Messages in this thread |  | | From | Roger Larsson <> | Date | Sat, 25 Nov 2000 20:03:49 +0100 | Subject | Re: *_trylock return on success? |
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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
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