TLA Line data Source code
1 : //
2 : // Copyright (c) 2025 Vinnie Falco (vinnie.falco@gmail.com)
3 : // Copyright (c) 2026 Steve Gerbino
4 : // Copyright (c) 2026 Michael Vandeberg
5 : //
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)
8 : //
9 : // Official repository: https://github.com/cppalliance/corosio
10 : //
11 :
12 : #ifndef BOOST_COROSIO_IO_CONTEXT_HPP
13 : #define BOOST_COROSIO_IO_CONTEXT_HPP
14 :
15 : #include <boost/corosio/detail/config.hpp>
16 : #include <boost/corosio/detail/continuation_op.hpp>
17 : #include <boost/corosio/detail/platform.hpp>
18 : #include <boost/corosio/detail/scheduler.hpp>
19 : #include <boost/capy/continuation.hpp>
20 : #include <boost/capy/ex/execution_context.hpp>
21 :
22 : #include <chrono>
23 : #include <coroutine>
24 : #include <cstddef>
25 : #include <limits>
26 : #include <thread>
27 :
28 : namespace boost::corosio {
29 :
30 : /** Runtime tuning options for @ref io_context.
31 :
32 : All fields have defaults that match the library's built-in
33 : values, so constructing a default `io_context_options` produces
34 : identical behavior to an unconfigured context.
35 :
36 : Options that apply only to a specific backend family are
37 : silently ignored when the active backend does not support them.
38 :
39 : @par Example
40 : @code
41 : io_context_options opts;
42 : opts.max_events_per_poll = 256; // larger batch per syscall
43 : opts.inline_budget_max = 32; // more speculative completions
44 : opts.thread_pool_size = 4; // more file-I/O workers
45 :
46 : io_context ioc(opts);
47 : @endcode
48 :
49 : @see io_context, native_io_context
50 : */
51 : struct io_context_options
52 : {
53 : /** Maximum events fetched per reactor poll call.
54 :
55 : Controls the buffer size passed to `epoll_wait()` or
56 : `kevent()`. Larger values reduce syscall frequency under
57 : high load; smaller values improve fairness between
58 : connections. Ignored on IOCP and select backends.
59 : */
60 : unsigned max_events_per_poll = 128;
61 :
62 : /** Starting inline completion budget per handler chain.
63 :
64 : After a posted handler executes, the reactor grants this
65 : many speculative inline completions before forcing a
66 : re-queue. Applies to reactor backends only.
67 : */
68 : unsigned inline_budget_initial = 2;
69 :
70 : /** Hard ceiling on adaptive inline budget ramp-up.
71 :
72 : The budget doubles each cycle it is fully consumed, up to
73 : this limit. Applies to reactor backends only.
74 : */
75 : unsigned inline_budget_max = 16;
76 :
77 : /** Inline budget when no other thread assists the reactor.
78 :
79 : When only one thread is running the event loop, this
80 : value caps the inline budget to preserve fairness.
81 : Applies to reactor backends only.
82 : */
83 : unsigned unassisted_budget = 4;
84 :
85 : /** Maximum `GetQueuedCompletionStatus` timeout in milliseconds.
86 :
87 : Bounds how long the IOCP scheduler blocks between timer
88 : rechecks. Lower values improve timer responsiveness at the
89 : cost of more syscalls. Applies to IOCP only.
90 : */
91 : unsigned gqcs_timeout_ms = 500;
92 :
93 : /** Thread pool size for blocking I/O (file I/O, DNS resolution).
94 :
95 : Sets the number of worker threads in the shared thread pool
96 : used by POSIX file services and DNS resolution. Must be at
97 : least 1. Applies to POSIX backends only; ignored on IOCP
98 : where file I/O uses native overlapped I/O.
99 : */
100 : unsigned thread_pool_size = 1;
101 :
102 : /** Enable single-threaded mode (disable scheduler locking).
103 :
104 : When true, the scheduler skips all mutex lock/unlock and
105 : condition variable operations on the hot path. This
106 : eliminates synchronization overhead when only one thread
107 : calls `run()`.
108 :
109 : @par Restrictions
110 : - Only one thread may call `run()` (or any run variant).
111 : - Posting work from another thread is undefined behavior.
112 : - DNS resolution returns `operation_not_supported`.
113 : - POSIX file I/O returns `operation_not_supported`.
114 : - Signal sets should not be shared across contexts.
115 : */
116 : bool single_threaded = false;
117 : };
118 :
119 : namespace detail {
120 : struct timer_service_access;
121 : } // namespace detail
122 :
123 : /** An I/O context for running asynchronous operations.
124 :
125 : The io_context provides an execution environment for async
126 : operations. It maintains a queue of pending work items and
127 : processes them when `run()` is called.
128 :
129 : The default and unsigned constructors select the platform's
130 : native backend:
131 : - Windows: IOCP
132 : - Linux: epoll
133 : - BSD/macOS: kqueue
134 : - Other POSIX: select
135 :
136 : The template constructor accepts a backend tag value to
137 : choose a specific backend at compile time:
138 :
139 : @par Example
140 : @code
141 : io_context ioc; // platform default
142 : io_context ioc2(corosio::epoll); // explicit backend
143 : @endcode
144 :
145 : @par Thread Safety
146 : Distinct objects: Safe.@n
147 : Shared objects: Safe, if using a concurrency hint greater
148 : than 1.
149 :
150 : @see epoll_t, select_t, kqueue_t, iocp_t
151 : */
152 : class BOOST_COROSIO_DECL io_context : public capy::execution_context
153 : {
154 : friend struct detail::timer_service_access;
155 :
156 : /// Pre-create services that depend on options (before construct).
157 : void apply_options_pre_(io_context_options const& opts);
158 :
159 : /// Apply runtime tuning to the scheduler (after construct).
160 : void apply_options_post_(io_context_options const& opts);
161 :
162 : protected:
163 : detail::scheduler* sched_;
164 :
165 : public:
166 : /** The executor type for this context. */
167 : class executor_type;
168 :
169 : /** Construct with default concurrency and platform backend. */
170 : io_context();
171 :
172 : /** Construct with a concurrency hint and platform backend.
173 :
174 : @param concurrency_hint Hint for the number of threads
175 : that will call `run()`.
176 : */
177 : explicit io_context(unsigned concurrency_hint);
178 :
179 : /** Construct with runtime tuning options and platform backend.
180 :
181 : @param opts Runtime options controlling scheduler and
182 : service behavior.
183 : @param concurrency_hint Hint for the number of threads
184 : that will call `run()`.
185 : */
186 : explicit io_context(
187 : io_context_options const& opts,
188 : unsigned concurrency_hint = std::thread::hardware_concurrency());
189 :
190 : /** Construct with an explicit backend tag.
191 :
192 : @param backend The backend tag value selecting the I/O
193 : multiplexer (e.g. `corosio::epoll`).
194 : @param concurrency_hint Hint for the number of threads
195 : that will call `run()`.
196 : */
197 : template<class Backend>
198 : requires requires { Backend::construct; }
199 HIT 390 : explicit io_context(
200 : Backend backend,
201 : unsigned concurrency_hint = std::thread::hardware_concurrency())
202 : : capy::execution_context(this)
203 390 : , sched_(nullptr)
204 : {
205 : (void)backend;
206 390 : sched_ = &Backend::construct(*this, concurrency_hint);
207 390 : }
208 :
209 : /** Construct with an explicit backend tag and runtime options.
210 :
211 : @param backend The backend tag value selecting the I/O
212 : multiplexer (e.g. `corosio::epoll`).
213 : @param opts Runtime options controlling scheduler and
214 : service behavior.
215 : @param concurrency_hint Hint for the number of threads
216 : that will call `run()`.
217 : */
218 : template<class Backend>
219 : requires requires { Backend::construct; }
220 : explicit io_context(
221 : Backend backend,
222 : io_context_options const& opts,
223 : unsigned concurrency_hint = std::thread::hardware_concurrency())
224 : : capy::execution_context(this)
225 : , sched_(nullptr)
226 : {
227 : (void)backend;
228 : apply_options_pre_(opts);
229 : sched_ = &Backend::construct(*this, concurrency_hint);
230 : apply_options_post_(opts);
231 : }
232 :
233 : ~io_context();
234 :
235 : io_context(io_context const&) = delete;
236 : io_context& operator=(io_context const&) = delete;
237 :
238 : /** Return an executor for this context.
239 :
240 : The returned executor can be used to dispatch coroutines
241 : and post work items to this context.
242 :
243 : @return An executor associated with this context.
244 : */
245 : executor_type get_executor() const noexcept;
246 :
247 : /** Signal the context to stop processing.
248 :
249 : This causes `run()` to return as soon as possible. Any pending
250 : work items remain queued.
251 : */
252 5 : void stop()
253 : {
254 5 : sched_->stop();
255 5 : }
256 :
257 : /** Return whether the context has been stopped.
258 :
259 : @return `true` if `stop()` has been called and `restart()`
260 : has not been called since.
261 : */
262 21 : bool stopped() const noexcept
263 : {
264 21 : return sched_->stopped();
265 : }
266 :
267 : /** Restart the context after being stopped.
268 :
269 : This function must be called before `run()` can be called
270 : again after `stop()` has been called.
271 : */
272 91 : void restart()
273 : {
274 91 : sched_->restart();
275 91 : }
276 :
277 : /** Process all pending work items.
278 :
279 : This function blocks until all pending work items have been
280 : executed or `stop()` is called. The context is stopped
281 : when there is no more outstanding work.
282 :
283 : @note The context must be restarted with `restart()` before
284 : calling this function again after it returns.
285 :
286 : @return The number of handlers executed.
287 : */
288 388 : std::size_t run()
289 : {
290 388 : return sched_->run();
291 : }
292 :
293 : /** Process at most one pending work item.
294 :
295 : This function blocks until one work item has been executed
296 : or `stop()` is called. The context is stopped when there
297 : is no more outstanding work.
298 :
299 : @note The context must be restarted with `restart()` before
300 : calling this function again after it returns.
301 :
302 : @return The number of handlers executed (0 or 1).
303 : */
304 2 : std::size_t run_one()
305 : {
306 2 : return sched_->run_one();
307 : }
308 :
309 : /** Process work items for the specified duration.
310 :
311 : This function blocks until work items have been executed for
312 : the specified duration, or `stop()` is called. The context
313 : is stopped when there is no more outstanding work.
314 :
315 : @note The context must be restarted with `restart()` before
316 : calling this function again after it returns.
317 :
318 : @param rel_time The duration for which to process work.
319 :
320 : @return The number of handlers executed.
321 : */
322 : template<class Rep, class Period>
323 8 : std::size_t run_for(std::chrono::duration<Rep, Period> const& rel_time)
324 : {
325 8 : return run_until(std::chrono::steady_clock::now() + rel_time);
326 : }
327 :
328 : /** Process work items until the specified time.
329 :
330 : This function blocks until the specified time is reached
331 : or `stop()` is called. The context is stopped when there
332 : is no more outstanding work.
333 :
334 : @note The context must be restarted with `restart()` before
335 : calling this function again after it returns.
336 :
337 : @param abs_time The time point until which to process work.
338 :
339 : @return The number of handlers executed.
340 : */
341 : template<class Clock, class Duration>
342 : std::size_t
343 8 : run_until(std::chrono::time_point<Clock, Duration> const& abs_time)
344 : {
345 8 : std::size_t n = 0;
346 57 : while (run_one_until(abs_time))
347 49 : if (n != (std::numeric_limits<std::size_t>::max)())
348 49 : ++n;
349 8 : return n;
350 : }
351 :
352 : /** Process at most one work item for the specified duration.
353 :
354 : This function blocks until one work item has been executed,
355 : the specified duration has elapsed, or `stop()` is called.
356 : The context is stopped when there is no more outstanding work.
357 :
358 : @note The context must be restarted with `restart()` before
359 : calling this function again after it returns.
360 :
361 : @param rel_time The duration for which the call may block.
362 :
363 : @return The number of handlers executed (0 or 1).
364 : */
365 : template<class Rep, class Period>
366 2 : std::size_t run_one_for(std::chrono::duration<Rep, Period> const& rel_time)
367 : {
368 2 : return run_one_until(std::chrono::steady_clock::now() + rel_time);
369 : }
370 :
371 : /** Process at most one work item until the specified time.
372 :
373 : This function blocks until one work item has been executed,
374 : the specified time is reached, or `stop()` is called.
375 : The context is stopped when there is no more outstanding work.
376 :
377 : @note The context must be restarted with `restart()` before
378 : calling this function again after it returns.
379 :
380 : @param abs_time The time point until which the call may block.
381 :
382 : @return The number of handlers executed (0 or 1).
383 : */
384 : template<class Clock, class Duration>
385 : std::size_t
386 61 : run_one_until(std::chrono::time_point<Clock, Duration> const& abs_time)
387 : {
388 61 : typename Clock::time_point now = Clock::now();
389 61 : while (now < abs_time)
390 : {
391 61 : auto rel_time = abs_time - now;
392 61 : if (rel_time > std::chrono::seconds(1))
393 MIS 0 : rel_time = std::chrono::seconds(1);
394 :
395 HIT 61 : std::size_t s = sched_->wait_one(
396 : static_cast<long>(
397 61 : std::chrono::duration_cast<std::chrono::microseconds>(
398 : rel_time)
399 61 : .count()));
400 :
401 61 : if (s || stopped())
402 61 : return s;
403 :
404 MIS 0 : now = Clock::now();
405 : }
406 0 : return 0;
407 : }
408 :
409 : /** Process all ready work items without blocking.
410 :
411 : This function executes all work items that are ready to run
412 : without blocking for more work. The context is stopped
413 : when there is no more outstanding work.
414 :
415 : @note The context must be restarted with `restart()` before
416 : calling this function again after it returns.
417 :
418 : @return The number of handlers executed.
419 : */
420 HIT 6 : std::size_t poll()
421 : {
422 6 : return sched_->poll();
423 : }
424 :
425 : /** Process at most one ready work item without blocking.
426 :
427 : This function executes at most one work item that is ready
428 : to run without blocking for more work. The context is
429 : stopped when there is no more outstanding work.
430 :
431 : @note The context must be restarted with `restart()` before
432 : calling this function again after it returns.
433 :
434 : @return The number of handlers executed (0 or 1).
435 : */
436 4 : std::size_t poll_one()
437 : {
438 4 : return sched_->poll_one();
439 : }
440 : };
441 :
442 : /** An executor for dispatching work to an I/O context.
443 :
444 : The executor provides the interface for posting work items and
445 : dispatching coroutines to the associated context. It satisfies
446 : the `capy::Executor` concept.
447 :
448 : Executors are lightweight handles that can be copied and compared
449 : for equality. Two executors compare equal if they refer to the
450 : same context.
451 :
452 : @par Thread Safety
453 : Distinct objects: Safe.@n
454 : Shared objects: Safe.
455 : */
456 : class io_context::executor_type
457 : {
458 : io_context* ctx_ = nullptr;
459 :
460 : public:
461 : /** Default constructor.
462 :
463 : Constructs an executor not associated with any context.
464 : */
465 : executor_type() = default;
466 :
467 : /** Construct an executor from a context.
468 :
469 : @param ctx The context to associate with this executor.
470 : */
471 606 : explicit executor_type(io_context& ctx) noexcept : ctx_(&ctx) {}
472 :
473 : /** Return a reference to the associated execution context.
474 :
475 : @return Reference to the context.
476 : */
477 1278 : io_context& context() const noexcept
478 : {
479 1278 : return *ctx_;
480 : }
481 :
482 : /** Check if the current thread is running this executor's context.
483 :
484 : @return `true` if `run()` is being called on this thread.
485 : */
486 1290 : bool running_in_this_thread() const noexcept
487 : {
488 1290 : return ctx_->sched_->running_in_this_thread();
489 : }
490 :
491 : /** Informs the executor that work is beginning.
492 :
493 : Must be paired with `on_work_finished()`.
494 : */
495 1433 : void on_work_started() const noexcept
496 : {
497 1433 : ctx_->sched_->work_started();
498 1433 : }
499 :
500 : /** Informs the executor that work has completed.
501 :
502 : @par Preconditions
503 : A preceding call to `on_work_started()` on an equal executor.
504 : */
505 1407 : void on_work_finished() const noexcept
506 : {
507 1407 : ctx_->sched_->work_finished();
508 1407 : }
509 :
510 : /** Dispatch a continuation.
511 :
512 : Returns a handle for symmetric transfer. If called from
513 : within `run()`, returns `c.h`. Otherwise posts the
514 : enclosing continuation_op as a scheduler_op for later
515 : execution and returns `std::noop_coroutine()`.
516 :
517 : @param c The continuation to dispatch. Must be the `cont`
518 : member of a `detail::continuation_op`.
519 :
520 : @return A handle for symmetric transfer or `std::noop_coroutine()`.
521 : */
522 1288 : std::coroutine_handle<> dispatch(capy::continuation& c) const
523 : {
524 1288 : if (running_in_this_thread())
525 600 : return c.h;
526 688 : post(c);
527 688 : return std::noop_coroutine();
528 : }
529 :
530 : /** Post a continuation for deferred execution.
531 :
532 : If the continuation is backed by a continuation_op
533 : (tagged), posts it directly as a scheduler_op — zero
534 : heap allocation. Otherwise falls back to the
535 : heap-allocating post(coroutine_handle<>) path.
536 : */
537 9760 : void post(capy::continuation& c) const
538 : {
539 9760 : auto* op = detail::continuation_op::try_from_continuation(c);
540 9760 : if (op)
541 9069 : ctx_->sched_->post(op);
542 : else
543 691 : ctx_->sched_->post(c.h);
544 9760 : }
545 :
546 : /** Post a bare coroutine handle for deferred execution.
547 :
548 : Heap-allocates a scheduler_op to wrap the handle. Prefer
549 : posting through a continuation_op-backed continuation when
550 : the continuation has suitable lifetime.
551 :
552 : @param h The coroutine handle to post.
553 : */
554 1426 : void post(std::coroutine_handle<> h) const
555 : {
556 1426 : ctx_->sched_->post(h);
557 1426 : }
558 :
559 : /** Compare two executors for equality.
560 :
561 : @return `true` if both executors refer to the same context.
562 : */
563 1 : bool operator==(executor_type const& other) const noexcept
564 : {
565 1 : return ctx_ == other.ctx_;
566 : }
567 :
568 : /** Compare two executors for inequality.
569 :
570 : @return `true` if the executors refer to different contexts.
571 : */
572 : bool operator!=(executor_type const& other) const noexcept
573 : {
574 : return ctx_ != other.ctx_;
575 : }
576 : };
577 :
578 : inline io_context::executor_type
579 606 : io_context::get_executor() const noexcept
580 : {
581 606 : return executor_type(const_cast<io_context&>(*this));
582 : }
583 :
584 : } // namespace boost::corosio
585 :
586 : #endif // BOOST_COROSIO_IO_CONTEXT_HPP
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