. /include/boost/capy /ex /frame_alloc_mixin.hpp
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1   // 1   //
2   // Copyright (c) 2026 Michael Vandeberg 2   // Copyright (c) 2026 Michael Vandeberg
3   // 3   //
4   // Distributed under the Boost Software License, Version 1.0. (See accompanying 4   // Distributed under the Boost Software License, Version 1.0. (See accompanying
5   // file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt) 5   // file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
6   // 6   //
7   // Official repository: https://github.com/cppalliance/capy 7   // Official repository: https://github.com/cppalliance/capy
8   // 8   //
9   9  
10   #ifndef BOOST_CAPY_EX_FRAME_ALLOC_MIXIN_HPP 10   #ifndef BOOST_CAPY_EX_FRAME_ALLOC_MIXIN_HPP
11   #define BOOST_CAPY_EX_FRAME_ALLOC_MIXIN_HPP 11   #define BOOST_CAPY_EX_FRAME_ALLOC_MIXIN_HPP
12   12  
13   #include <boost/capy/detail/config.hpp> 13   #include <boost/capy/detail/config.hpp>
14   #include <boost/capy/ex/frame_allocator.hpp> 14   #include <boost/capy/ex/frame_allocator.hpp>
15   #include <boost/capy/ex/recycling_memory_resource.hpp> 15   #include <boost/capy/ex/recycling_memory_resource.hpp>
16   16  
17   #include <cstddef> 17   #include <cstddef>
18   #include <cstring> 18   #include <cstring>
19   #include <memory_resource> 19   #include <memory_resource>
20   20  
21   namespace boost { 21   namespace boost {
22   namespace capy { 22   namespace capy {
23   23  
24   /** Mixin that adds frame-allocator-aware allocation to a promise type. 24   /** Mixin that adds frame-allocator-aware allocation to a promise type.
25   25  
26   Inherit from this class in any coroutine promise type to opt into 26   Inherit from this class in any coroutine promise type to opt into
27   TLS-based frame allocation with the recycling memory resource 27   TLS-based frame allocation with the recycling memory resource
28   fast path. The mixin provides `operator new` and `operator delete` 28   fast path. The mixin provides `operator new` and `operator delete`
29   that: 29   that:
30   30  
31   1. Read the thread-local frame allocator set by `run_async` or `run`. 31   1. Read the thread-local frame allocator set by `run_async` or `run`.
32   2. Bypass virtual dispatch when the allocator is the default 32   2. Bypass virtual dispatch when the allocator is the default
33   recycling memory resource. 33   recycling memory resource.
34   3. Store the allocator pointer at the end of each frame for 34   3. Store the allocator pointer at the end of each frame for
35   correct deallocation even when TLS changes between allocation 35   correct deallocation even when TLS changes between allocation
36   and deallocation. 36   and deallocation.
37   37  
38   This is the same allocation strategy used by @ref 38   This is the same allocation strategy used by @ref
39   io_awaitable_promise_base. Use this mixin directly when your 39   io_awaitable_promise_base. Use this mixin directly when your
40   promise type does not need the full environment and continuation 40   promise type does not need the full environment and continuation
41   support that `io_awaitable_promise_base` provides. 41   support that `io_awaitable_promise_base` provides.
42   42  
43   @par Example 43   @par Example
44   @code 44   @code
45   struct my_internal_coroutine 45   struct my_internal_coroutine
46   { 46   {
47   struct promise_type : frame_alloc_mixin 47   struct promise_type : frame_alloc_mixin
48   { 48   {
49   my_internal_coroutine get_return_object(); 49   my_internal_coroutine get_return_object();
50   std::suspend_always initial_suspend() noexcept; 50   std::suspend_always initial_suspend() noexcept;
51   std::suspend_always final_suspend() noexcept; 51   std::suspend_always final_suspend() noexcept;
52   void return_void(); 52   void return_void();
53   void unhandled_exception() noexcept; 53   void unhandled_exception() noexcept;
54   }; 54   };
55   }; 55   };
56   @endcode 56   @endcode
57   57  
58   @par Thread Safety 58   @par Thread Safety
59   The allocation fast path uses thread-local storage and requires 59   The allocation fast path uses thread-local storage and requires
60   no synchronization. The global pool fallback is mutex-protected. 60   no synchronization. The global pool fallback is mutex-protected.
61   61  
62   @see io_awaitable_promise_base, frame_allocator, recycling_memory_resource 62   @see io_awaitable_promise_base, frame_allocator, recycling_memory_resource
63   */ 63   */
64   struct frame_alloc_mixin 64   struct frame_alloc_mixin
65   { 65   {
66   /** Allocate a coroutine frame. 66   /** Allocate a coroutine frame.
67   67  
68   Uses the thread-local frame allocator set by run_async. 68   Uses the thread-local frame allocator set by run_async.
69   Falls back to default memory resource if not set. 69   Falls back to default memory resource if not set.
70   Stores the allocator pointer at the end of each frame for 70   Stores the allocator pointer at the end of each frame for
71   correct deallocation even when TLS changes. Uses memcpy 71   correct deallocation even when TLS changes. Uses memcpy
72   to avoid alignment requirements on the trailing pointer. 72   to avoid alignment requirements on the trailing pointer.
73   Bypasses virtual dispatch for the recycling allocator. 73   Bypasses virtual dispatch for the recycling allocator.
  74 +
  75 + @param size The size, in bytes, of the coroutine frame.
  76 +
  77 + @return A pointer to storage for the frame.
  78 +
  79 + @throws Propagates any exception thrown by the underlying
  80 + memory resource's `allocate` (for example `std::bad_alloc`
  81 + from `::operator new`).
74   */ 82   */
HITCBC 75   5450 static void* operator new(std::size_t size) 83   5417 static void* operator new(std::size_t size)
76   { 84   {
HITCBC 77   5450 static auto* const rmr = get_recycling_memory_resource(); 85   5417 static auto* const rmr = get_recycling_memory_resource();
78   86  
HITCBC 79   5450 auto* mr = get_current_frame_allocator(); 87   5417 auto* mr = get_current_frame_allocator();
HITCBC 80   5450 if(!mr) 88   5417 if(!mr)
HITCBC 81   2871 mr = std::pmr::get_default_resource(); 89   2848 mr = std::pmr::get_default_resource();
82   90  
HITCBC 83   5450 auto total = size + sizeof(std::pmr::memory_resource*); 91   5417 auto total = size + sizeof(std::pmr::memory_resource*);
84   void* raw; 92   void* raw;
HITCBC 85   5450 if(mr == rmr) 93   5417 if(mr == rmr)
86   raw = static_cast<recycling_memory_resource*>(mr) 94   raw = static_cast<recycling_memory_resource*>(mr)
HITCBC 87   2158 ->allocate_fast(total, alignof(std::max_align_t)); 95   2149 ->allocate_fast(total, alignof(std::max_align_t));
88   else 96   else
HITCBC 89   3292 raw = mr->allocate(total, alignof(std::max_align_t)); 97   3268 raw = mr->allocate(total, alignof(std::max_align_t));
HITCBC 90   5450 std::memcpy(static_cast<char*>(raw) + size, &mr, sizeof(mr)); 98   5417 std::memcpy(static_cast<char*>(raw) + size, &mr, sizeof(mr));
HITCBC 91   5450 return raw; 99   5417 return raw;
92   } 100   }
93   101  
94   /** Deallocate a coroutine frame. 102   /** Deallocate a coroutine frame.
95   103  
96   Reads the allocator pointer stored at the end of the frame 104   Reads the allocator pointer stored at the end of the frame
97   to ensure correct deallocation regardless of current TLS. 105   to ensure correct deallocation regardless of current TLS.
98   Bypasses virtual dispatch for the recycling allocator. 106   Bypasses virtual dispatch for the recycling allocator.
99   */ 107   */
HITCBC 100   5450 static void operator delete(void* ptr, std::size_t size) noexcept 108   5417 static void operator delete(void* ptr, std::size_t size) noexcept
101   { 109   {
HITCBC 102   5450 static auto* const rmr = get_recycling_memory_resource(); 110   5417 static auto* const rmr = get_recycling_memory_resource();
103   111  
104   std::pmr::memory_resource* mr; 112   std::pmr::memory_resource* mr;
HITCBC 105   5450 std::memcpy(&mr, static_cast<char*>(ptr) + size, sizeof(mr)); 113   5417 std::memcpy(&mr, static_cast<char*>(ptr) + size, sizeof(mr));
HITCBC 106   5450 auto total = size + sizeof(std::pmr::memory_resource*); 114   5417 auto total = size + sizeof(std::pmr::memory_resource*);
HITCBC 107   5450 if(mr == rmr) 115   5417 if(mr == rmr)
108   static_cast<recycling_memory_resource*>(mr) 116   static_cast<recycling_memory_resource*>(mr)
HITCBC 109   2158 ->deallocate_fast(ptr, total, alignof(std::max_align_t)); 117   2149 ->deallocate_fast(ptr, total, alignof(std::max_align_t));
110   else 118   else
HITCBC 111   3292 mr->deallocate(ptr, total, alignof(std::max_align_t)); 119   3268 mr->deallocate(ptr, total, alignof(std::max_align_t));
HITCBC 112   5450 } 120   5417 }
113   }; 121   };
114   122  
115   } // namespace capy 123   } // namespace capy
116   } // namespace boost 124   } // namespace boost
117   125  
118   #endif 126   #endif