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APPLOCK_TEST (Transact-SQL)

Applies to: SQL Server Azure SQL Database Azure SQL Managed Instance SQL database in Microsoft Fabric

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.

Transact-SQL syntax conventions

Syntax

APPLOCK_TEST ( 'database_principal' , 'resource_name' , 'lock_mode' , 'lock_owner' )

Arguments

' 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 obtain 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.

Return types

smallint

Return value

0 if the lock cannot be granted to the specified owner, or 1 if the lock can be granted.

Function properties

Nondeterministic

Nonindexable

Nonparallelizable

Examples

Two users (User A and User B), with separate sessions, run the following sequence of Transact-SQL statements.

User A runs:

Note

In Azure SQL Database and SQL database in Microsoft Fabric, the USE statement isn't available. Instead, connect directly to intended database and run the rest of the code sample.

USE AdventureWorks2022;  
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 AdventureWorks2022;  
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

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