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Added thirdparty: boost library
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Viacheslav Demydiuk
+354
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//
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// Copyright (c) 2019 Vinnie Falco (vinnie.falco@gmail.com)
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// Copyright (c) 2020 Krystian Stasiowski (sdkrystian@gmail.com)
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//
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// Distributed under the Boost Software License, Version 1.0. (See accompanying
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// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
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//
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// Official repository: https://github.com/boostorg/json
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//
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#ifndef BOOST_JSON_MONOTONIC_RESOURCE_HPP
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#define BOOST_JSON_MONOTONIC_RESOURCE_HPP
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#include <boost/json/detail/config.hpp>
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#include <boost/json/memory_resource.hpp>
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#include <boost/json/storage_ptr.hpp>
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#include <cstddef>
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#include <utility>
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namespace boost {
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namespace json {
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#ifdef _MSC_VER
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#pragma warning(push)
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#pragma warning(disable: 4251) // class needs to have dll-interface to be used by clients of class
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#pragma warning(disable: 4275) // non dll-interface class used as base for dll-interface class
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#endif
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//----------------------------------------------------------
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/** A dynamically allocating resource with a trivial deallocate
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This memory resource is a special-purpose resource
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that releases allocated memory only when the resource
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is destroyed (or when @ref release is called).
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It has a trivial deallocate function; that is, the
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metafunction @ref is_deallocate_trivial returns `true`.
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\n
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The resource can be constructed with an initial buffer.
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If there is no initial buffer, or if the buffer is
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exhausted, subsequent dynamic allocations are made from
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the system heap. The size of buffers obtained in this
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fashion follow a geometric progression.
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\n
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The purpose of this resource is to optimize the use
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case for performing many allocations, followed by
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deallocating everything at once. This is precisely the
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pattern of memory allocation which occurs when parsing:
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allocation is performed for each parsed element, and
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when the the resulting @ref value is no longer needed,
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the entire structure is destroyed. However, it is not
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suited for modifying the value after parsing is
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complete; reallocations waste memory, since the
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older buffer is not reclaimed until the resource
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is destroyed.
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@par Example
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This parses a JSON text into a value which uses a local
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stack buffer, then prints the result.
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@code
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unsigned char buf[ 4000 ];
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monotonic_resource mr( buf );
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// Parse the string, using our memory resource
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auto const jv = parse( "[1,2,3]", &mr );
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// Print the JSON
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std::cout << jv;
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@endcode
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@note The total amount of memory dynamically
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allocated is monotonically increasing; That is,
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it never decreases.
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@par Thread Safety
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Members of the same instance may not be
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called concurrently.
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@see
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https://en.wikipedia.org/wiki/Region-based_memory_management
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*/
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class
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BOOST_JSON_DECL
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BOOST_SYMBOL_VISIBLE
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monotonic_resource final
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: public memory_resource
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{
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struct block;
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struct block_base
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{
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void* p;
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std::size_t avail;
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std::size_t size;
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block_base* next;
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};
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block_base buffer_;
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block_base* head_ = &buffer_;
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std::size_t next_size_ = 1024;
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storage_ptr upstream_;
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static constexpr std::size_t min_size_ = 1024;
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inline static constexpr std::size_t max_size();
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inline static std::size_t round_pow2(
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std::size_t n) noexcept;
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inline static std::size_t next_pow2(
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std::size_t n) noexcept;
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public:
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/// Copy constructor (deleted)
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monotonic_resource(
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monotonic_resource const&) = delete;
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/// Copy assignment (deleted)
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monotonic_resource& operator=(
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monotonic_resource const&) = delete;
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/** Destructor
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Deallocates all the memory owned by this resource.
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@par Effects
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@code
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this->release();
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@endcode
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@par Complexity
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Linear in the number of deallocations performed.
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@par Exception Safety
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No-throw guarantee.
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*/
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~monotonic_resource();
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/** Constructor
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This constructs the resource and indicates
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that the first internal dynamic allocation
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shall be at least `initial_size` bytes.
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\n
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This constructor is guaranteed not to perform
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any dynamic allocations.
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@par Complexity
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Constant.
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@par Exception Safety
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No-throw guarantee.
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@param initial_size The size of the first
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internal dynamic allocation. If this is lower
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than the implementation-defined lower limit, then
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the lower limit is used instead.
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@param upstream An optional upstream memory resource
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to use for performing internal dynamic allocations.
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If this parameter is omitted, the default resource
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is used.
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*/
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explicit
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monotonic_resource(
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std::size_t initial_size = 1024,
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storage_ptr upstream = {}) noexcept;
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/** Constructor
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This constructs the resource and indicates that
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subsequent allocations should use the specified
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caller-owned buffer.
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When this buffer is exhausted, dynamic allocations
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from the upstream resource are made.
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\n
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This constructor is guaranteed not to perform
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any dynamic allocations.
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@par Complexity
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Constant.
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@par Exception Safety
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No-throw guarantee.
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@param buffer The buffer to use.
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Ownership is not transferred; the caller is
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responsible for ensuring that the lifetime of
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the buffer extends until the resource is destroyed.
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@param size The number of valid bytes pointed
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to by `buffer`.
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@param upstream An optional upstream memory resource
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to use for performing internal dynamic allocations.
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If this parameter is omitted, the default resource
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is used.
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*/
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/** @{ */
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monotonic_resource(
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unsigned char* buffer,
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std::size_t size,
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storage_ptr upstream = {}) noexcept;
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#if defined(__cpp_lib_byte) || defined(BOOST_JSON_DOCS)
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monotonic_resource(
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std::byte* buffer,
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std::size_t size,
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storage_ptr upstream) noexcept
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: monotonic_resource(reinterpret_cast<
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unsigned char*>(buffer), size,
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std::move(upstream))
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{
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}
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#endif
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/** @} */
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/** Constructor
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This constructs the resource and indicates that
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subsequent allocations should use the specified
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caller-owned buffer.
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When this buffer is exhausted, dynamic allocations
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from the upstream resource are made.
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\n
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This constructor is guaranteed not to perform
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any dynamic allocations.
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@par Complexity
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Constant.
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@par Exception Safety
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No-throw guarantee.
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@param buffer The buffer to use.
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Ownership is not transferred; the caller is
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responsible for ensuring that the lifetime of
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the buffer extends until the resource is destroyed.
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@param upstream An optional upstream memory resource
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to use for performing internal dynamic allocations.
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If this parameter is omitted, the default resource
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is used.
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*/
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/** @{ */
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template<std::size_t N>
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explicit
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monotonic_resource(
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unsigned char(&buffer)[N],
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storage_ptr upstream = {}) noexcept
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: monotonic_resource(&buffer[0],
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N, std::move(upstream))
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{
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}
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#if defined(__cpp_lib_byte) || defined(BOOST_JSON_DOCS)
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template<std::size_t N>
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explicit
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monotonic_resource(
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std::byte(&buffer)[N],
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storage_ptr upstream = {}) noexcept
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: monotonic_resource(&buffer[0],
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N, std::move(upstream))
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{
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}
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#endif
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/** @} */
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#ifndef BOOST_JSON_DOCS
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// Safety net for accidental buffer overflows
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template<std::size_t N>
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monotonic_resource(
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unsigned char(&buffer)[N],
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std::size_t n,
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storage_ptr upstream = {}) noexcept
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: monotonic_resource(&buffer[0],
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n, std::move(upstream))
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{
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// If this goes off, check your parameters
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// closely, chances are you passed an array
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// thinking it was a pointer.
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BOOST_ASSERT(n <= N);
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}
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#ifdef __cpp_lib_byte
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// Safety net for accidental buffer overflows
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template<std::size_t N>
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monotonic_resource(
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std::byte(&buffer)[N],
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std::size_t n,
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storage_ptr upstream = {}) noexcept
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: monotonic_resource(&buffer[0],
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n, std::move(upstream))
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{
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// If this goes off, check your parameters
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// closely, chances are you passed an array
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// thinking it was a pointer.
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BOOST_ASSERT(n <= N);
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}
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#endif
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#endif
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/** Release all allocated memory.
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This function deallocates all allocated memory.
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If an initial buffer was provided upon construction,
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then all of the bytes will be available again for
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allocation. Allocated memory is deallocated even
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if deallocate has not been called for some of
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the allocated blocks.
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@par Complexity
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Linear in the number of deallocations performed.
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@par Exception Safety
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No-throw guarantee.
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*/
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void
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release() noexcept;
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protected:
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#ifndef BOOST_JSON_DOCS
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void*
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do_allocate(
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std::size_t n,
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std::size_t align) override;
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void
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do_deallocate(
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void* p,
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std::size_t n,
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std::size_t align) override;
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bool
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do_is_equal(
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memory_resource const& mr) const noexcept override;
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#endif
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};
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#ifdef _MSC_VER
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#pragma warning(pop)
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#endif
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template<>
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struct is_deallocate_trivial<
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monotonic_resource>
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{
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static constexpr bool value = true;
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};
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} // namespace json
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} // namespace boost
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#endif
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