Three ways to build a C # singleton pattern

1     /// <summary>2     ///double check Lock implementation single case3     /// </summary>4      Public Sealed classSingletondoublecheck5     {6         //The S_lock object is required for thread safety, and when defining this object, we assume that the cost of creating a singleton object is higher than creating a System.Object object7         //and assume that you might not need to create a singleton object at all, it would be more economical and easier to create a singleton object in a class builder8         Private StaticObject S_lock =NewObject ();9 Ten         //This field refers to a singleton object One         Private StaticSingletondoublecheck S_value =NULL; A  -         //The private constructor blocks any code outside this class from creating an instance -         PrivateSingletondoublecheck () the         { -  -         } -  +         //the following public static method returns a singleton object (creating it if necessary) -          Public StaticSingletondoublecheck Getsingleton () +         { A             //If the Singleton object is already created, return it directly at             if(S_value! =NULL) -             { -                 returnS_value; -             } -  -             //acquires an exclusive lock on the specified object in Monitor.Enter (s_lock); -  to             //Check again to see if you have created +             //Workaround: If multiple threads are entered at the first time (the Singleton object has not yet been created), then only one thread executes the following code (because there is a monitor), -             //when the thread (the first thread) finishes creating an instance, another thread (the second thread) immediately obtains the lock, and executes the following code, the             //Now that the instance has been created, the subsequent thread should return directly to it, so you can determine if the instance has been created.  *             if(S_value = =NULL) $             {Panax Notoginseng                 //create it if it is still not created -Singletondoublecheck Singleton =NewSingletondoublecheck (); the  +                 //give the singleton to S_value . A                 //The following code guarantees that references in Singleton are published to S_value only after the constructor finishes execution theVolatile.write (refS_value, singleton); +  -                 //Note: The following wording is not reliable $                 //because the compiler might do this: $                 //1. Allocating memory for Singletondoublecheck -                 //2. Publish the reference to (assign) S_value -                 //3. Calling the constructor the                 //Suppose that after a reference is published to S_value, but before the constructor is called, if another thread calls Getsingleton, -                 //at this point, s_value is not NULL, and the thread uses the object, but the constructor for the object has not yet finished executing. Wuyi                 //s_value = new Singletondoublecheck (); the             } -  Wu             //frees an exclusive lock on the specified object - Monitor.Exit (s_lock); About  $             returnS_value; -         } -     } -  A     /// <summary> +     ///simple construction of a single case method under C # the     ///The CLR has ensured that the construction of the class is thread-safe and that writing is simple -     ///The disadvantage is also obvious that the type constructor will be called when any member of the class is first accessed $     ///Therefore, if the class defines other static members, the object is created when any other static member is accessed the     /// </summary> the      Public Sealed classSingletonsimple the     { the         Private StaticSingletonsimple S_value =Newsingletonsimple (); -  in         //The private constructor blocks any code outside this class from creating an instance the         Privatesingletonsimple () the         { About  the         } the  the         //the following public static method returns a singleton object (creating it if necessary) +          Public Staticsingletonsimple Getsingleton () -         { the             returnS_value;Bayi         } the  the         //or -          Public Staticsingletonsimple singletoninstance -         { the             Get{returnS_value;} the         } the  the         //or -          Public StaticSingletonsimple Instance {Get; } =Newsingletonsimple (); the     } the  the     /// <summary>94     ///nested classes implementing a singleton the     ///multiple singletonnested objects may be created if multiple threads call Getsingleton at the same time the     ///However, due to the use of interlocked.compareexchange, it is guaranteed that only one reference will be published to S_value the     ///objects that are not pinned will be garbage collected98     ///this way does not block the thread About     /// </summary> -      Public Sealed classsingletonnested101     {102         Private Staticsingletonnested S_value =NULL;103 104         //The private constructor blocks any code outside this class from creating an instance the         Privatesingletonnested ()106         {107 108         }109  the         //the following public static method returns a singleton object (creating it if necessary)111          Public Staticsingletonnested Getsingleton () the         {113             //If the Singleton object is already created, return it directly the             if(S_value! =NULL) the             { the                 returnS_value;117             }118 119             //Create a new singleton object and pin it down (if another thread hasn't fixed it yet) -singletonnested singletonnested =Newsingletonnested ();121 122             //compares an instance of two specified reference types if T is equal, replaces the first if equal, and returns the S_value original value123             //S_value is compared with NULL, if equality is replaced with singletonnested s_value, otherwise it is not replaced124Interlocked.compareexchange (refS_value, singletonnested,NULL); the 126             //if the thread fails to compete, the newly created second single-instance object is garbage collected127  -             returnS_value;129         } the}

Three ways to build a C # singleton pattern