Expected behavior

When using the SQLite connector it should free resources in a timely fashion.

Actual behavior

Simply creating a SQLite session to a local file then closing the session will result in a 20 sec delay on Windows when destroying the session. This is noticeable when using the SQLite data connector from a Windows DLL and it hangs for 20 secs on unloading.

Steps to reproduce the problem

Create a Windows DLL containing the following code:

Poco::Data::SQLite::Connector::registerConnector();
Poco::Data::Session* session = new Poco::Data::Session("SQLite", <some local db>);
session->close();
delete session;

POCO version

Reproduced in POCO 1.8.1

Compiler and version

Visual C++ with v120 runtimes

Operating system and version

Windows 10

Other relevant information

This does not appear to be a connect or login timeout as I can see the connect succeed immediately, it appears to be an issue with how the SQLite connector is using thread pooling. The SQLite connector creates two thread pool threads and when the SQLite session is closed and destroyed, the thread pool is left to clean itself up and internally each pooled thread has a 10 second wait timeout before deletion occurs. It would be better if the SQLite connector could signal the threads when the session is closed to allow these threads to exit without waiting for timeout to occur.