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Diffstat (limited to 'ipc/chromium/src/base/time_win.cc')
| -rw-r--r-- | ipc/chromium/src/base/time_win.cc | 263 |
1 files changed, 263 insertions, 0 deletions
diff --git a/ipc/chromium/src/base/time_win.cc b/ipc/chromium/src/base/time_win.cc new file mode 100644 index 0000000000..d39416cd6d --- /dev/null +++ b/ipc/chromium/src/base/time_win.cc @@ -0,0 +1,263 @@ +/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */ +/* vim: set ts=8 sts=2 et sw=2 tw=80: */ +// Copyright (c) 2006-2008 The Chromium Authors. All rights reserved. +// Use of this source code is governed by a BSD-style license that can be +// found in the LICENSE file. + +// Windows Timer Primer +// +// A good article: http://www.ddj.com/windows/184416651 +// A good mozilla bug: http://bugzilla.mozilla.org/show_bug.cgi?id=363258 +// +// The default windows timer, GetSystemTimeAsFileTime is not very precise. +// It is only good to ~15.5ms. +// +// QueryPerformanceCounter is the logical choice for a high-precision timer. +// However, it is known to be buggy on some hardware. Specifically, it can +// sometimes "jump". On laptops, QPC can also be very expensive to call. +// It's 3-4x slower than timeGetTime() on desktops, but can be 10x slower +// on laptops. A unittest exists which will show the relative cost of various +// timers on any system. +// +// The next logical choice is timeGetTime(). timeGetTime has a precision of +// 1ms, but only if you call APIs (timeBeginPeriod()) which affect all other +// applications on the system. By default, precision is only 15.5ms. +// Unfortunately, we don't want to call timeBeginPeriod because we don't +// want to affect other applications. Further, on mobile platforms, use of +// faster multimedia timers can hurt battery life. See the intel +// article about this here: +// http://softwarecommunity.intel.com/articles/eng/1086.htm +// +// To work around all this, we're going to generally use timeGetTime(). We +// will only increase the system-wide timer if we're not running on battery +// power. Using timeBeginPeriod(1) is a requirement in order to make our +// message loop waits have the same resolution that our time measurements +// do. Otherwise, WaitForSingleObject(..., 1) will no less than 15ms when +// there is nothing else to waken the Wait. + +#include "base/time.h" + +#ifndef __MINGW32__ +# pragma comment(lib, "winmm.lib") +#endif +#include <windows.h> +#include <mmsystem.h> + +#include "base/basictypes.h" +#include "base/logging.h" +#include "mozilla/Casting.h" +#include "mozilla/StaticMutex.h" + +using base::Time; +using base::TimeDelta; +using base::TimeTicks; +using mozilla::BitwiseCast; + +namespace { + +// From MSDN, FILETIME "Contains a 64-bit value representing the number of +// 100-nanosecond intervals since January 1, 1601 (UTC)." +int64_t FileTimeToMicroseconds(const FILETIME& ft) { + // Need to BitwiseCast to fix alignment, then divide by 10 to convert + // 100-nanoseconds to milliseconds. This only works on little-endian + // machines. + return BitwiseCast<int64_t>(ft) / 10; +} + +void MicrosecondsToFileTime(int64_t us, FILETIME* ft) { + DCHECK(us >= 0) << "Time is less than 0, negative values are not " + "representable in FILETIME"; + + // Multiply by 10 to convert milliseconds to 100-nanoseconds. BitwiseCast will + // handle alignment problems. This only works on little-endian machines. + *ft = BitwiseCast<FILETIME>(us * 10); +} + +int64_t CurrentWallclockMicroseconds() { + FILETIME ft; + ::GetSystemTimeAsFileTime(&ft); + return FileTimeToMicroseconds(ft); +} + +// Time between resampling the un-granular clock for this API. 60 seconds. +const int kMaxMillisecondsToAvoidDrift = 60 * Time::kMillisecondsPerSecond; + +int64_t initial_time = 0; +TimeTicks initial_ticks; + +void InitializeClock() { + initial_ticks = TimeTicks::Now(); + initial_time = CurrentWallclockMicroseconds(); +} + +} // namespace + +// Time ----------------------------------------------------------------------- + +// The internal representation of Time uses FILETIME, whose epoch is 1601-01-01 +// 00:00:00 UTC. ((1970-1601)*365+89)*24*60*60*1000*1000, where 89 is the +// number of leap year days between 1601 and 1970: (1970-1601)/4 excluding +// 1700, 1800, and 1900. +// static +const int64_t Time::kTimeTToMicrosecondsOffset = GG_INT64_C(11644473600000000); + +// static +Time Time::Now() { + if (initial_time == 0) InitializeClock(); + + // We implement time using the high-resolution timers so that we can get + // timeouts which are smaller than 10-15ms. If we just used + // CurrentWallclockMicroseconds(), we'd have the less-granular timer. + // + // To make this work, we initialize the clock (initial_time) and the + // counter (initial_ctr). To compute the initial time, we can check + // the number of ticks that have elapsed, and compute the delta. + // + // To avoid any drift, we periodically resync the counters to the system + // clock. + while (true) { + TimeTicks ticks = TimeTicks::Now(); + + // Calculate the time elapsed since we started our timer + TimeDelta elapsed = ticks - initial_ticks; + + // Check if enough time has elapsed that we need to resync the clock. + if (elapsed.InMilliseconds() > kMaxMillisecondsToAvoidDrift) { + InitializeClock(); + continue; + } + + return Time(elapsed + Time(initial_time)); + } +} + +// static +Time Time::NowFromSystemTime() { + // Force resync. + InitializeClock(); + return Time(initial_time); +} + +// static +Time Time::FromExploded(bool is_local, const Exploded& exploded) { + // Create the system struct representing our exploded time. It will either be + // in local time or UTC. + SYSTEMTIME st; + st.wYear = exploded.year; + st.wMonth = exploded.month; + st.wDayOfWeek = exploded.day_of_week; + st.wDay = exploded.day_of_month; + st.wHour = exploded.hour; + st.wMinute = exploded.minute; + st.wSecond = exploded.second; + st.wMilliseconds = exploded.millisecond; + + // Convert to FILETIME. + FILETIME ft; + if (!SystemTimeToFileTime(&st, &ft)) { + NOTREACHED() << "Unable to convert time"; + return Time(0); + } + + // Ensure that it's in UTC. + if (is_local) { + FILETIME utc_ft; + LocalFileTimeToFileTime(&ft, &utc_ft); + return Time(FileTimeToMicroseconds(utc_ft)); + } + return Time(FileTimeToMicroseconds(ft)); +} + +void Time::Explode(bool is_local, Exploded* exploded) const { + // FILETIME in UTC. + FILETIME utc_ft; + MicrosecondsToFileTime(us_, &utc_ft); + + // FILETIME in local time if necessary. + BOOL success = TRUE; + FILETIME ft; + if (is_local) + success = FileTimeToLocalFileTime(&utc_ft, &ft); + else + ft = utc_ft; + + // FILETIME in SYSTEMTIME (exploded). + SYSTEMTIME st; + if (!success || !FileTimeToSystemTime(&ft, &st)) { + NOTREACHED() << "Unable to convert time, don't know why"; + ZeroMemory(exploded, sizeof(*exploded)); + return; + } + + exploded->year = st.wYear; + exploded->month = st.wMonth; + exploded->day_of_week = st.wDayOfWeek; + exploded->day_of_month = st.wDay; + exploded->hour = st.wHour; + exploded->minute = st.wMinute; + exploded->second = st.wSecond; + exploded->millisecond = st.wMilliseconds; +} + +// TimeTicks ------------------------------------------------------------------ +namespace { + +// We define a wrapper to adapt between the __stdcall and __cdecl call of the +// mock function, and to avoid a static constructor. Assigning an import to a +// function pointer directly would require setup code to fetch from the IAT. +DWORD timeGetTimeWrapper() { return timeGetTime(); } + +DWORD (*tick_function)(void) = &timeGetTimeWrapper; + +// This setup is a little gross: the `now` instance lives until libxul is +// unloaded, but leak checking runs prior to that, and would see a Mutex +// instance contained in NowSingleton as still live. Said instance would +// be reported as a leak...but it's not, really. To avoid that, we need +// to use StaticMutex (which is not leak-checked), but StaticMutex can't +// be a member variable. So we have to have this separate static variable. +static mozilla::StaticMutex sNowSingletonLock; + +// We use timeGetTime() to implement TimeTicks::Now(). This can be problematic +// because it returns the number of milliseconds since Windows has started, +// which will roll over the 32-bit value every ~49 days. We try to track +// rollover ourselves, which works if TimeTicks::Now() is called at least every +// 49 days. +class NowSingleton { + public: + TimeDelta Now() { + mozilla::StaticMutexAutoLock locked(sNowSingletonLock); + // We should hold the lock while calling tick_function to make sure that + // we keep our last_seen_ stay correctly in sync. + DWORD now = tick_function(); + if (now < last_seen_) + rollover_ += + TimeDelta::FromMilliseconds(GG_LONGLONG(0x100000000)); // ~49.7 days. + last_seen_ = now; + return TimeDelta::FromMilliseconds(now) + rollover_; + } + + static NowSingleton& instance() { + static NowSingleton now; + return now; + } + + private: + explicit NowSingleton() + : rollover_(TimeDelta::FromMilliseconds(0)), last_seen_(0) {} + ~NowSingleton() = default; + + TimeDelta rollover_ MOZ_GUARDED_BY( + sNowSingletonLock); // Accumulation of time lost due to rollover. + DWORD last_seen_ + MOZ_GUARDED_BY(sNowSingletonLock); // The last timeGetTime value we saw, + // to detect rollover. + + DISALLOW_COPY_AND_ASSIGN(NowSingleton); +}; + +} // namespace + +// static +TimeTicks TimeTicks::Now() { + return TimeTicks() + NowSingleton::instance().Now(); +} |