ceph/src/common/async/yield_context.h

   1 // -*- mode:C++; tab-width:8; c-basic-offset:2; indent-tabs-mode:t -*-
   2 // vim: ts=8 sw=2 smarttab
   3 /*
   4  * Ceph - scalable distributed file system
   5  *
   6  * Copyright (C) 2018 Red Hat, Inc
   7  *
   8  * This is free software; you can redistribute it and/or
   9  * modify it under the terms of the GNU Lesser General Public
  10  * License version 2.1, as published by the Free Software
  11  * Foundation.  See file COPYING.
  12  *
  13  */
  14
  15 #pragma once
  16
  17 #include <boost/range/begin.hpp>
  18 #include <boost/range/end.hpp>
  19 #include <boost/asio/io_context.hpp>
  20
  21 #include "acconfig.h"
  22
  23 #include <spawn/spawn.hpp>
  24
  25 // use explicit executor types instead of the type-erased boost::asio::executor.
  26 // coroutines wrap the default io_context executor with a strand executor
  27 using yield_context = spawn::basic_yield_context<
  28     boost::asio::executor_binder<void(*)(),
  29         boost::asio::strand<boost::asio::io_context::executor_type>>>;
  30
  31 /// optional-like wrapper for a spawn::yield_context and its associated
  32 /// boost::asio::io_context. operations that take an optional_yield argument
  33 /// will, when passed a non-empty yield context, suspend this coroutine instead
  34 /// of the blocking the thread of execution
  35 class optional_yield {
  36   boost::asio::io_context *c = nullptr;
  37   yield_context *y = nullptr;
  38  public:
  39   /// construct with a valid io and yield_context
  40   explicit optional_yield(boost::asio::io_context& c,
  41                           yield_context& y) noexcept
  42     : c(&c), y(&y) {}
  43
  44   /// type tag to construct an empty object
  45   struct empty_t {};
  46   optional_yield(empty_t) noexcept {}
  47
  48   /// implicit conversion to bool, returns true if non-empty
  49   operator bool() const noexcept { return y; }
  50
  51   /// return a reference to the associated io_context. only valid if non-empty
  52   boost::asio::io_context& get_io_context() const noexcept { return *c; }
  53
  54   /// return a reference to the yield_context. only valid if non-empty
  55   yield_context& get_yield_context() const noexcept { return *y; }
  56 };
  57
  58 // type tag object to construct an empty optional_yield
  59 static constexpr optional_yield::empty_t null_yield{};