[Feature] Use cache for dash padding

iSazonov · iSazonov · commit 7cc7d18ce067 · 2018-04-11T17:16:56.000+05:00
diff --git a/src/System.Management.Automation/FormatAndOutput/common/TableWriter.cs b/src/System.Management.Automation/FormatAndOutput/common/TableWriter.cs
@@ -180,7 +180,7 @@ internal void GenerateHeader(string[] values, LineOutput lo)
                 // NOTE: we can do this because "-" is a single cell character
                 // on all devices. If changed to some other character, this assumption
                 // would be invalidated
-                breakLine[k] = new string('-', count);
+                breakLine[k] = StringUtil.DashPadding(count);
             }
             GenerateRow(breakLine, lo, false, null, lo.DisplayCells);
         }
diff --git a/src/System.Management.Automation/utils/StringUtil.cs b/src/System.Management.Automation/utils/StringUtil.cs
@@ -81,6 +81,24 @@ internal static string Padding(int countOfSpaces)
 
             return result;
         }
+
+        private const int DashCacheMax = 120;
+        private static readonly string[] DashCache = new string[DashCacheMax];
+        internal static string DashPadding(int count)
+        {
+            if (count >= DashCacheMax)
+                return new string('-', count);
+
+            var result = DashCache[count];
+
+            if (result == null)
+            {
+                Interlocked.CompareExchange(ref DashCache[count], new string('-', count), null);
+                result = DashCache[count];
+            }
+
+            return result;
+        }
     }
 }   // namespace
 

Original file line number	Diff line number	Diff line change
`@@ -180,7 +180,7 @@ internal void GenerateHeader(string[] values, LineOutput lo)`
`180`	`180`	`// NOTE: we can do this because "-" is a single cell character`
`181`	`181`	`// on all devices. If changed to some other character, this assumption`
`182`	`182`	`// would be invalidated`
`183`		`- breakLine[k] = new string('-', count);`
	`183`	`+ breakLine[k] = StringUtil.DashPadding(count);`
`184`	`184`	`}`
`185`	`185`	`GenerateRow(breakLine, lo, false, null, lo.DisplayCells);`
`186`	`186`	`}`