Re: rw_lock_held

[Paul Goyette <paul%whooppee.com@localhost>]

On Wed, 7 Feb 2018, Ryota Ozaki wrote:

> > a better wording for the manpage could be:
> >
> >         Test the lock's condition and return non-zero if the lock is
> >         potentially held by the current LWP and matches the specified
> >         condition.  Otherwise, return zero.
> >
> > thus if we see that lock is held (in write mode) by some other LWP then
> > we know that is not even potentially held by the current LWP.
>
> I think we don't need "potentially" anymore. And "matches the specified
> condition" is unclear to me (I know it's the original wording). So I prefer
> the following one though it's a bit redundant:
>
>       rw_write_held() returns non-zero if the lock is held by the current
>       LWP for write.  rw_read_held() returns non-zero if the lock is held
>       by the current LWP for read.  rw_lock_held() returns non-zero if
>       the lock is held by the current LWP for write or read.  Otherwise,
>       these functions return zero.

I like this version much better.

It is also important to retain the restriction against using these 
functions for making run-time locking decisions...  In particular, it is 
not acceptable to do

	if (!rw_write_held(&my_lock))
		rw_enter(&my_lock, RW_WRITER);


:)




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