geant4/source/global/management/include/G4AllocatorPool.hh

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//
// G4AllocatorPool
//
// Class description:
//
// Class implementing a memory pool for fast allocation and deallocation
// of memory chunks.  The size of the chunks for small allocated objects
// is fixed to 1Kb and takes into account of memory alignment; for large
// objects it is set to 10 times the object's size.
// The implementation is derived from: B.Stroustrup, The C++ Programming
// Language, Third Edition.

//           -------------- G4AllocatorPool ----------------
//
// Author: G.Cosmo (CERN), November 2000
// --------------------------------------------------------------------
#ifndef G4AllocatorPool_hh
#define G4AllocatorPool_hh 1

class G4AllocatorPool
{
 public:
  explicit G4AllocatorPool(unsigned int n = 0);
  // Create a pool of elements of size n
  ~G4AllocatorPool();
  // Destructor. Return storage to the free store

  G4AllocatorPool(const G4AllocatorPool& right) = default;
  // Copy constructor
  G4AllocatorPool& operator=(const G4AllocatorPool& right);
  // Equality operator

  inline void* Alloc();
  // Allocate one element
  inline void Free(void* b);
  // Return an element back to the pool

  inline unsigned int Size() const;
  // Return storage size
  void Reset();
  // Return storage to the free store

  inline int GetNoPages() const;
  // Return the total number of allocated pages
  inline unsigned int GetPageSize() const;
  // Accessor for default page size
  inline void GrowPageSize(unsigned int factor);
  // Increase default page size by a given factor

 private:
  struct G4PoolLink
  {
    G4PoolLink* next;
  };
  class G4PoolChunk
  {
   public:
    explicit G4PoolChunk(unsigned int sz)
      : size(sz)
      , mem(new char[size])
      , next(nullptr)
    {
      ;
    }
    ~G4PoolChunk() { delete[] mem; }
    const unsigned int size;
    char* mem;
    G4PoolChunk* next;
  };

  void Grow();
  // Make pool larger

 private:
  const unsigned int esize;
  unsigned int csize;
  G4PoolChunk* chunks = nullptr;
  G4PoolLink* head    = nullptr;
  int nchunks         = 0;
};

// ------------------------------------------------------------
// Inline implementation
// ------------------------------------------------------------

// ************************************************************
// Alloc
// ************************************************************
//
inline void* G4AllocatorPool::Alloc()
{
  if(head == nullptr)
  {
    Grow();
  }
  G4PoolLink* p = head;  // return first element
  head          = p->next;
  return p;
}

// ************************************************************
// Free
// ************************************************************
//
inline void G4AllocatorPool::Free(void* b)
{
  auto* p = static_cast<G4PoolLink*>(b);
  p->next       = head;  // put b back as first element
  head          = p;
}

// ************************************************************
// Size
// ************************************************************
//
inline unsigned int G4AllocatorPool::Size() const { return nchunks * csize; }

// ************************************************************
// GetNoPages
// ************************************************************
//
inline int G4AllocatorPool::GetNoPages() const { return nchunks; }

// ************************************************************
// GetPageSize
// ************************************************************
//
inline unsigned int G4AllocatorPool::GetPageSize() const { return csize; }

// ************************************************************
// GrowPageSize
// ************************************************************
//
inline void G4AllocatorPool::GrowPageSize(unsigned int sz)
{
  csize = (sz) != 0u ? sz * csize : csize;
}

#endif