ECS 140A Programming Languages
About This Assignment
Winter 2021
Homework 5
This assignment asks you to complete programming tasks using the Go programming language.
You are only allowed to use the subset of Go that we have discussed in class. No credit will be given in this assignment if any of the problem solutions use material not discussed in class. Please use Piazza for any clarifications regarding this issue.
Especially, the use of the runtime and reflect packages is forbidden.
Although the package time is discussed in class, you are NOT allowed to use it
in this homework (e.g. time.Sleep).
Since the focus of this homework is concurrency, homework solutions are
required to be concurrent in order to receive credit.
To complete the assignment (i) download hw5-handout.zip from Canvas, (ii) mod-
ify the members.txt and .go files in the hw5-handout directory as per the instruc- tions in this document, and (iii) zip the hw5-handout directory into hw5-handout.zip and upload this zip file to Canvas by the due date.
Do not change the file names, create new files, or change the directory structure of hw5-handout.
This assignment can be worked on in a group of at most 4.
Listallthenamesandemailaddressesofallmembersofthegroupinthemembers.txt
file in the hw5-handout directory, one per line in the format name
If you are working individually, then only add your name and email to members.txt.
Refer to Homework 0 for instructions on installing the correct versions of the pro- gramming language as well as using CSIF computers.
Begin working on the homework early.
Apart from the description in this document, look at the unit tests provided to under- stand the requirements for the code you have to write.
Post questions on Piazza if you require any further clarifications. Use private posts if your question contains part of the solution to the homework.
Keep your homework solution after you submit it. You may need to use it for later assignments.
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Bug1 (10 points)
Modify code in hw5-handout/bug1/bug1.go to fix the concurrency bug.
Some unit tests are provided for you in hw5-handout/bug1/bug1_test.go. You are not allowed to make changes in hw5-handout/bug1/bug1_test.go to fix the bug.
Fromthehw5-handout/bug1directory,runthego testcommandtoruntheunit tests.
Run the go test -race command to run the unit tests with the race detector,1 a tool for finding race conditions in Go code.
From the hw5-handout/bug1 directory, run go test -cover command to see the current code coverage.
If needed, add more unit tests in hw5-handout/bug1/bug1_test.go to get 100% code coverage for the code in hw5-handout/bug1/bug1.go.
From the hw5-handout/bug1 directory, run the following two commands to see which statements are covered by the unit tests:
$ go test -coverprofile=temp.cov
$ go tool cover -html=temp.cov
NFA (20 points)
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A nondeterministic finite automaton (NFA) is defined by a set of states, symbols in an alphabet, and a transition function. A state is represented by an integer. A symbol is represented by a rune, i.e., a character. Given a state and a symbol, a transition function returns the set of states that the NFA can transition to after reading the given symbol. This set of next states could be empty.
A graphical representation of an NFA is shown below:
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a
0a2 b
In this example, {0,1,2} are the set of states, {a,b} are the set of symbols, and the transition function is represented by labelled arrows between states.
1https://blog.golang.org/race-detector
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b
If the NFA is in state 0 and it reads the symbol a, then it can transition to either state 1 or to state 2.
If the NFA is in state 0 and it reads the symbol b, then it can only transition to state 2.
If the NFA is in state 1 and it reads the symbol b, then it can only transition to state 0.
If the NFA is in state 1 and it reads the symbol a, it cannot make any transitions.
If the NFA is in state 2 and it reads the symbol a or b, it cannot make any transitions.
A given final state is said to be reachable from a given start state via a given input sequence of symbols if there exists a sequence of transitions such that if the NFA starts at the start state it would reach the final state after reading the entire sequence of input symbols.
In the example NFA above,
The state 1 is reachable from the state 0 via the input sequence abababa.
The state 1 is not reachable from the state 0 via the input sequence ababab. The state 2 is reachable from state 0 via the input sequence abababa.
The transition function for the NFA described above is represented by the expTransitions function in hw5-handout/nfa/nfa_test.go. Some unit tests have also been given to you in hw5-handout/nfa/nfa_test.go. From the hw5-handout/nfa directory, run the go test command to run the unit tests.
Write a concurrent implementation of the Reachable function in hw5-handout/nfa/nfa.go that returns true if a final state is reachable from the start state after reading an input sequence of symbols, and false, otherwise. The goal of this assignment is to test your knowledge on concurrency in Go, thus no credit will be given if your implementation is not concurrent.
If needed, write new tests, in hw5-handout/nfa/nfa_test.go to ensure that you get 100% code coverage for your code.
From the hw5-handout/nfa directory, run the go test -cover command to see the current code coverage.
From the hw5-handout/nfa directory, run the following two commands to see which statements are covered by the unit tests:
$ go test -coverprofile=temp.cov
$ go tool cover -html=temp.cov
Implementing a sequential version of Reachable will get you no points.
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OPTIONAL: From the hw5-handout/nfa directory, run the following command: $ go test -cpu 1,2,4,8 -bench=.
to benchmark2 your concurrent implementation of Reachable and see how your im- plementation scales with increasing number of CPUs.
2https://golang.org/pkg/testing/#hdr-Benchmarks
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