An automated double-door airlock system controls an inner door and an outer door. For safety reasons, both doors must never be open at the same time.

The system is controlled by the following algorithm:

1  WHILE (systemActive = True) DO
2
3      RECEIVE innerRequest FROM SENSOR_INNER
4      IF (innerRequest = True) THEN
5          SET innerDoor TO "Open"
6      END IF
7
8      RECEIVE outerRequest FROM SENSOR_OUTER
9      IF (outerRequest = True) THEN
10         SET outerDoor TO "Open"
11     END IF
12
13     IF (innerRequest = False) THEN
14         SET innerDoor TO "Closed"
15     END IF
16
17     IF (outerRequest = False) THEN
18         SET outerDoor TO "Closed"
19     END IF
20
21 END WHILE