face: Refactor internal PIT to use scheduled events

The commit also changes how face is paused when there are no pending
interests left and there are no registered prefixes with local
forwarder: data structures for pending interests and registered prefixes
will fire up a signal when they become empty.

Change-Id: I6b87a44b0c8bc766865a51962ecacaec85b4adad
Refs: #1372, #2518
diff --git a/src/detail/container-with-on-empty-signal.hpp b/src/detail/container-with-on-empty-signal.hpp
new file mode 100644
index 0000000..0c3e7c3
--- /dev/null
+++ b/src/detail/container-with-on-empty-signal.hpp
@@ -0,0 +1,108 @@
+/* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
+/**
+ * Copyright (c) 2013-2015 Regents of the University of California.
+ *
+ * This file is part of ndn-cxx library (NDN C++ library with eXperimental eXtensions).
+ *
+ * ndn-cxx library is free software: you can redistribute it and/or modify it under the
+ * terms of the GNU Lesser General Public License as published by the Free Software
+ * Foundation, either version 3 of the License, or (at your option) any later version.
+ *
+ * ndn-cxx library 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 Lesser General Public License for more details.
+ *
+ * You should have received copies of the GNU General Public License and GNU Lesser
+ * General Public License along with ndn-cxx, e.g., in COPYING.md file.  If not, see
+ * <http://www.gnu.org/licenses/>.
+ *
+ * See AUTHORS.md for complete list of ndn-cxx authors and contributors.
+ */
+
+#ifndef NDN_DETAIL_CONTAINER_WITH_ON_EMPTY_SIGNAL_HPP
+#define NDN_DETAIL_CONTAINER_WITH_ON_EMPTY_SIGNAL_HPP
+
+#include "../common.hpp"
+#include "../util/signal.hpp"
+
+namespace ndn {
+
+/**
+ * @brief A simple container that will fire up onEmpty signal when there are no entries left
+ */
+template<class T>
+class ContainerWithOnEmptySignal
+{
+public:
+  typedef std::list<T> Base;
+  typedef typename Base::value_type value_type;
+  typedef typename Base::iterator iterator;
+
+  iterator
+  begin()
+  {
+    return m_container.begin();
+  }
+
+  iterator
+  end()
+  {
+    return m_container.end();
+  }
+
+  size_t
+  size()
+  {
+    return m_container.size();
+  }
+
+  bool
+  empty()
+  {
+    return m_container.empty();
+  }
+
+  iterator
+  erase(iterator item)
+  {
+    iterator next = m_container.erase(item);
+    if (empty()) {
+      this->onEmpty();
+    }
+    return next;
+  }
+
+  void
+  clear()
+  {
+    m_container.clear();
+    this->onEmpty();
+  }
+
+  std::pair<iterator, bool>
+  insert(const value_type& value)
+  {
+    return {m_container.insert(end(), value), true};
+  }
+
+  template<class Predicate>
+  void remove_if(Predicate p)
+  {
+    m_container.remove_if(p);
+    if (empty()) {
+      this->onEmpty();
+    }
+  }
+
+public:
+  Base m_container;
+
+  /**
+   * @brief Signal to be fired when container becomes empty
+   */
+  util::Signal<ContainerWithOnEmptySignal<T>> onEmpty;
+};
+
+} // namespace ndn
+
+#endif // NDN_DETAIL_CONTAINER_WITH_ON_EMPTY_SIGNAL_HPP