/// <summary>
/// Retrieve or creates a new item at the specified index.
/// </summary>
/// <param name="index">The index.</param>
/// <returns>The value.</returns>
/// <exception cref="ArgumentOutOfRangeException">index;index must be greater or equal to 0 and less than capacity</exception>
public T Get(int index)
{
if (index < 0 || index >= _entries.Capacity)
{
throw new ArgumentOutOfRangeException(nameof(index), "index must be greater or equal to 0 and less than capacity");
}
// Using TryGetValue first just avoid wasting a needle
if (_entries.TryGetInternal(index, out var found))
{
// Null resistant
found.TryGetValue(out var previous);
return(previous);
// We don't donate because we didn't remove
}
var newNeedle = _needleIndexFactory(index);
if (_entries.InsertInternal(index, newNeedle, out found))
{
return(newNeedle.Value);
}
// we just failed to insert, meaning that we created a useless needle
// donate it
Reservoir.DonateNeedle(newNeedle);
return(found.Value);
}
/// <summary>
/// Adds the specified item. Will not overwrite existing items.
/// </summary>
/// <param name="item">The item.</param>
/// <returns>Returns the position where the item was added, -1 otherwise.</returns>
public int TryAdd(T item)
{
var index = Interlocked.Increment(ref _index) & (_capacity - 1);
if (_entries.InsertInternal(index, item))
{
return(index);
}
return(-1);
}
/// <summary>
/// Attempts to Adds the specified item.
/// </summary>
/// <param name="item">The item.</param>
/// <returns>
/// <c>true</c> if the item was added; otherwise, <c>false</c>.
/// </returns>
public bool TryAdd(T item)
{
if (_entries.Count < Capacity)
{
var preCount = Interlocked.Increment(ref _preCount);
if (preCount <= Capacity)
{
var index = (Interlocked.Increment(ref _indexEnqueue) - 1) & (Capacity - 1);
if (_entries.InsertInternal(index, item))
{
return(true);
}
}
Interlocked.Decrement(ref _preCount);
}
return(false);
}