This function returns information as to whether or not a lock can be granted on a particular application resource, for a specified lock owner, without acquisition of the lock. As an application lock function, APPLOCK_TEST operates on the current database. The database is the scope of the application locks.
APPLOCK_TEST ( 'database_principal' , 'resource_name' , 'lock_mode' , 'lock_owner' )
' database_principal '
The user, role, or application role that can be granted permissions to objects in the database. To successfully call the function, the function caller must be a member of database_principal, dbo, or the db_owner fixed database role.
' resource_name '
A lock resource name specified by the client application. The application must ensure a unique resource name. The specified name is hashed internally into a value that the SQL Server lock manager can internally store. resource_nameis nvarchar(255), with no default. resource_name is binary compared, and is case-sensitive regardless of the collation settings of the current database.
' lock_mode '
The lock mode to obtaine for a specific resource. lock_mode is nvarchar(32), with no default value. lock_mode can have any of these values: Shared, Update, IntentShared, IntentExclusive, Exclusive.
' lock_owner '
The owner of the lock, which is the lock_owner value when the lock was requested. lock_owner is nvarchar(32), and the value can be either Transaction (the default) or Session. If default or Transaction is explicitly specified, APPLOCK_TEST must be executed from within a transaction.
0 if the lock cannot be granted to the specified owner, or 1 if the lock can be granted.
Two users (User A and User B), with separate sessions, run the following sequence of Transact-SQL statements.
User A runs:
USE AdventureWorks2012; GO BEGIN TRAN; DECLARE @result int; EXEC @result=sp_getapplock @DbPrincipal='public', @Resource='Form1', @LockMode='Shared', @LockOwner='Transaction'; SELECT APPLOCK_MODE('public', 'Form1', 'Transaction'); GO
User B then runs:
Use AdventureWorks2012; GO BEGIN TRAN; SELECT APPLOCK_MODE('public', 'Form1', 'Transaction'); --Result set: NoLock SELECT APPLOCK_TEST('public', 'Form1', 'Shared', 'Transaction'); --Result set: 1 (Lock is grantable.) SELECT APPLOCK_TEST('public', 'Form1', 'Exclusive', 'Transaction'); --Result set: 0 (Lock is not grantable.) GO
User A then runs:
EXEC sp_releaseapplock @Resource='Form1', @DbPrincipal='public'; GO
User B then runs:
SELECT APPLOCK_TEST('public', 'Form1', 'Exclusive', 'Transaction'); --Result set: '1' (The lock is grantable.) GO
User A and User B then both run:
COMMIT TRAN; GO