gecko-dev/xpcom/glue/nsVoidArray.h

/* -*- 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/. */
#ifndef nsVoidArray_h___
#define nsVoidArray_h___

//#define DEBUG_VOIDARRAY 1

#include "nsDebug.h"

#include "mozilla/MemoryReporting.h"
#include <stdint.h>

// Comparator callback function for sorting array values.
typedef int (*nsVoidArrayComparatorFunc)(const void* aElement1,
                                         const void* aElement2, void* aData);

// Enumerator callback function. Return false to stop
typedef bool (*nsVoidArrayEnumFunc)(void* aElement, void* aData);
typedef bool (*nsVoidArrayEnumFuncConst)(const void* aElement, void* aData);

// SizeOfExcludingThis callback function.
typedef size_t (*nsVoidArraySizeOfElementIncludingThisFunc)(
  const void* aElement, mozilla::MallocSizeOf aMallocSizeOf, void* aData);

/// A basic zero-based array of void*'s that manages its own memory
class NS_COM_GLUE nsVoidArray
{
public:
  nsVoidArray();
  explicit nsVoidArray(int32_t aCount);  // initial count of aCount elements set to nullptr
  ~nsVoidArray();

  nsVoidArray& operator=(const nsVoidArray& aOther);

  inline int32_t Count() const { return mImpl ? mImpl->mCount : 0; }
  // If the array grows, the newly created entries will all be null
  bool SetCount(int32_t aNewCount);
  // returns the max number that can be held without allocating
  inline int32_t GetArraySize() const { return mImpl ? mImpl->mSize : 0; }

  void* FastElementAt(int32_t aIndex) const
  {
    NS_ASSERTION(aIndex >= 0 && aIndex < Count(),
                 "nsVoidArray::FastElementAt: index out of range");
    return mImpl->mArray[aIndex];
  }

  // This both asserts and bounds-checks, because (1) we don't want
  // people to write bad code, but (2) we don't want to change it to
  // crashing for backwards compatibility.  See bug 96108.
  void* ElementAt(int32_t aIndex) const
  {
    NS_ASSERTION(aIndex >= 0 && aIndex < Count(),
                 "nsVoidArray::ElementAt: index out of range");
    return SafeElementAt(aIndex);
  }

  // bounds-checked version
  void* SafeElementAt(int32_t aIndex) const
  {
    if (uint32_t(aIndex) >= uint32_t(Count())) { // handles aIndex < 0 too
      return nullptr;
    }
    // The bounds check ensures mImpl is non-null.
    return mImpl->mArray[aIndex];
  }

  void* operator[](int32_t aIndex) const { return ElementAt(aIndex); }

  int32_t IndexOf(void* aPossibleElement) const;

  bool InsertElementAt(void* aElement, int32_t aIndex);
  bool InsertElementsAt(const nsVoidArray& aOther, int32_t aIndex);

  bool ReplaceElementAt(void* aElement, int32_t aIndex);

  // useful for doing LRU arrays, sorting, etc
  bool MoveElement(int32_t aFrom, int32_t aTo);

  bool AppendElement(void* aElement)
  {
    return InsertElementAt(aElement, Count());
  }

  bool AppendElements(nsVoidArray& aElements)
  {
    return InsertElementsAt(aElements, Count());
  }

  bool RemoveElement(void* aElement);
  void RemoveElementsAt(int32_t aIndex, int32_t aCount);
  void RemoveElementAt(int32_t aIndex)
  {
    return RemoveElementsAt(aIndex, 1);
  }

  void Clear();

  bool SizeTo(int32_t aMin);
  // Subtly different - Compact() tries to be smart about whether we
  // should reallocate the array; SizeTo() always reallocates.
  void Compact();

  void Sort(nsVoidArrayComparatorFunc aFunc, void* aData);

  bool EnumerateForwards(nsVoidArrayEnumFunc aFunc, void* aData);
  bool EnumerateForwards(nsVoidArrayEnumFuncConst aFunc, void* aData) const;
  bool EnumerateBackwards(nsVoidArrayEnumFunc aFunc, void* aData);

  // Measures the size of the array's element storage, and if
  // |aSizeOfElementIncludingThis| is non-nullptr, measures the size of things
  // pointed to by elements.
  size_t SizeOfExcludingThis(
    nsVoidArraySizeOfElementIncludingThisFunc aSizeOfElementIncludingThis,
    mozilla::MallocSizeOf aMallocSizeOf, void* aData = nullptr) const;

protected:
  bool GrowArrayBy(int32_t aGrowBy);

  struct Impl
  {
    /**
     * The actual array size.
     */
    int32_t mSize;

    /**
     * The number of elements in the array
     */
    int32_t mCount;

    /**
     * Array data, padded out to the actual size of the array.
     */
    void*   mArray[1];
  };

  Impl* mImpl;
#if DEBUG_VOIDARRAY
  int32_t mMaxCount;
  int32_t mMaxSize;
  bool    mIsAuto;
#endif

  // bit twiddlers
  void SetArray(Impl* aNewImpl, int32_t aSize, int32_t aCount);

private:
  /// Copy constructors are not allowed
  nsVoidArray(const nsVoidArray& aOther);
};

//===================================================================
//  nsSmallVoidArray is not a general-purpose replacement for
//  ns(Auto)VoidArray because there is (some) extra CPU overhead for arrays
//  larger than 1 element, though not a lot.  It is appropriate for
//  space-sensitive uses where sizes of 0 or 1 are moderately common or
//  more, and where we're NOT storing arbitrary integers or arbitrary
//  pointers.

// NOTE: nsSmallVoidArray can ONLY be used for holding items that always
// have the low bit as a 0 - i.e. element & 1 == 0.  This happens to be
// true for allocated and object pointers for all the architectures we run
// on, but conceivably there might be some architectures/compilers for
// which it is NOT true.  We know this works for all existing architectures
// because if it didn't then nsCheapVoidArray would have failed.  Also note
// that we will ASSERT if this assumption is violated in DEBUG builds.

// XXX we're really re-implementing the whole nsVoidArray interface here -
// some form of abstract class would be useful

// I disagree on the abstraction here.  If the point of this class is to be
// as small as possible, and no one will ever derive from it, as I found
// today, there should not be any virtualness to it to avoid the vtable
// ptr overhead.

class NS_COM_GLUE nsSmallVoidArray : private nsVoidArray
{
public:
  ~nsSmallVoidArray();

  nsSmallVoidArray& operator=(nsSmallVoidArray& aOther);
  void* operator[](int32_t aIndex) const { return ElementAt(aIndex); }

  int32_t GetArraySize() const;

  int32_t Count() const;
  void* FastElementAt(int32_t aIndex) const;
  // This both asserts and bounds-checks, because (1) we don't want
  // people to write bad code, but (2) we don't want to change it to
  // crashing for backwards compatibility.  See bug 96108.
  void* ElementAt(int32_t aIndex) const
  {
    NS_ASSERTION(aIndex >= 0 && aIndex < Count(),
                 "nsSmallVoidArray::ElementAt: index out of range");
    return SafeElementAt(aIndex);
  }
  void* SafeElementAt(int32_t aIndex) const
  {
    // let compiler inline; it may be able to remove these checks
    if (uint32_t(aIndex) >= uint32_t(Count())) { // handles aIndex < 0 too
      return nullptr;
    }
    return FastElementAt(aIndex);
  }
  int32_t IndexOf(void* aPossibleElement) const;
  bool InsertElementAt(void* aElement, int32_t aIndex);
  bool InsertElementsAt(const nsVoidArray& aOther, int32_t aIndex);
  bool ReplaceElementAt(void* aElement, int32_t aIndex);
  bool MoveElement(int32_t aFrom, int32_t aTo);
  bool AppendElement(void* aElement);
  bool AppendElements(nsVoidArray& aElements)
  {
    return InsertElementsAt(aElements, Count());
  }
  bool RemoveElement(void* aElement);
  void RemoveElementsAt(int32_t aIndex, int32_t aCount);
  void RemoveElementAt(int32_t aIndex);

  void Clear();
  bool SizeTo(int32_t aMin);
  void Compact();
  void Sort(nsVoidArrayComparatorFunc aFunc, void* aData);

  bool EnumerateForwards(nsVoidArrayEnumFunc aFunc, void* aData);
  bool EnumerateBackwards(nsVoidArrayEnumFunc aFunc, void* aData);

private:

  bool HasSingle() const
  {
    return !!(reinterpret_cast<intptr_t>(mImpl) & 0x1);
  }
  void* GetSingle() const
  {
    NS_ASSERTION(HasSingle(), "wrong type");
    return reinterpret_cast<void*>(reinterpret_cast<intptr_t>(mImpl) & ~0x1);
  }
  void SetSingle(void* aChild)
  {
    NS_ASSERTION(HasSingle() || !mImpl, "overwriting array");
    mImpl = reinterpret_cast<Impl*>(reinterpret_cast<intptr_t>(aChild) | 0x1);
  }
  bool IsEmpty() const
  {
    // Note that this isn't the same as Count()==0
    return !mImpl;
  }
  const nsVoidArray* AsArray() const
  {
    NS_ASSERTION(!HasSingle(), "This is a single");
    return this;
  }
  nsVoidArray* AsArray()
  {
    NS_ASSERTION(!HasSingle(), "This is a single");
    return this;
  }
  bool EnsureArray();
};

#endif /* nsVoidArray_h___ */