MP4: Process Synchronization

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Introduction to Operating Systems
MP4: Process Synchronization
Important Notes
1. The project is based on the Linux operating system, not the Xv6.
2. Makesureyourprogramworksonlinprog.cs.fsu.edubecause thatiswhere itwillbegraded.
Programming Task
In this assignment, you will learn how to use fork to create
processes, and how to use Linux pipes and shared memory for process
synchronization. Specifically, you will create a program called
trans. The program takes two command line parameters, an input file
and an output file. It copies the input file to the output file using
the shared memory. For example, to invoke the program, type
trans input-file output-file
at the command line prompt.
Here is how the program works: your program will create two
processes, a parent process and a child process, using fork. These
two processes share two pipes, one pipe carries data from the parent
to the child and the other carries data in the opposite direction (a
regular pipe is unidirectional.) The parent and the child also
shares a 4KB memory. To transfer the file, the parent first reads a
block of 4KB data from the input file into the shared memory (the
last block of the data might be less than 4KB if the file size is
not a multiple of 4KB), and sends the block number and the block
length to the child through its pipe. After receiving the block
number and the block length, the child writes the data from the
shared memory to the output file, and the sends the block number back
to the parent as an acknowledgment through the other pipe. After
receiving the correct block number from the child, the parent
continues to transfer the next block. This process continues until
the whole input file has been written to the output file. The
following are some specific requirements:
1. Put all your code in a single file, called trans.c. Note that
programs using the POSIX shared memory API must be compiled with
gcc -lrt to link against the real-time library, librt. You can
use the following command to compile your code:
gcc -std=c99 -Wall -Wextra -D_XOPEN_SOURCE=700 -o trans trans.c -lrt
2. Your code must work with both binary and text files. For example,
you can test it with the generated transfile, which is a binary
file. You may use fread/fwrite to access files. It shall also print
out a helpful error message. It shall also prompt the user whether
to overwrite the file if the output file already exists.
3. Make sure the input and output files are the same after running
trans. You can compare their checksums using shasum.
4. Use Linux pipe to create pipes. You can find the API and an example
program at
5. Use the POSIX shared memory, NOT SysV shared memory. That is, your
program shall NOT use SysV APIs such as shmgetand shmat. Instead,
use shm_open and mmap. POSIX shared memory is the preferred way to
use shared memory on Linux.
You can find the man pages for POSIX shared memory at man7/shm_overview.7.html, and some
example code at
(use the last three files; the first two files are not complete.).
The shared memory must be created after the process has forked.
When you name your shared memory object, include your fsuid to
avoid conflicts. For example, use /fsuid_cop4610 as the name in
6. The data is transferred in blocks. Each block is 4KB bytes
(except maybe the last one). The block number counts how many
blocks have been transferred. It starts from 1. So, if you are
going to transfer a file of 10KB, the block numbers are 1,2, and
The block numbers and the block lengths shall be sent and
received as the standard C int. On linprog, it will be a 64-bit
integer since linprog uses 64-bit linux. On a 32-bit Linux system,
they will be 32-bit integers.
After all the blocks have been transferred, the parent process
sends block number 0 and length 0 to the child. After receiving
block number 0, the child replies the parent with block number 0
and then exit. The parent receives the child’s acknowledgment to
block 0 and exits too.
Therefore, the protocol to transfer the file is similar to the
tftp protocol. For example, to copy a 6KB file,
1. The parent writes the first 4KB data of the file to the shared
memory and send two integers, 1 and 4096, to the child via
the pipe.
2. The child receives these two numbers, copies 4096 bytes from
the shared memory to the output file, and it sends back 1 to
the parent via the other pipe.
3. After receiving 1, the parent copies the left 2KB data to the
shared memory and send 2 and 2048 to the child.
4. The child receives them from the pipe, copies 2048 bytes to
the output file, and replies with 2 to the parent.
5. The parent then sends 0, 0 to the child.
6. The child receives 0 and replies with a 0 and then exit.
7. The parent receives 0 and exits too.
It is clear that in this protocol only one process can access the
shared memory at a time.
7. Your code shall include necessary error handling. For example, it
shall check the errors for fork, pipes, and shared memory. Both
examples given previously have the necessary error handling.
Submit in the Canvas your trans.c and Makefile as a single zip
compressed tarball. The name of your attachment shall be
with your_fsuid replaced by your CS account name.

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