SQLite3 and threads

[Vitalie Colosov via Digitalmars-d-learn]

Hi,

I am not able to query SQLite3 database files using threads; 
without threads it is working fine.
I tried both etc.c.sqlite3 and d2sqlite3, and both seem to be 
facing the same issue:
They stuck when executing a select query (using sqlite3_exec(...) 
for etc.c.sqlite3 or using RowCache(db.execute(...)) in case of 
d2sqlite3).
Since d2sqlite3 is a wrapper for native sqlite3, I think it faces 
the same limitation which native sqlite does, so next lines will 
describe native SQLite3 code.

---------------------------------------------------------------
This works fine (non-relevant code and validations are omitted 
for simplicity)
---------------------------------------------------------------
import etc.c.sqlite3,...
...
extern(C) int myCallback(void *a_parm, int argc, char **argv, 
char **column)
{
	 printf("%s\n", argv[1] ? argv[1] : "NULL");	// this prints 
first column of each row, all is well
     return 0;
}
void querySQLite(string dbName)
{
        sqlite3* db;
        auto ret = sqlite3_open(toStringz(dbName), &db);
        string query = "SELECT * FROM my_table";
        sqlite3_exec(db,toStringz(query),&myCallback,null,null);
        sqlite3_close(db);
}
void main()
{
        querySQLite("db1.sl3");
        querySQLite("db2.sl3");
	...// in fact, here is a foreach loop which is calling 
querySQLite with about 30 database files
        querySQLite("db30.sl3");      
}

---------------------------------------------------------------
However, if I change main function to spawn querySQLite, instead 
of calling it in sequence from the main thread,
then "myCallback()" is not executed.
void main()
{
        spawn(&querySQLite,"db1.sl3");
        spawn(&querySQLite,"db2.sl3");
        ...
        spawn(&querySQLite,"db30.sl3");
}
It is stuck inside this line in querySQLite():
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
        sqlite3_exec(db,toStringz(query),&myCallback,null,null);
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
If I comment it, the flow continues and returns fine from all 
spawn-ed functions, so it is definitely something wrong in this 
line.
---------------------------------------------------------------

I think I am missing some kind of thread locking code in 
querySQLite() - since it is working with C code I think it needs 
more attention.

I tried to compile SQLite with different multithreading options, 
but that did not help.

Any advice is much appreciated.

Using dmd.2.066.1.linux
RedHat 5 64bit
Compiled using dmd
sqlite-amalgamation-3080803

Thanks,
Vitalie