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* This file is part of the GROMACS molecular simulation package.
*
* Copyright (c) 2017, by the GROMACS development team, led by
* Mark Abraham, David van der Spoel, Berk Hess, and Erik Lindahl,
* and including many others, as listed in the AUTHORS file in the
* top-level source directory and at http://www.gromacs.org.
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/*! \file
* \brief
* Declares gmx::Allocator template whose allocation functionality is
* configured both by type of object allocated and a policy class that
* configures the necessary matching malloc and free operation.
*
* \author Erik Lindahl <erik.lindahl@gmail.com>
* \author Mark Abraham <mark.j.abraham@gmail.com>
* \inpublicapi
* \ingroup module_utility
*/
#ifndef GMX_UTILITY_ALLOCATOR_H
#define GMX_UTILITY_ALLOCATOR_H
#include <cstddef>
#include <memory>
#include <new>
#include "gromacs/utility/basedefinitions.h"
namespace gmx
{
/*! \libinternal \brief Policy-based memory allocator.
*
* \tparam T Type of objects to allocate
* \tparam AllocationPolicy Policy of (matching) allocation and deallocation functions.
*
* This class can be used for the optional allocator template
* parameter in standard library containers. It must be configured
* with both the type of object to allocate, and an AllocationPolicy
* which effectively wraps a matching pair of malloc and free
* functions. This permits implementing a family of related allocators
* e.g. with SIMD alignment, GPU host-side page locking, or perhaps
* both, in a way that preserves a common programming interface and
* duplicates minimal code.
*
* AllocationPolicy is used as a base class, so that if
* AllocationPolicy is stateless, then the empty base optimization
* will ensure that Allocation is also stateless, and objects made
* with the Allocator will incur no size penalty. (Embedding an
* AllocationPolicy object incurs a size penalty always, even if the
* object is empty.) Normally a stateless allocator will be used.
*
* However, an AllocationPolicy with state might be desirable for
* simplifying writing code that needs to allocate suitably for a
* transfer to a GPU. That code needs to specify an Allocator that can
* do the right job, which can be stateless. However, if we have code
* that will not know until run time whether a GPU transfer will
* occur, then the allocator needs to be aware of the state. That
* will increase the size of a container that uses the stateful
* allocator.
*
* \throws std::bad_alloc Instead of a GROMACS exception object, we
* throw the standard one on allocation failures to make it as
* compatible as possible with the errors expected by code using the
* standard library containers.
*
* \inlibraryapi
* \ingroup module_utility
*/
template <class T, typename AllocationPolicy>
class Allocator : public AllocationPolicy
{
public:
// The standard library specification for a custom allocator
// requires these typedefs, with this capitalization/underscoring.
typedef T value_type; //!< Type of allocated elements
typedef T &reference; //!< Reference to allocated elements
typedef const T &const_reference; //!< Constant reference to allocated elements
typedef T * pointer; //!< Pointer to allocated elements
typedef const T * const_pointer; //!< Constant pointer to allocated elements
typedef std::size_t size_type; //!< Integer type to use for size of objects
typedef std::ptrdiff_t difference_type; //!< Type to hold differences between pointers
// This typedef is required by GROMACS for testing and assertions
typedef AllocationPolicy allocation_policy; //!< Type of the AllocationPolicy
/*! \libinternal \brief Standard-required typedef to use allocator with different class.
*
* \tparam U new class
*
* This is used for things like std::list where the size of each link
* is larger than the class stored in the link.
*
* Required by the specification for an allocator.
*/
template <class U>
struct rebind
{
typedef Allocator<U, AllocationPolicy> other; //!< Align class U with our alignment
};
/*! \brief Templated copy constructor
*
* This template constructor cannot be auto-generated, and is
* normally unused, except e.g. MSVC2015 standard library uses
* it in debug mode, presumably to implement some checks.
*/
template <class U>
explicit Allocator(const Allocator<U, AllocationPolicy> &) {}
/*! \brief Constructor
*
* No constructor can be auto-generated in the presence of any
* user-defined constructor, but we want the default constructor.
*/
Allocator() = default;
/*! \brief Constructor to accept an AllocationPolicy.
*
* This is useful for AllocationPolicies with state.
*/
Allocator(const AllocationPolicy &p) : AllocationPolicy(p) {}
/*! \brief Return address of an object
*
* \param r Reference to object of type T
* \return Pointer to T memory
*/
pointer
address(reference r) const { return &r; }
/*! \brief Return address of a const object
*
* \param r Const reference to object of type T
* \return Pointer to T memory
*/
const_pointer
address(const_reference r) const { return &r; }
/*! \brief Do the actual memory allocation
*
* \param n Number of elements of type T to allocate. n can be
* 0 bytes, which will return a non-null properly aligned
* and padded pointer that should not be used.
* \param hint Optional value returned from previous call to allocate.
* For now this is not used.
* \return Pointer to allocated memory
*
* \throws std::bad_alloc if the allocation fails.
*/
pointer
allocate(std::size_t n, typename std::allocator<void>::const_pointer gmx_unused hint = nullptr)
{
void *p = AllocationPolicy::malloc(n*sizeof(T));
if (p == nullptr)
{
throw std::bad_alloc();
}
else
{
return static_cast<pointer>(p);
}
}
/*! \brief Release memory
*
* \param p Pointer to previously allocated memory returned from allocate()
* \param n number of objects previously passed to allocate()
*/
void
deallocate(pointer p, std::size_t gmx_unused n)
{
AllocationPolicy::free(p);
}
//! Return the policy object for this allocator.
AllocationPolicy getPolicy() const
{
return *this;
}
/*! \brief Construct an object without allocating memory
*
* \tparam Args Variable-length list of types for constructor args
* \param p Adress of memory where to construct object
* \param args Variable-length list of arguments to constructor
*/
template<class ... Args>
void
construct(pointer p, Args && ... args) { ::new((void *)p)T(std::forward<Args>(args) ...); }
/*! \brief Call the destructor of object without releasing memory
*
* \param p Address of memory where to destroy object
*/
void
destroy(pointer p) { p->~value_type(); }
/*! \brief Return largest number of objects that can be allocated
*
* This will be set such that the number of objects T multiplied by
* the size of each object is the largest value that can be represented
* by size_type.
*/
std::size_t
max_size() const { return (static_cast<std::size_t>(0) - static_cast<std::size_t>(1)) / sizeof(T); }
/*! \brief Return true if two allocators are identical
*
* This is a member function of the left-hand-side allocator.
*/
template<class T2>
bool
operator==(const Allocator<T2, AllocationPolicy> &) const { return std::is_same<T, T2>::value; }
/*! \brief Return true if two allocators are different
*
* \param rhs Other allocator.
*
* This is a member function of the left-hand-side allocator.
*/
bool
operator!=(const Allocator &rhs) const { return !operator==(rhs); }
};
} // namespace gmx
#endif
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