Line data Source code
1 : //
2 : // Copyright (c) 2025 Vinnie Falco (vinnie.falco@gmail.com)
3 : // Copyright (c) 2026 Michael Vandeberg
4 : //
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)
7 : //
8 : // Official repository: https://github.com/boostorg/capy
9 : //
10 :
11 : #include <boost/capy/ex/thread_pool.hpp>
12 : #include <boost/capy/detail/intrusive.hpp>
13 : #include <boost/capy/detail/thread_name.hpp>
14 : #include <atomic>
15 : #include <condition_variable>
16 : #include <cstdio>
17 : #include <mutex>
18 : #include <thread>
19 : #include <vector>
20 :
21 : /*
22 : Thread pool implementation using a shared work queue.
23 :
24 : Work items are coroutine handles wrapped in intrusive list nodes, stored
25 : in a single queue protected by a mutex. Worker threads wait on a
26 : condition_variable until work is available or stop is requested.
27 :
28 : Threads are started lazily on first post() via std::call_once to avoid
29 : spawning threads for pools that are constructed but never used. Each
30 : thread is named with a configurable prefix plus index for debugger
31 : visibility.
32 :
33 : Shutdown sequence: stop() sets the stop flag and notifies all threads,
34 : then the destructor joins threads and destroys any remaining queued
35 : work without executing it.
36 : */
37 :
38 : namespace boost {
39 : namespace capy {
40 :
41 : //------------------------------------------------------------------------------
42 :
43 : class thread_pool::impl
44 : {
45 : struct work : detail::intrusive_queue<work>::node
46 : {
47 : coro h_;
48 :
49 121 : explicit work(coro h) noexcept
50 121 : : h_(h)
51 : {
52 121 : }
53 :
54 121 : void run()
55 : {
56 121 : auto h = h_;
57 121 : delete this;
58 121 : h.resume();
59 121 : }
60 :
61 0 : void destroy()
62 : {
63 0 : delete this;
64 0 : }
65 : };
66 :
67 : std::mutex mutex_;
68 : std::condition_variable cv_;
69 : detail::intrusive_queue<work> q_;
70 : std::vector<std::thread> threads_;
71 : std::atomic<bool> stop_{false};
72 : std::size_t num_threads_;
73 : char thread_name_prefix_[13]{}; // 12 chars max + null terminator
74 : std::once_flag start_flag_;
75 :
76 : public:
77 58 : ~impl()
78 : {
79 58 : stop();
80 94 : for(auto& t : threads_)
81 36 : if(t.joinable())
82 36 : t.join();
83 :
84 58 : while(auto* w = q_.pop())
85 0 : w->destroy();
86 58 : }
87 :
88 58 : impl(std::size_t num_threads, std::string_view thread_name_prefix)
89 58 : : num_threads_(num_threads)
90 : {
91 58 : if(num_threads_ == 0)
92 2 : num_threads_ = std::thread::hardware_concurrency();
93 58 : if(num_threads_ == 0)
94 0 : num_threads_ = 1;
95 :
96 : // Truncate prefix to 12 chars, leaving room for up to 3-digit index.
97 58 : auto n = thread_name_prefix.copy(thread_name_prefix_, 12);
98 58 : thread_name_prefix_[n] = '\0';
99 58 : }
100 :
101 : void
102 121 : post(coro h)
103 : {
104 121 : ensure_started();
105 121 : auto* w = new work(h);
106 : {
107 121 : std::lock_guard<std::mutex> lock(mutex_);
108 121 : q_.push(w);
109 121 : }
110 121 : cv_.notify_one();
111 121 : }
112 :
113 : void
114 58 : stop() noexcept
115 : {
116 58 : stop_.store(true, std::memory_order_release);
117 58 : cv_.notify_all();
118 58 : }
119 :
120 : private:
121 : void
122 121 : ensure_started()
123 : {
124 121 : std::call_once(start_flag_, [this]{
125 20 : threads_.reserve(num_threads_);
126 56 : for(std::size_t i = 0; i < num_threads_; ++i)
127 72 : threads_.emplace_back([this, i]{ run(i); });
128 20 : });
129 121 : }
130 :
131 : void
132 36 : run(std::size_t index)
133 : {
134 : // Build name; set_current_thread_name truncates to platform limits.
135 : char name[16];
136 36 : std::snprintf(name, sizeof(name), "%s%zu", thread_name_prefix_, index);
137 36 : detail::set_current_thread_name(name);
138 :
139 : for(;;)
140 : {
141 157 : work* w = nullptr;
142 : {
143 157 : std::unique_lock<std::mutex> lock(mutex_);
144 157 : cv_.wait(lock, [this]{
145 289 : return !q_.empty() ||
146 289 : stop_.load(std::memory_order_acquire);
147 : });
148 157 : if(stop_.load(std::memory_order_acquire) && q_.empty())
149 72 : return;
150 121 : w = q_.pop();
151 157 : }
152 121 : if(w)
153 121 : w->run();
154 121 : }
155 : }
156 : };
157 :
158 : //------------------------------------------------------------------------------
159 :
160 58 : thread_pool::
161 : ~thread_pool()
162 : {
163 58 : shutdown();
164 58 : destroy();
165 58 : delete impl_;
166 58 : }
167 :
168 58 : thread_pool::
169 58 : thread_pool(std::size_t num_threads, std::string_view thread_name_prefix)
170 58 : : impl_(new impl(num_threads, thread_name_prefix))
171 : {
172 58 : this->set_frame_allocator(std::allocator<void>{});
173 58 : }
174 :
175 : void
176 0 : thread_pool::
177 : stop() noexcept
178 : {
179 0 : impl_->stop();
180 0 : }
181 :
182 : //------------------------------------------------------------------------------
183 :
184 : void
185 121 : thread_pool::executor_type::
186 : post(coro h) const
187 : {
188 121 : pool_->impl_->post(h);
189 121 : }
190 :
191 : } // capy
192 : } // boost
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