Added LinkedObjectPool class, which will be used by RewindManager.

Thomas, please contact me for example usage of this class.

src/common/LinkedObjectPool.hxx

@@ -0,0 +1,133 @@
+//============================================================================
+//
+//   SSSS    tt          lll  lll
+//  SS  SS   tt           ll   ll
+//  SS     tttttt  eeee   ll   ll   aaaa
+//   SSSS    tt   ee  ee  ll   ll      aa
+//      SS   tt   eeeeee  ll   ll   aaaaa  --  "An Atari 2600 VCS Emulator"
+//  SS  SS   tt   ee      ll   ll  aa  aa
+//   SSSS     ttt  eeeee llll llll  aaaaa
+//
+// Copyright (c) 1995-2017 by Bradford W. Mott, Stephen Anthony
+// and the Stella Team
+//
+// See the file "License.txt" for information on usage and redistribution of
+// this file, and for a DISCLAIMER OF ALL WARRANTIES.
+//============================================================================
+
+#ifndef LINKED_OBJECT_POOL_HXX
+#define LINKED_OBJECT_POOL_HXX
+
+#include <list>
+#include "bspf.hxx"
+
+/**
+ * A fixed-size object-pool based doubly-linked list that makes use of
+ * multiple STL lists, to reduce frequent (de)allocations.
+ *
+ * This structure acts like a queue (adds to end, removes from beginning),
+ * but also allows for removal at any location in the queue.
+ *
+ * There are two internal lists; one stores active nodes, and the other
+ * stores pool nodes that have been 'deleted' from the active list (note
+ * that no actual deletion takes place; nodes are simply moved from one list
+ * to another).  Similarly, when a new node is added to the active list, it
+ * is simply moved from the pool list to the active list.
+ *
+ * NOTE: For efficiency reasons, none of the methods check for overflow or
+ *       underflow; that is the responsibility of the caller.
+ *
+ *       In the case of methods which wrap the C++ 'splice()' method, the
+ *       semantics of splice are followed wrt invalid/out-of-range/etc
+ *       iterators.  See the applicable documentation for such behaviour.
+ *
+ * @author Stephen Anthony
+ */
+namespace Common {
+
+template <class T, uInt32 CAPACITY = 100>
+class LinkedObjectPool
+{
+  public:
+    using iter = typename std::list<T>::iterator;
+    using const_iter = typename std::list<T>::const_iterator;
+
+    /*
+     * Create a pool of size CAPACITY; the active list starts out empty.
+     */
+    LinkedObjectPool<T, CAPACITY>() {
+      for(uInt32 i = 0; i < CAPACITY; ++i)
+        myPool.emplace_back(T());
+    }
+
+    /**
+     * Add a new node at the end of the active list, and return a reference to
+     * that node. The reference may then be modified; ie, you're able to change
+     * the data located at that node.
+     */
+    T& addLast() {
+      myList.splice(myList.end(), myPool, myPool.begin());
+      return myList.back();
+    }
+
+    /**
+     * Return a reference to the element at the first node.
+     * The reference may not be modified.
+     */
+    const T& first() const { return myList.front(); }
+
+    /**
+     * Remove a single element at position of the iterator +- the offset.
+     */
+    void remove(const_iter i, Int32 offset = 0) {
+      myPool.splice(myPool.end(), myList,
+                    offset >= 0 ? std::next(i, offset) : std::prev(i, -offset));
+    }
+
+    /**
+     * Remove a single element by index, offset from the beginning of the list.
+     * (ie, '0' means first element, '1' is second, and so on).
+     */
+    void remove(uInt32 index) {
+      myPool.splice(myPool.end(), myList, std::next(myList.begin(), index));
+    }
+
+    /**
+     * Convenience method to remove the first element in the list.
+     */
+    void removeFirst() {
+      myPool.splice(myPool.end(), myList, myList.begin());
+    }
+
+    /**
+     * Convenience method to remove a range of elements from 'index' to the
+     * end of the list.
+     */
+    void removeLast(uInt32 index) {
+      myPool.splice(myPool.end(), myList, std::next(myList.begin(), index), myList.end());
+    }
+
+    /** Access the list with iterators, just as you would a normal C++ STL list */
+    iter begin() { return myList.begin(); }
+    iter end()   { return myList.end();   }
+    const_iter begin() const { return myList.cbegin(); }
+    const_iter end() const   { return myList.cend();   }
+
+    uInt32 size() const { return myList.size();      }
+    bool empty() const  { return size() == 0;        }
+    bool full() const   { return size() >= CAPACITY; }
+
+  private:
+    std::list<T> myList, myPool;
+
+  private:
+    // Following constructors and assignment operators not supported
+    LinkedObjectPool(const LinkedObjectPool&) = delete;
+    LinkedObjectPool(LinkedObjectPool&&) = delete;
+    LinkedObjectPool& operator=(const LinkedObjectPool&) = delete;
+    LinkedObjectPool& operator=(LinkedObjectPool&&) = delete;
+};
+
+}  // Namespace Common
+
+#endif