Subj : Re: stl & threads
To   : comp.programming.threads
From : Torsten Robitzki
Date : Tue May 24 2005 08:11 pm

Uenal Mutlu wrote:
> "Lyonya" <leonews@optonline.com> wrote
> 
> And by using the following you can extend any object with a default
> contructor to a 'Lockable' object, for example all STL containers:
> 
> template<typename T> class Lockable : public T
>   {
>     public:
>       mutex mx;    // a mutex for the object
>       Lockable() {}
>     private:
>       Lockable(const Lockable&);   // copy ctor: prohibit copying
>   };

The mutex should prohibit the copying of this wrapper already or the 
mutex implementation is already broken.

> Then, in applic code one would use something like the following
> automatic helper object to do the actual locking/unlocking:
> 
> class Locker
>   {
>     public:
>       Locker(mutex& Amx) : mx(Amx) { mx.Lock();   }
>       ~Locker()                 { mx.Unlock(); }
>     private:
>       mutex& mx;
>   };

Here copying and assigning should be disabled or you can end up with 
doubled calls to Unlock().

But reuse is always better then rewrite:


Example usage:

std::pair<mutex, std::vector<mytype> > vec;

void* thrprocA(void* Ap)
{
   Locker L(vec.first);
   // it is safe to modify vec.second
}

sorry couldn't resist

regards
Torsten

.