Description
In this assignment, you are to write a multi-threaded C program for a bounded-buffer producer/consumer
application: file copying. You are required to use semaphores in your program to enforce mutually exclusive
access to the buffer and to synchronize the producer and the consumer with regard to buffer slots/items. Make
sure that your submitted program compiles and runs on Athena, the ECS Linux machine.
1. Your program should be run with two file names provided at the command line, say: infile and outfile.
Otherwise, your program prompts the user with the message: “Correct Usage: prog3 infile outfile” and
then terminates.
2. In your program, the main thread verifies the input, opens the infile, and creates the outfile. The main thread
then spawns a producer thread and a consumer thread, and waits for both the producer and the consumer to
finish before it terminates. The producer and the consumer share a buffer of 9 slots with each slot having a
size of 18 bytes. The producer reads a string of 18-byte at a time from the infile and places it into the next
available buffer slot. The consumer takes the next available string from a buffer slot and writes it into the
outfile. The outfile thus is a verbatim copy of the infile.
3. The buffer can only be accessed in a mutually exclusive fashion, which is enforced through the use of a
semaphore variable buf_lock and the sem_wait and sem_post operations.
4. When the buffer is full, the producer must wait until a buffer slot becomes free before it can place a string
into it. When the buffer is empty, the consumer must wait for a string to be available. When the producer
fills a slot, the consumer is notified of an item available; when the consumer empties a slot, the producer is
notified of a slot available. These synchronization conditions between the producer and the consumer are
facilitated by two additional semaphore variables slot_avail and item_avail, and the sem_wait and
sem_post operations.
5. Because the order in which the semaphore wait operations (sem_wait) are executed can be a cause for
deadlock, care must be exercised when using sem_wait. From the producer’s perspective, you want to
check to see if there is a buffer slot available (through slot_avail) before attempting to gain exclusive
access to the buffer (via buf_lock). Similarly, from the consumer’s standpoint, you need to make sure
that there is at least an item (a string) in a buffer slot (via item_avail) before the consumer attempts to
have exclusive control of the buffer (via buf_lock).
6. To be able to use semaphores in your program, include
slot_avail, and item_avail. Then use sem_init to initialize these variables:
sem_init(&buf_lock, 0, 1);
sem_init(&slot_avail, 0, 9);
sem_init(&item_avail, 0, 0);
If x is a semaphore variable, then we can have sem_wait(&x) and sem_post(&x). When compiling your
program in a Linux machine, use an additional switch “–Lposix4” (For a Solaris machine, the switch is “–
lposix4”).
7. The data type for the buffer are given as follows:
#define SLOTSIZE 18
#define SLOTCNT 9
char buffer[SLOTCNT][SLOTSIZE];
You may need to have additional variables to handle things such as (a) the next available slot for the
producer; (b) the next available item for the consumer; (c) number of items available in the buffer; (d)
number of bytes in a slot; and (e) a flag to indicate when the producing/consuming process ends.
8. Test your program with your own data. Then make sure that your program works for the infile that contains
the following:
Semaphores are effective tools for critical section solution and
synchronization of concurrent activities. In this exercise, we will
use semaphores to implement the bounded-buffer producer/consumer
approach for a file copying application. Specifically, you need to
create a producer thread and a consumer thread that work concurrently
with a buffer of 9 slots. The producer produces (reads) a string of
18-byte at a time from the input file, i.e., this file, and places
(writes) the string to the next available slot in the buffer in a
mutually exclusive manner. On the other hand, the consumer fetches a
an item (18-byte string) from the next filled buffer slot at a time,
and consumes it (writes it to the output file). When the process is
finished, the output file is a verbatim copy of the input file.
Three semaphores are used to enforce the mutually exclusive access to
the buffer and to synchronize the activities of the producer and
the consumer. A final note: the last string processed may not be
exactly 18-byte long.
9. Submission Requirements. Your program must include adequate commenting (points deduction for
programs with inadequate comments). Compile your program using the following:
gcc prog3.c -o prog3 -lpthread -Lposix4
Test your program to make sure it works correctly for the following scenario.
prog3 infile
ls
cat infile
prog3 infile outfile
cat outfile
Save your program as yourName_prog3.c and submit it to “Program 3 Submission” in SacCT.
