Subj : Re: stl & threads
To   : comp.programming.threads
From : Uenal Mutlu
Date : Tue May 24 2005 01:25 pm

"Lyonya" <leonews@optonline.com> wrote
> have anybody here tried c++'s stl with threads? any
> pitfalls/problems/tips? maybe a book/paper to read?

Here are the ingredients:
You should make each object you want to share (ie. use) among multiple
threads 'lockable'. I recommend to add a mutex to each such object
by using constructs like those below:

class mutex
  {
    public:
      mutex(bool AfRecursiveMutex = true);
      ~mutex();
      void Lock();
      void Unlock();
      bool IsLockedByAny() const;
      bool IsLockedByMe() const;
   // ...
  };

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
  };

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;
  };


Example usage:

Lockable<std::vector<mytype> > vec;

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

void* thrprocB(void* Ap)
{
  Locker L(vec.mx);
  // it is safe to modify vec
}

For a standard implementation of a recursive (and also non-recursive) mutex
under Windows see the following in the Win32 API:
  CRITICAL_SECTION,
  InitializeCriticalSection(),
  DeleteCriticalSection(),
  EnterCriticalSection(),
  LeaveCriticalSection()
A faster alternative is to use atomic counters. A description and code for this
you can find on the page of John M. Dlugosz :
http://www.dlugosz.com/Repertoire/refman/Classics/atomic_counter_whitepaper.html

Futher links:
http://www.codeguru.com/Cpp/W-P/win32/tutorials/article.php/c9823/
http://zthread.sourceforge.net/

.