TLA Line data Source code
1 : //
2 : // Copyright (c) 2026 Steve Gerbino
3 : //
4 : // Distributed under the Boost Software License, Version 1.0. (See accompanying
5 : // file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
6 : //
7 : // Official repository: https://github.com/cppalliance/corosio
8 : //
9 :
10 : #ifndef BOOST_COROSIO_DETAIL_CANCEL_AT_AWAITABLE_HPP
11 : #define BOOST_COROSIO_DETAIL_CANCEL_AT_AWAITABLE_HPP
12 :
13 : #include <boost/corosio/detail/timeout_coro.hpp>
14 : #include <boost/capy/ex/io_env.hpp>
15 :
16 : #include <chrono>
17 : #include <coroutine>
18 : #include <new>
19 : #include <optional>
20 : #include <stop_token>
21 : #include <type_traits>
22 : #include <utility>
23 :
24 : /* Races an inner IoAwaitable against a timer via a shared
25 : stop_source. await_suspend arms the timer by launching a
26 : fire-and-forget timeout_coro, then starts the inner op with
27 : an interposed stop_token. Whichever completes first signals
28 : the stop_source, cancelling the other.
29 :
30 : Parent cancellation is forwarded through a stop_callback
31 : stored in a placement-new buffer (stop_callback is not
32 : movable, but the awaitable must be movable for
33 : transform_awaiter). The buffer is inert during moves
34 : (before await_suspend) and constructed in-place once the
35 : awaitable is pinned on the coroutine frame.
36 :
37 : The timeout_coro can outlive this awaitable — it owns its
38 : env and self-destroys via suspend_never. When Owning is
39 : false the caller-supplied timer must outlive both; when
40 : Owning is true the timer lives in std::optional and is
41 : constructed lazily in await_suspend. */
42 :
43 : namespace boost::corosio::detail {
44 :
45 : /** Awaitable adapter that cancels an inner operation after a deadline.
46 :
47 : Races the inner awaitable against a timer. A shared stop_source
48 : ties them together: whichever completes first cancels the other.
49 : Parent cancellation is forwarded via stop_callback.
50 :
51 : When @p Owning is `false` (default), the caller supplies a timer
52 : reference that must outlive the awaitable. When @p Owning is
53 : `true`, the timer is constructed internally in `await_suspend`
54 : from the execution context in `io_env`.
55 :
56 : @tparam A The inner IoAwaitable type (decayed).
57 : @tparam Timer The timer type (`timer` or `native_timer<B>`).
58 : @tparam Owning When `true`, the awaitable owns its timer.
59 : */
60 : template<typename A, typename Timer, bool Owning = false>
61 : struct cancel_at_awaitable
62 : {
63 : struct stop_forwarder
64 : {
65 : std::stop_source* src_;
66 HIT 2 : void operator()() const noexcept
67 : {
68 2 : src_->request_stop();
69 2 : }
70 : };
71 :
72 : using time_point = std::chrono::steady_clock::time_point;
73 : using stop_cb_type = std::stop_callback<stop_forwarder>;
74 : using timer_storage =
75 : std::conditional_t<Owning, std::optional<Timer>, Timer*>;
76 :
77 : A inner_;
78 : timer_storage timer_;
79 : time_point deadline_;
80 : std::stop_source stop_src_;
81 : capy::io_env inner_env_;
82 : alignas(stop_cb_type) unsigned char cb_buf_[sizeof(stop_cb_type)];
83 : bool cb_active_ = false;
84 :
85 : /// Construct with a caller-supplied timer reference.
86 18 : cancel_at_awaitable(A&& inner, Timer& timer, time_point deadline)
87 : requires(!Owning)
88 18 : : inner_(std::move(inner))
89 18 : , timer_(&timer)
90 18 : , deadline_(deadline)
91 : {
92 18 : }
93 :
94 : /// Construct without a timer (created in `await_suspend`).
95 6 : cancel_at_awaitable(A&& inner, time_point deadline)
96 : requires Owning
97 6 : : inner_(std::move(inner))
98 6 : , deadline_(deadline)
99 : {
100 6 : }
101 :
102 48 : ~cancel_at_awaitable()
103 : {
104 48 : destroy_parent_cb();
105 48 : }
106 :
107 : // Only moved before await_suspend, when cb_active_ is false
108 24 : cancel_at_awaitable(cancel_at_awaitable&& o) noexcept(
109 : std::is_nothrow_move_constructible_v<A>)
110 24 : : inner_(std::move(o.inner_))
111 24 : , timer_(std::move(o.timer_))
112 24 : , deadline_(o.deadline_)
113 24 : , stop_src_(std::move(o.stop_src_))
114 : {
115 24 : }
116 :
117 : cancel_at_awaitable(cancel_at_awaitable const&) = delete;
118 : cancel_at_awaitable& operator=(cancel_at_awaitable const&) = delete;
119 : cancel_at_awaitable& operator=(cancel_at_awaitable&&) = delete;
120 :
121 24 : bool await_ready() const noexcept
122 : {
123 24 : return false;
124 : }
125 :
126 24 : auto await_suspend(std::coroutine_handle<> h, capy::io_env const* env)
127 : {
128 : if constexpr (Owning)
129 6 : timer_.emplace(env->executor.context());
130 :
131 24 : timer_->expires_at(deadline_);
132 :
133 : // Launch fire-and-forget timeout (starts suspended)
134 24 : auto timeout = make_timeout(*timer_, stop_src_);
135 48 : timeout.h_.promise().set_env_owned(
136 24 : {env->executor, stop_src_.get_token(), env->frame_allocator});
137 : // Runs synchronously until timer.wait() suspends
138 24 : timeout.h_.resume();
139 : // timeout goes out of scope; destructor is a no-op,
140 : // the coroutine self-destroys via suspend_never
141 :
142 : // Forward parent cancellation
143 24 : new (cb_buf_) stop_cb_type(env->stop_token, stop_forwarder{&stop_src_});
144 24 : cb_active_ = true;
145 :
146 : // Start the inner op with our interposed stop_token
147 24 : inner_env_ = {
148 24 : env->executor, stop_src_.get_token(), env->frame_allocator};
149 48 : return inner_.await_suspend(h, &inner_env_);
150 48 : }
151 :
152 24 : decltype(auto) await_resume()
153 : {
154 : // Cancel whichever is still pending (idempotent)
155 24 : stop_src_.request_stop();
156 24 : destroy_parent_cb();
157 24 : return inner_.await_resume();
158 : }
159 :
160 72 : void destroy_parent_cb() noexcept
161 : {
162 72 : if (cb_active_)
163 : {
164 24 : std::launder(reinterpret_cast<stop_cb_type*>(cb_buf_))
165 24 : ->~stop_cb_type();
166 24 : cb_active_ = false;
167 : }
168 72 : }
169 : };
170 :
171 : } // namespace boost::corosio::detail
172 :
173 : #endif
|
