> 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
