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