Guardian Application Conversion Guide

Ensuring Compatibility: The Inherited Force-Low Characteristic
System Compatibility
096047 Tandem Computers Incorporated C–5
Ensuring
Compatibility: The
Inherited Force-Low
Characteristic
Processes that create other processes often need to communicate with their descendent
processes. Communication problems can occur when a process running on a C-series
system creates a process running on a D-series system that in turn creates additional
processes, some of which run at a high PIN. Figure C-5 shows the problem.
Figure C-5. Process Creation Between C-Series and D-Series Systems
$A
$B
$C
$D
High PINs
Low PINsLow PINs
C-Series System D-Series System
Process $B can run only at a low PIN because it is created by a process running on a
C-series system and must therefore have been created by the NEWPROCESS
procedure. Processes created by $B, however, can run at a high PIN or low PIN,
because $B is running on a D-series system and therefore can use the
PROCESS_CREATE_ procedure.
Using the Inherited Force-
Low Characteristic
To help ensure compatibility, all processes created by process $B run at a low PIN by
default. The mechanism used to achieve this default action is the inherited force-low
characteristic.
If a process is started on a D-series system by a process on a C-series system, then the
new process not only runs at a low PIN but also has its inherited force-low
characteristic set. Because this flag normally propagates to all its descendent
processes, all descendents of the C-series process normally run at a low PIN.
A process also has its inherited force-low characteristic set if its creator used
PROCESS_CREATE_ with create-options .<15> set to 1 (the force-low flag), or if it
was created using the C-series-compatible NEWPROCESS procedure.