From 5f6f08e23626a3c7cc846d76d2d42e2e9ac05c6a Mon Sep 17 00:00:00 2001
From: stephentoub <stoub@microsoft.com>
Date: Sun, 10 Jan 2016 15:39:37 -0500
Subject: [PATCH] Add some optimizations to AppDomain.Setup string handling

- Paths are normalized from a delimited string into a delimited StringBuilder.  It's very likely that the resulting data in the StringBuilder will be the same length or approximately the same length as that in the input string,  So pre-size the StringBuilder to be the same as the input length.
- Reuse StringBuilder instance for handling each property that needs it.
- Reuse the char[] array created for the path sepator
---
 src/mscorlib/src/System/AppDomain.cs | 28 +++++++++++++++++++++-------
 1 file changed, 21 insertions(+), 7 deletions(-)

diff --git a/src/mscorlib/src/System/AppDomain.cs b/src/mscorlib/src/System/AppDomain.cs
index a672d6c..a97eddd 100644
--- a/src/mscorlib/src/System/AppDomain.cs
+++ b/src/mscorlib/src/System/AppDomain.cs
@@ -3623,6 +3623,8 @@ namespace System {
 
             if(propertyNames!=null && propertyValues != null)
             {
+                char[] pathSeparators = null;
+                StringBuilder normalisedAppPathList = null;
                 for (int i=0; i<propertyNames.Length; i++)
                 {
                     
@@ -3675,20 +3677,32 @@ namespace System {
                         nSetNativeDllSearchDirectories(paths);
                     }
                     else
-                    if (propertyNames[i]=="TRUSTED_PLATFORM_ASSEMBLIES" ||
-                        propertyNames[i]=="PLATFORM_RESOURCE_ROOTS" ||
-                        propertyNames[i]=="APP_PATHS" ||
-                        propertyNames[i]=="APP_NI_PATHS")
+                    if(propertyNames[i]=="TRUSTED_PLATFORM_ASSEMBLIES" ||
+                       propertyNames[i]=="PLATFORM_RESOURCE_ROOTS" ||
+                       propertyNames[i]=="APP_PATHS" ||
+                       propertyNames[i]=="APP_NI_PATHS")
                     {
                         if(propertyValues[i]==null)
                             throw new ArgumentNullException(propertyNames[i]);
 
-                        StringBuilder normalisedAppPathList = new StringBuilder();
-                        foreach(string path in propertyValues[i].Split(Path.PathSeparator))
+                        int estimatedLength = propertyValues[i].Length + 1; // +1 for extra separator temporarily added at end
+                        if (normalisedAppPathList == null) {
+                            normalisedAppPathList = new StringBuilder(estimatedLength);
+                        }
+                        else {
+                            normalisedAppPathList.Clear();
+                            if (normalisedAppPathList.Capacity < estimatedLength)
+                                normalisedAppPathList.Capacity = estimatedLength;
+                        }
+
+                        if (pathSeparators == null)
+                            pathSeparators = new[] { Path.PathSeparator };
+
+                        foreach(string path in propertyValues[i].Split(pathSeparators))
                         {
                             if( path.Length==0 )                  // skip empty dirs
                                 continue;
-                               
+
                             if (Path.IsRelative(path))
                                 throw new ArgumentException( Environment.GetResourceString( "Argument_AbsolutePathRequired" ) );
 
-- 
2.7.4