Object Oriented Simulation
with OOSimL
Models with Resources
Fall 2015
Resources
Processes are the active components of
system
 Resources are passive components of a
system
 In the process-interaction approach to
simulation, resource pools are defined
and created. Processes can acquire a
number of resource items from a
resource pool.

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Types of Resources
Standard resources that are accessed in a
mutually exclusive manner by processes.
These resource objects represent a finite
pool of resource units and are created with
the Res class.
 Detachable resources that are consumed by
the processes. These resource objects
represent infinite pools of resource units and
are created with the Bin class.

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Resource Pools
A system can include zero or more
resource pools
 Each resource pool has a number of
resource items
 A number of these resource items can
be acquired by one or more processes

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Resource Allocation and
Deallocation
Every process follows the sequence:
 Request a number of resource items from a
resource pool, wait until these become
available
 Acquire a number of items from a resource
pool
 Use the resource items for a finite period
 Release the some or all resource items
acquired
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Standard Resources
A resource pool is an passive object
 A simulation model must declare a
resource pool and create the resource
pool object with a number of resource
items
 A specific number of items of a resource
pool can be used by at most one
process

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Resource Contention Mechanism
Processes compete for a limited number
of resource items.
 When there are not sufficient resource
items for a request, the requesting process
is suspended and placed in an internal
queue by priority.
 The processes waiting for resource items
are reactivated when another process
releases sufficient items.

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Resource Classes in OOSimL
A resource pool is an object of class Res
 The resource pool object is created with a
number of resource items
 The resource pool object includes
mechanism for processes to compete in a
mutual exclusive manner for resources by

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Using Resources in OOSimL
For example, to declare and create a resource with 50
chairs:
define chairs of class Res // chairs as a resource pool
....
create chairs of class Res using “Wood chairs”, 50
A process acquires 15 chairs then releases 10:
acquire 15 from chairs
…
release 10 of chairs
// acquire 15 chairs
// release 10 chairs
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Get Available Resources
The following lines of code get the current number of
available resource units in the resource pool
chairs, which was defined above, and assigns this
value to variable num_res.
define num_res of type integer
...
assign available units of chairs to num_res
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Checking for Available Items
A process may want to first check the number
of available resource items before
attempting to acquire items.
assign available units of chairs to items_left
if items_left >= 15 then
acquire 15 from chairs
else
// carry out some other activity
endif
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A Simple Model of a Warehouse
Trucks arrive periodically to a busy
warehouse to unload goods
 Trucks need to wait for an unloading bay
 Small trucks need two workers for
unloading
 Big trucks need three workers for unloading

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Resources and Processes in the
Warehouse Model

Warehouse resources:
2
unloading bays
 5 workers for unloading

Processes:
 small
trucks
 big trucks
 arrivals for small trucks
 arrivals for big trucks
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Workload and Performance
Both types of trucks have different mean
arrival rates and different mean
unloading periods.
 Some of the performance measures
calculated for this model are:

 Average
wait period for each type of truck
 Number of trucks serviced of each type
 Resource utilization
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Executing The Warehouse Model
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Executing The Warehouse Model
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Executing The Warehouse Model
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Executing The Warehouse Model
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Executing The Warehouse Model
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Executing The Warehouse Model
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Executing The Warehouse Model
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Output of a Simulation Run of
The Warehouse Model
End Simulation of Busy Warehouse System
date: 6/17/2009 time: 15:42
Elapsed computer time: 907 millisec
Total small trucks serviced: 42
Average period small truck spends in warehouse: 23.981
Small truck average wait period: 16.285
Total number of big trucks serviced: 54
Big truck average wait period: 20.659
Avg per btruck in warehouse: 33.006
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Allocating Resources with Priorities
Priorities are assigned to every process
that needs resources
 Processes compete for resources based
on their priorities
 To implement priorities, use an integer
value for the priority

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Using Priorities with OOSimL

Invoke method set_prio with an integer
argument in the class definition for the
processes
define my_prio = 3 of type integer
// priority
…
fix priority my_prio // set priority
…
assign priority my_prio // get priority of this process

In OOSimL, priority 0 is the highest priority.
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Deadlock
When processes compete for resources,
deadlock may occur.
 Deadlock is a situation in which a set
processes are waiting indefinitely for each
other to release resources.
 Good synchronization is necessary to
prevent or avoid deadlock.

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Deadlock Example
Processes P1 and P2 are waiting for each
other
 Process P1 holds on item of resource R2
and is requesting one item of resource R1,
which is held by P2
 Process P2 holds one item of resource R1
and is requesting one item of resource R2,
which is held by P1

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