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libs/capy/src/ex/thread_pool.cpp

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libs/capy/src/ex/thread_pool.cpp
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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
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 121 delete this;
58
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 121 h.resume();
59 121 }
60
61 ✗ void destroy()
62 {
63 ✗ delete this;
64 ✗ }
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
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 94 for(auto& t : threads_)
81
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 36 if(t.joinable())
82 36 t.join();
83
84
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 58 while(auto* w = q_.pop())
85 ✗ 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
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 58 if(num_threads_ == 0)
92 2 num_threads_ = std::thread::hardware_concurrency();
93
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 58 if(num_threads_ == 0)
94 ✗ num_threads_ = 1;
95
96 // Truncate prefix to 12 chars, leaving room for up to 3-digit index.
97
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 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
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 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
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 121 std::call_once(start_flag_, [this]{
125 20 threads_.reserve(num_threads_);
126
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 56 for(std::size_t i = 0; i < num_threads_; ++i)
127
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 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
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 157 std::unique_lock<std::mutex> lock(mutex_);
144
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 157 cv_.wait(lock, [this]{
145
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 289 return !q_.empty() ||
146 289 stop_.load(std::memory_order_acquire);
147 });
148
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 157 if(stop_.load(std::memory_order_acquire) && q_.empty())
149 72 return;
150 121 w = q_.pop();
151 157 }
152
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 121 if(w)
153
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 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
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 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
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 58 : impl_(new impl(num_threads, thread_name_prefix))
171 {
172
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 58 this->set_frame_allocator(std::allocator<void>{});
173 58 }
174
175 void
176 ✗ thread_pool::
177 stop() noexcept
178 {
179 ✗ impl_->stop();
180 ✗ }
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
193