Re: Singleton_pattern and Thread Safety

Victor Bazarov <v.bazarov@comcast.invalid>
Thu, 09 Dec 2010 11:35:26 -0500
On 12/9/2010 11:19 AM, Pallav singh wrote:

HI All ,

i have a query using given singleton that its not thread Safe ?

Are you asking or are you telling?

Since function getInstance() is returning the static object singleton
AS far my knowlege, static object is intialized only first time when
reaches there. The second time control Thread reached there , compiler
skipps the initialization part.

Yes, usually. What's your query?

You probably need to get familiar with the problem of thread safety of
static object initialization. It's not very common, but it's been
studied enough to have left a trail that you could find using your
favorite Web search engine.

// This version solves the problems of the minimalist Singleton above,
// but strictly speaking only in a single-threaded environment,
// and use in a multithreaded environment when relying on the ABI
// may still pose problems at program termination time.

class Singleton
   Singleton() {}
   ~Singleton() {}
   Singleton(const Singleton&); // intentionally undefined
   Singleton& operator=(const Singleton&); // intentionally undefined

   static Singleton&getInstance();

// Source file (.cpp)
Singleton& Singleton::getInstance()
   // Static Variables are initialized only first time Thread of
   // Execution reaches here first time.
   static Singleton instance;
   return instance;


Not sure for what...

Pallav Singh

I do not respond to top-posted replies, please don't ask

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