comments for thread-safe singleton

tk-codes · tk-codes · commit 77bf9eb6c897 · 2016-12-21T22:53:34.000+01:00
diff --git a/CreationalPatterns/Singleton/ChocolateBoiler_ThreadSafe.cs b/CreationalPatterns/Singleton/ChocolateBoiler_ThreadSafe.cs
@@ -12,6 +12,7 @@ public sealed class ChocolateBuilder_ThreadSafe
         public bool Boiled { get; set; }
 
         // singleton instance
+        // the volatile keyword ensures that multiple threads handle the singleton instance variable correctly
         private static volatile ChocolateBuilder_ThreadSafe instance;
         private static object syncLock = new object();
 
@@ -25,10 +26,12 @@ public static ChocolateBuilder_ThreadSafe Instance
         {
             get
             {
+                // Check for an instance and if there isn't one, enter a locked block
                 if (instance == null)
                 {
                     lock (syncLock)
                     {
+                        // Once in the block, check again and if still null
                         if(instance == null)
                         {
                             instance = new ChocolateBuilder_ThreadSafe();

Original file line number	Diff line number	Diff line change
`@@ -12,6 +12,7 @@ public sealed class ChocolateBuilder_ThreadSafe`
`12`	`12`	`public bool Boiled { get; set; }`
`13`	`13`
`14`	`14`	`// singleton instance`
	`15`	`+ // the volatile keyword ensures that multiple threads handle the singleton instance variable correctly`
`15`	`16`	`private static volatile ChocolateBuilder_ThreadSafe instance;`
`16`	`17`	`private static object syncLock = new object();`
`17`	`18`
`@@ -25,10 +26,12 @@ public static ChocolateBuilder_ThreadSafe Instance`
`25`	`26`	`{`
`26`	`27`	`get`
`27`	`28`	`{`
	`29`	`+ // Check for an instance and if there isn't one, enter a locked block`
`28`	`30`	`if (instance == null)`
`29`	`31`	`{`
`30`	`32`	`lock (syncLock)`
`31`	`33`	`{`
	`34`	`+ // Once in the block, check again and if still null`
`32`	`35`	`if(instance == null)`
`33`	`36`	`{`
`34`	`37`	`instance = new ChocolateBuilder_ThreadSafe();`