HW5: SYNCHRONIZATION of PRODUCER and CONSUMER Threads

This assignment requires creation of multiple producer and consumer threads that access a buffer using synchronization. You will implement a solution for the bounded-buffer producer-consumer problem using threads in Java. 




    1. Description of Task

You are required to implement this assignment in Java. It assumes that n items are to be produced and consumed.

    1. The Bounded Buffer (Bdbuffer.java): This buffer can hold a fixed number of items. This buffer

needs to be a first-in first-out (FIFO) buffer. You should implement this as a Circular Buffer that satisfies the FIFO. There should be exactly one instance of the buffer. The producer and the consumers must reference the same buffer.


    2. Producers (Producer.java): The producers are responsible for producing data items to be added

to the buffer. If the buffer is full, a producer must wait for a consumer to consume at least one item before it can add a new item to the buffer. If there are p producers, each producer is required to produce n/p items. The item that the producer adds to the buffer is a random character (with values between ‘a’ and ‘z’, both inclusive).

When a producer successfully inserts an item in the buffer it should print the location of insertion and time when insertion occurs with microsecond resolution, using this format:

Producer    2 inserted v at index    1 at time 2021-10-12 14:28:37.392914


When the random character is generated, you must also add it to a String so that it contains all the elements that the Producer generates. getProducedStr() method is used to return this generated string back to the Invoker.java file.


    3. Consumers (Consumer.java): The consumers are responsible for consuming elements, generated

by the producer, from the buffer. If the buffer is empty, the consumers must wait for the producer to add an item to the buffer. There may be one or more consumer threads running at the same time.

When a consumer successfully removes an item from the buffer it should print the location of removal and time when removal occurs with microsecond resolution, using this format:

Consumer    2 consumed q at index    6 at time 2021-10-12 14:28:37.394665

When a consumer successfully consumes an item from the buffer it should also add it to the string. This class should have a function named getConsumedStr(), which returns the string consumed by the Consumer.
CS 370: OPERATING SYSTEMS Fall 2021    Colorado State University




Mind that the statement of Producers producing an item should be underlined, so that it is easy to distinguish a statement from Producer and Consumer.

You will use wait() and notify() as the primitives to synchronize access to the buffer.

The producer class object should take these arguments:

    i. Copy of the instance of the buffer it will access in common with other Producers and other Consumers,

    ii. Number of elements that producer should generate,

    iii. The ID, which is the number of the producer thread (i.e.: the first producer thread should be 1, the second should be 2, etc.)

    iv. The seed which is used by the random number generator to generate the random numbers to be inserted.

The consumer class objects should take these arguments:

        i. Copy of the instance of the buffer it will access in common with the Producers and other Consumers,

        ii. Number of elements that this thread of consumer should consume. This is the total number of elements to be consumed divided by the total number of consumers (if it is evenly matched),

        iii. The ID, which is the number of the consumer thread (i.e.: the first consumer thread should be 1, the second should be 2, etc.)

    4. Main / Calling program (Invoker.java): Your main program should accept the seed command line argument. Using this seed, the following elements must be randomly initialized.

i.
Number of elements in buffer/buffer size
(between 5 and 10)
i.e. [5,10)
ii.
Number of items to be produced and consumed (between 10 and 20)
i.e. [10,20)
iii.
Number of consumers
(between 2 and 5)
i.e. [2,5)
iv.
Number of producers
(between 2 and 5)
i.e. [2,5)



Each producer thread terminates when the specified number of items has been produced. After this, you need to use the methods, getProducedStr() and getConsumedStr(), for each of the Producers and Consumers to get the full Produced/Consumed string.

Since the strings at the consumer end are not always in order, the main/calling function must sort both the strings obtained. Finally, if the sorted strings are the same, the Invoker.java program prints the following:

The sorted Produced and Consumed strings are the same as shown: hhmmmmqqssuuvv



Correctness Verification:

    • The items produced should match the items consumed.

    • The circular buffer should work as intended. Only one thread should be able to access the buffer at a time.

    • An item can be consumed only after it has been produced. However, if the consumption is very quick, within the smallest time resolution, production/consumption may appear to happen at
CS 370: OPERATING SYSTEMS Fall 2021    Colorado State University


the same time, and the reports may get printed in wrong order, if the consumer printing occurs first. To avoid this use System.out.flush()




    2. Task Requirements

        1. Implement the FIFO Circular Buffer and ensure that the buffer can hold the right number items at a time, and the access to it is synchronized.

        2. The number of items to be consumed should be equally distributed among the consumer threads (whenever possible). Verify that the number of elements can be perfectly divided among the consumers with no fractions involved, if not arrange for one of the consumer threads to handle the difference. Also, a seed is to be passed to the producer.

        3. A producer should wait if the buffer is full.

        4. A consumer should wait if the buffer is empty.

        5. Make sure that the printing requirements are met, specifically the underlined statements.

        6. Your solution must satisfy the correctness constraint (i.e.: you consume each item exactly once, in the order that it was produced, and demonstrate this by printing out the items produced and consumed, along with the location and the timestamp with microsecond resolution). The code to get the timestamp with microsecond resolution is provided to you, in Invoker.java. The produced string of all Producer threads should be obtained after the join of each Producer object, by calling getProducedStr() in the Producer class. The consumed string of each Consumer thread is obtained after each Consumer thread join, by calling getConsumedStr() in the

Consumer class. The sorted string of all the Consumers should be the same as the sorted string of all the Producers.

        7. There should be no deadlock. Your program will be executed multiple times, and it should run to completion every time without a deadlock.

        8. Your program should work for any combination of the number of consumers, producers, number of elements, and buffer size.



    3. Files Provided

Files provided for this assignment include: the description file (this file), a README, and skeleton Invoker.java and Producer.java files. This can be downloaded as a package from the course Canvas assignment page.

Please refer to the README.txt file inside the package for the questions. You need to answer the questions in the README file.
CS 370: OPERATING SYSTEMS Fall 2021    Colorado State University


    4. Example Outputs:

    1. Example 1: Set Seed as 13

~$ java Invoker 13



[Invoker] Buffer Size: 9



[Invoker] Total Items: 12



[Invoker] No. of Producers: 2



[Invoker] No. of Consumers: 3



Producer
1
inserted m at index
0
at time 2021-10-13 19:54:15.605070






Consumer
3
consumed m at index
0
at time 2021-10-13 19:54:15.612287
Producer
2
inserted m at index
1
at time 2021-10-13 19:54:15.612916






Consumer
2
consumed m at index
1
at time 2021-10-13 19:54:15.613265
Producer
1
inserted a at index
2
at time 2021-10-13 19:54:15.627417






Consumer
1
consumed a at index
2
at time 2021-10-13 19:54:15.627819
Producer
1
inserted j at index
3
at time 2021-10-13 19:54:15.628321






Consumer
3
consumed j at index
3
at time 2021-10-13 19:54:15.628638
Producer
2
inserted a at index
4
at time 2021-10-13 19:54:15.628959






Consumer
2
consumed a at index
4
at time 2021-10-13 19:54:15.629272
Producer
2
inserted j at index
5
at time 2021-10-13 19:54:15.629606






Consumer
3
consumed j at index
5
at time 2021-10-13 19:54:15.629908
Producer
1
inserted o at index
6
at time 2021-10-13 19:54:15.630230






Consumer
1
consumed o at index
6
at time 2021-10-13 19:54:15.630563
Producer
1
inserted r at index
7
at time 2021-10-13 19:54:15.631084






Consumer
3
consumed r at index
7
at time 2021-10-13 19:54:15.631408
Producer
2
inserted o at index
8
at time 2021-10-13 19:54:15.631711






Consumer
2
consumed o at index
8
at time 2021-10-13 19:54:15.632059
Producer
2
inserted r at index
0
at time 2021-10-13 19:54:15.632335






Producer
1
inserted q at index
1
at time 2021-10-13 19:54:15.632617






Consumer
1
consumed r at index
0
at time 2021-10-13 19:54:15.632919
Producer
2
inserted q at index
2
at time 2021-10-13 19:54:15.633344






Consumer
2
consumed q at index
1
at time 2021-10-13 19:54:15.633653
Consumer
1
consumed q at index
2
at time 2021-10-13 19:54:15.633935

The sorted Produced and Consumed strings are the same as shown: aajjmmooqqrr
CS 370: OPERATING SYSTEMS Fall 2021    Colorado State University


    2. Example 2: Set Seed as 6

~$ java Invoker 6 [Invoker] Buffer Size: 6

[Invoker] Total Items: 18

[Invoker] No. of Producers: 2



[Invoker] No. of Consumers: 4



Producer
1
inserted r at index
0
at time 2021-10-13 19:55:55.096322






Consumer
4
consumed r at index
0
at time 2021-10-13 19:55:55.103695
Producer
2
inserted r at index
1
at time 2021-10-13 19:55:55.104359






Consumer
3
consumed r at index
1
at time 2021-10-13 19:55:55.104701
Producer
2
inserted g at index
2
at time 2021-10-13 19:55:55.118666






Consumer
1
consumed g at index
2
at time 2021-10-13 19:55:55.119071
Producer
2
inserted s at index
3
at time 2021-10-13 19:55:55.119400






Consumer
2
consumed s at index
3
at time 2021-10-13 19:55:55.119904
Producer
1
inserted g at index
4
at time 2021-10-13 19:55:55.120379






Consumer
3
consumed g at index
4
at time 2021-10-13 19:55:55.120696
Producer
1
inserted s at index
5
at time 2021-10-13 19:55:55.121028






Consumer
2
consumed s at index
5
at time 2021-10-13 19:55:55.121325
Producer
2
inserted w at index
0
at time 2021-10-13 19:55:55.121846






Consumer
1
consumed w at index
0
at time 2021-10-13 19:55:55.122183
Producer
2
inserted j at index
1
at time 2021-10-13 19:55:55.122520






Producer
2
inserted l at index
2
at time 2021-10-13 19:55:55.122819






Producer
2
inserted h at index
3
at time 2021-10-13 19:55:55.123121






Consumer
4
consumed j at index
1
at time 2021-10-13 19:55:55.123408
Consumer
2
consumed l at index
2
at time 2021-10-13 19:55:55.123724
Consumer
2
consumed h at index
3
at time 2021-10-13 19:55:55.124163
Producer
1
inserted w at index
4
at time 2021-10-13 19:55:55.124674






Consumer
3
consumed w at index
4
at time 2021-10-13 19:55:55.125012
Producer
1
inserted j at index
5
at time 2021-10-13 19:55:55.125315






Consumer
4
consumed j at index
5
at time 2021-10-13 19:55:55.125593
Producer
2
inserted g at index
0
at time 2021-10-13 19:55:55.125852






Consumer
1
consumed g at index
0
at time 2021-10-13 19:55:55.126110
Producer
2
inserted s at index
1
at time 2021-10-13 19:55:55.126374






Consumer
4
consumed s at index
1
at time 2021-10-13 19:55:55.126612
Producer
1
inserted l at index
2
at time 2021-10-13 19:55:55.126908






Consumer
3
consumed l at index
2
at time 2021-10-13 19:55:55.127186
Producer
1
inserted h at index
3
at time 2021-10-13 19:55:55.127470






Consumer
4
consumed h at index
3
at time 2021-10-13 19:55:55.127757
Producer
1
inserted g at index
4
at time 2021-10-13 19:55:55.128007






Consumer
1
consumed g at index
4
at time 2021-10-13 19:55:55.128223
Producer
1
inserted s at index
5
at time 2021-10-13 19:55:55.128546






Consumer
4
consumed s at index
5
at time 2021-10-13 19:55:55.128789

The sorted Produced and Consumed strings are the same as shown: gggghhjjllrrssssww
CS 370: OPERATING SYSTEMS Fall 2021    Colorado State University




    5. What to Submit

Use the CS370 Canvas to submit a single .zip or .tar file that contains:

    • All .java files listed below and descriptive comments within, o Invoker.java

o Producer.java o Consumer.java o Bdbuffer.java

    • a Makefile that performs both a make build as well as a make clean,

    • a README.txt file containing a description of each file and any information you feel the grader needs to grade your program, and answers for the 4 questions

For this and all other assignments, ensure that you have submitted a valid .zip/.tar file. After submitting your file, you can download it and examine it to make sure it is indeed a valid zip/tar file, by trying to extract it.

Filename Convention: The archive file must be named as: <FirstName>-<LastName>-HW5.<tar/zip>. E.g. if you are John Doe and submitting for assignment 1, then the tar file should be named John-Doe-HW5.tar




    6. Grading

The assignments must compile and function correctly on machines in the CSB-120 Lab. Assignments that work on your laptop on your particular flavor of Linux/Mac OS X, but not on the Lab machines are considered unacceptable.

The grading will also be done on a 100 point scale. The points are broken up as follows:


Objective

Points

Correctly performing Tasks 1-8 (10 points each)

80 points

Providing a working Makefile.

5 points

Questions in the README file

5 points

Text alignment and underlining

5 points

Descriptive comments

5 points
Questions: (see README.txt file in the skeleton provided)

Restriction and Deductions:


[R1]. There is a 100-point deduction if you use an unbounded buffer for this assignment.


[R2]. There is a 100-point deduction if you use Thread.sleep() to synchronize access to the buffer. You can only use wait() and notify() as the primitives to synchronize access to the buffer. Thread.sleep() may be used for inserting random delays.
CS 370: OPERATING SYSTEMS Fall 2021    Colorado State University




[R3]. Java has advanced classes for synchronization. These cannot be used for this assignment. Hence, there is a 100-point deduction for using any classes other than the following:

1. java.util.Random

2. java.lang.Exception

3. java.time.Instant

4. java.time.Clock

5. java.time.Duration

6. java.util.Formatter

7. java.util.Arrays

There is a 100-point deduction for using any external library.

[R4]. There is an 80-point deduction for using a Boolean flag or any variable that toggles in values so that your producer and consumer take turns adding to or consuming from the buffer. The solution must be based entirely on the use of wait() and notify().


You are required to work alone on this assignment.

Notes:

    1. The output should have Producer statements underlined. You can use “\033[0;4m” to start underline formatting and “\033[0;0m” to stop the underline formatting in your print statement.

    2. Look at the spacing for the word ‘at’ in Producer and the word ‘from’ in Consumer. Maintain the same spacing as only then the time stamps line up correctly and can be viewed easily.

    3. Use %3d for the formatter to display the ID aligned next to the Consumer and next to the Producer. In other words, outputs from both, Consumer and Producer, should be aligned.

    4. The number of elements to be consumed might be a multiple of the number of consumers (when divided evenly), otherwise one of the consumers might have to take on a few more elements.

    5. The number of elements to be produced might be a multiple of the number of producers (when divided evenly), otherwise one of the producers might have to take on a few more elements.

    6. Do not define a package inside of your programs which includes all your programs, as this will raise an issue when the programs are run on terminals using command line.



    7. Late Policy

Click here for the class policy on submitting late assignments.

Revisions: Any revisions in the assignment will be noted below.