Singleton: Difference between revisions
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(Added non-thread-safe C++ version, subcategorized ObjC and C++ examples.) |
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// Release our mutex so that other application threads can use this function |
// Release our mutex so that other application threads can use this function |
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ReleaseMutex( hMutex ); |
ReleaseMutex( hMutex ); |
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// Free the handle |
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CloseHandle( hMutex ); |
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// Return a pointer to our mutex instance. |
// Return a pointer to our mutex instance. |
Revision as of 14:48, 6 February 2008
Singleton
You are encouraged to solve this task according to the task description, using any language you may know.
You are encouraged to solve this task according to the task description, using any language you may know.
A Global Singleton is a class of which only one instance exists within a program. Any attempt to use non-static members of the class involves performing operations on this one instance.
C++
Thread-safe
Operating System: Microsoft Windows NT/XP/Vista
class Singleton { public: static Singleton* Instance() { // We need to ensure that we don't accidentally create two Singletons HANDLE hMutex = CreateMutex(NULL, FALSE, "MySingletonMutex"); WaitForSingleObject(hMutex, INFINITE); // Create the instance of the class. // Since it's a static variable, if the class has already been created, // It won't be created again. static Singleton myInstance; // Release our mutex so that other application threads can use this function ReleaseMutex( hMutex ); // Free the handle CloseHandle( hMutex ); // Return a pointer to our mutex instance. return &myInstance; } // Any other public methods protected: Singleton() { // Constructor code goes here. } ~Singleton() { // Destructor code goes here. } // And any other protected methods. }
Non-Thread-Safe
This version doesn't require any operating-system or platform-specific features, but it is not safe in a multi-threaded environment.
class Singleton { public: static Singleton* Instance() { // Since it's a static variable, if the class has already been created, // It won't be created again. static Singleton myInstance; // Return a pointer to our mutex instance. return &myInstance; } // Any other public methods protected: Singleton() { // Constructor code goes here. } ~Singleton() { // Destructor code goes here. } // And any other protected methods. }
Objective-C
Non-Thread-Safe
(Using Cocoa's NSObject as a base class)
// SomeSingleton.h @interface SomeSingleton : NSObject { // any instance variables } + (SomeSingleton*)sharedInstance; @end
// SomeSingleton.m @implementation SomeSingleton + (SomeSingleton*) sharedInstance { static sharedInstance = nil; if(!sharedInstance) { sharedInstance = [[SomeSingleton alloc] init]; } return sharedInstance; } @end