, 0);
396 DCHECK_LT(ts.tv_nsec, kNanosecondsPerSecond);
397 if (ts.tv_nsec == 0 && ts.tv_sec == 0) {
398 return Time();
399 }
400 if (ts.tv_nsec == static_cast<long>(kNanosecondsPerSecond - 1) && // NOLINT
401 ts.tv_sec == std::numeric_limits<time_t>::max()) {
402 return Max();
403 }
404 return Time(ts.tv_sec * kMicrosecondsPerSecond +
405 ts.tv_nsec / kNanosecondsPerMicrosecond);
406 }
407
408
ToTimespec() const409 struct timespec Time::ToTimespec() const {
410 struct timespec ts;
411 if (IsNull()) {
412 ts.tv_sec = 0;
413 ts.tv_nsec = 0;
414 return ts;
415 }
416 if (IsMax()) {
417 ts.tv_sec = std::numeric_limits<time_t>::max();
418 ts.tv_nsec = static_cast<long>(kNanosecondsPerSecond - 1); // NOLINT
419 return ts;
420 }
421 ts.tv_sec = static_cast<time_t>(us_ / kMicrosecondsPerSecond);
422 ts.tv_nsec = (us_ % kMicrosecondsPerSecond) * kNanosecondsPerMicrosecond;
423 return ts;
424 }
425
426
FromTimeval(struct timeval tv)427 Time Time::FromTimeval(struct timeval tv) {
428 DCHECK_GE(tv.tv_usec, 0);
429 DCHECK(tv.tv_usec < static_cast<suseconds_t>(kMicrosecondsPerSecond));
430 if (tv.tv_usec == 0 && tv.tv_sec == 0) {
431 return Time();
432 }
433 if (tv.tv_usec == static_cast<suseconds_t>(kMicrosecondsPerSecond - 1) &&
434 tv.tv_sec == std::numeric_limits<time_t>::max()) {
435 return Max();
436 }
437 return Time(tv.tv_sec * kMicrosecondsPerSecond + tv.tv_usec);
438 }
439
440
ToTimeval() const441 struct timeval Time::ToTimeval() const {
442 struct timeval tv;
443 if (IsNull()) {
444 tv.tv_sec = 0;
445 tv.tv_usec = 0;
446 return tv;
447 }
448 if (IsMax()) {
449 tv.tv_sec = std::numeric_limits<time_t>::max();
450 tv.tv_usec = static_cast<suseconds_t>(kMicrosecondsPerSecond - 1);
451 return tv;
452 }
453 tv.tv_sec = static_cast<time_t>(us_ / kMicrosecondsPerSecond);
454 tv.tv_usec = us_ % kMicrosecondsPerSecond;
455 return tv;
456 }
457
458 #endif // V8_OS_WIN
459
460 // static
HighResolutionNow()461 TimeTicks TimeTicks::HighResolutionNow() {
462 // a DCHECK of TimeTicks::IsHighResolution() was removed from here
463 // as it turns out this path is used in the wild for logs and counters.
464 //
465 // TODO(hpayer) We may eventually want to split TimedHistograms based
466 // on low resolution clocks to avoid polluting metrics
467 return TimeTicks::Now();
468 }
469
FromJsTime(double ms_since_epoch)470 Time Time::FromJsTime(double ms_since_epoch) {
471 // The epoch is a valid time, so this constructor doesn't interpret
472 // 0 as the null time.
473 if (ms_since_epoch == std::numeric_limits<double>::max()) {
474 return Max();
475 }
476 return Time(
477 static_cast<int64_t>(ms_since_epoch * kMicrosecondsPerMillisecond));
478 }
479
480
ToJsTime() const481 double Time::ToJsTime() const {
482 if (IsNull()) {
483 // Preserve 0 so the invalid result doesn't depend on the platform.
484 return 0;
485 }
486 if (IsMax()) {
487 // Preserve max without offset to prevent overflow.
488 return std::numeric_limits<double>::max();
489 }
490 return static_cast<double>(us_) / kMicrosecondsPerMillisecond;
491 }
492
493
operator <<(std::ostream & os,const Time & time)494 std::ostream& operator<<(std::ostream& os, const Time& time) {
495 return os << time.ToJsTime();
496 }
497
498
499 #if V8_OS_WIN
500
501 namespace {
502
503 // We define a wrapper to adapt between the __stdcall and __cdecl call of the
504 // mock function, and to avoid a static constructor. Assigning an import to a
505 // function pointer directly would require setup code to fetch from the IAT.
timeGetTimeWrapper()506 DWORD timeGetTimeWrapper() { return timeGetTime(); }
507
508 DWORD (*g_tick_function)(void) = &timeGetTimeWrapper;
509
510 // A structure holding the most significant bits of "last seen" and a
511 // "rollover" counter.
512 union LastTimeAndRolloversState {
513 // The state as a single 32-bit opaque value.
514 base::Atomic32 as_opaque_32;
515
516 // The state as usable values.
517 struct {
518 // The top 8-bits of the "last" time. This is enough to check for rollovers
519 // and the small bit-size means fewer CompareAndSwap operations to store
520 // changes in state, which in turn makes for fewer retries.
521 uint8_t last_8;
522 // A count of the number of detected rollovers. Using this as bits 47-32
523 // of the upper half of a 64-bit value results in a 48-bit tick counter.
524 // This extends the total rollover period from about 49 days to about 8800
525 // years while still allowing it to be stored with last_8 in a single
526 // 32-bit value.
527 uint16_t rollovers;
528 } as_values;
529 };
530 base::Atomic32 g_last_time_and_rollovers = 0;
531 static_assert(sizeof(LastTimeAndRolloversState) <=
532 sizeof(g_last_time_and_rollovers),
533 "LastTimeAndRolloversState does not fit in a single atomic word");
534
535 // We use timeGetTime() to implement TimeTicks::Now(). This can be problematic
536 // because it returns the number of milliseconds since Windows has started,
537 // which will roll over the 32-bit value every ~49 days. We try to track
538 // rollover ourselves, which works if TimeTicks::Now() is called at least every
539 // 48.8 days (not 49 days because only changes in the top 8 bits get noticed).
RolloverProtectedNow()540 TimeTicks RolloverProtectedNow() {
541 LastTimeAndRolloversState state;
542 DWORD now; // DWORD is always unsigned 32 bits.
543
544 while (true) {
545 // Fetch the "now" and "last" tick values, updating "last" with "now" and
546 // incrementing the "rollovers" counter if the tick-value has wrapped back
547 // around. Atomic operations ensure that both "last" and "rollovers" are
548 // always updated together.
549 int32_t original = base::Acquire_Load(&g_last_time_and_rollovers);
550 state.as_opaque_32 = original;
551 now = g_tick_function();
552 uint8_t now_8 = static_cast<uint8_t>(now >> 24);
553 if (now_8 < state.as_values.last_8) ++state.as_values.rollovers;
554 state.as_values.last_8 = now_8;
555
556 // If the state hasn't changed, exit the loop.
557 if (state.as_opaque_32 == original) break;
558
559 // Save the changed state. If the existing value is unchanged from the
560 // original, exit the loop.
561 int32_t check = base::Release_CompareAndSwap(&g_last_time_and_rollovers,
562 original, state.as_opaque_32);
563 if (check == original) break;
564
565 // Another thread has done something in between so retry from the top.
566 }
567
568 return TimeTicks() +
569 TimeDelta::FromMilliseconds(
570 now + (static_cast<uint64_t>(state.as_values.rollovers) << 32));
571 }
572
573 // Discussion of tick counter options on Windows:
574 //
575 // (1) CPU cycle counter. (Retrieved via RDTSC)
576 // The CPU counter provides the highest resolution time stamp and is the least
577 // expensive to retrieve. However, on older CPUs, two issues can affect its
578 // reliability: First it is maintained per processor and not synchronized
579 // between processors. Also, the counters will change frequency due to thermal
580 // and power changes, and stop in some states.
581 //
582 // (2) QueryPerformanceCounter (QPC). The QPC counter provides a high-
583 // resolution (<1 microsecond) time stamp. On most hardware running today, it
584 // auto-detects and uses the constant-rate RDTSC counter to provide extremely
585 // efficient and reliable time stamps.
586 //
587 // On older CPUs where RDTSC is unreliable, it falls back to using more
588 // expensive (20X to 40X more costly) alternate clocks, such as HPET or the ACPI
589 // PM timer, and can involve system calls; and all this is up to the HAL (with
590 // some help from ACPI). According to
591 // http://blogs.msdn.com/oldnewthing/archive/2005/09/02/459952.aspx, in the
592 // worst case, it gets the counter from the rollover interrupt on the
593 // programmable interrupt timer. In best cases, the HAL may conclude that the
594 // RDTSC counter runs at a constant frequency, then it uses that instead. On
595 // multiprocessor machines, it will try to verify the values returned from
596 // RDTSC on each processor are consistent with each other, and apply a handful
597 // of workarounds for known buggy hardware. In other words, QPC is supposed to
598 // give consistent results on a multiprocessor computer, but for older CPUs it
599 // can be unreliable due bugs in BIOS or HAL.
600 //
601 // (3) System time. The system time provides a low-resolution (from ~1 to ~15.6
602 // milliseconds) time stamp but is comparatively less expensive to retrieve and
603 // more reliable. Time::EnableHighResolutionTimer() and
604 // Time::ActivateHighResolutionTimer() can be called to alter the resolution of
605 // this timer; and also other Windows applications can alter it, affecting this
606 // one.
607
608 TimeTicks InitialTimeTicksNowFunction();
609
610 // See "threading notes" in InitializeNowFunctionPointer() for details on how
611 // concurrent reads/writes to these globals has been made safe.
612 using TimeTicksNowFunction = decltype(&TimeTicks::Now);
613 TimeTicksNowFunction g_time_ticks_now_function = &InitialTimeTicksNowFunction;
614 int64_t g_qpc_ticks_per_second = 0;
615
616 // As of January 2015, use of <atomic> is forbidden in Chromium code. This is
617 // what std::atomic_thread_fence does on Windows on all Intel architectures when
618 // the memory_order argument is anything but std::memory_order_seq_cst:
619 #define ATOMIC_THREAD_FENCE(memory_order) _ReadWriteBarrier();
620
QPCValueToTimeDelta(LONGLONG qpc_value)621 TimeDelta QPCValueToTimeDelta(LONGLONG qpc_value) {
622 // Ensure that the assignment to |g_qpc_ticks_per_second|, made in
623 // InitializeNowFunctionPointer(), has happened by this point.
624 ATOMIC_THREAD_FENCE(memory_order_acquire);
625
626 DCHECK_GT(g_qpc_ticks_per_second, 0);
627
628 // If the QPC Value is below the overflow threshold, we proceed with
629 // simple multiply and divide.
630 if (qpc_value < TimeTicks::kQPCOverflowThreshold) {
631 return TimeDelta::FromMicroseconds(
632 qpc_value * TimeTicks::kMicrosecondsPerSecond / g_qpc_ticks_per_second);
633 }
634 // Otherwise, calculate microseconds in a round about manner to avoid
635 // overflow and precision issues.
636 int64_t whole_seconds = qpc_value / g_qpc_ticks_per_second;
637 int64_t leftover_ticks = qpc_value - (whole_seconds * g_qpc_ticks_per_second);
638 return TimeDelta::FromMicroseconds(
639 (whole_seconds * TimeTicks::kMicrosecondsPerSecond) +
640 ((leftover_ticks * TimeTicks::kMicrosecondsPerSecond) /
641 g_qpc_ticks_per_second));
642 }
643
QPCNow()644 TimeTicks QPCNow() { return TimeTicks() + QPCValueToTimeDelta(QPCNowRaw()); }
645
IsBuggyAthlon(const CPU & cpu)646 bool IsBuggyAthlon(const CPU& cpu) {
647 // On Athlon X2 CPUs (e.g. model 15) QueryPerformanceCounter is unreliable.
648 return strcmp(cpu.vendor(), "AuthenticAMD") == 0 && cpu.family() == 15;
649 }
650
InitializeTimeTicksNowFunctionPointer()651 void InitializeTimeTicksNowFunctionPointer() {
652 LARGE_INTEGER ticks_per_sec = {};
653 if (!QueryPerformanceFrequency(&ticks_per_sec)) ticks_per_sec.QuadPart = 0;
654
655 // If Windows cannot provide a QPC implementation, TimeTicks::Now() must use
656 // the low-resolution clock.
657 //
658 // If the QPC implementation is expensive and/or unreliable, TimeTicks::Now()
659 // will still use the low-resolution clock. A CPU lacking a non-stop time
660 // counter will cause Windows to provide an alternate QPC implementation that
661 // works, but is expensive to use. Certain Athlon CPUs are known to make the
662 // QPC implementation unreliable.
663 //
664 // Otherwise, Now uses the high-resolution QPC clock. As of 21 August 2015,
665 // ~72% of users fall within this category.
666 TimeTicksNowFunction now_function;
667 CPU cpu;
668 if (ticks_per_sec.QuadPart <= 0 || !cpu.has_non_stop_time_stamp_counter() ||
669 IsBuggyAthlon(cpu)) {
670 now_function = &RolloverProtectedNow;
671 } else {
672 now_function = &QPCNow;
673 }
674
675 // Threading note 1: In an unlikely race condition, it's possible for two or
676 // more threads to enter InitializeNowFunctionPointer() in parallel. This is
677 // not a problem since all threads should end up writing out the same values
678 // to the global variables.
679 //
680 // Threading note 2: A release fence is placed here to ensure, from the
681 // perspective of other threads using the function pointers, that the
682 // assignment to |g_qpc_ticks_per_second| happens before the function pointers
683 // are changed.
684 g_qpc_ticks_per_second = ticks_per_sec.QuadPart;
685 ATOMIC_THREAD_FENCE(memory_order_release);
686 g_time_ticks_now_function = now_function;
687 }
688
InitialTimeTicksNowFunction()689 TimeTicks InitialTimeTicksNowFunction() {
690 InitializeTimeTicksNowFunctionPointer();
691 return g_time_ticks_now_function();
692 }
693
694 #undef ATOMIC_THREAD_FENCE
695
696 } // namespace
697
698 // static
Now()699 TimeTicks TimeTicks::Now() {
700 // Make sure we never return 0 here.
701 TimeTicks ticks(g_time_ticks_now_function());
702 DCHECK(!ticks.IsNull());
703 return ticks;
704 }
705
706 // static
IsHighResolution()707 bool TimeTicks::IsHighResolution() {
708 if (g_time_ticks_now_function == &InitialTimeTicksNowFunction)
709 InitializeTimeTicksNowFunctionPointer();
710 return g_time_ticks_now_function == &QPCNow;
711 }
712
713 #else // V8_OS_WIN
714
Now()715 TimeTicks TimeTicks::Now() {
716 int64_t ticks;
717 #if V8_OS_MACOSX
718 static struct mach_timebase_info info;
719 if (info.denom == 0) {
720 kern_return_t result = mach_timebase_info(&info);
721 DCHECK_EQ(KERN_SUCCESS, result);
722 USE(result);
723 }
724 ticks = (mach_absolute_time() / Time::kNanosecondsPerMicrosecond *
725 info.numer / info.denom);
726 #elif V8_OS_SOLARIS
727 ticks = (gethrtime() / Time::kNanosecondsPerMicrosecond);
728 #elif V8_OS_POSIX
729 ticks = ClockNow(CLOCK_MONOTONIC);
730 #else
731 #error platform does not implement TimeTicks::HighResolutionNow.
732 #endif // V8_OS_MACOSX
733 // Make sure we never return 0 here.
734 return TimeTicks(ticks + 1);
735 }
736
737 // static
IsHighResolution()738 bool TimeTicks::IsHighResolution() { return true; }
739
740 #endif // V8_OS_WIN
741
742
IsSupported()743 bool ThreadTicks::IsSupported() {
744 #if (defined(_POSIX_THREAD_CPUTIME) && (_POSIX_THREAD_CPUTIME >= 0)) || \
745 defined(V8_OS_MACOSX) || defined(V8_OS_ANDROID) || defined(V8_OS_SOLARIS)
746 return true;
747 #elif defined(V8_OS_WIN)
748 return IsSupportedWin();
749 #else
750 return false;
751 #endif
752 }
753
754
Now()755 ThreadTicks ThreadTicks::Now() {
756 #if V8_OS_MACOSX
757 return ThreadTicks(ComputeThreadTicks());
758 #elif(defined(_POSIX_THREAD_CPUTIME) && (_POSIX_THREAD_CPUTIME >= 0)) || \
759 defined(V8_OS_ANDROID)
760 return ThreadTicks(ClockNow(CLOCK_THREAD_CPUTIME_ID));
761 #elif V8_OS_SOLARIS
762 return ThreadTicks(gethrvtime() / Time::kNanosecondsPerMicrosecond);
763 #elif V8_OS_WIN
764 return ThreadTicks::GetForThread(::GetCurrentThread());
765 #else
766 UNREACHABLE();
767 #endif
768 }
769
770
771 #if V8_OS_WIN
GetForThread(const HANDLE & thread_handle)772 ThreadTicks ThreadTicks::GetForThread(const HANDLE& thread_handle) {
773 DCHECK(IsSupported());
774
775 // Get the number of TSC ticks used by the current thread.
776 ULONG64 thread_cycle_time = 0;
777 ::QueryThreadCycleTime(thread_handle, &thread_cycle_time);
778
779 // Get the frequency of the TSC.
780 double tsc_ticks_per_second = TSCTicksPerSecond();
781 if (tsc_ticks_per_second == 0)
782 return ThreadTicks();
783
784 // Return the CPU time of the current thread.
785 double thread_time_seconds = thread_cycle_time / tsc_ticks_per_second;
786 return ThreadTicks(
787 static_cast<int64_t>(thread_time_seconds * Time::kMicrosecondsPerSecond));
788 }
789
790 // static
IsSupportedWin()791 bool ThreadTicks::IsSupportedWin() {
792 static bool is_supported = base::CPU().has_non_stop_time_stamp_counter() &&
793 !IsQPCReliable();
794 return is_supported;
795 }
796
797 // static
WaitUntilInitializedWin()798 void ThreadTicks::WaitUntilInitializedWin() {
799 while (TSCTicksPerSecond() == 0)
800 ::Sleep(10);
801 }
802
TSCTicksPerSecond()803 double ThreadTicks::TSCTicksPerSecond() {
804 DCHECK(IsSupported());
805
806 // The value returned by QueryPerformanceFrequency() cannot be used as the TSC
807 // frequency, because there is no guarantee that the TSC frequency is equal to
808 // the performance counter frequency.
809
810 // The TSC frequency is cached in a static variable because it takes some time
811 // to compute it.
812 static double tsc_ticks_per_second = 0;
813 if (tsc_ticks_per_second != 0)
814 return tsc_ticks_per_second;
815
816 // Increase the thread priority to reduces the chances of having a context
817 // switch during a reading of the TSC and the performance counter.
818 int previous_priority = ::GetThreadPriority(::GetCurrentThread());
819 ::SetThreadPriority(::GetCurrentThread(), THREAD_PRIORITY_HIGHEST);
820
821 // The first time that this function is called, make an initial reading of the
822 // TSC and the performance counter.
823 static const uint64_t tsc_initial = __rdtsc();
824 static const uint64_t perf_counter_initial = QPCNowRaw();
825
826 // Make a another reading of the TSC and the performance counter every time
827 // that this function is called.
828 uint64_t tsc_now = __rdtsc();
829 uint64_t perf_counter_now = QPCNowRaw();
830
831 // Reset the thread priority.
832 ::SetThreadPriority(::GetCurrentThread(), previous_priority);
833
834 // Make sure that at least 50 ms elapsed between the 2 readings. The first
835 // time that this function is called, we don't expect this to be the case.
836 // Note: The longer the elapsed time between the 2 readings is, the more
837 // accurate the computed TSC frequency will be. The 50 ms value was
838 // chosen because local benchmarks show that it allows us to get a
839 // stddev of less than 1 tick/us between multiple runs.
840 // Note: According to the MSDN documentation for QueryPerformanceFrequency(),
841 // this will never fail on systems that run XP or later.
842 // https://msdn.microsoft.com/library/windows/desktop/ms644905.aspx
843 LARGE_INTEGER perf_counter_frequency = {};
844 ::QueryPerformanceFrequency(&perf_counter_frequency);
845 DCHECK_GE(perf_counter_now, perf_counter_initial);
846 uint64_t perf_counter_ticks = perf_counter_now - perf_counter_initial;
847 double elapsed_time_seconds =
848 perf_counter_ticks / static_cast<double>(perf_counter_frequency.QuadPart);
849
850 const double kMinimumEvaluationPeriodSeconds = 0.05;
851 if (elapsed_time_seconds < kMinimumEvaluationPeriodSeconds)
852 return 0;
853
854 // Compute the frequency of the TSC.
855 DCHECK_GE(tsc_now, tsc_initial);
856 uint64_t tsc_ticks = tsc_now - tsc_initial;
857 tsc_ticks_per_second = tsc_ticks / elapsed_time_seconds;
858
859 return tsc_ticks_per_second;
860 }
861 #endif // V8_OS_WIN
862
863 } // namespace base
864 } // namespace v8
865