gdbsupport/forward-scope-exit.h

   1 /* Copyright (C) 2019-2021 Free Software Foundation, Inc.
   2
   3    This file is part of GDB.
   4
   5    This program is free software; you can redistribute it and/or modify
   6    it under the terms of the GNU General Public License as published by
   7    the Free Software Foundation; either version 3 of the License, or
   8    (at your option) any later version.
   9
  10    This program is distributed in the hope that it will be useful,
  11    but WITHOUT ANY WARRANTY; without even the implied warranty of
  12    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  13    GNU General Public License for more details.
  14
  15    You should have received a copy of the GNU General Public License
  16    along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
  17
  18 #ifndef COMMON_FORWARD_SCOPE_EXIT_H
  19 #define COMMON_FORWARD_SCOPE_EXIT_H
  20
  21 #include "gdbsupport/scope-exit.h"
  22 #include <functional>
  23
  24 /* A forward_scope_exit is like scope_exit, but instead of giving it a
  25    callable, you instead specialize it for a given cleanup function,
  26    and the generated class automatically has a constructor with the
  27    same interface as the cleanup function.  forward_scope_exit
  28    captures the arguments passed to the ctor, and in turn passes those
  29    as arguments to the wrapped cleanup function, when it is called at
  30    scope exit time, from within the forward_scope_exit dtor.  The
  31    forward_scope_exit class can take any number of arguments, and is
  32    cancelable if needed.
  33
  34    This allows usage like this:
  35
  36       void
  37       delete_longjmp_breakpoint (int arg)
  38       {
  39         // Blah, blah, blah...
  40       }
  41
  42       using longjmp_breakpoint_cleanup
  43         = FORWARD_SCOPE_EXIT (delete_longjmp_breakpoint);
  44
  45    This above created a new cleanup class `longjmp_breakpoint_cleanup`
  46    than can then be used like this:
  47
  48       longjmp_breakpoint_cleanup obj (thread);
  49
  50       // Blah, blah, blah...
  51
  52       obj.release ();  // Optional cancel if needed.
  53
  54    forward_scope_exit is also handy when you would need to wrap a
  55    scope_exit in a gdb::optional:
  56
  57       gdb::optional<longjmp_breakpoint_cleanup> cleanup;
  58       if (some condition)
  59         cleanup.emplace (thread);
  60       ...
  61       if (cleanup)
  62         cleanup->release ();
  63
  64    since with scope exit, you would have to know the scope_exit's
  65    callable template type when you create the gdb::optional:
  66
  67      gdb:optional<scope_exit<what goes here?>>
  68
  69    The "forward" naming fits both purposes shown above -- the class
  70    "forwards" ctor arguments to the wrapped cleanup function at scope
  71    exit time, and can also be used to "forward declare"
  72    scope_exit-like objects.  */
  73
  74 namespace detail
  75 {
  76
  77 /* Function and Signature are passed in the same type, in order to
  78    extract Function's arguments' types in the specialization below.
  79    Those are used to generate the constructor.  */
  80
  81 template<typename Function, Function *function, typename Signature>
  82 struct forward_scope_exit;
  83
  84 template<typename Function, Function *function,
  85          typename Res, typename... Args>
  86 class forward_scope_exit<Function, function, Res (Args...)>
  87   : public scope_exit_base<forward_scope_exit<Function,
  88                                               function,
  89                                               Res (Args...)>>
  90 {
  91   /* For access to on_exit().  */
  92   friend scope_exit_base<forward_scope_exit<Function,
  93                                             function,
  94                                             Res (Args...)>>;
  95
  96 public:
  97   explicit forward_scope_exit (Args ...args)
  98     : m_bind_function (function, args...)
  99   {
 100     /* Nothing.  */
 101   }
 102
 103 private:
 104   void on_exit ()
 105   {
 106     m_bind_function ();
 107   }
 108
 109   /* The function and the arguments passed to the ctor, all packed in
 110      a std::bind.  */
 111   decltype (std::bind (function, std::declval<Args> ()...))
 112     m_bind_function;
 113 };
 114
 115 } /* namespace detail */
 116
 117 /* This is the "public" entry point.  It's a macro to avoid having to
 118    name FUNC more than once.  */
 119
 120 #define FORWARD_SCOPE_EXIT(FUNC) \
 121   detail::forward_scope_exit<decltype (FUNC), FUNC, decltype (FUNC)>
 122
 123 #endif /* COMMON_FORWARD_SCOPE_EXIT_H */