In serialized mode, SQLite will acquire the mutex when it detects you are "starting to use" the database handle (somewhere between entering sqlite3_prepare and the first sqlite3_step) and then HANG ON TO IT, NOT LETTING GO until the calling thread is "finished" (like when sqlite3_step returns SQLITE_DONE or the thread calls sqlite3_reset or sqlite3_finalize).
In multithread mode, you are taking over this responsibility; if you take care, you may nest several selects from different threads into a single transaction, but need to be aware of the fact that they will all commit or rollback together. -----Ursprüngliche Nachricht----- Von: Neo Anderson [mailto:neo_in_mat...@msn.com] Gesendet: Montag, 09. Februar 2015 06:34 An: General Discussion of SQLite Database Betreff: Re: [sqlite] Multi-thread mode question > Does the application work if you configure SQLite to serialized mode? Yes. But I am confused why serialized mode works while multi-thread mode always cause crashes because I also wrap calls around statement handle. > even if you wrap the sqlite3_ calls... you'll need to wrap the entire > lifetime of the statment... Do I need to do this in serialized mode (suppose I use a single connection across multiple threads)? ---------------------------------------- > Date: Sun, 8 Feb 2015 03:31:46 -0800 > From: d3c...@gmail.com > To: sqlite-users@sqlite.org > Subject: Re: [sqlite] Multi-thread mode question > > it's better to use a connection per thread... the connection resource > isn't very big... > even if you wrap the sqlite3_ calls... you'll need to wrap the entire > lifetime of the statment... if you do a execute and then start > stepping and getting values while another thread starts another > statement... that's 3 individual locks, but it doesn't lock the > context of the statement being used... it will lead to bizarre crashes > in the database; similar to double-releasing memory or delayed > reference of memory that has been released. > > On Sun, Feb 8, 2015 at 3:00 AM, Dan Kennedy <danielk1...@gmail.com> wrote: > >> On 02/08/2015 04:30 PM, Neo Anderson wrote: >> >>> The doc says: >>> >>> Multi-thread. >>> In this mode, SQLite can be safely used by multiple threads provided >>> that no single database connection is used simultaneously in two or >>> more threads. >>> >>> I have a scenario that every sqlite3_calls around a single database >>> connection is protected by a recursive mutex, but I have very >>> strange runtime error in sqlite3.c and each time the error occurs at >>> a different place. >>> >>> Does this mean the following statement is true: >>> >>> In muti-thead mode, a single database connection cannot be shared >>> among threads even if any activity around the connection is protected by a >>> mutex. >>> >> >> Not true. >> >> The only difference between multi-threaded and serialized mode is >> that, internally, every sqlite3_xxx() API call grabs a recursive >> mutex to prevent two threads from simultaneously accessing the database >> handle structure. >> i.e. the same thing your code is doing externally. >> >> Note that calls on statement handles (i.e. sqlite3_step(), >> sqlite3_column_text() etc.) count as calls on the database handle >> that created them. So you need to protect them with the same mutex. >> >> Does the application work if you configure SQLite to serialized mode? >> >> Dan. >> >> >> >> _______________________________________________ >> 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 ___________________________________________ Gunter Hick Software Engineer Scientific Games International GmbH FN 157284 a, HG Wien Klitschgasse 2-4, A-1130 Vienna, Austria Tel: +43 1 80100 0 E-Mail: h...@scigames.at This communication (including any attachments) is intended for the use of the intended recipient(s) only and may contain information that is confidential, privileged or legally protected. Any unauthorized use or dissemination of this communication is strictly prohibited. If you have received this communication in error, please immediately notify the sender by return e-mail message and delete all copies of the original communication. Thank you for your cooperation. _______________________________________________ sqlite-users mailing list sqlite-users@sqlite.org http://sqlite.org:8080/cgi-bin/mailman/listinfo/sqlite-users
