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include/asio/detail/scheduler.hpp

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+//
+// detail/scheduler.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_SCHEDULER_HPP
+#define ASIO_DETAIL_SCHEDULER_HPP
+
+#if defined(_MSC_VER) && (_MSC_VER >= 1200)
+# pragma once
+#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
+
+#include "asio/detail/config.hpp"
+
+#include "asio/error_code.hpp"
+#include "asio/execution_context.hpp"
+#include "asio/detail/atomic_count.hpp"
+#include "asio/detail/conditionally_enabled_event.hpp"
+#include "asio/detail/conditionally_enabled_mutex.hpp"
+#include "asio/detail/op_queue.hpp"
+#include "asio/detail/scheduler_operation.hpp"
+#include "asio/detail/scheduler_task.hpp"
+#include "asio/detail/thread.hpp"
+#include "asio/detail/thread_context.hpp"
+
+#include "asio/detail/push_options.hpp"
+
+namespace asio {
+namespace detail {
+
+struct scheduler_thread_info;
+
+class scheduler
+  : public execution_context_service_base<scheduler>,
+    public thread_context
+{
+public:
+  typedef scheduler_operation operation;
+
+  // Tag type used for constructing as an internal scheduler.
+  struct internal {};
+
+  // The type of a function used to obtain a task instance.
+  typedef scheduler_task* (*get_task_func_type)(
+      asio::execution_context&);
+
+  // Constructor.
+  ASIO_DECL scheduler(asio::execution_context& ctx,
+      bool own_thread = true,
+      get_task_func_type get_task = &scheduler::get_default_task);
+
+  // Construct as an internal scheduler.
+  ASIO_DECL scheduler(internal, asio::execution_context& ctx);
+
+  // Destructor.
+  ASIO_DECL ~scheduler();
+
+  // Destroy all user-defined handler objects owned by the service.
+  ASIO_DECL void shutdown();
+
+  // Initialise the task, if required.
+  ASIO_DECL void init_task();
+
+  // Run the event loop until interrupted or no more work.
+  ASIO_DECL std::size_t run(asio::error_code& ec);
+
+  // Run until interrupted or one operation is performed.
+  ASIO_DECL std::size_t run_one(asio::error_code& ec);
+
+  // Run until timeout, interrupted, or one operation is performed.
+  ASIO_DECL std::size_t wait_one(
+      long usec, asio::error_code& ec);
+
+  // Poll for operations without blocking.
+  ASIO_DECL std::size_t poll(asio::error_code& ec);
+
+  // Poll for one operation without blocking.
+  ASIO_DECL std::size_t poll_one(asio::error_code& ec);
+
+  // Interrupt the event processing loop.
+  ASIO_DECL void stop();
+
+  // Determine whether the scheduler is stopped.
+  ASIO_DECL bool stopped() const;
+
+  // Restart in preparation for a subsequent run invocation.
+  ASIO_DECL void restart();
+
+  // Notify that some work has started.
+  void work_started()
+  {
+    ++outstanding_work_;
+  }
+
+  // Used to compensate for a forthcoming work_finished call. Must be called
+  // from within a scheduler-owned thread.
+  ASIO_DECL void compensating_work_started();
+
+  // Notify that some work has finished.
+  void work_finished()
+  {
+    if (--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.
+  ASIO_DECL void post_immediate_completion(
+      operation* op, bool is_continuation);
+
+  // Request invocation of the given operations and return immediately. Assumes
+  // that work_started() has not yet been called for the operations.
+  ASIO_DECL void post_immediate_completions(std::size_t n,
+      op_queue<operation>& ops, bool is_continuation);
+
+  // 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(operation* op);
+
+  // Request invocation of the given operations and return immediately. Assumes
+  // that work_started() was previously called for each operation.
+  ASIO_DECL void post_deferred_completions(op_queue<operation>& ops);
+
+  // Enqueue the given operation following a failed attempt to dispatch the
+  // operation for immediate invocation.
+  ASIO_DECL void do_dispatch(operation* op);
+
+  // Process unfinished operations as part of a shutdownoperation. Assumes that
+  // work_started() was previously called for the operations.
+  ASIO_DECL void abandon_operations(op_queue<operation>& ops);
+
+private:
+  // The mutex type used by this scheduler.
+  typedef conditionally_enabled_mutex mutex;
+
+  // The event type used by this scheduler.
+  typedef conditionally_enabled_event event;
+
+  // Structure containing thread-specific data.
+  typedef scheduler_thread_info thread_info;
+
+  // Run at most one operation. May block.
+  ASIO_DECL std::size_t do_run_one(mutex::scoped_lock& lock,
+      thread_info& this_thread, const asio::error_code& ec);
+
+  // Run at most one operation with a timeout. May block.
+  ASIO_DECL std::size_t do_wait_one(mutex::scoped_lock& lock,
+      thread_info& this_thread, long usec, const asio::error_code& ec);
+
+  // Poll for at most one operation.
+  ASIO_DECL std::size_t do_poll_one(mutex::scoped_lock& lock,
+      thread_info& this_thread, const asio::error_code& ec);
+
+  // Stop the task and all idle threads.
+  ASIO_DECL void stop_all_threads(mutex::scoped_lock& lock);
+
+  // Wake a single idle thread, or the task, and always unlock the mutex.
+  ASIO_DECL void wake_one_thread_and_unlock(
+      mutex::scoped_lock& lock);
+
+  // Get the default task.
+  ASIO_DECL static scheduler_task* get_default_task(
+      asio::execution_context& ctx);
+
+  // Helper class to run the scheduler in its own thread.
+  class thread_function;
+  friend class thread_function;
+
+  // Helper class to perform task-related operations on block exit.
+  struct task_cleanup;
+  friend struct task_cleanup;
+
+  // Helper class to call work-related operations on block exit.
+  struct work_cleanup;
+  friend struct work_cleanup;
+
+  // Whether to optimise for single-threaded use cases.
+  const bool one_thread_;
+
+  // Mutex to protect access to internal data.
+  mutable mutex mutex_;
+
+  // Event to wake up blocked threads.
+  event wakeup_event_;
+
+  // The task to be run by this service.
+  scheduler_task* task_;
+
+  // The function used to get the task.
+  get_task_func_type get_task_;
+
+  // Operation object to represent the position of the task in the queue.
+  struct task_operation : operation
+  {
+    task_operation() : operation(0) {}
+  } task_operation_;
+
+  // Whether the task has been interrupted.
+  bool task_interrupted_;
+
+  // Flag to indicate that the dispatcher has been stopped.
+  bool stopped_;
+
+  // Flag to indicate that the dispatcher has been shut down.
+  bool shutdown_;
+
+  // The count of unfinished work.
+  atomic_count outstanding_work_;
+
+  // The queue of handlers that are ready to be delivered.
+  op_queue<operation> op_queue_;
+
+  // The time limit on running the scheduler task, in microseconds.
+  const long task_usec_;
+
+  // The time limit on waiting when the queue is empty, in microseconds.
+  const long wait_usec_;
+
+  // The thread that is running the scheduler.
+  asio::detail::thread thread_;
+};
+
+} // namespace detail
+} // namespace asio
+
+#include "asio/detail/pop_options.hpp"
+
+#if defined(ASIO_HEADER_ONLY)
+# include "asio/detail/impl/scheduler.ipp"
+#endif // defined(ASIO_HEADER_ONLY)
+
+#endif // ASIO_DETAIL_SCHEDULER_HPP