Returns information about whether or not a lock can be granted on a particular application resource for a specified lock owner without acquiring the lock. APPLOCK_TEST is an application lock function, and it operates on the current database. The scope of application locks is the database.
- ' database_principal '
Is the user, role, or application role that can be granted permissions to objects in the database. The caller of the function must be a member of database_principal, dbo, or the db_owner fixed database role in order to call the function successfully.
- ' resource_name '
Is a lock resource name specified by the client application. The application must ensure that the resource is unique. The specified name is hashed internally into a value that can be stored in the SQL Server lock manager. resource_name is 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 '
Is the lock mode to be obtained for a particular resource. lock_mode is nvarchar(32) and has no default value. The value can be any of the following: Shared, Update, IntentShared, IntentExclusive, Exclusive.
- ' lock_owner '
Is the owner of the lock, which is the lock_owner value when the lock was requested. lock_owner is nvarchar(32). The value can be Transaction (the default) or Session. If default or Transaction is explicitly specified, APPLOCK_TEST must be executed from within a transaction.
In the following example, two users (User A and User B) with separate sessions run the following sequence of Transact-SQL statements.
User A runs:
USE AdventureWorks; 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 AdventureWorks; 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