How would you write a program in c++ that uses fork and pipe to create processes
ID: 3601110 • Letter: H
Question
How would you write a program in c++ that uses fork and pipe to create processes to add up all numbers in a file. The user will enter a number (1, 2, or 4) of parallel processes to create for processing the numbers. The system will then create this many processes, evenly dividing the file contents between the processes. For example, if the file has 1000 numbers and the user wants 4 processes, then each process would process 250 numbers in the file.
Parent process. This process allows user to input the number of processes to create (1, 2, or 4). It determines what portion of the file each process must work on and informs the process via a pipe. More specifically, the first child process handles the first block in the file, and the second child process handles the second one and so on. The parent then waits for each child to report its result. Once each result is received, it combines the results prints the overall result.
Child process. Receive which part of the file to calculate from the parent process through pipe. Process the file and send the result back to the parent process through pipe.
There are 4 given files named file1.dat, file2.dat, file3.dat, file4.dat
this program should output the result and record the run time for each process 1,2, and 4
Explanation / Answer
#include <unistd.h>
#include <stdio.h>
#include <iostream>
#include <fstream>
#include <cstring>
#include <sstream>
#include <time.h>
#define RUNS 1000
using namespace std;
int main()
{
int child_count = 1;
string line;
stringstream ss;
time_t start,finish;
//Promp the user
cout << "Which file to use? ";
cin >> line;
cout << "How many child processes would you like to make [1, 2, 4] ";
cin >> child_count;
cout << "Computing Sum..." << endl;
char * cstr = new char [line.size()+1]; //Create C-String
strcpy (cstr, line.c_str()); //Copy line (file name) to the C-string
ifstream myfile (cstr); // Loads the file to read. Requires a C-String
int line_count = 0; // Number of Lines in the file or number count
int fds[child_count+1][2];//Stuff for the pipe.
if (myfile.is_open())
{
while ( myfile.good() )
{
getline (myfile,line); //Read Line
if(line != "")
{
line_count++; // increment line count
}
}
int numbers[line_count]; // Instantiate an array of numbers
ifstream myfile (cstr); // Re-Load the file to insert values into the array
int x = 0;
while ( myfile.good() )
{
getline (myfile,line);
if(line != "")
{
ss << line;
ss >> numbers[x];
x++;
}
}
start = time(NULL); // Start our timer for calculating run time.
// The loop for running to the program.
for(int n = 0; n < RUNS; n++) {
pipe(fds[child_count]); //We're using the last File Descriptor for Child -> Parent
for(int x = 0; x < child_count; x++)
{
pipe(fds[x]); // Instantiate the pipe
int indexes[2]; //This is an array of integers that determine the begginning and end of the Child's loop
indexes[0] = ((x)*(line_count/child_count)); //The beginning index
indexes[1] = ((x+1)*(line_count/child_count)); //The ending index
write(fds[x][1], &indexes, 2*sizeof(int)); //Send our array of indexes to child
if(fork() == 0) //If it is child
{
int temp = 0; //Temp variable for the sum
int indexes2[2];
read(fds[x][0], &indexes2, 2*sizeof(int)); //Read the index's from pipe
for(int k = indexes2[0]; k < indexes2[1] ; k++)
{
temp += numbers[k];
}
//Write the child's partion of the sum to the pipe
write(fds[child_count][1], &temp, sizeof(int));
_exit(0); //Exit the child process
}
}
int tmp, total;
total = 0;
for(int m =0; m < child_count; m++) {
read(fds[child_count][0], &tmp, sizeof(int));
total += tmp;
}
cout << "DONE Calculating!" << endl;
// cout << "TIME TOOK TO CALCULATE: " << time << " microseconds" << endl;
cout << "TOTAL OF NUMBERS: " << total << endl;
}
finish = time(NULL);
cout << "START " << start << " FINISH " << finish << endl;
float runtime = (float)((finish - start))/(RUNS);
cout << "AVERAGE RUN TIME: " << runtime << " seconds!" << endl;
cout << "EOP" << endl;
}
else
{
cout << "File Unable to Open!" << endl;
}
}
Please find this code also
int main()
{
int fd1[2]; // Used to store two ends of first pipe
int fd2[2]; // Used to store two ends of second pipe
char fixed_str[] = "forgeeks.org";
char input_str[100];
pid_t p;
if (pipe(fd1)==-1)
{
fprintf(stderr, "Pipe Failed" );
return 1;
}
if (pipe(fd2)==-1)
{
fprintf(stderr, "Pipe Failed" );
return 1;
}
scanf("%s", input_str);
p = fork();
if (p < 0)
{
fprintf(stderr, "fork Failed" );
return 1;
}
else if (p > 0)
{
char concat_str[100];
close(fd1[0]); // Close reading end of first pipe
write(fd1[1], input_str, strlen(input_str)+1);
close(fd1[1]);
wait(NULL);
close(fd2[1]); // Close writing end of second pipe
read(fd2[0], concat_str, 100);
printf("Concatenated string %s ", concat_str);
close(fd2[0]);
}
else
{
close(fd1[1]); // Close writing end of first pipe
char concat_str[100];
read(fd1[0], concat_str, 100);
int k = strlen(concat_str);
int i;
for (i=0; i<strlen(fixed_str); i++)
concat_str[k++] = fixed_str[i];
concat_str[k] = ''; // string ends with ''
close(fd1[0]);
close(fd2[0]);
write(fd2[1], concat_str, strlen(concat_str)+1);
close(fd2[1]);
exit(0);
}
}
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