Subj : Re: Challenge: Multithreading & Synchronization
To   : comp.programming.threads
From : Uenal Mutlu
Date : Fri May 20 2005 11:14 pm

"Maciej Sobczak" wrote
> Uenal Mutlu wrote:
>
> >>The terminal?
> >
> > Of course:
> > Question: Is in your application the terminal shared by multiple threads?
> > Answer: YES
> > Then: make the terminal lockable
>
> No. I have specifically used the puts() function to show you that there
> are cases where there might be no "object" which you can "physically"
> grab and wrap. This example was extremely simple, yet you have rejected
> to see the point and have converted the example to use cout - just to
> fit it to your broken idea?
>
> Let's say there is no cout, but instead the "print" function:
>
> print("I'm doing something");
>
> Show me how you make it lockable. Forget about streams, cout, stdout or
> any other object.

If you cannot assign a mutex to an object (funny imagination in MT app, btw)
then use a wrapper + mutex for it. Like this one:
mutex gm;
void myprint(char* Apsz)
{
  Locker L(gm);
  print(Apsz);
}

> Yes, you can make a class around this single function, create an object
> out of it (singleton or monostate) and then make it lockable, but it is
> still not the point - I can have many different "unit" actions (even
> belonging to different libraries) that I want to orchestrate to achieve
> some sequence that will be well-defined according to some protocol.
> Mutex per object will not help me with this.

If you think so, then it indeed will not help you. I was thinking you
were looking for a practical solution, but it seems you are after artifical
situations where it seems impossible (to you). Take my advice: there's always a way!

> > How: of course by a mutex; see below
>
> >>Again - think in terms of actions, not in terms of objects
> >>(multithreading is about "doing", not about "values"). Then you will
> >>maybe discover that your concept of embedding mutexes in all value
> >>objects brings you nowhere.
> >
> > Time will prove you wrong.
>
> Time's already proved that I was wrong a few times in my life, so I'm ready.

Sorry to hear about this.

> > But, in case you really don't know:
> >
> > In your case actually you want to use 2 objects in a shared manner:
> >   1) the output stream
> >   2) the vector
>
> In this specific case, fine.
>
> > Using the "mutex per object" method gives you a simple and elegant solution:
>
> Except when there is no object? (see the print function above)

Everything is an object.

> > Some people will argue that just 1 mutex would be sufficient. Let them think so.
> > The above is the recommended method.
>
> Could you reference some books or articles recommending it?

I don't know if anybody else is recommending this method, but I for sure do it.
Just do your own research --> google.

.