APPLOCK_TEST (Transact-SQL)

Článek
05/16/2013

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.

Topic link icon Transact-SQL Syntax Conventions

Syntax

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

Arguments

' 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.

Return Types

smallint

Return Value

Returns 0 when the lock cannot be granted to the specified owner and returns 1 if the lock can be granted.

Function Properties

Nondeterministic

Nonindexable

Nonparallelizable

Examples

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 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

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