"Marco Bambini" <ma...@sqlabs.net> wrote in message news:aa7dd05f-4679-43dd-9dd3-2ba6b98af...@sqlabs.net > I have two threads that are writing 2000 rows each to the same > database at the same time. > I am using sqlite 3.6.13 compiled with SQLITE_THREADSAFE=1. > > Each client executes this code (pseudo C code): > void write (sqlite3 *db) { > int i; > > for (i=1; i<=2000; i++) { > if (sqlite3_get_autocommit(db) != 0) sqlite3_exec(db, "BEGIN > IMMEDIATE;", ...); > sqlite3_exec(db, "INSERT INTO....", ...); > if (sqlite3_get_autocommit(db) == 0) sqlite3_exec(db, "COMMIT;", ...); > } > } > and db is shared between the two clients.
You have a race condition here: between the calls to sqlite3_get_autocommit and sqlite3_exec, the other thread could very well have issued a BEGIN or a COMMIT of its own. Between the time you check the condition and the time you act on it, the condition could have changed. Besides, the documentation on sqlite3_get_autocommit has this sentence: If another thread changes the autocommit status of the database connection while this routine is running, then the return value is undefined. In other words, sqlite3_get_autocommit is explicitly not thread-safe. Since you only run one INSERT per transaction anyway, why do you feel you need explicit BEGIN and COMMIT? > At the end of the loop, instead of having 4000 rows I have 3976 rows > (it's random, sometimes I have 3972 or 3974). > sqlite3_exec doesn't returns any error during the INSERT statement, > but I have some errors during the BEGIN IMMEDIATE, errors are all: > SQL logic error or missing database (printed with sqlite3_errmsg). Your use of sqlite3_errmsg is itself very likely a race. Between the time you detect an error and the time you retrieve error message, the other thread could have run some statements that modify the error message. Moreover, between the time you call sqlite3_errmsg and the time you actually print the string pointed to by the char* pointer the function returns, the string may be modified or even deallocated. Igor Tandetnik _______________________________________________ sqlite-users mailing list sqlite-users@sqlite.org http://sqlite.org:8080/cgi-bin/mailman/listinfo/sqlite-users
