Subj : Re: recursive mutexes
To   : comp.programming.threads
From : Uenal Mutlu
Date : Mon May 16 2005 05:30 pm

"Torsten Robitzki" wrote
> Uenal Mutlu wrote:
>
> > "doug" wrote
> >
> >>>You seem to not understand what I'm talking about.
> >>>Do you understand this fact: "Recursive locking is defined for the current
> >>>lock owning thread only"?
> >>>Since you already have the lock you can do what ever you want since nobody
> >>>else can change anything, but you can do! You simply increment it in
> >>>Lock()
> >>>and decrement it in Unlock(). Because it is safe because you already have
> >>>it locked.
> >>>
> >>
> >>Think carefully.  How is this possible?
> >
> > It is really basic stuff. Ask yourself how you would extend a non-recursive
> > locking method to make it recursive? Recursivity starts with the 2nd Lock()
> > call on the same object within the same thread, true?
>
> First one have to check if this lock request comes from the thread
> holding the mutex or not. This can not be implemented by a simple
> increment.

I can only repeat: The code which increments the counter cannot be
executed by anyone else but the current lock holding thread.
Do you know what a critical section is?

In your other posting you wrote:

> P.S. never used recursive locks and never had any serious problems with
> deadlocks.

May I ask: have you ever either implemented any mutex (recursive or non-recursive)
by yourself or have you ever used a non-recursive mutex in your projects?
For which OS and using which threading pkg do you develop?

.