Re: [PATCH 1/19] MUTEX: Introduce simple mutex implementation

Thomas Gleixner
2005-12-16T22:06:18Z

On Fri, 2005-12-16 at 13:41 -0800, Linus Torvalds wrote:
>
> > > No one. It's not really a mutex, but a completion.
> >
> > Well, then let us use a completion and not some semantically wrong
> > workaround
>
> It is _not_ wrong to have a semaphore start out in locked state.
>
> For example, it makes perfect sense if the data structures that the
> semaphore needs need initialization. The way you _should_ handle that is
> to make the semaphore come up as locked, and the data structures in some
> "don't matter" state, and then the thing that initializes stuff can do so
> properly and then release the semaphore.
>
> Yes, in some cases such a locked semaphore is only used once, and ends up
> being a "completion", but that doesn't invalidate the fact that this is
> a perfectly fine way to handle a real issue.

Well, in case of a semaphore it is a semantically correct use case. In
case of of a mutex it is not.

Gerd was talking about a mutex. The fact that a mutex is implemented on
top (or on actually the same) mechanism as a semaphore - for what ever
reason - does not change the semantical difference between semaphores
and mutexes.

tglx