If the connection is lost and you reconnect with
mysql_ping(), the thread ID
changes. This means you should not get the thread ID and store
it for later. You should get it when you need it.
This function does not work correctly if thread IDs become
larger than 32 bits, which can occur on some systems. To
avoid problems with
mysql_thread_id(), do not
use it. To get the connection ID, execute a
CONNECTION_ID() query and retrieve the result.