Unicenter CA-Scheduler Job Management for VSE User Guide

5.4 What Is Wrong with These Examples?
Example 3
Criteria for job JOBA:
MON AND JOBB SCHED1 OR WED
Criteria for job JOBB:
MON OR WED AND JOBA SCHED1
Here is another problem. Why do not JOBA and JOBB in schedule SCHED01
run when expected? Both jobs are supposed to run Mondays and
Wednesdays. On Mondays, JOBB should be the predecessor to JOBA, but
conversely on Wednesdays.
The meaning of these criteria statements is confusing until you add some
parentheses to show how the system will interpret this:
Criteria for job JOBA:
(MON AND JOBB SCHED1) OR WED
Criteria for job JOBB:
MON OR (WED AND JOBA SCHED1)
Now it is a bit clearer. First, look at the selection criteria. Both jobs are always
selected on Mondays and Wednesdays:
■
■
JOBA is always selected on Wednesdays, so JOBB is, too.
JOBB is always selected on Mondays, so JOBA is also selected on
Mondays.
That seems in order, so look at the predecessor conditions, remembering the
rule for evaluating predecessors:
There are no OR relationships with selection-defined explicit predecessors. All
ORs become ANDs.
The preceding means the explicit predecessor of JOBA is JOBB, and the explicit
predecessor of JOBB is JOBA. When jobs require each other as predecessors,
that creates a predecessor loop, which is also called predecessor deadlock.
Although these deadlocked jobs are selected properly, neither job ever runs
because their predecessors are never satisfied. You can run the Analyze
Report at any time to detect deadlocks automatically.
Example 4
Criteria for job JOBA:
NOT MON OR NOT TUE
5-26 Unicenter CA-Scheduler User Guide