signals.h

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/*
 * Copyright (C) 2009-2016 Paul Davis <paul@linuxaudiosystems.com>
 * Copyright (C) 2010-2012 Carl Hetherington <carl@carlh.net>
 * Copyright (C) 2013 John Emmas <john@creativepost.co.uk>
 * Copyright (C) 2015-2017 Robin Gareus <robin@gareus.org>
 *
 * 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 2 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, write to the Free Software Foundation, Inc.,
 * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
 */
 
#ifndef __pbd_signals_h__
#define __pbd_signals_h__
 
#include <csignal>
 
#include <list>
#include <map>
 
#ifdef nil
#undef nil
#endif
 
#include <atomic>
 
#include <glibmm/threads.h>
 
#include <boost/noncopyable.hpp>
#include <boost/bind.hpp>
#include <boost/bind/protect.hpp>
#include <boost/function.hpp>
#include <boost/enable_shared_from_this.hpp>
#include <boost/optional.hpp>
 
#include "pbd/libpbd_visibility.h"
#include "pbd/event_loop.h"
 
#ifndef NDEBUG
#define DEBUG_PBD_SIGNAL_CONNECTIONS
#endif
 
#ifdef DEBUG_PBD_SIGNAL_CONNECTIONS
#include "pbd/stacktrace.h"
#include <iostream>
#endif
 
namespace PBD {
 
class LIBPBD_API Connection;
 
class LIBPBD_API SignalBase
{
public:
        SignalBase ()
        : _in_dtor (false)
#ifdef DEBUG_PBD_SIGNAL_CONNECTIONS
        , _debug_connection (false)
#endif
        {}
        virtual ~SignalBase () { }
        virtual void disconnect (std::shared_ptr<Connection>) = 0;
#ifdef DEBUG_PBD_SIGNAL_CONNECTIONS
        void set_debug_connection (bool yn) { _debug_connection = yn; }
#endif
 
protected:
        mutable Glib::Threads::Mutex _mutex;
        std::atomic<bool>            _in_dtor;
#ifdef DEBUG_PBD_SIGNAL_CONNECTIONS
        bool _debug_connection;
#endif
};
 
class LIBPBD_API Connection : public std::enable_shared_from_this<Connection>
{
public:
        Connection (SignalBase* b, PBD::EventLoop::InvalidationRecord* ir)
                : _signal (b)
                , _invalidation_record (ir)
        {
                if (_invalidation_record) {
                        _invalidation_record->ref ();
                }
        }
 
        void disconnect ()
        {
                Glib::Threads::Mutex::Lock lm (_mutex);
                SignalBase* signal = _signal.exchange (0, std::memory_order_acq_rel);
                if (signal) {
                        /* It is safe to assume that signal has not been destructed.
                         * If ~Signal d'tor runs, it will call our signal_going_away()
                         * which will block until we're done here.
                         *
                         * This will lock Signal::_mutex, and call disconnected ()
                         * or return immediately if Signal is being destructed.
                         */
                        signal->disconnect (shared_from_this ());
                }
        }
 
        void disconnected ()
        {
                if (_invalidation_record) {
                        _invalidation_record->unref ();
                }
        }
 
        void signal_going_away ()
        {
                /* called with Signal::_mutex held */
                if (!_signal.exchange (0, std::memory_order_acq_rel)) {
                        /* disconnect () grabbed the signal, but signal->disconnect()
                         * has not [yet] removed the entry from the list.
                         *
                         * Allow disconnect () to complete, which will
                         * be an effective NO-OP since SignalBase::_in_dtor is true,
                         * then we can proceed.
                         */
                        Glib::Threads::Mutex::Lock lm (_mutex);
                }
                if (_invalidation_record) {
                        _invalidation_record->unref ();
                }
        }
 
private:
        Glib::Threads::Mutex     _mutex;
        std::atomic<SignalBase*> _signal;
        PBD::EventLoop::InvalidationRecord* _invalidation_record;
};
 
template<typename R>
class /*LIBPBD_API*/ OptionalLastValue
{
public:
        typedef boost::optional<R> result_type;
 
        template <typename Iter>
        result_type operator() (Iter first, Iter last) const {
                result_type r;
                while (first != last) {
                        r = *first;
                        ++first;
                }
 
                return r;
        }
};
 
typedef std::shared_ptr<Connection> UnscopedConnection;
 
class LIBPBD_API ScopedConnection
{
public:
        ScopedConnection () {}
        ScopedConnection (UnscopedConnection c) : _c (c) {}
        ~ScopedConnection () {
                disconnect ();
        }
 
        void disconnect ()
        {
                if (_c) {
                        _c->disconnect ();
                }
        }
 
        ScopedConnection& operator= (UnscopedConnection const & o)
        {
                if (_c == o) {
                        return *this;
                }
 
                disconnect ();
                _c = o;
                return *this;
        }
 
        UnscopedConnection const & the_connection() const { return _c; }
 
private:
        UnscopedConnection _c;
};
 
class LIBPBD_API ScopedConnectionList  : public boost::noncopyable
{
  public:
        ScopedConnectionList();
        virtual ~ScopedConnectionList ();
 
        void add_connection (const UnscopedConnection& c);
        void drop_connections ();
 
  private:
        /* this class is not copyable */
        ScopedConnectionList(const ScopedConnectionList&);
 
        /* Even though our signals code is thread-safe, this additional list of
           scoped connections needs to be protected in 2 cases:
 
           (1) (unlikely) we make a connection involving a callback on the
               same object from 2 threads. (wouldn't that just be appalling
               programming style?)
 
           (2) where we are dropping connections in one thread and adding
               one from another.
         */
 
        Glib::Threads::Mutex _scoped_connection_lock;
 
        typedef std::list<ScopedConnection*> ConnectionList;
        ConnectionList _scoped_connection_list;
};
 
#include "pbd/signals_generated.h"
 
} /* namespace */
 
#endif /* __pbd_signals_h__ */