AccessViolation Exception in wpf while connecting to db due to multiple threads - wpf

Question

I am working on a multithreaded wpf application I get "AccessViolationException" saying Attempted to read or write protected memory. This is often an indication that other memory is corrupt.
in my ConnectionOpen().
my code is as follows.
public class DatabaseServices
{
static SQLiteConnection connection;
static object conLock = new object();
static object conCloseLock = new object();
public static SQLiteDataReader ConnectionOpen(string Query)
{
lock (conLock)
{
if (connection != null && connection.State != System.Data.ConnectionState.Open)
{
connection = new SQLiteConnection("Data Source=Database/abc.sqlite");
connection.Open();
}
else if (connection == null)
{
connection = new SQLiteConnection("Data Source=Database/abc.sqlite");
connection.Open();
}
SQLiteCommand mycommand = new SQLiteCommand(Query, connection);
SQLiteDataReader sqlite_datareader = mycommand.ExecuteReader();
return sqlite_datareader;
}
}
public static void ConnectionClose()
{
lock (conCloseLock)
{
connection.Close();
}
}
}
I've used lock as well for thread safe code but its not working.why?

Answer 1

The SQLiteConnection is not thread safe. Like all other database connections, you are supposed to open one per thread. The fact that your code has a few parts that won't work even if it were thread safe, does not help either. For example, anybody can close a connection, while somebody else is just querying on it.
Keep to the well-established patterns. Do not use database connections across threads. Do not write your own connection caching. Open a conection, do your work and then close it. If you definetly need connection caching, look into the documentation of your database and find out how the inbuilt mechanism works.

Answer 2

SQLite does not support Multiple Active ResultSets (MARS)
So you cannot have multiple DataReaders served by the same connection.
After connecting (and dropping the lock) you hand out a DataReader. I assume the client code calls this ConnectionOpen method twice resulting (or rather attempting) to re-use the same connection.
Create a connection per DataReader.
When you use connection pooling:
Data Source=c:\mydb.db;Version=3;Pooling=True;Max Pool Size=100;
connections will be recycled/pooled when closed properly. This will lessen the overhead of the creation and opening of the connections.