PaulH
Mon Jun 25 13:34:53 CDT 2007
On Jun 25, 1:07 pm, ampar...@gmail.com wrote:
> On Jun 25, 10:57 am, PaulH <paul.h...@gmail.com> 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 below.
>
> > The only funny thing I am doing is to load the DLL from two threads
> > simultaneously (thus the need for the singleton). But, according to
> > other posts I've read, the OS will point them both to the same
> > instance of the DLL so that only one thread actually loads the DLL.
>
> If the two threads are from the same process, then there will be only
> one instance of the DLL.
> Having said that, even if the threads are from different process with
> each process having different instanced of the DLL, you need to
> synchronize to have one unique instance of the class.
>
>
>
>
>
> > Can anybody point out where I may be going wrong?
>
> > Thanks,
> > PaulH
>
> > //singletonclass.h
> > class SingletonClass : BaseClass
> > {
> > public:
> > static SingletonClass& Instance();
> > ~SingletonClass();
> > //... Implement BaseClass functions
> > private:
> > static std::auto_ptr< SingletonClass > _theInstance;
> > static Mutex* _m;
>
> > }
>
> > //singletonclass.cpp
> > std::auto_ptr< SingletonClass > SingletonClass::_theInstance;
> > Mutex* SingletonClass::_m;
>
> > /*static*/ SingletonClass& SingletonClass::Instance()
> > {
> > Mutex::Create( &_m );
> > _m->lock();
> > if( _theInstance.get() == NULL )
> > _theInstance.reset( new SingletonClass() );
> > _m->unlock();
> > return *_theInstance;
>
> > }
>
> > //dll.cpp
> > MY_API BaseClass* Create()
> > {
> > return &SingletonClass::Instance();
>
> > }- Hide quoted text -
>
> > - Show quoted text -
>
> Looks ok though one thing I cannot know is you implementation of
> Mutex class ? How are you implementing it internally ? Are you
> implementing it as a Critical Section or as Regular Mutex ? Because
> Critical Section guarentees synchonization only within a process and
> not across processes and so if your threads are from different
> processes, then there could be a problem.
This only needs to work between threads of a single process. I didn't
realize the difference between the CS and the Mutex. I have it
implemented as below as a CS, so the "Mutex" name is a misnomer.
-Paul
class Mutex
{
public:
static HRESULT Create( Mutex** ppMutex )
{
Mutex *pMutex = new Mutex();
if( !pMutex )
{
return E_OUTOFMEMORY;
}
if( !InitializeCriticalSectionAndSpinCount( &pMutex->_cs,
0 ) )
{
HRESULT hr = HRESULT_FROM_WIN32( GetLastError() );
delete pMutex;
return hr;
}
pMutex->_Initialized = TRUE;
*ppMutex = pMutex;
pMutex = NULL;
return S_OK;
};
~Mutex()
{
if( this->_Initialized )
DeleteCriticalSection( &this->_cs );
};
void lock()
{
EnterCriticalSection( &this->_cs );
};
void unlock()
{
LeaveCriticalSection( &this->_cs );
};
private:
Mutex(){};
CRITICAL_SECTION _cs;
BOOL _Initialized;
};