diff -r 000000000000 -r 6474c204b198 xpcom/ds/TimeStamp.h
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/xpcom/ds/TimeStamp.h	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,377 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim:set ts=2 sw=2 sts=2 et cindent: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_TimeStamp_h
+#define mozilla_TimeStamp_h
+
+#include <stdint.h>
+#include "mozilla/Assertions.h"
+#include "mozilla/Attributes.h"
+#include "nscore.h"
+
+namespace IPC {
+template <typename T> struct ParamTraits;
+}
+
+#ifdef XP_WIN
+// defines TimeStampValue as a complex value keeping both
+// GetTickCount and QueryPerformanceCounter values
+#include "TimeStamp_windows.h"
+#endif
+
+namespace mozilla {
+
+#ifndef XP_WIN
+typedef uint64_t TimeStampValue;
+#endif
+
+class TimeStamp;
+
+/**
+ * Instances of this class represent the length of an interval of time.
+ * Negative durations are allowed, meaning the end is before the start.
+ * 
+ * Internally the duration is stored as a int64_t in units of
+ * PR_TicksPerSecond() when building with NSPR interval timers, or a
+ * system-dependent unit when building with system clocks.  The
+ * system-dependent unit must be constant, otherwise the semantics of
+ * this class would be broken.
+ */
+class TimeDuration
+{
+public:
+  // The default duration is 0.
+  MOZ_CONSTEXPR TimeDuration() : mValue(0) {}
+  // Allow construction using '0' as the initial value, for readability,
+  // but no other numbers (so we don't have any implicit unit conversions).
+  struct _SomethingVeryRandomHere;
+  TimeDuration(_SomethingVeryRandomHere* aZero) : mValue(0) {
+    MOZ_ASSERT(!aZero, "Who's playing funny games here?");
+  }
+  // Default copy-constructor and assignment are OK
+
+  double ToSeconds() const;
+  // Return a duration value that includes digits of time we think to
+  // be significant.  This method should be used when displaying a
+  // time to humans.
+  double ToSecondsSigDigits() const;
+  double ToMilliseconds() const {
+    return ToSeconds() * 1000.0;
+  }
+  double ToMicroseconds() const {
+    return ToMilliseconds() * 1000.0;
+  }
+
+  // Using a double here is safe enough; with 53 bits we can represent
+  // durations up to over 280,000 years exactly.  If the units of
+  // mValue do not allow us to represent durations of that length,
+  // long durations are clamped to the max/min representable value
+  // instead of overflowing.
+  static inline TimeDuration FromSeconds(double aSeconds) {
+    return FromMilliseconds(aSeconds * 1000.0);
+  }
+  static TimeDuration FromMilliseconds(double aMilliseconds);
+  static inline TimeDuration FromMicroseconds(double aMicroseconds) {
+    return FromMilliseconds(aMicroseconds / 1000.0);
+  }
+
+  static TimeDuration Forever() {
+    return FromTicks(INT64_MAX);
+  }
+
+  TimeDuration operator+(const TimeDuration& aOther) const {
+    return TimeDuration::FromTicks(mValue + aOther.mValue);
+  }
+  TimeDuration operator-(const TimeDuration& aOther) const {
+    return TimeDuration::FromTicks(mValue - aOther.mValue);
+  }
+  TimeDuration& operator+=(const TimeDuration& aOther) {
+    mValue += aOther.mValue;
+    return *this;
+  }
+  TimeDuration& operator-=(const TimeDuration& aOther) {
+    mValue -= aOther.mValue;
+    return *this;
+  }
+
+private:
+  // Block double multiplier (slower, imprecise if long duration) - Bug 853398.
+  // If required, use MultDouble explicitly and with care.
+  TimeDuration operator*(const double aMultiplier) const MOZ_DELETE;
+
+public:
+  TimeDuration MultDouble(double aMultiplier) const {
+    return TimeDuration::FromTicks(static_cast<int64_t>(mValue * aMultiplier));
+  }
+  TimeDuration operator*(const int32_t aMultiplier) const {
+    return TimeDuration::FromTicks(mValue * int64_t(aMultiplier));
+  }
+  TimeDuration operator*(const uint32_t aMultiplier) const {
+    return TimeDuration::FromTicks(mValue * int64_t(aMultiplier));
+  }
+  TimeDuration operator*(const int64_t aMultiplier) const {
+    return TimeDuration::FromTicks(mValue * int64_t(aMultiplier));
+  }
+  TimeDuration operator/(const int64_t aDivisor) const {
+    return TimeDuration::FromTicks(mValue / aDivisor);
+  }
+  double operator/(const TimeDuration& aOther) const {
+    return static_cast<double>(mValue) / aOther.mValue;
+  }
+
+  bool operator<(const TimeDuration& aOther) const {
+    return mValue < aOther.mValue;
+  }
+  bool operator<=(const TimeDuration& aOther) const {
+    return mValue <= aOther.mValue;
+  }
+  bool operator>=(const TimeDuration& aOther) const {
+    return mValue >= aOther.mValue;
+  }
+  bool operator>(const TimeDuration& aOther) const {
+    return mValue > aOther.mValue;
+  }
+  bool operator==(const TimeDuration& aOther) const {
+    return mValue == aOther.mValue;
+  }
+
+  // Return a best guess at the system's current timing resolution,
+  // which might be variable.  TimeDurations below this order of
+  // magnitude are meaningless, and those at the same order of
+  // magnitude or just above are suspect.
+  static TimeDuration Resolution();
+
+  // We could define additional operators here:
+  // -- convert to/from other time units
+  // -- scale duration by a float
+  // but let's do that on demand.
+  // Comparing durations for equality will only lead to bugs on
+  // platforms with high-resolution timers.
+
+private:
+  friend class TimeStamp;
+  friend struct IPC::ParamTraits<mozilla::TimeDuration>;
+
+  static TimeDuration FromTicks(int64_t aTicks) {
+    TimeDuration t;
+    t.mValue = aTicks;
+    return t;
+  }
+
+  static TimeDuration FromTicks(double aTicks) {
+    // NOTE: this MUST be a >= test, because int64_t(double(INT64_MAX))
+    // overflows and gives INT64_MIN.
+    if (aTicks >= double(INT64_MAX))
+      return TimeDuration::FromTicks(INT64_MAX);
+
+    // This MUST be a <= test.
+    if (aTicks <= double(INT64_MIN))
+      return TimeDuration::FromTicks(INT64_MIN);
+
+    return TimeDuration::FromTicks(int64_t(aTicks));
+  }
+
+  // Duration, result is implementation-specific difference of two TimeStamps
+  int64_t mValue;
+};
+
+/**
+ * Instances of this class represent moments in time, or a special
+ * "null" moment. We do not use the non-monotonic system clock or
+ * local time, since they can be reset, causing apparent backward
+ * travel in time, which can confuse algorithms. Instead we measure
+ * elapsed time according to the system.  This time can never go
+ * backwards (i.e. it never wraps around, at least not in less than
+ * five million years of system elapsed time). It might not advance
+ * while the system is sleeping. If TimeStamp::SetNow() is not called
+ * at all for hours or days, we might not notice the passage of some
+ * of that time.
+ * 
+ * We deliberately do not expose a way to convert TimeStamps to some
+ * particular unit. All you can do is compute a difference between two
+ * TimeStamps to get a TimeDuration. You can also add a TimeDuration
+ * to a TimeStamp to get a new TimeStamp. You can't do something
+ * meaningless like add two TimeStamps.
+ *
+ * Internally this is implemented as either a wrapper around
+ *   - high-resolution, monotonic, system clocks if they exist on this
+ *     platform
+ *   - PRIntervalTime otherwise.  We detect wraparounds of
+ *     PRIntervalTime and work around them.
+ *
+ * This class is similar to C++11's time_point, however it is
+ * explicitly nullable and provides an IsNull() method. time_point
+ * is initialized to the clock's epoch and provides a
+ * time_since_epoch() method that functions similiarly. i.e.
+ * t.IsNull() is equivalent to t.time_since_epoch() == decltype(t)::duration::zero();
+ */
+class TimeStamp
+{
+public:
+  /**
+   * Initialize to the "null" moment
+   */
+  MOZ_CONSTEXPR TimeStamp() : mValue(0) {}
+  // Default copy-constructor and assignment are OK
+
+  /**
+   * Return true if this is the "null" moment
+   */
+  bool IsNull() const { return mValue == 0; }
+  /**
+   * Return a timestamp reflecting the current elapsed system time. This
+   * is monotonically increasing (i.e., does not decrease) over the
+   * lifetime of this process' XPCOM session.
+   *
+   * Now() is trying to ensure the best possible precision on each platform,
+   * at least one millisecond.
+   *
+   * NowLoRes() has been introduced to workaround performance problems of
+   * QueryPerformanceCounter on the Windows platform.  NowLoRes() is giving
+   * lower precision, usually 15.6 ms, but with very good performance benefit.
+   * Use it for measurements of longer times, like >200ms timeouts.
+   */
+  static TimeStamp Now() { return Now(true); }
+  static TimeStamp NowLoRes() { return Now(false); }
+
+  /**
+   * Return a timestamp representing the time when the current process was
+   * created which will be comparable with other timestamps taken with this
+   * class. If the actual process creation time is detected to be inconsistent
+   * the @a aIsInconsistent parameter will be set to true, the returned
+   * timestamp however will still be valid though inaccurate.
+   *
+   * @param aIsInconsistent Set to true if an inconsistency was detected in the
+   * process creation time
+   * @returns A timestamp representing the time when the process was created,
+   * this timestamp is always valid even when errors are reported
+   */
+  static TimeStamp ProcessCreation(bool& aIsInconsistent);
+
+  /**
+   * Records a process restart. After this call ProcessCreation() will return
+   * the time when the browser was restarted instead of the actual time when
+   * the process was created.
+   */
+  static void RecordProcessRestart();
+
+  /**
+   * Compute the difference between two timestamps. Both must be non-null.
+   */
+  TimeDuration operator-(const TimeStamp& aOther) const {
+    MOZ_ASSERT(!IsNull(), "Cannot compute with a null value");
+    MOZ_ASSERT(!aOther.IsNull(), "Cannot compute with aOther null value");
+    static_assert(-INT64_MAX > INT64_MIN, "int64_t sanity check");
+    int64_t ticks = int64_t(mValue - aOther.mValue);
+    // Check for overflow.
+    if (mValue > aOther.mValue) {
+      if (ticks < 0) {
+        ticks = INT64_MAX;
+      }
+    } else {
+      if (ticks > 0) {
+        ticks = INT64_MIN;
+      }
+    }
+    return TimeDuration::FromTicks(ticks);
+  }
+
+  TimeStamp operator+(const TimeDuration& aOther) const {
+    MOZ_ASSERT(!IsNull(), "Cannot compute with a null value");
+    return TimeStamp(mValue + aOther.mValue);
+  }
+  TimeStamp operator-(const TimeDuration& aOther) const {
+    MOZ_ASSERT(!IsNull(), "Cannot compute with a null value");
+    return TimeStamp(mValue - aOther.mValue);
+  }
+  TimeStamp& operator+=(const TimeDuration& aOther) {
+    MOZ_ASSERT(!IsNull(), "Cannot compute with a null value");
+    mValue += aOther.mValue;
+    return *this;
+  }
+  TimeStamp& operator-=(const TimeDuration& aOther) {
+    MOZ_ASSERT(!IsNull(), "Cannot compute with a null value");
+    mValue -= aOther.mValue;
+    return *this;
+  }
+
+  bool operator<(const TimeStamp& aOther) const {
+    MOZ_ASSERT(!IsNull(), "Cannot compute with a null value");
+    MOZ_ASSERT(!aOther.IsNull(), "Cannot compute with aOther null value");
+    return mValue < aOther.mValue;
+  }
+  bool operator<=(const TimeStamp& aOther) const {
+    MOZ_ASSERT(!IsNull(), "Cannot compute with a null value");
+    MOZ_ASSERT(!aOther.IsNull(), "Cannot compute with aOther null value");
+    return mValue <= aOther.mValue;
+  }
+  bool operator>=(const TimeStamp& aOther) const {
+    MOZ_ASSERT(!IsNull(), "Cannot compute with a null value");
+    MOZ_ASSERT(!aOther.IsNull(), "Cannot compute with aOther null value");
+    return mValue >= aOther.mValue;
+  }
+  bool operator>(const TimeStamp& aOther) const {
+    MOZ_ASSERT(!IsNull(), "Cannot compute with a null value");
+    MOZ_ASSERT(!aOther.IsNull(), "Cannot compute with aOther null value");
+    return mValue > aOther.mValue;
+  }
+  bool operator==(const TimeStamp& aOther) const {
+    // Maybe it's ok to check == with null timestamps?
+    MOZ_ASSERT(!IsNull() && "Cannot compute with a null value");
+    MOZ_ASSERT(!aOther.IsNull(), "Cannot compute with aOther null value");
+    return mValue == aOther.mValue;
+  }
+  bool operator!=(const TimeStamp& aOther) const {
+    // Maybe it's ok to check != with null timestamps?
+    MOZ_ASSERT(!IsNull(), "Cannot compute with a null value");
+    MOZ_ASSERT(!aOther.IsNull(), "Cannot compute with aOther null value");
+    return mValue != aOther.mValue;
+  }
+
+  // Comparing TimeStamps for equality should be discouraged. Adding
+  // two TimeStamps, or scaling TimeStamps, is nonsense and must never
+  // be allowed.
+
+  static NS_HIDDEN_(nsresult) Startup();
+  static NS_HIDDEN_(void) Shutdown();
+
+private:
+  friend struct IPC::ParamTraits<mozilla::TimeStamp>;
+  friend void StartupTimelineRecordExternal(int, uint64_t);
+
+  TimeStamp(TimeStampValue aValue) : mValue(aValue) {}
+
+  static TimeStamp Now(bool aHighResolution);
+
+  /**
+   * Computes the uptime of the current process in microseconds. The result
+   * is platform-dependent and needs to be checked against existing timestamps
+   * for consistency.
+   *
+   * @returns The number of microseconds since the calling process was started
+   *          or 0 if an error was encountered while computing the uptime
+   */
+  static uint64_t ComputeProcessUptime();
+
+  /**
+   * When built with PRIntervalTime, a value of 0 means this instance
+   * is "null". Otherwise, the low 32 bits represent a PRIntervalTime,
+   * and the high 32 bits represent a counter of the number of
+   * rollovers of PRIntervalTime that we've seen. This counter starts
+   * at 1 to avoid a real time colliding with the "null" value.
+   * 
+   * PR_INTERVAL_MAX is set at 100,000 ticks per second. So the minimum
+   * time to wrap around is about 2^64/100000 seconds, i.e. about
+   * 5,849,424 years.
+   *
+   * When using a system clock, a value is system dependent.
+   */
+  TimeStampValue mValue;
+};
+
+}
+
+#endif /* mozilla_TimeStamp_h */