content/common/inter_process_time_ticks_converter.h

   1 // Copyright (c) 2011 The Chromium 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 #ifndef CONTENT_COMMON_INTER_PROCESS_TIME_TICKS_CONVERTER_H_
   6 #define CONTENT_COMMON_INTER_PROCESS_TIME_TICKS_CONVERTER_H_
   7
   8 #include "base/time/time.h"
   9 #include "content/common/content_export.h"
  10
  11 namespace content {
  12
  13 class LocalTimeDelta;
  14 class LocalTimeTicks;
  15 class RemoteTimeDelta;
  16 class RemoteTimeTicks;
  17
  18 // On Windows, TimeTicks are not consistent between processes. Often, the values
  19 // on one process have a static offset relative to another. Occasionally, these
  20 // offsets shift while running.
  21 //
  22 // To combat this, any TimeTicks values sent from the remote process to the
  23 // local process must be tweaked in order to appear monotonic.
  24 //
  25 // In order to properly tweak ticks, we need 4 reference points:
  26 //
  27 // - |local_lower_bound|:  A known point, recorded on the local process, that
  28 //                         occurs before any remote values that will be
  29 //                         converted.
  30 // - |remote_lower_bound|: The equivalent point on the remote process. This
  31 //                         should be recorded immediately after
  32 //                         |local_lower_bound|.
  33 // - |local_upper_bound|:  A known point, recorded on the local process, that
  34 //                         occurs after any remote values that will be
  35 //                         converted.
  36 // - |remote_upper_bound|: The equivalent point on the remote process. This
  37 //                         should be recorded immediately before
  38 //                         |local_upper_bound|.
  39 //
  40 // Once these bounds are determined, values within the remote process's range
  41 // can be converted to the local process's range. The values are converted as
  42 // follows:
  43 //
  44 // 1. If the remote's range exceeds the local's range, it is scaled to fit.
  45 //    Any values converted will have the same scale factor applied.
  46 //
  47 // 2. The remote's range is shifted so that it is centered within the
  48 //    local's range. Any values converted will be shifted the same amount.
  49 class CONTENT_EXPORT InterProcessTimeTicksConverter {
  50  public:
  51   InterProcessTimeTicksConverter(const LocalTimeTicks& local_lower_bound,
  52                                  const LocalTimeTicks& local_upper_bound,
  53                                  const RemoteTimeTicks& remote_lower_bound,
  54                                  const RemoteTimeTicks& remote_upper_bound);
  55
  56   // Returns the value within the local's bounds that correlates to
  57   // |remote_ms|.
  58   LocalTimeTicks ToLocalTimeTicks(const RemoteTimeTicks& remote_ms) const;
  59
  60   // Returns the equivalent delta after applying remote-to-local scaling to
  61   // |remote_delta|.
  62   LocalTimeDelta ToLocalTimeDelta(const RemoteTimeDelta& remote_delta) const;
  63
  64  private:
  65   int64 Convert(int64 value) const;
  66
  67   // The local time which |remote_lower_bound_| is mapped to.
  68   int64 local_base_time_;
  69
  70   int64 numerator_;
  71   int64 denominator_;
  72
  73   int64 remote_lower_bound_;
  74   int64 remote_upper_bound_;
  75 };
  76
  77 class CONTENT_EXPORT LocalTimeDelta {
  78  public:
  79   int ToInt32() const { return value_; }
  80
  81  private:
  82   friend class InterProcessTimeTicksConverter;
  83   friend class LocalTimeTicks;
  84
  85   LocalTimeDelta(int value) : value_(value) {}
  86
  87   int value_;
  88 };
  89
  90 class CONTENT_EXPORT LocalTimeTicks {
  91  public:
  92   static LocalTimeTicks FromTimeTicks(const base::TimeTicks& value) {
  93     return LocalTimeTicks(value.ToInternalValue());
  94   }
  95
  96   base::TimeTicks ToTimeTicks() {
  97     return base::TimeTicks::FromInternalValue(value_);
  98   }
  99
 100   LocalTimeTicks operator+(const LocalTimeDelta& delta) {
 101     return LocalTimeTicks(value_ + delta.value_);
 102   }
 103
 104  private:
 105   friend class InterProcessTimeTicksConverter;
 106
 107   LocalTimeTicks(int64 value) : value_(value) {}
 108
 109   int64 value_;
 110 };
 111
 112 class CONTENT_EXPORT RemoteTimeDelta {
 113  public:
 114   static RemoteTimeDelta FromRawDelta(int delta) {
 115     return RemoteTimeDelta(delta);
 116   }
 117
 118  private:
 119   friend class InterProcessTimeTicksConverter;
 120   friend class RemoteTimeTicks;
 121
 122   RemoteTimeDelta(int value) : value_(value) {}
 123
 124   int value_;
 125 };
 126
 127 class CONTENT_EXPORT RemoteTimeTicks {
 128  public:
 129   static RemoteTimeTicks FromTimeTicks(const base::TimeTicks& ticks) {
 130     return RemoteTimeTicks(ticks.ToInternalValue());
 131   }
 132
 133   RemoteTimeDelta operator-(const RemoteTimeTicks& rhs) const {
 134     return RemoteTimeDelta(value_ - rhs.value_);
 135   }
 136
 137  private:
 138   friend class InterProcessTimeTicksConverter;
 139
 140   RemoteTimeTicks(int64 value) : value_(value) {}
 141
 142   int64 value_;
 143 };
 144
 145 }  // namespace content
 146
 147 #endif  // CONTENT_COMMON_INTER_PROCESS_TIME_TICKS_CONVERTER_H_