Threaded Process

Given a process with two threads, each with their own "active" connection to the same database make different select queries concurrently, will the queries be executed and acted upon concurrently by the server? Or will the first thread to submit the query cause the other thread to block until the first query returns? Or are threads the wrong way to implement it. Can a process with its own connection to the database cause another process to block also? I am running Informix 7.2