mfbt/RangedPtr.h
author Boris Zbarsky <bzbarsky@mit.edu>
Wed, 24 Jun 2015 00:42:46 -0700
changeset 250045 4267b74ee795e8127ffce4d45d00384cd8170130
parent 227241 de42116d5ef3aa8a26c1a601675786faa9bb5179
child 254975 02f08045a3bc004fcd2849fcaca05a220eee72c4
permissions -rw-r--r--
Bug 1176083. Remove the now-dead code for the XPCOM version of setTimeout/setInterval. r=smaug I claim this code is dead because on the one hand it's no longer called from JS (because Window is always on WebIDL bindings, but on the other hand it can't really be called from C++ because it depends on examining the XPConnect call information. I think removing this completely, including from the IDL, is safe, because nothing directly returns nsIDOMJSWindow, so anyone using its vtable would have to QI to it and we're changing the IID.

/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* vim: set ts=8 sts=2 et sw=2 tw=80: */
/* 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/. */

/*
 * Implements a smart pointer asserted to remain within a range specified at
 * construction.
 */

#ifndef mozilla_RangedPtr_h
#define mozilla_RangedPtr_h

#include "mozilla/ArrayUtils.h"
#include "mozilla/Assertions.h"
#include "mozilla/Attributes.h"

#include <stdint.h>

namespace mozilla {

/*
 * RangedPtr is a smart pointer restricted to an address range specified at
 * creation.  The pointer (and any smart pointers derived from it) must remain
 * within the range [start, end] (inclusive of end to facilitate use as
 * sentinels).  Dereferencing or indexing into the pointer (or pointers derived
 * from it) must remain within the range [start, end).  All the standard pointer
 * operators are defined on it; in debug builds these operations assert that the
 * range specified at construction is respected.
 *
 * In theory passing a smart pointer instance as an argument can be slightly
 * slower than passing a T* (due to ABI requirements for passing structs versus
 * passing pointers), if the method being called isn't inlined.  If you are in
 * extremely performance-critical code, you may want to be careful using this
 * smart pointer as an argument type.
 *
 * RangedPtr<T> intentionally does not implicitly convert to T*.  Use get() to
 * explicitly convert to T*.  Keep in mind that the raw pointer of course won't
 * implement bounds checking in debug builds.
 */
template<typename T>
class RangedPtr
{
  T* mPtr;

#ifdef DEBUG
  T* const mRangeStart;
  T* const mRangeEnd;
#endif

  void checkSanity()
  {
    MOZ_ASSERT(mRangeStart <= mPtr);
    MOZ_ASSERT(mPtr <= mRangeEnd);
  }

  /* Creates a new pointer for |aPtr|, restricted to this pointer's range. */
  RangedPtr<T> create(T* aPtr) const
  {
#ifdef DEBUG
    return RangedPtr<T>(aPtr, mRangeStart, mRangeEnd);
#else
    return RangedPtr<T>(aPtr, nullptr, size_t(0));
#endif
  }

  uintptr_t asUintptr() const { return reinterpret_cast<uintptr_t>(mPtr); }

public:
  RangedPtr(T* aPtr, T* aStart, T* aEnd)
    : mPtr(aPtr)
#ifdef DEBUG
    , mRangeStart(aStart), mRangeEnd(aEnd)
#endif
  {
    MOZ_ASSERT(mRangeStart <= mRangeEnd);
    checkSanity();
  }
  RangedPtr(T* aPtr, T* aStart, size_t aLength)
    : mPtr(aPtr)
#ifdef DEBUG
    , mRangeStart(aStart), mRangeEnd(aStart + aLength)
#endif
  {
    MOZ_ASSERT(aLength <= size_t(-1) / sizeof(T));
    MOZ_ASSERT(reinterpret_cast<uintptr_t>(mRangeStart) + aLength * sizeof(T) >=
               reinterpret_cast<uintptr_t>(mRangeStart));
    checkSanity();
  }

  /* Equivalent to RangedPtr(aPtr, aPtr, aLength). */
  RangedPtr(T* aPtr, size_t aLength)
    : mPtr(aPtr)
#ifdef DEBUG
    , mRangeStart(aPtr), mRangeEnd(aPtr + aLength)
#endif
  {
    MOZ_ASSERT(aLength <= size_t(-1) / sizeof(T));
    MOZ_ASSERT(reinterpret_cast<uintptr_t>(mRangeStart) + aLength * sizeof(T) >=
               reinterpret_cast<uintptr_t>(mRangeStart));
    checkSanity();
  }

  /* Equivalent to RangedPtr(aArr, aArr, N). */
  template<size_t N>
  RangedPtr(T (&aArr)[N])
    : mPtr(aArr)
#ifdef DEBUG
    , mRangeStart(aArr), mRangeEnd(aArr + N)
#endif
  {
    checkSanity();
  }

  T* get() const { return mPtr; }

  explicit operator bool() const { return mPtr != nullptr; }

  /*
   * You can only assign one RangedPtr into another if the two pointers have
   * the same valid range:
   *
   *   char arr1[] = "hi";
   *   char arr2[] = "bye";
   *   RangedPtr<char> p1(arr1, 2);
   *   p1 = RangedPtr<char>(arr1 + 1, arr1, arr1 + 2); // works
   *   p1 = RangedPtr<char>(arr2, 3);                  // asserts
   */
  RangedPtr<T>& operator=(const RangedPtr<T>& aOther)
  {
    MOZ_ASSERT(mRangeStart == aOther.mRangeStart);
    MOZ_ASSERT(mRangeEnd == aOther.mRangeEnd);
    mPtr = aOther.mPtr;
    checkSanity();
    return *this;
  }

  RangedPtr<T> operator+(size_t aInc)
  {
    MOZ_ASSERT(aInc <= size_t(-1) / sizeof(T));
    MOZ_ASSERT(asUintptr() + aInc * sizeof(T) >= asUintptr());
    return create(mPtr + aInc);
  }

  RangedPtr<T> operator-(size_t aDec)
  {
    MOZ_ASSERT(aDec <= size_t(-1) / sizeof(T));
    MOZ_ASSERT(asUintptr() - aDec * sizeof(T) <= asUintptr());
    return create(mPtr - aDec);
  }

  /*
   * You can assign a raw pointer into a RangedPtr if the raw pointer is
   * within the range specified at creation.
   */
  template <typename U>
  RangedPtr<T>& operator=(U* aPtr)
  {
    *this = create(aPtr);
    return *this;
  }

  template <typename U>
  RangedPtr<T>& operator=(const RangedPtr<U>& aPtr)
  {
    MOZ_ASSERT(mRangeStart <= aPtr.mPtr);
    MOZ_ASSERT(aPtr.mPtr <= mRangeEnd);
    mPtr = aPtr.mPtr;
    checkSanity();
    return *this;
  }

  RangedPtr<T>& operator++()
  {
    return (*this += 1);
  }

  RangedPtr<T> operator++(int)
  {
    RangedPtr<T> rcp = *this;
    ++*this;
    return rcp;
  }

  RangedPtr<T>& operator--()
  {
    return (*this -= 1);
  }

  RangedPtr<T> operator--(int)
  {
    RangedPtr<T> rcp = *this;
    --*this;
    return rcp;
  }

  RangedPtr<T>& operator+=(size_t aInc)
  {
    *this = *this + aInc;
    return *this;
  }

  RangedPtr<T>& operator-=(size_t aDec)
  {
    *this = *this - aDec;
    return *this;
  }

  T& operator[](int aIndex) const
  {
    MOZ_ASSERT(size_t(aIndex > 0 ? aIndex : -aIndex) <= size_t(-1) / sizeof(T));
    return *create(mPtr + aIndex);
  }

  T& operator*() const
  {
    MOZ_ASSERT(mPtr >= mRangeStart);
    MOZ_ASSERT(mPtr < mRangeEnd);
    return *mPtr;
  }

  template <typename U>
  bool operator==(const RangedPtr<U>& aOther) const
  {
    return mPtr == aOther.mPtr;
  }
  template <typename U>
  bool operator!=(const RangedPtr<U>& aOther) const
  {
    return !(*this == aOther);
  }

  template<typename U>
  bool operator==(const U* u) const
  {
    return mPtr == u;
  }
  template<typename U>
  bool operator!=(const U* u) const
  {
    return !(*this == u);
  }

  template <typename U>
  bool operator<(const RangedPtr<U>& aOther) const
  {
    return mPtr < aOther.mPtr;
  }
  template <typename U>
  bool operator<=(const RangedPtr<U>& aOther) const
  {
    return mPtr <= aOther.mPtr;
  }

  template <typename U>
  bool operator>(const RangedPtr<U>& aOther) const
  {
    return mPtr > aOther.mPtr;
  }
  template <typename U>
  bool operator>=(const RangedPtr<U>& aOther) const
  {
    return mPtr >= aOther.mPtr;
  }

  size_t operator-(const RangedPtr<T>& aOther) const
  {
    MOZ_ASSERT(mPtr >= aOther.mPtr);
    return PointerRangeSize(aOther.mPtr, mPtr);
  }

private:
  RangedPtr() = delete;
  T* operator&() = delete;
};

} /* namespace mozilla */

#endif /* mozilla_RangedPtr_h */