Find records that do not have matching closing value
If the process with some PID was started, but was not finished, there is only one record for it.

SELECT pid
FROM table
GROUP BY pid
HAVING COUNT(pid) = 1


If process with the same PIDcan start/finish more than once, working process have odd records count.

HAVING 1 = (COUNT(pid) MOD 2)


Having PIDs list you can easily obtain the whole records.