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DbRLock Function

Lock a record in a shared database file, optionally retaining previous record locks.

Namespace:  XSharp.RT
Assembly:  XSharp.RT (in XSharp.RT.dll) Version: 2.5
Syntax
 FUNCTION DbRLock(
	uRecId AS USUAL
) AS USUAL

Parameters

uRecId
Type: Usual
The ID (usually a record number) of the record to be locked.
If specified, record locks held by the current process are retained.
If not specified, all locks held by the current process are released and the current record is assumed.

Return Value

Type: Usual
TRUE if the record lock is obtained; otherwise, FALSE.
An attempt to lock a record in an empty database returns TRUE.
Remarks
If a database file is opened in shared mode, you must obtain a record lock before attempting any operation that writes to the database file. For each invocation of DBRLock(), there is one attempt to lock the target record, and the result is returned as a logical value.
An attempt to obtain a record lock fails if another process currently has a file lock or record lock on the target record. If DBRLock() is successful, the record is locked and other processes are prevented from updating the record until the lock is released.  DBRLock() provides a shared lock, allowing other users read-only access to the locked record while allowing only the current process to modify it. A record lock remains in effect until you explicitly unlock it (with DBUnLock(), for example), close the database file, or attempt another file or record lock (with RLock() or DBRLock() with no argument).  DBRLock() when specified with an argument does not release records locks held by the current process.  Instead, it adds the newly locked records to the lock list (see DBRLockList()). By default, this function operates on the currently selected work area.
It can be made to operate on an unselected work area by specifying it within an aliased expression
This feature is useful since DBRLock() does not automatically attempt a record lock for related files.
Examples
This example deletes a record from a shared database file DBRLock():
X#
 1USE customer INDEX custname SHARED NEW
 2SEEK "Smith"
 3IF Found()
 4    IF Customer->DBRLock()
 5        DELETE
 6        QOut("Smith deleted")
 7    ELSE
 8        QOut("Record in use by another")
 9    ENDIF
10ELSE
11    QOut("Smith not in customer file")
12ENDIF
13CLOSE
This example specifies DBRLock() as an aliased expression to lock a record in an unselected work area:
X#
1USE sales SHARED NEW
2USE customer SHARED NEW
3IF !Sales->DBRLock()
4    QOut("The current sales record is in use")
5ENDIF
See Also