Bug 1181445 (part 1) - Implement iterators for nsTHashtable and nsBaseHashtable. r=froydnj.

nsBaseHashtable has both EnumerateRead() and Enumerate(). A comment claims that
the latter locks the table, but this is false, so I removed the comment. Other
than that the only notable difference between them is that they have slightly
different types for dealing with values (|UserDataType| vs |DataType&|) so I've
implemented both GetUserData() and GetData(), allowing either type to be used.

--HG--
extra : rebase_source : 9d61cc8f4c14082c9f1939ff3ced2b697e043f42

xpcom/glue/nsBaseHashtable.h

@@ -162,6 +162,7 @@ public:
 
   /**
    * enumerate entries in the hashtable, without allowing changes
+   * WARNING: this function is deprecated. Please use Iterator instead.
    * @param aEnumFunc enumeration callback
    * @param aUserArg passed unchanged to the EnumReadFunction
    */
@@ -196,8 +197,9 @@ public:
                                           void* aUserArg);
 
   /**
-   * enumerate entries in the hashtable, allowing changes. This
-   * functions write-locks the hashtable.
+   * enumerate entries in the hashtable, allowing changes.
+   * WARNING: this function is deprecated. Please use Iterator and/or
+   * MutatingIterator instead.
    * @param aEnumFunc enumeration callback
    * @param aUserArg passed unchanged to the EnumFunction
    */
@@ -218,6 +220,47 @@ public:
     return n;
   }
 
+  // This is an iterator that also allows entry removal. Example usage:
+  //
+  //   for (auto iter = table.Iter(); !iter.Done(); iter.Next()) {
+  //     const KeyType key = iter.GetKey();
+  //     const UserDataType data = iter.GetUserData();
+  //     // or
+  //     const DataType& data = iter.GetData();
+  //     // ... do stuff with |key| and/or |data| ...
+  //     // ... possibly call iter.Remove() once ...
+  //   }
+  //
+  class Iterator : public PLDHashTable::Iterator
+  {
+  public:
+    typedef PLDHashTable::Iterator Base;
+
+    explicit Iterator(nsBaseHashtable* aTable) : Base(&aTable->mTable) {}
+    Iterator(Iterator&& aOther) : Base(aOther.mTable) {}
+    ~Iterator() {}
+
+    KeyType GetKey() const { return static_cast<EntryType*>(Get())->GetKey(); }
+    UserDataType GetUserData() const
+    {
+      return static_cast<EntryType*>(Get())->mData;
+    }
+    DataType& GetData() const { return static_cast<EntryType*>(Get())->mData; }
+
+  private:
+    Iterator() = delete;
+    Iterator(const Iterator&) = delete;
+    Iterator& operator=(const Iterator&) = delete;
+    Iterator& operator=(const Iterator&&) = delete;
+  };
+
+  Iterator Iter() { return Iterator(this); }
+
+  Iterator ConstIter() const
+  {
+    return Iterator(const_cast<nsBaseHashtable*>(this));
+  }
+
   /**
    * reset the hashtable, removing all entries
    */

xpcom/glue/nsTHashtable.h

@@ -205,6 +205,7 @@ public:
    * a PL_DHASH_REMOVE return value from |aEnumFunc|, the table may be shrunk
    * at the end. Use RawRemoveEntry() instead if you wish to remove an entry
    * without possibly shrinking the table.
+   * WARNING: this function is deprecated. Please use Iterator instead.
    * @param     enumFunc the <code>Enumerator</code> function to call
    * @param     userArg a pointer to pass to the
    *            <code>Enumerator</code> function
@@ -227,6 +228,39 @@ public:
     return n;
   }
 
+  // This is an iterator that also allows entry removal. Example usage:
+  //
+  //   for (auto iter = table.Iter(); !iter.Done(); iter.Next()) {
+  //     Entry* entry = iter.Get();
+  //     // ... do stuff with |entry| ...
+  //     // ... possibly call iter.Remove() once ...
+  //   }
+  //
+  class Iterator : public PLDHashTable::Iterator
+  {
+  public:
+    typedef PLDHashTable::Iterator Base;
+
+    explicit Iterator(nsTHashtable* aTable) : Base(&aTable->mTable) {}
+    Iterator(Iterator&& aOther) : Base(aOther.mTable) {}
+    ~Iterator() {}
+
+    EntryType* Get() const { return static_cast<EntryType*>(Base::Get()); }
+
+  private:
+    Iterator() = delete;
+    Iterator(const Iterator&) = delete;
+    Iterator& operator=(const Iterator&) = delete;
+    Iterator& operator=(const Iterator&&) = delete;
+  };
+
+  Iterator Iter() { return Iterator(this); }
+
+  Iterator ConstIter() const
+  {
+    return Iterator(const_cast<nsTHashtable*>(this));
+  }
+
   /**
    * Remove all entries, return hashtable to "pristine" state. It's
    * conceptually the same as calling the destructor and then re-calling the