unwind-prot.h

Go to the documentation of this file.

/*

Copyright (C) 1993-2012 John W. Eaton
Copyright (C) 2009-2010 VZLU Prague

This file is part of Octave.

Octave 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.

Octave 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 Octave; see the file COPYING.  If not, see
<http://www.gnu.org/licenses/>.

*/

#if !defined (octave_unwind_prot_h)
#define octave_unwind_prot_h 1

#include <cstddef>

#include <string>
#include <memory>

// This class allows registering cleanup actions.
class
OCTINTERP_API
unwind_protect
{
public:

  // A generic unwind_protect element. Knows how to run itself and discard itself.
  // Also, contains a pointer to the next element.
  class elem
  {
    elem *next;

  public:
    elem (void) : next (0) { }

    virtual void run (void) { }

    virtual ~elem (void) { }

    friend class unwind_protect;

  private:

    // No copying!

    elem (const elem&);

    elem& operator = (const elem&);
  };

  // An element that merely runs a void (*)(void) function.

  class fcn_elem : public elem
  {
  public:
    fcn_elem (void (*fptr) (void))
      : e_fptr (fptr) { }

    void run (void) { e_fptr (); }

  private:
    void (*e_fptr) (void);
  };

  // An element that stores a variable of type T along with a void (*) (T)
  // function pointer, and calls the function with the parameter.

  template <class T>
  class fcn_arg_elem : public elem
  {
  public:
    fcn_arg_elem (void (*fcn) (T), T arg)
      : e_fcn (fcn), e_arg (arg) { }

    void run (void) { e_fcn (e_arg); }

  private:

    // No copying!

    fcn_arg_elem (const fcn_arg_elem&);

    fcn_arg_elem& operator = (const fcn_arg_elem&);

    void (*e_fcn) (T);
    T e_arg;
  };

  // An element that stores a variable of type T along with a void (*) (const T&)
  // function pointer, and calls the function with the parameter.

  template <class T>
  class fcn_crefarg_elem : public elem
  {
  public:
    fcn_crefarg_elem (void (*fcn) (const T&), T arg)
      : e_fcn (fcn), e_arg (arg) { }

    void run (void) { e_fcn (e_arg); }

  private:
    void (*e_fcn) (const T&);
    T e_arg;
  };

  // An element for calling a member function.

  template <class T>
  class method_elem : public elem
  {
  public:
    method_elem (T *obj, void (T::*method) (void))
      : e_obj (obj), e_method (method) { }

    void run (void) { (e_obj->*e_method) (); }

  private:

    T *e_obj;
    void (T::*e_method) (void);

    // No copying!

    method_elem (const method_elem&);

    method_elem operator = (const method_elem&);
  };

  // An element that stores arbitrary variable, and restores it.

  template <class T>
  class restore_var_elem : public elem
  {
  public:
    restore_var_elem (T& ref, const T& val)
      : e_ptr (&ref), e_val (val) { }

    void run (void) { *e_ptr = e_val; }

  private:

    // No copying!

    restore_var_elem (const restore_var_elem&);

    restore_var_elem& operator = (const restore_var_elem&);

    T *e_ptr, e_val;
  };

  // Deletes a class allocated using new.

  template <class T>
  class delete_ptr_elem : public elem
  {
  public:
    delete_ptr_elem (T *ptr)
      : e_ptr (ptr) { }

    void run (void) { delete e_ptr; }

  private:

    T *e_ptr;

    // No copying!

    delete_ptr_elem (const delete_ptr_elem&);

    delete_ptr_elem operator = (const delete_ptr_elem&);
  };

  unwind_protect (void) : head () { }

  void add (elem *new_elem)
    {
      new_elem->next = head;
      head = new_elem;
    }

  // For backward compatibility.
  void add (void (*fcn) (void *), void *ptr = 0)
    {
      add (new fcn_arg_elem<void *> (fcn, ptr));
    }

  // Call to void func (void).
  void add_fcn (void (*fcn) (void))
    {
      add (new fcn_elem (fcn));
    }

  // Call to void func (T).
  template <class T>
  void add_fcn (void (*action) (T), T val)
    {
      add (new fcn_arg_elem<T> (action, val));
    }

  // Call to void func (const T&).
  template <class T>
  void add_fcn (void (*action) (const T&), T val)
    {
      add (new fcn_crefarg_elem<T> (action, val));
    }

  // Call to T::method (void).
  template <class T>
  void add_method (T *obj, void (T::*method) (void))
    {
      add (new method_elem<T> (obj, method));
    }

  // Call to delete (T*).

  template <class T>
  void add_delete (T *obj)
    {
      add (new delete_ptr_elem<T> (obj));
    }

  // Protect any variable.
  template <class T>
  void protect_var (T& var)
    {
      add (new restore_var_elem<T> (var, var));
    }

  // Protect any variable, value given.
  template <class T>
  void protect_var (T& var, const T& val)
    {
      add (new restore_var_elem<T> (var, val));
    }

  operator bool (void) const
    {
      return head != 0;
    }

  void run_top (void)
    {
      if (head)
        {
          // No leak on exception!
          std::auto_ptr<elem> ptr (head);
          head = ptr->next;
          ptr->run ();
        }
    }

  void run_top (int num)
    {
      while (num-- > 0)
        run_top ();
    }

  void discard_top (void)
    {
      if (head)
        {
          elem *ptr = head;
          head = ptr->next;
          delete ptr;
        }
    }

  void discard_top (int num)
    {
      while (num-- > 0)
        discard_top ();
    }

  void run (void)
    {
      while (head)
        run_top ();
    }

  void discard (void)
    {
      while (head)
        discard_top ();
    }

  // Destructor should not raise an exception, so all actions registered should
  // be exception-safe (but setting error_state is allowed). If you're not sure,
  // see unwind_protect_safe.
  ~unwind_protect (void)
    {
      run ();
    }

private:

  elem *head;

  // No copying!

  unwind_protect (const unwind_protect&);

  unwind_protect& operator = (const unwind_protect&);
};

// Like unwind_protect, but this one will guard against the possibility of seeing
// an exception (or interrupt) in the cleanup actions. Not that we can do much about
// it, but at least we won't crash.

class
OCTINTERP_API
unwind_protect_safe : public unwind_protect
{
  static void gripe_exception (void);

public:
  ~unwind_protect_safe (void)
    {
      while (*this)
        {
          try
            {
              run_top ();
            }
          catch (...) // Yes, the black hole. Remember we're in a dtor.
            {
              gripe_exception ();
            }
        }
    }
};

#endif