File buffer.mdj contains a Star UML State Chart giving the outline of the controller for a circular buffer.

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File buffer.mdj contains a Star UML State Chart (reproduced above) giving the outline of the controller for a circular buffer. This buffer is accessed by two concurrent processes, Producer and Consumer, who communicate with the buffer controller using two channels, put and get. The producer repeatedly does a put! and the consumer similarly does a get?, and the buffer controller performs the respective complementary operations.

File Circular_Buffer.java contains a Java program providing an outline of the implementation of the above scenario using the Message Passing Library (see Slides below). It gives the main program, the classes Producer and Consumer, and also the outline of class Circular_Buffer.

Class Circular_Buffer uses an integer array, data, of size n in order to hold its data. It has a field count that gives, at any given time, the number of values that can be taken out of the buffer. It also has two indices p and g to point, respectively, to the places in the array where the next value is to be put by the producer and taken out by the consumer. These indices are incremented (modulo n) as put/get operations take place. The actual insertion and retrieval of values are performed by two methods put() and get() respectively.

What you should do:

1. Complete the Star UML State Chart by providing suitable labels on the four transitions shown. Each label is of the form event [ guard ] / action – see slides below for details. The labels should collectively express the synchronization policy of the buffer controller, namely, that:

(i) when the buffer is empty (count == 0) only a put operation is permitted;

(ii) when the buffer is full (count == n) only a get operation is permitted;

(iii) otherwise, both put and get are permitted - the selection is non-deterministic.

In specifying the transition labels in Star UML:

(i) each event is a channel send/receive, and is specified as a Trigger Event;

(ii) each guard is a boolean expression and specified in the Properties section; and

(iii) each action is a call on one of the methods put() or get(), and specified as an Effect Behavior → OpaqueBehavior.

Update the state chart buffer.mdj as per the above specification.

2. Complete the run() method in class Circular_Buffer providing an implementation of the above synchronization policy. As the state chart specifies that the buffer controller operates in a repetitive cycle, the top level of the run() method should be a while(true) {…}

In Eclipse, right-click on the project, then select Build Path → Configure Build Path → Add External JAR → browse and select MessagePassing2.jar. The file MessagePassing2.jar is given in here as attachment.

Run the completed program under JIVE after adding Scheduler.* to Debug Configurations → JIVE → Exclusion Filter. Check that the Console output shows the strings Put:1 … Put:10 and Get:1 … Get:10. This output will be interleaved with the underlying scheduler’s log showing that it scheduled 20 send-receive pairs.

Save the Execution Trace in a file, buffer.csv, and load it into the Property Checker. Add Circular_Buffer:1.state to the Key Attributes. Enter Circular_Buffer:1.state = s in the Abbreviations textbox. Finally, copy the contents of the file property.txt (with comments) into the Properties textbox. Press Validate and check that all properties are satisfied; otherwise, the program has an error which needs to be corrected.

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