. /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   1382 explicit implementation(timer_service& svc) noexcept : svc_(&svc) {} 126   1399 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   28704 bool already_expired() const noexcept 135   28763 bool already_expired() const noexcept
136   { 136   {
HITCBC 137   86112 return heap_index_.load(std::memory_order_relaxed) == npos && 137   86289 return heap_index_.load(std::memory_order_relaxed) == npos &&
HITCBC 138 - 28704 (expiry_ == 138 + 56862 (expiry_ == (std::chrono::steady_clock::time_point::min)() ||
DCB 139 - 56744 (std::chrono::steady_clock::time_point::min)() ||  
HITCBC 140   56744 expiry_ <= std::chrono::steady_clock::now()); 139   56862 expiry_ <= std::chrono::steady_clock::now());
141   } 140   }
142   141  
143   /** Asynchronously wait for the timer to expire. 142   /** Asynchronously wait for the timer to expire.
144   143  
145   Publishes the waiter into the service's heap and the 144   Publishes the waiter into the service's heap and the
146   timer's waiter slot, after which it may complete on any 145   timer's waiter slot, after which it may complete on any
147   thread. If the timer is already expired and not in the 146   thread. If the timer is already expired and not in the
148   heap, completes by posting the continuation without 147   heap, completes by posting the continuation without
149   publishing. 148   publishing.
150   149  
151   @par Preconditions 150   @par Preconditions
152   @p w is fully initialized, and its storage (the awaitable 151   @p w is fully initialized, and its storage (the awaitable
153   on the suspended coroutine's frame) outlives the wait. 152   on the suspended coroutine's frame) outlives the wait.
154   153  
155   @param w The waiter to publish. 154   @param w The waiter to publish.
156   */ 155   */
157   // Exported at member level: dllexport on the enclosing timer 156   // Exported at member level: dllexport on the enclosing timer
158   // class does not extend to nested classes, and header-inline 157   // class does not extend to nested classes, and header-inline
159   // callers (wait_awaitable::await_suspend) reference this 158   // callers (wait_awaitable::await_suspend) reference this
160   // symbol from outside the corosio DLL. 159   // symbol from outside the corosio DLL.
161   BOOST_COROSIO_DECL 160   BOOST_COROSIO_DECL
162   std::coroutine_handle<> wait(waiter_node& w); 161   std::coroutine_handle<> wait(waiter_node& w);
163   162  
164   /** Publish a waiter unconditionally. 163   /** Publish a waiter unconditionally.
165   164  
166   Like `wait`, but never takes the elapsed fast path. The 165   Like `wait`, but never takes the elapsed fast path. The
167   fast path posts the continuation directly, bypassing the 166   fast path posts the continuation directly, bypassing the
168   embedded op; hook-driven waits must observe every 167   embedded op; hook-driven waits must observe every
169   completion through the op, where the re-arm hook runs. 168   completion through the op, where the re-arm hook runs.
170   169  
171   @par Preconditions 170   @par Preconditions
172   Same as `wait`. 171   Same as `wait`.
173   172  
174   @param w The waiter to publish. 173   @param w The waiter to publish.
175   */ 174   */
176   std::coroutine_handle<> publish(waiter_node& w); 175   std::coroutine_handle<> publish(waiter_node& w);
177   }; 176   };
178   177  
179   /// The clock type used for time operations. 178   /// The clock type used for time operations.
180   using clock_type = std::chrono::steady_clock; 179   using clock_type = std::chrono::steady_clock;
181   180  
182   /// The time point type for absolute expiry times. 181   /// The time point type for absolute expiry times.
183   using time_point = clock_type::time_point; 182   using time_point = clock_type::time_point;
184   183  
185   /// The duration type for relative expiry times. 184   /// The duration type for relative expiry times.
186   using duration = clock_type::duration; 185   using duration = clock_type::duration;
187   186  
188   /** Destructor. 187   /** Destructor.
189   188  
190   Cancels any pending operations and releases timer resources. 189   Cancels any pending operations and releases timer resources.
191   */ 190   */
192   ~timer() override; 191   ~timer() override;
193   192  
194   /** Construct a timer from an execution context. 193   /** Construct a timer from an execution context.
195   194  
196   @param ctx The execution context that will own this timer. It 195   @param ctx The execution context that will own this timer. It
197   must be a corosio io_context; otherwise the constructor 196   must be a corosio io_context; otherwise the constructor
198   throws (a timer service is required). 197   throws (a timer service is required).
199   198  
200   @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.
201   */ 200   */
202   explicit timer(capy::execution_context& ctx); 201   explicit timer(capy::execution_context& ctx);
203   202  
204   /** Move constructor. 203   /** Move constructor.
205   204  
206   Transfers ownership of the timer resources. Required so a 205   Transfers ownership of the timer resources. Required so a
207   disengaged `std::optional<timer>` is movable; a timer is never 206   disengaged `std::optional<timer>` is movable; a timer is never
208   moved while a wait is published. 207   moved while a wait is published.
209   208  
210   @pre No awaitables returned by @p other's methods exist. 209   @pre No awaitables returned by @p other's methods exist.
211   */ 210   */
MISUBC 212   ✗ timer(timer&&) noexcept = default; 211   ✗ timer(timer&&) noexcept = default;
213   212  
214   /** Move assignment operator. 213   /** Move assignment operator.
215   214  
216   Closes any existing timer and transfers ownership. 215   Closes any existing timer and transfers ownership.
217   216  
218   @pre No awaitables returned by either `*this` or @p other's 217   @pre No awaitables returned by either `*this` or @p other's
219   methods exist. 218   methods exist.
220   */ 219   */
221   timer& operator=(timer&&) noexcept = default; 220   timer& operator=(timer&&) noexcept = default;
222   221  
223   timer(timer const&) = delete; 222   timer(timer const&) = delete;
224   timer& operator=(timer const&) = delete; 223   timer& operator=(timer const&) = delete;
225   224  
226   /** Return the timer's expiry time as an absolute time. 225   /** Return the timer's expiry time as an absolute time.
227   226  
228   @return The expiry time point. If no expiry has been set, 227   @return The expiry time point. If no expiry has been set,
229   returns a default-constructed time_point. 228   returns a default-constructed time_point.
230   */ 229   */
231   time_point expiry() const noexcept 230   time_point expiry() const noexcept
232   { 231   {
233   return get().expiry_; 232   return get().expiry_;
234   } 233   }
235   234  
236   /** Set the timer's expiry time as an absolute time. 235   /** Set the timer's expiry time as an absolute time.
237   236  
238   @par Preconditions 237   @par Preconditions
239   No wait is published on this timer. 238   No wait is published on this timer.
240   239  
241   @param t The expiry time to be used for the timer. 240   @param t The expiry time to be used for the timer.
242   */ 241   */
HITCBC 243   16 void expires_at(time_point t) 242   16 void expires_at(time_point t)
244   { 243   {
HITCBC 245   16 auto& impl = get(); 244   16 auto& impl = get();
HITCBC 246   32 BOOST_COROSIO_ASSERT( 245   32 BOOST_COROSIO_ASSERT(
247   impl.heap_index_.load(std::memory_order_relaxed) == 246   impl.heap_index_.load(std::memory_order_relaxed) ==
248   implementation::npos); 247   implementation::npos);
HITCBC 249   16 impl.expiry_ = t; 248   16 impl.expiry_ = t;
HITCBC 250   16 } 249   16 }
251   250  
252   /** Set the timer's expiry time relative to now. 251   /** Set the timer's expiry time relative to now.
253   252  
254   @par Preconditions 253   @par Preconditions
255   No wait is published on this timer. 254   No wait is published on this timer.
256   255  
257   @param d The expiry time relative to now. 256   @param d The expiry time relative to now.
258   */ 257   */
HITCBC 259   19083 void expires_after(duration d) 258   19281 void expires_after(duration d)
260   { 259   {
HITCBC 261   19083 auto& impl = get(); 260   19281 auto& impl = get();
HITCBC 262   38166 BOOST_COROSIO_ASSERT( 261   38562 BOOST_COROSIO_ASSERT(
263   impl.heap_index_.load(std::memory_order_relaxed) == 262   impl.heap_index_.load(std::memory_order_relaxed) ==
264   implementation::npos); 263   implementation::npos);
HITCBC 265   19083 if (d <= duration::zero()) 264   19281 if (d <= duration::zero())
HITCBC 266   680 impl.expiry_ = (time_point::min)(); 265   681 impl.expiry_ = (time_point::min)();
267   else 266   else
268   { 267   {
269   // Saturate rather than overflow: a clamped near-max duration 268   // Saturate rather than overflow: a clamped near-max duration
270   // (e.g. delay(hours::max())) would wrap now() + d past the 269   // (e.g. delay(hours::max())) would wrap now() + d past the
271   // clock's range and appear already elapsed. 270   // clock's range and appear already elapsed.
HITCBC 272   18403 auto const now = clock_type::now(); 271   18600 auto const now = clock_type::now();
HITCBC 273 - 18403 impl.expiry_ = ((time_point::max)() - now < d) 272 + 18600 impl.expiry_ =
HITCBC 274 - 36802 ? (time_point::max)() 273 + 18600 ((time_point::max)() - now < d) ? (time_point::max)() : now + d;
DCB 275 - 18399 : now + d;  
276   } 274   }
HITCBC 277   19083 } 275   19281 }
278   276  
279   /** Set the timer's expiry time relative to now. 277   /** Set the timer's expiry time relative to now.
280   278  
281   This is a convenience overload that accepts any duration type 279   This is a convenience overload that accepts any duration type
282   and converts it to the timer's native duration type. 280   and converts it to the timer's native duration type.
283   281  
284   @param d The expiry time relative to now. 282   @param d The expiry time relative to now.
285   */ 283   */
286   template<class Rep, class Period> 284   template<class Rep, class Period>
287   void expires_after(std::chrono::duration<Rep, Period> d) 285   void expires_after(std::chrono::duration<Rep, Period> d)
288   { 286   {
289   expires_after(std::chrono::duration_cast<duration>(d)); 287   expires_after(std::chrono::duration_cast<duration>(d));
290   } 288   }
291   289  
292   /** Wait for the timer to expire. 290   /** Wait for the timer to expire.
293   291  
294   At most one wait may be outstanding at a time. 292   At most one wait may be outstanding at a time.
295   293  
296   The operation supports cancellation via `std::stop_token` through 294   The operation supports cancellation via `std::stop_token` through
297   the affine awaitable protocol. If the associated stop token is 295   the affine awaitable protocol. If the associated stop token is
298   triggered, only that waiter completes with an error that 296   triggered, only that waiter completes with an error that
299   compares equal to `capy::cond::canceled`. 297   compares equal to `capy::cond::canceled`.
300   298  
301   This timer must outlive the returned awaitable. 299   This timer must outlive the returned awaitable.
302   300  
303   @return An awaitable that completes with `io_result<>`. 301   @return An awaitable that completes with `io_result<>`.
304   */ 302   */
305   // Defined below wait_awaitable, which needs timer complete. 303   // Defined below wait_awaitable, which needs timer complete.
306   wait_awaitable wait(); 304   wait_awaitable wait();
307   305  
308   /** Publish a hook-driven wait. 306   /** Publish a hook-driven wait.
309   307  
310   Bypasses the elapsed fast path so every completion is 308   Bypasses the elapsed fast path so every completion is
311   delivered through the waiter's embedded op, where the 309   delivered through the waiter's embedded op, where the
312   re-arm hook is consulted. Used by awaitables that 310   re-arm hook is consulted. Used by awaitables that
313   re-publish the waiter to continue a logical wait across 311   re-publish the waiter to continue a logical wait across
314   several timer expirations. 312   several timer expirations.
315   313  
316   @par Preconditions 314   @par Preconditions
317   @p w is fully initialized ( handle, executor, stop token, 315   @p w is fully initialized ( handle, executor, stop token,
318   hook fields ) and its storage outlives the wait. 316   hook fields ) and its storage outlives the wait.
319   317  
320   @param w The waiter to publish. 318   @param w The waiter to publish.
321   319  
322   @return `std::noop_coroutine()`. 320   @return `std::noop_coroutine()`.
323   */ 321   */
324   std::coroutine_handle<> publish_wait(waiter_node& w); 322   std::coroutine_handle<> publish_wait(waiter_node& w);
325   323  
326   /** Re-arm an already-fired waiter with a new relative expiry. 324   /** Re-arm an already-fired waiter with a new relative expiry.
327   325  
328   Stores the ( saturated ) expiry and re-publishes @p w. The 326   Stores the ( saturated ) expiry and re-publishes @p w. The
329   waiter's original work count and stop callback remain in 327   waiter's original work count and stop callback remain in
330   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,
331   where the waiter has been popped from the service but not 329   where the waiter has been popped from the service but not
332   yet resumed. 330   yet resumed.
333   331  
334   @par Preconditions 332   @par Preconditions
335   The timer has no other waiters — this is what makes the 333   The timer has no other waiters — this is what makes the
336   unlocked expiry write race-free. 334   unlocked expiry write race-free.
337   335  
338   Re-publication needs heap capacity and can fail under 336   Re-publication needs heap capacity and can fail under
339   allocation pressure. On failure the waiter is left exactly as 337   allocation pressure. On failure the waiter is left exactly as
340   the hook received it, so the caller completes the wait through 338   the hook received it, so the caller completes the wait through
341   the normal resume path instead of re-arming. 339   the normal resume path instead of re-arming.
342   340  
343   @param w The waiter to re-publish. 341   @param w The waiter to re-publish.
344   @param d The next expiry relative to now. 342   @param d The next expiry relative to now.
345   343  
346   @return `true` if re-published; `false` if allocation failed. 344   @return `true` if re-published; `false` if allocation failed.
347   */ 345   */
348   [[nodiscard]] bool rearm_wait(waiter_node& w, duration d) noexcept; 346   [[nodiscard]] bool rearm_wait(waiter_node& w, duration d) noexcept;
349   347  
350   protected: 348   protected:
351   explicit timer(handle h) noexcept : io_object(std::move(h)) {} 349   explicit timer(handle h) noexcept : io_object(std::move(h)) {}
352   350  
353   private: 351   private:
354   /// Return the underlying implementation. 352   /// Return the underlying implementation.
HITCBC 355   38198 implementation& get() const noexcept 353   38594 implementation& get() const noexcept
356   { 354   {
HITCBC 357   38198 return *static_cast<implementation*>(h_.get()); 355   38594 return *static_cast<implementation*>(h_.get());
358   } 356   }
359   }; 357   };
360   358  
361   /** Frame-resident per-wait state for a timer wait. 359   /** Frame-resident per-wait state for a timer wait.
362   360  
363   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
364   awaitable on the suspended coroutine's frame — never allocated. 362   awaitable on the suspended coroutine's frame — never allocated.
365   Once published by `implementation::wait()` the node may be 363   Once published by `implementation::wait()` the node may be
366   completed from any thread; every completion path finishes 364   completed from any thread; every completion path finishes
367   touching the node before resuming or destroying the coroutine, 365   touching the node before resuming or destroying the coroutine,
368   because either act may end the node's storage. 366   because either act may end the node's storage.
369   367  
370   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
371   awaiting chain's `io_env` (which outlives the suspension) and 369   awaiting chain's `io_env` (which outlives the suspension) and
372   the stop callback is managed manually in `cb_buf_`, destroyed on 370   the stop callback is managed manually in `cb_buf_`, destroyed on
373   every completion path before the frame can die. 371   every completion path before the frame can die.
374   */ 372   */
375   struct BOOST_COROSIO_SYMBOL_VISIBLE waiter_node 373   struct BOOST_COROSIO_SYMBOL_VISIBLE waiter_node
376   : intrusive_list<waiter_node>::node 374   : intrusive_list<waiter_node>::node
377   { 375   {
378   // Embedded completion op — avoids heap allocation per fire/cancel. 376   // Embedded completion op — avoids heap allocation per fire/cancel.
379   // Members are exported and defined non-inline in timer.cpp: the 377   // Members are exported and defined non-inline in timer.cpp: the
380   // inline waiter_node constructor references do_complete and the 378   // inline waiter_node constructor references do_complete and the
381   // vtable from translation units that reach this header through 379   // vtable from translation units that reach this header through
382   // delay.hpp without ever including timer_service.hpp, so the one 380   // delay.hpp without ever including timer_service.hpp, so the one
383   // strong definition must live in a TU that is always linked. 381   // strong definition must live in a TU that is always linked.
384   struct BOOST_COROSIO_SYMBOL_VISIBLE completion_op final : scheduler_op 382   struct BOOST_COROSIO_SYMBOL_VISIBLE completion_op final : scheduler_op
385   { 383   {
386   waiter_node* waiter_ = nullptr; 384   waiter_node* waiter_ = nullptr;
387   385  
388   BOOST_COROSIO_DECL 386   BOOST_COROSIO_DECL
389   static void do_complete( 387   static void do_complete(
390   void* owner, scheduler_op* base, std::uint32_t, std::uint32_t); 388   void* owner, scheduler_op* base, std::uint32_t, std::uint32_t);
391   389  
HITCBC 392   32062 completion_op() noexcept : scheduler_op(&do_complete) {} 390   32122 completion_op() noexcept : scheduler_op(&do_complete) {}
393   391  
394   BOOST_COROSIO_DECL void operator()() override; 392   BOOST_COROSIO_DECL void operator()() override;
395   BOOST_COROSIO_DECL void destroy() override; 393   BOOST_COROSIO_DECL void destroy() override;
396   }; 394   };
397   395  
398   // Per-waiter stop_token cancellation 396   // Per-waiter stop_token cancellation
399   struct canceller 397   struct canceller
400   { 398   {
401   waiter_node* waiter_; 399   waiter_node* waiter_;
402   BOOST_COROSIO_DECL void operator()() const; 400   BOOST_COROSIO_DECL void operator()() const;
403   }; 401   };
404   402  
405   using stop_cb_type = std::stop_callback<canceller>; 403   using stop_cb_type = std::stop_callback<canceller>;
406   404  
407   // nullptr once unpublished from the timer ( concurrency marker ) 405   // nullptr once unpublished from the timer ( concurrency marker )
408   /// The timer this waiter is published on, or `nullptr`. 406   /// The timer this waiter is published on, or `nullptr`.
409   timer::implementation* impl_ = nullptr; 407   timer::implementation* impl_ = nullptr;
410   408  
411   /// The timer service that completes this waiter. 409   /// The timer service that completes this waiter.
412   timer_service* svc_ = nullptr; 410   timer_service* svc_ = nullptr;
413   411  
414   /// The suspended coroutine, destroyed by the shutdown drains. 412   /// The suspended coroutine, destroyed by the shutdown drains.
415   std::coroutine_handle<> h_; 413   std::coroutine_handle<> h_;
416   414  
417   /// The continuation posted to resume the coroutine. 415   /// The continuation posted to resume the coroutine.
418   capy::continuation cont_; 416   capy::continuation cont_;
419   417  
420   /// The executor the continuation is posted through. 418   /// The executor the continuation is posted through.
421   capy::executor_ref d_; 419   capy::executor_ref d_;
422   420  
423   // Borrowed from the awaiting chain's io_env, which outlives the 421   // Borrowed from the awaiting chain's io_env, which outlives the
424   // suspension; the node holds no owning state. 422   // suspension; the node holds no owning state.
425   /// The stop token observed for cancellation. 423   /// The stop token observed for cancellation.
426   std::stop_token const* token_ = nullptr; 424   std::stop_token const* token_ = nullptr;
427   425  
428   /// The completion result read by `await_resume`. 426   /// The completion result read by `await_resume`.
429   std::error_code ec_; 427   std::error_code ec_;
430   428  
431   // Consulted by the completion op before resuming; lets a 429   // Consulted by the completion op before resuming; lets a
432   // clock-facade wait re-publish itself instead of completing. 430   // clock-facade wait re-publish itself instead of completing.
433   // Never consulted on the shutdown destroy path. Consulted on 431   // Never consulted on the shutdown destroy path. Consulted on
434   // every completion, including cancellation ( `ec_` set ) — the 432   // every completion, including cancellation ( `ec_` set ) — the
435   // 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
436   // waiter. Runs inside the completion path; must not throw. 434   // waiter. Runs inside the completion path; must not throw.
437   /// Re-arm hook: return true to skip resumption ( wait continues ). 435   /// Re-arm hook: return true to skip resumption ( wait continues ).
438   bool (*on_fire_)(void*) noexcept = nullptr; 436   bool (*on_fire_)(void*) noexcept = nullptr;
439   437  
440   /// Context passed to `on_fire_` ( the owning awaitable ). 438   /// Context passed to `on_fire_` ( the owning awaitable ).
441   void* on_fire_ctx_ = nullptr; 439   void* on_fire_ctx_ = nullptr;
442   440  
443   /// The embedded completion op posted to the scheduler. 441   /// The embedded completion op posted to the scheduler.
444   completion_op op_; 442   completion_op op_;
445   443  
446   // stop_callback is neither movable nor assignable; construct it 444   // stop_callback is neither movable nor assignable; construct it
447   // 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
448   // destroy it manually on every completion path. 446   // destroy it manually on every completion path.
449   /// Storage for the armed stop callback. 447   /// Storage for the armed stop callback.
450   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)];
451   449  
452   /// True while `cb_buf_` holds a live stop callback. 450   /// True while `cb_buf_` holds a live stop callback.
453   bool cb_active_ = false; 451   bool cb_active_ = false;
454   452  
HITCBC 455   32062 waiter_node() noexcept 453   32122 waiter_node() noexcept
HITCBC 456   32062 { 454   32122 {
HITCBC 457   32062 op_.waiter_ = this; 455   32122 op_.waiter_ = this;
HITCBC 458   32062 } 456   32122 }
459   457  
460   // The embedded op self-points and the list hooks are published 458   // The embedded op self-points and the list hooks are published
461   // to other threads; the node never moves. 459   // to other threads; the node never moves.
462   waiter_node(waiter_node const&) = delete; 460   waiter_node(waiter_node const&) = delete;
463   waiter_node& operator=(waiter_node const&) = delete; 461   waiter_node& operator=(waiter_node const&) = delete;
464   462  
465   /** Bind the coroutine and its environment before publication. 463   /** Bind the coroutine and its environment before publication.
466   464  
467   The single definition of the fields every wait must populate 465   The single definition of the fields every wait must populate
468   before the node is published; hook-driven waits additionally 466   before the node is published; hook-driven waits additionally
469   set `on_fire_` / `on_fire_ctx_`. 467   set `on_fire_` / `on_fire_ctx_`.
470   468  
471   @param h The coroutine to resume on completion. 469   @param h The coroutine to resume on completion.
472   @param env The awaiting chain's environment; must outlive 470   @param env The awaiting chain's environment; must outlive
473   the suspension. 471   the suspension.
474   */ 472   */
HITCBC 475   15025 void bind(std::coroutine_handle<> h, capy::io_env const& env) noexcept 473   15056 void bind(std::coroutine_handle<> h, capy::io_env const& env) noexcept
476   { 474   {
HITCBC 477   15025 h_ = h; 475   15056 h_ = h;
HITCBC 478   15025 cont_.h = h; 476   15056 cont_.h = h;
HITCBC 479   15025 d_ = env.executor; 477   15056 d_ = env.executor;
HITCBC 480   15025 token_ = &env.stop_token; 478   15056 token_ = &env.stop_token;
HITCBC 481   15025 } 479   15056 }
482   480  
483   /** Arm the stop callback. 481   /** Arm the stop callback.
484   482  
485   @par Preconditions 483   @par Preconditions
486   `token_` is set. 484   `token_` is set.
487   */ 485   */
HITCBC 488   1576 void arm_stop_cb() 486   1584 void arm_stop_cb()
489   { 487   {
HITCBC 490   1576 new (cb_buf_) stop_cb_type(*token_, canceller{this}); 488   1584 new (cb_buf_) stop_cb_type(*token_, canceller{this});
HITCBC 491   1576 cb_active_ = true; 489   1584 cb_active_ = true;
HITCBC 492   1576 } 490   1584 }
493   491  
494   /// Destroy the stop callback if armed. 492   /// Destroy the stop callback if armed.
HITCBC 495   14173 void reset_stop_cb() noexcept 493   14203 void reset_stop_cb() noexcept
496   { 494   {
HITCBC 497   14173 if (cb_active_) 495   14203 if (cb_active_)
498   { 496   {
HITCBC 499   1576 std::launder(reinterpret_cast<stop_cb_type*>(cb_buf_)) 497   1584 std::launder(reinterpret_cast<stop_cb_type*>(cb_buf_))
HITCBC 500   1576 ->~stop_cb_type(); 498   1584 ->~stop_cb_type();
HITCBC 501   1576 cb_active_ = false; 499   1584 cb_active_ = false;
502   } 500   }
HITCBC 503   14173 } 501   14203 }
504   }; 502   };
505   503  
506   /** Awaitable returned by `timer::wait()`. 504   /** Awaitable returned by `timer::wait()`.
507   505  
508   Carries the waiter node so a wait performs no allocation. The 506   Carries the waiter node so a wait performs no allocation. The
509   awaitable is movable only before `await_suspend` publishes the 507   awaitable is movable only before `await_suspend` publishes the
510   node (a move builds a fresh, quiescent node); afterwards it is 508   node (a move builds a fresh, quiescent node); afterwards it is
511   pinned on the coroutine frame until the wait completes. 509   pinned on the coroutine frame until the wait completes.
512   */ 510   */
513   struct wait_awaitable 511   struct wait_awaitable
514   { 512   {
515   timer& t_; 513   timer& t_;
516   waiter_node w_; 514   waiter_node w_;
517   515  
HITCBC 518   14778 explicit wait_awaitable(timer& t) noexcept : t_(t) {} 516   14808 explicit wait_awaitable(timer& t) noexcept : t_(t) {}
519   517  
HITCBC 520   14778 wait_awaitable(wait_awaitable&& o) noexcept : t_(o.t_) {} 518   14808 wait_awaitable(wait_awaitable&& o) noexcept : t_(o.t_) {}
521   519  
522   wait_awaitable(wait_awaitable const&) = delete; 520   wait_awaitable(wait_awaitable const&) = delete;
523   wait_awaitable& operator=(wait_awaitable const&) = delete; 521   wait_awaitable& operator=(wait_awaitable const&) = delete;
524   wait_awaitable& operator=(wait_awaitable&&) = delete; 522   wait_awaitable& operator=(wait_awaitable&&) = delete;
525   523  
HITCBC 526   2053 bool await_ready() const noexcept 524   2053 bool await_ready() const noexcept
527   { 525   {
HITCBC 528   2053 return false; 526   2053 return false;
529   } 527   }
530   528  
531   // Cancellation surfaces through w_.ec_: the stop_token path in 529   // Cancellation surfaces through w_.ec_: the stop_token path in
532   // wait() completes the waiter with error::canceled written to 530   // wait() completes the waiter with error::canceled written to
533   // it, so there is no separate token to consult here. 531   // it, so there is no separate token to consult here.
HITCBC 534   14749 [[nodiscard]] capy::io_result<> await_resume() const noexcept 532   14779 [[nodiscard]] capy::io_result<> await_resume() const noexcept
535   { 533   {
HITCBC 536   14749 return {w_.ec_}; 534   14779 return {w_.ec_};
537   } 535   }
538   536  
HITCBC 539   14778 auto await_suspend(std::coroutine_handle<> h, capy::io_env const* env) 537   14808 auto await_suspend(std::coroutine_handle<> h, capy::io_env const* env)
540   -> std::coroutine_handle<> 538   -> std::coroutine_handle<>
541   { 539   {
HITCBC 542   14778 auto& impl = t_.get(); 540   14808 auto& impl = t_.get();
HITCBC 543   14778 w_.bind(h, *env); 541   14808 w_.bind(h, *env);
544   542  
545   // Inline fast path: already expired and not in the heap. 543   // Inline fast path: already expired and not in the heap.
546   // Post instead of dispatch so the coroutine yields to the 544   // Post instead of dispatch so the coroutine yields to the
547   // scheduler, allowing other queued work to run. 545   // scheduler, allowing other queued work to run.
HITCBC 548   14778 if (impl.already_expired()) 546   14808 if (impl.already_expired())
549   { 547   {
HITCBC 550   852 w_.ec_ = {}; 548   853 w_.ec_ = {};
HITCBC 551   852 w_.d_.post(w_.cont_); 549   853 w_.d_.post(w_.cont_);
HITCBC 552   852 return std::noop_coroutine(); 550   853 return std::noop_coroutine();
553   } 551   }
554   552  
HITCBC 555   13926 return impl.wait(w_); 553   13955 return impl.wait(w_);
556   } 554   }
557   }; 555   };
558   556  
559   inline wait_awaitable 557   inline wait_awaitable
HITCBC 560   14778 timer::wait() 558   14808 timer::wait()
561   { 559   {
HITCBC 562   14778 return wait_awaitable(*this); 560   14808 return wait_awaitable(*this);
563   } 561   }
564   562  
565   } // namespace boost::corosio::detail 563   } // namespace boost::corosio::detail
566   564  
567   #endif 565   #endif