Merge pull request ceph#65062 from adamemerson/wip-redirect-error

common/async: improved `redirect_error`, `run_coro`, and tests

Reviewed-by: Anthony D'Atri [email protected]
Reviewed-by: Casey Bodley [email protected]
Reviewed-by: Jesse F. Williamson [email protected]

Author: adamemerson

COPYING

@@ -211,6 +211,12 @@ Copyright: 2020 Red Hat <[email protected]>
            2003-2019 Christopher M. Kohlhoff <[email protected]>
 License: Boost Software License, Version 1.0
 
+Files: src/common/async/redirect_error.h,
+       src/test/common/test_async_redirect_error.cc
+Copyright: 2025 Contributors to the Ceph Project
+           2003-2024 Christopher M. Kohlhoff <[email protected]>
+License: Boost Software License, Version 1.0
+
 Files: src/script/backport-create-issue
 Copyright: 2015 Red Hat <[email protected]>
            2018 SUSE LLC

src/common/async/blocked_completion.h

@@ -16,30 +16,44 @@
 #ifndef CEPH_COMMON_ASYNC_BLOCKED_COMPLETION_H
 #define CEPH_COMMON_ASYNC_BLOCKED_COMPLETION_H
 
+/// \file common/async/blocked_completion.h
+///
+/// \brief A blocking `completion token`
+///
+/// This completion token will actually hard-block your thread. Do not
+/// do so within an `io_context` thread.
+
 #include <condition_variable>
 #include <mutex>
 #include <optional>
 
 #include <boost/asio/async_result.hpp>
-#include <boost/asio/redirect_error.hpp>
+#include <boost/asio/disposition.hpp>
 
 #include <boost/system/error_code.hpp>
 
-#include <common/async/concepts.h>
+#include "common/async/redirect_error.h"
 
 namespace ceph::async {
-
-namespace bs = boost::system;
-
+/// A \ref `completion token` type that blocks the current thread
+/// until the operation completes.
+///
+/// \warning Keep deadlocks in mind. Do not use in threads that expect
+/// to be asynchronous.
 class use_blocked_t {
 public:
   use_blocked_t() = default;
 
-  auto operator [](bs::error_code& ec) const {
-    return boost::asio::redirect_error(use_blocked_t{}, ec);
+  /// Redirect the \ref `disposition` of the operation to a
+  /// variable. (A `disposition` is a concept generalizing error codes
+  /// and exceptions.)
+  template<boost::asio::disposition Disposition>
+  auto operator [](Disposition& d) const {
+    return redirect_error(use_blocked_t{}, d);
   }
 };
 
+/// The archetypical instance of `use_blocked_t`
 inline constexpr use_blocked_t use_blocked;
 
 namespace detail {