libcxx/include/__memory_resource/monotonic_buffer_resource.h

   1 //===----------------------------------------------------------------------===//
   2 //
   3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
   4 // See https://llvm.org/LICENSE.txt for license information.
   5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   6 //
   7 //===----------------------------------------------------------------------===//
   8
   9 #ifndef _LIBCPP___MEMORY_RESOURCE_MONOTONIC_BUFFER_RESOURCE_H
  10 #define _LIBCPP___MEMORY_RESOURCE_MONOTONIC_BUFFER_RESOURCE_H
  11
  12 #include <__availability>
  13 #include <__config>
  14 #include <__memory/addressof.h>
  15 #include <__memory_resource/memory_resource.h>
  16 #include <cstddef>
  17
  18 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
  19 #  pragma GCC system_header
  20 #endif
  21
  22 #if _LIBCPP_STD_VER >= 17
  23
  24 _LIBCPP_BEGIN_NAMESPACE_STD
  25
  26 namespace pmr {
  27
  28 // [mem.res.monotonic.buffer]
  29
  30 class _LIBCPP_AVAILABILITY_PMR _LIBCPP_EXPORTED_FROM_ABI monotonic_buffer_resource : public memory_resource {
  31   static const size_t __default_buffer_capacity  = 1024;
  32   static const size_t __default_buffer_alignment = 16;
  33
  34   struct __chunk_footer {
  35     __chunk_footer* __next_;
  36     char* __start_;
  37     char* __cur_;
  38     size_t __align_;
  39     _LIBCPP_HIDE_FROM_ABI size_t __allocation_size() {
  40       return (reinterpret_cast<char*>(this) - __start_) + sizeof(*this);
  41     }
  42     void* __try_allocate_from_chunk(size_t, size_t);
  43   };
  44
  45   struct __initial_descriptor {
  46     char* __start_;
  47     char* __cur_;
  48     union {
  49       char* __end_;
  50       size_t __size_;
  51     };
  52     void* __try_allocate_from_chunk(size_t, size_t);
  53   };
  54
  55 public:
  56   _LIBCPP_HIDE_FROM_ABI monotonic_buffer_resource()
  57       : monotonic_buffer_resource(nullptr, __default_buffer_capacity, get_default_resource()) {}
  58
  59   _LIBCPP_HIDE_FROM_ABI explicit monotonic_buffer_resource(size_t __initial_size)
  60       : monotonic_buffer_resource(nullptr, __initial_size, get_default_resource()) {}
  61
  62   _LIBCPP_HIDE_FROM_ABI monotonic_buffer_resource(void* __buffer, size_t __buffer_size)
  63       : monotonic_buffer_resource(__buffer, __buffer_size, get_default_resource()) {}
  64
  65   _LIBCPP_HIDE_FROM_ABI explicit monotonic_buffer_resource(memory_resource* __upstream)
  66       : monotonic_buffer_resource(nullptr, __default_buffer_capacity, __upstream) {}
  67
  68   _LIBCPP_HIDE_FROM_ABI monotonic_buffer_resource(size_t __initial_size, memory_resource* __upstream)
  69       : monotonic_buffer_resource(nullptr, __initial_size, __upstream) {}
  70
  71   _LIBCPP_HIDE_FROM_ABI monotonic_buffer_resource(void* __buffer, size_t __buffer_size, memory_resource* __upstream)
  72       : __res_(__upstream) {
  73     __initial_.__start_ = static_cast<char*>(__buffer);
  74     if (__buffer != nullptr) {
  75       __initial_.__cur_ = static_cast<char*>(__buffer) + __buffer_size;
  76       __initial_.__end_ = static_cast<char*>(__buffer) + __buffer_size;
  77     } else {
  78       __initial_.__cur_  = nullptr;
  79       __initial_.__size_ = __buffer_size;
  80     }
  81     __chunks_ = nullptr;
  82   }
  83
  84   monotonic_buffer_resource(const monotonic_buffer_resource&) = delete;
  85
  86   _LIBCPP_HIDE_FROM_ABI_VIRTUAL ~monotonic_buffer_resource() override { release(); }
  87
  88   monotonic_buffer_resource& operator=(const monotonic_buffer_resource&) = delete;
  89
  90   _LIBCPP_HIDE_FROM_ABI void release() {
  91     if (__initial_.__start_ != nullptr)
  92       __initial_.__cur_ = __initial_.__end_;
  93     while (__chunks_ != nullptr) {
  94       __chunk_footer* __next = __chunks_->__next_;
  95       __res_->deallocate(__chunks_->__start_, __chunks_->__allocation_size(), __chunks_->__align_);
  96       __chunks_ = __next;
  97     }
  98   }
  99
 100   _LIBCPP_HIDE_FROM_ABI memory_resource* upstream_resource() const { return __res_; }
 101
 102 protected:
 103   void* do_allocate(size_t __bytes, size_t __alignment) override; // key function
 104
 105   _LIBCPP_HIDE_FROM_ABI_VIRTUAL void do_deallocate(void*, size_t, size_t) override {}
 106
 107   _LIBCPP_HIDE_FROM_ABI_VIRTUAL bool do_is_equal(const memory_resource& __other) const _NOEXCEPT override {
 108     return this == std::addressof(__other);
 109   }
 110
 111 private:
 112   __initial_descriptor __initial_;
 113   __chunk_footer* __chunks_;
 114   memory_resource* __res_;
 115 };
 116
 117 } // namespace pmr
 118
 119 _LIBCPP_END_NAMESPACE_STD
 120
 121 #endif // _LIBCPP_STD_VER >= 17
 122
 123 #endif // _LIBCPP___MEMORY_RESOURCE_MONOTONIC_BUFFER_RESOURCE_H