LOCK and UNLOCK

LOCK/UNLOCK are used to secure (or release) a file for exclusive use. These commands are designed for use on multitasking or network systems to prevent two users or two processes from using the same file at the same time, preventing them from making conflicting transactions.

10 ASSIGN @Path TO "airline.seats"

20 ASSIGN @Travelagency TO 705

30 ENTER @Travelagency;Requested

40 REPEAT

50 LOCK @Path;CONDITIONAL Notlocked

60 Locked= NOT Notlocked

70 UNTIL Locked

80 ENTER @Path;Available,Booked

90 IF Requested>Available THEN

100 UNLOCK @Path

110 OUTPUT @Travelagency;"Only ";Available;" available"

120 ELSE

130 RESET @Path

140 Available=Available-Requested

150 Booked=Booked+Requested

160 OUTPUT @Path;Available,Booked

170 UNLOCK @Path

180 OUTPUT @Travelagency;"OK"

190 END IF

200 ASSIGN @Path TO *

210 END