Re: Understanding SWI's relationship with a C++ app's working directory.

I recommend NOT using the official working directory except for initial orientation. That way, your program is in charge of the matter and you needn't worry about, e.g. a file-open dialog changing the directory without your explicit acknowledgement of the change.

Alan Baljeu

On 2014-03-04, at 3:12 PM, Jan Wielemaker <[email protected]> wrote:

> On 03/04/2014 08:43 PM, Kaitain Jones wrote:
>>> If nobody messes with it anyway, caching it cannot be a bad idea.
>> 
>> I'm troubled by the fact that I can't set what I am thinking of as being
>> the "SWI Prolog WD" without that automatically affecting the WD of the
>> entire app, i.e. that there is no concept of a WD just for the SWI
>> session (presumably it is too complex and/or time-consuming to use this
>> approach). Am I perhaps taking a completely wrong-headed approach by
>> setting the WD at all?
> 
> I don't know. The WD is (in all OSes I know) a setting of the process
> that determines how a not-absolute-file-names are resolved. It can be set
> and queried and all parts of the process must maintain a coherent view
> of it. There is basically no way to do that in a multi-threaded
> environment except for setting the WD while initializing the process and
> not touching it afterwards.
> 
> SWI-Prolog, once commonly in control of the process, maintains a cached
> value of the WD. That is coherent with the above. If the app however
> modifies the WD, it must inform SWI-Prolog. If that is infeasible (which
> it can be), we have some options. One (as said in my previous mail) is
> not to use cached values at all. Another might be to have some setting
> that tells Prolog whether or not to use caching.  That depends whether or
> not the old motivation to cache this value for performance reasons still
> makes as much sense as it did when the caching was added.
> 
> Definitely, in a platform independent way, modifying WD in components
> of a process and especially in threads is asking for trouble.
> 
>    Cheers --- Jan
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