🚀 go-pugleaf

"mataus" <mataus@gmail.com> wrote in message 
news:4784d07b@newsgroups.borland.com...

> I have a question about threads and Critical Sections.  I need my main
> thread to tell another thread of some state change.  This is shows with an
> integer or boolean in the second thread.  Must i use Critical Section when
> updating or is it safe to change an integer value?

Always use a critical section or some other semaphore for data that can be 
accessed from multiple threads.  You should encapsulate the critical section 
inside the thread that owns the variable.  For example:

  class TThread1
  {
    private:
      TCriticalSection* fSync;
      bool fSomeState;

      ...

      bool get_SomeState();
      void set_SomeState(bool Value);

      ...

      void SomeInternalMethod();

    public:
      ...

      __property SomeState =
        { read = get_SomeState, write = set_SomeState };
  };

  bool TThread1::get_SomeState()
  {
    bool result;
    fSync->Acquire();
    result = fSomeState;
    fSync->Release();
    return result;
  }

  void TThread1::set_SomeState(bool Value)
  {
    fSync->Acquire();
    fSomeState = Value;
    fSync->Release();
  }

  void TThread1::SomeInternalMethod()
  {
    // The thread should always access the variable via the semaphore
    //  not directly.
    if (SomeState)
    {
    }
  }

Notes:

Since a semaphore is not tied to any specific memory location a single one 
can be used to protect access to multiple variables (if needed).

To increase efficiency for reads use a semaphore like 
TMultiReadExclusiveWrite so that multiple inspection requests are not 
blocked unless there is a write happening.

Clayton