SIMSCRIPT II.5 Programming Language

SIMSCRIPT II.5 Programming Language
Table 5-10. Before and After Arguments
Operation Before After
creating an entity (not allowed) Entity identifier
destroying an entity Entity identifier (not allowed)
scheduling an event Entity identifier, time Entity identifier, time
canceling an event Entity identifier Entity identifier
filing in a set Entity identifier, set subscripts Entity identifier, set subscripts
removing from a set Entity identifier, set subscripts Entity identifier, set subscripts
Note: In file before and file after statements, the identifier of the second named entity is not
passed as an argument.
In some implementations the entity identifier passed for a remove first or remove last has a
zero value.
Removals from the events set by the timing routine may not be monitored by the above statements,
as these are not done in the usual way. SIMSCRIPT II.5 does provide a mechanism by which, under
program control, the activation of events or processes may be monitored. A subprogram variable,
between.v, may be assigned the name of a routine which will then be called immediately before
each new activation of a process or event routine. At the time that the between.v routine is called,
the simulation time, time.v, will already have advanced to the time.a attribute of the selected
event or process notice, the global variable event.v has been updated to the event or process priority
class, and the global variable of the same name as the event or process type holds the pointer
to the event or process notice, allowing the attributes to be referenced. This event tracing may be
inhibited at any time by resetting between.v to zero.
5.7 Synchronous Variables
Recall that it is possible for two or more process interactions or events to be scheduled for precisely
the same instant in simulation time. The order of activation of the associated routines is then determined
from the class or priority of each, while the value of time.v remains constant. This operation,
however, may not prove satisfactory if two or more of these routines must access the same
variable. If it is modified by the first, this modified value is the one accessed by the second. What
is required is a mechanism by which such values appear unchanged until all events at an instant have
been completed, and the simulation time has been advanced. Such a mechanism may be programmed,
using the between.v feature. In the following example, we assume that the values
which may be accessed by "parallel interactions" are elements of a one-dimensional array. A memo
entity is created, through left-hand monitoring of these values (discussed in paragraph 6.10), for
each assignment to any value. A routine called through the between.v variable updates the values
appropriately, using an equivalenced name to inhibit monitoring, at the first change in simulation
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