Lab 5: Unix Pipes

Lab 5: Unix Pipes
COP4600 – Operating Systems
Overview
The aim of this lab is to familiarize you with pipes in Linux. Pipes are a common form of inter-process
communication.
Structure
The assignment is broken into three main parts. In each part, you will learn about a different way to
implement pipes. The three parts are as follows:
1. Basic Pipes
2. Named Pipes
3. Pipe System Call
Basic Pipes
Basic pipes can be created in the terminal by placing the “|” operator between commands. Using “|”
causes the output of the left command to be piped in as the input to the right command. For example,
running “cat result.txt | grep -o "COP4600" | wc -l" would return the number of times that the pattern
“COP4600” is found in result.txt. The contents of the file are being piped into the grep command which
then passed any matches into the wc command. The “wc -l” option returns the number of newlines
which, in this case, equals the number of occurrences of the pattern.
For this part, an executable file named “part1.o” is provided via Canvas. When run, the executable will
perform basic operations until it encounters a failure. The amount of successful operations completed
before failing will vary. Here is a sample output of this program:
Your task is to create a C++ program that, when the output of “part1.o” is piped in, determines which
operation number caused the failure. For example, your program would print “Program failed on
operation 12” if it were run with the information from the above screenshot. For this part you will need
to submit a screenshot that shows your code successfully running twice with input provided by “part1.o”
through a basic pipe.
Named Pipes
Named pipes, also known as FIFOs (first-in first-out), are functionally similar to basic pipes except they
are represented as a special file and are, therefore, a non-temporary part of the filesystem. A FIFO can
be created using the “mkfifo [name]” command (similar to mkdir). A FIFO does not store the
communicated data in the file system and only acts as a reference point for processes to establish a
connection. Because of this, when a writer process opens the FIFO, it will block until a reader process
opens the other end. Utilizing named pipes through the command line, therefore, will likely require
multiple terminal windows.
For this part, implement the following:
1. Create a named pipe.
2. Modify your part 1 C++ code to read its input from a file (your named pipe). This program
should be named “lastname_part2.cpp” where “lastname” is your last name.
3. Run “part1.o” and redirect its output into the named pipe.
4. Compile and run your part 2 program (input should not be redirected from the command line).
5. Repeat steps 3 and 4 then take a screenshot that shows the programs running to completion
twice. Be sure to include all terminal windows that were used.
Pipe System Call
Both piping methods used above have required some form of post-compile time actions (i.e. redirecting
output or creating a named pipe). In many cases, this may be a drawback. To set up a pipe entirely
within the process’ code, the pipe system call can be used.
For this part you will use the “fork()” and “pipe()” system calls to implement the following:
1. Create a new C++ program named “lastname_part3.cpp” where “lastname” is your last name.
The program should accept 5 command-line arguments (all integers).
2. The program should create two new child processes and utilize four pipes.
3. The parent process will send the 5 integers to the first child process using a pipe. This child will
sort the integers and send the result to the parent process and the second child process using one
pipe for each. The parent will print the result.
4. After receiving the sorted list from the first child process, the second child process will identify
the median value of the list and send the result to the parent using a pipe. The parent will print
the result.
5. Take a screenshot of the program running with the following integers passed in as command-line
arguments (in the specified order): 42, 15, 8, 16, and 23.
Submissions
You will submit the following at the end of this exercise on Canvas:
● Screenshot of the output from running your part 1 program with a basic pipe twice.
● Screenshot of the output from running your part 2 program with a named pipe twice.
● C++ source file for your part 2 program named “lastname_part2.cpp” where “lastname” is your
last name.
● Screenshot of the output from running your part 3 program with the required values.
● C++ source file for your part 3 program named “lastname_part3.cpp” where “lastname” is your
last name.
Helpful Links
https://www.linuxjournal.com/article/2156
https://www.tldp.org/LDP/tlk/ipc/ipc.html
http://www.cplusplus.com/doc/tutorial/files/
http://www.gnu.org/software/libc/manual/html_node/Creating-a-Pipe.html
http://man7.org/linux/man-pages/man2/pipe.2.html