Merge pull request #2192 from dasMulli/random-seeding-improvements

System.Random: Parameterless constructor seeding improvement #1919

1 files changed, 46 insertions, 12 deletions

diff --git a/src/mscorlib/src/System/Random.cs b/src/mscorlib/src/System/Random.cs
index b8ff967a5f..4059b4cfde 100644
--- a/src/mscorlib/src/System/Random.cs
+++ b/src/mscorlib/src/System/Random.cs
@@ -11,13 +11,14 @@
 ** 
 ===========================================================*/
 namespace System {
-    
+
     using System;
     using System.Runtime;
     using System.Runtime.CompilerServices;
     using System.Globalization;
     using System.Diagnostics.Contracts;
-[System.Runtime.InteropServices.ComVisible(true)]
+
+    [System.Runtime.InteropServices.ComVisible(true)]
     [Serializable]
     public class Random {
       //
@@ -46,11 +47,17 @@ namespace System {
       //
       // Constructors
       //
-    
+      
+      /*=========================================================================================
+      **Action: Initializes a new instance of the Random class, using a default seed value
+      ===========================================================================================*/
       public Random() 
-        : this(Environment.TickCount) {
+        : this(GenerateSeed()) {
       }
-    
+      
+      /*=========================================================================================
+      **Action: Initializes a new instance of the Random class, using a specified seed value
+      ===========================================================================================*/
       public Random(int Seed) {
         int ii = 0;
         int mj, mk;
@@ -79,11 +86,11 @@ namespace System {
         inextp = 21;
         Seed = 1;
       }
-    
+
       //
       // Package Private Methods
       //
-    
+
       /*====================================Sample====================================
       **Action: Return a new random number [0..1) and reSeed the Seed array.
       **Returns: A double [0..1)
@@ -117,11 +124,41 @@ namespace System {
           return retVal;
       }
 
+
+      [ThreadStatic]
+      private static Random t_threadRandom;
+      private static readonly Random s_globalRandom = new Random(GenerateGlobalSeed());
+
+      /*=====================================GenerateSeed=====================================
+      **Returns: An integer that can be used as seed values for consecutively
+                 creating lots of instances on the same thread within a short period of time.
+      ========================================================================================*/
+      private static int GenerateSeed() {
+          Random rnd = t_threadRandom;
+          if (rnd == null) {
+              int seed;
+              lock (s_globalRandom) {
+                  seed = s_globalRandom.Next();
+              }
+              rnd = new Random(seed);
+              t_threadRandom = rnd;
+          }
+          return rnd.Next();
+      }
+
+      /*==================================GenerateGlobalSeed====================================
+      **Action:  Creates a number to use as global seed.
+      **Returns: An integer that is safe to use as seed values for thread-local seed generators.
+      ==========================================================================================*/
+      private static int GenerateGlobalSeed() {
+          return Guid.NewGuid().GetHashCode();
+      }
+
       //
       // Public Instance Methods
       // 
-    
-    
+
+
       /*=====================================Next=====================================
       **Returns: An int [0..Int32.MaxValue)
       **Arguments: None
@@ -210,7 +247,4 @@ namespace System {
         }
       }
     }
-
-
-
 }