enable_observer_pointer.h

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// -----------------------------------------------------------------------------
//
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception OR LGPL-2.1-or-later
// Copyright (C) 1998 - 2025 by the deal.II authors
//
// This file is part of the deal.II library.
//
// Detailed license information governing the source code and contributions
// can be found in LICENSE.md and CONTRIBUTING.md at the top level directory.
//
// -----------------------------------------------------------------------------
 
#ifndef dealii_enable_observer_pointer_h
#define dealii_enable_observer_pointer_h
 
 
#include <deal.II/base/config.h>
 
#include <deal.II/base/exceptions.h>
 
#include <atomic>
#include <map>
#include <mutex>
#include <ostream>
#include <string>
#include <typeinfo>
#include <vector>
 
DEAL_II_NAMESPACE_OPEN
 
 
// Forward declaration
template <typename T, typename P>
class ObserverPointer;
 
 
class EnableObserverPointer
{
public:
  EnableObserverPointer();
 
  EnableObserverPointer(const EnableObserverPointer &);
 
  EnableObserverPointer(EnableObserverPointer &&) noexcept;
 
  virtual ~EnableObserverPointer();
 
  EnableObserverPointer &
  operator=(const EnableObserverPointer &);
 
  EnableObserverPointer &
  operator=(EnableObserverPointer &&) noexcept;
 
  unsigned int
  n_subscriptions() const;
 
  template <typename StreamType>
  void
  list_subscribers(StreamType &stream) const;
 
  void
  list_subscribers() const;
 
  DeclException3(ExcInUse,
                 int,
                 std::string,
                 std::string,
                 << "Object of class " << arg2 << " is still used by " << arg1
                 << " other objects."
                 << "\n\n"
                 << "(Additional information: " << arg3 << ")\n\n"
                 << "See the entry in the Frequently Asked Questions of "
                 << "deal.II (linked to from http://dealii.org/) for "
                 << "a lot more information on what this error means and "
                 << "how to fix programs in which it happens.");
 
  DeclException2(ExcNoSubscriber,
                 std::string,
                 std::string,
                 << "No subscriber with identifier <"
                 << (arg2.empty() ? "unknown subscriber" : arg2.c_str())
                 << "> subscribes to this object of class " << arg1
                 << ". Consequently, it cannot be unsubscribed.");
  template <class Archive>
  void
  serialize(Archive &ar, const unsigned int version);
 
private:
  mutable std::atomic<unsigned int> counter;
 
  mutable std::map<std::string, unsigned int> counter_map;
 
  mutable std::vector<std::atomic<bool> *> validity_pointers;
 
  mutable const std::type_info *object_info;
 
  static std::mutex mutex;
 
  void
  subscribe(std::atomic<bool> *const validity,
            const std::string       &identifier = "") const;
 
  void
  unsubscribe(std::atomic<bool> *const validity,
              const std::string       &identifier = "") const;
 
  void
  check_no_subscribers() const noexcept;
 
  template <typename, typename>
  friend class ObserverPointer;
 
};
 
 
//---------------------------------------------------------------------------
 
inline EnableObserverPointer::EnableObserverPointer()
  : counter(0)
  , object_info(nullptr)
{}
 
 
 
inline EnableObserverPointer::EnableObserverPointer(
  const EnableObserverPointer &)
  : counter(0)
  , object_info(nullptr)
{}
 
 
 
inline EnableObserverPointer &
EnableObserverPointer::operator=(const EnableObserverPointer &s)
{
  object_info = s.object_info;
  return *this;
}
 
 
 
inline unsigned int
EnableObserverPointer::n_subscriptions() const
{
  return counter;
}
 
 
 
template <class Archive>
inline void
EnableObserverPointer::serialize(Archive &, const unsigned int)
{
  // do nothing, as explained in the
  // documentation of this function
}
 
template <typename StreamType>
inline void
EnableObserverPointer::list_subscribers(StreamType &stream) const
{
  std::scoped_lock lock(mutex);
 
  for (const auto &it : counter_map)
    stream << it.second << '/' << counter << " subscriptions from \""
           << it.first << '\"' << std::endl;
}
 
DEAL_II_NAMESPACE_CLOSE
 
#endif