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 //
 // detail/impl/win_iocp_io_context.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_WIN_IOCP_IO_CONTEXT_IPP
 #define BOOST_ASIO_DETAIL_IMPL_WIN_IOCP_IO_CONTEXT_IPP
 
 #if defined(_MSC_VER) && (_MSC_VER >= 1200)
 # pragma once
 #endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
 
 #include <boost/asio/detail/config.hpp>
 
 #if defined(BOOST_ASIO_HAS_IOCP)
 
 #include <boost/asio/config.hpp>
 #include <boost/asio/error.hpp>
 #include <boost/asio/detail/cstdint.hpp>
 #include <boost/asio/detail/handler_alloc_helpers.hpp>
 #include <boost/asio/detail/limits.hpp>
 #include <boost/asio/detail/thread.hpp>
 #include <boost/asio/detail/throw_error.hpp>
 #include <boost/asio/detail/win_iocp_io_context.hpp>
 
 #include <boost/asio/detail/push_options.hpp>
 
 namespace boost {
 namespace asio {
 namespace detail {
 
 struct win_iocp_io_context::thread_function
 {
   explicit thread_function(win_iocp_io_context* s)
     : this_(s)
   {
   }
 
   void operator()()
   {
     boost::system::error_code ec;
     this_->run(ec);
   }
 
   win_iocp_io_context* this_;
 };
 
 struct win_iocp_io_context::work_finished_on_block_exit
 {
   ~work_finished_on_block_exit() noexcept(false)
   {
     io_context_->work_finished();
   }
 
   win_iocp_io_context* io_context_;
 };
 
 struct win_iocp_io_context::timer_thread_function
 {
   void operator()()
   {
     while (::InterlockedExchangeAdd(&io_context_->shutdown_, 0) == 0)
     {
       if (::WaitForSingleObject(io_context_->waitable_timer_.handle,
             INFINITE) == WAIT_OBJECT_0)
       {
         ::InterlockedExchange(&io_context_->dispatch_required_, 1);
         ::PostQueuedCompletionStatus(io_context_->iocp_.handle,
             0, wake_for_dispatch, 0);
       }
     }
   }
 
   win_iocp_io_context* io_context_;
 };
 
 win_iocp_io_context::win_iocp_io_context(
     boost::asio::execution_context& ctx, bool own_thread)
   : execution_context_service_base<win_iocp_io_context>(ctx),
     iocp_(),
     outstanding_work_(0),
     stopped_(0),
     stop_event_posted_(0),
     shutdown_(0),
     gqcs_timeout_(get_gqcs_timeout()),
     dispatch_required_(0),
     concurrency_hint_(config(ctx).get("scheduler", "concurrency_hint", -1))
 {
   BOOST_ASIO_HANDLER_TRACKING_INIT;
 
   iocp_.handle = ::CreateIoCompletionPort(INVALID_HANDLE_VALUE, 0, 0,
       static_cast<DWORD>(concurrency_hint_ >= 0
         ? concurrency_hint_ : DWORD(~0)));
   if (!iocp_.handle)
   {
     DWORD last_error = ::GetLastError();
     boost::system::error_code ec(last_error,
         boost::asio::error::get_system_category());
     boost::asio::detail::throw_error(ec, "iocp");
   }
 
   if (own_thread)
   {
     ::InterlockedIncrement(&outstanding_work_);
     thread_.reset(new boost::asio::detail::thread(thread_function(this)));
   }
 }
 
 win_iocp_io_context::~win_iocp_io_context()
 {
   if (thread_.get())
   {
     stop();
     thread_->join();
     thread_.reset();
   }
 }
 
 void win_iocp_io_context::shutdown()
 {
   ::InterlockedExchange(&shutdown_, 1);
 
   if (timer_thread_.get())
   {
     LARGE_INTEGER timeout;
     timeout.QuadPart = 1;
     ::SetWaitableTimer(waitable_timer_.handle, &timeout, 1, 0, 0, FALSE);
   }
 
   if (thread_.get())
   {
     stop();
     thread_->join();
     thread_.reset();
     ::InterlockedDecrement(&outstanding_work_);
   }
 
   while (::InterlockedExchangeAdd(&outstanding_work_, 0) > 0)
   {
     op_queue<win_iocp_operation> ops;
     timer_queues_.get_all_timers(ops);
     ops.push(completed_ops_);
     if (!ops.empty())
     {
       while (win_iocp_operation* op = ops.front())
       {
         ops.pop();
         ::InterlockedDecrement(&outstanding_work_);
         op->destroy();
       }
     }
     else
     {
       DWORD bytes_transferred = 0;
       dword_ptr_t completion_key = 0;
       LPOVERLAPPED overlapped = 0;
       ::GetQueuedCompletionStatus(iocp_.handle, &bytes_transferred,
           &completion_key, &overlapped, gqcs_timeout_);
       if (overlapped)
       {
         ::InterlockedDecrement(&outstanding_work_);
         static_cast<win_iocp_operation*>(overlapped)->destroy();
       }
     }
   }
 
   if (timer_thread_.get())
   {
     timer_thread_->join();
     timer_thread_.reset();
   }
 }
 
 boost::system::error_code win_iocp_io_context::register_handle(
     HANDLE handle, boost::system::error_code& ec)
 {
   if (::CreateIoCompletionPort(handle, iocp_.handle, 0, 0) == 0)
   {
     DWORD last_error = ::GetLastError();
     ec = boost::system::error_code(last_error,
         boost::asio::error::get_system_category());
   }
   else
   {
     ec = boost::system::error_code();
   }
   return ec;
 }
 
 size_t win_iocp_io_context::run(boost::system::error_code& ec)
 {
   if (::InterlockedExchangeAdd(&outstanding_work_, 0) == 0)
   {
     stop();
     ec = boost::system::error_code();
     return 0;
   }
 
   win_iocp_thread_info this_thread;
   thread_call_stack::context ctx(this, this_thread);
 
   size_t n = 0;
   while (do_one(INFINITE, this_thread, ec))
     if (n != (std::numeric_limits<size_t>::max)())
       ++n;
   return n;
 }
 
 size_t win_iocp_io_context::run_one(boost::system::error_code& ec)
 {
   if (::InterlockedExchangeAdd(&outstanding_work_, 0) == 0)
   {
     stop();
     ec = boost::system::error_code();
     return 0;
   }
 
   win_iocp_thread_info this_thread;
   thread_call_stack::context ctx(this, this_thread);
 
   return do_one(INFINITE, this_thread, ec);
 }
 
 size_t win_iocp_io_context::wait_one(long usec, boost::system::error_code& ec)
 {
   if (::InterlockedExchangeAdd(&outstanding_work_, 0) == 0)
   {
     stop();
     ec = boost::system::error_code();
     return 0;
   }
 
   win_iocp_thread_info this_thread;
   thread_call_stack::context ctx(this, this_thread);
 
   return do_one(usec < 0 ? INFINITE : ((usec - 1) / 1000 + 1), this_thread, ec);
 }
 
 size_t win_iocp_io_context::poll(boost::system::error_code& ec)
 {
   if (::InterlockedExchangeAdd(&outstanding_work_, 0) == 0)
   {
     stop();
     ec = boost::system::error_code();
     return 0;
   }
 
   win_iocp_thread_info this_thread;
   thread_call_stack::context ctx(this, this_thread);
 
   size_t n = 0;
   while (do_one(0, this_thread, ec))
     if (n != (std::numeric_limits<size_t>::max)())
       ++n;
   return n;
 }
 
 size_t win_iocp_io_context::poll_one(boost::system::error_code& ec)
 {
   if (::InterlockedExchangeAdd(&outstanding_work_, 0) == 0)
   {
     stop();
     ec = boost::system::error_code();
     return 0;
   }
 
   win_iocp_thread_info this_thread;
   thread_call_stack::context ctx(this, this_thread);
 
   return do_one(0, this_thread, ec);
 }
 
 void win_iocp_io_context::stop()
 {
   if (::InterlockedExchange(&stopped_, 1) == 0)
   {
     if (::InterlockedExchange(&stop_event_posted_, 1) == 0)
     {
       if (!::PostQueuedCompletionStatus(iocp_.handle, 0, 0, 0))
       {
         DWORD last_error = ::GetLastError();
         boost::system::error_code ec(last_error,
             boost::asio::error::get_system_category());
         boost::asio::detail::throw_error(ec, "pqcs");
       }
     }
   }
 }
 
 bool win_iocp_io_context::can_dispatch()
 {
   return thread_call_stack::contains(this) != 0;
 }
 
 void win_iocp_io_context::capture_current_exception()
 {
   if (thread_info_base* this_thread = thread_call_stack::contains(this))
     this_thread->capture_current_exception();
 }
 
 void win_iocp_io_context::post_deferred_completion(win_iocp_operation* op)
 {
   // Flag the operation as ready.
   op->ready_ = 1;
 
   // Enqueue the operation on the I/O completion port.
   if (!::PostQueuedCompletionStatus(iocp_.handle, 0, 0, op))
   {
     // Out of resources. Put on completed queue instead.
     mutex::scoped_lock lock(dispatch_mutex_);
     completed_ops_.push(op);
     ::InterlockedExchange(&dispatch_required_, 1);
   }
 }
 
 void win_iocp_io_context::post_deferred_completions(
     op_queue<win_iocp_operation>& ops)
 {
   while (win_iocp_operation* op = ops.front())
   {
     ops.pop();
 
     // Flag the operation as ready.
     op->ready_ = 1;
 
     // Enqueue the operation on the I/O completion port.
     if (!::PostQueuedCompletionStatus(iocp_.handle, 0, 0, op))
     {
       // Out of resources. Put on completed queue instead.
       mutex::scoped_lock lock(dispatch_mutex_);
       completed_ops_.push(op);
       completed_ops_.push(ops);
       ::InterlockedExchange(&dispatch_required_, 1);
     }
   }
 }
 
 void win_iocp_io_context::abandon_operations(
     op_queue<win_iocp_operation>& ops)
 {
   while (win_iocp_operation* op = ops.front())
   {
     ops.pop();
     ::InterlockedDecrement(&outstanding_work_);
     op->destroy();
   }
 }
 
 void win_iocp_io_context::on_pending(win_iocp_operation* op)
 {
   if (::InterlockedCompareExchange(&op->ready_, 1, 0) == 1)
   {
     // Enqueue the operation on the I/O completion port.
     if (!::PostQueuedCompletionStatus(iocp_.handle,
           0, overlapped_contains_result, op))
     {
       // Out of resources. Put on completed queue instead.
       mutex::scoped_lock lock(dispatch_mutex_);
       completed_ops_.push(op);
       ::InterlockedExchange(&dispatch_required_, 1);
     }
   }
 }
 
 void win_iocp_io_context::on_completion(win_iocp_operation* op,
     DWORD last_error, DWORD bytes_transferred)
 {
   // Flag that the operation is ready for invocation.
   op->ready_ = 1;
 
   // Store results in the OVERLAPPED structure.
   op->Internal = reinterpret_cast<ulong_ptr_t>(
       &boost::asio::error::get_system_category());
   op->Offset = last_error;
   op->OffsetHigh = bytes_transferred;
 
   // Enqueue the operation on the I/O completion port.
   if (!::PostQueuedCompletionStatus(iocp_.handle,
         0, overlapped_contains_result, op))
   {
     // Out of resources. Put on completed queue instead.
     mutex::scoped_lock lock(dispatch_mutex_);
     completed_ops_.push(op);
     ::InterlockedExchange(&dispatch_required_, 1);
   }
 }
 
 void win_iocp_io_context::on_completion(win_iocp_operation* op,
     const boost::system::error_code& ec, DWORD bytes_transferred)
 {
   // Flag that the operation is ready for invocation.
   op->ready_ = 1;
 
   // Store results in the OVERLAPPED structure.
   op->Internal = reinterpret_cast<ulong_ptr_t>(&ec.category());
   op->Offset = ec.value();
   op->OffsetHigh = bytes_transferred;
 
   // Enqueue the operation on the I/O completion port.
   if (!::PostQueuedCompletionStatus(iocp_.handle,
         0, overlapped_contains_result, op))
   {
     // Out of resources. Put on completed queue instead.
     mutex::scoped_lock lock(dispatch_mutex_);
     completed_ops_.push(op);
     ::InterlockedExchange(&dispatch_required_, 1);
   }
 }
 
 size_t win_iocp_io_context::do_one(DWORD msec,
     win_iocp_thread_info& this_thread, boost::system::error_code& ec)
 {
   for (;;)
   {
     // Try to acquire responsibility for dispatching timers and completed ops.
     if (::InterlockedCompareExchange(&dispatch_required_, 0, 1) == 1)
     {
       mutex::scoped_lock lock(dispatch_mutex_);
 
       // Dispatch pending timers and operations.
       op_queue<win_iocp_operation> ops;
       ops.push(completed_ops_);
       timer_queues_.get_ready_timers(ops);
       post_deferred_completions(ops);
       update_timeout();
     }
 
     // Get the next operation from the queue.
     DWORD bytes_transferred = 0;
     dword_ptr_t completion_key = 0;
     LPOVERLAPPED overlapped = 0;
     ::SetLastError(0);
     BOOL ok = ::GetQueuedCompletionStatus(iocp_.handle,
         &bytes_transferred, &completion_key, &overlapped,
         msec < gqcs_timeout_ ? msec : gqcs_timeout_);
     DWORD last_error = ::GetLastError();
 
     if (overlapped)
     {
       win_iocp_operation* op = static_cast<win_iocp_operation*>(overlapped);
       boost::system::error_code result_ec(last_error,
           boost::asio::error::get_system_category());
 
       // We may have been passed the last_error and bytes_transferred in the
       // OVERLAPPED structure itself.
       if (completion_key == overlapped_contains_result)
       {
         result_ec = boost::system::error_code(static_cast<int>(op->Offset),
             *reinterpret_cast<boost::system::error_category*>(op->Internal));
         bytes_transferred = op->OffsetHigh;
       }
 
       // Otherwise ensure any result has been saved into the OVERLAPPED
       // structure.
       else
       {
         op->Internal = reinterpret_cast<ulong_ptr_t>(&result_ec.category());
         op->Offset = result_ec.value();
         op->OffsetHigh = bytes_transferred;
       }
 
       // Dispatch the operation only if ready. The operation may not be ready
       // if the initiating function (e.g. a call to WSARecv) has not yet
       // returned. This is because the initiating function still wants access
       // to the operation's OVERLAPPED structure.
       if (::InterlockedCompareExchange(&op->ready_, 1, 0) == 1)
       {
         // Ensure the count of outstanding work is decremented on block exit.
         work_finished_on_block_exit on_exit = { this };
         (void)on_exit;
 
         op->complete(this, result_ec, bytes_transferred);
         this_thread.rethrow_pending_exception();
         ec = boost::system::error_code();
         return 1;
       }
     }
     else if (!ok)
     {
       if (last_error != WAIT_TIMEOUT)
       {
         ec = boost::system::error_code(last_error,
             boost::asio::error::get_system_category());
         return 0;
       }
 
       // If we're waiting indefinitely we need to keep going until we get a
       // real handler.
       if (msec == INFINITE)
         continue;
 
       ec = boost::system::error_code();
       return 0;
     }
     else if (completion_key == wake_for_dispatch)
     {
       // We have been woken up to try to acquire responsibility for dispatching
       // timers and completed operations.
     }
     else
     {
       // Indicate that there is no longer an in-flight stop event.
       ::InterlockedExchange(&stop_event_posted_, 0);
 
       // The stopped_ flag is always checked to ensure that any leftover
       // stop events from a previous run invocation are ignored.
       if (::InterlockedExchangeAdd(&stopped_, 0) != 0)
       {
         // Wake up next thread that is blocked on GetQueuedCompletionStatus.
         if (::InterlockedExchange(&stop_event_posted_, 1) == 0)
         {
           if (!::PostQueuedCompletionStatus(iocp_.handle, 0, 0, 0))
           {
             last_error = ::GetLastError();
             ec = boost::system::error_code(last_error,
                 boost::asio::error::get_system_category());
             return 0;
           }
         }
 
         ec = boost::system::error_code();
         return 0;
       }
     }
   }
 }
 
 DWORD win_iocp_io_context::get_gqcs_timeout()
 {
 #if !defined(_WIN32_WINNT) || (_WIN32_WINNT < 0x0600)
   OSVERSIONINFOEX osvi;
   ZeroMemory(&osvi, sizeof(osvi));
   osvi.dwOSVersionInfoSize = sizeof(osvi);
   osvi.dwMajorVersion = 6ul;
 
   const uint64_t condition_mask = ::VerSetConditionMask(
       0, VER_MAJORVERSION, VER_GREATER_EQUAL);
 
   if (!!::VerifyVersionInfo(&osvi, VER_MAJORVERSION, condition_mask))
     return INFINITE;
 
   return default_gqcs_timeout;
 #else // !defined(_WIN32_WINNT) || (_WIN32_WINNT < 0x0600)
   return INFINITE;
 #endif // !defined(_WIN32_WINNT) || (_WIN32_WINNT < 0x0600)
 }
 
 void win_iocp_io_context::do_add_timer_queue(timer_queue_base& queue)
 {
   mutex::scoped_lock lock(dispatch_mutex_);
 
   timer_queues_.insert(&queue);
 
   if (!waitable_timer_.handle)
   {
     waitable_timer_.handle = ::CreateWaitableTimer(0, FALSE, 0);
     if (waitable_timer_.handle == 0)
     {
       DWORD last_error = ::GetLastError();
       boost::system::error_code ec(last_error,
           boost::asio::error::get_system_category());
       boost::asio::detail::throw_error(ec, "timer");
     }
 
     LARGE_INTEGER timeout;
     timeout.QuadPart = -max_timeout_usec;
     timeout.QuadPart *= 10;
     ::SetWaitableTimer(waitable_timer_.handle,
         &timeout, max_timeout_msec, 0, 0, FALSE);
   }
 
   if (!timer_thread_.get())
   {
     timer_thread_function thread_function = { this };
     timer_thread_.reset(new thread(thread_function, 65536));
   }
 }
 
 void win_iocp_io_context::do_remove_timer_queue(timer_queue_base& queue)
 {
   mutex::scoped_lock lock(dispatch_mutex_);
 
   timer_queues_.erase(&queue);
 }
 
 void win_iocp_io_context::update_timeout()
 {
   if (timer_thread_.get())
   {
     // There's no point updating the waitable timer if the new timeout period
     // exceeds the maximum timeout. In that case, we might as well wait for the
     // existing period of the timer to expire.
     long timeout_usec = timer_queues_.wait_duration_usec(max_timeout_usec);
     if (timeout_usec < max_timeout_usec)
     {
       LARGE_INTEGER timeout;
       timeout.QuadPart = -timeout_usec;
       timeout.QuadPart *= 10;
       ::SetWaitableTimer(waitable_timer_.handle,
           &timeout, max_timeout_msec, 0, 0, FALSE);
     }
   }
 }
 
 } // namespace detail
 } // namespace asio
 } // namespace boost
 
 #include <boost/asio/detail/pop_options.hpp>
 
 #endif // defined(BOOST_ASIO_HAS_IOCP)
 
 #endif // BOOST_ASIO_DETAIL_IMPL_WIN_IOCP_IO_CONTEXT_IPP

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