src/weakset.h

   1 /*
   2   Copyright (c) 2006 Paolo Capriotti <p.capriotti@sns.it>
   3             (c) 2006 Maurizio Monge <maurizio.monge@kdemail.net>
   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 2 of the License, or
   8   (at your option) any later version.
   9 */
  10
  11 #ifndef WEAK_SET
  12 #define WEAK_SET
  13
  14 #include <boost/weak_ptr.hpp>
  15 #include <list>
  16
  17 #ifdef WEAK_SET_DEBUG
  18   #include <iostream>
  19   using namespace std;
  20 #endif // WEAK_SET_DEBUG
  21
  22 /**
  23   * @brief An implementation of a set of weak references.
  24   *
  25   * weak_set is a set of weak_pointers which are automatically collected
  26   * and removed when the pointed object is destroyed.
  27   */
  28 template <typename T>
  29 class weak_set {
  30   typedef std::list<boost::weak_ptr<T> > inner_set;
  31   typedef typename inner_set::iterator inner_iterator;
  32   friend class iterator;
  33   mutable inner_set m_set;
  34 public:
  35   class iterator {
  36     friend class weak_set<T>;
  37     mutable inner_iterator m_it;
  38     boost::shared_ptr<T> obj; // this prevents the stored object from being collected
  39     weak_set<T>& m_parent;
  40
  41     iterator(const inner_iterator& it, weak_set<T>& parent)
  42     : m_it(it)
  43     , m_parent(parent) {
  44       skip_garbage();
  45     }
  46
  47     void skip_garbage() {
  48       #ifdef WEAK_SET_DEBUG
  49       cout << "skipping garbage" << endl;
  50       uint c = 0;
  51       #endif // WEAK_SET_DEBUG
  52       while (true) {
  53         if (m_it == m_parent.m_set.end()) break;
  54         boost::weak_ptr<T> wp = *m_it;
  55         if (obj = wp.lock()) break;
  56
  57 //      while (m_it != m_parent.m_set.end() && !(obj = (*m_it).lock())) {
  58         #ifdef WEAK_SET_DEBUG
  59         cout << "iteration " << c++ << endl;
  60         #endif // WEAK_SET_DEBUG
  61
  62         // the current reference is dangling:
  63         // remove it from the list and get the next one
  64         #ifdef WEAK_SET_DEBUG
  65         cout << "dangling reference! removing it" << endl;
  66         #endif // WEAK_SET_DEBUG
  67         m_it = m_parent.m_set.erase(m_it);
  68       }
  69       // at this point either
  70       // m_it < m_parent.m_set.end() _and_ obj is a valid shared_ptr
  71       // or
  72       // m_it == m_parent.m_set.end()
  73       #ifdef WEAK_SET_DEBUG
  74       if (obj)
  75         cout << "no iteration done: uses = " << obj.use_count() << ", obj = " << *obj << endl;
  76       else
  77         cout << "we're at the end" << endl;
  78       #endif // WEAK_SET_DEBUG
  79     }
  80   public:
  81     /**
  82       * Check two iterators for equality.
  83       */
  84     bool operator==(const iterator& other) { return m_it == other.m_it; }
  85
  86     /**
  87       * Equivalent to !operator==.
  88       */
  89     bool operator!=(const iterator& other) { return !operator==(other); }
  90
  91     /**
  92       * Pre-increment operator. Modifity the iterator so
  93       * that it points to the next valid object.
  94       * @return The incremented iterator.
  95       */
  96     iterator& operator++() {
  97       #ifdef WEAK_SET_DEBUG
  98       cout << "incrementing" << endl;
  99       #endif // WEAK_SET_DEBUG
 100       ++m_it;
 101       obj.reset();
 102       skip_garbage();
 103       #ifdef WEAK_SET_DEBUG
 104       cout << "done incrementing" << endl;
 105       #endif // WEAK_SET_DEBUG
 106       return *this;
 107     }
 108
 109     /**
 110       * Post-increment operator. Modifity the iterator so
 111       * that it points to the next valid object.
 112       * @return The iterator before being incremented.
 113       */
 114 //    iterator operator++(int) { return iterator(m_it++, m_parent); }
 115
 116     /**
 117       * @return a pointer to the stored object.
 118       * @note This function is guaranteed to return a valid
 119       * non-null pointer if the iterator is valid
 120       * and less than the past-the-end iterator.
 121       */
 122     T* get() { return obj.get(); }
 123
 124     /**
 125       * @return a pointer to the stored object.
 126       * @sa get
 127       */
 128     T* operator->() { return get(); }
 129
 130     /**
 131       * @return a reference to the stored object.
 132       * @sa get
 133       */
 134     T& operator*() { return *get(); }
 135   };
 136
 137   /**
 138     * Add an object to the container.
 139     * @return an iterator referring to the newly inserted object.
 140     * @note No iterator is invalidated by an insert operation.
 141     */
 142   iterator insert(const boost::shared_ptr<T>& x) {
 143     return iterator(m_set.insert(m_set.end(), x), *this);
 144   }
 145
 146   /**
 147     * @return an iterator pointing to the first element of
 148     *         the container, which can be used for iterating.
 149     */
 150   iterator begin() {
 151     return iterator(m_set.begin(), *this);
 152   }
 153
 154   /**
 155     * @return a past-the-end iterator.
 156     */
 157   iterator end() {
 158     return iterator(m_set.end(), *this);
 159   }
 160 };
 161
 162 #endif // WEAK_SET
 163