Multi-Threaded SQLite Crash

Question

I'm trying to use SQLite 3.7.5 in a multi-threaded C++ program. I've narrowed it down to a few simple lines of code:

sqlite3 *Database;
sqlite3_stmt *Stmt;

int retval=sqlite3_open("database.db3",&Database);
retVal=sqlite3_prepare(&Database,"CREATE TABLE RawData (Key CHAR(5))",-1,&Stmt,0);
retval=sqlite3_step(Stmt);
retval=sqlite3_finalize(Stmt);

When I call this code directly from my main process, it works fine. However, if I use CreateThread() to create a thread:

unsigned long ThreadId;
CreateThread(0,0,(LPTHREAD_START_ROUTINE) InserterThread,&Info,0,&ThreadId);

I get a "buffer overrun" Visual Studio message on the sqlite3_step call. If I debug, I see the crash location is in _CRT_DEBUGGER_HOOK in dbghook.c.

I'm using the Multi-threaded Static VC libraries, and am compiling with the defines:

SQLITE_THREADSAFE=2
THREADSAFE=2

I have verified with sqlite3_threadsafe().

I can trace a bit into the SQLite 3 code, but I'm hoping some one will spot an obvious problem with my code and save me the aggrevation.

Answer 1

It appears that the SQLITE_THREADSAFE define is for compiling, they don't force the library into the behavior, just make it available.

You still have to tell sqlite that you want multi-threaded behavior, either when you start up the database or during runtime.

Start-time selection of threading mode

Assuming that the compile-time threading mode is not single-thread, then the threading mode can be changed during initialization using the sqlite3_config() interface. The SQLITE_CONFIG_SINGLETHREAD verb puts SQLite into single-thread mode, the SQLITE_CONFIG_MULTITHREAD verb sets multi-thread mode, and the SQLITE_CONFIG_SERIALIZED verb sets serialized mode.

Run-time selection of threading mode

If single-thread mode has not been selected at compile-time or start-time, then individual database connections can be created as either multi-thread or serialized. It is not possible to downgrade an individual database connection to single-thread mode. Nor is it possible to escalate an individual database connection if the compile-time or start-time mode is single-thread.

The threading mode for an individual database connection is determined by flags given as the third argument to sqlite3_open_v2(). The SQLITE_OPEN_NOMUTEX flag causes the database connection to be in the multi-thread mode and the SQLITE_OPEN_FULLMUTEX flag causes the connection to be in serialized mode. If neither flag is specified or if sqlite3_open() or sqlite3_open16() are used instead of sqlite3_open_v2(), then the default mode determined by the compile-time and start-time settings is used.

Referenced from http://www.sqlite.org/threadsafe.html