- Simulation:
- Simulation = perform the tasks of a real-life system using a computer program to measure certain attributes of the real-life system
- The gist of a
simulation:
- We do not wish
to perform the
tasks
literally with a
computer program
Furthermore:
- It is impossible to
perform the
tasks
literally with a
computer program
E.g.: service a car....
- It is impossible to
perform the
tasks
literally with a
computer program
- We wish to
obtain information on
the performance aspect of
the real-life system !!!
Therefore:
- We only simulate the passing of time to perform the task
- We do not wish
to perform the
tasks
literally with a
computer program
- Example of a real life system:
- Post office with
one server:
Process:
- Clients
arrive at
random times to the
post office into a
queue
- A server
will service
the first client in the
queue
- The service time is random
- Clients
arrive at
random times to the
post office into a
queue
- Post office with
one server:
- Aspect of the
real life system studied:
- What is the average time for a client to obtain service from the post office ???
- System system:
- Simulation system =
a software system that
implements a
virtual time system
used to schedule
events to
take place
- A simulation system provides:
- Operations to
create
agents
- Operations to schedule execution at certain (virtual) time
- Operations to
create
agents
- Simulation system =
a software system that
implements a
virtual time system
used to schedule
events to
take place
- Simulation model of the
single server system:
Explanation:
- The clerk in the
post office is
simulated by the
serverProc object
- The arrival of
client to the
post office is
simulated by the
generatorProc object
- A client to the post office is simulated by the ClientProc object
- The clerk in the
post office is
simulated by the
serverProc object
- Psuedo code for the
Generator object:
/* ==================================================== Simulate a "random arrival" of clients ==================================================== */ while( true ) { Hold( a random amount of time ); // Wait a random amount of time Generate( ClientProc ); // Create a client object }
- Psuedo code for the
Server object:
/* ==================================================== Simulate the "service" of clients in the queue ==================================================== */ while ( true ) { if ( queue is empty ) { sleep( ); // Process must be re-activated by a client } Client = Dequeue( ); // Remove first client from queue Hold( random "service" time ); // Simulate providing service !!! ReActivate( Client ); // Client has "finished" service }
- Psuedo code for a
Client object:
ArrivalTime = readSysTime( ); // Record the time that the client was created Enqueue( serverQueue ); // Enter the service queue ReActivate ( Server ); // Wake up the server Sleep( ); // Wait until service is complete /* ========================================================== Client will run again when the service is complete !!! ========================================================== */ CompleteTime = readSysTime( ); // Record the time that the client completes AccDelay = AccDelay + ( CompleteTime - ArrivalTime ); // Time to serve NClients = NClients + 1; // Note: AccDelay/NClient = the average service time of clients !! Terminate( );
- Example Program:
(Demo above code)
cd demo/ProSim main1 arrivalRate servicerate SimulationLength (main1 1 2 1000)