PriorityThreadPool didn't have very good error handling. If something
failed it would just ignore whatever was being processed. This could
lead to a query continuing without retreiving all of the required data.
This patch adds error handling, sending a message back to the client
and a log message. It also destroys and recreates the pool thread.
ByteStream::advance can throw an exception if there isn't enough data in
the buffer yet. PrimProc's BPP processor would not catch this causing a
thread to be leaked every time. This was happening on BPP destroy and
abort.
If ExeMgr disconnects (such as a crash) whilst queries are being
executed some BPP threads get orphaned. This patch tracks the BPP usage
for each threads and cleans up appropriately.
