[pysqlite] PySqlite threading concurrency issue

Hello all,

I've ran accross a problem when I have multiple threads in python
attempting to select/update the same database.  I get the dreaded
"database is locked" error.  The following bit of code reproduces the
problem fairly reliably (within about 45 seconds on my machine), and I
was wondering if anyone had any insight into what might be going on?

from pysqlite2 import dbapi2 as sqlite3
import datetime
import thread, time, os
db = 'test.db'

def aa():
    while True:
        conn = sqlite3.connect(db, timeout=10)
        conn.isolation_level = None
        c = conn.cursor()
        c.execute('SELECT a from t1 where b=1')
        print list(c)
        #conn.commit()
        conn.close()
        time.sleep(10)

def bb():
    while True:
        conn = sqlite3.connect(db, timeout=10)
        conn.isolation_level = 'EXCLUSIVE'
        c = conn.cursor()
        c.execute('UPDATE t1 set a=? where b=0', (datetime.datetime.now(),) )
        #conn.commit()
        conn.close()
        time.sleep(.1)


try:
    os.unlink('test.db')
except OSError:
    pass

with sqliteutil.cursor(db, isolation_level = 'EXCLUSIVE', timeout=60) as c:
    c.execute('create table t1(a real, b real)')
    c.executemany('insert into t1 values(?, ?)', ( (0, 0) for i in
xrange(10000)) )
    c.execute('insert into t1 values(0, 1)')

thread.start_new_thread(bb, ())
aa()


When I run it, I get the following:
$  python test_lock.py
[(0.0,)]
Traceback (most recent call last):
  File "test_lock.py", line 59, in <module>
    aa()
  File "test_lock.py", line 14, in aa
    c.execute('SELECT a from t1 where b=1')
pysqlite2.dbapi2.OperationalError: database is locked


Any help would be much appreciated.

Thanks.