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include/asio/detail/win_iocp_io_context.hpp

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+//
+// detail/win_iocp_io_context.hpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// 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 ASIO_DETAIL_WIN_IOCP_IO_CONTEXT_HPP
+#define ASIO_DETAIL_WIN_IOCP_IO_CONTEXT_HPP
+
+#if defined(_MSC_VER) && (_MSC_VER >= 1200)
+# pragma once
+#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
+
+#include "asio/detail/config.hpp"
+
+#if defined(ASIO_HAS_IOCP)
+
+#include "asio/detail/limits.hpp"
+#include "asio/detail/mutex.hpp"
+#include "asio/detail/op_queue.hpp"
+#include "asio/detail/socket_types.hpp"
+#include "asio/detail/thread.hpp"
+#include "asio/detail/thread_context.hpp"
+#include "asio/detail/timer_queue_base.hpp"
+#include "asio/detail/timer_queue_set.hpp"
+#include "asio/detail/wait_op.hpp"
+#include "asio/detail/win_iocp_operation.hpp"
+#include "asio/detail/win_iocp_thread_info.hpp"
+#include "asio/execution_context.hpp"
+
+#include "asio/detail/push_options.hpp"
+
+namespace asio {
+namespace detail {
+
+class wait_op;
+
+class win_iocp_io_context
+  : public execution_context_service_base<win_iocp_io_context>,
+    public thread_context
+{
+public:
+  // Tag type used for constructing as an internal scheduler.
+  struct internal {};
+
+  // Constructor.
+  ASIO_DECL win_iocp_io_context(
+      asio::execution_context& ctx, bool own_thread = true);
+
+  // Construct as an internal scheduler.
+  ASIO_DECL win_iocp_io_context(internal,
+      asio::execution_context& ctx);
+
+  // Destructor.
+  ASIO_DECL ~win_iocp_io_context();
+
+  // Destroy all user-defined handler objects owned by the service.
+  ASIO_DECL void shutdown();
+
+  // Initialise the task. Nothing to do here.
+  void init_task()
+  {
+  }
+
+  // Register a handle with the IO completion port.
+  ASIO_DECL asio::error_code register_handle(
+      HANDLE handle, asio::error_code& ec);
+
+  // Run the event loop until stopped or no more work.
+  ASIO_DECL size_t run(asio::error_code& ec);
+
+  // Run until stopped or one operation is performed.
+  ASIO_DECL size_t run_one(asio::error_code& ec);
+
+  // Run until timeout, interrupted, or one operation is performed.
+  ASIO_DECL size_t wait_one(long usec, asio::error_code& ec);
+
+  // Poll for operations without blocking.
+  ASIO_DECL size_t poll(asio::error_code& ec);
+
+  // Poll for one operation without blocking.
+  ASIO_DECL size_t poll_one(asio::error_code& ec);
+
+  // Stop the event processing loop.
+  ASIO_DECL void stop();
+
+  // Determine whether the io_context is stopped.
+  bool stopped() const
+  {
+    return ::InterlockedExchangeAdd(&stopped_, 0) != 0;
+  }
+
+  // Restart in preparation for a subsequent run invocation.
+  void restart()
+  {
+    ::InterlockedExchange(&stopped_, 0);
+  }
+
+  // Notify that some work has started.
+  void work_started()
+  {
+    ::InterlockedIncrement(&outstanding_work_);
+  }
+
+  // Notify that some work has finished.
+  void work_finished()
+  {
+    if (::InterlockedDecrement(&outstanding_work_) == 0)
+      stop();
+  }
+
+  // Return whether a handler can be dispatched immediately.
+  ASIO_DECL bool can_dispatch();
+
+  /// Capture the current exception so it can be rethrown from a run function.
+  ASIO_DECL void capture_current_exception();
+
+  // Request invocation of the given operation and return immediately. Assumes
+  // that work_started() has not yet been called for the operation.
+  void post_immediate_completion(win_iocp_operation* op, bool)
+  {
+    work_started();
+    post_deferred_completion(op);
+  }
+
+  // Request invocation of the given operation and return immediately. Assumes
+  // that work_started() was previously called for the operation.
+  ASIO_DECL void post_deferred_completion(win_iocp_operation* op);
+
+  // Request invocation of the given operation and return immediately. Assumes
+  // that work_started() was previously called for the operations.
+  ASIO_DECL void post_deferred_completions(
+      op_queue<win_iocp_operation>& ops);
+
+  // Request invocation of the given operation using the thread-private queue
+  // and return immediately. Assumes that work_started() has not yet been
+  // called for the operation.
+  void post_private_immediate_completion(win_iocp_operation* op)
+  {
+    post_immediate_completion(op, false);
+  }
+
+  // Request invocation of the given operation using the thread-private queue
+  // and return immediately. Assumes that work_started() was previously called
+  // for the operation.
+  void post_private_deferred_completion(win_iocp_operation* op)
+  {
+    post_deferred_completion(op);
+  }
+
+  // Enqueue the given operation following a failed attempt to dispatch the
+  // operation for immediate invocation.
+  void do_dispatch(operation* op)
+  {
+    post_immediate_completion(op, false);
+  }
+
+  // Process unfinished operations as part of a shutdown operation. Assumes
+  // that work_started() was previously called for the operations.
+  ASIO_DECL void abandon_operations(op_queue<operation>& ops);
+
+  // Called after starting an overlapped I/O operation that did not complete
+  // immediately. The caller must have already called work_started() prior to
+  // starting the operation.
+  ASIO_DECL void on_pending(win_iocp_operation* op);
+
+  // Called after starting an overlapped I/O operation that completed
+  // immediately. The caller must have already called work_started() prior to
+  // starting the operation.
+  ASIO_DECL void on_completion(win_iocp_operation* op,
+      DWORD last_error = 0, DWORD bytes_transferred = 0);
+
+  // Called after starting an overlapped I/O operation that completed
+  // immediately. The caller must have already called work_started() prior to
+  // starting the operation.
+  ASIO_DECL void on_completion(win_iocp_operation* op,
+      const asio::error_code& ec, DWORD bytes_transferred = 0);
+
+  // Add a new timer queue to the service.
+  template <typename TimeTraits, typename Allocator>
+  void add_timer_queue(timer_queue<TimeTraits, Allocator>& timer_queue);
+
+  // Remove a timer queue from the service.
+  template <typename TimeTraits, typename Allocator>
+  void remove_timer_queue(timer_queue<TimeTraits, Allocator>& timer_queue);
+
+  // Schedule a new operation in the given timer queue to expire at the
+  // specified absolute time.
+  template <typename TimeTraits, typename Allocator>
+  void schedule_timer(timer_queue<TimeTraits, Allocator>& queue,
+      const typename TimeTraits::time_type& time,
+      typename timer_queue<TimeTraits, Allocator>::per_timer_data& timer,
+      wait_op* op);
+
+  // Cancel the timer associated with the given token. Returns the number of
+  // handlers that have been posted or dispatched.
+  template <typename TimeTraits, typename Allocator>
+  std::size_t cancel_timer(timer_queue<TimeTraits, Allocator>& queue,
+      typename timer_queue<TimeTraits, Allocator>::per_timer_data& timer,
+      std::size_t max_cancelled = (std::numeric_limits<std::size_t>::max)());
+
+  // Cancel the timer operations associated with the given key.
+  template <typename TimeTraits, typename Allocator>
+  void cancel_timer_by_key(timer_queue<TimeTraits, Allocator>& queue,
+      typename timer_queue<TimeTraits, Allocator>::per_timer_data* timer,
+      void* cancellation_key);
+
+  // Move the timer operations associated with the given timer.
+  template <typename TimeTraits, typename Allocator>
+  void move_timer(timer_queue<TimeTraits, Allocator>& queue,
+      typename timer_queue<TimeTraits, Allocator>::per_timer_data& to,
+      typename timer_queue<TimeTraits, Allocator>::per_timer_data& from);
+
+private:
+#if defined(WINVER) && (WINVER < 0x0500)
+  typedef DWORD dword_ptr_t;
+  typedef ULONG ulong_ptr_t;
+#else // defined(WINVER) && (WINVER < 0x0500)
+  typedef DWORD_PTR dword_ptr_t;
+  typedef ULONG_PTR ulong_ptr_t;
+#endif // defined(WINVER) && (WINVER < 0x0500)
+
+  // Dequeues at most one operation from the I/O completion port, and then
+  // executes it. Returns the number of operations that were dequeued (i.e.
+  // either 0 or 1).
+  ASIO_DECL size_t do_one(DWORD msec,
+      win_iocp_thread_info& this_thread, asio::error_code& ec);
+
+  // Helper to calculate the GetQueuedCompletionStatus timeout.
+  ASIO_DECL static DWORD get_gqcs_timeout();
+
+  // Helper function to add a new timer queue.
+  ASIO_DECL void do_add_timer_queue(timer_queue_base& queue);
+
+  // Helper function to remove a timer queue.
+  ASIO_DECL void do_remove_timer_queue(timer_queue_base& queue);
+
+  // Called to recalculate and update the timeout.
+  ASIO_DECL void update_timeout();
+
+  // Helper class to call work_finished() on block exit.
+  struct work_finished_on_block_exit;
+
+  // Helper class for managing a HANDLE.
+  struct auto_handle
+  {
+    HANDLE handle;
+    auto_handle() : handle(0) {}
+    ~auto_handle() { if (handle) ::CloseHandle(handle); }
+  };
+
+  // The IO completion port used for queueing operations.
+  auto_handle iocp_;
+
+  // The count of unfinished work.
+  long outstanding_work_;
+
+  // Flag to indicate whether the event loop has been stopped.
+  mutable long stopped_;
+
+  // Flag to indicate whether there is an in-flight stop event. Every event
+  // posted using PostQueuedCompletionStatus consumes non-paged pool, so to
+  // avoid exhausting this resource we limit the number of outstanding events.
+  long stop_event_posted_;
+
+  // Flag to indicate whether the service has been shut down.
+  long shutdown_;
+
+  enum
+  {
+#if !defined(_WIN32_WINNT) || (_WIN32_WINNT < 0x0600)
+    // Timeout to use with GetQueuedCompletionStatus on older versions of
+    // Windows. Some versions of windows have a "bug" where a call to
+    // GetQueuedCompletionStatus can appear stuck even though there are events
+    // waiting on the queue. Using a timeout helps to work around the issue.
+    default_gqcs_timeout = 500,
+#endif // !defined(_WIN32_WINNT) || (_WIN32_WINNT < 0x0600)
+
+    // Maximum waitable timer timeout, in milliseconds.
+    max_timeout_msec = 5 * 60 * 1000,
+
+    // Maximum waitable timer timeout, in microseconds.
+    max_timeout_usec = max_timeout_msec * 1000,
+
+    // Completion key value used to wake up a thread to dispatch timers or
+    // completed operations.
+    wake_for_dispatch = 1,
+
+    // Completion key value to indicate that an operation has posted with the
+    // original last_error and bytes_transferred values stored in the fields of
+    // the OVERLAPPED structure.
+    overlapped_contains_result = 2
+  };
+
+  // Timeout to use with GetQueuedCompletionStatus.
+  const DWORD gqcs_timeout_;
+
+  // Helper class to run the scheduler in its own thread.
+  struct thread_function;
+  friend struct thread_function;
+
+  // Function object for processing timeouts in a background thread.
+  struct timer_thread_function;
+  friend struct timer_thread_function;
+
+  // Background thread used for processing timeouts.
+  asio::detail::thread timer_thread_;
+
+  // A waitable timer object used for waiting for timeouts.
+  auto_handle waitable_timer_;
+
+  // Non-zero if timers or completed operations need to be dispatched.
+  long dispatch_required_;
+
+  // Mutex for protecting access to the timer queues and completed operations.
+  mutex dispatch_mutex_;
+
+  // The timer queues.
+  timer_queue_set timer_queues_;
+
+  // The operations that are ready to dispatch.
+  op_queue<win_iocp_operation> completed_ops_;
+
+  // The concurrency hint used to initialise the io_context.
+  const int concurrency_hint_;
+
+  // The thread that is running the io_context.
+  asio::detail::thread thread_;
+};
+
+} // namespace detail
+} // namespace asio
+
+#include "asio/detail/pop_options.hpp"
+
+#include "asio/detail/impl/win_iocp_io_context.hpp"
+#if defined(ASIO_HEADER_ONLY)
+# include "asio/detail/impl/win_iocp_io_context.ipp"
+#endif // defined(ASIO_HEADER_ONLY)
+
+#endif // defined(ASIO_HAS_IOCP)
+
+#endif // ASIO_DETAIL_WIN_IOCP_IO_CONTEXT_HPP