Article #15976: FILE MODE LOCKING/UNLOCKING ON A NETWORK

 Technical Notes Database

TN976D.txt   FILE MODE LOCKING/UNLOCKING ON A NETWORK
Category   :Pascal
Platform    :All
Product    :Turbo Pascal  4.0+

Description:
Q.  How can I access my data on a network when I have more than one user?
A.  The routine in the following unit will help.
    Using the fm* constants you can set the FILEMODE byte to match
    the amount of sharing that you wish to take place.

    example:  FileMode := fmReadWr+fmDenyNone;

    Using the Lock function you can lock a record or a series of records.
    Lock returns True if the request to lock the record was successful.  If
    Lock returns False it can be assumed that the record was locked by someone
    else and not available for editing at this time.

    Locking Needs to take place anytime that a user will be allowed to change
    the data.  If your program in in a view mode you can safely leave the
    record unlocked.

Unit NETio;
Interface

Const {File Open Mode Constants}
                    { I SSS R AAA    I= Inheritance Flag     }
 fmRead       = $00;{ _ ___ 0 000    S= Sharing Mode Field   }
 fmWrite      = $01;{ _ ___ 0 001    R= Reserved (must Be 0) }
 fmReadWr     = $02;{ _ ___ 0 010    A= Access Field         }
 fmCompat     = $00 { _ 000 0 ___                            }
 fmDenyReadWr = $10 { _ 001 0 ___                            }
 fmDenyWrite  = $20 { _ 010 0 ___                            }
 fmDenyRead   = $30 { _ 011 0 ___                            }
 fmDenyNone   = $40 { _ 100 0 ___                            }
 fmNotInher   = $80 { 1 ___ 0 ___                            }

Const
  Lock   = 0;
  UnLock = 1;

Function Lock( Var FilVar; RecordNumber: longint;

Function LockRegion( Var FilVar; RecordNumber,NumRec: longint;
                         Lock_Unlock:byte ) : Word;

Implementation

Function LockRegion( Var FilVar; RecordNumber,NumRec: longint;
                         Lock_Unlock:byte ) : Word;
Var
  R : registers;
  ByteOffset : Longint;

begin
  With FileRec(FilVar) do
    Begin
      ByteOffset := Recordnumber * RecSize;
      NumRec     := NumRec       * RecSize;
      With R do
        Begin
          AH := $5C;
          AL := Lock_Unlock;
          BX := Handle;
          CX := (ByteOffset and $FFFF0000) shr 16;
          DX := (ByteOffset and $0000FFFF);
          SI := (NumRec     and $FFFF0000) shr 16;
          DI := (NumRec     and $0000FFFF);
        End;
      Intr( $21, R );
      if (R.Flags and 1) = 1 then
        LockRegion := R.AX
      Else
        LockRegion := 0;
    End;
end;

Function Locklock( Var FilVar; RecordNumber: longint;
                         Lock_Unlock:byte ) : Word;
Begin
  Lock := LockRegion( FilVar, RecordNumber, 1, Lock_Unlock );
End;
ENd.


Reference:


7/16/98 4:35:38 PM
 

Last Modified: 01-SEP-99