. /include/boost/corosio /detail /timer.hpp
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1   // 1   //
2   // Copyright (c) 2025 Vinnie Falco (vinnie.falco@gmail.com) 2   // Copyright (c) 2025 Vinnie Falco (vinnie.falco@gmail.com)
3   // Copyright (c) 2026 Steve Gerbino 3   // Copyright (c) 2026 Steve Gerbino
4   // 4   //
5   // Distributed under the Boost Software License, Version 1.0. (See accompanying 5   // Distributed under the Boost Software License, Version 1.0. (See accompanying
6   // file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt) 6   // file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
7   // 7   //
8   // Official repository: https://github.com/cppalliance/corosio 8   // Official repository: https://github.com/cppalliance/corosio
9   // 9   //
10   10  
11   #ifndef BOOST_COROSIO_DETAIL_TIMER_HPP 11   #ifndef BOOST_COROSIO_DETAIL_TIMER_HPP
12   #define BOOST_COROSIO_DETAIL_TIMER_HPP 12   #define BOOST_COROSIO_DETAIL_TIMER_HPP
13   13  
14   #include <boost/corosio/detail/config.hpp> 14   #include <boost/corosio/detail/config.hpp>
15   #include <boost/corosio/detail/intrusive.hpp> 15   #include <boost/corosio/detail/intrusive.hpp>
16   #include <boost/corosio/detail/scheduler_op.hpp> 16   #include <boost/corosio/detail/scheduler_op.hpp>
17   #include <boost/corosio/io/io_object.hpp> 17   #include <boost/corosio/io/io_object.hpp>
18   #include <boost/capy/continuation.hpp> 18   #include <boost/capy/continuation.hpp>
19   #include <boost/capy/io_result.hpp> 19   #include <boost/capy/io_result.hpp>
20   #include <boost/capy/error.hpp> 20   #include <boost/capy/error.hpp>
21   #include <boost/capy/ex/executor_ref.hpp> 21   #include <boost/capy/ex/executor_ref.hpp>
22   #include <boost/capy/ex/execution_context.hpp> 22   #include <boost/capy/ex/execution_context.hpp>
23   #include <boost/capy/ex/io_env.hpp> 23   #include <boost/capy/ex/io_env.hpp>
24   24  
25   #include <atomic> 25   #include <atomic>
26   #include <chrono> 26   #include <chrono>
27   #include <coroutine> 27   #include <coroutine>
28   #include <cstddef> 28   #include <cstddef>
29   #include <limits> 29   #include <limits>
30   #include <new> 30   #include <new>
31   #include <stop_token> 31   #include <stop_token>
32   #include <system_error> 32   #include <system_error>
33   33  
34   namespace boost::corosio::detail { 34   namespace boost::corosio::detail {
35   35  
36   // timer_service is defined in timer_service.hpp, which includes this 36   // timer_service is defined in timer_service.hpp, which includes this
37   // header. waiter_node and wait_awaitable are defined below the timer 37   // header. waiter_node and wait_awaitable are defined below the timer
38   // class: waiter_node stores a timer::implementation*, which cannot be 38   // class: waiter_node stores a timer::implementation*, which cannot be
39   // forward-declared as a nested type. implementation stores only a 39   // forward-declared as a nested type. implementation stores only a
40   // waiter_node pointer, so this forward declaration suffices for its 40   // waiter_node pointer, so this forward declaration suffices for its
41   // data layout. 41   // data layout.
42   class timer_service; 42   class timer_service;
43   struct waiter_node; 43   struct waiter_node;
44   struct wait_awaitable; 44   struct wait_awaitable;
45   45  
46   /** An asynchronous timer for coroutine I/O. 46   /** An asynchronous timer for coroutine I/O.
47   47  
48   This class provides asynchronous timer operations that return 48   This class provides asynchronous timer operations that return
49   awaitable types. The timer can be used to schedule operations 49   awaitable types. The timer can be used to schedule operations
50   to occur after a specified duration or at a specific time point. 50   to occur after a specified duration or at a specific time point.
51   51  
52   Each timer carries at most one wait: `delay` and `timeout` own a 52   Each timer carries at most one wait: `delay` and `timeout` own a
53   private timer per `co_await`. When the timer expires the waiter 53   private timer per `co_await`. When the timer expires the waiter
54   completes with success; a cancelled wait completes with an error 54   completes with success; a cancelled wait completes with an error
55   that compares equal to `capy::cond::canceled`. 55   that compares equal to `capy::cond::canceled`.
56   56  
57   Each timer operation participates in the affine awaitable protocol, 57   Each timer operation participates in the affine awaitable protocol,
58   ensuring coroutines resume on the correct executor. 58   ensuring coroutines resume on the correct executor.
59   59  
60   @par Thread Safety 60   @par Thread Safety
61   Distinct objects: Safe.@n 61   Distinct objects: Safe.@n
62   Shared objects: Unsafe. 62   Shared objects: Unsafe.
63   63  
64   @par Semantics 64   @par Semantics
65   Timers are not backed by per-timer kernel objects. The io_context's 65   Timers are not backed by per-timer kernel objects. The io_context's
66   timer service keeps a process-side min-heap of pending expirations; 66   timer service keeps a process-side min-heap of pending expirations;
67   the nearest expiry drives the reactor's poll timeout, and expirations 67   the nearest expiry drives the reactor's poll timeout, and expirations
68   are processed in the run loop. 68   are processed in the run loop.
69   */ 69   */
70   class BOOST_COROSIO_DECL timer : public io_object 70   class BOOST_COROSIO_DECL timer : public io_object
71   { 71   {
72   friend struct wait_awaitable; 72   friend struct wait_awaitable;
73   73  
74   public: 74   public:
75   /** Backend state and wait entry point for a timer. 75   /** Backend state and wait entry point for a timer.
76   76  
77   Holds per-timer state ( expiry, heap position, the single waiter ) and 77   Holds per-timer state ( expiry, heap position, the single waiter ) and
78   the `wait` entry point used by the awaitable returned from 78   the `wait` entry point used by the awaitable returned from
79   @ref timer::wait. There is exactly one concrete timer backend, 79   @ref timer::wait. There is exactly one concrete timer backend,
80   so `wait` is a plain member function rather than a virtual 80   so `wait` is a plain member function rather than a virtual
81   dispatch point. 81   dispatch point.
82   */ 82   */
83   struct implementation : io_object::implementation 83   struct implementation : io_object::implementation
84   { 84   {
85   /// Sentinel value indicating the timer is not in the heap. 85   /// Sentinel value indicating the timer is not in the heap.
86   static constexpr std::size_t npos = 86   static constexpr std::size_t npos =
87   (std::numeric_limits<std::size_t>::max)(); 87   (std::numeric_limits<std::size_t>::max)();
88   88  
89   // Only mutated by the owning thread (expires_at/expires_after) 89   // Only mutated by the owning thread (expires_at/expires_after)
90   // before a wait is published; cross-thread consumers read the 90   // before a wait is published; cross-thread consumers read the
91   // heap entry's copied time_, never this field, so it needs no 91   // heap entry's copied time_, never this field, so it needs no
92   // atomicity. 92   // atomicity.
93   /// The absolute expiry time point. 93   /// The absolute expiry time point.
94   std::chrono::steady_clock::time_point expiry_{}; 94   std::chrono::steady_clock::time_point expiry_{};
95   95  
96   // heap_index_ and might_have_pending_waits_ are cross-thread 96   // heap_index_ and might_have_pending_waits_ are cross-thread
97   // hints, not authoritative state: the real state lives in the 97   // hints, not authoritative state: the real state lives in the
98   // heap and the published waiter under timer_service::mutex_. Every 98   // heap and the published waiter under timer_service::mutex_. Every
99   // unlocked fast-out that reads them is either re-validated under 99   // unlocked fast-out that reads them is either re-validated under
100   // the mutex or safe under a stale value in both directions, and 100   // the mutex or safe under a stale value in both directions, and
101   // any locked writer / locked reader pair is already ordered by 101   // any locked writer / locked reader pair is already ordered by
102   // the mutex. All accesses therefore use memory_order_relaxed, 102   // the mutex. All accesses therefore use memory_order_relaxed,
103   // which keeps the lock-free fast paths fence-free while making 103   // which keeps the lock-free fast paths fence-free while making
104   // the concurrent reads well-defined. 104   // the concurrent reads well-defined.
105   /// Index in the timer service's min-heap, or `npos`. 105   /// Index in the timer service's min-heap, or `npos`.
106   std::atomic<std::size_t> heap_index_{npos}; 106   std::atomic<std::size_t> heap_index_{npos};
107   107  
108   // false implies waiter_ is null: both are cleared together 108   // false implies waiter_ is null: both are cleared together
109   // under the service mutex. 109   // under the service mutex.
110   /// True if `wait()` has been called since last cancel. 110   /// True if `wait()` has been called since last cancel.
111   std::atomic<bool> might_have_pending_waits_{false}; 111   std::atomic<bool> might_have_pending_waits_{false};
112   112  
113   /// The timer service that owns this implementation. 113   /// The timer service that owns this implementation.
114   timer_service* svc_ = nullptr; 114   timer_service* svc_ = nullptr;
115   115  
116   // Exactly one wait may be outstanding: delay and timeout own 116   // Exactly one wait may be outstanding: delay and timeout own
117   // a private timer per co_await, and the service's drains rely 117   // a private timer per co_await, and the service's drains rely
118   // on the one-to-one pairing. 118   // on the one-to-one pairing.
119   /// The waiter published on this timer, or `nullptr`. 119   /// The waiter published on this timer, or `nullptr`.
120   waiter_node* waiter_ = nullptr; 120   waiter_node* waiter_ = nullptr;
121   121  
122   /// Free list linkage, reused when this impl is recycled. 122   /// Free list linkage, reused when this impl is recycled.
123   implementation* next_free_ = nullptr; 123   implementation* next_free_ = nullptr;
124   124  
125   /// Construct bound to the given timer service. 125   /// Construct bound to the given timer service.
HITCBC 126   1372 explicit implementation(timer_service& svc) noexcept : svc_(&svc) {} 126   1806 explicit implementation(timer_service& svc) noexcept : svc_(&svc) {}
127   127  
128   /** Check whether the timer is expired and absent from the heap. 128   /** Check whether the timer is expired and absent from the heap.
129   129  
130   The single definition of the already-expired fast-path 130   The single definition of the already-expired fast-path
131   predicate: `await_suspend` tests it inline and `wait()` 131   predicate: `await_suspend` tests it inline and `wait()`
132   re-tests it because the expiry can elapse between the two 132   re-tests it because the expiry can elapse between the two
133   reads. 133   reads.
134   */ 134   */
HITCBC 135   28315 bool already_expired() const noexcept 135   28837 bool already_expired() const noexcept
136   { 136   {
HITCBC 137   84945 return heap_index_.load(std::memory_order_relaxed) == npos && 137   86511 return heap_index_.load(std::memory_order_relaxed) == npos &&
HITCBC 138   55966 (expiry_ == (std::chrono::steady_clock::time_point::min)() || 138   57010 (expiry_ == (std::chrono::steady_clock::time_point::min)() ||
HITCBC 139   55966 expiry_ <= std::chrono::steady_clock::now()); 139   57010 expiry_ <= std::chrono::steady_clock::now());
140   } 140   }
141   141  
142   /** Asynchronously wait for the timer to expire. 142   /** Asynchronously wait for the timer to expire.
143   143  
144   Publishes the waiter into the service's heap and the 144   Publishes the waiter into the service's heap and the
145   timer's waiter slot, after which it may complete on any 145   timer's waiter slot, after which it may complete on any
146   thread. If the timer is already expired and not in the 146   thread. If the timer is already expired and not in the
147   heap, completes by posting the continuation without 147   heap, completes by posting the continuation without
148   publishing. 148   publishing.
149   149  
150   @pre @p w is fully initialized, and its storage (the awaitable 150   @pre @p w is fully initialized, and its storage (the awaitable
151   on the suspended coroutine's frame) outlives the wait. 151   on the suspended coroutine's frame) outlives the wait.
152   152  
153   @param w The waiter to publish. 153   @param w The waiter to publish.
154   */ 154   */
155   // Exported at member level: dllexport on the enclosing timer 155   // Exported at member level: dllexport on the enclosing timer
156   // class does not extend to nested classes, and header-inline 156   // class does not extend to nested classes, and header-inline
157   // callers (wait_awaitable::await_suspend) reference this 157   // callers (wait_awaitable::await_suspend) reference this
158   // symbol from outside the corosio DLL. 158   // symbol from outside the corosio DLL.
159   BOOST_COROSIO_DECL 159   BOOST_COROSIO_DECL
160   std::coroutine_handle<> wait(waiter_node& w); 160   std::coroutine_handle<> wait(waiter_node& w);
161   161  
162   /** Publish a waiter unconditionally. 162   /** Publish a waiter unconditionally.
163   163  
164   Like `wait`, but never takes the elapsed fast path. The 164   Like `wait`, but never takes the elapsed fast path. The
165   fast path posts the continuation directly, bypassing the 165   fast path posts the continuation directly, bypassing the
166   embedded op; hook-driven waits must observe every 166   embedded op; hook-driven waits must observe every
167   completion through the op, where the re-arm hook runs. 167   completion through the op, where the re-arm hook runs.
168   168  
169   @pre Same as `wait`. 169   @pre Same as `wait`.
170   170  
171   @param w The waiter to publish. 171   @param w The waiter to publish.
172   */ 172   */
173   std::coroutine_handle<> publish(waiter_node& w); 173   std::coroutine_handle<> publish(waiter_node& w);
174   }; 174   };
175   175  
176   /// The clock type used for time operations. 176   /// The clock type used for time operations.
177   using clock_type = std::chrono::steady_clock; 177   using clock_type = std::chrono::steady_clock;
178   178  
179   /// The time point type for absolute expiry times. 179   /// The time point type for absolute expiry times.
180   using time_point = clock_type::time_point; 180   using time_point = clock_type::time_point;
181   181  
182   /// The duration type for relative expiry times. 182   /// The duration type for relative expiry times.
183   using duration = clock_type::duration; 183   using duration = clock_type::duration;
184   184  
185   /** Destructor. 185   /** Destructor.
186   186  
187   Cancels any pending operations and releases timer resources. 187   Cancels any pending operations and releases timer resources.
188   */ 188   */
189   ~timer() override; 189   ~timer() override;
190   190  
191   /** Construct a timer from an execution context. 191   /** Construct a timer from an execution context.
192   192  
193   @param ctx The execution context that will own this timer. It 193   @param ctx The execution context that will own this timer. It
194   must be a corosio io_context; otherwise the constructor 194   must be a corosio io_context; otherwise the constructor
195   throws (a timer service is required). 195   throws (a timer service is required).
196   196  
197   @throws std::logic_error if @p ctx is not an io_context. 197   @throws std::logic_error if @p ctx is not an io_context.
198   */ 198   */
199   explicit timer(capy::execution_context& ctx); 199   explicit timer(capy::execution_context& ctx);
200   200  
201   /** Move constructor. 201   /** Move constructor.
202   202  
203   Transfers ownership of the timer resources. Required so a 203   Transfers ownership of the timer resources. Required so a
204   disengaged `std::optional<timer>` is movable; a timer is never 204   disengaged `std::optional<timer>` is movable; a timer is never
205   moved while a wait is published. 205   moved while a wait is published.
206   206  
207   @pre No awaitables returned by @p other's methods exist. 207   @pre No awaitables returned by @p other's methods exist.
208   */ 208   */
MISUBC 209   ✗ timer(timer&&) noexcept = default; 209   ✗ timer(timer&&) noexcept = default;
210   210  
211   /** Move assignment operator. 211   /** Move assignment operator.
212   212  
213   Closes any existing timer and transfers ownership. 213   Closes any existing timer and transfers ownership.
214   214  
215   @pre No awaitables returned by either `*this` or @p other's 215   @pre No awaitables returned by either `*this` or @p other's
216   methods exist. 216   methods exist.
217   */ 217   */
218   timer& operator=(timer&&) noexcept = default; 218   timer& operator=(timer&&) noexcept = default;
219   219  
220   timer(timer const&) = delete; 220   timer(timer const&) = delete;
221   timer& operator=(timer const&) = delete; 221   timer& operator=(timer const&) = delete;
222   222  
223   /** Return the timer's expiry time as an absolute time. 223   /** Return the timer's expiry time as an absolute time.
224   224  
225   @return The expiry time point. If no expiry has been set, 225   @return The expiry time point. If no expiry has been set,
226   returns a default-constructed time_point. 226   returns a default-constructed time_point.
227   */ 227   */
228   time_point expiry() const noexcept 228   time_point expiry() const noexcept
229   { 229   {
230   return get().expiry_; 230   return get().expiry_;
231   } 231   }
232   232  
233   /** Set the timer's expiry time as an absolute time. 233   /** Set the timer's expiry time as an absolute time.
234   234  
235   @pre No wait is published on this timer. 235   @pre No wait is published on this timer.
236   236  
237   @param t The expiry time to be used for the timer. 237   @param t The expiry time to be used for the timer.
238   */ 238   */
HITCBC 239   16 void expires_at(time_point t) 239   16 void expires_at(time_point t)
240   { 240   {
HITCBC 241   16 auto& impl = get(); 241   16 auto& impl = get();
HITCBC 242   32 BOOST_COROSIO_ASSERT( 242   32 BOOST_COROSIO_ASSERT(
243   impl.heap_index_.load(std::memory_order_relaxed) == 243   impl.heap_index_.load(std::memory_order_relaxed) ==
244   implementation::npos); 244   implementation::npos);
HITCBC 245   16 impl.expiry_ = t; 245   16 impl.expiry_ = t;
HITCBC 246   16 } 246   16 }
247   247  
248   /** Set the timer's expiry time relative to now. 248   /** Set the timer's expiry time relative to now.
249   249  
250   @pre No wait is published on this timer. 250   @pre No wait is published on this timer.
251   251  
252   @param d The expiry time relative to now. 252   @param d The expiry time relative to now.
253   */ 253   */
HITCBC 254   18782 void expires_after(duration d) 254   19213 void expires_after(duration d)
255   { 255   {
HITCBC 256   18782 auto& impl = get(); 256   19213 auto& impl = get();
HITCBC 257   37564 BOOST_COROSIO_ASSERT( 257   38426 BOOST_COROSIO_ASSERT(
258   impl.heap_index_.load(std::memory_order_relaxed) == 258   impl.heap_index_.load(std::memory_order_relaxed) ==
259   implementation::npos); 259   implementation::npos);
HITCBC 260   18782 if (d <= duration::zero()) 260   19213 if (d <= duration::zero())
HITCBC 261   680 impl.expiry_ = (time_point::min)(); 261   680 impl.expiry_ = (time_point::min)();
262   else 262   else
263   { 263   {
264   // Saturate rather than overflow: a clamped near-max duration 264   // Saturate rather than overflow: a clamped near-max duration
265   // (e.g. delay(hours::max())) would wrap now() + d past the 265   // (e.g. delay(hours::max())) would wrap now() + d past the
266   // clock's range and appear already elapsed. 266   // clock's range and appear already elapsed.
HITCBC 267   18102 auto const now = clock_type::now(); 267   18533 auto const now = clock_type::now();
HITCBC 268   18102 impl.expiry_ = 268   18533 impl.expiry_ =
HITCBC 269   18102 ((time_point::max)() - now < d) ? (time_point::max)() : now + d; 269   18533 ((time_point::max)() - now < d) ? (time_point::max)() : now + d;
270   } 270   }
HITCBC 271   18782 } 271   19213 }
272   272  
273   /** Set the timer's expiry time relative to now. 273   /** Set the timer's expiry time relative to now.
274   274  
275   This is a convenience overload that accepts any duration type 275   This is a convenience overload that accepts any duration type
276   and converts it to the timer's native duration type. 276   and converts it to the timer's native duration type.
277   277  
278   @param d The expiry time relative to now. 278   @param d The expiry time relative to now.
279   */ 279   */
280   template<class Rep, class Period> 280   template<class Rep, class Period>
281   void expires_after(std::chrono::duration<Rep, Period> d) 281   void expires_after(std::chrono::duration<Rep, Period> d)
282   { 282   {
283   expires_after(std::chrono::duration_cast<duration>(d)); 283   expires_after(std::chrono::duration_cast<duration>(d));
284   } 284   }
285   285  
286   /** Wait for the timer to expire. 286   /** Wait for the timer to expire.
287   287  
288   At most one wait may be outstanding at a time. 288   At most one wait may be outstanding at a time.
289   289  
290   The operation supports cancellation via `std::stop_token` through 290   The operation supports cancellation via `std::stop_token` through
291   the affine awaitable protocol. If the associated stop token is 291   the affine awaitable protocol. If the associated stop token is
292   triggered, only that waiter completes with an error that 292   triggered, only that waiter completes with an error that
293   compares equal to `capy::cond::canceled`. 293   compares equal to `capy::cond::canceled`.
294   294  
295   This timer must outlive the returned awaitable. 295   This timer must outlive the returned awaitable.
296   296  
297   @return An awaitable that completes with `io_result<>`. 297   @return An awaitable that completes with `io_result<>`.
298   */ 298   */
299   // Defined below wait_awaitable, which needs timer complete. 299   // Defined below wait_awaitable, which needs timer complete.
300   wait_awaitable wait(); 300   wait_awaitable wait();
301   301  
302   /** Publish a hook-driven wait. 302   /** Publish a hook-driven wait.
303   303  
304   Bypasses the elapsed fast path so every completion is 304   Bypasses the elapsed fast path so every completion is
305   delivered through the waiter's embedded op, where the 305   delivered through the waiter's embedded op, where the
306   re-arm hook is consulted. Used by awaitables that 306   re-arm hook is consulted. Used by awaitables that
307   re-publish the waiter to continue a logical wait across 307   re-publish the waiter to continue a logical wait across
308   several timer expirations. 308   several timer expirations.
309   309  
310   @pre @p w is fully initialized ( handle, executor, stop token, 310   @pre @p w is fully initialized ( handle, executor, stop token,
311   hook fields ) and its storage outlives the wait. 311   hook fields ) and its storage outlives the wait.
312   312  
313   @param w The waiter to publish. 313   @param w The waiter to publish.
314   314  
315   @return `std::noop_coroutine()`. 315   @return `std::noop_coroutine()`.
316   */ 316   */
317   std::coroutine_handle<> publish_wait(waiter_node& w); 317   std::coroutine_handle<> publish_wait(waiter_node& w);
318   318  
319   /** Re-arm an already-fired waiter with a new relative expiry. 319   /** Re-arm an already-fired waiter with a new relative expiry.
320   320  
321   Stores the ( saturated ) expiry and re-publishes @p w. The 321   Stores the ( saturated ) expiry and re-publishes @p w. The
322   waiter's original work count and stop callback remain in 322   waiter's original work count and stop callback remain in
323   effect. Must only be called from the waiter's re-arm hook, 323   effect. Must only be called from the waiter's re-arm hook,
324   where the waiter has been popped from the service but not 324   where the waiter has been popped from the service but not
325   yet resumed. 325   yet resumed.
326   326  
327   @pre The timer has no other waiters — this is what makes the 327   @pre The timer has no other waiters — this is what makes the
328   unlocked expiry write race-free. 328   unlocked expiry write race-free.
329   329  
330   Re-publication needs heap capacity and can fail under 330   Re-publication needs heap capacity and can fail under
331   allocation pressure. On failure the waiter is left exactly as 331   allocation pressure. On failure the waiter is left exactly as
332   the hook received it, so the caller completes the wait through 332   the hook received it, so the caller completes the wait through
333   the normal resume path instead of re-arming. 333   the normal resume path instead of re-arming.
334   334  
335   @param w The waiter to re-publish. 335   @param w The waiter to re-publish.
336   @param d The next expiry relative to now. 336   @param d The next expiry relative to now.
337   337  
338   @return `true` if re-published; `false` if allocation failed. 338   @return `true` if re-published; `false` if allocation failed.
339   */ 339   */
340   [[nodiscard]] bool rearm_wait(waiter_node& w, duration d) noexcept; 340   [[nodiscard]] bool rearm_wait(waiter_node& w, duration d) noexcept;
341   341  
342   protected: 342   protected:
343   explicit timer(handle h) noexcept : io_object(std::move(h)) {} 343   explicit timer(handle h) noexcept : io_object(std::move(h)) {}
344   344  
345   private: 345   private:
346   /// Return the underlying implementation. 346   /// Return the underlying implementation.
HITCBC 347   37596 implementation& get() const noexcept 347   38458 implementation& get() const noexcept
348   { 348   {
HITCBC 349   37596 return *static_cast<implementation*>(h_.get()); 349   38458 return *static_cast<implementation*>(h_.get());
350   } 350   }
351   }; 351   };
352   352  
353   /** Frame-resident per-wait state for a timer wait. 353   /** Frame-resident per-wait state for a timer wait.
354   354  
355   One node exists per `co_await` on a timer, embedded in the 355   One node exists per `co_await` on a timer, embedded in the
356   awaitable on the suspended coroutine's frame — never allocated. 356   awaitable on the suspended coroutine's frame — never allocated.
357   Once published by `implementation::wait()` the node may be 357   Once published by `implementation::wait()` the node may be
358   completed from any thread; every completion path finishes 358   completed from any thread; every completion path finishes
359   touching the node before resuming or destroying the coroutine, 359   touching the node before resuming or destroying the coroutine,
360   because either act may end the node's storage. 360   because either act may end the node's storage.
361   361  
362   The node owns no resources: the stop token is borrowed from the 362   The node owns no resources: the stop token is borrowed from the
363   awaiting chain's `io_env` (which outlives the suspension) and 363   awaiting chain's `io_env` (which outlives the suspension) and
364   the stop callback is managed manually in `cb_buf_`, destroyed on 364   the stop callback is managed manually in `cb_buf_`, destroyed on
365   every completion path before the frame can die. 365   every completion path before the frame can die.
366   */ 366   */
367   struct BOOST_COROSIO_SYMBOL_VISIBLE waiter_node 367   struct BOOST_COROSIO_SYMBOL_VISIBLE waiter_node
368   : intrusive_list<waiter_node>::node 368   : intrusive_list<waiter_node>::node
369   { 369   {
370   // Embedded completion op — avoids heap allocation per fire/cancel. 370   // Embedded completion op — avoids heap allocation per fire/cancel.
371   // Members are exported and defined non-inline in timer.cpp: the 371   // Members are exported and defined non-inline in timer.cpp: the
372   // inline waiter_node constructor references do_complete and the 372   // inline waiter_node constructor references do_complete and the
373   // vtable from translation units that reach this header through 373   // vtable from translation units that reach this header through
374   // delay.hpp without ever including timer_service.hpp, so the one 374   // delay.hpp without ever including timer_service.hpp, so the one
375   // strong definition must live in a TU that is always linked. 375   // strong definition must live in a TU that is always linked.
376   struct BOOST_COROSIO_SYMBOL_VISIBLE completion_op final : scheduler_op 376   struct BOOST_COROSIO_SYMBOL_VISIBLE completion_op final : scheduler_op
377   { 377   {
378   waiter_node* waiter_ = nullptr; 378   waiter_node* waiter_ = nullptr;
379   379  
380   BOOST_COROSIO_DECL 380   BOOST_COROSIO_DECL
381   static void do_complete( 381   static void do_complete(
382   void* owner, scheduler_op* base, std::uint32_t, std::uint32_t); 382   void* owner, scheduler_op* base, std::uint32_t, std::uint32_t);
383   383  
HITCBC 384   31664 completion_op() noexcept : scheduler_op(&do_complete) {} 384   32184 completion_op() noexcept : scheduler_op(&do_complete) {}
385   385  
386   BOOST_COROSIO_DECL void operator()() override; 386   BOOST_COROSIO_DECL void operator()() override;
387   BOOST_COROSIO_DECL void destroy() override; 387   BOOST_COROSIO_DECL void destroy() override;
388   }; 388   };
389   389  
390   // Per-waiter stop_token cancellation 390   // Per-waiter stop_token cancellation
391   struct canceller 391   struct canceller
392   { 392   {
393   waiter_node* waiter_; 393   waiter_node* waiter_;
394   BOOST_COROSIO_DECL void operator()() const; 394   BOOST_COROSIO_DECL void operator()() const;
395   }; 395   };
396   396  
397   using stop_cb_type = std::stop_callback<canceller>; 397   using stop_cb_type = std::stop_callback<canceller>;
398   398  
399   // nullptr once unpublished from the timer ( concurrency marker ) 399   // nullptr once unpublished from the timer ( concurrency marker )
400   /// The timer this waiter is published on, or `nullptr`. 400   /// The timer this waiter is published on, or `nullptr`.
401   timer::implementation* impl_ = nullptr; 401   timer::implementation* impl_ = nullptr;
402   402  
403   /// The timer service that completes this waiter. 403   /// The timer service that completes this waiter.
404   timer_service* svc_ = nullptr; 404   timer_service* svc_ = nullptr;
405   405  
406   /// The suspended coroutine, destroyed by the shutdown drains. 406   /// The suspended coroutine, destroyed by the shutdown drains.
407   std::coroutine_handle<> h_; 407   std::coroutine_handle<> h_;
408   408  
409   /// The continuation posted to resume the coroutine. 409   /// The continuation posted to resume the coroutine.
410   capy::continuation cont_; 410   capy::continuation cont_;
411   411  
412   /// The executor the continuation is posted through. 412   /// The executor the continuation is posted through.
413   capy::executor_ref d_; 413   capy::executor_ref d_;
414   414  
415   // Borrowed from the awaiting chain's io_env, which outlives the 415   // Borrowed from the awaiting chain's io_env, which outlives the
416   // suspension; the node holds no owning state. 416   // suspension; the node holds no owning state.
417   /// The stop token observed for cancellation. 417   /// The stop token observed for cancellation.
418   std::stop_token const* token_ = nullptr; 418   std::stop_token const* token_ = nullptr;
419   419  
420   /// The completion result read by `await_resume`. 420   /// The completion result read by `await_resume`.
421   std::error_code ec_; 421   std::error_code ec_;
422   422  
423   // Consulted by the completion op before resuming; lets a 423   // Consulted by the completion op before resuming; lets a
424   // clock-facade wait re-publish itself instead of completing. 424   // clock-facade wait re-publish itself instead of completing.
425   // Never consulted on the shutdown destroy path. Consulted on 425   // Never consulted on the shutdown destroy path. Consulted on
426   // every completion, including cancellation ( `ec_` set ) — the 426   // every completion, including cancellation ( `ec_` set ) — the
427   // hook must inspect `w`'s `ec_` and must not re-arm a canceled 427   // hook must inspect `w`'s `ec_` and must not re-arm a canceled
428   // waiter. Runs inside the completion path; must not throw. 428   // waiter. Runs inside the completion path; must not throw.
429   /// Re-arm hook: return true to skip resumption ( wait continues ). 429   /// Re-arm hook: return true to skip resumption ( wait continues ).
430   bool (*on_fire_)(void*) noexcept = nullptr; 430   bool (*on_fire_)(void*) noexcept = nullptr;
431   431  
432   /// Context passed to `on_fire_` ( the owning awaitable ). 432   /// Context passed to `on_fire_` ( the owning awaitable ).
433   void* on_fire_ctx_ = nullptr; 433   void* on_fire_ctx_ = nullptr;
434   434  
435   /// The embedded completion op posted to the scheduler. 435   /// The embedded completion op posted to the scheduler.
436   completion_op op_; 436   completion_op op_;
437   437  
438   // stop_callback is neither movable nor assignable; construct it 438   // stop_callback is neither movable nor assignable; construct it
439   // in place once the node is pinned on the coroutine frame, and 439   // in place once the node is pinned on the coroutine frame, and
440   // destroy it manually on every completion path. 440   // destroy it manually on every completion path.
441   /// Storage for the armed stop callback. 441   /// Storage for the armed stop callback.
442   alignas(stop_cb_type) unsigned char cb_buf_[sizeof(stop_cb_type)]; 442   alignas(stop_cb_type) unsigned char cb_buf_[sizeof(stop_cb_type)];
443   443  
444   /// True while `cb_buf_` holds a live stop callback. 444   /// True while `cb_buf_` holds a live stop callback.
445   bool cb_active_ = false; 445   bool cb_active_ = false;
446   446  
HITCBC 447   31664 waiter_node() noexcept 447   32184 waiter_node() noexcept
HITCBC 448   31664 { 448   32184 {
HITCBC 449   31664 op_.waiter_ = this; 449   32184 op_.waiter_ = this;
HITCBC 450   31664 } 450   32184 }
451   451  
452   // The embedded op self-points and the list hooks are published 452   // The embedded op self-points and the list hooks are published
453   // to other threads; the node never moves. 453   // to other threads; the node never moves.
454   waiter_node(waiter_node const&) = delete; 454   waiter_node(waiter_node const&) = delete;
455   waiter_node& operator=(waiter_node const&) = delete; 455   waiter_node& operator=(waiter_node const&) = delete;
456   456  
457   /** Bind the coroutine and its environment before publication. 457   /** Bind the coroutine and its environment before publication.
458   458  
459   The single definition of the fields every wait must populate 459   The single definition of the fields every wait must populate
460   before the node is published; hook-driven waits additionally 460   before the node is published; hook-driven waits additionally
461   set `on_fire_` / `on_fire_ctx_`. 461   set `on_fire_` / `on_fire_ctx_`.
462   462  
463   @param h The coroutine to resume on completion. 463   @param h The coroutine to resume on completion.
464   @param env The awaiting chain's environment; must outlive 464   @param env The awaiting chain's environment; must outlive
465   the suspension. 465   the suspension.
466   */ 466   */
HITCBC 467   14826 void bind(std::coroutine_handle<> h, capy::io_env const& env) noexcept 467   15086 void bind(std::coroutine_handle<> h, capy::io_env const& env) noexcept
468   { 468   {
HITCBC 469   14826 h_ = h; 469   15086 h_ = h;
HITCBC 470   14826 cont_.h = h; 470   15086 cont_.h = h;
HITCBC 471   14826 d_ = env.executor; 471   15086 d_ = env.executor;
HITCBC 472   14826 token_ = &env.stop_token; 472   15086 token_ = &env.stop_token;
HITCBC 473   14826 } 473   15086 }
474   474  
475   /** Arm the stop callback. 475   /** Arm the stop callback.
476   476  
477   @pre `token_` is set. 477   @pre `token_` is set.
478   */ 478   */
HITCBC 479   1573 void arm_stop_cb() 479   1785 void arm_stop_cb()
480   { 480   {
HITCBC 481   1573 new (cb_buf_) stop_cb_type(*token_, canceller{this}); 481   1785 new (cb_buf_) stop_cb_type(*token_, canceller{this});
HITCBC 482   1573 cb_active_ = true; 482   1785 cb_active_ = true;
HITCBC 483   1573 } 483   1785 }
484   484  
485   /// Destroy the stop callback if armed. 485   /// Destroy the stop callback if armed.
HITCBC 486   13971 void reset_stop_cb() noexcept 486   14233 void reset_stop_cb() noexcept
487   { 487   {
HITCBC 488   13971 if (cb_active_) 488   14233 if (cb_active_)
489   { 489   {
HITCBC 490   1573 std::launder(reinterpret_cast<stop_cb_type*>(cb_buf_)) 490   1785 std::launder(reinterpret_cast<stop_cb_type*>(cb_buf_))
HITCBC 491   1573 ->~stop_cb_type(); 491   1785 ->~stop_cb_type();
HITCBC 492   1573 cb_active_ = false; 492   1785 cb_active_ = false;
493   } 493   }
HITCBC 494   13971 } 494   14233 }
495   }; 495   };
496   496  
497   /** Awaitable returned by `timer::wait()`. 497   /** Awaitable returned by `timer::wait()`.
498   498  
499   Carries the waiter node so a wait performs no allocation. The 499   Carries the waiter node so a wait performs no allocation. The
500   awaitable is movable only before `await_suspend` publishes the 500   awaitable is movable only before `await_suspend` publishes the
501   node (a move builds a fresh, quiescent node); afterwards it is 501   node (a move builds a fresh, quiescent node); afterwards it is
502   pinned on the coroutine frame until the wait completes. 502   pinned on the coroutine frame until the wait completes.
503   */ 503   */
504   struct wait_awaitable 504   struct wait_awaitable
505   { 505   {
506   timer& t_; 506   timer& t_;
507   waiter_node w_; 507   waiter_node w_;
508   508  
HITCBC 509   14585 explicit wait_awaitable(timer& t) noexcept : t_(t) {} 509   14845 explicit wait_awaitable(timer& t) noexcept : t_(t) {}
510   510  
HITCBC 511   14585 wait_awaitable(wait_awaitable&& o) noexcept : t_(o.t_) {} 511   14845 wait_awaitable(wait_awaitable&& o) noexcept : t_(o.t_) {}
512   512  
513   wait_awaitable(wait_awaitable const&) = delete; 513   wait_awaitable(wait_awaitable const&) = delete;
514   wait_awaitable& operator=(wait_awaitable const&) = delete; 514   wait_awaitable& operator=(wait_awaitable const&) = delete;
515   wait_awaitable& operator=(wait_awaitable&&) = delete; 515   wait_awaitable& operator=(wait_awaitable&&) = delete;
516   516  
HITCBC 517   2053 bool await_ready() const noexcept 517   2053 bool await_ready() const noexcept
518   { 518   {
HITCBC 519   2053 return false; 519   2053 return false;
520   } 520   }
521   521  
522   // Cancellation surfaces through w_.ec_: the stop_token path in 522   // Cancellation surfaces through w_.ec_: the stop_token path in
523   // wait() completes the waiter with error::canceled written to 523   // wait() completes the waiter with error::canceled written to
524   // it, so there is no separate token to consult here. 524   // it, so there is no separate token to consult here.
HITCBC 525   14556 [[nodiscard]] capy::io_result<> await_resume() const noexcept 525   14816 [[nodiscard]] capy::io_result<> await_resume() const noexcept
526   { 526   {
HITCBC 527   14556 return {w_.ec_}; 527   14816 return {w_.ec_};
528   } 528   }
529   529  
HITCBC 530   14585 auto await_suspend(std::coroutine_handle<> h, capy::io_env const* env) 530   14845 auto await_suspend(std::coroutine_handle<> h, capy::io_env const* env)
531   -> std::coroutine_handle<> 531   -> std::coroutine_handle<>
532   { 532   {
HITCBC 533   14585 auto& impl = t_.get(); 533   14845 auto& impl = t_.get();
HITCBC 534   14585 w_.bind(h, *env); 534   14845 w_.bind(h, *env);
535   535  
536   // Inline fast path: already expired and not in the heap. 536   // Inline fast path: already expired and not in the heap.
537   // Post instead of dispatch so the coroutine yields to the 537   // Post instead of dispatch so the coroutine yields to the
538   // scheduler, allowing other queued work to run. 538   // scheduler, allowing other queued work to run.
HITCBC 539   14585 if (impl.already_expired()) 539   14845 if (impl.already_expired())
540   { 540   {
HITCBC 541   855 w_.ec_ = {}; 541   853 w_.ec_ = {};
HITCBC 542   855 w_.d_.post(w_.cont_); 542   853 w_.d_.post(w_.cont_);
HITCBC 543   855 return std::noop_coroutine(); 543   853 return std::noop_coroutine();
544   } 544   }
545   545  
HITCBC 546   13730 return impl.wait(w_); 546   13992 return impl.wait(w_);
547   } 547   }
548   }; 548   };
549   549  
550   inline wait_awaitable 550   inline wait_awaitable
HITCBC 551   14585 timer::wait() 551   14845 timer::wait()
552   { 552   {
HITCBC 553   14585 return wait_awaitable(*this); 553   14845 return wait_awaitable(*this);
554   } 554   }
555   555  
556   } // namespace boost::corosio::detail 556   } // namespace boost::corosio::detail
557   557  
558   #endif 558   #endif