The Tor Browser: xpcom/glue/nsTArray.h@97036ab72558 (annotated)

xpcom/glue/nsTArray.h@97036ab72558 (annotated)

xpcom/glue/nsTArray.h

Tue, 06 Jan 2015 21:39:09 +0100

author: Michael Schloh von Bennewitz <michael@schloh.com>
date: Tue, 06 Jan 2015 21:39:09 +0100
branch: TOR_BUG_9701
changeset 8: 97036ab72558
permissions: -rw-r--r--

Conditionally force memory storage according to privacy.thirdparty.isolate;
This solves Tor bug #9701, complying with disk avoidance documented in
https://www.torproject.org/projects/torbrowser/design/#disk-avoidance.

 /* -*- 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 nsTArray_h__
 #define nsTArray_h__
 #include "nsTArrayForwardDeclare.h"
 #include "mozilla/Alignment.h"
 #include "mozilla/Assertions.h"
 #include "mozilla/MemoryReporting.h"
 #include "mozilla/TypeTraits.h"
 #include <string.h>
 #include "nsCycleCollectionNoteChild.h"
 #include "nsAlgorithm.h"
 #include "nscore.h"
 #include "nsQuickSort.h"
 #include "nsDebug.h"
 #include "nsISupportsImpl.h"
 #include <new>
 namespace JS {
 template <class T>
 class Heap;
 } /* namespace JS */
 class nsRegion;
 class nsIntRegion;
 //
 // nsTArray is a resizable array class, like std::vector.
 //
 // Unlike std::vector, which follows C++'s construction/destruction rules,
 // nsTArray assumes that your "T" can be memmoved()'ed safely.
 //
 // The public classes defined in this header are
 //
 //   nsTArray<T>,
 //   FallibleTArray<T>,
 //   nsAutoTArray<T, N>, and
 //   AutoFallibleTArray<T, N>.
 //
 // nsTArray and nsAutoTArray are infallible; if one tries to make an allocation
 // which fails, it crashes the program.  In contrast, FallibleTArray and
 // AutoFallibleTArray are fallible; if you use one of these classes, you must
 // check the return values of methods such as Append() which may allocate.  If
 // in doubt, choose an infallible type.
 //
 // InfallibleTArray and AutoInfallibleTArray are aliases for nsTArray and
 // nsAutoTArray.
 //
 // If you just want to declare the nsTArray types (e.g., if you're in a header
 // file and don't need the full nsTArray definitions) consider including
 // nsTArrayForwardDeclare.h instead of nsTArray.h.
 //
 // The template parameter (i.e., T in nsTArray<T>) specifies the type of the
 // elements and has the following requirements:
 //
 //   T MUST be safely memmove()'able.
 //   T MUST define a copy-constructor.
 //   T MAY define operator< for sorting.
 //   T MAY define operator== for searching.
 //
 // (Note that the memmove requirement may be relaxed for certain types - see
 // nsTArray_CopyChooser below.)
 //
 // For methods taking a Comparator instance, the Comparator must be a class
 // defining the following methods:
 //
 //   class Comparator {
 //     public:
 //       /** @return True if the elements are equals; false otherwise. */
 //       bool Equals(const elem_type& a, const Item& b) const;
 //
 //       /** @return True if (a < b); false otherwise. */
 //       bool LessThan(const elem_type& a, const Item& b) const;
 //   };
 //
 // The Equals method is used for searching, and the LessThan method is used for
 // searching and sorting.  The |Item| type above can be arbitrary, but must
 // match the Item type passed to the sort or search function.
 //
 //
 // nsTArrayFallibleResult and nsTArrayInfallibleResult types are proxy types
 // which are used because you cannot use a templated type which is bound to
 // void as an argument to a void function.  In order to work around that, we
 // encode either a void or a boolean inside these proxy objects, and pass them
 // to the aforementioned function instead, and then use the type information to
 // decide what to do in the function.
 //
 // Note that public nsTArray methods should never return a proxy type.  Such
 // types are only meant to be used in the internal nsTArray helper methods.
 // Public methods returning non-proxy types cannot be called from other
 // nsTArray members.
 //
 struct nsTArrayFallibleResult
 {
   // Note: allows implicit conversions from and to bool
   nsTArrayFallibleResult(bool result)
     : mResult(result)
   {}
   operator bool() {
     return mResult;
   }
 private:
   bool mResult;
 };
 struct nsTArrayInfallibleResult
 {
 };
 //
 // nsTArray*Allocators must all use the same |free()|, to allow swap()'ing
 // between fallible and infallible variants.
 //
 struct nsTArrayFallibleAllocatorBase
 {
   typedef bool ResultType;
   typedef nsTArrayFallibleResult ResultTypeProxy;
   static ResultType Result(ResultTypeProxy result) {
     return result;
   }
   static bool Successful(ResultTypeProxy result) {
     return result;
   }
   static ResultTypeProxy SuccessResult() {
     return true;
   }
   static ResultTypeProxy FailureResult() {
     return false;
   }
   static ResultType ConvertBoolToResultType(bool aValue) {
     return aValue;
   }
 };
 struct nsTArrayInfallibleAllocatorBase
 {
   typedef void ResultType;
   typedef nsTArrayInfallibleResult ResultTypeProxy;
   static ResultType Result(ResultTypeProxy result) {
   }
   static bool Successful(ResultTypeProxy) {
     return true;
   }
   static ResultTypeProxy SuccessResult() {
     return ResultTypeProxy();
   }
   static ResultTypeProxy FailureResult() {
     NS_RUNTIMEABORT("Infallible nsTArray should never fail");
     return ResultTypeProxy();
   }
   static ResultType ConvertBoolToResultType(bool aValue) {
     if (!aValue) {
       NS_RUNTIMEABORT("infallible nsTArray should never convert false to ResultType");
     }
   }
 };
 #if defined(MOZALLOC_HAVE_XMALLOC)
 #include "mozilla/mozalloc_abort.h"
 struct nsTArrayFallibleAllocator : nsTArrayFallibleAllocatorBase
 {
   static void* Malloc(size_t size) {
     return moz_malloc(size);
   }
   static void* Realloc(void* ptr, size_t size) {
     return moz_realloc(ptr, size);
   }
   static void Free(void* ptr) {
     moz_free(ptr);
   }
   static void SizeTooBig(size_t) {
   }
 };
 struct nsTArrayInfallibleAllocator : nsTArrayInfallibleAllocatorBase
 {
   static void* Malloc(size_t size) {
     return moz_xmalloc(size);
   }
   static void* Realloc(void* ptr, size_t size) {
     return moz_xrealloc(ptr, size);
   }
   static void Free(void* ptr) {
     moz_free(ptr);
   }
   static void SizeTooBig(size_t size) {
     NS_ABORT_OOM(size);
   }
 };
 #else
 #include <stdlib.h>
 struct nsTArrayFallibleAllocator : nsTArrayFallibleAllocatorBase
 {
   static void* Malloc(size_t size) {
     return malloc(size);
   }
   static void* Realloc(void* ptr, size_t size) {
     return realloc(ptr, size);
   }
   static void Free(void* ptr) {
     free(ptr);
   }
   static void SizeTooBig(size_t) {
   }
 };
 struct nsTArrayInfallibleAllocator : nsTArrayInfallibleAllocatorBase
 {
   static void* Malloc(size_t size) {
     void* ptr = malloc(size);
     if (MOZ_UNLIKELY(!ptr)) {
       NS_ABORT_OOM(size);
     }
     return ptr;
   }
   static void* Realloc(void* ptr, size_t size) {
     void* newptr = realloc(ptr, size);
     if (MOZ_UNLIKELY(!ptr && size)) {
       NS_ABORT_OOM(size);
     }
     return newptr;
   }
   static void Free(void* ptr) {
     free(ptr);
   }
   static void SizeTooBig(size_t size) {
     NS_ABORT_OOM(size);
   }
 };
 #endif
 // nsTArray_base stores elements into the space allocated beyond
 // sizeof(*this).  This is done to minimize the size of the nsTArray
 // object when it is empty.
 struct NS_COM_GLUE nsTArrayHeader
 {
   static nsTArrayHeader sEmptyHdr;
   uint32_t mLength;
   uint32_t mCapacity : 31;
   uint32_t mIsAutoArray : 1;
 };
 // This class provides a SafeElementAt method to nsTArray<T*> which does
 // not take a second default value parameter.
 template <class E, class Derived>
 struct nsTArray_SafeElementAtHelper
 {
   typedef E*       elem_type;
   typedef uint32_t index_type;
   // No implementation is provided for these two methods, and that is on
   // purpose, since we don't support these functions on non-pointer type
   // instantiations.
   elem_type& SafeElementAt(index_type i);
   const elem_type& SafeElementAt(index_type i) const;
 };
 template <class E, class Derived>
 struct nsTArray_SafeElementAtHelper<E*, Derived>
 {
   typedef E*       elem_type;
   typedef uint32_t index_type;
   elem_type SafeElementAt(index_type i) {
     return static_cast<Derived*> (this)->SafeElementAt(i, nullptr);
   }
   const elem_type SafeElementAt(index_type i) const {
     return static_cast<const Derived*> (this)->SafeElementAt(i, nullptr);
   }
 };
 // E is the base type that the smart pointer is templated over; the
 // smart pointer can act as E*.
 template <class E, class Derived>
 struct nsTArray_SafeElementAtSmartPtrHelper
 {
   typedef E*       elem_type;
   typedef uint32_t index_type;
   elem_type SafeElementAt(index_type i) {
     return static_cast<Derived*> (this)->SafeElementAt(i, nullptr);
   }
   const elem_type SafeElementAt(index_type i) const {
     return static_cast<const Derived*> (this)->SafeElementAt(i, nullptr);
   }
 };
 template <class T> class nsCOMPtr;
 template <class E, class Derived>
 struct nsTArray_SafeElementAtHelper<nsCOMPtr<E>, Derived> :
   public nsTArray_SafeElementAtSmartPtrHelper<E, Derived>
 {
 };
 template <class T> class nsRefPtr;
 template <class E, class Derived>
 struct nsTArray_SafeElementAtHelper<nsRefPtr<E>, Derived> :
   public nsTArray_SafeElementAtSmartPtrHelper<E, Derived>
 {
 };
 //
 // This class serves as a base class for nsTArray.  It shouldn't be used
 // directly.  It holds common implementation code that does not depend on the
 // element type of the nsTArray.
 //
 template<class Alloc, class Copy>
 class nsTArray_base
 {
   // Allow swapping elements with |nsTArray_base|s created using a
   // different allocator.  This is kosher because all allocators use
   // the same free().
   template<class Allocator, class Copier>
   friend class nsTArray_base;
 protected:
   typedef nsTArrayHeader Header;
 public:
   typedef uint32_t size_type;
   typedef uint32_t index_type;
   // @return The number of elements in the array.
   size_type Length() const {
     return mHdr->mLength;
   }
   // @return True if the array is empty or false otherwise.
   bool IsEmpty() const {
     return Length() == 0;
   }
   // @return The number of elements that can fit in the array without forcing
   // the array to be re-allocated.  The length of an array is always less
   // than or equal to its capacity.
   size_type Capacity() const {
     return mHdr->mCapacity;
   }
 #ifdef DEBUG
   void* DebugGetHeader() const {
     return mHdr;
   }
 #endif
 protected:
   nsTArray_base();
   ~nsTArray_base();
   // Resize the storage if necessary to achieve the requested capacity.
   // @param capacity     The requested number of array elements.
   // @param elemSize     The size of an array element.
   // @return False if insufficient memory is available; true otherwise.
   typename Alloc::ResultTypeProxy EnsureCapacity(size_type capacity, size_type elemSize);
   // Resize the storage to the minimum required amount.
   // @param elemSize     The size of an array element.
   // @param elemAlign    The alignment in bytes of an array element.
   void ShrinkCapacity(size_type elemSize, size_t elemAlign);
   // This method may be called to resize a "gap" in the array by shifting
   // elements around.  It updates mLength appropriately.  If the resulting
   // array has zero elements, then the array's memory is free'd.
   // @param start        The starting index of the gap.
   // @param oldLen       The current length of the gap.
   // @param newLen       The desired length of the gap.
   // @param elemSize     The size of an array element.
   // @param elemAlign    The alignment in bytes of an array element.
   void ShiftData(index_type start, size_type oldLen, size_type newLen,
                  size_type elemSize, size_t elemAlign);
   // This method increments the length member of the array's header.
   // Note that mHdr may actually be sEmptyHdr in the case where a
   // zero-length array is inserted into our array. But then n should
   // always be 0.
   void IncrementLength(uint32_t n) {
     if (mHdr == EmptyHdr()) {
       if (MOZ_UNLIKELY(n != 0)) {
         // Writing a non-zero length to the empty header would be extremely bad.
         MOZ_CRASH();
       }
     } else {
       mHdr->mLength += n;
     }
   }
   // This method inserts blank slots into the array.
   // @param index the place to insert the new elements. This must be no
   //              greater than the current length of the array.
   // @param count the number of slots to insert
   // @param elementSize the size of an array element.
   // @param elemAlign the alignment in bytes of an array element.
   bool InsertSlotsAt(index_type index, size_type count,
                        size_type elementSize, size_t elemAlign);
 protected:
   template<class Allocator>
   typename Alloc::ResultTypeProxy
   SwapArrayElements(nsTArray_base<Allocator, Copy>& other,
                     size_type elemSize,
                     size_t elemAlign);
   // This is an RAII class used in SwapArrayElements.
   class IsAutoArrayRestorer {
     public:
       IsAutoArrayRestorer(nsTArray_base<Alloc, Copy> &array, size_t elemAlign);
       ~IsAutoArrayRestorer();
     private:
       nsTArray_base<Alloc, Copy> &mArray;
       size_t mElemAlign;
       bool mIsAuto;
   };
   // Helper function for SwapArrayElements. Ensures that if the array
   // is an nsAutoTArray that it doesn't use the built-in buffer.
   bool EnsureNotUsingAutoArrayBuffer(size_type elemSize);
   // Returns true if this nsTArray is an nsAutoTArray with a built-in buffer.
   bool IsAutoArray() const {
     return mHdr->mIsAutoArray;
   }
   // Returns a Header for the built-in buffer of this nsAutoTArray.
   Header* GetAutoArrayBuffer(size_t elemAlign) {
     MOZ_ASSERT(IsAutoArray(), "Should be an auto array to call this");
     return GetAutoArrayBufferUnsafe(elemAlign);
   }
   const Header* GetAutoArrayBuffer(size_t elemAlign) const {
     MOZ_ASSERT(IsAutoArray(), "Should be an auto array to call this");
     return GetAutoArrayBufferUnsafe(elemAlign);
   }
   // Returns a Header for the built-in buffer of this nsAutoTArray, but doesn't
   // assert that we are an nsAutoTArray.
   Header* GetAutoArrayBufferUnsafe(size_t elemAlign) {
     return const_cast<Header*>(static_cast<const nsTArray_base<Alloc, Copy>*>(this)->
                                GetAutoArrayBufferUnsafe(elemAlign));
   }
   const Header* GetAutoArrayBufferUnsafe(size_t elemAlign) const;
   // Returns true if this is an nsAutoTArray and it currently uses the
   // built-in buffer to store its elements.
   bool UsesAutoArrayBuffer() const;
   // The array's elements (prefixed with a Header).  This pointer is never
   // null.  If the array is empty, then this will point to sEmptyHdr.
   Header *mHdr;
   Header* Hdr() const {
     return mHdr;
   }
   Header** PtrToHdr() {
     return &mHdr;
   }
   static Header* EmptyHdr() {
     return &Header::sEmptyHdr;
   }
 };
 //
 // This class defines convenience functions for element specific operations.
 // Specialize this template if necessary.
 //
 template<class E>
 class nsTArrayElementTraits
 {
 public:
   // Invoke the default constructor in place.
   static inline void Construct(E *e) {
     // Do NOT call "E()"! That triggers C++ "default initialization"
     // which zeroes out POD ("plain old data") types such as regular
     // ints.  We don't want that because it can be a performance issue
     // and people don't expect it; nsTArray should work like a regular
     // C/C++ array in this respect.
     new (static_cast<void *>(e)) E;
   }
   // Invoke the copy-constructor in place.
   template<class A>
   static inline void Construct(E *e, const A &arg) {
     typedef typename mozilla::RemoveCV<E>::Type E_NoCV;
     typedef typename mozilla::RemoveCV<A>::Type A_NoCV;
     static_assert(!mozilla::IsSame<E_NoCV*, A_NoCV>::value,
                   "For safety, we disallow constructing nsTArray<E> elements "
                   "from E* pointers. See bug 960591.");
     new (static_cast<void *>(e)) E(arg);
   }
   // Invoke the destructor in place.
   static inline void Destruct(E *e) {
     e->~E();
   }
 };
 // The default comparator used by nsTArray
 template<class A, class B>
 class nsDefaultComparator
 {
 public:
   bool Equals(const A& a, const B& b) const {
     return a == b;
   }
   bool LessThan(const A& a, const B& b) const {
     return a < b;
   }
 };
 template <class E> class InfallibleTArray;
 template <class E> class FallibleTArray;
 template<bool IsPod, bool IsSameType>
 struct AssignRangeAlgorithm {
   template<class Item, class ElemType, class IndexType, class SizeType>
   static void implementation(ElemType* elements, IndexType start,
                              SizeType count, const Item *values) {
     ElemType *iter = elements + start, *end = iter + count;
     for (; iter != end; ++iter, ++values)
       nsTArrayElementTraits<ElemType>::Construct(iter, *values);
   }
 };
 template<>
 struct AssignRangeAlgorithm<true, true> {
   template<class Item, class ElemType, class IndexType, class SizeType>
   static void implementation(ElemType* elements, IndexType start,
                              SizeType count, const Item *values) {
     memcpy(elements + start, values, count * sizeof(ElemType));
   }
 };
 //
 // Normally elements are copied with memcpy and memmove, but for some element
 // types that is problematic.  The nsTArray_CopyChooser template class can be
 // specialized to ensure that copying calls constructors and destructors
 // instead, as is done below for JS::Heap<E> elements.
 //
 //
 // A class that defines how to copy elements using memcpy/memmove.
 //
 struct nsTArray_CopyWithMemutils
 {
   const static bool allowRealloc = true;
   static void CopyElements(void* dest, const void* src, size_t count, size_t elemSize) {
     memcpy(dest, src, count * elemSize);
   }
   static void CopyHeaderAndElements(void* dest, const void* src, size_t count, size_t elemSize) {
     memcpy(dest, src, sizeof(nsTArrayHeader) + count * elemSize);
   }
   static void MoveElements(void* dest, const void* src, size_t count, size_t elemSize) {
     memmove(dest, src, count * elemSize);
   }
 };
 //
 // A template class that defines how to copy elements calling their constructors
 // and destructors appropriately.
 //
 template <class ElemType>
 struct nsTArray_CopyWithConstructors
 {
   typedef nsTArrayElementTraits<ElemType> traits;
   const static bool allowRealloc = false;
   static void CopyElements(void* dest, void* src, size_t count, size_t elemSize) {
     ElemType* destElem = static_cast<ElemType*>(dest);
     ElemType* srcElem = static_cast<ElemType*>(src);
     ElemType* destElemEnd = destElem + count;
 #ifdef DEBUG
     ElemType* srcElemEnd = srcElem + count;
     MOZ_ASSERT(srcElemEnd <= destElem || srcElemEnd > destElemEnd);
 #endif
     while (destElem != destElemEnd) {
       traits::Construct(destElem, *srcElem);
       traits::Destruct(srcElem);
       ++destElem;
       ++srcElem;
     }
   }
   static void CopyHeaderAndElements(void* dest, void* src, size_t count, size_t elemSize) {
     nsTArrayHeader* destHeader = static_cast<nsTArrayHeader*>(dest);
     nsTArrayHeader* srcHeader = static_cast<nsTArrayHeader*>(src);
     *destHeader = *srcHeader;
     CopyElements(static_cast<uint8_t*>(dest) + sizeof(nsTArrayHeader),
                  static_cast<uint8_t*>(src) + sizeof(nsTArrayHeader),
                  count, elemSize);
   }
   static void MoveElements(void* dest, void* src, size_t count, size_t elemSize) {
     ElemType* destElem = static_cast<ElemType*>(dest);
     ElemType* srcElem = static_cast<ElemType*>(src);
     ElemType* destElemEnd = destElem + count;
     ElemType* srcElemEnd = srcElem + count;
     if (destElem == srcElem) {
       return;  // In practice, we don't do this.
     } else if (srcElemEnd > destElem && srcElemEnd < destElemEnd) {
       while (destElemEnd != destElem) {
         --destElemEnd;
         --srcElemEnd;
         traits::Construct(destElemEnd, *srcElemEnd);
         traits::Destruct(srcElem);
       }
     } else {
       CopyElements(dest, src, count, elemSize);
     }
   }
 };
 //
 // The default behaviour is to use memcpy/memmove for everything.
 //
 template <class E>
 struct nsTArray_CopyChooser {
   typedef nsTArray_CopyWithMemutils Type;
 };
 //
 // Some classes require constructors/destructors to be called, so they are
 // specialized here.
 //
 template <class E>
 struct nsTArray_CopyChooser<JS::Heap<E> > {
   typedef nsTArray_CopyWithConstructors<JS::Heap<E> > Type;
 };
 template<>
 struct nsTArray_CopyChooser<nsRegion> {
   typedef nsTArray_CopyWithConstructors<nsRegion> Type;
 };
 template<>
 struct nsTArray_CopyChooser<nsIntRegion> {
   typedef nsTArray_CopyWithConstructors<nsIntRegion> Type;
 };
 //
 // Base class for nsTArray_Impl that is templated on element type and derived
 // nsTArray_Impl class, to allow extra conversions to be added for specific
 // types.
 //
 template <class E, class Derived>
 struct nsTArray_TypedBase : public nsTArray_SafeElementAtHelper<E, Derived> {};
 //
 // Specialization of nsTArray_TypedBase for arrays containing JS::Heap<E>
 // elements.
 //
 // These conversions are safe because JS::Heap<E> and E share the same
 // representation, and since the result of the conversions are const references
 // we won't miss any barriers.
 //
 // The static_cast is necessary to obtain the correct address for the derived
 // class since we are a base class used in multiple inheritance.
 //
 template <class E, class Derived>
 struct nsTArray_TypedBase<JS::Heap<E>, Derived>
  : public nsTArray_SafeElementAtHelper<JS::Heap<E>, Derived>
 {
   operator const nsTArray<E>& () {
     static_assert(sizeof(E) == sizeof(JS::Heap<E>),
                   "JS::Heap<E> must be binary compatible with E.");
     Derived* self = static_cast<Derived*>(this);
     return *reinterpret_cast<nsTArray<E> *>(self);
   }
   operator const FallibleTArray<E>& () {
     Derived* self = static_cast<Derived*>(this);
     return *reinterpret_cast<FallibleTArray<E> *>(self);
   }
 };
 //
 // nsTArray_Impl contains most of the guts supporting nsTArray, FallibleTArray,
 // nsAutoTArray, and AutoFallibleTArray.
 //
 // The only situation in which you might need to use nsTArray_Impl in your code
 // is if you're writing code which mutates a TArray which may or may not be
 // infallible.
 //
 // Code which merely reads from a TArray which may or may not be infallible can
 // simply cast the TArray to |const nsTArray&|; both fallible and infallible
 // TArrays can be cast to |const nsTArray&|.
 //
 template<class E, class Alloc>
 class nsTArray_Impl : public nsTArray_base<Alloc, typename nsTArray_CopyChooser<E>::Type>,
                       public nsTArray_TypedBase<E, nsTArray_Impl<E, Alloc> >
 {
 public:
   typedef typename nsTArray_CopyChooser<E>::Type     copy_type;
   typedef nsTArray_base<Alloc, copy_type>            base_type;
   typedef typename base_type::size_type              size_type;
   typedef typename base_type::index_type             index_type;
   typedef E                                          elem_type;
   typedef nsTArray_Impl<E, Alloc>                    self_type;
   typedef nsTArrayElementTraits<E>                   elem_traits;
   typedef nsTArray_SafeElementAtHelper<E, self_type> safeelementat_helper_type;
   using safeelementat_helper_type::SafeElementAt;
   using base_type::EmptyHdr;
   // A special value that is used to indicate an invalid or unknown index
   // into the array.
   enum {
     NoIndex = index_type(-1)
   };
   using base_type::Length;
   //
   // Finalization method
   //
   ~nsTArray_Impl() { Clear(); }
   //
   // Initialization methods
   //
   nsTArray_Impl() {}
   // Initialize this array and pre-allocate some number of elements.
   explicit nsTArray_Impl(size_type capacity) {
     SetCapacity(capacity);
   }
   // The array's copy-constructor performs a 'deep' copy of the given array.
   // @param other  The array object to copy.
   //
   // It's very important that we declare this method as taking |const
   // self_type&| as opposed to taking |const nsTArray_Impl<E, OtherAlloc>| for
   // an arbitrary OtherAlloc.
   //
   // If we don't declare a constructor taking |const self_type&|, C++ generates
   // a copy-constructor for this class which merely copies the object's
   // members, which is obviously wrong.
   //
   // You can pass an nsTArray_Impl<E, OtherAlloc> to this method because
   // nsTArray_Impl<E, X> can be cast to const nsTArray_Impl<E, Y>&.  So the
   // effect on the API is the same as if we'd declared this method as taking
   // |const nsTArray_Impl<E, OtherAlloc>&|.
   explicit nsTArray_Impl(const self_type& other) {
     AppendElements(other);
   }
   // Allow converting to a const array with a different kind of allocator,
   // Since the allocator doesn't matter for const arrays
   template<typename Allocator>
   operator const nsTArray_Impl<E, Allocator>&() const {
     return *reinterpret_cast<const nsTArray_Impl<E, Allocator>*>(this);
   }
   // And we have to do this for our subclasses too
   operator const nsTArray<E>&() const {
     return *reinterpret_cast<const InfallibleTArray<E>*>(this);
   }
   operator const FallibleTArray<E>&() const {
     return *reinterpret_cast<const FallibleTArray<E>*>(this);
   }
   // The array's assignment operator performs a 'deep' copy of the given
   // array.  It is optimized to reuse existing storage if possible.
   // @param other  The array object to copy.
   self_type& operator=(const self_type& other) {
     ReplaceElementsAt(0, Length(), other.Elements(), other.Length());
     return *this;
   }
   // Return true if this array has the same length and the same
   // elements as |other|.
   template<typename Allocator>
   bool operator==(const nsTArray_Impl<E, Allocator>& other) const {
     size_type len = Length();
     if (len != other.Length())
       return false;
     // XXX std::equal would be as fast or faster here
     for (index_type i = 0; i < len; ++i)
       if (!(operator[](i) == other[i]))
         return false;
     return true;
   }
   // Return true if this array does not have the same length and the same
   // elements as |other|.
   bool operator!=(const self_type& other) const {
     return !operator==(other);
   }
   template<typename Allocator>
   self_type& operator=(const nsTArray_Impl<E, Allocator>& other) {
     ReplaceElementsAt(0, Length(), other.Elements(), other.Length());
     return *this;
   }
   // @return The amount of memory used by this nsTArray_Impl, excluding
   // sizeof(*this).
   size_t SizeOfExcludingThis(mozilla::MallocSizeOf mallocSizeOf) const {
     if (this->UsesAutoArrayBuffer() || Hdr() == EmptyHdr())
       return 0;
     return mallocSizeOf(this->Hdr());
   }
   // @return The amount of memory used by this nsTArray_Impl, including
   // sizeof(*this).
   size_t SizeOfIncludingThis(mozilla::MallocSizeOf mallocSizeOf) const {
     return mallocSizeOf(this) + SizeOfExcludingThis(mallocSizeOf);
   }
   //
   // Accessor methods
   //
   // This method provides direct access to the array elements.
   // @return A pointer to the first element of the array.  If the array is
   // empty, then this pointer must not be dereferenced.
   elem_type* Elements() {
     return reinterpret_cast<elem_type *>(Hdr() + 1);
   }
   // This method provides direct, readonly access to the array elements.
   // @return A pointer to the first element of the array.  If the array is
   // empty, then this pointer must not be dereferenced.
   const elem_type* Elements() const {
     return reinterpret_cast<const elem_type *>(Hdr() + 1);
   }
   // This method provides direct access to the i'th element of the array.
   // The given index must be within the array bounds.
   // @param i  The index of an element in the array.
   // @return   A reference to the i'th element of the array.
   elem_type& ElementAt(index_type i) {
     MOZ_ASSERT(i < Length(), "invalid array index");
     return Elements()[i];
   }
   // This method provides direct, readonly access to the i'th element of the
   // array.  The given index must be within the array bounds.
   // @param i  The index of an element in the array.
   // @return   A const reference to the i'th element of the array.
   const elem_type& ElementAt(index_type i) const {
     MOZ_ASSERT(i < Length(), "invalid array index");
     return Elements()[i];
   }
   // This method provides direct access to the i'th element of the array in
   // a bounds safe manner. If the requested index is out of bounds the
   // provided default value is returned.
   // @param i  The index of an element in the array.
   // @param def The value to return if the index is out of bounds.
   elem_type& SafeElementAt(index_type i, elem_type& def) {
     return i < Length() ? Elements()[i] : def;
   }
   // This method provides direct access to the i'th element of the array in
   // a bounds safe manner. If the requested index is out of bounds the
   // provided default value is returned.
   // @param i  The index of an element in the array.
   // @param def The value to return if the index is out of bounds.
   const elem_type& SafeElementAt(index_type i, const elem_type& def) const {
     return i < Length() ? Elements()[i] : def;
   }
   // Shorthand for ElementAt(i)
   elem_type& operator[](index_type i) {
     return ElementAt(i);
   }
   // Shorthand for ElementAt(i)
   const elem_type& operator[](index_type i) const {
     return ElementAt(i);
   }
   // Shorthand for ElementAt(length - 1)
   elem_type& LastElement() {
     return ElementAt(Length() - 1);
   }
   // Shorthand for ElementAt(length - 1)
   const elem_type& LastElement() const {
     return ElementAt(Length() - 1);
   }
   // Shorthand for SafeElementAt(length - 1, def)
   elem_type& SafeLastElement(elem_type& def) {
     return SafeElementAt(Length() - 1, def);
   }
   // Shorthand for SafeElementAt(length - 1, def)
   const elem_type& SafeLastElement(const elem_type& def) const {
     return SafeElementAt(Length() - 1, def);
   }
   //
   // Search methods
   //
   // This method searches for the first element in this array that is equal
   // to the given element.
   // @param item   The item to search for.
   // @param comp   The Comparator used to determine element equality.
   // @return       true if the element was found.
   template<class Item, class Comparator>
   bool Contains(const Item& item, const Comparator& comp) const {
     return IndexOf(item, 0, comp) != NoIndex;
   }
   // This method searches for the first element in this array that is equal
   // to the given element.  This method assumes that 'operator==' is defined
   // for elem_type.
   // @param item   The item to search for.
   // @return       true if the element was found.
   template<class Item>
   bool Contains(const Item& item) const {
     return IndexOf(item) != NoIndex;
   }
   // This method searches for the offset of the first element in this
   // array that is equal to the given element.
   // @param item   The item to search for.
   // @param start  The index to start from.
   // @param comp   The Comparator used to determine element equality.
   // @return       The index of the found element or NoIndex if not found.
   template<class Item, class Comparator>
   index_type IndexOf(const Item& item, index_type start,
                      const Comparator& comp) const {
     const elem_type* iter = Elements() + start, *end = Elements() + Length();
     for (; iter != end; ++iter) {
       if (comp.Equals(*iter, item))
         return index_type(iter - Elements());
     }
     return NoIndex;
   }
   // This method searches for the offset of the first element in this
   // array that is equal to the given element.  This method assumes
   // that 'operator==' is defined for elem_type.
   // @param item   The item to search for.
   // @param start  The index to start from.
   // @return       The index of the found element or NoIndex if not found.
   template<class Item>
   index_type IndexOf(const Item& item, index_type start = 0) const {
     return IndexOf(item, start, nsDefaultComparator<elem_type, Item>());
   }
   // This method searches for the offset of the last element in this
   // array that is equal to the given element.
   // @param item   The item to search for.
   // @param start  The index to start from.  If greater than or equal to the
   //               length of the array, then the entire array is searched.
   // @param comp   The Comparator used to determine element equality.
   // @return       The index of the found element or NoIndex if not found.
   template<class Item, class Comparator>
   index_type LastIndexOf(const Item& item, index_type start,
                          const Comparator& comp) const {
     size_type endOffset = start >= Length() ? Length() : start + 1;
     const elem_type* end = Elements() - 1, *iter = end + endOffset;
     for (; iter != end; --iter) {
       if (comp.Equals(*iter, item))
         return index_type(iter - Elements());
     }
     return NoIndex;
   }
   // This method searches for the offset of the last element in this
   // array that is equal to the given element.  This method assumes
   // that 'operator==' is defined for elem_type.
   // @param item   The item to search for.
   // @param start  The index to start from.  If greater than or equal to the
   //               length of the array, then the entire array is searched.
   // @return       The index of the found element or NoIndex if not found.
   template<class Item>
   index_type LastIndexOf(const Item& item,
                          index_type start = NoIndex) const {
     return LastIndexOf(item, start, nsDefaultComparator<elem_type, Item>());
   }
   // This method searches for the offset for the element in this array
   // that is equal to the given element. The array is assumed to be sorted.
   // @param item   The item to search for.
   // @param comp   The Comparator used.
   // @return       The index of the found element or NoIndex if not found.
   template<class Item, class Comparator>
   index_type BinaryIndexOf(const Item& item, const Comparator& comp) const {
     index_type low = 0, high = Length();
     while (high > low) {
       index_type mid = (high + low) >> 1;
       if (comp.Equals(ElementAt(mid), item))
         return mid;
       if (comp.LessThan(ElementAt(mid), item))
         low = mid + 1;
       else
         high = mid;
     }
     return NoIndex;
   }
   // This method searches for the offset for the element in this array
   // that is equal to the given element. The array is assumed to be sorted.
   // This method assumes that 'operator==' and 'operator<' are defined.
   // @param item   The item to search for.
   // @return       The index of the found element or NoIndex if not found.
   template<class Item>
   index_type BinaryIndexOf(const Item& item) const {
     return BinaryIndexOf(item, nsDefaultComparator<elem_type, Item>());
   }
   //
   // Mutation methods
   //
   // This method call the destructor on each element of the array, empties it,
   // but does not shrink the array's capacity.
   // See also SetLengthAndRetainStorage.
   // Make sure to call Compact() if needed to avoid keeping a huge array
   // around.
   void ClearAndRetainStorage() {
     if (base_type::mHdr == EmptyHdr()) {
       return;
     }
     DestructRange(0, Length());
     base_type::mHdr->mLength = 0;
   }
   // This method modifies the length of the array, but unlike SetLength
   // it doesn't deallocate/reallocate the current internal storage.
   // The new length MUST be shorter than or equal to the current capacity.
   // If the new length is larger than the existing length of the array,
   // then new elements will be constructed using elem_type's default
   // constructor.  If shorter, elements will be destructed and removed.
   // See also ClearAndRetainStorage.
   // @param newLen  The desired length of this array.
   void SetLengthAndRetainStorage(size_type newLen) {
     MOZ_ASSERT(newLen <= base_type::Capacity());
     size_type oldLen = Length();
     if (newLen > oldLen) {
       InsertElementsAt(oldLen, newLen - oldLen);
       return;
     }
     if (newLen < oldLen) {
       DestructRange(newLen, oldLen - newLen);
       base_type::mHdr->mLength = newLen;
     }
   }
   // This method replaces a range of elements in this array.
   // @param start     The starting index of the elements to replace.
   // @param count     The number of elements to replace.  This may be zero to
   //                  insert elements without removing any existing elements.
   // @param array     The values to copy into this array.  Must be non-null,
   //                  and these elements must not already exist in the array
   //                  being modified.
   // @param arrayLen  The number of values to copy into this array.
   // @return          A pointer to the new elements in the array, or null if
   //                  the operation failed due to insufficient memory.
   template<class Item>
   elem_type *ReplaceElementsAt(index_type start, size_type count,
                                const Item* array, size_type arrayLen) {
     // Adjust memory allocation up-front to catch errors.
     if (!Alloc::Successful(this->EnsureCapacity(Length() + arrayLen - count, sizeof(elem_type))))
       return nullptr;
     DestructRange(start, count);
     this->ShiftData(start, count, arrayLen, sizeof(elem_type), MOZ_ALIGNOF(elem_type));
     AssignRange(start, arrayLen, array);
     return Elements() + start;
   }
   // A variation on the ReplaceElementsAt method defined above.
   template<class Item>
   elem_type *ReplaceElementsAt(index_type start, size_type count,
                                const nsTArray<Item>& array) {
     return ReplaceElementsAt(start, count, array.Elements(), array.Length());
   }
   // A variation on the ReplaceElementsAt method defined above.
   template<class Item>
   elem_type *ReplaceElementsAt(index_type start, size_type count,
                                const Item& item) {
     return ReplaceElementsAt(start, count, &item, 1);
   }
   // A variation on the ReplaceElementsAt method defined above.
   template<class Item>
   elem_type *ReplaceElementAt(index_type index, const Item& item) {
     return ReplaceElementsAt(index, 1, &item, 1);
   }
   // A variation on the ReplaceElementsAt method defined above.
   template<class Item>
   elem_type *InsertElementsAt(index_type index, const Item* array,
                               size_type arrayLen) {
     return ReplaceElementsAt(index, 0, array, arrayLen);
   }
   // A variation on the ReplaceElementsAt method defined above.
   template<class Item, class Allocator>
   elem_type *InsertElementsAt(index_type index, const nsTArray_Impl<Item, Allocator>& array) {
     return ReplaceElementsAt(index, 0, array.Elements(), array.Length());
   }
   // A variation on the ReplaceElementsAt method defined above.
   template<class Item>
   elem_type *InsertElementAt(index_type index, const Item& item) {
     return ReplaceElementsAt(index, 0, &item, 1);
   }
   // Insert a new element without copy-constructing. This is useful to avoid
   // temporaries.
   // @return A pointer to the newly inserted element, or null on OOM.
   elem_type* InsertElementAt(index_type index) {
     if (!Alloc::Successful(this->EnsureCapacity(Length() + 1, sizeof(elem_type))))
       return nullptr;
     this->ShiftData(index, 0, 1, sizeof(elem_type), MOZ_ALIGNOF(elem_type));
     elem_type *elem = Elements() + index;
     elem_traits::Construct(elem);
     return elem;
   }
   // This method searches for the smallest index of an element that is strictly
   // greater than |item|.  If |item| is inserted at this index, the array will
   // remain sorted and |item| would come after all elements that are equal to
   // it.  If |item| is greater than or equal to all elements in the array, the
   // array length is returned.
   //
   // Note that consumers who want to know whether there are existing items equal
   // to |item| in the array can just check that the return value here is > 0 and
   // indexing into the previous slot gives something equal to |item|.
   //
   //
   // @param item   The item to search for.
   // @param comp   The Comparator used.
   // @return        The index of greatest element <= to |item|
   // @precondition The array is sorted
   template<class Item, class Comparator>
   index_type
   IndexOfFirstElementGt(const Item& item,
                         const Comparator& comp) const {
     // invariant: low <= [idx] <= high
     index_type low = 0, high = Length();
     while (high > low) {
       index_type mid = (high + low) >> 1;
       // Comparators are not required to provide a LessThan(Item&, elem_type),
       // so we can't do comp.LessThan(item, ElementAt(mid)).
       if (comp.LessThan(ElementAt(mid), item) ||
           comp.Equals(ElementAt(mid), item)) {
         // item >= ElementAt(mid), so our desired index is at least mid+1.
         low = mid + 1;
       } else {
         // item < ElementAt(mid).  Our desired index is therefore at most mid.
         high = mid;
       }
     }
     MOZ_ASSERT(high == low);
     return low;
   }
   // A variation on the IndexOfFirstElementGt method defined above.
   template<class Item>
   index_type
   IndexOfFirstElementGt(const Item& item) const {
     return IndexOfFirstElementGt(item, nsDefaultComparator<elem_type, Item>());
   }
   // Inserts |item| at such an index to guarantee that if the array
   // was previously sorted, it will remain sorted after this
   // insertion.
   template<class Item, class Comparator>
   elem_type *InsertElementSorted(const Item& item, const Comparator& comp) {
     index_type index = IndexOfFirstElementGt(item, comp);
     return InsertElementAt(index, item);
   }
   // A variation on the InsertElementSorted method defined above.
   template<class Item>
   elem_type *InsertElementSorted(const Item& item) {
     return InsertElementSorted(item, nsDefaultComparator<elem_type, Item>());
   }
   // This method appends elements to the end of this array.
   // @param array     The elements to append to this array.
   // @param arrayLen  The number of elements to append to this array.
   // @return          A pointer to the new elements in the array, or null if
   //                  the operation failed due to insufficient memory.
   template<class Item>
   elem_type *AppendElements(const Item* array, size_type arrayLen) {
     if (!Alloc::Successful(this->EnsureCapacity(Length() + arrayLen, sizeof(elem_type))))
       return nullptr;
     index_type len = Length();
     AssignRange(len, arrayLen, array);
     this->IncrementLength(arrayLen);
     return Elements() + len;
   }
   // A variation on the AppendElements method defined above.
   template<class Item, class Allocator>
   elem_type *AppendElements(const nsTArray_Impl<Item, Allocator>& array) {
     return AppendElements(array.Elements(), array.Length());
   }
   // A variation on the AppendElements method defined above.
   template<class Item>
   elem_type *AppendElement(const Item& item) {
     return AppendElements(&item, 1);
   }
   // Append new elements without copy-constructing. This is useful to avoid
   // temporaries.
   // @return A pointer to the newly appended elements, or null on OOM.
   elem_type *AppendElements(size_type count) {
     if (!Alloc::Successful(this->EnsureCapacity(Length() + count, sizeof(elem_type))))
       return nullptr;
     elem_type *elems = Elements() + Length();
     size_type i;
     for (i = 0; i < count; ++i) {
       elem_traits::Construct(elems + i);
     }
     this->IncrementLength(count);
     return elems;
   }
   // Append a new element without copy-constructing. This is useful to avoid
   // temporaries.
   // @return A pointer to the newly appended element, or null on OOM.
   elem_type *AppendElement() {
     return AppendElements(1);
   }
   // Move all elements from another array to the end of this array without
   // calling copy constructors or destructors.
   // @return A pointer to the newly appended elements, or null on OOM.
   template<class Item, class Allocator>
   elem_type *MoveElementsFrom(nsTArray_Impl<Item, Allocator>& array) {
     MOZ_ASSERT(&array != this, "argument must be different array");
     index_type len = Length();
     index_type otherLen = array.Length();
     if (!Alloc::Successful(this->EnsureCapacity(len + otherLen, sizeof(elem_type))))
       return nullptr;
     copy_type::CopyElements(Elements() + len, array.Elements(), otherLen, sizeof(elem_type));
     this->IncrementLength(otherLen);
     array.ShiftData(0, otherLen, 0, sizeof(elem_type), MOZ_ALIGNOF(elem_type));
     return Elements() + len;
   }
   // This method removes a range of elements from this array.
   // @param start  The starting index of the elements to remove.
   // @param count  The number of elements to remove.
   void RemoveElementsAt(index_type start, size_type count) {
     MOZ_ASSERT(count == 0 || start < Length(), "Invalid start index");
     MOZ_ASSERT(start + count <= Length(), "Invalid length");
     // Check that the previous assert didn't overflow
     MOZ_ASSERT(start <= start + count, "Start index plus length overflows");
     DestructRange(start, count);
     this->ShiftData(start, count, 0, sizeof(elem_type), MOZ_ALIGNOF(elem_type));
   }
   // A variation on the RemoveElementsAt method defined above.
   void RemoveElementAt(index_type index) {
     RemoveElementsAt(index, 1);
   }
   // A variation on the RemoveElementsAt method defined above.
   void Clear() {
     RemoveElementsAt(0, Length());
   }
   // This helper function combines IndexOf with RemoveElementAt to "search
   // and destroy" the first element that is equal to the given element.
   // @param item  The item to search for.
   // @param comp  The Comparator used to determine element equality.
   // @return true if the element was found
   template<class Item, class Comparator>
   bool RemoveElement(const Item& item, const Comparator& comp) {
     index_type i = IndexOf(item, 0, comp);
     if (i == NoIndex)
       return false;
     RemoveElementAt(i);
     return true;
   }
   // A variation on the RemoveElement method defined above that assumes
   // that 'operator==' is defined for elem_type.
   template<class Item>
   bool RemoveElement(const Item& item) {
     return RemoveElement(item, nsDefaultComparator<elem_type, Item>());
   }
   // This helper function combines IndexOfFirstElementGt with
   // RemoveElementAt to "search and destroy" the last element that
   // is equal to the given element.
   // @param item  The item to search for.
   // @param comp  The Comparator used to determine element equality.
   // @return true if the element was found
   template<class Item, class Comparator>
   bool RemoveElementSorted(const Item& item, const Comparator& comp) {
     index_type index = IndexOfFirstElementGt(item, comp);
     if (index > 0 && comp.Equals(ElementAt(index - 1), item)) {
       RemoveElementAt(index - 1);
       return true;
     }
     return false;
   }
   // A variation on the RemoveElementSorted method defined above.
   template<class Item>
   bool RemoveElementSorted(const Item& item) {
     return RemoveElementSorted(item, nsDefaultComparator<elem_type, Item>());
   }
   // This method causes the elements contained in this array and the given
   // array to be swapped.
   template<class Allocator>
   typename Alloc::ResultType
   SwapElements(nsTArray_Impl<E, Allocator>& other) {
     return Alloc::Result(this->SwapArrayElements(other, sizeof(elem_type),
                                                  MOZ_ALIGNOF(elem_type)));
   }
   //
   // Allocation
   //
   // This method may increase the capacity of this array object by the
   // specified amount.  This method may be called in advance of several
   // AppendElement operations to minimize heap re-allocations.  This method
   // will not reduce the number of elements in this array.
   // @param capacity  The desired capacity of this array.
   // @return True if the operation succeeded; false if we ran out of memory
   typename Alloc::ResultType SetCapacity(size_type capacity) {
     return Alloc::Result(this->EnsureCapacity(capacity, sizeof(elem_type)));
   }
   // This method modifies the length of the array.  If the new length is
   // larger than the existing length of the array, then new elements will be
   // constructed using elem_type's default constructor.  Otherwise, this call
   // removes elements from the array (see also RemoveElementsAt).
   // @param newLen  The desired length of this array.
   // @return        True if the operation succeeded; false otherwise.
   // See also TruncateLength if the new length is guaranteed to be
   // smaller than the old.
   typename Alloc::ResultType SetLength(size_type newLen) {
     size_type oldLen = Length();
     if (newLen > oldLen) {
       return Alloc::ConvertBoolToResultType(InsertElementsAt(oldLen, newLen - oldLen) != nullptr);
     }
     TruncateLength(newLen);
     return Alloc::ConvertBoolToResultType(true);
   }
   // This method modifies the length of the array, but may only be
   // called when the new length is shorter than the old.  It can
   // therefore be called when elem_type has no default constructor,
   // unlike SetLength.  It removes elements from the array (see also
   // RemoveElementsAt).
   // @param newLen  The desired length of this array.
   void TruncateLength(size_type newLen) {
     size_type oldLen = Length();
     NS_ABORT_IF_FALSE(newLen <= oldLen,
                       "caller should use SetLength instead");
     RemoveElementsAt(newLen, oldLen - newLen);
   }
   // This method ensures that the array has length at least the given
   // length.  If the current length is shorter than the given length,
   // then new elements will be constructed using elem_type's default
   // constructor.
   // @param minLen  The desired minimum length of this array.
   // @return        True if the operation succeeded; false otherwise.
 typename Alloc::ResultType EnsureLengthAtLeast(size_type minLen) {
     size_type oldLen = Length();
     if (minLen > oldLen) {
       return Alloc::ConvertBoolToResultType(!!InsertElementsAt(oldLen, minLen - oldLen));
     }
     return Alloc::ConvertBoolToResultType(true);
   }
   // This method inserts elements into the array, constructing
   // them using elem_type's default constructor.
   // @param index the place to insert the new elements. This must be no
   //              greater than the current length of the array.
   // @param count the number of elements to insert
   elem_type *InsertElementsAt(index_type index, size_type count) {
     if (!base_type::InsertSlotsAt(index, count, sizeof(elem_type), MOZ_ALIGNOF(elem_type))) {
       return nullptr;
     }
     // Initialize the extra array elements
     elem_type *iter = Elements() + index, *end = iter + count;
     for (; iter != end; ++iter) {
       elem_traits::Construct(iter);
     }
     return Elements() + index;
   }
   // This method inserts elements into the array, constructing them
   // elem_type's copy constructor (or whatever one-arg constructor
   // happens to match the Item type).
   // @param index the place to insert the new elements. This must be no
   //              greater than the current length of the array.
   // @param count the number of elements to insert.
   // @param item the value to use when constructing the new elements.
   template<class Item>
   elem_type *InsertElementsAt(index_type index, size_type count,
                               const Item& item) {
     if (!base_type::InsertSlotsAt(index, count, sizeof(elem_type), MOZ_ALIGNOF(elem_type))) {
       return nullptr;
     }
     // Initialize the extra array elements
     elem_type *iter = Elements() + index, *end = iter + count;
     for (; iter != end; ++iter) {
       elem_traits::Construct(iter, item);
     }
     return Elements() + index;
   }
   // This method may be called to minimize the memory used by this array.
   void Compact() {
     ShrinkCapacity(sizeof(elem_type), MOZ_ALIGNOF(elem_type));
   }
   //
   // Sorting
   //
   // This function is meant to be used with the NS_QuickSort function.  It
   // maps the callback API expected by NS_QuickSort to the Comparator API
   // used by nsTArray_Impl.  See nsTArray_Impl::Sort.
   template<class Comparator>
   static int Compare(const void* e1, const void* e2, void *data) {
     const Comparator* c = reinterpret_cast<const Comparator*>(data);
     const elem_type* a = static_cast<const elem_type*>(e1);
     const elem_type* b = static_cast<const elem_type*>(e2);
     return c->LessThan(*a, *b) ? -1 : (c->Equals(*a, *b) ? 0 : 1);
   }
   // This method sorts the elements of the array.  It uses the LessThan
   // method defined on the given Comparator object to collate elements.
   // @param comp The Comparator used to collate elements.
   template<class Comparator>
   void Sort(const Comparator& comp) {
     NS_QuickSort(Elements(), Length(), sizeof(elem_type),
                  Compare<Comparator>, const_cast<Comparator*>(&comp));
   }
   // A variation on the Sort method defined above that assumes that
   // 'operator<' is defined for elem_type.
   void Sort() {
     Sort(nsDefaultComparator<elem_type, elem_type>());
   }
   //
   // Binary Heap
   //
   // Sorts the array into a binary heap.
   // @param comp The Comparator used to create the heap
   template<class Comparator>
   void MakeHeap(const Comparator& comp) {
     if (!Length()) {
       return;
     }
     index_type index = (Length() - 1) / 2;
     do {
       SiftDown(index, comp);
     } while (index--);
   }
   // A variation on the MakeHeap method defined above.
   void MakeHeap() {
     MakeHeap(nsDefaultComparator<elem_type, elem_type>());
   }
   // Adds an element to the heap
   // @param item The item to add
   // @param comp The Comparator used to sift-up the item
   template<class Item, class Comparator>
   elem_type *PushHeap(const Item& item, const Comparator& comp) {
     if (!base_type::InsertSlotsAt(Length(), 1, sizeof(elem_type), MOZ_ALIGNOF(elem_type))) {
       return nullptr;
     }
     // Sift up the new node
     elem_type *elem = Elements();
     index_type index = Length() - 1;
     index_type parent_index = (index - 1) / 2;
     while (index && comp.LessThan(elem[parent_index], item)) {
       elem[index] = elem[parent_index];
       index = parent_index;
       parent_index = (index - 1) / 2;
     }
     elem[index] = item;
     return &elem[index];
   }
   // A variation on the PushHeap method defined above.
   template<class Item>
   elem_type *PushHeap(const Item& item) {
     return PushHeap(item, nsDefaultComparator<elem_type, Item>());
   }
   // Delete the root of the heap and restore the heap
   // @param comp The Comparator used to restore the heap
   template<class Comparator>
   void PopHeap(const Comparator& comp) {
     if (!Length()) {
       return;
     }
     index_type last_index = Length() - 1;
     elem_type *elem = Elements();
     elem[0] = elem[last_index];
     TruncateLength(last_index);
     if (Length()) {
       SiftDown(0, comp);
     }
   }
   // A variation on the PopHeap method defined above.
   void PopHeap() {
     PopHeap(nsDefaultComparator<elem_type, elem_type>());
   }
 protected:
   using base_type::Hdr;
   using base_type::ShrinkCapacity;
   // This method invokes elem_type's destructor on a range of elements.
   // @param start  The index of the first element to destroy.
   // @param count  The number of elements to destroy.
   void DestructRange(index_type start, size_type count) {
     elem_type *iter = Elements() + start, *end = iter + count;
     for (; iter != end; ++iter) {
       elem_traits::Destruct(iter);
     }
   }
   // This method invokes elem_type's copy-constructor on a range of elements.
   // @param start   The index of the first element to construct.
   // @param count   The number of elements to construct.
   // @param values  The array of elements to copy.
   template<class Item>
   void AssignRange(index_type start, size_type count,
                    const Item *values) {
     AssignRangeAlgorithm<mozilla::IsPod<Item>::value,
                          mozilla::IsSame<Item, elem_type>::value>
       ::implementation(Elements(), start, count, values);
   }
   // This method sifts an item down to its proper place in a binary heap
   // @param index The index of the node to start sifting down from
   // @param comp  The Comparator used to sift down
   template<class Comparator>
   void SiftDown(index_type index, const Comparator& comp) {
     elem_type *elem = Elements();
     elem_type item = elem[index];
     index_type end = Length() - 1;
     while ((index * 2) < end) {
       const index_type left = (index * 2) + 1;
       const index_type right = (index * 2) + 2;
       const index_type parent_index = index;
       if (comp.LessThan(item, elem[left])) {
         if (left < end &&
             comp.LessThan(elem[left], elem[right])) {
           index = right;
         } else {
           index = left;
         }
       } else if (left < end &&
                  comp.LessThan(item, elem[right])) {
         index = right;
       } else {
         break;
       }
       elem[parent_index] = elem[index];
     }
     elem[index] = item;
   }
 };
 template <typename E, typename Alloc>
 inline void
 ImplCycleCollectionUnlink(nsTArray_Impl<E, Alloc>& aField)
 {
   aField.Clear();
 }
 template <typename E, typename Alloc>
 inline void
 ImplCycleCollectionTraverse(nsCycleCollectionTraversalCallback& aCallback,
                             nsTArray_Impl<E, Alloc>& aField,
                             const char* aName,
                             uint32_t aFlags = 0)
 {
   aFlags |= CycleCollectionEdgeNameArrayFlag;
   uint32_t length = aField.Length();
   for (uint32_t i = 0; i < length; ++i) {
     ImplCycleCollectionTraverse(aCallback, aField[i], aName, aFlags);
   }
 }
 //
 // nsTArray is an infallible vector class.  See the comment at the top of this
 // file for more details.
 //
 template <class E>
 class nsTArray : public nsTArray_Impl<E, nsTArrayInfallibleAllocator>
 {
 public:
   typedef nsTArray_Impl<E, nsTArrayInfallibleAllocator> base_type;
   typedef nsTArray<E>                                   self_type;
   typedef typename base_type::size_type                 size_type;
   nsTArray() {}
   explicit nsTArray(size_type capacity) : base_type(capacity) {}
   explicit nsTArray(const nsTArray& other) : base_type(other) {}
   template<class Allocator>
   explicit nsTArray(const nsTArray_Impl<E, Allocator>& other) : base_type(other) {}
 };
 //
 // FallibleTArray is a fallible vector class.
 //
 template <class E>
 class FallibleTArray : public nsTArray_Impl<E, nsTArrayFallibleAllocator>
 {
 public:
   typedef nsTArray_Impl<E, nsTArrayFallibleAllocator>   base_type;
   typedef FallibleTArray<E>                             self_type;
   typedef typename base_type::size_type                 size_type;
   FallibleTArray() {}
   explicit FallibleTArray(size_type capacity) : base_type(capacity) {}
   explicit FallibleTArray(const FallibleTArray<E>& other) : base_type(other) {}
   template<class Allocator>
   explicit FallibleTArray(const nsTArray_Impl<E, Allocator>& other) : base_type(other) {}
 };
 //
 // nsAutoArrayBase is a base class for AutoFallibleTArray and nsAutoTArray.
 // You shouldn't use this class directly.
 //
 template <class TArrayBase, uint32_t N>
 class nsAutoArrayBase : public TArrayBase
 {
 public:
   typedef nsAutoArrayBase<TArrayBase, N> self_type;
   typedef TArrayBase base_type;
   typedef typename base_type::Header Header;
   typedef typename base_type::elem_type elem_type;
   template<typename Allocator>
   self_type& operator=(const nsTArray_Impl<elem_type, Allocator>& other) {
     base_type::operator=(other);
     return *this;
   }
 protected:
   nsAutoArrayBase() {
     Init();
   }
   // We need this constructor because nsAutoTArray and friends all have
   // implicit copy-constructors.  If we don't have this method, those
   // copy-constructors will call nsAutoArrayBase's implicit copy-constructor,
   // which won't call Init() and set up the auto buffer!
   nsAutoArrayBase(const self_type &aOther) {
     Init();
     this->AppendElements(aOther);
   }
 private:
   // nsTArray_base casts itself as an nsAutoArrayBase in order to get a pointer
   // to mAutoBuf.
   template<class Allocator, class Copier>
   friend class nsTArray_base;
   void Init() {
     static_assert(MOZ_ALIGNOF(elem_type) <= 8,
                   "can't handle alignments greater than 8, "
                   "see nsTArray_base::UsesAutoArrayBuffer()");
     // Temporary work around for VS2012 RC compiler crash
     Header** phdr = base_type::PtrToHdr();
     *phdr = reinterpret_cast<Header*>(&mAutoBuf);
     (*phdr)->mLength = 0;
     (*phdr)->mCapacity = N;
     (*phdr)->mIsAutoArray = 1;
     MOZ_ASSERT(base_type::GetAutoArrayBuffer(MOZ_ALIGNOF(elem_type)) ==
                reinterpret_cast<Header*>(&mAutoBuf),
                "GetAutoArrayBuffer needs to be fixed");
   }
   // Declare mAutoBuf aligned to the maximum of the header's alignment and
   // elem_type's alignment.  We need to use a union rather than
   // MOZ_ALIGNED_DECL because GCC is picky about what goes into
   // __attribute__((aligned(foo))).
   union {
     char mAutoBuf[sizeof(nsTArrayHeader) + N * sizeof(elem_type)];
     // Do the max operation inline to ensure that it is a compile-time constant.
     mozilla::AlignedElem<(MOZ_ALIGNOF(Header) > MOZ_ALIGNOF(elem_type))
                          ? MOZ_ALIGNOF(Header) : MOZ_ALIGNOF(elem_type)> mAlign;
   };
 };
 //
 // nsAutoTArray<E, N> is an infallible vector class with N elements of inline
 // storage.  If you try to store more than N elements inside an
 // nsAutoTArray<E, N>, we'll call malloc() and store them all on the heap.
 //
 // Note that you can cast an nsAutoTArray<E, N> to
 // |const AutoFallibleTArray<E, N>&|.
 //
 template<class E, uint32_t N>
 class nsAutoTArray : public nsAutoArrayBase<nsTArray<E>, N>
 {
   typedef nsAutoTArray<E, N> self_type;
   typedef nsAutoArrayBase<nsTArray<E>, N> Base;
 public:
   nsAutoTArray() {}
   template<typename Allocator>
   explicit nsAutoTArray(const nsTArray_Impl<E, Allocator>& other) {
     Base::AppendElements(other);
   }
   operator const AutoFallibleTArray<E, N>&() const {
     return *reinterpret_cast<const AutoFallibleTArray<E, N>*>(this);
   }
 };
 //
 // AutoFallibleTArray<E, N> is a fallible vector class with N elements of
 // inline storage.
 //
 template<class E, uint32_t N>
 class AutoFallibleTArray : public nsAutoArrayBase<FallibleTArray<E>, N>
 {
   typedef AutoFallibleTArray<E, N> self_type;
   typedef nsAutoArrayBase<FallibleTArray<E>, N> Base;
 public:
   AutoFallibleTArray() {}
   template<typename Allocator>
   explicit AutoFallibleTArray(const nsTArray_Impl<E, Allocator>& other) {
     Base::AppendElements(other);
   }
   operator const nsAutoTArray<E, N>&() const {
     return *reinterpret_cast<const nsAutoTArray<E, N>*>(this);
   }
 };
 // Assert that nsAutoTArray doesn't have any extra padding inside.
 //
 // It's important that the data stored in this auto array takes up a multiple of
 // 8 bytes; e.g. nsAutoTArray<uint32_t, 1> wouldn't work.  Since nsAutoTArray
 // contains a pointer, its size must be a multiple of alignof(void*).  (This is
 // because any type may be placed into an array, and there's no padding between
 // elements of an array.)  The compiler pads the end of the structure to
 // enforce this rule.
 //
 // If we used nsAutoTArray<uint32_t, 1> below, this assertion would fail on a
 // 64-bit system, where the compiler inserts 4 bytes of padding at the end of
 // the auto array to make its size a multiple of alignof(void*) == 8 bytes.
 static_assert(sizeof(nsAutoTArray<uint32_t, 2>) ==
               sizeof(void*) + sizeof(nsTArrayHeader) + sizeof(uint32_t) * 2,
               "nsAutoTArray shouldn't contain any extra padding, "
               "see the comment");
 // Definitions of nsTArray_Impl methods
 #include "nsTArray-inl.h"
 #endif  // nsTArray_h__

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xpcom/glue/nsTArray.h