Mar*_*ang 5 c++ boost-asio asio c++20 c++-coroutine
我有一个库是使用cppcoro编写的，并希望将它与 ASIO 一起使用。但是每当我尝试co_spawn从所述库中使用协程时。Boost 抱怨 awaitable 类型不正确。
例如：
#include <asio/io_context.hpp>
#include <asio/coroutine.hpp>
#include <asio/co_spawn.hpp>
#include <asio/detached.hpp>
#include <asio/awaitable.hpp>
#include <cppcoro/task.hpp>
cppcoro::task<int> foo()
{
co_return 1;
}
int main()
{
asio::io_context ctx;
asio::co_spawn(ctx, foo(), asio::detached);
ctx.run();
}
Boost 抱怨cppcoro::task<int>并非源自asio::awaitable
asio_cppcoro.cpp: In function ‘int main()’:
asio_cppcoro.cpp:15:43: error: no matching function for call to ‘co_spawn(asio::io_context&, cppcoro::task<int>, const asio::detached_t&)’
15 | asio::co_spawn(ctx, foo(), asio::detached);
| ^
In file included from /usr/include/asio/co_spawn.hpp:467,
from asio_cppcoro.cpp:3:
/usr/include/asio/impl/co_spawn.hpp:199:1: note: candidate: ‘template<class Executor, class T, class AwaitableExecutor, class CompletionToken> requires completion_token_for<CompletionToken, void()> auto asio::co_spawn(const Executor&, asio::awaitable<T, AwaitableExecutor>, CompletionToken&&, typename std::enable_if<((asio::is_executor<Executor>::value || asio::execution::is_executor<T>::value) && std::is_convertible<Executor, AwaitableExecutor>::value)>::type*)’
199 | co_spawn(const Executor& ex,
| ^~~~~~~~
/usr/include/asio/impl/co_spawn.hpp:199:1: note: template argument deduction/substitution failed:
asio_cppcoro.cpp:15:43: note: ‘cppcoro::task<int>’ is not derived from ‘asio::awaitable<T, AwaitableExecutor>’
15 | asio::co_spawn(ctx, foo(), asio::detached);
我也尝试将我的协程包装在 a 中asio::awaitable，但没有成功。
asio_cppcoro.cpp: In function ‘int main()’:
asio_cppcoro.cpp:15:43: error: no matching function for call to ‘co_spawn(asio::io_context&, cppcoro::task<int>, const asio::detached_t&)’
15 | asio::co_spawn(ctx, foo(), asio::detached);
| ^
In file included from /usr/include/asio/co_spawn.hpp:467,
from asio_cppcoro.cpp:3:
/usr/include/asio/impl/co_spawn.hpp:199:1: note: candidate: ‘template<class Executor, class T, class AwaitableExecutor, class CompletionToken> requires completion_token_for<CompletionToken, void()> auto asio::co_spawn(const Executor&, asio::awaitable<T, AwaitableExecutor>, CompletionToken&&, typename std::enable_if<((asio::is_executor<Executor>::value || asio::execution::is_executor<T>::value) && std::is_convertible<Executor, AwaitableExecutor>::value)>::type*)’
199 | co_spawn(const Executor& ex,
| ^~~~~~~~
/usr/include/asio/impl/co_spawn.hpp:199:1: note: template argument deduction/substitution failed:
asio_cppcoro.cpp:15:43: note: ‘cppcoro::task<int>’ is not derived from ‘asio::awaitable<T, AwaitableExecutor>’
15 | asio::co_spawn(ctx, foo(), asio::detached);
编译器抱怨它不能将这两种类型包装在一起
? c++ asio_cppcoro.cpp -o asio_cppcoro -std=c++20 -fcoroutines
asio_cppcoro.cpp: In function ‘asio::awaitable<int> bar()’:
asio_cppcoro.cpp:15:25: error: no matching function for call to ‘asio::detail::awaitable_frame<int, asio::execution::any_executor<asio::execution::context_as_t<asio::execution_context&>, asio::execution::detail::blocking::never_t<0>, asio::execution::prefer_only<asio::execution::detail::blocking::possibly_t<0> >, asio::execution::prefer_only<asio::execution::detail::outstanding_work::tracked_t<0> >, asio::execution::prefer_only<asio::execution::detail::outstanding_work::untracked_t<0> >, asio::execution::prefer_only<asio::execution::detail::relationship::fork_t<0> >, asio::execution::prefer_only<asio::execution::detail::relationship::continuation_t<0> > > >::await_transform(cppcoro::task<int>)’
15 | co_return co_await foo();
| ^
In file included from /usr/include/asio/awaitable.hpp:129,
from /usr/include/asio/co_spawn.hpp:22,
from asio_cppcoro.cpp:3:
/usr/include/asio/impl/awaitable.hpp:150:8: note: candidate: ‘template<class T> auto asio::detail::awaitable_frame_base<Executor>::await_transform(asio::awaitable<T, Executor>) const [with T = T; Executor = asio::execution::any_executor<asio::execution::context_as_t<asio::execution_context&>, asio::execution::detail::blocking::never_t<0>, asio::execution::prefer_only<asio::execution::detail::blocking::possibly_t<0> >, asio::execution::prefer_only<asio::execution::detail::outstanding_work::tracked_t<0> >, asio::execution::prefer_only<asio::execution::detail::outstanding_work::untracked_t<0> >, asio::execution::prefer_only<asio::execution::detail::relationship::fork_t<0> >, asio::execution::prefer_only<asio::execution::detail::relationship::continuation_t<0> > >]’
150 | auto await_transform(awaitable<T, Executor> a) const
| ^~~~~~~~~~~~~~~
/usr/include/asio/impl/awaitable.hpp:150:8: note: template argument deduction/substitution failed:
asio_cppcoro.cpp:15:25: note: ‘cppcoro::task<int>’ is not derived from ‘asio::awaitable<T, asio::execution::any_executor<asio::execution::context_as_t<asio::execution_context&>, asio::execution::detail::blocking::never_t<0>, asio::execution::prefer_only<asio::execution::detail::blocking::possibly_t<0> >, asio::execution::prefer_only<asio::execution::detail::outstanding_work::tracked_t<0> >, asio::execution::prefer_only<asio::execution::detail::outstanding_work::untracked_t<0> >, asio::execution::prefer_only<asio::execution::detail::relationship::fork_t<0> >, asio::execution::prefer_only<asio::execution::detail::relationship::continuation_t<0> > > >’
15 | co_return co_await foo();
|
有没有办法cppcoro::task<>从 ASIO 的 io_context调用基于协程？另外，为什么会发生这种情况？AKAIF C++ 协程是无堆栈的，因此应该可以为任何协程实现生成新的堆栈帧。为什么ASIO阻止我这样做？
编译器：GCC 10.2 ASIO：1.18.1（不是 Boost ASIO。这是独立版本）
小智 4
不幸的是，asio 可等待对象和 cppcoro 可等待对象不能相互 co_await'ed。发生这种情况是因为 asio 可等待对象需要调用者和被调用者之间的合作来协调关闭/所有权。这就是为什么 asio 可等待不满足 cppcoroAwaitable概念。github上有一个issue详细解释了这个问题：https://github.com/lewissbaker/cppcoro/issues/131
尽管如此，您可以通过为 asio 提供协程包装器来将 asio 与 cppcoro 一起使用。为此，您可以使用 asio 的回调方法，并提供cppcoro::single_consumer_event给处理程序，并event.set()在那里调用。
这是一个示例：https://gist.github.com/isergeyam/ce10bef00abfaee3d0ec7f31a21c4b95