[Pkg-octave-devel] Bug#550823: Updating load-path cache based on modification times probably a bad idea (was: Race condition between Octave 3.2.3 and unlink())

[Jaroslav Hajek <highegg@gmail.com>]

2009/10/20 Thomas Weber <thomas.weber.mail@gmail.com>:
> Hi,
>
> On Thu, Oct 15, 2009 at 02:09:30PM +0000, Sébastien Villemot wrote:
>> Hi,
>>
>> I think I found the culprit for what I thought was a race condition in
>> Octave.
>>
>> The problem has to do with the way Octave 3.2 updates its load-path: it
>> only updates its cache of the current directory if the modification time
>> of the directory changes (see load_path::dir_info::update() in
>> src/load-path.cc).
>
> In case it's not clear: this is a real problem and not some artificially
> found issue. It makes software using Octave randomly fail at build time.
>
>        Thomas
>

I don't understand - what you mean by "build time"? Most software
using Octave is not dynamically creating m-files, so is not affected.
The problem is in load_path::update, which checks the directory's
modification time to decide on whether to rescan it. The resolution is
only in seconds, though. But some check is surely wanted because you
want to avoid useless rescans. I don't have a better idea. One could
even say this is a limitation of the system, which provides no way to
tell whether the directory has changed during the last second. Maybe
rehash() could ignore the stamp for some directories? But which ones?

-- 
RNDr. Jaroslav Hajek
computing expert & GNU Octave developer
Aeronautical Research and Test Institute (VZLU)
Prague, Czech Republic
url: www.highegg.matfyz.cz