. /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   74  
75   @param size The size, in bytes, of the coroutine frame. 75   @param size The size, in bytes, of the coroutine frame.
76   76  
77   @return A pointer to storage for the frame. 77   @return A pointer to storage for the frame.
78   78  
79   @throws Propagates any exception thrown by the underlying 79   @throws Propagates any exception thrown by the underlying
80   memory resource's `allocate` (for example `std::bad_alloc` 80   memory resource's `allocate` (for example `std::bad_alloc`
81   from `::operator new`). 81   from `::operator new`).
82   */ 82   */
HITCBC 83   4992 static void* operator new(std::size_t size) 83   4959 static void* operator new(std::size_t size)
84   { 84   {
HITCBC 85   4992 static auto* const rmr = get_recycling_memory_resource(); 85   4959 static auto* const rmr = get_recycling_memory_resource();
86   86  
HITCBC 87   4992 auto* mr = get_current_frame_allocator(); 87   4959 auto* mr = get_current_frame_allocator();
HITCBC 88   4992 if(!mr) 88   4959 if(!mr)
HITCBC 89   2533 mr = std::pmr::get_default_resource(); 89   2508 mr = std::pmr::get_default_resource();
90   90  
HITCBC 91   4992 auto total = size + sizeof(std::pmr::memory_resource*); 91   4959 auto total = size + sizeof(std::pmr::memory_resource*);
92   void* raw; 92   void* raw;
HITCBC 93   4992 if(mr == rmr) 93   4959 if(mr == rmr)
94   raw = static_cast<recycling_memory_resource*>(mr) 94   raw = static_cast<recycling_memory_resource*>(mr)
HITCBC 95   1947 ->allocate_fast(total, alignof(std::max_align_t)); 95   1947 ->allocate_fast(total, alignof(std::max_align_t));
96   else 96   else
HITCBC 97   3045 raw = mr->allocate(total, alignof(std::max_align_t)); 97   3012 raw = mr->allocate(total, alignof(std::max_align_t));
HITCBC 98   4992 std::memcpy(static_cast<char*>(raw) + size, &mr, sizeof(mr)); 98   4959 std::memcpy(static_cast<char*>(raw) + size, &mr, sizeof(mr));
HITCBC 99   4992 return raw; 99   4959 return raw;
100   } 100   }
101   101  
102   /** Deallocate a coroutine frame. 102   /** Deallocate a coroutine frame.
103   103  
104   Reads the allocator pointer stored at the end of the frame 104   Reads the allocator pointer stored at the end of the frame
105   to ensure correct deallocation regardless of current TLS. 105   to ensure correct deallocation regardless of current TLS.
106   Bypasses virtual dispatch for the recycling allocator. 106   Bypasses virtual dispatch for the recycling allocator.
107   */ 107   */
HITCBC 108   4992 static void operator delete(void* ptr, std::size_t size) noexcept 108   4959 static void operator delete(void* ptr, std::size_t size) noexcept
109   { 109   {
HITCBC 110   4992 static auto* const rmr = get_recycling_memory_resource(); 110   4959 static auto* const rmr = get_recycling_memory_resource();
111   111  
112   std::pmr::memory_resource* mr; 112   std::pmr::memory_resource* mr;
HITCBC 113   4992 std::memcpy(&mr, static_cast<char*>(ptr) + size, sizeof(mr)); 113   4959 std::memcpy(&mr, static_cast<char*>(ptr) + size, sizeof(mr));
HITCBC 114   4992 auto total = size + sizeof(std::pmr::memory_resource*); 114   4959 auto total = size + sizeof(std::pmr::memory_resource*);
HITCBC 115   4992 if(mr == rmr) 115   4959 if(mr == rmr)
116   static_cast<recycling_memory_resource*>(mr) 116   static_cast<recycling_memory_resource*>(mr)
HITCBC 117   1947 ->deallocate_fast(ptr, total, alignof(std::max_align_t)); 117   1947 ->deallocate_fast(ptr, total, alignof(std::max_align_t));
118   else 118   else
HITCBC 119   3045 mr->deallocate(ptr, total, alignof(std::max_align_t)); 119   3012 mr->deallocate(ptr, total, alignof(std::max_align_t));
HITCBC 120   4992 } 120   4959 }
121   }; 121   };
122   122  
123   } // namespace capy 123   } // namespace capy
124   } // namespace boost 124   } // namespace boost
125   125  
126   #endif 126   #endif