src/gromacs/utility/allocator.h

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  35 /*! \file
  36  * \brief
  37  * Declares gmx::Allocator template whose allocation functionality is
  38  * configured both by type of object allocated and a policy class that
  39  * configures the necessary matching malloc and free operation.
  40  *
  41  * \author Erik Lindahl <erik.lindahl@gmail.com>
  42  * \author Mark Abraham <mark.j.abraham@gmail.com>
  43  * \inpublicapi
  44  * \ingroup module_utility
  45  */
  46 #ifndef GMX_UTILITY_ALLOCATOR_H
  47 #define GMX_UTILITY_ALLOCATOR_H
  48
  49 #include <cstddef>
  50
  51 #include <memory>
  52 #include <new>
  53
  54 #include "gromacs/utility/basedefinitions.h"
  55
  56 namespace gmx
  57 {
  58
  59 /*! \libinternal \brief Policy-based memory allocator.
  60  *
  61  *  \tparam T                 Type of objects to allocate
  62  *  \tparam AllocationPolicy  Policy of (matching) allocation and deallocation functions.
  63  *
  64  * This class can be used for the optional allocator template
  65  * parameter in standard library containers. It must be configured
  66  * with both the type of object to allocate, and an AllocationPolicy
  67  * which effectively wraps a matching pair of malloc and free
  68  * functions. This permits implementing a family of related allocators
  69  * e.g. with SIMD alignment, GPU host-side page locking, or perhaps
  70  * both, in a way that preserves a common programming interface and
  71  * duplicates minimal code.
  72  *
  73  * AllocationPolicy is used as a base class, so that if
  74  * AllocationPolicy is stateless, then the empty base optimization
  75  * will ensure that Allocation is also stateless, and objects made
  76  * with the Allocator will incur no size penalty. (Embedding an
  77  * AllocationPolicy object incurs a size penalty always, even if the
  78  * object is empty.) Normally a stateless allocator will be used.
  79  *
  80  * However, an AllocationPolicy with state might be desirable for
  81  * simplifying writing code that needs to allocate suitably for a
  82  * transfer to a GPU. That code needs to specify an Allocator that can
  83  * do the right job, which can be stateless. However, if we have code
  84  * that will not know until run time whether a GPU transfer will
  85  * occur, then the allocator needs to be aware of the state.  That
  86  * will increase the size of a container that uses the stateful
  87  * allocator.
  88  *
  89  * \throws std::bad_alloc Instead of a GROMACS exception object, we
  90  * throw the standard one on allocation failures to make it as
  91  * compatible as possible with the errors expected by code using the
  92  * standard library containers.
  93  *
  94  * \inlibraryapi
  95  * \ingroup module_utility
  96  */
  97 template <class T, typename AllocationPolicy>
  98 class Allocator : public AllocationPolicy
  99 {
 100     public:
 101         // The standard library specification for a custom allocator
 102         // requires these typedefs, with this capitalization/underscoring.
 103         typedef T              value_type;      //!< Type of allocated elements
 104         typedef T             &reference;       //!< Reference to allocated elements
 105         typedef const T       &const_reference; //!< Constant reference to allocated elements
 106         typedef T *            pointer;         //!< Pointer to allocated elements
 107         typedef const T *      const_pointer;   //!< Constant pointer to allocated elements
 108         typedef std::size_t    size_type;       //!< Integer type to use for size of objects
 109         typedef std::ptrdiff_t difference_type; //!< Type to hold differences between pointers
 110
 111         // This typedef is required by GROMACS for testing and assertions
 112         typedef AllocationPolicy allocation_policy; //!< Type of the AllocationPolicy
 113
 114         /*! \libinternal \brief Standard-required typedef to use allocator with different class.
 115          *
 116          *  \tparam U new class
 117          *
 118          *  This is used for things like std::list where the size of each link
 119          *  is larger than the class stored in the link.
 120          *
 121          *  Required by the specification for an allocator.
 122          */
 123         template <class U>
 124         struct rebind
 125         {
 126             typedef Allocator<U, AllocationPolicy> other; //!< Align class U with our alignment
 127         };
 128
 129         /*! \brief Templated copy constructor
 130          *
 131          * This template constructor cannot be auto-generated, and is
 132          * normally unused, except e.g. MSVC2015 standard library uses
 133          * it in debug mode, presumably to implement some checks.
 134          */
 135         template <class U>
 136         explicit Allocator(const Allocator<U, AllocationPolicy> & /*unused*/) {}
 137
 138         /*! \brief Constructor
 139          *
 140          * No constructor can be auto-generated in the presence of any
 141          * user-defined constructor, but we want the default constructor.
 142          */
 143         Allocator() = default;
 144
 145         /*! \brief Constructor to accept an AllocationPolicy.
 146          *
 147          * This is useful for AllocationPolicies with state.
 148          */
 149         Allocator(const AllocationPolicy &p) : AllocationPolicy(p) {}
 150
 151         /*! \brief Return address of an object
 152          *
 153          *  \param r Reference to object of type T
 154          *  \return Pointer to T memory
 155          */
 156         pointer
 157         address(reference r) const { return &r; }
 158
 159         /*! \brief Return address of a const object
 160          *
 161          *  \param r Const reference to object of type T
 162          *  \return Pointer to T memory
 163          */
 164         const_pointer
 165         address(const_reference r) const { return &r; }
 166
 167         /*! \brief Do the actual memory allocation
 168          *
 169          *  \param n    Number of elements of type T to allocate. n can be
 170          *              0 bytes, which will return a non-null properly aligned
 171          *              and padded pointer that should not be used.
 172          *  \param hint Optional value returned from previous call to allocate.
 173          *              For now this is not used.
 174          *  \return Pointer to allocated memory
 175          *
 176          *  \throws std::bad_alloc if the allocation fails.
 177          */
 178         pointer
 179         allocate(std::size_t n, typename std::allocator<void>::const_pointer gmx_unused hint = nullptr)
 180         {
 181             void *p = AllocationPolicy::malloc(n*sizeof(T));
 182
 183             if (p == nullptr)
 184             {
 185                 throw std::bad_alloc();
 186             }
 187             else
 188             {
 189                 return static_cast<pointer>(p);
 190             }
 191         }
 192
 193         /*! \brief Release memory
 194          *
 195          * \param p  Pointer to previously allocated memory returned from allocate()
 196          * \param n  number of objects previously passed to allocate()
 197          */
 198         void
 199         deallocate(pointer p, std::size_t gmx_unused n)
 200         {
 201             AllocationPolicy::free(p);
 202         }
 203
 204         //! Return the policy object for this allocator.
 205         AllocationPolicy getPolicy() const
 206         {
 207             return *this;
 208         }
 209
 210         /*! \brief Construct an object without allocating memory
 211          *
 212          * \tparam Args  Variable-length list of types for constructor args
 213          * \param p      Adress of memory where to construct object
 214          * \param args   Variable-length list of arguments to constructor
 215          */
 216         template<class ... Args>
 217         void
 218         construct(pointer p, Args && ... args) { ::new(p)T(std::forward<Args>(args) ...); }
 219
 220         /*! \brief Call the destructor of object without releasing memory
 221          *
 222          * \param p  Address of memory where to destroy object
 223          */
 224         void
 225         destroy(pointer p) { p->~value_type(); }
 226
 227         /*! \brief Return largest number of objects that can be allocated
 228          *
 229          * This will be set such that the number of objects T multiplied by
 230          * the size of each object is the largest value that can be represented
 231          * by size_type.
 232          */
 233         std::size_t
 234         max_size() const { return (static_cast<std::size_t>(0) - static_cast<std::size_t>(1)) / sizeof(T); }
 235
 236         /*! \brief Return true if two allocators are identical
 237          *
 238          * This is a member function of the left-hand-side allocator.
 239          */
 240         template<class T2>
 241         bool
 242         operator==(const Allocator<T2, AllocationPolicy> & /*unused*/) const { return std::is_same<T, T2>::value; }
 243
 244         /*! \brief Return true if two allocators are different
 245          *
 246          * \param rhs Other allocator.
 247          *
 248          * This is a member function of the left-hand-side allocator.
 249          */
 250         bool
 251         operator!=(const Allocator &rhs) const { return !operator==(rhs); }
 252 };
 253
 254 }      // namespace gmx
 255
 256 #endif