Hello Pavel, I don't want per-say to remove my pthread_rwlock() but the main point of this discussion is I should not have to use pthread_rwlock(). Others have mentioned I should be using SQLite-specific mechanisms to achieve the same results. I am just trying to understand how to do that. Pthread_rwlock() works fine.
Thanks, John --- On Tue, 5/24/11, Pavel Ivanov <paiva...@gmail.com> wrote: > From: Pavel Ivanov <paiva...@gmail.com> > Subject: Re: [sqlite] Multi-threading Common Problem > To: "General Discussion of SQLite Database" <sqlite-users@sqlite.org> > Date: Tuesday, May 24, 2011, 9:51 AM > > I have all writes in > transactions. If I deactivate my pthread_rwlock() that > enforce the above, several writes fail with a "database > locked" error (I assume it is returning SQLITE_BUSY). > > > > So how do I implement the equivalent of a > pthread_rwlock() using SQLite mechinisms? > > When SQLITE_BUSY in a reader transaction is returned just > wait a > little bit and try again. Also you can benefit from > sqlite3_busy_timeout (http://www.sqlite.org/c3ref/busy_timeout.html). > > Another question is why do you want to get read of > pthread_rwlock if > it works for you? > > > Pavel > > > On Tue, May 24, 2011 at 7:43 AM, John Deal <bassd...@yahoo.com> > wrote: > > Hello Roger, > > > > Sorry to be so brain-dead but I am still confused. I > have multiple threads, each with their own DB connection. > I want to allow multiple readers accessing the DB at the > same time since nothing is changing. However, if a writes > is to take place, I want all readers to finish their reads > and give the writer exclusive access. Once the writer is > done, the readers can come back in. > > > > I have all writes in transactions. If I deactivate > my pthread_rwlock() that enforce the above, several writes > fail with a "database locked" error (I assume it is > returning SQLITE_BUSY). With my pthread_rwlock(), I have > multiple threads reading the DB and my writes get the > exclusive access they need. Now I could loop on the write > until it gets in but that seems very wasteful. > > > > So how do I implement the equivalent of a > pthread_rwlock() using SQLite mechinisms? > > > > Thanks, > > > > John > > > > --- On Tue, 5/24/11, Roger Binns <rog...@rogerbinns.com> > wrote: > > > >> From: Roger Binns <rog...@rogerbinns.com> > >> Subject: Re: [sqlite] Multi-threading Common > Problem > >> To: "General Discussion of SQLite Database" <sqlite-users@sqlite.org> > >> Date: Tuesday, May 24, 2011, 3:10 AM > >> -----BEGIN PGP SIGNED MESSAGE----- > >> Hash: SHA1 > >> > >> On 05/23/2011 09:12 PM, John Deal wrote: > >> > I guess I am lost on how to obtain a many > reader or > >> one writer mutex in SQLite. > >> > >> You are confusing locks on the database and locks > in the > >> library on a > >> sqlite3 pointer. The latter is what the mutex > alloc > >> function you reference > >> is about and there there is no reader/writer > >> mechanism. Access has to be > >> serialized. > >> > >> > You are correct in the locking article > referenced I > >> want a mutex that can have the lock states of > shared, > >> pending, and exclusive. > >> > >> Those are locks on the database which you get > through > >> regular operations and > >> transactions. > >> > >> Roger > >> -----BEGIN PGP SIGNATURE----- > >> Version: GnuPG v1.4.11 (GNU/Linux) > >> > >> > iEYEARECAAYFAk3bWeIACgkQmOOfHg372QQf8QCgjlawQMJWJ1I3/6OqMkczXswk > >> VWQAmgLzGifXbh9UJpuEdUTTZl8e8xYp > >> =rXCY > >> -----END PGP SIGNATURE----- > >> _______________________________________________ > >> sqlite-users mailing list > >> sqlite-users@sqlite.org > >> http://sqlite.org:8080/cgi-bin/mailman/listinfo/sqlite-users > >> > > _______________________________________________ > > sqlite-users mailing list > > sqlite-users@sqlite.org > > http://sqlite.org:8080/cgi-bin/mailman/listinfo/sqlite-users > > > _______________________________________________ > sqlite-users mailing list > sqlite-users@sqlite.org > http://sqlite.org:8080/cgi-bin/mailman/listinfo/sqlite-users > _______________________________________________ sqlite-users mailing list sqlite-users@sqlite.org http://sqlite.org:8080/cgi-bin/mailman/listinfo/sqlite-users
