. /include/boost/corosio /io_context.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   // Copyright (c) 2026 Michael Vandeberg 4   // Copyright (c) 2026 Michael Vandeberg
5   // 5   //
6   // Distributed under the Boost Software License, Version 1.0. (See accompanying 6   // Distributed under the Boost Software License, Version 1.0. (See accompanying
7   // file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt) 7   // file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
8   // 8   //
9   // Official repository: https://github.com/cppalliance/corosio 9   // Official repository: https://github.com/cppalliance/corosio
10   // 10   //
11   11  
12   #ifndef BOOST_COROSIO_IO_CONTEXT_HPP 12   #ifndef BOOST_COROSIO_IO_CONTEXT_HPP
13   #define BOOST_COROSIO_IO_CONTEXT_HPP 13   #define BOOST_COROSIO_IO_CONTEXT_HPP
14   14  
15   #include <boost/corosio/detail/config.hpp> 15   #include <boost/corosio/detail/config.hpp>
16   #include <boost/corosio/detail/continuation_op.hpp> 16   #include <boost/corosio/detail/continuation_op.hpp>
17   #include <boost/corosio/detail/platform.hpp> 17   #include <boost/corosio/detail/platform.hpp>
18   #include <boost/corosio/detail/scheduler.hpp> 18   #include <boost/corosio/detail/scheduler.hpp>
19   #include <boost/capy/continuation.hpp> 19   #include <boost/capy/continuation.hpp>
20   #include <boost/capy/ex/execution_context.hpp> 20   #include <boost/capy/ex/execution_context.hpp>
21   21  
22   #include <chrono> 22   #include <chrono>
23   #include <coroutine> 23   #include <coroutine>
24   #include <cstddef> 24   #include <cstddef>
25   #include <limits> 25   #include <limits>
26   #include <thread> 26   #include <thread>
27   27  
28   namespace boost::corosio { 28   namespace boost::corosio {
29   29  
30   /** Runtime tuning options for @ref io_context. 30   /** Runtime tuning options for @ref io_context.
31   31  
32   All fields have defaults that match the library's built-in 32   All fields have defaults that match the library's built-in
33   values, so constructing a default `io_context_options` produces 33   values, so constructing a default `io_context_options` produces
34   identical behavior to an unconfigured context. 34   identical behavior to an unconfigured context.
35   35  
36   Options that apply only to a specific backend family are 36   Options that apply only to a specific backend family are
37   silently ignored when the active backend does not support them. 37   silently ignored when the active backend does not support them.
38   38  
39   @par Example 39   @par Example
40   @code 40   @code
41   io_context_options opts; 41   io_context_options opts;
42   opts.max_events_per_poll = 256; // larger batch per syscall 42   opts.max_events_per_poll = 256; // larger batch per syscall
43   opts.inline_budget_max = 32; // more speculative completions 43   opts.inline_budget_max = 32; // more speculative completions
44   opts.thread_pool_size = 4; // more file-I/O workers 44   opts.thread_pool_size = 4; // more file-I/O workers
45   45  
46   io_context ioc(opts); 46   io_context ioc(opts);
47   @endcode 47   @endcode
48   48  
49   @see io_context, native_io_context 49   @see io_context, native_io_context
50   */ 50   */
51   struct io_context_options 51   struct io_context_options
52   { 52   {
53   /** Maximum events fetched per reactor poll call. 53   /** Maximum events fetched per reactor poll call.
54   54  
55   Controls the buffer size passed to `epoll_wait()` or 55   Controls the buffer size passed to `epoll_wait()` or
56   `kevent()`. Larger values reduce syscall frequency under 56   `kevent()`. Larger values reduce syscall frequency under
57   high load; smaller values improve fairness between 57   high load; smaller values improve fairness between
58   connections. Ignored on IOCP and select backends. 58   connections. Ignored on IOCP and select backends.
59   */ 59   */
60   unsigned max_events_per_poll = 128; 60   unsigned max_events_per_poll = 128;
61   61  
62   /** Starting inline completion budget per handler chain. 62   /** Starting inline completion budget per handler chain.
63   63  
64   After a posted handler executes, the reactor grants this 64   After a posted handler executes, the reactor grants this
65   many speculative inline completions before forcing a 65   many speculative inline completions before forcing a
66   re-queue. Applies to reactor backends only. 66   re-queue. Applies to reactor backends only.
67   67  
68   @note Constructing an `io_context` with `concurrency_hint > 1` 68   @note Constructing an `io_context` with `concurrency_hint > 1`
69   and all three budget fields at their defaults overrides 69   and all three budget fields at their defaults overrides
70   them to disable inline completion (post-everything mode), 70   them to disable inline completion (post-everything mode),
71   since multi-thread workloads benefit from cross-thread 71   since multi-thread workloads benefit from cross-thread
72   work-stealing. Setting any budget field to a non-default 72   work-stealing. Setting any budget field to a non-default
73   value disables the override. 73   value disables the override.
74   */ 74   */
75   unsigned inline_budget_initial = 2; 75   unsigned inline_budget_initial = 2;
76   76  
77   /** Hard ceiling on adaptive inline budget ramp-up. 77   /** Hard ceiling on adaptive inline budget ramp-up.
78   78  
79   The budget doubles each cycle it is fully consumed, up to 79   The budget doubles each cycle it is fully consumed, up to
80   this limit. Applies to reactor backends only. 80   this limit. Applies to reactor backends only.
81   */ 81   */
82   unsigned inline_budget_max = 16; 82   unsigned inline_budget_max = 16;
83   83  
84   /** Inline budget when no other thread assists the reactor. 84   /** Inline budget when no other thread assists the reactor.
85   85  
86   When only one thread is running the event loop, this 86   When only one thread is running the event loop, this
87   value caps the inline budget to preserve fairness. 87   value caps the inline budget to preserve fairness.
88   Applies to reactor backends only. 88   Applies to reactor backends only.
89   */ 89   */
90   unsigned unassisted_budget = 4; 90   unsigned unassisted_budget = 4;
91   91  
92   /** Maximum `GetQueuedCompletionStatus` timeout in milliseconds. 92   /** Maximum `GetQueuedCompletionStatus` timeout in milliseconds.
93   93  
94   Bounds how long the IOCP scheduler blocks between timer 94   Bounds how long the IOCP scheduler blocks between timer
95   rechecks. Lower values improve timer responsiveness at the 95   rechecks. Lower values improve timer responsiveness at the
96   cost of more syscalls. Applies to IOCP only. 96   cost of more syscalls. Applies to IOCP only.
97   */ 97   */
98   unsigned gqcs_timeout_ms = 500; 98   unsigned gqcs_timeout_ms = 500;
99   99  
100   /** Thread pool size for blocking I/O (file I/O, DNS resolution). 100   /** Thread pool size for blocking I/O (file I/O, DNS resolution).
101   101  
102   Sets the number of worker threads in the shared thread pool 102   Sets the number of worker threads in the shared thread pool
103   used by POSIX file services and DNS resolution. Must be at 103   used by POSIX file services and DNS resolution. Must be at
104   least 1. Applies to POSIX backends only; ignored on IOCP 104   least 1. Applies to POSIX backends only; ignored on IOCP
105   where file I/O uses native overlapped I/O. 105   where file I/O uses native overlapped I/O.
106   */ 106   */
107   unsigned thread_pool_size = 1; 107   unsigned thread_pool_size = 1;
108   108  
109   /** Enable single-threaded mode (disable scheduler locking). 109   /** Enable single-threaded mode (disable scheduler locking).
110   110  
111   When true, the scheduler skips all mutex lock/unlock and 111   When true, the scheduler skips all mutex lock/unlock and
112   condition variable operations on the hot path. This 112   condition variable operations on the hot path. This
113   eliminates synchronization overhead when only one thread 113   eliminates synchronization overhead when only one thread
114   calls `run()`. 114   calls `run()`.
115   115  
116   @par Restrictions 116   @par Restrictions
117   - Only one thread may call `run()` (or any run variant). 117   - Only one thread may call `run()` (or any run variant).
118   - Posting work from another thread is undefined behavior. 118   - Posting work from another thread is undefined behavior.
119   - DNS resolution returns `operation_not_supported`. 119   - DNS resolution returns `operation_not_supported`.
120   - POSIX file I/O returns `operation_not_supported`. 120   - POSIX file I/O returns `operation_not_supported`.
121   - Signal sets should not be shared across contexts. 121   - Signal sets should not be shared across contexts.
122   122  
123   @note Constructing an `io_context` with `concurrency_hint == 1` 123   @note Constructing an `io_context` with `concurrency_hint == 1`
124   automatically enables single-threaded mode regardless of 124   automatically enables single-threaded mode regardless of
125   this field's value, matching asio's convention. To opt out, 125   this field's value, matching asio's convention. To opt out,
126   pass `concurrency_hint > 1`. 126   pass `concurrency_hint > 1`.
127   */ 127   */
128   bool single_threaded = false; 128   bool single_threaded = false;
129   129  
130   /** Enable IORING_SETUP_SQPOLL on the io_uring backend. 130   /** Enable IORING_SETUP_SQPOLL on the io_uring backend.
131   131  
132   With SQPOLL, the kernel forks a thread that busy-polls the 132   With SQPOLL, the kernel forks a thread that busy-polls the
133   submission ring; submission becomes a userspace-only memory 133   submission ring; submission becomes a userspace-only memory
134   store, eliminating the io_uring_enter syscall on the submit 134   store, eliminating the io_uring_enter syscall on the submit
135   path. Most useful for sustained traffic. Idle thread parks 135   path. Most useful for sustained traffic. Idle thread parks
136   after `sq_thread_idle_ms` of no activity. 136   after `sq_thread_idle_ms` of no activity.
137   137  
138   Independent of `single_threaded`. Default: off. 138   Independent of `single_threaded`. Default: off.
139   139  
140   Ignored on non-io_uring backends. 140   Ignored on non-io_uring backends.
141   */ 141   */
142   bool enable_sqpoll = false; 142   bool enable_sqpoll = false;
143   143  
144   /** SQ-poll idle timeout in milliseconds. 144   /** SQ-poll idle timeout in milliseconds.
145   145  
146   After this many ms of no submissions, the kernel polling 146   After this many ms of no submissions, the kernel polling
147   thread sleeps; next submit re-wakes it via SQ_WAKEUP. 0 147   thread sleeps; next submit re-wakes it via SQ_WAKEUP. 0
148   means use the kernel default (1ms). Recommended for bursty 148   means use the kernel default (1ms). Recommended for bursty
149   workloads: 100-1000ms (avoids park/unpark thrash). 149   workloads: 100-1000ms (avoids park/unpark thrash).
150   150  
151   Ignored unless `enable_sqpoll` is true. Ignored on 151   Ignored unless `enable_sqpoll` is true. Ignored on
152   non-io_uring backends. 152   non-io_uring backends.
153   */ 153   */
154   unsigned sq_thread_idle_ms = 0; 154   unsigned sq_thread_idle_ms = 0;
155   155  
156   /** Pin the SQ-poll kernel thread to this CPU. 156   /** Pin the SQ-poll kernel thread to this CPU.
157   157  
158   -1 means do not pin (kernel scheduler picks). Pinning off 158   -1 means do not pin (kernel scheduler picks). Pinning off
159   the dispatch core is recommended on latency-sensitive 159   the dispatch core is recommended on latency-sensitive
160   deployments to avoid cache contention. 160   deployments to avoid cache contention.
161   161  
162   Ignored unless `enable_sqpoll` is true. Ignored on 162   Ignored unless `enable_sqpoll` is true. Ignored on
163   non-io_uring backends. 163   non-io_uring backends.
164   */ 164   */
165   int sq_thread_cpu = -1; 165   int sq_thread_cpu = -1;
166   }; 166   };
167   167  
168   namespace detail { 168   namespace detail {
169   class timer_service; 169   class timer_service;
170   struct timer_service_access; 170   struct timer_service_access;
171   } // namespace detail 171   } // namespace detail
172   172  
173   /** An I/O context for running asynchronous operations. 173   /** An I/O context for running asynchronous operations.
174   174  
175   The io_context provides an execution environment for async 175   The io_context provides an execution environment for async
176   operations. It maintains a queue of pending work items and 176   operations. It maintains a queue of pending work items and
177   processes them when `run()` is called. 177   processes them when `run()` is called.
178   178  
179   The default and unsigned constructors select the platform's 179   The default and unsigned constructors select the platform's
180   native backend: 180   native backend:
181   - Windows: IOCP 181   - Windows: IOCP
182   - Linux: epoll 182   - Linux: epoll
183   - BSD/macOS: kqueue 183   - BSD/macOS: kqueue
184   - Other POSIX: select 184   - Other POSIX: select
185   185  
186   The template constructor accepts a backend tag value to 186   The template constructor accepts a backend tag value to
187   choose a specific backend at compile time: 187   choose a specific backend at compile time:
188   188  
189   @par Example 189   @par Example
190   @code 190   @code
191   io_context ioc; // platform default 191   io_context ioc; // platform default
192   io_context ioc2(corosio::epoll); // explicit backend 192   io_context ioc2(corosio::epoll); // explicit backend
193   @endcode 193   @endcode
194   194  
195   @par Thread Safety 195   @par Thread Safety
196   Distinct objects: Safe.@n 196   Distinct objects: Safe.@n
197   Shared objects: Safe, if using a concurrency hint greater 197   Shared objects: Safe, if using a concurrency hint greater
198   than 1. 198   than 1.
199   199  
200   @see epoll_t, select_t, kqueue_t, iocp_t 200   @see epoll_t, select_t, kqueue_t, iocp_t
201   */ 201   */
202   class BOOST_COROSIO_DECL io_context : public capy::execution_context 202   class BOOST_COROSIO_DECL io_context : public capy::execution_context
203   { 203   {
204   friend struct detail::timer_service_access; 204   friend struct detail::timer_service_access;
205   205  
206   /// Pre-create services that depend on options (before construct). 206   /// Pre-create services that depend on options (before construct).
207   void apply_options_pre_(io_context_options const& opts); 207   void apply_options_pre_(io_context_options const& opts);
208   208  
209   /// Apply runtime tuning to the scheduler (after construct). 209   /// Apply runtime tuning to the scheduler (after construct).
210   void apply_options_post_( 210   void apply_options_post_(
211   io_context_options const& opts, 211   io_context_options const& opts,
212   unsigned concurrency_hint); 212   unsigned concurrency_hint);
213   213  
214   /// Switch the scheduler to single-threaded (lockless) mode. 214   /// Switch the scheduler to single-threaded (lockless) mode.
215   void configure_single_threaded_(); 215   void configure_single_threaded_();
216   216  
217   protected: 217   protected:
218   detail::timer_service* timer_svc_ = nullptr; 218   detail::timer_service* timer_svc_ = nullptr;
219   detail::scheduler* sched_; 219   detail::scheduler* sched_;
220   220  
221   public: 221   public:
222   /** The executor type for this context. */ 222   /** The executor type for this context. */
223   class executor_type; 223   class executor_type;
224   224  
225   /** Construct with default concurrency and platform backend. 225   /** Construct with default concurrency and platform backend.
226   226  
227   Uses `std::thread::hardware_concurrency()` clamped to a minimum 227   Uses `std::thread::hardware_concurrency()` clamped to a minimum
228   of 2 as the concurrency hint, so the default constructor never 228   of 2 as the concurrency hint, so the default constructor never
229   silently engages single-threaded mode (see 229   silently engages single-threaded mode (see
230   @ref io_context_options::single_threaded). Pass an explicit 230   @ref io_context_options::single_threaded). Pass an explicit
231   `concurrency_hint == 1` to opt into single-threaded mode. 231   `concurrency_hint == 1` to opt into single-threaded mode.
232   */ 232   */
233   io_context(); 233   io_context();
234   234  
235   /** Construct with a concurrency hint and platform backend. 235   /** Construct with a concurrency hint and platform backend.
236   236  
237   @param concurrency_hint Hint for the number of threads 237   @param concurrency_hint Hint for the number of threads
238   that will call `run()`. 238   that will call `run()`.
239   */ 239   */
240   explicit io_context(unsigned concurrency_hint); 240   explicit io_context(unsigned concurrency_hint);
241   241  
242   /** Construct with runtime tuning options and platform backend. 242   /** Construct with runtime tuning options and platform backend.
243   243  
244   @param opts Runtime options controlling scheduler and 244   @param opts Runtime options controlling scheduler and
245   service behavior. 245   service behavior.
246   @param concurrency_hint Hint for the number of threads 246   @param concurrency_hint Hint for the number of threads
247   that will call `run()`. 247   that will call `run()`.
248   */ 248   */
249   explicit io_context( 249   explicit io_context(
250   io_context_options const& opts, 250   io_context_options const& opts,
251   unsigned concurrency_hint = std::thread::hardware_concurrency()); 251   unsigned concurrency_hint = std::thread::hardware_concurrency());
252   252  
253   /** Construct with an explicit backend tag. 253   /** Construct with an explicit backend tag.
254   254  
255   @param backend The backend tag value selecting the I/O 255   @param backend The backend tag value selecting the I/O
256   multiplexer (e.g. `corosio::epoll`). 256   multiplexer (e.g. `corosio::epoll`).
257   @param concurrency_hint Hint for the number of threads 257   @param concurrency_hint Hint for the number of threads
258   that will call `run()`. 258   that will call `run()`.
259   */ 259   */
260   template<class Backend> 260   template<class Backend>
261   requires requires { Backend::construct; } 261   requires requires { Backend::construct; }
HITCBC 262   848 explicit io_context( 262   848 explicit io_context(
263   Backend backend, 263   Backend backend,
264   unsigned concurrency_hint = std::thread::hardware_concurrency()) 264   unsigned concurrency_hint = std::thread::hardware_concurrency())
265   : capy::execution_context(this) 265   : capy::execution_context(this)
HITCBC 266   848 , sched_(nullptr) 266   848 , sched_(nullptr)
267   { 267   {
268   (void)backend; 268   (void)backend;
HITCBC 269   848 sched_ = &Backend::construct(*this, concurrency_hint); 269   848 sched_ = &Backend::construct(*this, concurrency_hint);
HITCBC 270   848 if (concurrency_hint == 1) 270   848 if (concurrency_hint == 1)
HITCBC 271   2 configure_single_threaded_(); 271   2 configure_single_threaded_();
HITCBC 272   848 } 272   848 }
273   273  
274   /** Construct with an explicit backend tag and runtime options. 274   /** Construct with an explicit backend tag and runtime options.
275   275  
276   @param backend The backend tag value selecting the I/O 276   @param backend The backend tag value selecting the I/O
277   multiplexer (e.g. `corosio::epoll`). 277   multiplexer (e.g. `corosio::epoll`).
278   @param opts Runtime options controlling scheduler and 278   @param opts Runtime options controlling scheduler and
279   service behavior. 279   service behavior.
280   @param concurrency_hint Hint for the number of threads 280   @param concurrency_hint Hint for the number of threads
281   that will call `run()`. 281   that will call `run()`.
282   */ 282   */
283   template<class Backend> 283   template<class Backend>
284   requires requires { Backend::construct; } 284   requires requires { Backend::construct; }
HITCBC 285   8 explicit io_context( 285   8 explicit io_context(
286   Backend backend, 286   Backend backend,
287   io_context_options const& opts, 287   io_context_options const& opts,
288   unsigned concurrency_hint = std::thread::hardware_concurrency()) 288   unsigned concurrency_hint = std::thread::hardware_concurrency())
289   : capy::execution_context(this) 289   : capy::execution_context(this)
HITCBC 290   8 , sched_(nullptr) 290   8 , sched_(nullptr)
291   { 291   {
292   (void)backend; 292   (void)backend;
HITCBC 293   8 apply_options_pre_(opts); 293   8 apply_options_pre_(opts);
HITCBC 294   8 sched_ = &Backend::construct(*this, concurrency_hint); 294   8 sched_ = &Backend::construct(*this, concurrency_hint);
HITCBC 295   8 apply_options_post_(opts, concurrency_hint); 295   8 apply_options_post_(opts, concurrency_hint);
HITCBC 296   8 } 296   8 }
297   297  
298   ~io_context(); 298   ~io_context();
299   299  
300   io_context(io_context const&) = delete; 300   io_context(io_context const&) = delete;
301   io_context& operator=(io_context const&) = delete; 301   io_context& operator=(io_context const&) = delete;
302   302  
303   /** Return an executor for this context. 303   /** Return an executor for this context.
304   304  
305   The returned executor can be used to dispatch coroutines 305   The returned executor can be used to dispatch coroutines
306   and post work items to this context. 306   and post work items to this context.
307   307  
308   @return An executor associated with this context. 308   @return An executor associated with this context.
309   */ 309   */
310   executor_type get_executor() const noexcept; 310   executor_type get_executor() const noexcept;
311   311  
312   /** Signal the context to stop processing. 312   /** Signal the context to stop processing.
313   313  
314   This causes `run()` to return as soon as possible. Any pending 314   This causes `run()` to return as soon as possible. Any pending
315   work items remain queued. 315   work items remain queued.
316   */ 316   */
HITCBC 317   5 void stop() 317   5 void stop()
318   { 318   {
HITCBC 319   5 sched_->stop(); 319   5 sched_->stop();
HITCBC 320   5 } 320   5 }
321   321  
322   /** Return whether the context has been stopped. 322   /** Return whether the context has been stopped.
323   323  
324   @return `true` if `stop()` has been called and `restart()` 324   @return `true` if `stop()` has been called and `restart()`
325   has not been called since. 325   has not been called since.
326   */ 326   */
HITCBC 327   34 bool stopped() const noexcept 327   34 bool stopped() const noexcept
328   { 328   {
HITCBC 329   34 return sched_->stopped(); 329   34 return sched_->stopped();
330   } 330   }
331   331  
332   /** Restart the context after being stopped. 332   /** Restart the context after being stopped.
333   333  
334   This function must be called before `run()` can be called 334   This function must be called before `run()` can be called
335   again after `stop()` has been called. 335   again after `stop()` has been called.
336   */ 336   */
HITCBC 337   156 void restart() 337   156 void restart()
338   { 338   {
HITCBC 339   156 sched_->restart(); 339   156 sched_->restart();
HITCBC 340   156 } 340   156 }
341   341  
342   /** Process all pending work items. 342   /** Process all pending work items.
343   343  
344   This function blocks until all pending work items have been 344   This function blocks until all pending work items have been
345   executed or `stop()` is called. The context is stopped 345   executed or `stop()` is called. The context is stopped
346   when there is no more outstanding work. 346   when there is no more outstanding work.
347   347  
348   @note The context must be restarted with `restart()` before 348   @note The context must be restarted with `restart()` before
349   calling this function again after it returns. 349   calling this function again after it returns.
350   350  
351   @return The number of handlers executed. 351   @return The number of handlers executed.
352   */ 352   */
HITCBC 353   667 std::size_t run() 353   667 std::size_t run()
354   { 354   {
HITCBC 355   667 return sched_->run(); 355   667 return sched_->run();
356   } 356   }
357   357  
358   /** Process at most one pending work item. 358   /** Process at most one pending work item.
359   359  
360   This function blocks until one work item has been executed 360   This function blocks until one work item has been executed
361   or `stop()` is called. The context is stopped when there 361   or `stop()` is called. The context is stopped when there
362   is no more outstanding work. 362   is no more outstanding work.
363   363  
364   @note The context must be restarted with `restart()` before 364   @note The context must be restarted with `restart()` before
365   calling this function again after it returns. 365   calling this function again after it returns.
366   366  
367   @return The number of handlers executed (0 or 1). 367   @return The number of handlers executed (0 or 1).
368   */ 368   */
HITCBC 369   2 std::size_t run_one() 369   2 std::size_t run_one()
370   { 370   {
HITCBC 371   2 return sched_->run_one(); 371   2 return sched_->run_one();
372   } 372   }
373   373  
374   /** Process work items for the specified duration. 374   /** Process work items for the specified duration.
375   375  
376   This function blocks until work items have been executed for 376   This function blocks until work items have been executed for
377   the specified duration, or `stop()` is called. The context 377   the specified duration, or `stop()` is called. The context
378   is stopped when there is no more outstanding work. 378   is stopped when there is no more outstanding work.
379   379  
380   @note The context must be restarted with `restart()` before 380   @note The context must be restarted with `restart()` before
381   calling this function again after it returns. 381   calling this function again after it returns.
382   382  
383   @param rel_time The duration for which to process work. 383   @param rel_time The duration for which to process work.
384   384  
385   @return The number of handlers executed. 385   @return The number of handlers executed.
386   */ 386   */
387   template<class Rep, class Period> 387   template<class Rep, class Period>
HITCBC 388   5 std::size_t run_for(std::chrono::duration<Rep, Period> const& rel_time) 388   5 std::size_t run_for(std::chrono::duration<Rep, Period> const& rel_time)
389   { 389   {
HITCBC 390   5 return run_until(std::chrono::steady_clock::now() + rel_time); 390   5 return run_until(std::chrono::steady_clock::now() + rel_time);
391   } 391   }
392   392  
393   /** Process work items until the specified time. 393   /** Process work items until the specified time.
394   394  
395   This function blocks until the specified time is reached 395   This function blocks until the specified time is reached
396   or `stop()` is called. The context is stopped when there 396   or `stop()` is called. The context is stopped when there
397   is no more outstanding work. 397   is no more outstanding work.
398   398  
399   @note The context must be restarted with `restart()` before 399   @note The context must be restarted with `restart()` before
400   calling this function again after it returns. 400   calling this function again after it returns.
401   401  
402   @param abs_time The time point until which to process work. 402   @param abs_time The time point until which to process work.
403   403  
404   @return The number of handlers executed. 404   @return The number of handlers executed.
405   */ 405   */
406   template<class Clock, class Duration> 406   template<class Clock, class Duration>
407   std::size_t 407   std::size_t
HITCBC 408   5 run_until(std::chrono::time_point<Clock, Duration> const& abs_time) 408   5 run_until(std::chrono::time_point<Clock, Duration> const& abs_time)
409   { 409   {
HITCBC 410   5 std::size_t n = 0; 410   5 std::size_t n = 0;
HITCBC 411   14 while (run_one_until(abs_time)) 411   14 while (run_one_until(abs_time))
HITCBC 412   9 if (n != (std::numeric_limits<std::size_t>::max)()) 412   9 if (n != (std::numeric_limits<std::size_t>::max)())
HITCBC 413   9 ++n; 413   9 ++n;
HITCBC 414   5 return n; 414   5 return n;
415   } 415   }
416   416  
417   /** Process at most one work item for the specified duration. 417   /** Process at most one work item for the specified duration.
418   418  
419   This function blocks until one work item has been executed, 419   This function blocks until one work item has been executed,
420   the specified duration has elapsed, or `stop()` is called. 420   the specified duration has elapsed, or `stop()` is called.
421   The context is stopped when there is no more outstanding work. 421   The context is stopped when there is no more outstanding work.
422   422  
423   @note The context must be restarted with `restart()` before 423   @note The context must be restarted with `restart()` before
424   calling this function again after it returns. 424   calling this function again after it returns.
425   425  
426   @param rel_time The duration for which the call may block. 426   @param rel_time The duration for which the call may block.
427   427  
428   @return The number of handlers executed (0 or 1). 428   @return The number of handlers executed (0 or 1).
429   */ 429   */
430   template<class Rep, class Period> 430   template<class Rep, class Period>
HITCBC 431   3 std::size_t run_one_for(std::chrono::duration<Rep, Period> const& rel_time) 431   3 std::size_t run_one_for(std::chrono::duration<Rep, Period> const& rel_time)
432   { 432   {
HITCBC 433   3 return run_one_until(std::chrono::steady_clock::now() + rel_time); 433   3 return run_one_until(std::chrono::steady_clock::now() + rel_time);
434   } 434   }
435   435  
436   /** Process at most one work item until the specified time. 436   /** Process at most one work item until the specified time.
437   437  
438   This function blocks until one work item has been executed, 438   This function blocks until one work item has been executed,
439   the specified time is reached, or `stop()` is called. 439   the specified time is reached, or `stop()` is called.
440   The context is stopped when there is no more outstanding work. 440   The context is stopped when there is no more outstanding work.
441   441  
442   @note The context must be restarted with `restart()` before 442   @note The context must be restarted with `restart()` before
443   calling this function again after it returns. 443   calling this function again after it returns.
444   444  
445   @param abs_time The time point until which the call may block. 445   @param abs_time The time point until which the call may block.
446   446  
447   @return The number of handlers executed (0 or 1). 447   @return The number of handlers executed (0 or 1).
448   */ 448   */
449   template<class Clock, class Duration> 449   template<class Clock, class Duration>
450   std::size_t 450   std::size_t
HITCBC 451   21 run_one_until(std::chrono::time_point<Clock, Duration> const& abs_time) 451   21 run_one_until(std::chrono::time_point<Clock, Duration> const& abs_time)
452   { 452   {
HITCBC 453   21 typename Clock::time_point now = Clock::now(); 453   21 typename Clock::time_point now = Clock::now();
HITCBC 454   4 for (;;) 454   4 for (;;)
455   { 455   {
HITCBC 456   25 auto rel_time = abs_time - now; 456   25 auto rel_time = abs_time - now;
457   using rel_type = decltype(rel_time); 457   using rel_type = decltype(rel_time);
HITCBC 458   25 if (rel_time < rel_type::zero()) 458   25 if (rel_time < rel_type::zero())
HITCBC 459   2 rel_time = rel_type::zero(); 459   2 rel_time = rel_type::zero();
HITCBC 460   23 else if (rel_time > std::chrono::seconds(1)) 460   23 else if (rel_time > std::chrono::seconds(1))
HITCBC 461   11 rel_time = std::chrono::seconds(1); 461   11 rel_time = std::chrono::seconds(1);
462   462  
HITCBC 463   25 std::size_t s = sched_->wait_one( 463   25 std::size_t s = sched_->wait_one(
464   static_cast<long>( 464   static_cast<long>(
HITCBC 465   25 std::chrono::duration_cast<std::chrono::microseconds>( 465   25 std::chrono::duration_cast<std::chrono::microseconds>(
466   rel_time) 466   rel_time)
HITCBC 467   25 .count())); 467   25 .count()));
468   468  
HITCBC 469   25 if (s || stopped()) 469   25 if (s || stopped())
HITCBC 470   21 return s; 470   21 return s;
471   471  
HITCBC 472   6 now = Clock::now(); 472   6 now = Clock::now();
HITCBC 473   6 if (now >= abs_time) 473   6 if (now >= abs_time)
HITCBC 474   2 return 0; 474   2 return 0;
475   } 475   }
476   } 476   }
477   477  
478   /** Process all ready work items without blocking. 478   /** Process all ready work items without blocking.
479   479  
480   This function executes all work items that are ready to run 480   This function executes all work items that are ready to run
481   without blocking for more work. The context is stopped 481   without blocking for more work. The context is stopped
482   when there is no more outstanding work. 482   when there is no more outstanding work.
483   483  
484   @note The context must be restarted with `restart()` before 484   @note The context must be restarted with `restart()` before
485   calling this function again after it returns. 485   calling this function again after it returns.
486   486  
487   @return The number of handlers executed. 487   @return The number of handlers executed.
488   */ 488   */
HITCBC 489   24 std::size_t poll() 489   24 std::size_t poll()
490   { 490   {
HITCBC 491   24 return sched_->poll(); 491   24 return sched_->poll();
492   } 492   }
493   493  
494   /** Process at most one ready work item without blocking. 494   /** Process at most one ready work item without blocking.
495   495  
496   This function executes at most one work item that is ready 496   This function executes at most one work item that is ready
497   to run without blocking for more work. The context is 497   to run without blocking for more work. The context is
498   stopped when there is no more outstanding work. 498   stopped when there is no more outstanding work.
499   499  
500   @note The context must be restarted with `restart()` before 500   @note The context must be restarted with `restart()` before
501   calling this function again after it returns. 501   calling this function again after it returns.
502   502  
503   @return The number of handlers executed (0 or 1). 503   @return The number of handlers executed (0 or 1).
504   */ 504   */
HITCBC 505   4 std::size_t poll_one() 505   4 std::size_t poll_one()
506   { 506   {
HITCBC 507   4 return sched_->poll_one(); 507   4 return sched_->poll_one();
508   } 508   }
509   }; 509   };
510   510  
511   /** An executor for dispatching work to an I/O context. 511   /** An executor for dispatching work to an I/O context.
512   512  
513   The executor provides the interface for posting work items and 513   The executor provides the interface for posting work items and
514   dispatching coroutines to the associated context. It satisfies 514   dispatching coroutines to the associated context. It satisfies
515   the `capy::Executor` concept. 515   the `capy::Executor` concept.
516   516  
517   Executors are lightweight handles that can be copied and compared 517   Executors are lightweight handles that can be copied and compared
518   for equality. Two executors compare equal if they refer to the 518   for equality. Two executors compare equal if they refer to the
519   same context. 519   same context.
520   520  
521   @par Thread Safety 521   @par Thread Safety
522   Distinct objects: Safe.@n 522   Distinct objects: Safe.@n
523   Shared objects: Safe. 523   Shared objects: Safe.
524   */ 524   */
525   class io_context::executor_type 525   class io_context::executor_type
526   { 526   {
527   io_context* ctx_ = nullptr; 527   io_context* ctx_ = nullptr;
528   528  
529   public: 529   public:
530   /** Default constructor. 530   /** Default constructor.
531   531  
532   Constructs an executor not associated with any context. 532   Constructs an executor not associated with any context.
533   */ 533   */
534   executor_type() = default; 534   executor_type() = default;
535   535  
536   /** Construct an executor from a context. 536   /** Construct an executor from a context.
537   537  
538   @param ctx The context to associate with this executor. 538   @param ctx The context to associate with this executor.
539   */ 539   */
HITCBC 540   937 explicit executor_type(io_context& ctx) noexcept : ctx_(&ctx) {} 540   937 explicit executor_type(io_context& ctx) noexcept : ctx_(&ctx) {}
541   541  
542   /** Return a reference to the associated execution context. 542   /** Return a reference to the associated execution context.
543   543  
544   @return Reference to the context. 544   @return Reference to the context.
545   */ 545   */
HITCBC 546   1738 io_context& context() const noexcept 546   1738 io_context& context() const noexcept
547   { 547   {
HITCBC 548   1738 return *ctx_; 548   1738 return *ctx_;
549   } 549   }
550   550  
551   /** Check if the current thread is running this executor's context. 551   /** Check if the current thread is running this executor's context.
552   552  
553   @return `true` if `run()` is being called on this thread. 553   @return `true` if `run()` is being called on this thread.
554   */ 554   */
HITCBC 555   1766 bool running_in_this_thread() const noexcept 555   1766 bool running_in_this_thread() const noexcept
556   { 556   {
HITCBC 557   1766 return ctx_->sched_->running_in_this_thread(); 557   1766 return ctx_->sched_->running_in_this_thread();
558   } 558   }
559   559  
560   /** Informs the executor that work is beginning. 560   /** Informs the executor that work is beginning.
561   561  
562   Must be paired with `on_work_finished()`. 562   Must be paired with `on_work_finished()`.
563   */ 563   */
HITCBC 564   1930 void on_work_started() const noexcept 564   1930 void on_work_started() const noexcept
565   { 565   {
HITCBC 566   1930 ctx_->sched_->work_started(); 566   1930 ctx_->sched_->work_started();
HITCBC 567   1930 } 567   1930 }
568   568  
569   /** Informs the executor that work has completed. 569   /** Informs the executor that work has completed.
570   570  
571   @par Preconditions 571   @par Preconditions
572   A preceding call to `on_work_started()` on an equal executor. 572   A preceding call to `on_work_started()` on an equal executor.
573   */ 573   */
HITCBC 574   1897 void on_work_finished() const noexcept 574   1897 void on_work_finished() const noexcept
575   { 575   {
HITCBC 576   1897 ctx_->sched_->work_finished(); 576   1897 ctx_->sched_->work_finished();
HITCBC 577   1897 } 577   1897 }
578   578  
579   /** Dispatch a continuation. 579   /** Dispatch a continuation.
580   580  
581   Returns a handle for symmetric transfer. If called from 581   Returns a handle for symmetric transfer. If called from
582   within `run()`, returns `c.h`. Otherwise posts the 582   within `run()`, returns `c.h`. Otherwise posts the
583   enclosing continuation_op as a scheduler_op for later 583   enclosing continuation_op as a scheduler_op for later
584   execution and returns `std::noop_coroutine()`. 584   execution and returns `std::noop_coroutine()`.
585   585  
586   @param c The continuation to dispatch. Must be the `cont` 586   @param c The continuation to dispatch. Must be the `cont`
587   member of a `detail::continuation_op`. 587   member of a `detail::continuation_op`.
588   588  
589   @return A handle for symmetric transfer or `std::noop_coroutine()`. 589   @return A handle for symmetric transfer or `std::noop_coroutine()`.
590   */ 590   */
HITCBC 591   1764 std::coroutine_handle<> dispatch(capy::continuation& c) const 591   1764 std::coroutine_handle<> dispatch(capy::continuation& c) const
592   { 592   {
HITCBC 593   1764 if (running_in_this_thread()) 593   1764 if (running_in_this_thread())
HITCBC 594   623 return c.h; 594   623 return c.h;
HITCBC 595   1141 post(c); 595   1141 post(c);
HITCBC 596   1141 return std::noop_coroutine(); 596   1141 return std::noop_coroutine();
597   } 597   }
598   598  
599   /** Post a continuation for deferred execution. 599   /** Post a continuation for deferred execution.
600   600  
601   If the continuation is backed by a continuation_op 601   If the continuation is backed by a continuation_op
602   (tagged), posts it directly as a scheduler_op — zero 602   (tagged), posts it directly as a scheduler_op — zero
603   heap allocation. Otherwise falls back to the 603   heap allocation. Otherwise falls back to the
604   heap-allocating post(coroutine_handle<>) path. 604   heap-allocating post(coroutine_handle<>) path.
605   */ 605   */
HITCBC 606   9513 void post(capy::continuation& c) const 606   9000 void post(capy::continuation& c) const
607   { 607   {
HITCBC 608   9513 auto* op = detail::continuation_op::try_from_continuation(c); 608   9000 auto* op = detail::continuation_op::try_from_continuation(c);
HITCBC 609   9513 if (op) 609   9000 if (op)
HITCBC 610   8369 ctx_->sched_->post(op); 610   7856 ctx_->sched_->post(op);
611   else 611   else
HITCBC 612   1144 ctx_->sched_->post(c.h); 612   1144 ctx_->sched_->post(c.h);
HITCBC 613   9513 } 613   9000 }
614   614  
615   /** Post a bare coroutine handle for deferred execution. 615   /** Post a bare coroutine handle for deferred execution.
616   616  
617   Heap-allocates a scheduler_op to wrap the handle. Prefer 617   Heap-allocates a scheduler_op to wrap the handle. Prefer
618   posting through a continuation_op-backed continuation when 618   posting through a continuation_op-backed continuation when
619   the continuation has suitable lifetime. 619   the continuation has suitable lifetime.
620   620  
621   @param h The coroutine handle to post. 621   @param h The coroutine handle to post.
622   */ 622   */
HITCBC 623   1441 void post(std::coroutine_handle<> h) const 623   1441 void post(std::coroutine_handle<> h) const
624   { 624   {
HITCBC 625   1441 ctx_->sched_->post(h); 625   1441 ctx_->sched_->post(h);
HITCBC 626   1441 } 626   1441 }
627   627  
628   /** Compare two executors for equality. 628   /** Compare two executors for equality.
629   629  
630   @return `true` if both executors refer to the same context. 630   @return `true` if both executors refer to the same context.
631   */ 631   */
HITCBC 632   1 bool operator==(executor_type const& other) const noexcept 632   1 bool operator==(executor_type const& other) const noexcept
633   { 633   {
HITCBC 634   1 return ctx_ == other.ctx_; 634   1 return ctx_ == other.ctx_;
635   } 635   }
636   636  
637   /** Compare two executors for inequality. 637   /** Compare two executors for inequality.
638   638  
639   @return `true` if the executors refer to different contexts. 639   @return `true` if the executors refer to different contexts.
640   */ 640   */
641   bool operator!=(executor_type const& other) const noexcept 641   bool operator!=(executor_type const& other) const noexcept
642   { 642   {
643   return ctx_ != other.ctx_; 643   return ctx_ != other.ctx_;
644   } 644   }
645   }; 645   };
646   646  
647   inline io_context::executor_type 647   inline io_context::executor_type
HITCBC 648   937 io_context::get_executor() const noexcept 648   937 io_context::get_executor() const noexcept
649   { 649   {
HITCBC 650   937 return executor_type(const_cast<io_context&>(*this)); 650   937 return executor_type(const_cast<io_context&>(*this));
651   } 651   }
652   652  
653   } // namespace boost::corosio 653   } // namespace boost::corosio
654   654  
655   #endif // BOOST_COROSIO_IO_CONTEXT_HPP 655   #endif // BOOST_COROSIO_IO_CONTEXT_HPP