Using shell commands versus C equivalents

[Rick C. Petty]

On Wed, Jun 13, 2007 at 10:23:36AM -0700, youshi10 at u.washington.edu wrote:
> On Wed, 13 Jun 2007, Joerg Sonnenberger wrote:
> 
> Should I briefly lock (flock) the file when running open/fstat/fchmod then 
> to avoid issues? This may become a problem as pkg_*/make becomes more 
> parallelized (another student's goals for his SoC project).

I wouldn't bother.  What issue are you trying to avoid?  If one process is
trying to chmod +x and another is trying to do a chmod -x, it shouldn't
matter if you lock between the fstat/fchmod-- someone is going to win
anyway.  This operation is not something that needs to be thread-safe.

> Needless to say, pkg_* is by no means threadsafe in its current form 
> though. It uses some global vars that are currently not mutex locked, and 
> this type of file access is another issue (I wonder if spinlocking or 
> sleeping waiting for flock to finish would be better in this case).

Does pkg_* use multiple threads?  I was under the impression each pkg tool
used a single thread (i.e. no threads) to do its operations and that they
wait for system(2)-type calls as needed.  Maybe I'm not clear by what you
mean when you say "global vars".

Now another question is whether the pkg_* tools can handle multiple
processes managing the ports at the same time.  For the mostpart, this is
true.  Without looking at the code, I would expect that the only
contentions would be when trying to update the +REQUIRED_BY files.
Everything else should be just fine;  you're not supposed to be installing
the same port multiple times at the exact same time, but maybe a lock could
be held on the package directory (i.e. /var/db/pkg/$PKG_NAME).  Again, I
don't believe this is strictly necessary.

-- Rick C. Petty