[v3,03/17] Introduce forward_scope_exit
Commit Message
This adds a template that can be used to automatically instantiate
scope_exit-like types that wrap some cleanup function. The
instantiated type has a ctor that has the same interface as the
wrapped function. While the "magic" is just straight C++11, the
intended use is via the FORWARD_SCOPE_EXIT macro, which is a minimal
macro that avoids spelling out the wrapped function name more than
once:
void some_function (int foo, object *bar);
using some_function_fce = FORWARD_SCOPE_EXIT (some_function);
some_function_fce cleanup (some_int, some_obj_ptr);
The above runs:
some_function (some_int, some_obj_ptr);
at scope exit.
This is mainly useful as opposed to a simpler SCOPE_EXIT when you need
to:
- cancel the scope_exit, in which case you need the object's name
- wrap the scope_exit in a gdb::optional, in which case you need the
scope_exit's type in advance.
More details in the code comments.
gdb/ChangeLog
yyyy-mm-dd Pedro Alves <palves@redhat.com>
Andrew Burgess <andrew.burgess@embecosm.com>
* common/forward-scope-exit.h: New file.
---
gdb/common/forward-scope-exit.h | 123 ++++++++++++++++++++++++++++++++++++++++
1 file changed, 123 insertions(+)
create mode 100644 gdb/common/forward-scope-exit.h
new file mode 100644
@@ -0,0 +1,123 @@
+/* Copyright (C) 2019 Free Software Foundation, Inc.
+
+ This file is part of GDB.
+
+ This program is free software; you can redistribute it and/or modify
+ it under the terms of the GNU General Public License as published by
+ the Free Software Foundation; either version 3 of the License, or
+ (at your option) any later version.
+
+ This program is distributed in the hope that it will be useful,
+ but WITHOUT ANY WARRANTY; without even the implied warranty of
+ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ GNU General Public License for more details.
+
+ You should have received a copy of the GNU General Public License
+ along with this program. If not, see <http://www.gnu.org/licenses/>. */
+
+#ifndef COMMON_FORWARD_SCOPE_EXIT_H
+#define COMMON_FORWARD_SCOPE_EXIT_H
+
+#include "common/scope-exit.h"
+#include <functional>
+
+/* A forward_scope_exit is like scope_exit, but instead of giving it a
+ callable, you instead specialize it for a given cleanup function,
+ and the generated class automatically has a constructor with the
+ same interface as the cleanup function. forward_scope_exit
+ captures the arguments passed to the ctor, and in turn passes those
+ as arguments to the wrapped cleanup function, when it is called at
+ scope exit time, from within the forward_scope_exit dtor. The
+ forward_scope_exit class can take any number of arguments, and is
+ cancelable if needed.
+
+ This allows usage like this:
+
+ void
+ delete_longjmp_breakpoint (int arg)
+ {
+ // Blah, blah, blah...
+ }
+
+ using longjmp_breakpoint_cleanup
+ = FORWARD_SCOPE_EXIT (delete_longjmp_breakpoint);
+
+ This above created a new cleanup class `longjmp_breakpoint_cleanup`
+ than can then be used like this:
+
+ longjmp_breakpoint_cleanup obj (thread);
+
+ // Blah, blah, blah...
+
+ obj.release (); // Optional cancel if needed.
+
+ forward_scope_exit is also handy when you would need to wrap a
+ scope_exit in a gdb::optional:
+
+ gdb::optional<longjmp_breakpoint_cleanup> cleanup;
+ if (some condition)
+ cleanup.emplace (thread);
+ ...
+ if (cleanup)
+ cleanup->release ();
+
+ since with scope exit, you would have to know the scope_exit's
+ callable template type when you create the gdb::optional:
+
+ gdb:optional<scope_exit<what goes here?>>
+
+ The "forward" naming fits both purposes shown above -- the class
+ "forwards" ctor arguments to the wrapped cleanup function at scope
+ exit time, and can also be used to "forward declare"
+ scope_exit-like objects. */
+
+namespace detail
+{
+
+/* Function and Signature are passed in the same type, in order to
+ extract Function's arguments' types in the specialization below.
+ Those are used to generate the constructor. */
+
+template<typename Function, Function *function, typename Signature>
+struct forward_scope_exit;
+
+template<typename Function, Function *function,
+ typename Res, typename... Args>
+class forward_scope_exit<Function, function, Res (Args...)>
+ : public scope_exit_base<forward_scope_exit<Function,
+ function,
+ Res (Args...)>>
+{
+ /* For access to on_exit(). */
+ friend scope_exit_base<forward_scope_exit<Function,
+ function,
+ Res (Args...)>>;
+
+public:
+ explicit forward_scope_exit (Args ...args)
+ : m_bind_function (std::bind (function, args...))
+ {
+ /* Nothing. */
+ }
+
+private:
+ void on_exit ()
+ {
+ m_bind_function ();
+ }
+
+ /* The function and the arguments passed to the ctor, all packed in
+ a std::bind. */
+ decltype (std::bind (function, std::declval<Args> ()...))
+ m_bind_function;
+};
+
+} /* namespace detail */
+
+/* This is the "public" entry point. It's a macro to avoid having to
+ name FUNC more than once. */
+
+#define FORWARD_SCOPE_EXIT(FUNC) \
+ detail::forward_scope_exit<decltype (FUNC), FUNC, decltype (FUNC)>
+
+#endif /* COMMON_FORWARD_SCOPE_EXIT_H */