About Threads and Concurrency
The Mule app controls the lifecycle connections. When the app determines that a given connection is not needed anymore, it checks the setting of Disable Session Invalidation. When the setting is disabled, the app will automatically destroy that connection for the session. To prevent a session from closing in this case, you can check the Disable Session Invalidation checkbox.
Salesforce uses the same session for all your threads, so for example, if your session is active and you log in again, Salesforce will use the existing session instead of creating a new one.