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//
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//
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// Copyright (c) 2025 Vinnie Falco (vinnie.falco@gmail.com)
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// Copyright (c) 2025 Vinnie Falco (vinnie.falco@gmail.com)
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// Copyright (c) 2026 Michael Vandeberg
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// Copyright (c) 2026 Michael Vandeberg
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//
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//
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// Distributed under the Boost Software License, Version 1.0. (See accompanying
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// Distributed under the Boost Software License, Version 1.0. (See accompanying
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// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
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// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
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//
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//
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// Official repository: https://github.com/boostorg/capy
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// Official repository: https://github.com/boostorg/capy
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//
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//
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#include <boost/capy/ex/thread_pool.hpp>
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#include <boost/capy/ex/thread_pool.hpp>
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#include <boost/capy/detail/intrusive.hpp>
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#include <boost/capy/detail/intrusive.hpp>
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#include <boost/capy/test/thread_name.hpp>
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#include <boost/capy/test/thread_name.hpp>
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#include <atomic>
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#include <atomic>
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#include <condition_variable>
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#include <condition_variable>
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#include <cstdio>
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#include <cstdio>
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#include <mutex>
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#include <mutex>
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#include <thread>
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#include <thread>
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#include <vector>
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#include <vector>
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20  
21   
/*
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/*
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    Thread pool implementation using a shared work queue.
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    Thread pool implementation using a shared work queue.
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23  
24   
    Work items are coroutine handles wrapped in intrusive list nodes, stored
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    Work items are coroutine handles wrapped in intrusive list nodes, stored
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    in a single queue protected by a mutex. Worker threads wait on a
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    in a single queue protected by a mutex. Worker threads wait on a
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    condition_variable until work is available or stop is requested.
26   
    condition_variable until work is available or stop is requested.
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27  
28   
    Threads are started lazily on first post() via std::call_once to avoid
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    Threads are started lazily on first post() via std::call_once to avoid
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    spawning threads for pools that are constructed but never used. Each
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    spawning threads for pools that are constructed but never used. Each
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    thread is named with a configurable prefix plus index for debugger
30   
    thread is named with a configurable prefix plus index for debugger
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    visibility.
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    visibility.
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    Shutdown sequence: stop() sets the stop flag and notifies all threads,
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    Shutdown sequence: stop() sets the stop flag and notifies all threads,
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    then the destructor joins threads and destroys any remaining queued
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    then the destructor joins threads and destroys any remaining queued
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    work without executing it.
35   
    work without executing it.
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*/
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*/
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37  
38   
namespace boost {
38   
namespace boost {
39   
namespace capy {
39   
namespace capy {
40  
40  
41   
//------------------------------------------------------------------------------
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//------------------------------------------------------------------------------
42  
42  
43   
class thread_pool::impl
43   
class thread_pool::impl
44   
{
44   
{
45   
    struct work : detail::intrusive_queue<work>::node
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    struct work : detail::intrusive_queue<work>::node
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    {
46   
    {
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        std::coroutine_handle<> h_;
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        std::coroutine_handle<> h_;
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48  
49   
        explicit work(std::coroutine_handle<> h) noexcept
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        explicit work(std::coroutine_handle<> h) noexcept
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            : h_(h)
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            : h_(h)
51   
        {
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        {
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        }
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        }
53  
53  
54   
        void run()
54   
        void run()
55   
        {
55   
        {
56   
            auto h = h_;
56   
            auto h = h_;
57   
            delete this;
57   
            delete this;
58   
            h.resume();
58   
            h.resume();
59   
        }
59   
        }
60  
60  
61   
        void destroy()
61   
        void destroy()
62   
        {
62   
        {
63   
            delete this;
63   
            delete this;
64   
        }
64   
        }
65   
    };
65   
    };
66  
66  
67   
    std::mutex mutex_;
67   
    std::mutex mutex_;
68   
    std::condition_variable cv_;
68   
    std::condition_variable cv_;
69   
    detail::intrusive_queue<work> q_;
69   
    detail::intrusive_queue<work> q_;
70   
    std::vector<std::thread> threads_;
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    std::vector<std::thread> threads_;
71   
    std::atomic<bool> stop_{false};
71   
    std::atomic<bool> stop_{false};
72   
    std::size_t num_threads_;
72   
    std::size_t num_threads_;
73   
    char thread_name_prefix_[13]{};  // 12 chars max + null terminator
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    char thread_name_prefix_[13]{};  // 12 chars max + null terminator
74   
    std::once_flag start_flag_;
74   
    std::once_flag start_flag_;
75  
75  
76   
public:
76   
public:
77   
    ~impl()
77   
    ~impl()
78   
    {
78   
    {
79   
        stop();
79   
        stop();
80   
        for(auto& t : threads_)
80   
        for(auto& t : threads_)
81   
            if(t.joinable())
81   
            if(t.joinable())
82   
                t.join();
82   
                t.join();
83  
83  
84   
        while(auto* w = q_.pop())
84   
        while(auto* w = q_.pop())
85   
            w->destroy();
85   
            w->destroy();
86   
    }
86   
    }
87  
87  
88   
    impl(std::size_t num_threads, std::string_view thread_name_prefix)
88   
    impl(std::size_t num_threads, std::string_view thread_name_prefix)
89   
        : num_threads_(num_threads)
89   
        : num_threads_(num_threads)
90   
    {
90   
    {
91   
        if(num_threads_ == 0)
91   
        if(num_threads_ == 0)
92   
            num_threads_ = std::thread::hardware_concurrency();
92   
            num_threads_ = std::thread::hardware_concurrency();
93   
        if(num_threads_ == 0)
93   
        if(num_threads_ == 0)
94   
            num_threads_ = 1;
94   
            num_threads_ = 1;
95  
95  
96   
        // Truncate prefix to 12 chars, leaving room for up to 3-digit index.
96   
        // Truncate prefix to 12 chars, leaving room for up to 3-digit index.
97   
        auto n = thread_name_prefix.copy(thread_name_prefix_, 12);
97   
        auto n = thread_name_prefix.copy(thread_name_prefix_, 12);
98   
        thread_name_prefix_[n] = '\0';
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        thread_name_prefix_[n] = '\0';
99   
    }
99   
    }
100  
100  
101   
    void
101   
    void
102   
    post(std::coroutine_handle<> h)
102   
    post(std::coroutine_handle<> h)
103   
    {
103   
    {
104   
        ensure_started();
104   
        ensure_started();
105   
        auto* w = new work(h);
105   
        auto* w = new work(h);
106   
        {
106   
        {
107   
            std::lock_guard<std::mutex> lock(mutex_);
107   
            std::lock_guard<std::mutex> lock(mutex_);
108   
            q_.push(w);
108   
            q_.push(w);
109   
        }
109   
        }
110   
        cv_.notify_one();
110   
        cv_.notify_one();
111   
    }
111   
    }
112  
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113 - 
    join() noexcept
 
114 - 
    {
 
115 - 
        stop();
 
116 - 
        for(auto& t : threads_)
 
117 - 
            if(t.joinable())
 
118 - 
                t.join();
 
119 - 
    }
 
120 -
 
121 - 
    void
 
122   
    void
113   
    void
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    stop() noexcept
114   
    stop() noexcept
124   
    {
115   
    {
125   
        stop_.store(true, std::memory_order_release);
116   
        stop_.store(true, std::memory_order_release);
126   
        cv_.notify_all();
117   
        cv_.notify_all();
127   
    }
118   
    }
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129   
private:
120   
private:
130   
    void
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    void
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    ensure_started()
122   
    ensure_started()
132   
    {
123   
    {
133   
        std::call_once(start_flag_, [this]{
124   
        std::call_once(start_flag_, [this]{
134   
            threads_.reserve(num_threads_);
125   
            threads_.reserve(num_threads_);
135   
            for(std::size_t i = 0; i < num_threads_; ++i)
126   
            for(std::size_t i = 0; i < num_threads_; ++i)
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                threads_.emplace_back([this, i]{ run(i); });
127   
                threads_.emplace_back([this, i]{ run(i); });
137   
        });
128   
        });
138   
    }
129   
    }
139  
130  
140   
    void
131   
    void
141   
    run(std::size_t index)
132   
    run(std::size_t index)
142   
    {
133   
    {
143   
        // Build name; set_current_thread_name truncates to platform limits.
134   
        // Build name; set_current_thread_name truncates to platform limits.
144   
        char name[16];
135   
        char name[16];
145   
        std::snprintf(name, sizeof(name), "%s%zu", thread_name_prefix_, index);
136   
        std::snprintf(name, sizeof(name), "%s%zu", thread_name_prefix_, index);
146   
        set_current_thread_name(name);
137   
        set_current_thread_name(name);
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148   
        for(;;)
139   
        for(;;)
149   
        {
140   
        {
150   
            work* w = nullptr;
141   
            work* w = nullptr;
151   
            {
142   
            {
152   
                std::unique_lock<std::mutex> lock(mutex_);
143   
                std::unique_lock<std::mutex> lock(mutex_);
153   
                cv_.wait(lock, [this]{
144   
                cv_.wait(lock, [this]{
154   
                    return !q_.empty() ||
145   
                    return !q_.empty() ||
155   
                        stop_.load(std::memory_order_acquire);
146   
                        stop_.load(std::memory_order_acquire);
156   
                });
147   
                });
157   
                if(stop_.load(std::memory_order_acquire) && q_.empty())
148   
                if(stop_.load(std::memory_order_acquire) && q_.empty())
158   
                    return;
149   
                    return;
159   
                w = q_.pop();
150   
                w = q_.pop();
160   
            }
151   
            }
161   
            if(w)
152   
            if(w)
162   
                w->run();
153   
                w->run();
163   
        }
154   
        }
164   
    }
155   
    }
165   
};
156   
};
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157  
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//------------------------------------------------------------------------------
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//------------------------------------------------------------------------------
168  
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169   
thread_pool::
160   
thread_pool::
170   
~thread_pool()
161   
~thread_pool()
171 - 
    impl_->join();
 
172   
{
162   
{
173   
    shutdown();
163   
    shutdown();
174   
    destroy();
164   
    destroy();
175   
    delete impl_;
165   
    delete impl_;
176   
}
166   
}
177  
167  
178   
thread_pool::
168   
thread_pool::
179   
thread_pool(std::size_t num_threads, std::string_view thread_name_prefix)
169   
thread_pool(std::size_t num_threads, std::string_view thread_name_prefix)
180   
    : impl_(new impl(num_threads, thread_name_prefix))
170   
    : impl_(new impl(num_threads, thread_name_prefix))
181   
{
171   
{
182   
    this->set_frame_allocator(std::allocator<void>{});
172   
    this->set_frame_allocator(std::allocator<void>{});
183   
}
173   
}
184  
174  
185   
void
175   
void
186   
thread_pool::
176   
thread_pool::
187   
stop() noexcept
177   
stop() noexcept
188   
{
178   
{
189   
    impl_->stop();
179   
    impl_->stop();
190   
}
180   
}
191  
181  
192 -
 
193 - 
thread_pool::executor_type
 
194 - 
thread_pool::
 
195 - 
get_executor() const noexcept
 
196 - 
{
 
197 - 
    return executor_type(
 
198 - 
        const_cast<thread_pool&>(*this));
 
199 - 
}
 
200   
//------------------------------------------------------------------------------
182   
//------------------------------------------------------------------------------
201  
183  
202   
void
184   
void
203   
thread_pool::executor_type::
185   
thread_pool::executor_type::
204   
post(std::coroutine_handle<> h) const
186   
post(std::coroutine_handle<> h) const
205   
{
187   
{
206   
    pool_->impl_->post(h);
188   
    pool_->impl_->post(h);
207   
}
189   
}
208  
190  
209   
} // capy
191   
} // capy
210   
} // boost
192   
} // boost