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Lower alloc KeyValueAccumulator for common path

This commit is contained in:
Ben Adams 2016-02-04 21:35:13 +00:00 committed by Chris R
parent 1f754f65d3
commit 8c72741992
1 changed files with 45 additions and 17 deletions
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62
src/Microsoft.AspNetCore.WebUtilities/KeyValueAccumulator.cs
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@ -9,24 +9,55 @@ namespace Microsoft.AspNetCore.WebUtilities
{
public struct KeyValueAccumulator
{
private Dictionary<string, List<string>> _accumulator;
private Dictionary<string, StringValues> _accumulator;
private Dictionary<string, List<string>> _expandingAccumulator;
public void Append(string key, string value)
{
if (_accumulator == null)
{
_accumulator = new Dictionary<string, List<string>>(StringComparer.OrdinalIgnoreCase);
_accumulator = new Dictionary<string, StringValues>(StringComparer.OrdinalIgnoreCase);
}
List<string> values;
StringValues values;
if (_accumulator.TryGetValue(key, out values))
{
values.Add(value);
if (values.Count == 0)
{
// Marker entry for this key to indicate entry already in expanding list dictionary
_expandingAccumulator[key].Add(value);
}
else if (values.Count == 1)
{
// Second value for this key
_accumulator[key] = new string[] { values[0], value };
}
else
{
// Third value for this key
// Add zero count entry and move to data to expanding list dictionary
_accumulator[key] = default(StringValues);
if (_expandingAccumulator == null)
{
_expandingAccumulator = new Dictionary<string, List<string>>(StringComparer.OrdinalIgnoreCase);
}
// Already 3 entries so use starting allocated as 8; then use List's expansion mechanism for more
var list = new List<string>(8);
var array = values.ToArray();
list.Add(array[0]);
list.Add(array[1]);
list.Add(value);
_expandingAccumulator[key] = list;
}
}
else
{
values = new List<string>(1);
values.Add(value);
_accumulator[key] = values;
// First value for this key
_accumulator[key] = new StringValues(value);
}
}
@ -34,19 +65,16 @@ namespace Microsoft.AspNetCore.WebUtilities
public Dictionary<string, StringValues> GetResults()
{
if (_accumulator == null)
if (_expandingAccumulator != null)
{
return new Dictionary<string, StringValues>(StringComparer.OrdinalIgnoreCase);
// Coalesce count 3+ multi-value entries into _accumulator dictionary
foreach (var entry in _expandingAccumulator)
{
_accumulator[entry.Key] = new StringValues(entry.Value.ToArray());
}
}
var results = new Dictionary<string, StringValues>(_accumulator.Count, StringComparer.OrdinalIgnoreCase);
foreach (var kv in _accumulator)
{
results.Add(kv.Key, kv.Value.Count == 1 ? new StringValues(kv.Value[0]) : new StringValues(kv.Value.ToArray()));
}
return results;
return _accumulator ?? new Dictionary<string, StringValues>(0, StringComparer.OrdinalIgnoreCase);
}
}
}