The file header also provides M lock information, specifically whether any resource names belonging to the database region are locked. M code commonly uses locks as flags or semaphores controlling access to global data. Generally the LOCK argument specifies the resource of the same name as the name of the global variable that requires protected access. For more information about LOCKs, refer to the "M LOCK Utility" chapter and the LOCK section in the "Commands" chapter in the GT.M Programmer's Guide.