How to ensure thread-safety

[Kim Walisch]

Awesome, thanks!

On Feb 9, 2018 8:33 PM, "James Aylett" <james-xapian at tartarus.org> wrote:

> On 8 Feb 2018, at 15:18, Kim Walisch <kim.walisch at gmail.com> wrote:
>
> > I have read the concurrency webpage from the Xapian documentation:
> >
> > http://getting-started-with-xapian.readthedocs.io/en/
> latest/concepts/concurrency.html
> >
> > But it is still not clear to me how to ensure thread-safety when using
> > libxapian (C++ API).
> >
> > 1) Can many thread search the
> > database provided each thread uses their own Xapian database object and
> > none of the threads updates/indexes the database?
>
> This is covered explicitly in the document you linked to:
>
> > Xapian doesn’t maintain any global state, so you can safely use Xapian
> in a multi-threaded program provided you don’t share objects between
> threads. In practice this restriction is often not a problem - each thread
> can create its own xapian.Database object, and everything will work fine.
>
>
> So the answer is 'yes'.
>
> > 2) What about when one thread indexes a new document? Do I need to
> > ensure (by locking) that no other thread reads or write the database
> until
> > the first thread has finished indexing?
>
> This isn't a problem either; Xapian takes care of lock management for you.
> It's covered in a different part of the manual:
> https://getting-started-with-xapian.readthedocs.io/en/
> latest/concepts/indexing/databases.html#concurrent-access
>
> > Currently, all the backends only support a single writer existing at a
> given time; attempting to open another writer on the same database will
> throw xapian.DatabaseLockError to indicate that it wasn’t possible to
> acquire a lock. Multiple concurrent readers are supported (in addition to
> the writer).
>
>
> Note the caution there about the number of versions that can exist in
> Xapian's MVCC, and how to deal with DatabaseModifiedError.
>
> J
>
> --
>  James Aylett, occasional troublemaker & project governance
>  xapian.org
>
>