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 //
 // detail/impl/scheduler.ipp
 // ~~~~~~~~~~~~~~~~~~~~~~~~~
 //
 // Copyright (c) 2003-2025 Christopher M. Kohlhoff (chris at kohlhoff dot com)
 //
 // Distributed under the Boost Software License, Version 1.0. (See accompanying
 // file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
 //
 
 #ifndef BOOST_ASIO_DETAIL_IMPL_SCHEDULER_IPP
 #define BOOST_ASIO_DETAIL_IMPL_SCHEDULER_IPP
 
 #if defined(_MSC_VER) && (_MSC_VER >= 1200)
 # pragma once
 #endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
 
 #include <boost/asio/detail/config.hpp>
 
 #include <boost/asio/config.hpp>
 #include <boost/asio/detail/event.hpp>
 #include <boost/asio/detail/limits.hpp>
 #include <boost/asio/detail/scheduler.hpp>
 #include <boost/asio/detail/scheduler_thread_info.hpp>
 #include <boost/asio/detail/signal_blocker.hpp>
 
 #if defined(BOOST_ASIO_HAS_IO_URING_AS_DEFAULT)
 # include <boost/asio/detail/io_uring_service.hpp>
 #else // defined(BOOST_ASIO_HAS_IO_URING_AS_DEFAULT)
 # include <boost/asio/detail/reactor.hpp>
 #endif // defined(BOOST_ASIO_HAS_IO_URING_AS_DEFAULT)
 
 #include <boost/asio/detail/push_options.hpp>
 
 namespace boost {
 namespace asio {
 namespace detail {
 
 class scheduler::thread_function
 {
 public:
   explicit thread_function(scheduler* s)
     : this_(s)
   {
   }
 
   void operator()()
   {
     boost::system::error_code ec;
     this_->run(ec);
   }
 
 private:
   scheduler* this_;
 };
 
 struct scheduler::task_cleanup
 {
   ~task_cleanup()
   {
     if (this_thread_->private_outstanding_work > 0)
     {
       boost::asio::detail::increment(
           scheduler_->outstanding_work_,
           this_thread_->private_outstanding_work);
     }
     this_thread_->private_outstanding_work = 0;
 
     // Enqueue the completed operations and reinsert the task at the end of
     // the operation queue.
     lock_->lock();
     scheduler_->task_interrupted_ = true;
     scheduler_->op_queue_.push(this_thread_->private_op_queue);
     scheduler_->op_queue_.push(&scheduler_->task_operation_);
   }
 
   scheduler* scheduler_;
   mutex::scoped_lock* lock_;
   thread_info* this_thread_;
 };
 
 struct scheduler::work_cleanup
 {
   ~work_cleanup()
   {
     if (this_thread_->private_outstanding_work > 1)
     {
       boost::asio::detail::increment(
           scheduler_->outstanding_work_,
           this_thread_->private_outstanding_work - 1);
     }
     else if (this_thread_->private_outstanding_work < 1)
     {
       scheduler_->work_finished();
     }
     this_thread_->private_outstanding_work = 0;
 
 #if defined(BOOST_ASIO_HAS_THREADS)
     if (!this_thread_->private_op_queue.empty())
     {
       lock_->lock();
       scheduler_->op_queue_.push(this_thread_->private_op_queue);
     }
 #endif // defined(BOOST_ASIO_HAS_THREADS)
   }
 
   scheduler* scheduler_;
   mutex::scoped_lock* lock_;
   thread_info* this_thread_;
 };
 
 scheduler::scheduler(boost::asio::execution_context& ctx,
     bool own_thread, get_task_func_type get_task)
   : boost::asio::detail::execution_context_service_base<scheduler>(ctx),
     one_thread_(config(ctx).get("scheduler", "concurrency_hint", 0) == 1),
     mutex_(config(ctx).get("scheduler", "locking", true),
         config(ctx).get("scheduler", "locking_spin_count", 0)),
     task_(0),
     get_task_(get_task),
     task_interrupted_(true),
     outstanding_work_(0),
     stopped_(false),
     shutdown_(false),
     concurrency_hint_(config(ctx).get("scheduler", "concurrency_hint", 0)),
     task_usec_(config(ctx).get("scheduler", "task_usec", -1L)),
     wait_usec_(config(ctx).get("scheduler", "wait_usec", -1L)),
     thread_(0)
 {
   BOOST_ASIO_HANDLER_TRACKING_INIT;
 
   if (own_thread)
   {
     ++outstanding_work_;
     boost::asio::detail::signal_blocker sb;
     thread_ = new boost::asio::detail::thread(thread_function(this));
   }
 }
 
 scheduler::~scheduler()
 {
   if (thread_)
   {
     mutex::scoped_lock lock(mutex_);
     shutdown_ = true;
     stop_all_threads(lock);
     lock.unlock();
     thread_->join();
     delete thread_;
   }
 }
 
 void scheduler::shutdown()
 {
   mutex::scoped_lock lock(mutex_);
   shutdown_ = true;
   if (thread_)
     stop_all_threads(lock);
   lock.unlock();
 
   // Join thread to ensure task operation is returned to queue.
   if (thread_)
   {
     thread_->join();
     delete thread_;
     thread_ = 0;
   }
 
   // Destroy handler objects.
   while (!op_queue_.empty())
   {
     operation* o = op_queue_.front();
     op_queue_.pop();
     if (o != &task_operation_)
       o->destroy();
   }
 
   // Reset to initial state.
   task_ = 0;
 }
 
 void scheduler::init_task()
 {
   mutex::scoped_lock lock(mutex_);
   if (!shutdown_ && !task_)
   {
     task_ = get_task_(this->context());
     op_queue_.push(&task_operation_);
     wake_one_thread_and_unlock(lock);
   }
 }
 
 std::size_t scheduler::run(boost::system::error_code& ec)
 {
   ec = boost::system::error_code();
   if (outstanding_work_ == 0)
   {
     stop();
     return 0;
   }
 
   thread_info this_thread;
   this_thread.private_outstanding_work = 0;
   thread_call_stack::context ctx(this, this_thread);
 
   mutex::scoped_lock lock(mutex_);
 
   std::size_t n = 0;
   for (; do_run_one(lock, this_thread, ec); lock.lock())
     if (n != (std::numeric_limits<std::size_t>::max)())
       ++n;
   return n;
 }
 
 std::size_t scheduler::run_one(boost::system::error_code& ec)
 {
   ec = boost::system::error_code();
   if (outstanding_work_ == 0)
   {
     stop();
     return 0;
   }
 
   thread_info this_thread;
   this_thread.private_outstanding_work = 0;
   thread_call_stack::context ctx(this, this_thread);
 
   mutex::scoped_lock lock(mutex_);
 
   return do_run_one(lock, this_thread, ec);
 }
 
 std::size_t scheduler::wait_one(long usec, boost::system::error_code& ec)
 {
   ec = boost::system::error_code();
   if (outstanding_work_ == 0)
   {
     stop();
     return 0;
   }
 
   thread_info this_thread;
   this_thread.private_outstanding_work = 0;
   thread_call_stack::context ctx(this, this_thread);
 
   mutex::scoped_lock lock(mutex_);
 
   return do_wait_one(lock, this_thread, usec, ec);
 }
 
 std::size_t scheduler::poll(boost::system::error_code& ec)
 {
   ec = boost::system::error_code();
   if (outstanding_work_ == 0)
   {
     stop();
     return 0;
   }
 
   thread_info this_thread;
   this_thread.private_outstanding_work = 0;
   thread_call_stack::context ctx(this, this_thread);
 
   mutex::scoped_lock lock(mutex_);
 
 #if defined(BOOST_ASIO_HAS_THREADS)
   // We want to support nested calls to poll() and poll_one(), so any handlers
   // that are already on a thread-private queue need to be put on to the main
   // queue now.
   if (one_thread_)
     if (thread_info* outer_info = static_cast<thread_info*>(ctx.next_by_key()))
       op_queue_.push(outer_info->private_op_queue);
 #endif // defined(BOOST_ASIO_HAS_THREADS)
 
   std::size_t n = 0;
   for (; do_poll_one(lock, this_thread, ec); lock.lock())
     if (n != (std::numeric_limits<std::size_t>::max)())
       ++n;
   return n;
 }
 
 std::size_t scheduler::poll_one(boost::system::error_code& ec)
 {
   ec = boost::system::error_code();
   if (outstanding_work_ == 0)
   {
     stop();
     return 0;
   }
 
   thread_info this_thread;
   this_thread.private_outstanding_work = 0;
   thread_call_stack::context ctx(this, this_thread);
 
   mutex::scoped_lock lock(mutex_);
 
 #if defined(BOOST_ASIO_HAS_THREADS)
   // We want to support nested calls to poll() and poll_one(), so any handlers
   // that are already on a thread-private queue need to be put on to the main
   // queue now.
   if (one_thread_)
     if (thread_info* outer_info = static_cast<thread_info*>(ctx.next_by_key()))
       op_queue_.push(outer_info->private_op_queue);
 #endif // defined(BOOST_ASIO_HAS_THREADS)
 
   return do_poll_one(lock, this_thread, ec);
 }
 
 void scheduler::stop()
 {
   mutex::scoped_lock lock(mutex_);
   stop_all_threads(lock);
 }
 
 bool scheduler::stopped() const
 {
   mutex::scoped_lock lock(mutex_);
   return stopped_;
 }
 
 void scheduler::restart()
 {
   mutex::scoped_lock lock(mutex_);
   stopped_ = false;
 }
 
 void scheduler::compensating_work_started()
 {
   thread_info_base* this_thread = thread_call_stack::contains(this);
   BOOST_ASIO_ASSUME(this_thread != 0); // Only called from inside scheduler.
   ++static_cast<thread_info*>(this_thread)->private_outstanding_work;
 }
 
 bool scheduler::can_dispatch()
 {
   return thread_call_stack::contains(this) != 0;
 }
 
 void scheduler::capture_current_exception()
 {
   if (thread_info_base* this_thread = thread_call_stack::contains(this))
     this_thread->capture_current_exception();
 }
 
 void scheduler::post_immediate_completion(
     scheduler::operation* op, bool is_continuation)
 {
 #if defined(BOOST_ASIO_HAS_THREADS)
   if (one_thread_ || is_continuation)
   {
     if (thread_info_base* this_thread = thread_call_stack::contains(this))
     {
       ++static_cast<thread_info*>(this_thread)->private_outstanding_work;
       static_cast<thread_info*>(this_thread)->private_op_queue.push(op);
       return;
     }
   }
 #else // defined(BOOST_ASIO_HAS_THREADS)
   (void)is_continuation;
 #endif // defined(BOOST_ASIO_HAS_THREADS)
 
   work_started();
   mutex::scoped_lock lock(mutex_);
   op_queue_.push(op);
   wake_one_thread_and_unlock(lock);
 }
 
 void scheduler::post_immediate_completions(std::size_t n,
     op_queue<scheduler::operation>& ops, bool is_continuation)
 {
 #if defined(BOOST_ASIO_HAS_THREADS)
   if (one_thread_ || is_continuation)
   {
     if (thread_info_base* this_thread = thread_call_stack::contains(this))
     {
       static_cast<thread_info*>(this_thread)->private_outstanding_work
         += static_cast<long>(n);
       static_cast<thread_info*>(this_thread)->private_op_queue.push(ops);
       return;
     }
   }
 #else // defined(BOOST_ASIO_HAS_THREADS)
   (void)is_continuation;
 #endif // defined(BOOST_ASIO_HAS_THREADS)
 
   increment(outstanding_work_, static_cast<long>(n));
   mutex::scoped_lock lock(mutex_);
   op_queue_.push(ops);
   wake_one_thread_and_unlock(lock);
 }
 
 void scheduler::post_deferred_completion(scheduler::operation* op)
 {
 #if defined(BOOST_ASIO_HAS_THREADS)
   if (one_thread_)
   {
     if (thread_info_base* this_thread = thread_call_stack::contains(this))
     {
       static_cast<thread_info*>(this_thread)->private_op_queue.push(op);
       return;
     }
   }
 #endif // defined(BOOST_ASIO_HAS_THREADS)
 
   mutex::scoped_lock lock(mutex_);
   op_queue_.push(op);
   wake_one_thread_and_unlock(lock);
 }
 
 void scheduler::post_deferred_completions(
     op_queue<scheduler::operation>& ops)
 {
   if (!ops.empty())
   {
 #if defined(BOOST_ASIO_HAS_THREADS)
     if (one_thread_)
     {
       if (thread_info_base* this_thread = thread_call_stack::contains(this))
       {
         static_cast<thread_info*>(this_thread)->private_op_queue.push(ops);
         return;
       }
     }
 #endif // defined(BOOST_ASIO_HAS_THREADS)
 
     mutex::scoped_lock lock(mutex_);
     op_queue_.push(ops);
     wake_one_thread_and_unlock(lock);
   }
 }
 
 void scheduler::do_dispatch(
     scheduler::operation* op)
 {
   work_started();
   mutex::scoped_lock lock(mutex_);
   op_queue_.push(op);
   wake_one_thread_and_unlock(lock);
 }
 
 void scheduler::abandon_operations(
     op_queue<scheduler::operation>& ops)
 {
   op_queue<scheduler::operation> ops2;
   ops2.push(ops);
 }
 
 std::size_t scheduler::do_run_one(mutex::scoped_lock& lock,
     scheduler::thread_info& this_thread,
     const boost::system::error_code& ec)
 {
   while (!stopped_)
   {
     if (!op_queue_.empty())
     {
       // Prepare to execute first handler from queue.
       operation* o = op_queue_.front();
       op_queue_.pop();
       bool more_handlers = (!op_queue_.empty());
 
       if (o == &task_operation_)
       {
         task_interrupted_ = more_handlers || task_usec_ == 0;
 
         if (more_handlers && !one_thread_ && wait_usec_ != 0)
           wakeup_event_.unlock_and_signal_one(lock);
         else
           lock.unlock();
 
         task_cleanup on_exit = { this, &lock, &this_thread };
         (void)on_exit;
 
         // Run the task. May throw an exception. Only block if the operation
         // queue is empty and we're not polling, otherwise we want to return
         // as soon as possible.
         task_->run(more_handlers ? 0 : task_usec_,
             this_thread.private_op_queue);
       }
       else
       {
         std::size_t task_result = o->task_result_;
 
         if (more_handlers && !one_thread_)
           wake_one_thread_and_unlock(lock);
         else
           lock.unlock();
 
         // Ensure the count of outstanding work is decremented on block exit.
         work_cleanup on_exit = { this, &lock, &this_thread };
         (void)on_exit;
 
         // Complete the operation. May throw an exception. Deletes the object.
         o->complete(this, ec, task_result);
         this_thread.rethrow_pending_exception();
 
         return 1;
       }
     }
     else
     {
       if (wait_usec_ == 0)
       {
         lock.unlock();
         lock.lock();
       }
       else
       {
         wakeup_event_.clear(lock);
         if (wait_usec_ > 0)
           wakeup_event_.wait_for_usec(lock, wait_usec_);
         else
           wakeup_event_.wait(lock);
       }
     }
   }
 
   return 0;
 }
 
 std::size_t scheduler::do_wait_one(mutex::scoped_lock& lock,
     scheduler::thread_info& this_thread, long usec,
     const boost::system::error_code& ec)
 {
   if (stopped_)
     return 0;
 
   operation* o = op_queue_.front();
   if (o == 0)
   {
     wakeup_event_.clear(lock);
     usec = (wait_usec_ >= 0 && wait_usec_ < usec) ? wait_usec_ : usec;
     wakeup_event_.wait_for_usec(lock, usec);
     usec = 0; // Wait at most once.
     o = op_queue_.front();
   }
 
   if (o == &task_operation_)
   {
     op_queue_.pop();
     bool more_handlers = (!op_queue_.empty());
 
     usec = (task_usec_ >= 0 && task_usec_ < usec) ? task_usec_ : usec;
     task_interrupted_ = more_handlers || usec == 0;
 
     if (more_handlers && !one_thread_ && wait_usec_ != 0)
       wakeup_event_.unlock_and_signal_one(lock);
     else
       lock.unlock();
 
     {
       task_cleanup on_exit = { this, &lock, &this_thread };
       (void)on_exit;
 
       // Run the task. May throw an exception. Only block if the operation
       // queue is empty and we're not polling, otherwise we want to return
       // as soon as possible.
       task_->run(more_handlers ? 0 : usec, this_thread.private_op_queue);
     }
 
     o = op_queue_.front();
     if (o == &task_operation_)
     {
       if (!one_thread_)
         wakeup_event_.maybe_unlock_and_signal_one(lock);
       return 0;
     }
   }
 
   if (o == 0)
     return 0;
 
   op_queue_.pop();
   bool more_handlers = (!op_queue_.empty());
 
   std::size_t task_result = o->task_result_;
 
   if (more_handlers && !one_thread_)
     wake_one_thread_and_unlock(lock);
   else
     lock.unlock();
 
   // Ensure the count of outstanding work is decremented on block exit.
   work_cleanup on_exit = { this, &lock, &this_thread };
   (void)on_exit;
 
   // Complete the operation. May throw an exception. Deletes the object.
   o->complete(this, ec, task_result);
   this_thread.rethrow_pending_exception();
 
   return 1;
 }
 
 std::size_t scheduler::do_poll_one(mutex::scoped_lock& lock,
     scheduler::thread_info& this_thread,
     const boost::system::error_code& ec)
 {
   if (stopped_)
     return 0;
 
   operation* o = op_queue_.front();
   if (o == &task_operation_)
   {
     op_queue_.pop();
     lock.unlock();
 
     {
       task_cleanup c = { this, &lock, &this_thread };
       (void)c;
 
       // Run the task. May throw an exception. Only block if the operation
       // queue is empty and we're not polling, otherwise we want to return
       // as soon as possible.
       task_->run(0, this_thread.private_op_queue);
     }
 
     o = op_queue_.front();
     if (o == &task_operation_)
     {
       wakeup_event_.maybe_unlock_and_signal_one(lock);
       return 0;
     }
   }
 
   if (o == 0)
     return 0;
 
   op_queue_.pop();
   bool more_handlers = (!op_queue_.empty());
 
   std::size_t task_result = o->task_result_;
 
   if (more_handlers && !one_thread_)
     wake_one_thread_and_unlock(lock);
   else
     lock.unlock();
 
   // Ensure the count of outstanding work is decremented on block exit.
   work_cleanup on_exit = { this, &lock, &this_thread };
   (void)on_exit;
 
   // Complete the operation. May throw an exception. Deletes the object.
   o->complete(this, ec, task_result);
   this_thread.rethrow_pending_exception();
 
   return 1;
 }
 
 void scheduler::stop_all_threads(
     mutex::scoped_lock& lock)
 {
   stopped_ = true;
   wakeup_event_.signal_all(lock);
 
   if (!task_interrupted_ && task_)
   {
     task_interrupted_ = true;
     task_->interrupt();
   }
 }
 
 void scheduler::wake_one_thread_and_unlock(
     mutex::scoped_lock& lock)
 {
   if (wait_usec_ == 0 || !wakeup_event_.maybe_unlock_and_signal_one(lock))
   {
     if (!task_interrupted_ && task_)
     {
       task_interrupted_ = true;
       task_->interrupt();
     }
     lock.unlock();
   }
 }
 
 scheduler_task* scheduler::get_default_task(boost::asio::execution_context& ctx)
 {
 #if defined(BOOST_ASIO_HAS_IO_URING_AS_DEFAULT)
   return &use_service<io_uring_service>(ctx);
 #else // defined(BOOST_ASIO_HAS_IO_URING_AS_DEFAULT)
   return &use_service<reactor>(ctx);
 #endif // defined(BOOST_ASIO_HAS_IO_URING_AS_DEFAULT)
 }
 
 } // namespace detail
 } // namespace asio
 } // namespace boost
 
 #include <boost/asio/detail/pop_options.hpp>
 
 #endif // BOOST_ASIO_DETAIL_IMPL_SCHEDULER_IPP

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