Hello Pavel, Thanks. This is the conclusion I was arriving at. I do use the Sqlite3 utility but only for looking at test results when the server is in an inactive state.
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, 10:32 AM > > 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(). > > I'd say pthread_rwlock and SQLite-specific mechanisms work > completely > differently and you should choose depending on what you > want to do. As > you saw to use SQLite's mechanisms you should write > additional code > waiting when write lock is released. As you said it's not > effective > and prone to starvation. But it works across process > boundaries when > pthread_rwlock works only inside your process although it > does all > waiting very effectively on a kernel level. > So if you will ever want to connect to your database with > sqlite3 > command line tool for example while your application is > running, and > you will do some manipulations with the database, then > your > pthread_rwlock won't work and you will still get > SQLITE_BUSY. And now > you decide what mechanism is better for you. > > > Pavel > > > On Tue, May 24, 2011 at 10:11 AM, John Deal <bassd...@yahoo.com> > wrote: > > 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 > > > _______________________________________________ > 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
