Re: *_trylock return on success?

[Philipp Rumpf]

On Sat, Nov 25, 2000 at 03:49:25PM -0200, Rik van Riel wrote:
> On Sat, 25 Nov 2000, Roger Larsson wrote:
> 
> > Questions:
> >   What are _trylocks supposed to return?
> 
> It depends on the type of _trylock  ;(
> 
> >   Does spin_trylock and down_trylock behave differently?
> >   Why isn't the expected return value documented?
> 
> The whole trylock stuff is, IMHO, a big mess. When you
> change from one type of trylock to another, you may be
> forced to invert the logic of your code since the return
> code from the different locks is different.
> 
> For bitflags, for example, the trylock returns the state
> the bit had before the lock (ie. 1 if the thing was already
> locked).

I assume you're talking about test_and_{set,clear}_bit here.  Their return
value isn't consistent with the other _trylock functions since they're not
_trylock functions.

I think the real problem is that people use test_and_set_bit for locks,
which is almost never[1] a good idea.  The overhead for a semaphore shouldn't
be too much in most cases, and that way it is obvious what you want to do -
and, hopefully, even more obvious if you end up with a semaphore that can
be turned into a spinlock without further changes.

> For spinlocks, it'll probably return something else ;/

_trylock functions return 0 for success.