/// <summary>
/// Removes the head of the queue (node with minimum priority; ties are broken by order of insertion), and sets it to first.
/// Useful for multi-threading, where the queue may become empty between calls to Contains() and Dequeue()
/// Returns true if successful; false if queue was empty
/// O(log n)
/// </summary>
public bool TryDequeue(out TItem first)
{
lock (_queue)
{
if (_queue.Count <= 0)
{
first = default(TItem);
return(false);
}
SimpleNode node = _queue.Dequeue();
first = node.Data;
RemoveFromNodeCache(node);
return(true);
}
}
/// <summary>
/// Adds an item to the Node-cache to allow for many methods to be O(1) or O(log n)
/// </summary>
private void AddToNodeCache(SimpleNode node)
{
if (node.Data == null)
{
_nullNodesCache.Add(node);
return;
}
IList <SimpleNode> nodes;
if (!_itemToNodesCache.TryGetValue(node.Data, out nodes))
{
nodes = new List <SimpleNode>();
_itemToNodesCache[node.Data] = nodes;
}
nodes.Add(node);
}
/// <summary>
/// Enqueue a node to the priority queue. Lower values are placed in front. Ties are broken by first-in-first-out.
/// This queue automatically resizes itself, so there's no concern of the queue becoming 'full'.
/// Duplicates and null-values are allowed.
/// O(log n)
/// </summary>
public void Enqueue(TItem item, TPriority priority)
{
lock (_queue)
{
IList <SimpleNode> nodes;
if (item == null)
{
nodes = _nullNodesCache;
}
else if (!_itemToNodesCache.TryGetValue(item, out nodes))
{
nodes = new List <SimpleNode>();
_itemToNodesCache[item] = nodes;
}
SimpleNode node = EnqueueNoLockOrCache(item, priority);
nodes.Add(node);
}
}
/// <summary>
/// Removes an item to the Node-cache to allow for many methods to be O(1) or O(log n) (assuming no duplicates)
/// </summary>
private void RemoveFromNodeCache(SimpleNode node)
{
if (node.Data == null)
{
_nullNodesCache.Remove(node);
return;
}
IList <SimpleNode> nodes;
if (!_itemToNodesCache.TryGetValue(node.Data, out nodes))
{
return;
}
nodes.Remove(node);
if (nodes.Count == 0)
{
_itemToNodesCache.Remove(node.Data);
}
}