Subj : Re: How to return a value before leaving critical section?
To   : comp.programming.threads
From : David Schwartz
Date : Tue Jul 19 2005 01:06 pm


"MC" <nospam@nowhere.com> wrote in message 
news:aciqd1hcu4m0s7s44k3gakvd46k63udked@4ax.com...

> Threading newbie here.  This question has surely been answered 1000
> times.

> I have a member variable that I want to share between two threads.  I
> make it private and I write a public accessor function, inside which,
> I use a mutex--actually, I use a Windows CRITICAL_SECTION variable and
> then call Enter/LeaveCriticalSection() but I'm hoping that's beside
> the point.  The dilemna, of course, is that both statements need to be
> the last statement of the function:

> return m_MyMember;
>        *and*
> LeaveCriticalSection(m_pMyCrSection);

> I could use an output parameter instead of a return value but then the
> calling code gets uggggglyyy!  Is this the only solution?

    In C++, you have a very elegant solution where you create a 'lock 
holder' class and an instance of that class. You can then have the 
destructor release the lock.

    In C, why not just create a copy and return the copy? For most types, 
'return' returns a copy anyway. What type is 'm_MyMember'?

    DS

.