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The Tor Browser
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ProfileBufferIndex.h (4136B)

      1 /* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
      2 /* vim: set ts=8 sts=2 et sw=2 tw=80: */
      3 /* This Source Code Form is subject to the terms of the Mozilla Public
      4 * License, v. 2.0. If a copy of the MPL was not distributed with this
      5 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
      6 
      7 #ifndef ProfileBufferIndex_h
      8 #define ProfileBufferIndex_h
      9 
     10 #include "mozilla/Attributes.h"
     11 
     12 #include <cstddef>
     13 #include <cstdint>
     14 
     15 namespace mozilla {
     16 
     17 // Generic index into a Profiler buffer, mostly for internal usage.
     18 // Intended to appear infinite (it should effectively never wrap).
     19 // 0 (zero) is reserved as nullptr-like value; it may indicate failure result,
     20 // or it may point at the earliest available block.
     21 using ProfileBufferIndex = uint64_t;
     22 
     23 // Externally-opaque class encapsulating a block index, i.e. a
     24 // ProfileBufferIndex that is guaranteed to point at the start of a Profile
     25 // buffer block (until it is destroyed, but then that index cannot be reused and
     26 // functions should gracefully handle expired blocks).
     27 // Users may get these from Profile buffer functions, to later access previous
     28 // blocks; they should avoid converting and operating on their value.
     29 class ProfileBufferBlockIndex {
     30 public:
     31  // Default constructor with internal 0 value, for which Profile buffers must
     32  // guarantee that it is before any valid entries; All public APIs should
     33  // fail gracefully, doing and/or returning Nothing.
     34  ProfileBufferBlockIndex() : mBlockIndex(0) {}
     35 
     36  // Implicit conversion from literal `nullptr` to internal 0 value, to allow
     37  // convenient init/reset/comparison with 0 index.
     38  MOZ_IMPLICIT ProfileBufferBlockIndex(std::nullptr_t) : mBlockIndex(0) {}
     39 
     40  // Explicit conversion to bool, works in `if` and other tests.
     41  // Only returns false for default `ProfileBufferBlockIndex{}` value.
     42  explicit operator bool() const { return mBlockIndex != 0; }
     43 
     44  // Comparison operators. Default `ProfileBufferBlockIndex{}` value is always
     45  // the lowest.
     46  [[nodiscard]] bool operator==(const ProfileBufferBlockIndex& aRhs) const {
     47    return mBlockIndex == aRhs.mBlockIndex;
     48  }
     49  [[nodiscard]] bool operator!=(const ProfileBufferBlockIndex& aRhs) const {
     50    return mBlockIndex != aRhs.mBlockIndex;
     51  }
     52  [[nodiscard]] bool operator<(const ProfileBufferBlockIndex& aRhs) const {
     53    return mBlockIndex < aRhs.mBlockIndex;
     54  }
     55  [[nodiscard]] bool operator<=(const ProfileBufferBlockIndex& aRhs) const {
     56    return mBlockIndex <= aRhs.mBlockIndex;
     57  }
     58  [[nodiscard]] bool operator>(const ProfileBufferBlockIndex& aRhs) const {
     59    return mBlockIndex > aRhs.mBlockIndex;
     60  }
     61  [[nodiscard]] bool operator>=(const ProfileBufferBlockIndex& aRhs) const {
     62    return mBlockIndex >= aRhs.mBlockIndex;
     63  }
     64 
     65  // Explicit conversion to ProfileBufferIndex, mostly used by internal Profile
     66  // buffer code.
     67  [[nodiscard]] ProfileBufferIndex ConvertToProfileBufferIndex() const {
     68    return mBlockIndex;
     69  }
     70 
     71  // Explicit creation from ProfileBufferIndex, mostly used by internal
     72  // Profile buffer code.
     73  [[nodiscard]] static ProfileBufferBlockIndex CreateFromProfileBufferIndex(
     74      ProfileBufferIndex aIndex) {
     75    return ProfileBufferBlockIndex(aIndex);
     76  }
     77 
     78 private:
     79  // Private to prevent easy construction from any value. Use
     80  // `CreateFromProfileBufferIndex()` instead.
     81  // The main reason for this indirection is to make it harder to create these
     82  // objects, because only the profiler code should need to do it. Ideally, this
     83  // class should be used wherever a block index should be stored, but there is
     84  // so much code that uses `uint64_t` that it would be a big task to change
     85  // them all. So for now we allow conversions to/from numbers, but it's as ugly
     86  // as possible to make sure it doesn't get too common; and if one day we want
     87  // to tackle a global change, it should be easy to find all these locations
     88  // thanks to the explicit conversion functions.
     89  explicit ProfileBufferBlockIndex(ProfileBufferIndex aBlockIndex)
     90      : mBlockIndex(aBlockIndex) {}
     91 
     92  ProfileBufferIndex mBlockIndex;
     93 };
     94 
     95 }  // namespace mozilla
     96 
     97 #endif  // ProfileBufferIndex_h