TLocks

Source: source/classes/tlocks.prg

Standalone class

TLocks provides a record-locking mechanism for ODBC tables. It manages a lock table within the database that tracks which records are locked and by which connection. This enables basic pessimistic concurrency control for ODBC data sources that do not provide native record-level locking.

Key DATA Members

DATA	Type	Description
`oOdbc`	Object	TODBC connection object for database access
`cTable`	Character	Name of the table being locked
`nId`	Numeric	Connection or session identifier

Methods

Method	Description
`New( oOdbc, cTable )`	Create a new lock manager for the specified ODBC connection and table
`CreateEnviroment()`	Create the lock tracking environment (lock table) if it does not exist
`Lock( nRecNo )`	Lock a pseudo-record by record number
`UnLock( nRecNo )`	Release a lock on a pseudo-record
`RefreshLock( nRecNo )`	Refresh the lock timestamp to prevent timeout expiration
`SeekRegLock( nRecNo )`	Check if a pseudo-record is currently locked

Example: Lock/Unlock a Pseudo-Record

#include "FiveWin.ch"

function Main()

   local oOdbc, oLocks

   oOdbc := TODBC():New( "MyDSN", "user", "pass" )

   if oOdbc:lSuccess
      oLocks := TLocks():New( oOdbc, "CUSTOMERS" )

      // Ensure the lock environment exists
      oLocks:CreateEnviroment()

      // Lock record number 101
      if oLocks:Lock( 101 )
         MsgInfo( "Record 101 locked" )

         // Do work with the record...

         // Release the lock
         oLocks:UnLock( 101 )
         MsgInfo( "Record 101 unlocked" )
      else
         MsgAlert( "Could not lock record 101" )
      endif
   endif

return nil

Notes

TLocks uses a separate lock table in the ODBC database to track record-level locks. This table is created automatically by CreateEnviroment() and stores key information including record number, session ID, and lock timestamp.
Pessimistic locking means a lock is acquired before editing and held until explicitly released. Other sessions attempting to lock the same record will fail until the lock is released.
Use RefreshLock() periodically during long editing sessions to prevent the lock from timing out.
SeekRegLock() allows checking whether a specific record is currently locked without attempting to acquire the lock.
Always release locks with UnLock() as soon as the edit is complete to avoid blocking other users.

TLocks

Key DATA Members

Methods

Example: Lock/Unlock a Pseudo-Record

Notes

See Also