APPLOCK_TEST (Transact-SQL)

Artikkeli
09/03/2024

Applies to: SQL Server Azure SQL Database Azure SQL Managed Instance

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:

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

Jaa