libcxx/include/__coroutine/noop_coroutine_handle.h

   1 //===----------------------------------------------------------------------===//
   2 //
   3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
   4 // See https://llvm.org/LICENSE.txt for license information.
   5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   6 //
   7 //===----------------------------------------------------------------------===//
   8
   9 #ifndef _LIBCPP___COROUTINE_NOOP_COROUTINE_HANDLE_H
  10 #define _LIBCPP___COROUTINE_NOOP_COROUTINE_HANDLE_H
  11
  12 #include <__config>
  13 #include <__coroutine/coroutine_handle.h>
  14
  15 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
  16 #  pragma GCC system_header
  17 #endif
  18
  19 #if _LIBCPP_STD_VER >= 20
  20
  21 _LIBCPP_BEGIN_NAMESPACE_STD
  22
  23 #if __has_builtin(__builtin_coro_noop) || defined(_LIBCPP_COMPILER_GCC)
  24
  25 // [coroutine.noop]
  26 // [coroutine.promise.noop]
  27 struct noop_coroutine_promise {};
  28
  29 // [coroutine.handle.noop]
  30 template <>
  31 struct _LIBCPP_TEMPLATE_VIS coroutine_handle<noop_coroutine_promise> {
  32 public:
  33     // [coroutine.handle.noop.conv], conversion
  34     _LIBCPP_HIDE_FROM_ABI
  35     constexpr operator coroutine_handle<>() const noexcept {
  36         return coroutine_handle<>::from_address(address());
  37     }
  38
  39     // [coroutine.handle.noop.observers], observers
  40     _LIBCPP_HIDE_FROM_ABI
  41     constexpr explicit operator bool() const noexcept { return true; }
  42     _LIBCPP_HIDE_FROM_ABI
  43     constexpr bool done() const noexcept { return false; }
  44
  45     // [coroutine.handle.noop.resumption], resumption
  46     _LIBCPP_HIDE_FROM_ABI
  47     constexpr void operator()() const noexcept {}
  48     _LIBCPP_HIDE_FROM_ABI
  49     constexpr void resume() const noexcept {}
  50     _LIBCPP_HIDE_FROM_ABI
  51     constexpr void destroy() const noexcept {}
  52
  53     // [coroutine.handle.noop.promise], promise access
  54     _LIBCPP_HIDE_FROM_ABI
  55     noop_coroutine_promise& promise() const noexcept {
  56         return *static_cast<noop_coroutine_promise*>(
  57             __builtin_coro_promise(this->__handle_, alignof(noop_coroutine_promise), false));
  58     }
  59
  60     // [coroutine.handle.noop.address], address
  61     _LIBCPP_HIDE_FROM_ABI
  62     constexpr void* address() const noexcept { return __handle_; }
  63
  64 private:
  65     _LIBCPP_HIDE_FROM_ABI
  66     friend coroutine_handle<noop_coroutine_promise> noop_coroutine() noexcept;
  67
  68 #if __has_builtin(__builtin_coro_noop)
  69     _LIBCPP_HIDE_FROM_ABI coroutine_handle() noexcept {
  70         this->__handle_ = __builtin_coro_noop();
  71     }
  72
  73     void* __handle_ = nullptr;
  74
  75 #elif defined(_LIBCPP_COMPILER_GCC)
  76     // GCC doesn't implement __builtin_coro_noop().
  77     // Construct the coroutine frame manually instead.
  78     struct __noop_coroutine_frame_ty_ {
  79         static void __dummy_resume_destroy_func() { }
  80
  81         void (*__resume_)() = __dummy_resume_destroy_func;
  82         void (*__destroy_)() = __dummy_resume_destroy_func;
  83         struct noop_coroutine_promise __promise_;
  84     };
  85
  86     static __noop_coroutine_frame_ty_ __noop_coroutine_frame_;
  87
  88     void* __handle_ = &__noop_coroutine_frame_;
  89
  90     _LIBCPP_HIDE_FROM_ABI coroutine_handle() noexcept = default;
  91
  92 #endif // __has_builtin(__builtin_coro_noop)
  93 };
  94
  95 using noop_coroutine_handle = coroutine_handle<noop_coroutine_promise>;
  96
  97 #if defined(_LIBCPP_COMPILER_GCC)
  98 inline noop_coroutine_handle::__noop_coroutine_frame_ty_
  99     noop_coroutine_handle::__noop_coroutine_frame_{};
 100 #endif
 101
 102 // [coroutine.noop.coroutine]
 103 inline _LIBCPP_HIDE_FROM_ABI
 104 noop_coroutine_handle noop_coroutine() noexcept { return noop_coroutine_handle(); }
 105
 106 #endif // __has_builtin(__builtin_coro_noop) || defined(_LIBCPP_COMPILER_GCC)
 107
 108 _LIBCPP_END_NAMESPACE_STD
 109
 110 #endif // __LIBCPP_STD_VER >= 20
 111
 112 #endif // _LIBCPP___COROUTINE_NOOP_COROUTINE_HANDLE_H