sp_getapplock (Transact-SQL MetaData) Definition

Please note: that the following source code is provided and copyrighted by Microsoft and is for educational purpose only.
The meta data is from an SQL 2012 Server.

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Definition:

sys.sp_getapplock(nvarchar @Resource
, varchar @LockMode
, varchar @LockOwner
, int @LockTimeout
, nvarchar @DbPrincipal)

MetaData:

 create procedure sys.sp_getapplock -- - 1999/04/14 00:00  
 @Resource nvarchar (255) = NULL,           --  Resource to lock  
 @LockMode varchar (32),                    --  Lock mode  
 @LockOwner varchar (32) = 'Transaction',   --  Lock Owner - [D = Transaction]  
 @LockTimeout int = NULL,                   --  Lock timeout [D = Session setting]  
 @DbPrincipal sysname = N'public'        --  DB principal to use for name space and permissions  
as  
  
  declare @mode integer  
  declare @owner integer  
  declare @result integer  
  declare @dbid integer  
  
  select @mode =  
   CASE @LockMode  
     When ('Shared')            Then 3  
     When ('Update')            Then 4  
     When ('Exclusive')         Then 5  
     When ('IntentExclusive')   Then 8  
     When ('IntentShared')      Then 6  
     Else -1  
   END  
  
  if @mode = -1  
  begin  
    raiserror(15625, -1, -1, @LockMode, N'@LockMode')  
    return (-999)  
  end  
  
  select @owner =  
   CASE @LockOwner  
    When ('Transaction')    Then 1  
    When ('Session')        Then 3  
    Else -1  
   END  
  
  if @owner = -1  
  begin  
    raiserror(15625, -1, -1, @LockOwner, N'@LockOwner')  
    return (-999)  
  end  
  
  if @LockTimeout is null  
  begin  
    set @LockTimeout = @@LOCK_TIMEOUT  
  end  
  
  select @dbid = db_id ()  
  
  if @owner = 1 and @@trancount = 0  
  begin  
    raiserror(15626, -1, -1)  
    return (-999)  
  end  
  
  exec @result = sys.xp_userlock 0, @dbid, @DbPrincipal, @Resource, @mode, @owner, @LockTimeout  
  
  return @result