Locking scheme

D3 locks groups on a process basis. A port executing a program is locked from accessing items locked by the previous level.

Group Update Lock When an update lock is placed on a group, no other process is allowed into the group for reading or writing.
Item Lock When an item lock is placed on an item in a file, other items in that group are allowed to be accessed and updated. A Group lock is placed on the group to prevent shifting, the item is locked and the group is released, leaving the item lock in place. Item locks are used by the FlashBASIC readu, readvu, and matreadu statements and by the Update processor.


The following program shows how the FlashBASIC locked clause can be used. It shows how to display the file name, port number, and user that has the file locked:

prompt "";item=""
open ’’,’filename’ to f.filename else stop
open ’’,’users’ to f.users else stop
readu item from f.filename,ID locked
   execute "who ":port capturing var
   user.id = field(var," ",2)
   readv name from f.users,user.id,1 else stop
   print "Filename file is locked by port ":port:" ":name
   loop until port = 0 do
      sleep 5
      readu item from f.filename,ID locked else null
end else stop 202,ID