. /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   1782 explicit implementation(timer_service& svc) noexcept : svc_(&svc) {} 126   1906 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   28959 bool already_expired() const noexcept 135   29190 bool already_expired() const noexcept
136   { 136   {
HITCBC 137   86877 return heap_index_.load(std::memory_order_relaxed) == npos && 137   87570 return heap_index_.load(std::memory_order_relaxed) == npos &&
HITCBC 138   57254 (expiry_ == (std::chrono::steady_clock::time_point::min)() || 138   57716 (expiry_ == (std::chrono::steady_clock::time_point::min)() ||
HITCBC 139   57254 expiry_ <= std::chrono::steady_clock::now()); 139   57716 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   @par Preconditions 150   @par Preconditions
151   @p w is fully initialized, and its storage (the awaitable 151   @p w is fully initialized, and its storage (the awaitable
152   on the suspended coroutine's frame) outlives the wait. 152   on the suspended coroutine's frame) outlives the wait.
153   153  
154   @param w The waiter to publish. 154   @param w The waiter to publish.
155   */ 155   */
156   // Exported at member level: dllexport on the enclosing timer 156   // Exported at member level: dllexport on the enclosing timer
157   // class does not extend to nested classes, and header-inline 157   // class does not extend to nested classes, and header-inline
158   // callers (wait_awaitable::await_suspend) reference this 158   // callers (wait_awaitable::await_suspend) reference this
159   // symbol from outside the corosio DLL. 159   // symbol from outside the corosio DLL.
160   BOOST_COROSIO_DECL 160   BOOST_COROSIO_DECL
161   std::coroutine_handle<> wait(waiter_node& w); 161   std::coroutine_handle<> wait(waiter_node& w);
162   162  
163   /** Publish a waiter unconditionally. 163   /** Publish a waiter unconditionally.
164   164  
165   Like `wait`, but never takes the elapsed fast path. The 165   Like `wait`, but never takes the elapsed fast path. The
166   fast path posts the continuation directly, bypassing the 166   fast path posts the continuation directly, bypassing the
167   embedded op; hook-driven waits must observe every 167   embedded op; hook-driven waits must observe every
168   completion through the op, where the re-arm hook runs. 168   completion through the op, where the re-arm hook runs.
169   169  
170   @par Preconditions 170   @par Preconditions
171   Same as `wait`. 171   Same as `wait`.
172   172  
173   @param w The waiter to publish. 173   @param w The waiter to publish.
174   */ 174   */
175   std::coroutine_handle<> publish(waiter_node& w); 175   std::coroutine_handle<> publish(waiter_node& w);
176   }; 176   };
177   177  
178   /// The clock type used for time operations. 178   /// The clock type used for time operations.
179   using clock_type = std::chrono::steady_clock; 179   using clock_type = std::chrono::steady_clock;
180   180  
181   /// The time point type for absolute expiry times. 181   /// The time point type for absolute expiry times.
182   using time_point = clock_type::time_point; 182   using time_point = clock_type::time_point;
183   183  
184   /// The duration type for relative expiry times. 184   /// The duration type for relative expiry times.
185   using duration = clock_type::duration; 185   using duration = clock_type::duration;
186   186  
187   /** Destructor. 187   /** Destructor.
188   188  
189   Cancels any pending operations and releases timer resources. 189   Cancels any pending operations and releases timer resources.
190   */ 190   */
191   ~timer() override; 191   ~timer() override;
192   192  
193   /** Construct a timer from an execution context. 193   /** Construct a timer from an execution context.
194   194  
195   @param ctx The execution context that will own this timer. It 195   @param ctx The execution context that will own this timer. It
196   must be a corosio io_context; otherwise the constructor 196   must be a corosio io_context; otherwise the constructor
197   throws (a timer service is required). 197   throws (a timer service is required).
198   198  
199   @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.
200   */ 200   */
201   explicit timer(capy::execution_context& ctx); 201   explicit timer(capy::execution_context& ctx);
202   202  
203   /** Move constructor. 203   /** Move constructor.
204   204  
205   Transfers ownership of the timer resources. Required so a 205   Transfers ownership of the timer resources. Required so a
206   disengaged `std::optional<timer>` is movable; a timer is never 206   disengaged `std::optional<timer>` is movable; a timer is never
207   moved while a wait is published. 207   moved while a wait is published.
208   208  
209   @pre No awaitables returned by @p other's methods exist. 209   @pre No awaitables returned by @p other's methods exist.
210   */ 210   */
MISUBC 211   ✗ timer(timer&&) noexcept = default; 211   ✗ timer(timer&&) noexcept = default;
212   212  
213   /** Move assignment operator. 213   /** Move assignment operator.
214   214  
215   Closes any existing timer and transfers ownership. 215   Closes any existing timer and transfers ownership.
216   216  
217   @pre No awaitables returned by either `*this` or @p other's 217   @pre No awaitables returned by either `*this` or @p other's
218   methods exist. 218   methods exist.
219   */ 219   */
220   timer& operator=(timer&&) noexcept = default; 220   timer& operator=(timer&&) noexcept = default;
221   221  
222   timer(timer const&) = delete; 222   timer(timer const&) = delete;
223   timer& operator=(timer const&) = delete; 223   timer& operator=(timer const&) = delete;
224   224  
225   /** Return the timer's expiry time as an absolute time. 225   /** Return the timer's expiry time as an absolute time.
226   226  
227   @return The expiry time point. If no expiry has been set, 227   @return The expiry time point. If no expiry has been set,
228   returns a default-constructed time_point. 228   returns a default-constructed time_point.
229   */ 229   */
230   time_point expiry() const noexcept 230   time_point expiry() const noexcept
231   { 231   {
232   return get().expiry_; 232   return get().expiry_;
233   } 233   }
234   234  
235   /** Set the timer's expiry time as an absolute time. 235   /** Set the timer's expiry time as an absolute time.
236   236  
237   @par Preconditions 237   @par Preconditions
238   No wait is published on this timer. 238   No wait is published on this timer.
239   239  
240   @param t The expiry time to be used for the timer. 240   @param t The expiry time to be used for the timer.
241   */ 241   */
HITCBC 242   16 void expires_at(time_point t) 242   16 void expires_at(time_point t)
243   { 243   {
HITCBC 244   16 auto& impl = get(); 244   16 auto& impl = get();
HITCBC 245   32 BOOST_COROSIO_ASSERT( 245   32 BOOST_COROSIO_ASSERT(
246   impl.heap_index_.load(std::memory_order_relaxed) == 246   impl.heap_index_.load(std::memory_order_relaxed) ==
247   implementation::npos); 247   implementation::npos);
HITCBC 248   16 impl.expiry_ = t; 248   16 impl.expiry_ = t;
HITCBC 249   16 } 249   16 }
250   250  
251   /** Set the timer's expiry time relative to now. 251   /** Set the timer's expiry time relative to now.
252   252  
253   @par Preconditions 253   @par Preconditions
254   No wait is published on this timer. 254   No wait is published on this timer.
255   255  
256   @param d The expiry time relative to now. 256   @param d The expiry time relative to now.
257   */ 257   */
HITCBC 258   19385 void expires_after(duration d) 258   19333 void expires_after(duration d)
259   { 259   {
HITCBC 260   19385 auto& impl = get(); 260   19333 auto& impl = get();
HITCBC 261   38770 BOOST_COROSIO_ASSERT( 261   38666 BOOST_COROSIO_ASSERT(
262   impl.heap_index_.load(std::memory_order_relaxed) == 262   impl.heap_index_.load(std::memory_order_relaxed) ==
263   implementation::npos); 263   implementation::npos);
HITCBC 264   19385 if (d <= duration::zero()) 264   19333 if (d <= duration::zero())
HITCBC 265   680 impl.expiry_ = (time_point::min)(); 265   681 impl.expiry_ = (time_point::min)();
266   else 266   else
267   { 267   {
268   // Saturate rather than overflow: a clamped near-max duration 268   // Saturate rather than overflow: a clamped near-max duration
269   // (e.g. delay(hours::max())) would wrap now() + d past the 269   // (e.g. delay(hours::max())) would wrap now() + d past the
270   // clock's range and appear already elapsed. 270   // clock's range and appear already elapsed.
HITCBC 271   18705 auto const now = clock_type::now(); 271   18652 auto const now = clock_type::now();
HITCBC 272   18705 impl.expiry_ = 272   18652 impl.expiry_ =
HITCBC 273   18705 ((time_point::max)() - now < d) ? (time_point::max)() : now + d; 273   18652 ((time_point::max)() - now < d) ? (time_point::max)() : now + d;
274   } 274   }
HITCBC 275   19385 } 275   19333 }
276   276  
277   /** Set the timer's expiry time relative to now. 277   /** Set the timer's expiry time relative to now.
278   278  
279   This is a convenience overload that accepts any duration type 279   This is a convenience overload that accepts any duration type
280   and converts it to the timer's native duration type. 280   and converts it to the timer's native duration type.
281   281  
282   @param d The expiry time relative to now. 282   @param d The expiry time relative to now.
283   */ 283   */
284   template<class Rep, class Period> 284   template<class Rep, class Period>
285   void expires_after(std::chrono::duration<Rep, Period> d) 285   void expires_after(std::chrono::duration<Rep, Period> d)
286   { 286   {
287   expires_after(std::chrono::duration_cast<duration>(d)); 287   expires_after(std::chrono::duration_cast<duration>(d));
288   } 288   }
289   289  
290   /** Wait for the timer to expire. 290   /** Wait for the timer to expire.
291   291  
292   At most one wait may be outstanding at a time. 292   At most one wait may be outstanding at a time.
293   293  
294   The operation supports cancellation via `std::stop_token` through 294   The operation supports cancellation via `std::stop_token` through
295   the affine awaitable protocol. If the associated stop token is 295   the affine awaitable protocol. If the associated stop token is
296   triggered, only that waiter completes with an error that 296   triggered, only that waiter completes with an error that
297   compares equal to `capy::cond::canceled`. 297   compares equal to `capy::cond::canceled`.
298   298  
299   This timer must outlive the returned awaitable. 299   This timer must outlive the returned awaitable.
300   300  
301   @return An awaitable that completes with `io_result<>`. 301   @return An awaitable that completes with `io_result<>`.
302   */ 302   */
303   // Defined below wait_awaitable, which needs timer complete. 303   // Defined below wait_awaitable, which needs timer complete.
304   wait_awaitable wait(); 304   wait_awaitable wait();
305   305  
306   /** Publish a hook-driven wait. 306   /** Publish a hook-driven wait.
307   307  
308   Bypasses the elapsed fast path so every completion is 308   Bypasses the elapsed fast path so every completion is
309   delivered through the waiter's embedded op, where the 309   delivered through the waiter's embedded op, where the
310   re-arm hook is consulted. Used by awaitables that 310   re-arm hook is consulted. Used by awaitables that
311   re-publish the waiter to continue a logical wait across 311   re-publish the waiter to continue a logical wait across
312   several timer expirations. 312   several timer expirations.
313   313  
314   @par Preconditions 314   @par Preconditions
315   @p w is fully initialized ( handle, executor, stop token, 315   @p w is fully initialized ( handle, executor, stop token,
316   hook fields ) and its storage outlives the wait. 316   hook fields ) and its storage outlives the wait.
317   317  
318   @param w The waiter to publish. 318   @param w The waiter to publish.
319   319  
320   @return `std::noop_coroutine()`. 320   @return `std::noop_coroutine()`.
321   */ 321   */
322   std::coroutine_handle<> publish_wait(waiter_node& w); 322   std::coroutine_handle<> publish_wait(waiter_node& w);
323   323  
324   /** Re-arm an already-fired waiter with a new relative expiry. 324   /** Re-arm an already-fired waiter with a new relative expiry.
325   325  
326   Stores the ( saturated ) expiry and re-publishes @p w. The 326   Stores the ( saturated ) expiry and re-publishes @p w. The
327   waiter's original work count and stop callback remain in 327   waiter's original work count and stop callback remain in
328   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,
329   where the waiter has been popped from the service but not 329   where the waiter has been popped from the service but not
330   yet resumed. 330   yet resumed.
331   331  
332   @par Preconditions 332   @par Preconditions
333   The timer has no other waiters — this is what makes the 333   The timer has no other waiters — this is what makes the
334   unlocked expiry write race-free. 334   unlocked expiry write race-free.
335   335  
336   Re-publication needs heap capacity and can fail under 336   Re-publication needs heap capacity and can fail under
337   allocation pressure. On failure the waiter is left exactly as 337   allocation pressure. On failure the waiter is left exactly as
338   the hook received it, so the caller completes the wait through 338   the hook received it, so the caller completes the wait through
339   the normal resume path instead of re-arming. 339   the normal resume path instead of re-arming.
340   340  
341   @param w The waiter to re-publish. 341   @param w The waiter to re-publish.
342   @param d The next expiry relative to now. 342   @param d The next expiry relative to now.
343   343  
344   @return `true` if re-published; `false` if allocation failed. 344   @return `true` if re-published; `false` if allocation failed.
345   */ 345   */
346   [[nodiscard]] bool rearm_wait(waiter_node& w, duration d) noexcept; 346   [[nodiscard]] bool rearm_wait(waiter_node& w, duration d) noexcept;
347   347  
348   protected: 348   protected:
349   explicit timer(handle h) noexcept : io_object(std::move(h)) {} 349   explicit timer(handle h) noexcept : io_object(std::move(h)) {}
350   350  
351   private: 351   private:
352   /// Return the underlying implementation. 352   /// Return the underlying implementation.
HITCBC 353   38802 implementation& get() const noexcept 353   38698 implementation& get() const noexcept
354   { 354   {
HITCBC 355   38802 return *static_cast<implementation*>(h_.get()); 355   38698 return *static_cast<implementation*>(h_.get());
356   } 356   }
357   }; 357   };
358   358  
359   /** Frame-resident per-wait state for a timer wait. 359   /** Frame-resident per-wait state for a timer wait.
360   360  
361   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
362   awaitable on the suspended coroutine's frame — never allocated. 362   awaitable on the suspended coroutine's frame — never allocated.
363   Once published by `implementation::wait()` the node may be 363   Once published by `implementation::wait()` the node may be
364   completed from any thread; every completion path finishes 364   completed from any thread; every completion path finishes
365   touching the node before resuming or destroying the coroutine, 365   touching the node before resuming or destroying the coroutine,
366   because either act may end the node's storage. 366   because either act may end the node's storage.
367   367  
368   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
369   awaiting chain's `io_env` (which outlives the suspension) and 369   awaiting chain's `io_env` (which outlives the suspension) and
370   the stop callback is managed manually in `cb_buf_`, destroyed on 370   the stop callback is managed manually in `cb_buf_`, destroyed on
371   every completion path before the frame can die. 371   every completion path before the frame can die.
372   */ 372   */
373   struct BOOST_COROSIO_SYMBOL_VISIBLE waiter_node 373   struct BOOST_COROSIO_SYMBOL_VISIBLE waiter_node
374   : intrusive_list<waiter_node>::node 374   : intrusive_list<waiter_node>::node
375   { 375   {
376   // Embedded completion op — avoids heap allocation per fire/cancel. 376   // Embedded completion op — avoids heap allocation per fire/cancel.
377   // Members are exported and defined non-inline in timer.cpp: the 377   // Members are exported and defined non-inline in timer.cpp: the
378   // inline waiter_node constructor references do_complete and the 378   // inline waiter_node constructor references do_complete and the
379   // vtable from translation units that reach this header through 379   // vtable from translation units that reach this header through
380   // delay.hpp without ever including timer_service.hpp, so the one 380   // delay.hpp without ever including timer_service.hpp, so the one
381   // strong definition must live in a TU that is always linked. 381   // strong definition must live in a TU that is always linked.
382   struct BOOST_COROSIO_SYMBOL_VISIBLE completion_op final : scheduler_op 382   struct BOOST_COROSIO_SYMBOL_VISIBLE completion_op final : scheduler_op
383   { 383   {
384   waiter_node* waiter_ = nullptr; 384   waiter_node* waiter_ = nullptr;
385   385  
386   BOOST_COROSIO_DECL 386   BOOST_COROSIO_DECL
387   static void do_complete( 387   static void do_complete(
388   void* owner, scheduler_op* base, std::uint32_t, std::uint32_t); 388   void* owner, scheduler_op* base, std::uint32_t, std::uint32_t);
389   389  
HITCBC 390   32318 completion_op() noexcept : scheduler_op(&do_complete) {} 390   32550 completion_op() noexcept : scheduler_op(&do_complete) {}
391   391  
392   BOOST_COROSIO_DECL void operator()() override; 392   BOOST_COROSIO_DECL void operator()() override;
393   BOOST_COROSIO_DECL void destroy() override; 393   BOOST_COROSIO_DECL void destroy() override;
394   }; 394   };
395   395  
396   // Per-waiter stop_token cancellation 396   // Per-waiter stop_token cancellation
397   struct canceller 397   struct canceller
398   { 398   {
399   waiter_node* waiter_; 399   waiter_node* waiter_;
400   BOOST_COROSIO_DECL void operator()() const; 400   BOOST_COROSIO_DECL void operator()() const;
401   }; 401   };
402   402  
403   using stop_cb_type = std::stop_callback<canceller>; 403   using stop_cb_type = std::stop_callback<canceller>;
404   404  
405   // nullptr once unpublished from the timer ( concurrency marker ) 405   // nullptr once unpublished from the timer ( concurrency marker )
406   /// The timer this waiter is published on, or `nullptr`. 406   /// The timer this waiter is published on, or `nullptr`.
407   timer::implementation* impl_ = nullptr; 407   timer::implementation* impl_ = nullptr;
408   408  
409   /// The timer service that completes this waiter. 409   /// The timer service that completes this waiter.
410   timer_service* svc_ = nullptr; 410   timer_service* svc_ = nullptr;
411   411  
412   /// The suspended coroutine, destroyed by the shutdown drains. 412   /// The suspended coroutine, destroyed by the shutdown drains.
413   std::coroutine_handle<> h_; 413   std::coroutine_handle<> h_;
414   414  
415   /// The continuation posted to resume the coroutine. 415   /// The continuation posted to resume the coroutine.
416   capy::continuation cont_; 416   capy::continuation cont_;
417   417  
418   /// The executor the continuation is posted through. 418   /// The executor the continuation is posted through.
419   capy::executor_ref d_; 419   capy::executor_ref d_;
420   420  
421   // Borrowed from the awaiting chain's io_env, which outlives the 421   // Borrowed from the awaiting chain's io_env, which outlives the
422   // suspension; the node holds no owning state. 422   // suspension; the node holds no owning state.
423   /// The stop token observed for cancellation. 423   /// The stop token observed for cancellation.
424   std::stop_token const* token_ = nullptr; 424   std::stop_token const* token_ = nullptr;
425   425  
426   /// The completion result read by `await_resume`. 426   /// The completion result read by `await_resume`.
427   std::error_code ec_; 427   std::error_code ec_;
428   428  
429   // Consulted by the completion op before resuming; lets a 429   // Consulted by the completion op before resuming; lets a
430   // clock-facade wait re-publish itself instead of completing. 430   // clock-facade wait re-publish itself instead of completing.
431   // Never consulted on the shutdown destroy path. Consulted on 431   // Never consulted on the shutdown destroy path. Consulted on
432   // every completion, including cancellation ( `ec_` set ) — the 432   // every completion, including cancellation ( `ec_` set ) — the
433   // 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
434   // waiter. Runs inside the completion path; must not throw. 434   // waiter. Runs inside the completion path; must not throw.
435   /// Re-arm hook: return true to skip resumption ( wait continues ). 435   /// Re-arm hook: return true to skip resumption ( wait continues ).
436   bool (*on_fire_)(void*) noexcept = nullptr; 436   bool (*on_fire_)(void*) noexcept = nullptr;
437   437  
438   /// Context passed to `on_fire_` ( the owning awaitable ). 438   /// Context passed to `on_fire_` ( the owning awaitable ).
439   void* on_fire_ctx_ = nullptr; 439   void* on_fire_ctx_ = nullptr;
440   440  
441   /// The embedded completion op posted to the scheduler. 441   /// The embedded completion op posted to the scheduler.
442   completion_op op_; 442   completion_op op_;
443   443  
444   // stop_callback is neither movable nor assignable; construct it 444   // stop_callback is neither movable nor assignable; construct it
445   // 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
446   // destroy it manually on every completion path. 446   // destroy it manually on every completion path.
447   /// Storage for the armed stop callback. 447   /// Storage for the armed stop callback.
448   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)];
449   449  
450   /// True while `cb_buf_` holds a live stop callback. 450   /// True while `cb_buf_` holds a live stop callback.
451   bool cb_active_ = false; 451   bool cb_active_ = false;
452   452  
HITCBC 453   32318 waiter_node() noexcept 453   32550 waiter_node() noexcept
HITCBC 454   32318 { 454   32550 {
HITCBC 455   32318 op_.waiter_ = this; 455   32550 op_.waiter_ = this;
HITCBC 456   32318 } 456   32550 }
457   457  
458   // The embedded op self-points and the list hooks are published 458   // The embedded op self-points and the list hooks are published
459   // to other threads; the node never moves. 459   // to other threads; the node never moves.
460   waiter_node(waiter_node const&) = delete; 460   waiter_node(waiter_node const&) = delete;
461   waiter_node& operator=(waiter_node const&) = delete; 461   waiter_node& operator=(waiter_node const&) = delete;
462   462  
463   /** Bind the coroutine and its environment before publication. 463   /** Bind the coroutine and its environment before publication.
464   464  
465   The single definition of the fields every wait must populate 465   The single definition of the fields every wait must populate
466   before the node is published; hook-driven waits additionally 466   before the node is published; hook-driven waits additionally
467   set `on_fire_` / `on_fire_ctx_`. 467   set `on_fire_` / `on_fire_ctx_`.
468   468  
469   @param h The coroutine to resume on completion. 469   @param h The coroutine to resume on completion.
470   @param env The awaiting chain's environment; must outlive 470   @param env The awaiting chain's environment; must outlive
471   the suspension. 471   the suspension.
472   */ 472   */
HITCBC 473   15153 void bind(std::coroutine_handle<> h, capy::io_env const& env) noexcept 473   15270 void bind(std::coroutine_handle<> h, capy::io_env const& env) noexcept
474   { 474   {
HITCBC 475   15153 h_ = h; 475   15270 h_ = h;
HITCBC 476   15153 cont_.h = h; 476   15270 cont_.h = h;
HITCBC 477   15153 d_ = env.executor; 477   15270 d_ = env.executor;
HITCBC 478   15153 token_ = &env.stop_token; 478   15270 token_ = &env.stop_token;
HITCBC 479   15153 } 479   15270 }
480   480  
481   /** Arm the stop callback. 481   /** Arm the stop callback.
482   482  
483   @par Preconditions 483   @par Preconditions
484   `token_` is set. 484   `token_` is set.
485   */ 485   */
HITCBC 486   1775 void arm_stop_cb() 486   1864 void arm_stop_cb()
487   { 487   {
HITCBC 488   1775 new (cb_buf_) stop_cb_type(*token_, canceller{this}); 488   1864 new (cb_buf_) stop_cb_type(*token_, canceller{this});
HITCBC 489   1775 cb_active_ = true; 489   1864 cb_active_ = true;
HITCBC 490   1775 } 490   1864 }
491   491  
492   /// Destroy the stop callback if armed. 492   /// Destroy the stop callback if armed.
HITCBC 493   14300 void reset_stop_cb() noexcept 493   14416 void reset_stop_cb() noexcept
494   { 494   {
HITCBC 495   14300 if (cb_active_) 495   14416 if (cb_active_)
496   { 496   {
HITCBC 497   1775 std::launder(reinterpret_cast<stop_cb_type*>(cb_buf_)) 497   1864 std::launder(reinterpret_cast<stop_cb_type*>(cb_buf_))
HITCBC 498   1775 ->~stop_cb_type(); 498   1864 ->~stop_cb_type();
HITCBC 499   1775 cb_active_ = false; 499   1864 cb_active_ = false;
500   } 500   }
HITCBC 501   14300 } 501   14416 }
502   }; 502   };
503   503  
504   /** Awaitable returned by `timer::wait()`. 504   /** Awaitable returned by `timer::wait()`.
505   505  
506   Carries the waiter node so a wait performs no allocation. The 506   Carries the waiter node so a wait performs no allocation. The
507   awaitable is movable only before `await_suspend` publishes the 507   awaitable is movable only before `await_suspend` publishes the
508   node (a move builds a fresh, quiescent node); afterwards it is 508   node (a move builds a fresh, quiescent node); afterwards it is
509   pinned on the coroutine frame until the wait completes. 509   pinned on the coroutine frame until the wait completes.
510   */ 510   */
511   struct wait_awaitable 511   struct wait_awaitable
512   { 512   {
513   timer& t_; 513   timer& t_;
514   waiter_node w_; 514   waiter_node w_;
515   515  
HITCBC 516   14906 explicit wait_awaitable(timer& t) noexcept : t_(t) {} 516   15022 explicit wait_awaitable(timer& t) noexcept : t_(t) {}
517   517  
HITCBC 518   14906 wait_awaitable(wait_awaitable&& o) noexcept : t_(o.t_) {} 518   15022 wait_awaitable(wait_awaitable&& o) noexcept : t_(o.t_) {}
519   519  
520   wait_awaitable(wait_awaitable const&) = delete; 520   wait_awaitable(wait_awaitable const&) = delete;
521   wait_awaitable& operator=(wait_awaitable const&) = delete; 521   wait_awaitable& operator=(wait_awaitable const&) = delete;
522   wait_awaitable& operator=(wait_awaitable&&) = delete; 522   wait_awaitable& operator=(wait_awaitable&&) = delete;
523   523  
HITCBC 524   2053 bool await_ready() const noexcept 524   2053 bool await_ready() const noexcept
525   { 525   {
HITCBC 526   2053 return false; 526   2053 return false;
527   } 527   }
528   528  
529   // Cancellation surfaces through w_.ec_: the stop_token path in 529   // Cancellation surfaces through w_.ec_: the stop_token path in
530   // wait() completes the waiter with error::canceled written to 530   // wait() completes the waiter with error::canceled written to
531   // it, so there is no separate token to consult here. 531   // it, so there is no separate token to consult here.
HITCBC 532   14877 [[nodiscard]] capy::io_result<> await_resume() const noexcept 532   14993 [[nodiscard]] capy::io_result<> await_resume() const noexcept
533   { 533   {
HITCBC 534   14877 return {w_.ec_}; 534   14993 return {w_.ec_};
535   } 535   }
536   536  
HITCBC 537   14906 auto await_suspend(std::coroutine_handle<> h, capy::io_env const* env) 537   15022 auto await_suspend(std::coroutine_handle<> h, capy::io_env const* env)
538   -> std::coroutine_handle<> 538   -> std::coroutine_handle<>
539   { 539   {
HITCBC 540   14906 auto& impl = t_.get(); 540   15022 auto& impl = t_.get();
HITCBC 541   14906 w_.bind(h, *env); 541   15022 w_.bind(h, *env);
542   542  
543   // Inline fast path: already expired and not in the heap. 543   // Inline fast path: already expired and not in the heap.
544   // Post instead of dispatch so the coroutine yields to the 544   // Post instead of dispatch so the coroutine yields to the
545   // scheduler, allowing other queued work to run. 545   // scheduler, allowing other queued work to run.
HITCBC 546   14906 if (impl.already_expired()) 546   15022 if (impl.already_expired())
547   { 547   {
HITCBC 548   853 w_.ec_ = {}; 548   854 w_.ec_ = {};
HITCBC 549   853 w_.d_.post(w_.cont_); 549   854 w_.d_.post(w_.cont_);
HITCBC 550   853 return std::noop_coroutine(); 550   854 return std::noop_coroutine();
551   } 551   }
552   552  
HITCBC 553   14053 return impl.wait(w_); 553   14168 return impl.wait(w_);
554   } 554   }
555   }; 555   };
556   556  
557   inline wait_awaitable 557   inline wait_awaitable
HITCBC 558   14906 timer::wait() 558   15022 timer::wait()
559   { 559   {
HITCBC 560   14906 return wait_awaitable(*this); 560   15022 return wait_awaitable(*this);
561   } 561   }
562   562  
563   } // namespace boost::corosio::detail 563   } // namespace boost::corosio::detail
564   564  
565   #endif 565   #endif