defer.hpp 5.0 KB

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  1. //
  2. // defer.hpp
  3. // ~~~~~~~~~
  4. //
  5. // Copyright (c) 2003-2021 Christopher M. Kohlhoff (chris at kohlhoff dot com)
  6. //
  7. // Distributed under the Boost Software License, Version 1.0. (See accompanying
  8. // file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
  9. //
  10. #ifndef BOOST_ASIO_DEFER_HPP
  11. #define BOOST_ASIO_DEFER_HPP
  12. #if defined(_MSC_VER) && (_MSC_VER >= 1200)
  13. # pragma once
  14. #endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
  15. #include <boost/asio/detail/config.hpp>
  16. #include <boost/asio/async_result.hpp>
  17. #include <boost/asio/detail/type_traits.hpp>
  18. #include <boost/asio/execution_context.hpp>
  19. #include <boost/asio/execution/executor.hpp>
  20. #include <boost/asio/is_executor.hpp>
  21. #include <boost/asio/detail/push_options.hpp>
  22. namespace boost {
  23. namespace asio {
  24. /// Submits a completion token or function object for execution.
  25. /**
  26. * This function submits an object for execution using the object's associated
  27. * executor. The function object is queued for execution, and is never called
  28. * from the current thread prior to returning from <tt>defer()</tt>.
  29. *
  30. * The use of @c defer(), rather than @ref post(), indicates the caller's
  31. * preference that the executor defer the queueing of the function object. This
  32. * may allow the executor to optimise queueing for cases when the function
  33. * object represents a continuation of the current call context.
  34. *
  35. * This function has the following effects:
  36. *
  37. * @li Constructs a function object handler of type @c Handler, initialized
  38. * with <tt>handler(forward<CompletionToken>(token))</tt>.
  39. *
  40. * @li Constructs an object @c result of type <tt>async_result<Handler></tt>,
  41. * initializing the object as <tt>result(handler)</tt>.
  42. *
  43. * @li Obtains the handler's associated executor object @c ex by performing
  44. * <tt>get_associated_executor(handler)</tt>.
  45. *
  46. * @li Obtains the handler's associated allocator object @c alloc by performing
  47. * <tt>get_associated_allocator(handler)</tt>.
  48. *
  49. * @li Performs <tt>ex.defer(std::move(handler), alloc)</tt>.
  50. *
  51. * @li Returns <tt>result.get()</tt>.
  52. */
  53. template <BOOST_ASIO_COMPLETION_TOKEN_FOR(void()) CompletionToken>
  54. BOOST_ASIO_INITFN_AUTO_RESULT_TYPE(CompletionToken, void()) defer(
  55. BOOST_ASIO_MOVE_ARG(CompletionToken) token);
  56. /// Submits a completion token or function object for execution.
  57. /**
  58. * This function submits an object for execution using the specified executor.
  59. * The function object is queued for execution, and is never called from the
  60. * current thread prior to returning from <tt>defer()</tt>.
  61. *
  62. * The use of @c defer(), rather than @ref post(), indicates the caller's
  63. * preference that the executor defer the queueing of the function object. This
  64. * may allow the executor to optimise queueing for cases when the function
  65. * object represents a continuation of the current call context.
  66. *
  67. * This function has the following effects:
  68. *
  69. * @li Constructs a function object handler of type @c Handler, initialized
  70. * with <tt>handler(forward<CompletionToken>(token))</tt>.
  71. *
  72. * @li Constructs an object @c result of type <tt>async_result<Handler></tt>,
  73. * initializing the object as <tt>result(handler)</tt>.
  74. *
  75. * @li Obtains the handler's associated executor object @c ex1 by performing
  76. * <tt>get_associated_executor(handler)</tt>.
  77. *
  78. * @li Creates a work object @c w by performing <tt>make_work(ex1)</tt>.
  79. *
  80. * @li Obtains the handler's associated allocator object @c alloc by performing
  81. * <tt>get_associated_allocator(handler)</tt>.
  82. *
  83. * @li Constructs a function object @c f with a function call operator that
  84. * performs <tt>ex1.dispatch(std::move(handler), alloc)</tt> followed by
  85. * <tt>w.reset()</tt>.
  86. *
  87. * @li Performs <tt>Executor(ex).defer(std::move(f), alloc)</tt>.
  88. *
  89. * @li Returns <tt>result.get()</tt>.
  90. */
  91. template <typename Executor,
  92. BOOST_ASIO_COMPLETION_TOKEN_FOR(void()) CompletionToken
  93. BOOST_ASIO_DEFAULT_COMPLETION_TOKEN_TYPE(Executor)>
  94. BOOST_ASIO_INITFN_AUTO_RESULT_TYPE(CompletionToken, void()) defer(
  95. const Executor& ex,
  96. BOOST_ASIO_MOVE_ARG(CompletionToken) token
  97. BOOST_ASIO_DEFAULT_COMPLETION_TOKEN(Executor),
  98. typename constraint<
  99. execution::is_executor<Executor>::value || is_executor<Executor>::value
  100. >::type = 0);
  101. /// Submits a completion token or function object for execution.
  102. /**
  103. * @returns <tt>defer(ctx.get_executor(), forward<CompletionToken>(token))</tt>.
  104. */
  105. template <typename ExecutionContext,
  106. BOOST_ASIO_COMPLETION_TOKEN_FOR(void()) CompletionToken
  107. BOOST_ASIO_DEFAULT_COMPLETION_TOKEN_TYPE(
  108. typename ExecutionContext::executor_type)>
  109. BOOST_ASIO_INITFN_AUTO_RESULT_TYPE(CompletionToken, void()) defer(
  110. ExecutionContext& ctx,
  111. BOOST_ASIO_MOVE_ARG(CompletionToken) token
  112. BOOST_ASIO_DEFAULT_COMPLETION_TOKEN(
  113. typename ExecutionContext::executor_type),
  114. typename constraint<is_convertible<
  115. ExecutionContext&, execution_context&>::value>::type = 0);
  116. } // namespace asio
  117. } // namespace boost
  118. #include <boost/asio/detail/pop_options.hpp>
  119. #include <boost/asio/impl/defer.hpp>
  120. #endif // BOOST_ASIO_DEFER_HPP