C process problem

Question

Problem

Firstly, downloading two text files from the url:

https://drive.google.com/file/d/1fgJqOeWbJC4ghMKHkuxfIP6dh2F911-E

These file contains the 100000 ratings of 943 users for 1682 movies in the following format:

userID movieID rating timeStamp

userID movieID rating timeStamp

...

Secondly, you should write a program that spawns two child processes, and each of them will read a file and compute the average ratings of movies in the file. You implement the program by using shared memory method.

Answer 1

Download the Dataset: Get the text files from the specified Google Drive URL.

create a c program

Spawn two child processes.

Use shared memory to communicate between processes

Each process reads one file and computes average ratings.

download the files using a browser, or you can use command-line tools like wget or curl.

For example, using wget:

wget --no-check-certificate 'https://drive.google.com/uc?export=download&id=1fgJqOeWbJC4ghMKHkuxfIP6dh2F911-E' -O ratings.txt

Include Required Libraries:

<stdio.h>, <stdlib.h>, <string.h> for standard functions.

<unistd.h>, <sys/types.h>, <sys/wait.h> for process control.

<sys/ipc.h>, <sys/shm.h> for shared memory.

Create Shared Memory: Use shmget() to create shared memory space for storing the total ratings and count.

Spawn Processes: Use fork() to create child processes.

Read Files and Compute Averages:

Each process should read its respective file.

Calculate the total rating and the number of ratings.

Communicate Results Using Shared Memory: Store results in shared memory and ensure synchronization using appropriate mechanisms.

Example C Code:

#include <stdio.h>

#include <stdlib.h>

#include <string.h>

#include <unistd.h>

#include <sys/types.h>

#include <sys/wait.h>

#include <sys/ipc.h>

#include <sys/shm.h>

#define FILE1 "ratings1.txt"

#define FILE2 "ratings2.txt"

#define SHM_KEY 1234

int main() {

// Shared memory to hold total ratings and counts

int shmid;

float *shared_data;

// Allocate shared memory

shmid = shmget(SHM_KEY, 2 * sizeof(float), IPC_CREAT | 0666);

if (shmid < 0) {

perror("shmget");

exit(1);

}

shared_data = (float*)shmat(shmid, NULL, 0);

shared_data[0] = 0; // Total rating for process 1

shared_data[1] = 0; // Count for process 1

// Forking Process

pid_t pid1 = fork();

if (pid1 == 0) {

// Child process 1 reads FILE1

FILE *file1 = fopen(FILE1, "r");

if (!file1) {

perror("Opening file1");

exit(1);

}

float rating;

int count = 0;

while (fscanf(file1, "%*d %*d %f %*s", &rating) != EOF) {

shared_data[0] += rating; // Accumulate total rating

count++;

}

fclose(file1);

shared_data[1] = count; // Set count

exit(0);

}

pid_t pid2 = fork();

if (pid2 == 0) {

// Child process 2 reads FILE2

FILE *file2 = fopen(FILE2, "r");

if (!file2) {

perror("Opening file2");

exit(1);

}

float rating;

int count = 0;

while (fscanf(file2, "%*d %*d %f %*s", &rating) != EOF) {

shared_data[0] += rating; // Accumulate total rating

count++;

}

fclose(file2);

shared_data[1] += count; // Add this process's count

exit(0);

}

// Wait for both child processes to finish

wait(NULL);

wait(NULL);

// Calculate overall average

float average = shared_data[0] / shared_data[1];

printf("Overall Average Rating: %.2f\n", average);

// Detach and remove shared memory

shmdt(shared_data);

shmctl(shmid, IPC_RMID, NULL);

return 0;

}

Code Explained:

Shared Memory: The shared memory segment is created using shmget() and mapped into the process address space with shmat().

Child Processes:

Each child reads its respective file (you'll need two separate files named ratings1.txt and ratings2.txt).

The first value in shared_data stores the cumulative rating, while the second stores the total count.

Synchronization: The main process waits for both child processes to complete.

Average Calculation: After the processes finish, the main process calculates and prints the overall average rating.

Clean-Up: Shared memory is detached and removed after use.