sp_MSgetmakegenerationapplock (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_MSgetmakegenerationapplock()

MetaData:

   
create procedure sys.sp_MSgetmakegenerationapplock  
    @head_of_queue int OUTPUT  
    as  
    set nocount on  
  
    declare @retcode smallint  
    declare @lock_resource nvarchar(255)  
    declare @DbPrincipal sysname  
  
    --  Security check  
    exec @retcode = sys.sp_MSrepl_PAL_rolecheck   
    if (@retcode <> 0) or (@@error <> 0)  
            return 1  
      
      select @retcode = 0  
    select @head_of_queue = 0  
      
    select @lock_resource = N'MSinternal_makegeneration_inprogress' +   
                convert(nvarchar(11), db_id())  
    if exists (select * from sys.database_principals where name=N'MSmerge_PAL_role' and type = 'R')  
        select @DbPrincipal = N'MSmerge_PAL_role'  
    else  
        select @DbPrincipal = N'db_owner'  
      
    --  If someone else is making generations / has just made one, exit so  
    --  that we won't deadlock  
    exec @retcode = sp_getapplock @Resource = @lock_resource,  
                                  @LockMode = N'Exclusive',  
                                  @LockOwner = N'Session',  
                                  @LockTimeout = 0, --  do not wait at all.   
                                  @DbPrincipal = @DbPrincipal  
  
    if @@error <> 0 or @retcode < 0  
    begin  
        --  If the previous applock request timed out, then try again, this time using the default timeout.  
        --  Note that even though the -1 lock timeout means indefinite timeout, the query timeout set on the   
        --  session overrides the lock timeout. So it's okay even if the default @@lock_timeout is -1.  
        if (@retcode = -1)  
        begin  
            exec @retcode = sp_getapplock @Resource = @lock_resource,  
                        @LockMode = N'Exclusive',  
                        @LockOwner = N'Session',  
                        @DbPrincipal = @DbPrincipal  
  
            --  If we succeeded to get the lock, set @lock_acquired to 1 so that the exit code releases the lock.  
            if (@retcode >= 0)  
            begin  
                goto EXIT_PROC  
            end  
        end  
    end  
    else  
    begin  
        select @head_of_queue = 1  
    end  
  
EXIT_PROC:  
    return @retcode