SCIENCE 131A代写、Java编程设计代写

日期：2022-04-06 09:50

COMPUTER SCIENCE 131A

OPERATING SYSTEMS

PROGRAMMING ASSIGNMENT 4

CARS AND TUNNELS PREEMPTIVE PRIORITY

SCHEDULER

Description

Now that you have written a non-preemptive priority scheduler for Cars and Sleds you will

now add a preemptive priority scheduler that can also handle a new Vehicle type,

Ambulances.

Ambulance

The Ambulance is a Vehicle that is guaranteed to have the highest priority of any non-

Ambulance Vehicles.

PreemptiveTunnel

The PreemptiveTunnel class will contain logic governing a Vehicle admittance policy

that includes Ambulances.

At all times, the PreemptiveTunnel’s state must satisfy the same policy as the

BasicTunnel, however, it must also handle Ambulances according to the following rules:

- An Ambulance can always enter a PreemptiveTunnel unless there is another

Ambulance already inside.

- When an Ambulance enters a PreemptiveTunnel all other Vehicles in the

PreemptiveTunnel must stop and wait for the Ambulance to exit the Tunnel

before continuing.

- Any Vehicle entering a PreemptiveTunnel when an Ambulance is currently

inside should enter then pull over immediately.

When a Vehicle is pulled over part-way through the PreemptiveTunnel, it should

continue driving from where they left off.

For example, consider a Vehicle that requires 100 ms to travel through the Tunnel. Suppose

it sleeps 70 ms before being preempted by an Ambulance. After the Ambulance leaves the

Tunnel, it should only sleep for another 30 ms.

Use Java’s System.currentTimeMillis() method to implement this behavior.

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Pulling Over Vehicles

Before reading this section, you should first read the run method of the Vehicle class. In the

given implementation, the method simulating Vehicle behavior in a Tunnel,

doWhileInTunnel() simply has the Vehicle thread sleep for some amount of time

dependent on the speed field. In order to implement the concept of pulling over Vehicles in

the PreemptiveTunnel when an Ambulance enters, modifications need to be made to the

Vehicle’s doWhileInTunnel method.

You may use all of the multithreading concepts you have learned thus far in Java to solve this

problem, but you must use monitors to avoid busy waiting while an ambulance is in a

tunnel.

You may also add any additional fields or methods to the Vehicle class as you see fit. You

should not change the way log entries are entered in the Log.

Grading

There are no hidden unit tests that will be used for grading this assignment. To make sure you do

not have race conditions, set PrioritySchedulerTest.NUM_RUNS = 10.

Passing all of the test cases does not mean you will get a high score. Make sure that you:

● Properly achieve mutual exclusion using Java synchronization mechanisms. This includes

controlling access to shared data structures.

● Implement PreemptivePriorityScheduler’s admittance policy correctly. Your

solution must ensure that:

- Ambulances properly cause all other Tunnel occupants to cease driving till it

leaves. This includes the case of when a Vehicle enters a Tunnel occupied by

an Ambulance.

- Vehicles should properly resume driving after an Ambulance leaves.

- Ambulances should not wait unnecessarily for an opening.

Make sure you import and export the Eclipse project properly. The submitted project should

have a structure that looks exactly like the skeleton. An improperly structured project will

receive a 0.

Do not modify any files outside of the submission package. Failing to follow this

instruction will result in a 0.

The project needs to be renamed FirstnameLastnamePA4 (make sure to use Eclipse’s Refactor >

Rename). The zip file you submit should be named FirstnameLastnamePA4.zip.

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Allowed Libraries

The only additional classes related to concurrency and synchronization you can use are

Condition and Lock/ReentrantLock which can be found in

java.util.concurrent.locks. You are not allowed to use synchronized data structures

such as LinkedBlockingQueue.

Remarks

This is an individual assignment. Any sign of collaboration will result in a 0 score for the

assignment. Please check the academic integrity policies in the syllabus of the course.

Late policy: Please check the syllabus for the late submission policies of the course.