Re: singleton in a DLL loaded class

"Igor Tandetnik" <>
Mon, 25 Jun 2007 15:45:34 -0400
PaulH <> wrote:

On Jun 25, 2:00 pm, "Igor Tandetnik" <> wrote:

PaulH <> wrote:

On Jun 25, 1:29 pm, "Igor Tandetnik" <> wrote:

PaulH <> wrote:

I have a class loaded from a DLL that I would like to implement
as a multi-threadable singleton. Unfortunately, I seem to still be
getting two distinct instances of this class. It is implemented as

class SingletonClass : BaseClass
   static SingletonClass& Instance();
   //... Implement BaseClass functions
   static std::auto_ptr< SingletonClass > _theInstance;
   static Mutex* _m;

std::auto_ptr< SingletonClass > SingletonClass::_theInstance;
Mutex* SingletonClass::_m;

/*static*/ SingletonClass& SingletonClass::Instance()
   Mutex::Create( &_m );

What does Mutex::Create do? It appears you are creating a new mutex
every time Instance() is called.

I am.

But that defeats the whole point of having the mutex in the first

So how do I make them use the same mutex?

Initialize it when the DLL loads. Just have a global object with a
constructor specifically for this purpose:

struct MutexCreator {
    MutexCreator() {
        Mutex::Create( &SingletonClass::_m );
    // Perhaps a ~MutexCreator to destroy the mutex

// Runs the constructor during DLL initialization. Not used otherwise
MutexCreator mutex_creator;

With best wishes,
    Igor Tandetnik

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