. /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   */
HITCBC 75   5293 static void* operator new(std::size_t size) 75   5308 static void* operator new(std::size_t size)
76   { 76   {
HITCBC 77   5293 static auto* const rmr = get_recycling_memory_resource(); 77   5308 static auto* const rmr = get_recycling_memory_resource();
78   78  
HITCBC 79   5293 auto* mr = get_current_frame_allocator(); 79   5308 auto* mr = get_current_frame_allocator();
HITCBC 80   5293 if(!mr) 80   5308 if(!mr)
HITCBC 81   2802 mr = std::pmr::get_default_resource(); 81   2804 mr = std::pmr::get_default_resource();
82   82  
HITCBC 83   5293 auto total = size + sizeof(std::pmr::memory_resource*); 83   5308 auto total = size + sizeof(std::pmr::memory_resource*);
84   void* raw; 84   void* raw;
HITCBC 85   5293 if(mr == rmr) 85   5308 if(mr == rmr)
86   raw = static_cast<recycling_memory_resource*>(mr) 86   raw = static_cast<recycling_memory_resource*>(mr)
HITCBC 87   2079 ->allocate_fast(total, alignof(std::max_align_t)); 87   2092 ->allocate_fast(total, alignof(std::max_align_t));
88   else 88   else
HITCBC 89   3214 raw = mr->allocate(total, alignof(std::max_align_t)); 89   3216 raw = mr->allocate(total, alignof(std::max_align_t));
HITCBC 90   5293 std::memcpy(static_cast<char*>(raw) + size, &mr, sizeof(mr)); 90   5308 std::memcpy(static_cast<char*>(raw) + size, &mr, sizeof(mr));
HITCBC 91   5293 return raw; 91   5308 return raw;
92   } 92   }
93   93  
94   /** Deallocate a coroutine frame. 94   /** Deallocate a coroutine frame.
95   95  
96   Reads the allocator pointer stored at the end of the frame 96   Reads the allocator pointer stored at the end of the frame
97   to ensure correct deallocation regardless of current TLS. 97   to ensure correct deallocation regardless of current TLS.
98   Bypasses virtual dispatch for the recycling allocator. 98   Bypasses virtual dispatch for the recycling allocator.
99   */ 99   */
HITCBC 100   5293 static void operator delete(void* ptr, std::size_t size) noexcept 100   5308 static void operator delete(void* ptr, std::size_t size) noexcept
101   { 101   {
HITCBC 102   5293 static auto* const rmr = get_recycling_memory_resource(); 102   5308 static auto* const rmr = get_recycling_memory_resource();
103   103  
104   std::pmr::memory_resource* mr; 104   std::pmr::memory_resource* mr;
HITCBC 105   5293 std::memcpy(&mr, static_cast<char*>(ptr) + size, sizeof(mr)); 105   5308 std::memcpy(&mr, static_cast<char*>(ptr) + size, sizeof(mr));
HITCBC 106   5293 auto total = size + sizeof(std::pmr::memory_resource*); 106   5308 auto total = size + sizeof(std::pmr::memory_resource*);
HITCBC 107   5293 if(mr == rmr) 107   5308 if(mr == rmr)
108   static_cast<recycling_memory_resource*>(mr) 108   static_cast<recycling_memory_resource*>(mr)
HITCBC 109   2079 ->deallocate_fast(ptr, total, alignof(std::max_align_t)); 109   2092 ->deallocate_fast(ptr, total, alignof(std::max_align_t));
110   else 110   else
HITCBC 111   3214 mr->deallocate(ptr, total, alignof(std::max_align_t)); 111   3216 mr->deallocate(ptr, total, alignof(std::max_align_t));
HITCBC 112   5293 } 112   5308 }
113   }; 113   };
114   114  
115   } // namespace capy 115   } // namespace capy
116   } // namespace boost 116   } // namespace boost
117   117  
118   #endif 118   #endif