lkml.org 
[lkml]   [2000]   [Nov]   [25]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
From
Date
SubjectRe: *_trylock return on success?
On Saturday 25 November 2000 19:30, Philipp Rumpf wrote:
> 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.

Not spin_trylock

Simple example code from
code from include/asm-mips/spinlock.h:65
#define spin_trylock(lock) (!test_and_set_bit(0,(lock)))

/RogerL

> -
> To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
> the body of a message to majordomo@vger.kernel.org
> Please read the FAQ at http://www.tux.org/lkml/

--
--
Home page:
http://www.norran.net/nra02596/
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
Please read the FAQ at http://www.tux.org/lkml/

\
 
 \ /
  Last update: 2005-03-22 12:47    [W:0.046 / U:1.004 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site