Introduce forward_scope_exit
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: 2019-01-23 Pedro Alves <palves@redhat.com> Andrew Burgess <andrew.burgess@embecosm.com> * common/forward-scope-exit.h: New file.
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2019-01-23 Pedro Alves <palves@redhat.com>
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Andrew Burgess <andrew.burgess@embecosm.com>
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* common/forward-scope-exit.h: New file.
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2019-01-23 Pedro Alves <palves@redhat.com>
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2019-01-23 Pedro Alves <palves@redhat.com>
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Andrew Burgess <andrew.burgess@embecosm.com>
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Andrew Burgess <andrew.burgess@embecosm.com>
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Tom Tromey <tom@tromey.com>
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Tom Tromey <tom@tromey.com>
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/* Copyright (C) 2019 Free Software Foundation, Inc.
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This file is part of GDB.
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This program is free software; you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation; either version 3 of the License, or
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(at your option) any later version.
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This program is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with this program. If not, see <http://www.gnu.org/licenses/>. */
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#ifndef COMMON_FORWARD_SCOPE_EXIT_H
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#define COMMON_FORWARD_SCOPE_EXIT_H
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#include "common/scope-exit.h"
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#include <functional>
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/* A forward_scope_exit is like scope_exit, but instead of giving it a
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callable, you instead specialize it for a given cleanup function,
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and the generated class automatically has a constructor with the
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same interface as the cleanup function. forward_scope_exit
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captures the arguments passed to the ctor, and in turn passes those
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as arguments to the wrapped cleanup function, when it is called at
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scope exit time, from within the forward_scope_exit dtor. The
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forward_scope_exit class can take any number of arguments, and is
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cancelable if needed.
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This allows usage like this:
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void
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delete_longjmp_breakpoint (int arg)
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{
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// Blah, blah, blah...
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}
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using longjmp_breakpoint_cleanup
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= FORWARD_SCOPE_EXIT (delete_longjmp_breakpoint);
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This above created a new cleanup class `longjmp_breakpoint_cleanup`
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than can then be used like this:
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longjmp_breakpoint_cleanup obj (thread);
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// Blah, blah, blah...
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obj.release (); // Optional cancel if needed.
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forward_scope_exit is also handy when you would need to wrap a
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scope_exit in a gdb::optional:
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gdb::optional<longjmp_breakpoint_cleanup> cleanup;
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if (some condition)
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cleanup.emplace (thread);
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...
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if (cleanup)
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cleanup->release ();
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since with scope exit, you would have to know the scope_exit's
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callable template type when you create the gdb::optional:
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gdb:optional<scope_exit<what goes here?>>
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The "forward" naming fits both purposes shown above -- the class
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"forwards" ctor arguments to the wrapped cleanup function at scope
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exit time, and can also be used to "forward declare"
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scope_exit-like objects. */
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namespace detail
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{
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/* Function and Signature are passed in the same type, in order to
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extract Function's arguments' types in the specialization below.
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Those are used to generate the constructor. */
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template<typename Function, Function *function, typename Signature>
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struct forward_scope_exit;
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template<typename Function, Function *function,
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typename Res, typename... Args>
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class forward_scope_exit<Function, function, Res (Args...)>
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: public scope_exit_base<forward_scope_exit<Function,
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function,
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Res (Args...)>>
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{
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/* For access to on_exit(). */
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friend scope_exit_base<forward_scope_exit<Function,
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function,
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Res (Args...)>>;
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public:
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explicit forward_scope_exit (Args ...args)
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: m_bind_function (std::bind (function, args...))
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{
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/* Nothing. */
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}
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private:
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void on_exit ()
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{
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m_bind_function ();
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}
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/* The function and the arguments passed to the ctor, all packed in
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a std::bind. */
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decltype (std::bind (function, std::declval<Args> ()...))
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m_bind_function;
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};
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} /* namespace detail */
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/* This is the "public" entry point. It's a macro to avoid having to
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name FUNC more than once. */
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#define FORWARD_SCOPE_EXIT(FUNC) \
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detail::forward_scope_exit<decltype (FUNC), FUNC, decltype (FUNC)>
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#endif /* COMMON_FORWARD_SCOPE_EXIT_H */
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