Mutual Exclusion in GS/OS and ToolBox Calls

The Apple IIGS was not designed as a multitasking machine, and GS/OS and the Toolbox reflect this in their design. The most notable problem with making multitasking work on the Apple IIgs is the use of global (common to all processes) information, such as prefixes and direct page space for tool sets which includes information like SANE results, QuickDraw drawing information, etc. In most cases we've corrected these deficiencies by keeping track of such information on a per-process basis, that is, each process has its own copy of the information and changes to it do not affect any other process' information.

However, there were many other situations where this could not be done. Therefore, there is a limit of one process at a time inside either GS/OS or the ToolBox. GNO/ME automatically enforces this restriction whenever a tool or GS/OS call is made.

The method and details of making GS/OS calls does not change! The calls listed below have been expanded transparently. There are no new parameters and no new parameter values. In all cases, the corresponding ProDOS-16 interface calls are also supported, except ExpandPath and other calls which do not exist in ProDOS-16.