Re: CMultiLock example

From:

"Doug Harrison [MVP]" <dsh@mvps.org>

Newsgroups:

microsoft.public.vc.mfc

Date:

Wed, 19 Aug 2009 15:55:28 -0500

Message-ID:

<p5po85hc1o5sovkki3k5nmen57bakj3aep@4ax.com>

On Wed, 19 Aug 2009 16:39:32 -0400, Joseph M. Newcomer
<newcomer@flounder.com> wrote:

I find it best to build something like

template <class T> class CLockedList : public CList<T> {
    public:
    void Add(T p) { EnterCriticalSection(&lock);
                                          list.Add(p);
                                          LeaveCriticalSection(&lock); }
               void Remove(T p) { EnterCriticalSection(&lock);
                         list.Remove(p);
                                                 LeaveCriticalSection(&lock); }
    CLockedList<T>() { InitializeCriticalSection(&lock); }
    virtual ~CLockedList<T>() { DeleteCriticalSection(&lock); }
    protected:
        CList<T> list;
        CRITICAL_SECTION lock;
    };

The problem with that is always, "How do you lock around a series of
operations that must be atomic?" You can either expose the locking
mechanism or give up on making the class "inherently" thread-safe and
require users to impose locking entirely from the outside. STL containers
choose the latter. Also, I wouldn't derive publicly from CList, because
doing so allows users to manipulate the list through base class functions
which don't respect the locking. Oh wait, you also have "list" as a member
variable. That or (much less likely) private inheritance is the way I'd go.

--
Doug Harrison
Visual C++ MVP