Re: init (via ctor) of function local static var : not thread safe ????

From:

Hendrik Schober <Spamtrap@gmx.de>

Newsgroups:

microsoft.public.vc.language

Date:

Fri, 20 Jun 2008 18:12:42 +0200

Message-ID:

<uhSx5Bv0IHA.800@TK2MSFTNGP02.phx.gbl>

Giovanni Dicanio wrote:

"mario semo" <mario_semo@hotmail.com> ha scritto nel messaggio
news:F416F1C3-7C07-4CDA-8F33-138C8C304C7D@microsoft.com...

You may consider Win32 CRITICAL_SECTION if the threads that are going to
access the shared resource are in the same process.

mh, i have to say that currently i have no idea how to handle it.

First thing, I would define a C++ class to wrap CRITICAL_SECTION, something
like this:

<code>

class CriticalSection
{
  public:
      CriticalSection()
      {
          ::InitializeCriticalSection( &cs );
      }

      ~CriticalSection()
      {
          ::DeleteCriticalSection( &cs );
      }

      void Enter()
      {
          ::EnterCriticalSection( &cs );
      }

      void Leave()
      {
          ::LeaveCriticalSection( &cs );
      }

  private:
    CRITICAL_SECTION cs;

    // Ban copy
  private:
    CriticalSection( const CriticalSection & );
    CriticalSection & operator=( const CriticalSection & );
};

</code>

Next thing I would do is to write an exception-safe locker:

   class CSLocker {
     public:
       CSLocker(CriticalSection& cs) cs_(cs) {cs_.Enter();}
       ~CSLocker() {cs_.Leave();}
     private:
       CSLocker(const CSLocker&); // forbidden
       CSLocker& operator=(const CSLocker&); // verboten
       CriticalSection& cs_;
   };

Then, assuming that you have Foo defined somewhere, you can associate a
critical section to it:

   Foo foo;
   CriticalSection csFoo;

So, when you need to access 'foo' from some thread, you do:

   // Ask access to resource

   {
     Locker l(csFoo);
     // Modify foo....
     // Releasing is done automatically at the end of the scope
   }

HTH,
Giovanni

Schobi