1   
//
1   
//
2   
// Copyright (c) 2026 Steve Gerbino
2   
// Copyright (c) 2026 Steve Gerbino
3   
//
3   
//
4   
// Distributed under the Boost Software License, Version 1.0. (See accompanying
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)
5   
// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
6   
//
6   
//
7   
// Official repository: https://github.com/cppalliance/corosio
7   
// Official repository: https://github.com/cppalliance/corosio
8   
//
8   
//
9  
9  
10   
#ifndef BOOST_COROSIO_NATIVE_DETAIL_SELECT_SELECT_SCHEDULER_HPP
10   
#ifndef BOOST_COROSIO_NATIVE_DETAIL_SELECT_SELECT_SCHEDULER_HPP
11   
#define BOOST_COROSIO_NATIVE_DETAIL_SELECT_SELECT_SCHEDULER_HPP
11   
#define BOOST_COROSIO_NATIVE_DETAIL_SELECT_SELECT_SCHEDULER_HPP
12  
12  
13   
#include <boost/corosio/detail/platform.hpp>
13   
#include <boost/corosio/detail/platform.hpp>
14  
14  
15   
#if BOOST_COROSIO_HAS_SELECT
15   
#if BOOST_COROSIO_HAS_SELECT
16  
16  
17   
#include <boost/corosio/detail/config.hpp>
17   
#include <boost/corosio/detail/config.hpp>
18   
#include <boost/capy/ex/execution_context.hpp>
18   
#include <boost/capy/ex/execution_context.hpp>
19  
19  
20   
#include <boost/corosio/native/detail/reactor/reactor_scheduler.hpp>
20   
#include <boost/corosio/native/detail/reactor/reactor_scheduler.hpp>
21  
21  
22   
#include <boost/corosio/native/detail/select/select_op.hpp>
22   
#include <boost/corosio/native/detail/select/select_op.hpp>
23   
#include <boost/corosio/detail/timer_service.hpp>
23   
#include <boost/corosio/detail/timer_service.hpp>
24   
#include <boost/corosio/native/detail/make_err.hpp>
24   
#include <boost/corosio/native/detail/make_err.hpp>
25   
#include <boost/corosio/native/detail/posix/posix_resolver_service.hpp>
25   
#include <boost/corosio/native/detail/posix/posix_resolver_service.hpp>
26   
#include <boost/corosio/native/detail/posix/posix_signal_service.hpp>
26   
#include <boost/corosio/native/detail/posix/posix_signal_service.hpp>
27  
27  
28   
#include <boost/corosio/detail/except.hpp>
28   
#include <boost/corosio/detail/except.hpp>
29  
29  
30   
#include <sys/select.h>
30   
#include <sys/select.h>
31   
#include <unistd.h>
31   
#include <unistd.h>
32   
#include <errno.h>
32   
#include <errno.h>
33   
#include <fcntl.h>
33   
#include <fcntl.h>
34  
34  
35   
#include <atomic>
35   
#include <atomic>
36   
#include <chrono>
36   
#include <chrono>
37   
#include <cstdint>
37   
#include <cstdint>
38   
#include <limits>
38   
#include <limits>
39   
#include <mutex>
39   
#include <mutex>
40   
#include <unordered_map>
40   
#include <unordered_map>
41  
41  
42   
namespace boost::corosio::detail {
42   
namespace boost::corosio::detail {
43  
43  
44   
struct select_op;
44   
struct select_op;
45   
struct select_descriptor_state;
45   
struct select_descriptor_state;
46  
46  
47   
/** POSIX scheduler using select() for I/O multiplexing.
47   
/** POSIX scheduler using select() for I/O multiplexing.
48  
48  
49   
    This scheduler implements the scheduler interface using the POSIX select()
49   
    This scheduler implements the scheduler interface using the POSIX select()
50   
    call for I/O event notification. It inherits the shared reactor threading
50   
    call for I/O event notification. It inherits the shared reactor threading
51   
    model from reactor_scheduler_base: signal state machine, inline completion
51   
    model from reactor_scheduler_base: signal state machine, inline completion
52   
    budget, work counting, and the do_one event loop.
52   
    budget, work counting, and the do_one event loop.
53  
53  
54   
    The design mirrors epoll_scheduler for behavioral consistency:
54   
    The design mirrors epoll_scheduler for behavioral consistency:
55   
    - Same single-reactor thread coordination model
55   
    - Same single-reactor thread coordination model
56   
    - Same deferred I/O pattern (reactor marks ready; workers do I/O)
56   
    - Same deferred I/O pattern (reactor marks ready; workers do I/O)
57   
    - Same timer integration pattern
57   
    - Same timer integration pattern
58  
58  
59   
    Known Limitations:
59   
    Known Limitations:
60   
    - FD_SETSIZE (~1024) limits maximum concurrent connections
60   
    - FD_SETSIZE (~1024) limits maximum concurrent connections
61   
    - O(n) scanning: rebuilds fd_sets each iteration
61   
    - O(n) scanning: rebuilds fd_sets each iteration
62   
    - Level-triggered only (no edge-triggered mode)
62   
    - Level-triggered only (no edge-triggered mode)
63  
63  
64   
    @par Thread Safety
64   
    @par Thread Safety
65   
    All public member functions are thread-safe.
65   
    All public member functions are thread-safe.
66   
*/
66   
*/
67   
class BOOST_COROSIO_DECL select_scheduler final : public reactor_scheduler_base
67   
class BOOST_COROSIO_DECL select_scheduler final : public reactor_scheduler_base
68   
{
68   
{
69   
public:
69   
public:
70   
    /** Construct the scheduler.
70   
    /** Construct the scheduler.
71  
71  
72   
        Creates a self-pipe for reactor interruption.
72   
        Creates a self-pipe for reactor interruption.
73  
73  
74   
        @param ctx Reference to the owning execution_context.
74   
        @param ctx Reference to the owning execution_context.
75   
        @param concurrency_hint Hint for expected thread count (unused).
75   
        @param concurrency_hint Hint for expected thread count (unused).
76   
    */
76   
    */
77   
    select_scheduler(capy::execution_context& ctx, int concurrency_hint = -1);
77   
    select_scheduler(capy::execution_context& ctx, int concurrency_hint = -1);
78  
78  
79   
    /// Destroy the scheduler.
79   
    /// Destroy the scheduler.
80   
    ~select_scheduler() override;
80   
    ~select_scheduler() override;
81  
81  
82   
    select_scheduler(select_scheduler const&)            = delete;
82   
    select_scheduler(select_scheduler const&)            = delete;
83   
    select_scheduler& operator=(select_scheduler const&) = delete;
83   
    select_scheduler& operator=(select_scheduler const&) = delete;
84  
84  
85   
    /// Shut down the scheduler, draining pending operations.
85   
    /// Shut down the scheduler, draining pending operations.
86   
    void shutdown() override;
86   
    void shutdown() override;
87  
87  
88   
    /** Return the maximum file descriptor value supported.
88   
    /** Return the maximum file descriptor value supported.
89  
89  
90   
        Returns FD_SETSIZE - 1, the maximum fd value that can be
90   
        Returns FD_SETSIZE - 1, the maximum fd value that can be
91   
        monitored by select(). Operations with fd >= FD_SETSIZE
91   
        monitored by select(). Operations with fd >= FD_SETSIZE
92   
        will fail with EINVAL.
92   
        will fail with EINVAL.
93  
93  
94   
        @return The maximum supported file descriptor value.
94   
        @return The maximum supported file descriptor value.
95   
    */
95   
    */
96   
    static constexpr int max_fd() noexcept
96   
    static constexpr int max_fd() noexcept
97   
    {
97   
    {
98   
        return FD_SETSIZE - 1;
98   
        return FD_SETSIZE - 1;
99   
    }
99   
    }
100  
100  
101   
    /** Register a descriptor for persistent monitoring.
101   
    /** Register a descriptor for persistent monitoring.
102  
102  
103   
        The fd is added to the registered_descs_ map and will be
103   
        The fd is added to the registered_descs_ map and will be
104   
        included in subsequent select() calls. The reactor is
104   
        included in subsequent select() calls. The reactor is
105   
        interrupted so a blocked select() rebuilds its fd_sets.
105   
        interrupted so a blocked select() rebuilds its fd_sets.
106  
106  
107   
        @param fd The file descriptor to register.
107   
        @param fd The file descriptor to register.
108   
        @param desc Pointer to descriptor state for this fd.
108   
        @param desc Pointer to descriptor state for this fd.
109   
    */
109   
    */
110   
    void register_descriptor(int fd, select_descriptor_state* desc) const;
110   
    void register_descriptor(int fd, select_descriptor_state* desc) const;
111  
111  
112   
    /** Deregister a persistently registered descriptor.
112   
    /** Deregister a persistently registered descriptor.
113  
113  
114   
        @param fd The file descriptor to deregister.
114   
        @param fd The file descriptor to deregister.
115   
    */
115   
    */
116   
    void deregister_descriptor(int fd) const;
116   
    void deregister_descriptor(int fd) const;
117  
117  
118   
    /** Interrupt the reactor so it rebuilds its fd_sets.
118   
    /** Interrupt the reactor so it rebuilds its fd_sets.
119  
119  
120   
        Called when a write or connect op is registered after
120   
        Called when a write or connect op is registered after
121   
        the reactor's snapshot was taken. Without this, select()
121   
        the reactor's snapshot was taken. Without this, select()
122   
        may block not watching for writability on the fd.
122   
        may block not watching for writability on the fd.
123   
    */
123   
    */
124   
    void notify_reactor() const;
124   
    void notify_reactor() const;
125  
125  
126   
private:
126   
private:
127   
    void
127   
    void
128   
    run_task(std::unique_lock<std::mutex>& lock, context_type* ctx) override;
128   
    run_task(std::unique_lock<std::mutex>& lock, context_type* ctx) override;
129   
    void interrupt_reactor() const override;
129   
    void interrupt_reactor() const override;
130   
    long calculate_timeout(long requested_timeout_us) const;
130   
    long calculate_timeout(long requested_timeout_us) const;
131  
131  
132   
    // Self-pipe for interrupting select()
132   
    // Self-pipe for interrupting select()
133   
    int pipe_fds_[2]; // [0]=read, [1]=write
133   
    int pipe_fds_[2]; // [0]=read, [1]=write
134  
134  
135   
    // Per-fd tracking for fd_set building
135   
    // Per-fd tracking for fd_set building
136   
    mutable std::unordered_map<int, select_descriptor_state*> registered_descs_;
136   
    mutable std::unordered_map<int, select_descriptor_state*> registered_descs_;
137   
    mutable int max_fd_ = -1;
137   
    mutable int max_fd_ = -1;
138   
};
138   
};
139  
139  
140   
inline select_scheduler::select_scheduler(capy::execution_context& ctx, int)
140   
inline select_scheduler::select_scheduler(capy::execution_context& ctx, int)
141   
    : pipe_fds_{-1, -1}
141   
    : pipe_fds_{-1, -1}
142   
    , max_fd_(-1)
142   
    , max_fd_(-1)
143   
{
143   
{
144   
    if (::pipe(pipe_fds_) < 0)
144   
    if (::pipe(pipe_fds_) < 0)
145   
        detail::throw_system_error(make_err(errno), "pipe");
145   
        detail::throw_system_error(make_err(errno), "pipe");
146  
146  
147   
    for (int i = 0; i < 2; ++i)
147   
    for (int i = 0; i < 2; ++i)
148   
    {
148   
    {
149   
        int flags = ::fcntl(pipe_fds_[i], F_GETFL, 0);
149   
        int flags = ::fcntl(pipe_fds_[i], F_GETFL, 0);
150   
        if (flags == -1)
150   
        if (flags == -1)
151   
        {
151   
        {
152   
            int errn = errno;
152   
            int errn = errno;
153   
            ::close(pipe_fds_[0]);
153   
            ::close(pipe_fds_[0]);
154   
            ::close(pipe_fds_[1]);
154   
            ::close(pipe_fds_[1]);
155   
            detail::throw_system_error(make_err(errn), "fcntl F_GETFL");
155   
            detail::throw_system_error(make_err(errn), "fcntl F_GETFL");
156   
        }
156   
        }
157   
        if (::fcntl(pipe_fds_[i], F_SETFL, flags | O_NONBLOCK) == -1)
157   
        if (::fcntl(pipe_fds_[i], F_SETFL, flags | O_NONBLOCK) == -1)
158   
        {
158   
        {
159   
            int errn = errno;
159   
            int errn = errno;
160   
            ::close(pipe_fds_[0]);
160   
            ::close(pipe_fds_[0]);
161   
            ::close(pipe_fds_[1]);
161   
            ::close(pipe_fds_[1]);
162   
            detail::throw_system_error(make_err(errn), "fcntl F_SETFL");
162   
            detail::throw_system_error(make_err(errn), "fcntl F_SETFL");
163   
        }
163   
        }
164   
        if (::fcntl(pipe_fds_[i], F_SETFD, FD_CLOEXEC) == -1)
164   
        if (::fcntl(pipe_fds_[i], F_SETFD, FD_CLOEXEC) == -1)
165   
        {
165   
        {
166   
            int errn = errno;
166   
            int errn = errno;
167   
            ::close(pipe_fds_[0]);
167   
            ::close(pipe_fds_[0]);
168   
            ::close(pipe_fds_[1]);
168   
            ::close(pipe_fds_[1]);
169   
            detail::throw_system_error(make_err(errn), "fcntl F_SETFD");
169   
            detail::throw_system_error(make_err(errn), "fcntl F_SETFD");
170   
        }
170   
        }
171   
    }
171   
    }
172  
172  
173   
    timer_svc_ = &get_timer_service(ctx, *this);
173   
    timer_svc_ = &get_timer_service(ctx, *this);
174   
    timer_svc_->set_on_earliest_changed(
174   
    timer_svc_->set_on_earliest_changed(
175   
        timer_service::callback(this, [](void* p) {
175   
        timer_service::callback(this, [](void* p) {
176   
            static_cast<select_scheduler*>(p)->interrupt_reactor();
176   
            static_cast<select_scheduler*>(p)->interrupt_reactor();
177   
        }));
177   
        }));
178  
178  
179   
    get_resolver_service(ctx, *this);
179   
    get_resolver_service(ctx, *this);
180   
    get_signal_service(ctx, *this);
180   
    get_signal_service(ctx, *this);
181  
181  
182   
    completed_ops_.push(&task_op_);
182   
    completed_ops_.push(&task_op_);
183   
}
183   
}
184  
184  
185   
inline select_scheduler::~select_scheduler()
185   
inline select_scheduler::~select_scheduler()
186   
{
186   
{
187   
    if (pipe_fds_[0] >= 0)
187   
    if (pipe_fds_[0] >= 0)
188   
        ::close(pipe_fds_[0]);
188   
        ::close(pipe_fds_[0]);
189   
    if (pipe_fds_[1] >= 0)
189   
    if (pipe_fds_[1] >= 0)
190   
        ::close(pipe_fds_[1]);
190   
        ::close(pipe_fds_[1]);
191   
}
191   
}
192  
192  
193   
inline void
193   
inline void
194   
select_scheduler::shutdown()
194   
select_scheduler::shutdown()
195   
{
195   
{
196   
    shutdown_drain();
196   
    shutdown_drain();
197  
197  
198   
    if (pipe_fds_[1] >= 0)
198   
    if (pipe_fds_[1] >= 0)
199   
        interrupt_reactor();
199   
        interrupt_reactor();
200   
}
200   
}
201  
201  
202   
inline void
202   
inline void
203   
select_scheduler::register_descriptor(
203   
select_scheduler::register_descriptor(
204   
    int fd, select_descriptor_state* desc) const
204   
    int fd, select_descriptor_state* desc) const
205   
{
205   
{
206   
    if (fd < 0 || fd >= FD_SETSIZE)
206   
    if (fd < 0 || fd >= FD_SETSIZE)
207   
        detail::throw_system_error(make_err(EINVAL), "select: fd out of range");
207   
        detail::throw_system_error(make_err(EINVAL), "select: fd out of range");
208  
208  
209   
    desc->registered_events = reactor_event_read | reactor_event_write;
209   
    desc->registered_events = reactor_event_read | reactor_event_write;
210   
    desc->fd                = fd;
210   
    desc->fd                = fd;
211   
    desc->scheduler_        = this;
211   
    desc->scheduler_        = this;
212   
    desc->ready_events_.store(0, std::memory_order_relaxed);
212   
    desc->ready_events_.store(0, std::memory_order_relaxed);
213  
213  
214   
    {
214   
    {
215   
        std::lock_guard lock(desc->mutex);
215   
        std::lock_guard lock(desc->mutex);
216   
        desc->impl_ref_.reset();
216   
        desc->impl_ref_.reset();
217   
        desc->read_ready  = false;
217   
        desc->read_ready  = false;
218   
        desc->write_ready = false;
218   
        desc->write_ready = false;
219   
    }
219   
    }
220  
220  
221   
    {
221   
    {
222   
        std::lock_guard lock(mutex_);
222   
        std::lock_guard lock(mutex_);
223   
        registered_descs_[fd] = desc;
223   
        registered_descs_[fd] = desc;
224   
        if (fd > max_fd_)
224   
        if (fd > max_fd_)
225   
            max_fd_ = fd;
225   
            max_fd_ = fd;
226   
    }
226   
    }
227  
227  
228   
    interrupt_reactor();
228   
    interrupt_reactor();
229   
}
229   
}
230  
230  
231   
inline void
231   
inline void
232   
select_scheduler::deregister_descriptor(int fd) const
232   
select_scheduler::deregister_descriptor(int fd) const
233   
{
233   
{
234   
    std::lock_guard lock(mutex_);
234   
    std::lock_guard lock(mutex_);
235  
235  
236   
    auto it = registered_descs_.find(fd);
236   
    auto it = registered_descs_.find(fd);
237   
    if (it == registered_descs_.end())
237   
    if (it == registered_descs_.end())
238   
        return;
238   
        return;
239  
239  
240   
    registered_descs_.erase(it);
240   
    registered_descs_.erase(it);
241  
241  
242   
    if (fd == max_fd_)
242   
    if (fd == max_fd_)
243   
    {
243   
    {
244   
        max_fd_ = pipe_fds_[0];
244   
        max_fd_ = pipe_fds_[0];
245   
        for (auto& [registered_fd, state] : registered_descs_)
245   
        for (auto& [registered_fd, state] : registered_descs_)
246   
        {
246   
        {
247   
            if (registered_fd > max_fd_)
247   
            if (registered_fd > max_fd_)
248   
                max_fd_ = registered_fd;
248   
                max_fd_ = registered_fd;
249   
        }
249   
        }
250   
    }
250   
    }
251   
}
251   
}
252  
252  
253   
inline void
253   
inline void
254   
select_scheduler::notify_reactor() const
254   
select_scheduler::notify_reactor() const
255   
{
255   
{
256   
    interrupt_reactor();
256   
    interrupt_reactor();
257   
}
257   
}
258  
258  
259   
inline void
259   
inline void
260   
select_scheduler::interrupt_reactor() const
260   
select_scheduler::interrupt_reactor() const
261   
{
261   
{
262   
    char byte               = 1;
262   
    char byte               = 1;
263   
    [[maybe_unused]] auto r = ::write(pipe_fds_[1], &byte, 1);
263   
    [[maybe_unused]] auto r = ::write(pipe_fds_[1], &byte, 1);
264   
}
264   
}
265  
265  
266   
inline long
266   
inline long
267   
select_scheduler::calculate_timeout(long requested_timeout_us) const
267   
select_scheduler::calculate_timeout(long requested_timeout_us) const
268   
{
268   
{
269   
    if (requested_timeout_us == 0)
269   
    if (requested_timeout_us == 0)
270   
        return 0;
270   
        return 0;
271  
271  
272   
    auto nearest = timer_svc_->nearest_expiry();
272   
    auto nearest = timer_svc_->nearest_expiry();
273   
    if (nearest == timer_service::time_point::max())
273   
    if (nearest == timer_service::time_point::max())
274   
        return requested_timeout_us;
274   
        return requested_timeout_us;
275  
275  
276   
    auto now = std::chrono::steady_clock::now();
276   
    auto now = std::chrono::steady_clock::now();
277   
    if (nearest <= now)
277   
    if (nearest <= now)
278   
        return 0;
278   
        return 0;
279  
279  
280   
    auto timer_timeout_us =
280   
    auto timer_timeout_us =
281   
        std::chrono::duration_cast<std::chrono::microseconds>(nearest - now)
281   
        std::chrono::duration_cast<std::chrono::microseconds>(nearest - now)
282   
            .count();
282   
            .count();
283  
283  
284   
    constexpr auto long_max =
284   
    constexpr auto long_max =
285   
        static_cast<long long>((std::numeric_limits<long>::max)());
285   
        static_cast<long long>((std::numeric_limits<long>::max)());
286   
    auto capped_timer_us =
286   
    auto capped_timer_us =
287   
        (std::min)((std::max)(static_cast<long long>(timer_timeout_us),
287   
        (std::min)((std::max)(static_cast<long long>(timer_timeout_us),
288   
                              static_cast<long long>(0)),
288   
                              static_cast<long long>(0)),
289   
                   long_max);
289   
                   long_max);
290  
290  
291   
    if (requested_timeout_us < 0)
291   
    if (requested_timeout_us < 0)
292   
        return static_cast<long>(capped_timer_us);
292   
        return static_cast<long>(capped_timer_us);
293  
293  
294   
    return static_cast<long>(
294   
    return static_cast<long>(
295   
        (std::min)(static_cast<long long>(requested_timeout_us),
295   
        (std::min)(static_cast<long long>(requested_timeout_us),
296   
                   capped_timer_us));
296   
                   capped_timer_us));
297   
}
297   
}
298  
298  
299   
inline void
299   
inline void
300   
select_scheduler::run_task(
300   
select_scheduler::run_task(
301   
    std::unique_lock<std::mutex>& lock, context_type* ctx)
301   
    std::unique_lock<std::mutex>& lock, context_type* ctx)
302   
{
302   
{
303   
    long effective_timeout_us = task_interrupted_ ? 0 : calculate_timeout(-1);
303   
    long effective_timeout_us = task_interrupted_ ? 0 : calculate_timeout(-1);
304  
304  
305   
    // Snapshot registered descriptors while holding lock.
305   
    // Snapshot registered descriptors while holding lock.
306   
    // Record which fds need write monitoring to avoid a hot loop:
306   
    // Record which fds need write monitoring to avoid a hot loop:
307   
    // select is level-triggered so writable sockets (nearly always
307   
    // select is level-triggered so writable sockets (nearly always
308   
    // writable) would cause select() to return immediately every
308   
    // writable) would cause select() to return immediately every
309   
    // iteration if unconditionally added to write_fds.
309   
    // iteration if unconditionally added to write_fds.
310   
    struct fd_entry
310   
    struct fd_entry
311   
    {
311   
    {
312   
        int fd;
312   
        int fd;
313   
        select_descriptor_state* desc;
313   
        select_descriptor_state* desc;
314   
        bool needs_write;
314   
        bool needs_write;
315   
    };
315   
    };
316   
    fd_entry snapshot[FD_SETSIZE];
316   
    fd_entry snapshot[FD_SETSIZE];
317   
    int snapshot_count = 0;
317   
    int snapshot_count = 0;
318  
318  
319   
    for (auto& [fd, desc] : registered_descs_)
319   
    for (auto& [fd, desc] : registered_descs_)
320   
    {
320   
    {
321   
        if (snapshot_count < FD_SETSIZE)
321   
        if (snapshot_count < FD_SETSIZE)
322   
        {
322   
        {
323   
            std::lock_guard desc_lock(desc->mutex);
323   
            std::lock_guard desc_lock(desc->mutex);
324   
            snapshot[snapshot_count].fd   = fd;
324   
            snapshot[snapshot_count].fd   = fd;
325   
            snapshot[snapshot_count].desc = desc;
325   
            snapshot[snapshot_count].desc = desc;
326   
            snapshot[snapshot_count].needs_write =
326   
            snapshot[snapshot_count].needs_write =
327   
                (desc->write_op || desc->connect_op);
327   
                (desc->write_op || desc->connect_op);
328   
            ++snapshot_count;
328   
            ++snapshot_count;
329   
        }
329   
        }
330   
    }
330   
    }
331  
331  
332   
    if (lock.owns_lock())
332   
    if (lock.owns_lock())
333   
        lock.unlock();
333   
        lock.unlock();
334  
334  
335   
    task_cleanup on_exit{this, &lock, ctx};
335   
    task_cleanup on_exit{this, &lock, ctx};
336  
336  
337   
    fd_set read_fds, write_fds, except_fds;
337   
    fd_set read_fds, write_fds, except_fds;
338   
    FD_ZERO(&read_fds);
338   
    FD_ZERO(&read_fds);
339   
    FD_ZERO(&write_fds);
339   
    FD_ZERO(&write_fds);
340   
    FD_ZERO(&except_fds);
340   
    FD_ZERO(&except_fds);
341  
341  
342   
    FD_SET(pipe_fds_[0], &read_fds);
342   
    FD_SET(pipe_fds_[0], &read_fds);
343   
    int nfds = pipe_fds_[0];
343   
    int nfds = pipe_fds_[0];
344  
344  
345   
    for (int i = 0; i < snapshot_count; ++i)
345   
    for (int i = 0; i < snapshot_count; ++i)
346   
    {
346   
    {
347   
        int fd = snapshot[i].fd;
347   
        int fd = snapshot[i].fd;
348   
        FD_SET(fd, &read_fds);
348   
        FD_SET(fd, &read_fds);
349   
        if (snapshot[i].needs_write)
349   
        if (snapshot[i].needs_write)
350   
            FD_SET(fd, &write_fds);
350   
            FD_SET(fd, &write_fds);
351   
        FD_SET(fd, &except_fds);
351   
        FD_SET(fd, &except_fds);
352   
        if (fd > nfds)
352   
        if (fd > nfds)
353   
            nfds = fd;
353   
            nfds = fd;
354   
    }
354   
    }
355  
355  
356   
    struct timeval tv;
356   
    struct timeval tv;
357   
    struct timeval* tv_ptr = nullptr;
357   
    struct timeval* tv_ptr = nullptr;
358   
    if (effective_timeout_us >= 0)
358   
    if (effective_timeout_us >= 0)
359   
    {
359   
    {
360   
        tv.tv_sec  = effective_timeout_us / 1000000;
360   
        tv.tv_sec  = effective_timeout_us / 1000000;
361   
        tv.tv_usec = effective_timeout_us % 1000000;
361   
        tv.tv_usec = effective_timeout_us % 1000000;
362   
        tv_ptr     = &tv;
362   
        tv_ptr     = &tv;
363   
    }
363   
    }
364  
364  
365   
    int ready = ::select(nfds + 1, &read_fds, &write_fds, &except_fds, tv_ptr);
365   
    int ready = ::select(nfds + 1, &read_fds, &write_fds, &except_fds, tv_ptr);
366  
366  
367   
    // EINTR: signal interrupted select(), just retry.
367   
    // EINTR: signal interrupted select(), just retry.
368   
    // EBADF: an fd was closed between snapshot and select(); retry
368   
    // EBADF: an fd was closed between snapshot and select(); retry
369   
    // with a fresh snapshot from registered_descs_.
369   
    // with a fresh snapshot from registered_descs_.
370   
    if (ready < 0)
370   
    if (ready < 0)
371   
    {
371   
    {
372   
        if (errno == EINTR || errno == EBADF)
372   
        if (errno == EINTR || errno == EBADF)
373   
            return;
373   
            return;
374   
        detail::throw_system_error(make_err(errno), "select");
374   
        detail::throw_system_error(make_err(errno), "select");
375   
    }
375   
    }
376  
376  
377   
    // Process timers outside the lock
377   
    // Process timers outside the lock
378   
    timer_svc_->process_expired();
378   
    timer_svc_->process_expired();
379  
379  
380   
    op_queue local_ops;
380   
    op_queue local_ops;
381  
381  
382   
    if (ready > 0)
382   
    if (ready > 0)
383   
    {
383   
    {
384   
        if (FD_ISSET(pipe_fds_[0], &read_fds))
384   
        if (FD_ISSET(pipe_fds_[0], &read_fds))
385   
        {
385   
        {
386   
            char buf[256];
386   
            char buf[256];
387   
            while (::read(pipe_fds_[0], buf, sizeof(buf)) > 0)
387   
            while (::read(pipe_fds_[0], buf, sizeof(buf)) > 0)
388   
            {
388   
            {
389   
            }
389   
            }
390   
        }
390   
        }
391  
391  
392   
        for (int i = 0; i < snapshot_count; ++i)
392   
        for (int i = 0; i < snapshot_count; ++i)
393   
        {
393   
        {
394   
            int fd                        = snapshot[i].fd;
394   
            int fd                        = snapshot[i].fd;
395   
            select_descriptor_state* desc = snapshot[i].desc;
395   
            select_descriptor_state* desc = snapshot[i].desc;
396  
396  
397   
            std::uint32_t flags = 0;
397   
            std::uint32_t flags = 0;
398   
            if (FD_ISSET(fd, &read_fds))
398   
            if (FD_ISSET(fd, &read_fds))
399   
                flags |= reactor_event_read;
399   
                flags |= reactor_event_read;
400   
            if (FD_ISSET(fd, &write_fds))
400   
            if (FD_ISSET(fd, &write_fds))
401   
                flags |= reactor_event_write;
401   
                flags |= reactor_event_write;
402   
            if (FD_ISSET(fd, &except_fds))
402   
            if (FD_ISSET(fd, &except_fds))
403   
                flags |= reactor_event_error;
403   
                flags |= reactor_event_error;
404  
404  
405   
            if (flags == 0)
405   
            if (flags == 0)
406   
                continue;
406   
                continue;
407  
407  
408   
            desc->add_ready_events(flags);
408   
            desc->add_ready_events(flags);
409  
409  
410   
            bool expected = false;
410   
            bool expected = false;
411   
            if (desc->is_enqueued_.compare_exchange_strong(
411   
            if (desc->is_enqueued_.compare_exchange_strong(
412   
                    expected, true, std::memory_order_release,
412   
                    expected, true, std::memory_order_release,
413   
                    std::memory_order_relaxed))
413   
                    std::memory_order_relaxed))
414   
            {
414   
            {
415   
                local_ops.push(desc);
415   
                local_ops.push(desc);
416   
            }
416   
            }
417   
        }
417   
        }
418   
    }
418   
    }
419  
419  
420   
    lock.lock();
420   
    lock.lock();
421  
421  
422   
    if (!local_ops.empty())
422   
    if (!local_ops.empty())
423   
        completed_ops_.splice(local_ops);
423   
        completed_ops_.splice(local_ops);
424   
}
424   
}
425  
425  
426   
} // namespace boost::corosio::detail
426   
} // namespace boost::corosio::detail
427  
427  
428   
#endif // BOOST_COROSIO_HAS_SELECT
428   
#endif // BOOST_COROSIO_HAS_SELECT
429  
429  
430   
#endif // BOOST_COROSIO_NATIVE_DETAIL_SELECT_SELECT_SCHEDULER_HPP
430   
#endif // BOOST_COROSIO_NATIVE_DETAIL_SELECT_SELECT_SCHEDULER_HPP