MonitorsLast updated: February 4th 2019, at 12.39pm1 Problem StatementConsider the following problem statement:• There is one resource that may only be accessed by one process at anyone time;• There are many processes that access the resource using the methodsrequestResource(int priority) and releaseResource();• The parameter priority is an integer with a value between 0 and 10, i.e.0 ≤ priority ≤ 10;• The value of priority is not bound to a process, i.e. any process may callrequestResource with any (legal) value of priority;• The implementation should give priority to resource requests with thehighest priority.Assume that you can use a Java-like programming language (or pseudocode)with the following constructs:• Monitor definitions of the form:monitor name f/* variable declarations, e.g. */int variableName = 0;/* method declarations, e.g. */void proc() f…ggwhich may contain any number of method definitions and local variables.1Monitors• a Condition class, with the methods wait() and signal().Nested monitors are not allowed, and monitors cannot be assigned a priority.The implementation of monitors satisfies the immediate resumption requirement.2 Exercises1. (Pen and paper) Using constructs described above define a monitor containing (at least) the two methods requestResource(int priority) andreleaseResource(), such that these satisfy the given problem statement.Hint: assign a Condition object to each priority.2. Logbook question. Implement your solution in Java, using Locks andConditions. I.e., implement a LockResourceManager class that usesLocks and Conditions to implement the requestResource(int priority)and releaseResource() methods described above. Use the code provided(see section 3) to test your implementation, and try some tests of your own.3. Model question. Now implement your solution in raw” Java | i.e.without using Locks and Conditions, only synchronised methods and/orsynchronised statements. Hint: define your own lock() and unlock()methods, giving you a finer control over mutual exclusion in the code.I.e., implement a RawResourceManager class that this time uses synchronised methods and/or statements to implement the requestResource(intpriority) and releaseResource() methods described above. Use thecode provided (see section 3) to test your implementation, and try sometests of your own.3 The CodeSome code is provided to get you started with questions 2 and 3. This codedefines the following classes:Resource Models a simple resource.ResourceManager Specifies the resource manager interface | i.e. defines thesignatures of all the methods that a resource manager should implement.BasicResourceManager Implements all the methods required by ResourceManager,except requestResource(int priority) and releaseResource().ResourceUser Models a resource user.ResourceSystem Combines Resources, ResourceManagers and ResourceUsersto define a system where there is a set of resources and a set of users, withall users trying to make use of all resources, and with access to theseresources managed by the resource managers.2MonitorsNote that this code will not currently compile | see below.ResourceSystemTest Used to define some tester code. Note that this code doesnot test the resource system in the sense of reporting a pass or a fail ina test. It simply runs the resource system specified in the test. It is upto the user to inspect the output produced by this test to check that thesystem displays the behaviour expected.ResourceError Basic error handling for errors arising from the managementand use of resources.See the code and its documentation for further details.Note that ResourceSystem, and hence ResourceSystemTest, will not currently compile. This is because the addResource(String name,int maxUseages)method in ResourceSystem includes code that tries to create an instance ofResourceManager (this is on line 58 of ResourceSystem.java). It is not possible to instantiate an interface. When you have completed your implementationof LockResourceManager and/or RawResourceManager you can test the implementation by replacing the attempted instantiation of ResourceManager by acall of the constructor for your class.The code bundle also includes an implementation of the car park systemdiscussed in the lecture. This is for information only, and does not form part ofthe code for this week’s exercises.3
