On 24 May 2011, at 12:43pm, John Deal wrote: > Sorry to be so brain-dead but I am still confused. I have multiple threads, > each with their own DB connection.
Read http://www.sqlite.org/threadsafe.html If it's not clear to you please ask specific questions about what's on that page, since your questions will help us to work out how to improve it. > 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). The documentation on how to handle this is a little lacking, but if your app has no principles of its own, just loop until the problem goes away. > 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? You use transactions correctly. Pay especial attention to the differences between BEGIN BEGIN IMMEDIATE BEGIN EXCLUSIVE BEGIN DEFERRED See the following page http://www.sqlite.org/lang_transaction.html However, you may have done something to defeat SQLite's built in mechanism. Have you done any of the following: Have you set any of SQLite's compiler directives in your compilation ? I'm thinking especially of SQLITE_THREADSAFE. I'm not completely familiar with SQLite's model, but it seems to me as if you should be using '-DSQLITE_THREADSAFE=2'. The explanation of this is on the first web page I pointed to above. Have you set any PRAGMAs which are related to threading ? Especially 'PRAGMA temp_store_directory' and 'PRAGMA read_uncommitted' ? If so, try removing your PRAGMAs and see if this fixes your problem. Simon. _______________________________________________ sqlite-users mailing list sqlite-users@sqlite.org http://sqlite.org:8080/cgi-bin/mailman/listinfo/sqlite-users
