Inter-Process Communication Using FIFO (Named Pipes)

Subject: OS (Operating Systems)

Contributed By: Nunugoppula Ajay

Created At: March 10, 2025

Question:

Develop a two-way communication system between two processes using FIFO (Named Pipes) in a Linux environment. The two processes will act as User1 and User2, enabling them to send and receive messages in an alternating manner, similar to a chat system.

Explanation Video:

Explanation:

Problem Description:

Two separate programs (fifo1.c and fifo2.c) will communicate using a named pipe (/tmp/myfifo).
User1 starts by writing a message, and User2 reads it.
User2 then writes a response, and User1 reads it.
This cycle continues, allowing a conversation between both users.
Both programs should properly open, write, read, and close the FIFO in each iteration.

Constraints:

Use mkfifo() to create a named pipe (/tmp/myfifo).
Use open(), write(), and read() system calls.
Ensure proper synchronization (one process writes while the other reads).
The program should run indefinitely until manually stopped (or until an exit condition is implemented).

Example Execution:

Terminal 1 (Running `fifo1.c`)

Terminal 2 (Running `fifo2.c`)

Expected Outcome:

A working chat-like system between two users.
Correct message synchronization (User1 writes → User2 reads → User2 writes → User1 reads).
FIFO file is used as an intermediary for communication.

Source Code:

//fifo1.c

#include <stdio.h>
#include <string.h>
#include <fcntl.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <unistd.h>

int main() {
    int fd;
    char *myfifo = "/tmp/myfifo";  // FIFO file path
    mkfifo(myfifo, 0666);  // Create FIFO if it doesn’t exist

    char str1[80], str2[80];

    while (1) {
        // Write first
        fd = open(myfifo, O_WRONLY);  // Open FIFO for writing
        printf("User1: ");
        fgets(str2, 80, stdin);  // Get user input
        write(fd, str2, strlen(str2) + 1);
        close(fd);

        // Read response
        fd = open(myfifo, O_RDONLY);  // Open FIFO for reading
        read(fd, str1, sizeof(str1));
        printf("User2: %s\n", str1);
        close(fd);
    }

    return 0;
}

//fifo2.c

#include <stdio.h>
#include <string.h>
#include <fcntl.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <unistd.h>

int main() {
    int fd;
    char *myfifo = "/tmp/myfifo";  // FIFO file path
    mkfifo(myfifo, 0666);  // Create FIFO if it doesn’t exist

    char str1[80], str2[80];

    while (1) {
        // Read first
        fd = open(myfifo, O_RDONLY);  // Open FIFO for reading
        read(fd, str1, sizeof(str1));
        printf("User1: %s\n", str1);
        close(fd);

        // Write response
        fd = open(myfifo, O_WRONLY);  // Open FIFO for writing
        printf("User2: ");
        fgets(str2, 80, stdin);  // Get user input
        write(fd, str2, strlen(str2) + 1);
        close(fd);
    }

    return 0;
}

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