. /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   1140 explicit implementation(timer_service& svc) noexcept : svc_(&svc) {} 126   1470 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   28365 bool already_expired() const noexcept 135   28456 bool already_expired() const noexcept
136   { 136   {
HITCBC 137   85095 return heap_index_.load(std::memory_order_relaxed) == npos && 137   85368 return heap_index_.load(std::memory_order_relaxed) == npos &&
HITCBC 138   56066 (expiry_ == (std::chrono::steady_clock::time_point::min)() || 138   56248 (expiry_ == (std::chrono::steady_clock::time_point::min)() ||
HITCBC 139   56066 expiry_ <= std::chrono::steady_clock::now()); 139   56248 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 + @par Preconditions
151 - on the suspended coroutine's frame) outlives the wait. 151 + @p w is fully initialized, and its storage (the awaitable
  152 + on the suspended coroutine's frame) outlives the wait.
152   153  
153   @param w The waiter to publish. 154   @param w The waiter to publish.
154   */ 155   */
155   // Exported at member level: dllexport on the enclosing timer 156   // Exported at member level: dllexport on the enclosing timer
156   // class does not extend to nested classes, and header-inline 157   // class does not extend to nested classes, and header-inline
157   // callers (wait_awaitable::await_suspend) reference this 158   // callers (wait_awaitable::await_suspend) reference this
158   // symbol from outside the corosio DLL. 159   // symbol from outside the corosio DLL.
159   BOOST_COROSIO_DECL 160   BOOST_COROSIO_DECL
160   std::coroutine_handle<> wait(waiter_node& w); 161   std::coroutine_handle<> wait(waiter_node& w);
161   162  
162   /** Publish a waiter unconditionally. 163   /** Publish a waiter unconditionally.
163   164  
164   Like `wait`, but never takes the elapsed fast path. The 165   Like `wait`, but never takes the elapsed fast path. The
165   fast path posts the continuation directly, bypassing the 166   fast path posts the continuation directly, bypassing the
166   embedded op; hook-driven waits must observe every 167   embedded op; hook-driven waits must observe every
167   completion through the op, where the re-arm hook runs. 168   completion through the op, where the re-arm hook runs.
168   169  
169 - @pre Same as `wait`. 170 + @par Preconditions
  171 + Same as `wait`.
170   172  
171   @param w The waiter to publish. 173   @param w The waiter to publish.
172   */ 174   */
173   std::coroutine_handle<> publish(waiter_node& w); 175   std::coroutine_handle<> publish(waiter_node& w);
174   }; 176   };
175   177  
176   /// The clock type used for time operations. 178   /// The clock type used for time operations.
177   using clock_type = std::chrono::steady_clock; 179   using clock_type = std::chrono::steady_clock;
178   180  
179   /// The time point type for absolute expiry times. 181   /// The time point type for absolute expiry times.
180   using time_point = clock_type::time_point; 182   using time_point = clock_type::time_point;
181   183  
182   /// The duration type for relative expiry times. 184   /// The duration type for relative expiry times.
183   using duration = clock_type::duration; 185   using duration = clock_type::duration;
184   186  
185   /** Destructor. 187   /** Destructor.
186   188  
187   Cancels any pending operations and releases timer resources. 189   Cancels any pending operations and releases timer resources.
188   */ 190   */
189   ~timer() override; 191   ~timer() override;
190   192  
191   /** Construct a timer from an execution context. 193   /** Construct a timer from an execution context.
192   194  
193   @param ctx The execution context that will own this timer. It 195   @param ctx The execution context that will own this timer. It
194   must be a corosio io_context; otherwise the constructor 196   must be a corosio io_context; otherwise the constructor
195   throws (a timer service is required). 197   throws (a timer service is required).
196   198  
197   @throws std::logic_error if @p ctx is not an io_context. 199   @throws std::logic_error if @p ctx is not an io_context.
198   */ 200   */
199   explicit timer(capy::execution_context& ctx); 201   explicit timer(capy::execution_context& ctx);
200   202  
201   /** Move constructor. 203   /** Move constructor.
202   204  
203   Transfers ownership of the timer resources. Required so a 205   Transfers ownership of the timer resources. Required so a
204   disengaged `std::optional<timer>` is movable; a timer is never 206   disengaged `std::optional<timer>` is movable; a timer is never
205   moved while a wait is published. 207   moved while a wait is published.
206   208  
207   @pre No awaitables returned by @p other's methods exist. 209   @pre No awaitables returned by @p other's methods exist.
208   */ 210   */
MISUBC 209   ✗ timer(timer&&) noexcept = default; 211   ✗ timer(timer&&) noexcept = default;
210   212  
211   /** Move assignment operator. 213   /** Move assignment operator.
212   214  
213   Closes any existing timer and transfers ownership. 215   Closes any existing timer and transfers ownership.
214   216  
215   @pre No awaitables returned by either `*this` or @p other's 217   @pre No awaitables returned by either `*this` or @p other's
216   methods exist. 218   methods exist.
217   */ 219   */
218   timer& operator=(timer&&) noexcept = default; 220   timer& operator=(timer&&) noexcept = default;
219   221  
220   timer(timer const&) = delete; 222   timer(timer const&) = delete;
221   timer& operator=(timer const&) = delete; 223   timer& operator=(timer const&) = delete;
222   224  
223   /** Return the timer's expiry time as an absolute time. 225   /** Return the timer's expiry time as an absolute time.
224   226  
225   @return The expiry time point. If no expiry has been set, 227   @return The expiry time point. If no expiry has been set,
226   returns a default-constructed time_point. 228   returns a default-constructed time_point.
227   */ 229   */
228   time_point expiry() const noexcept 230   time_point expiry() const noexcept
229   { 231   {
230   return get().expiry_; 232   return get().expiry_;
231   } 233   }
232   234  
233   /** Set the timer's expiry time as an absolute time. 235   /** Set the timer's expiry time as an absolute time.
234   236  
235 - @pre No wait is published on this timer. 237 + @par Preconditions
  238 + No wait is published on this timer.
236   239  
237   @param t The expiry time to be used for the timer. 240   @param t The expiry time to be used for the timer.
238   */ 241   */
HITCBC 239   16 void expires_at(time_point t) 242   16 void expires_at(time_point t)
240   { 243   {
HITCBC 241   16 auto& impl = get(); 244   16 auto& impl = get();
HITCBC 242   32 BOOST_COROSIO_ASSERT( 245   32 BOOST_COROSIO_ASSERT(
243   impl.heap_index_.load(std::memory_order_relaxed) == 246   impl.heap_index_.load(std::memory_order_relaxed) ==
244   implementation::npos); 247   implementation::npos);
HITCBC 245   16 impl.expiry_ = t; 248   16 impl.expiry_ = t;
HITCBC 246   16 } 249   16 }
247   250  
248   /** Set the timer's expiry time relative to now. 251   /** Set the timer's expiry time relative to now.
249   252  
250 - @pre No wait is published on this timer. 253 + @par Preconditions
  254 + No wait is published on this timer.
251   255  
252   @param d The expiry time relative to now. 256   @param d The expiry time relative to now.
253   */ 257   */
HITCBC 254   18923 void expires_after(duration d) 258   18908 void expires_after(duration d)
255   { 259   {
HITCBC 256   18923 auto& impl = get(); 260   18908 auto& impl = get();
HITCBC 257   37846 BOOST_COROSIO_ASSERT( 261   37816 BOOST_COROSIO_ASSERT(
258   impl.heap_index_.load(std::memory_order_relaxed) == 262   impl.heap_index_.load(std::memory_order_relaxed) ==
259   implementation::npos); 263   implementation::npos);
HITCBC 260   18923 if (d <= duration::zero()) 264   18908 if (d <= duration::zero())
HITCBC 261   680 impl.expiry_ = (time_point::min)(); 265   680 impl.expiry_ = (time_point::min)();
262   else 266   else
263   { 267   {
264   // Saturate rather than overflow: a clamped near-max duration 268   // Saturate rather than overflow: a clamped near-max duration
265   // (e.g. delay(hours::max())) would wrap now() + d past the 269   // (e.g. delay(hours::max())) would wrap now() + d past the
266   // clock's range and appear already elapsed. 270   // clock's range and appear already elapsed.
HITCBC 267   18243 auto const now = clock_type::now(); 271   18228 auto const now = clock_type::now();
HITCBC 268   18243 impl.expiry_ = 272   18228 impl.expiry_ =
HITCBC 269   18243 ((time_point::max)() - now < d) ? (time_point::max)() : now + d; 273   18228 ((time_point::max)() - now < d) ? (time_point::max)() : now + d;
270   } 274   }
HITCBC 271   18923 } 275   18908 }
272   276  
273   /** Set the timer's expiry time relative to now. 277   /** Set the timer's expiry time relative to now.
274   278  
275   This is a convenience overload that accepts any duration type 279   This is a convenience overload that accepts any duration type
276   and converts it to the timer's native duration type. 280   and converts it to the timer's native duration type.
277   281  
278   @param d The expiry time relative to now. 282   @param d The expiry time relative to now.
279   */ 283   */
280   template<class Rep, class Period> 284   template<class Rep, class Period>
281   void expires_after(std::chrono::duration<Rep, Period> d) 285   void expires_after(std::chrono::duration<Rep, Period> d)
282   { 286   {
283   expires_after(std::chrono::duration_cast<duration>(d)); 287   expires_after(std::chrono::duration_cast<duration>(d));
284   } 288   }
285   289  
286   /** Wait for the timer to expire. 290   /** Wait for the timer to expire.
287   291  
288   At most one wait may be outstanding at a time. 292   At most one wait may be outstanding at a time.
289   293  
290   The operation supports cancellation via `std::stop_token` through 294   The operation supports cancellation via `std::stop_token` through
291   the affine awaitable protocol. If the associated stop token is 295   the affine awaitable protocol. If the associated stop token is
292   triggered, only that waiter completes with an error that 296   triggered, only that waiter completes with an error that
293   compares equal to `capy::cond::canceled`. 297   compares equal to `capy::cond::canceled`.
294   298  
295   This timer must outlive the returned awaitable. 299   This timer must outlive the returned awaitable.
296   300  
297   @return An awaitable that completes with `io_result<>`. 301   @return An awaitable that completes with `io_result<>`.
298   */ 302   */
299   // Defined below wait_awaitable, which needs timer complete. 303   // Defined below wait_awaitable, which needs timer complete.
300   wait_awaitable wait(); 304   wait_awaitable wait();
301   305  
302   /** Publish a hook-driven wait. 306   /** Publish a hook-driven wait.
303   307  
304   Bypasses the elapsed fast path so every completion is 308   Bypasses the elapsed fast path so every completion is
305   delivered through the waiter's embedded op, where the 309   delivered through the waiter's embedded op, where the
306   re-arm hook is consulted. Used by awaitables that 310   re-arm hook is consulted. Used by awaitables that
307   re-publish the waiter to continue a logical wait across 311   re-publish the waiter to continue a logical wait across
308   several timer expirations. 312   several timer expirations.
309   313  
310 - @pre @p w is fully initialized ( handle, executor, stop token, 314 + @par Preconditions
311 - hook fields ) and its storage outlives the wait. 315 + @p w is fully initialized ( handle, executor, stop token,
  316 + hook fields ) and its storage outlives the wait.
312   317  
313   @param w The waiter to publish. 318   @param w The waiter to publish.
314   319  
315   @return `std::noop_coroutine()`. 320   @return `std::noop_coroutine()`.
316   */ 321   */
317   std::coroutine_handle<> publish_wait(waiter_node& w); 322   std::coroutine_handle<> publish_wait(waiter_node& w);
318   323  
319   /** Re-arm an already-fired waiter with a new relative expiry. 324   /** Re-arm an already-fired waiter with a new relative expiry.
320   325  
321   Stores the ( saturated ) expiry and re-publishes @p w. The 326   Stores the ( saturated ) expiry and re-publishes @p w. The
322   waiter's original work count and stop callback remain in 327   waiter's original work count and stop callback remain in
323   effect. Must only be called from the waiter's re-arm hook, 328   effect. Must only be called from the waiter's re-arm hook,
324   where the waiter has been popped from the service but not 329   where the waiter has been popped from the service but not
325   yet resumed. 330   yet resumed.
326   331  
327 - @pre The timer has no other waiters — this is what makes the 332 + @par Preconditions
328 - unlocked expiry write race-free. 333 + The timer has no other waiters — this is what makes the
  334 + unlocked expiry write race-free.
329   335  
330   Re-publication needs heap capacity and can fail under 336   Re-publication needs heap capacity and can fail under
331   allocation pressure. On failure the waiter is left exactly as 337   allocation pressure. On failure the waiter is left exactly as
332   the hook received it, so the caller completes the wait through 338   the hook received it, so the caller completes the wait through
333   the normal resume path instead of re-arming. 339   the normal resume path instead of re-arming.
334   340  
335   @param w The waiter to re-publish. 341   @param w The waiter to re-publish.
336   @param d The next expiry relative to now. 342   @param d The next expiry relative to now.
337   343  
338   @return `true` if re-published; `false` if allocation failed. 344   @return `true` if re-published; `false` if allocation failed.
339   */ 345   */
340   [[nodiscard]] bool rearm_wait(waiter_node& w, duration d) noexcept; 346   [[nodiscard]] bool rearm_wait(waiter_node& w, duration d) noexcept;
341   347  
342   protected: 348   protected:
343   explicit timer(handle h) noexcept : io_object(std::move(h)) {} 349   explicit timer(handle h) noexcept : io_object(std::move(h)) {}
344   350  
345   private: 351   private:
346   /// Return the underlying implementation. 352   /// Return the underlying implementation.
HITCBC 347   37878 implementation& get() const noexcept 353   37848 implementation& get() const noexcept
348   { 354   {
HITCBC 349   37878 return *static_cast<implementation*>(h_.get()); 355   37848 return *static_cast<implementation*>(h_.get());
350   } 356   }
351   }; 357   };
352   358  
353   /** Frame-resident per-wait state for a timer wait. 359   /** Frame-resident per-wait state for a timer wait.
354   360  
355   One node exists per `co_await` on a timer, embedded in the 361   One node exists per `co_await` on a timer, embedded in the
356   awaitable on the suspended coroutine's frame — never allocated. 362   awaitable on the suspended coroutine's frame — never allocated.
357   Once published by `implementation::wait()` the node may be 363   Once published by `implementation::wait()` the node may be
358   completed from any thread; every completion path finishes 364   completed from any thread; every completion path finishes
359   touching the node before resuming or destroying the coroutine, 365   touching the node before resuming or destroying the coroutine,
360   because either act may end the node's storage. 366   because either act may end the node's storage.
361   367  
362   The node owns no resources: the stop token is borrowed from the 368   The node owns no resources: the stop token is borrowed from the
363   awaiting chain's `io_env` (which outlives the suspension) and 369   awaiting chain's `io_env` (which outlives the suspension) and
364   the stop callback is managed manually in `cb_buf_`, destroyed on 370   the stop callback is managed manually in `cb_buf_`, destroyed on
365   every completion path before the frame can die. 371   every completion path before the frame can die.
366   */ 372   */
367   struct BOOST_COROSIO_SYMBOL_VISIBLE waiter_node 373   struct BOOST_COROSIO_SYMBOL_VISIBLE waiter_node
368   : intrusive_list<waiter_node>::node 374   : intrusive_list<waiter_node>::node
369   { 375   {
370   // Embedded completion op — avoids heap allocation per fire/cancel. 376   // Embedded completion op — avoids heap allocation per fire/cancel.
371   // Members are exported and defined non-inline in timer.cpp: the 377   // Members are exported and defined non-inline in timer.cpp: the
372   // inline waiter_node constructor references do_complete and the 378   // inline waiter_node constructor references do_complete and the
373   // vtable from translation units that reach this header through 379   // vtable from translation units that reach this header through
374   // delay.hpp without ever including timer_service.hpp, so the one 380   // delay.hpp without ever including timer_service.hpp, so the one
375   // strong definition must live in a TU that is always linked. 381   // strong definition must live in a TU that is always linked.
376   struct BOOST_COROSIO_SYMBOL_VISIBLE completion_op final : scheduler_op 382   struct BOOST_COROSIO_SYMBOL_VISIBLE completion_op final : scheduler_op
377   { 383   {
378   waiter_node* waiter_ = nullptr; 384   waiter_node* waiter_ = nullptr;
379   385  
380   BOOST_COROSIO_DECL 386   BOOST_COROSIO_DECL
381   static void do_complete( 387   static void do_complete(
382   void* owner, scheduler_op* base, std::uint32_t, std::uint32_t); 388   void* owner, scheduler_op* base, std::uint32_t, std::uint32_t);
383   389  
HITCBC 384   31724 completion_op() noexcept : scheduler_op(&do_complete) {} 390   31816 completion_op() noexcept : scheduler_op(&do_complete) {}
385   391  
386   BOOST_COROSIO_DECL void operator()() override; 392   BOOST_COROSIO_DECL void operator()() override;
387   BOOST_COROSIO_DECL void destroy() override; 393   BOOST_COROSIO_DECL void destroy() override;
388   }; 394   };
389   395  
390   // Per-waiter stop_token cancellation 396   // Per-waiter stop_token cancellation
391   struct canceller 397   struct canceller
392   { 398   {
393   waiter_node* waiter_; 399   waiter_node* waiter_;
394   BOOST_COROSIO_DECL void operator()() const; 400   BOOST_COROSIO_DECL void operator()() const;
395   }; 401   };
396   402  
397   using stop_cb_type = std::stop_callback<canceller>; 403   using stop_cb_type = std::stop_callback<canceller>;
398   404  
399   // nullptr once unpublished from the timer ( concurrency marker ) 405   // nullptr once unpublished from the timer ( concurrency marker )
400   /// The timer this waiter is published on, or `nullptr`. 406   /// The timer this waiter is published on, or `nullptr`.
401   timer::implementation* impl_ = nullptr; 407   timer::implementation* impl_ = nullptr;
402   408  
403   /// The timer service that completes this waiter. 409   /// The timer service that completes this waiter.
404   timer_service* svc_ = nullptr; 410   timer_service* svc_ = nullptr;
405   411  
406   /// The suspended coroutine, destroyed by the shutdown drains. 412   /// The suspended coroutine, destroyed by the shutdown drains.
407   std::coroutine_handle<> h_; 413   std::coroutine_handle<> h_;
408   414  
409   /// The continuation posted to resume the coroutine. 415   /// The continuation posted to resume the coroutine.
410   capy::continuation cont_; 416   capy::continuation cont_;
411   417  
412   /// The executor the continuation is posted through. 418   /// The executor the continuation is posted through.
413   capy::executor_ref d_; 419   capy::executor_ref d_;
414   420  
415   // Borrowed from the awaiting chain's io_env, which outlives the 421   // Borrowed from the awaiting chain's io_env, which outlives the
416   // suspension; the node holds no owning state. 422   // suspension; the node holds no owning state.
417   /// The stop token observed for cancellation. 423   /// The stop token observed for cancellation.
418   std::stop_token const* token_ = nullptr; 424   std::stop_token const* token_ = nullptr;
419   425  
420   /// The completion result read by `await_resume`. 426   /// The completion result read by `await_resume`.
421   std::error_code ec_; 427   std::error_code ec_;
422   428  
423   // Consulted by the completion op before resuming; lets a 429   // Consulted by the completion op before resuming; lets a
424   // clock-facade wait re-publish itself instead of completing. 430   // clock-facade wait re-publish itself instead of completing.
425   // Never consulted on the shutdown destroy path. Consulted on 431   // Never consulted on the shutdown destroy path. Consulted on
426   // every completion, including cancellation ( `ec_` set ) — the 432   // every completion, including cancellation ( `ec_` set ) — the
427   // hook must inspect `w`'s `ec_` and must not re-arm a canceled 433   // hook must inspect `w`'s `ec_` and must not re-arm a canceled
428   // waiter. Runs inside the completion path; must not throw. 434   // waiter. Runs inside the completion path; must not throw.
429   /// Re-arm hook: return true to skip resumption ( wait continues ). 435   /// Re-arm hook: return true to skip resumption ( wait continues ).
430   bool (*on_fire_)(void*) noexcept = nullptr; 436   bool (*on_fire_)(void*) noexcept = nullptr;
431   437  
432   /// Context passed to `on_fire_` ( the owning awaitable ). 438   /// Context passed to `on_fire_` ( the owning awaitable ).
433   void* on_fire_ctx_ = nullptr; 439   void* on_fire_ctx_ = nullptr;
434   440  
435   /// The embedded completion op posted to the scheduler. 441   /// The embedded completion op posted to the scheduler.
436   completion_op op_; 442   completion_op op_;
437   443  
438   // stop_callback is neither movable nor assignable; construct it 444   // stop_callback is neither movable nor assignable; construct it
439   // in place once the node is pinned on the coroutine frame, and 445   // in place once the node is pinned on the coroutine frame, and
440   // destroy it manually on every completion path. 446   // destroy it manually on every completion path.
441   /// Storage for the armed stop callback. 447   /// Storage for the armed stop callback.
442   alignas(stop_cb_type) unsigned char cb_buf_[sizeof(stop_cb_type)]; 448   alignas(stop_cb_type) unsigned char cb_buf_[sizeof(stop_cb_type)];
443   449  
444   /// True while `cb_buf_` holds a live stop callback. 450   /// True while `cb_buf_` holds a live stop callback.
445   bool cb_active_ = false; 451   bool cb_active_ = false;
446   452  
HITCBC 447   31724 waiter_node() noexcept 453   31816 waiter_node() noexcept
HITCBC 448   31724 { 454   31816 {
HITCBC 449   31724 op_.waiter_ = this; 455   31816 op_.waiter_ = this;
HITCBC 450   31724 } 456   31816 }
451   457  
452   // The embedded op self-points and the list hooks are published 458   // The embedded op self-points and the list hooks are published
453   // to other threads; the node never moves. 459   // to other threads; the node never moves.
454   waiter_node(waiter_node const&) = delete; 460   waiter_node(waiter_node const&) = delete;
455   waiter_node& operator=(waiter_node const&) = delete; 461   waiter_node& operator=(waiter_node const&) = delete;
456   462  
457   /** Bind the coroutine and its environment before publication. 463   /** Bind the coroutine and its environment before publication.
458   464  
459   The single definition of the fields every wait must populate 465   The single definition of the fields every wait must populate
460   before the node is published; hook-driven waits additionally 466   before the node is published; hook-driven waits additionally
461   set `on_fire_` / `on_fire_ctx_`. 467   set `on_fire_` / `on_fire_ctx_`.
462   468  
463   @param h The coroutine to resume on completion. 469   @param h The coroutine to resume on completion.
464   @param env The awaiting chain's environment; must outlive 470   @param env The awaiting chain's environment; must outlive
465   the suspension. 471   the suspension.
466   */ 472   */
HITCBC 467   14856 void bind(std::coroutine_handle<> h, capy::io_env const& env) noexcept 473   14902 void bind(std::coroutine_handle<> h, capy::io_env const& env) noexcept
468   { 474   {
HITCBC 469   14856 h_ = h; 475   14902 h_ = h;
HITCBC 470   14856 cont_.h = h; 476   14902 cont_.h = h;
HITCBC 471   14856 d_ = env.executor; 477   14902 d_ = env.executor;
HITCBC 472   14856 token_ = &env.stop_token; 478   14902 token_ = &env.stop_token;
HITCBC 473   14856 } 479   14902 }
474   480  
475   /** Arm the stop callback. 481   /** Arm the stop callback.
476   482  
477 - @pre `token_` is set. 483 + @par Preconditions
  484 + `token_` is set.
478   */ 485   */
HITCBC 479   1449 void arm_stop_cb() 486   1613 void arm_stop_cb()
480   { 487   {
HITCBC 481   1449 new (cb_buf_) stop_cb_type(*token_, canceller{this}); 488   1613 new (cb_buf_) stop_cb_type(*token_, canceller{this});
HITCBC 482   1449 cb_active_ = true; 489   1613 cb_active_ = true;
HITCBC 483   1449 } 490   1613 }
484   491  
485   /// Destroy the stop callback if armed. 492   /// Destroy the stop callback if armed.
HITCBC 486   14003 void reset_stop_cb() noexcept 493   14048 void reset_stop_cb() noexcept
487   { 494   {
HITCBC 488   14003 if (cb_active_) 495   14048 if (cb_active_)
489   { 496   {
HITCBC 490   1449 std::launder(reinterpret_cast<stop_cb_type*>(cb_buf_)) 497   1613 std::launder(reinterpret_cast<stop_cb_type*>(cb_buf_))
HITCBC 491   1449 ->~stop_cb_type(); 498   1613 ->~stop_cb_type();
HITCBC 492   1449 cb_active_ = false; 499   1613 cb_active_ = false;
493   } 500   }
HITCBC 494   14003 } 501   14048 }
495   }; 502   };
496   503  
497   /** Awaitable returned by `timer::wait()`. 504   /** Awaitable returned by `timer::wait()`.
498   505  
499   Carries the waiter node so a wait performs no allocation. The 506   Carries the waiter node so a wait performs no allocation. The
500   awaitable is movable only before `await_suspend` publishes the 507   awaitable is movable only before `await_suspend` publishes the
501   node (a move builds a fresh, quiescent node); afterwards it is 508   node (a move builds a fresh, quiescent node); afterwards it is
502   pinned on the coroutine frame until the wait completes. 509   pinned on the coroutine frame until the wait completes.
503   */ 510   */
504   struct wait_awaitable 511   struct wait_awaitable
505   { 512   {
506   timer& t_; 513   timer& t_;
507   waiter_node w_; 514   waiter_node w_;
508   515  
HITCBC 509   14609 explicit wait_awaitable(timer& t) noexcept : t_(t) {} 516   14655 explicit wait_awaitable(timer& t) noexcept : t_(t) {}
510   517  
HITCBC 511   14609 wait_awaitable(wait_awaitable&& o) noexcept : t_(o.t_) {} 518   14655 wait_awaitable(wait_awaitable&& o) noexcept : t_(o.t_) {}
512   519  
513   wait_awaitable(wait_awaitable const&) = delete; 520   wait_awaitable(wait_awaitable const&) = delete;
514   wait_awaitable& operator=(wait_awaitable const&) = delete; 521   wait_awaitable& operator=(wait_awaitable const&) = delete;
515   wait_awaitable& operator=(wait_awaitable&&) = delete; 522   wait_awaitable& operator=(wait_awaitable&&) = delete;
516   523  
HITCBC 517   2053 bool await_ready() const noexcept 524   2053 bool await_ready() const noexcept
518   { 525   {
HITCBC 519   2053 return false; 526   2053 return false;
520   } 527   }
521   528  
522   // Cancellation surfaces through w_.ec_: the stop_token path in 529   // Cancellation surfaces through w_.ec_: the stop_token path in
523   // wait() completes the waiter with error::canceled written to 530   // wait() completes the waiter with error::canceled written to
524   // it, so there is no separate token to consult here. 531   // it, so there is no separate token to consult here.
HITCBC 525   14580 [[nodiscard]] capy::io_result<> await_resume() const noexcept 532   14626 [[nodiscard]] capy::io_result<> await_resume() const noexcept
526   { 533   {
HITCBC 527   14580 return {w_.ec_}; 534   14626 return {w_.ec_};
528   } 535   }
529   536  
HITCBC 530   14609 auto await_suspend(std::coroutine_handle<> h, capy::io_env const* env) 537   14655 auto await_suspend(std::coroutine_handle<> h, capy::io_env const* env)
531   -> std::coroutine_handle<> 538   -> std::coroutine_handle<>
532   { 539   {
HITCBC 533   14609 auto& impl = t_.get(); 540   14655 auto& impl = t_.get();
HITCBC 534   14609 w_.bind(h, *env); 541   14655 w_.bind(h, *env);
535   542  
536   // Inline fast path: already expired and not in the heap. 543   // Inline fast path: already expired and not in the heap.
537   // Post instead of dispatch so the coroutine yields to the 544   // Post instead of dispatch so the coroutine yields to the
538   // scheduler, allowing other queued work to run. 545   // scheduler, allowing other queued work to run.
HITCBC 539   14609 if (impl.already_expired()) 546   14655 if (impl.already_expired())
540   { 547   {
HITCBC 541   853 w_.ec_ = {}; 548   854 w_.ec_ = {};
HITCBC 542   853 w_.d_.post(w_.cont_); 549   854 w_.d_.post(w_.cont_);
HITCBC 543   853 return std::noop_coroutine(); 550   854 return std::noop_coroutine();
544   } 551   }
545   552  
HITCBC 546   13756 return impl.wait(w_); 553   13801 return impl.wait(w_);
547   } 554   }
548   }; 555   };
549   556  
550   inline wait_awaitable 557   inline wait_awaitable
HITCBC 551   14609 timer::wait() 558   14655 timer::wait()
552   { 559   {
HITCBC 553   14609 return wait_awaitable(*this); 560   14655 return wait_awaitable(*this);
554   } 561   }
555   562  
556   } // namespace boost::corosio::detail 563   } // namespace boost::corosio::detail
557   564  
558   #endif 565   #endif