Revert OS::TimeCurrentMillis on Windows introduced in r16413.

BUG=chromium:288924
R=danno@chromium.org, jkummerow@chromium.org

Review URL: https://codereview.chromium.org/24529002

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@16938 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/platform-win32.cc

@@ -240,12 +240,16 @@ void MathSetup() {
 class Win32Time {
  public:
   // Constructors.
+  Win32Time();
   explicit Win32Time(double jstime);
   Win32Time(int year, int mon, int day, int hour, int min, int sec);
 
   // Convert timestamp to JavaScript representation.
   double ToJSTime();
 
+  // Set timestamp to current time.
+  void SetToCurrentTime();
+
   // Returns the local timezone offset in milliseconds east of UTC. This is
   // the number of milliseconds you must add to UTC to get local time, i.e.
   // LocalOffset(CET) = 3600000 and LocalOffset(PST) = -28800000. This
@@ -314,6 +318,12 @@ char Win32Time::std_tz_name_[kTzNameSize];
 char Win32Time::dst_tz_name_[kTzNameSize];
 
 
+// Initialize timestamp to start of epoc.
+Win32Time::Win32Time() {
+  t() = 0;
+}
+
+
 // Initialize timestamp from a JavaScript timestamp.
 Win32Time::Win32Time(double jstime) {
   t() = static_cast<int64_t>(jstime) * kTimeScaler + kTimeEpoc;
@@ -340,6 +350,62 @@ double Win32Time::ToJSTime() {
 }
 
 
+// Set timestamp to current time.
+void Win32Time::SetToCurrentTime() {
+  // The default GetSystemTimeAsFileTime has a ~15.5ms resolution.
+  // Because we're fast, we like fast timers which have at least a
+  // 1ms resolution.
+  //
+  // timeGetTime() provides 1ms granularity when combined with
+  // timeBeginPeriod().  If the host application for v8 wants fast
+  // timers, it can use timeBeginPeriod to increase the resolution.
+  //
+  // Using timeGetTime() has a drawback because it is a 32bit value
+  // and hence rolls-over every ~49days.
+  //
+  // To use the clock, we use GetSystemTimeAsFileTime as our base;
+  // and then use timeGetTime to extrapolate current time from the
+  // start time.  To deal with rollovers, we resync the clock
+  // any time when more than kMaxClockElapsedTime has passed or
+  // whenever timeGetTime creates a rollover.
+
+  static bool initialized = false;
+  static TimeStamp init_time;
+  static DWORD init_ticks;
+  static const int64_t kHundredNanosecondsPerSecond = 10000000;
+  static const int64_t kMaxClockElapsedTime =
+      60*kHundredNanosecondsPerSecond;  // 1 minute
+
+  // If we are uninitialized, we need to resync the clock.
+  bool needs_resync = !initialized;
+
+  // Get the current time.
+  TimeStamp time_now;
+  GetSystemTimeAsFileTime(&time_now.ft_);
+  DWORD ticks_now = timeGetTime();
+
+  // Check if we need to resync due to clock rollover.
+  needs_resync |= ticks_now < init_ticks;
+
+  // Check if we need to resync due to elapsed time.
+  needs_resync |= (time_now.t_ - init_time.t_) > kMaxClockElapsedTime;
+
+  // Check if we need to resync due to backwards time change.
+  needs_resync |= time_now.t_ < init_time.t_;
+
+  // Resync the clock if necessary.
+  if (needs_resync) {
+    GetSystemTimeAsFileTime(&init_time.ft_);
+    init_ticks = ticks_now = timeGetTime();
+    initialized = true;
+  }
+
+  // Finally, compute the actual time.  Why is this so hard.
+  DWORD elapsed = ticks_now - init_ticks;
+  this->time_.t_ = init_time.t_ + (static_cast<int64_t>(elapsed) * 10000);
+}
+
+
 // Guess the name of the timezone from the bias.
 // The guess is very biased towards the northern hemisphere.
 const char* Win32Time::GuessTimezoneNameFromBias(int bias) {
@@ -529,7 +595,9 @@ int OS::GetUserTime(uint32_t* secs,  uint32_t* usecs) {
 // Returns current time as the number of milliseconds since
 // 00:00:00 UTC, January 1, 1970.
 double OS::TimeCurrentMillis() {
-  return Time::Now().ToJsTime();
+  Win32Time t;
+  t.SetToCurrentTime();
+  return t.ToJSTime();
 }
 
 

test/mjsunit/timer.js

+// Copyright 2013 the V8 project authors. All rights reserved.
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+//       notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+//       copyright notice, this list of conditions and the following
+//       disclaimer in the documentation and/or other materials provided
+//       with the distribution.
+//     * Neither the name of Google Inc. nor the names of its
+//       contributors may be used to endorse or promote products derived
+//       from this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+// Tests timer milliseconds granularity.
+
+var start = Date.now();
+var end = Date.now();
+while (end - start == 0) {
+  end = Date.now();
+}
+assertTrue(end - start <= 2);