CSCI 237

Computer Organization

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Lab 7: A Simple Dictionary Client

Overview

In this lab, you will gain a little experience with sockets and threads. You will complete the implementation of a simple multi-threaded client that supports the dict protocol.

I encourage you to work with a partner on this lab. Groups of three or more are not permitted. If you choose to work with a partner, make sure that both members of the group are contributing equally.

Instructions

Start by extracting lab7.tar to a directory where you plan to do your work:

	$ wget http://www.cs.williams.edu/~jeannie/cs237/labs/lab7/lab7.tar
	$ tar xvf lab7.tar

This will cause a number of files to be unpacked in a directory called lab7. The only file you will modify and turn in is dictclient.c. You can compile your code with the provided Makefile.

The dict procotol is fully described in this RFC. In a nutshell, you can connect to one of their servers (which mostly run on port 2628), and use a simple text-based protocol to look up the definition of words in various dictionaries (or databases). For example, after connecting to dict.org at port 2628 using telnet, you can ask for the definition of the word "dog":

	-> telnet www.dict.org 2628
	Trying 216.18.20.172...
	Connected to dictionary-server.dict.org.
	Escape character is '^]'.
	220 pan.alephnull.com dictd 1.12.1/rf on Linux 4.4.0-1-amd64  <21101961.7401.1525352621@pan.alephnull.com>
	define wn dog

This will return the following results:

	150 1 definitions retrieved
	151 "dog" wn "WordNet (r) 3.0 (2006)"
	dog
		n 1: a member of the genus Canis (probably descended from the
		   common wolf) that has been domesticated by man since
		   prehistoric times; occurs in many breeds; "the dog barked
		   all night" [syn: {dog}, {domestic dog}, {Canis familiaris}]
		2: a dull unattractive unpleasant girl or woman; "she got a
		   reputation as a frump"; "she's a real dog" [syn: {frump},
		   {dog}]
		3: informal term for a man; "you lucky dog"
		4: someone who is morally reprehensible; "you dirty dog" [syn:
		   {cad}, {bounder}, {blackguard}, {dog}, {hound}, {heel}]
		5: a smooth-textured sausage of minced beef or pork usually
		   smoked; often served on a bread roll [syn: {frank},
		   {frankfurter}, {hotdog}, {hot dog}, {dog}, {wiener},
		   {wienerwurst}, {weenie}]
		6: a hinged catch that fits into a notch of a ratchet to move a
		   wheel forward or prevent it from moving backward [syn:
		   {pawl}, {detent}, {click}, {dog}]
		7: metal supports for logs in a fireplace; "the andirons were
		   too hot to touch" [syn: {andiron}, {firedog}, {dog}, {dog-
		   iron}]
		v 1: go after with the intent to catch; "The policeman chased
		   the mugger down the alley"; "the dog chased the rabbit"
		   [syn: {chase}, {chase after}, {trail}, {tail}, {tag}, {give
		   chase}, {dog}, {go after}, {track}]
		.
	250 ok [d/m/c = 1/0/16; 0.000r 0.000u 0.000s]
	q
	221 bye [d/m/c = 0/0/0; 461.000r 0.000u 0.000s]

Type "q" to disconnect. Similarly, you can say:

	define moby-thesaurus computer	

This will return the following results:

	150 1 definitions retrieved
	151 "computer" moby-thesaurus "Moby Thesaurus II by Grady Ward, 1.0"
	50 Moby Thesaurus words for "computer":
	IBM machine, IDA, Teleplotter, Telereader, abacist, accountant,
	actuary, adder, analog computer, analytical control unit, analyzer,
   	bookkeeper, calculator, coder, collator, compiler,
   	computer hardware, computer unit, data processor, decoder,
   	detector, differential, differential analyzer, digital computer,
   	digital graph plotter, divider, electronic brain,
   	electronic computer, estimator, figurer, hardware,
   	information machine, integrator, memory tubes, multiplier,
   	phase discriminator, position coder, printer, printing calculator,
   	receptor, reckoner, relay, selective calculator, selector,
   	statistician, storage unit, telecomputer, thinking machine,
   	transmitter, tristimulus computer
   	
	.
	250 ok [d/m/c = 1/0/15; 0.000r 0.000u 0.000s]

I encourage you to try a few examples on your own to better understand how the protocol works.

Part A

Though there are other word databases, for this lab, we will be using the moby-thesaurus word database. In particular, your task for Part A is to take a single word as input and find its first synonym as returned by the server. Here is an example output:

	-> ./dictclient 
	Enter a word: computer
	Synonym: IBM machine  

The dictclient.c file I have given you contains some helper functions for parsing the output from the server. In particular, you will find the find_synonym() function to be very useful. Your task is to fill in setup_socket() and part_a() functions to perform the following tasks:

1. part_a(): Get word from stdin
2. setup_socket(): Create socket and connect to server
3. find_synonym(): Create request that will be sent to server
4. find_synonym(): Send request to server
5. find_synonym(): Read and parse result from socket
6. find_synonym(): Close socket
7. part_a(): Print result to stdout

Part B

Finding synonyms is fun, but it's more fun to generate entire phrases or even sentences using the results returned from moby-thesaurus. Thus rather than using a single word as input, in Part B you will take a simple phrase and substitute each word in the phrase with its first synonym as returned by the server. The result will be some pretty silly and weird sentences.

Of course, there is a catch. Rather than iteratively looking up each word in the phrase, we want to exploit parallelism. Thus each word should be sent to a separate thread. Each thread will create a socket, lookup the word passed to it, and store/return the result. We must make sure we read the results in the same order as the threads were created, however. Here is some sample output:

	-> ./dictclient 
	Enter phrase: The green car is fast
	New phrase: The Astroturf Pullman is Barmecidal feast
	-> ./dictclient
	Enter phrase: the quick brown fox jumped over the lazy dog
	New phrase: the Daedalian Argos brown African hunting dog jumped SOL the Micawberish Afghan hound

Using your solution from Part A, only a few minor changes are necessary to implement Part B. Specifically, you should:

1. Fill in the code for thread_func_single_word(), which defines the execution for a single thread. To achieve this, you should copy the relevant code from Part A into the thread function. The thread function should include the code necessary to process a single word. Most of this code probably already resides in your part_a() function.
2. Update your main function to use call part_b() instead of part_a(). part_b() reads and parses a phrase with multiple words instead of just a single word.
3. Note that each word is passed to a separate thread for processing in part_b(). Also note that We use pthread_join to force your main thread to wait for all peer threads to complete.
4. Finally, we print the resulting sentence/phrase.

Remember that we have to avoid data races. Be careful when passing shared variables around between threads. We malloc space on the heap for each word. We also copy the resulting synonyms back to the heap as well. Note that use of memcpy for copying results to specific locations in memory. Be sure to free as needed.

You might find it useful to look at echoserver-threads.c, a multi-threaded server, echoclient.c, a simple client, and hello.c, a simple threaded program, for guidance. Note that you are making a multi-threaded client, not a server.

You should be able to complete this lab during the lab session if you use your time wisely.

Evaluation

Your grade will be determined by the quality of your code (style) as well as correctness.

Getting Started

• Read these instructions.
• Read over the provided code.
• Compile and test often!
• gdb can be useful for debugging.