Write a C program that takes exactly one command-line argument that specifies th

Question

Write a C program that takes exactly one command-line argument that specifies the maximum number of simultaneous execution. The program runs up to pr_limit processes at a time.

Follow this outline for the program

• Check the appropriate command-line argument and output a usage message if the command line is incorrect.
• Initialize pr_limit from the command line. The pr_limit variable specifies the maximum number of children allowed to execute at a time.
• The pr_count variable holds the number of active children. Initialize it to 0.
• Execute the following main loop until the end-of-file is reached on standard input:
o If pr_count is pr_limit, wait for a child to finish and decrement pr_count.
o Read a line from standard input (fgets) of up to MAX_BUF characters and execute a program corresponding to that command line by forking a child and execute the file.
o Increment pr_count to track the number of active children.
o Check to see if any of the children have finished (**). Decrement pr_count for each child that has completed.
• After encountering end-of-file on standard input, wait for all of the remaining children to finish and then exit.
• For each terminated child, prints out its exit code value.

Try and use perror in the submission

** A parent process can check if one of its children terminated without blocking itself by using waitpid() system call as follow waitpid(-1, &status, WNOHANG). The system call returns 0 if there are still children to be waited for, or the pid of the terminated child.
In this exercise, use the program to run multiple copies of the testsim program. The testsim program is given below. It takes two command-line arguments: the sleep time and the repeat factor. The testsim program loops repeat factor times. In the loop, testsim sleeps for the specified sleep time and then output a message with its process ID to standard output.

/* testsim.c */
#include <stdio.h>
int main(int argc, char *argv[])
{
int n;
CS 2750 System Programming and Tools Programming Assignment 6
_____________________________________________________________________________________
2
int sec;
if (argc <= 2) {
fprintf(stderr, “Usage: %s sleep_time repeat_factor ”, argv[0]);
exit(1);
}
sscanf(argv[1], “%d”, &sec);
sscanf(argv[2], “%d”, &n);
while (n-- > 0)
sleep(sec);
printf(“Process ID = %d ”, getpid());
return sec;
}

Below program creates a fan of n processes where n is passed as a command-line argument. You can expand on this to create the program.
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
int main (int argc, char *argv[]) {
pid_t childpid = 0;
int i, n;
if (argc != 2){ /* check for valid number of command-line arguments */
fprintf(stderr, "Usage: %s processes ", argv[0]);
return 1;
}
n = atoi(argv[1]);
for (i = 1; i < n; i++)
if ((childpid = fork()) <= 0)
break;
fprintf(stderr, "i:%d process ID:%ld parent ID:%ld child ID:%ld ",
i, getpid(), getppid(), childpid);
return 0;
}

MUST BE IN C

Explanation / Answer

#include <fcntl.h>
#include <sys/types.h>
#include <sys/stat.h>
const char* USAGE = "Usage: mycat [-n] [file ...] [@ file] [file ...] ";
const mode_t OPENMODE = S_IRUSR|S_IWUSR|S_IXUSR|
S_IRGRP|S_IWGRP|S_IXGRP|
S_IROTH|S_IWOTH|S_IXOTH;
const int OPENFLAGS = O_CREAT|O_TRUNC|O_WRONLY;
void writeLineNumber(int output, int number) {
char *stringValue;
sprintf(stringValue, "%d: ", number);
write(output, stringValue, strlen(stringValue));
}
void readfile(char* filename, int output, char numLines) {
int fd = open(filename, O_RDONLY);
int lineNum = 1;
if (fd < 0) {
write(output, "Failed to read file: ", 21);
write(output, filename, strlen(filename));
write(output, " ", 1);
  
return;
}
// Write the first line number, if it is desired
if (numLines) { writeLineNumber(output, lineNum); }
char *character;
while(read(fd, character, 1)) {
write(output, character, 1);
if (*character == ' ' && numLines) {
lineNum++;
writeLineNumber(output, lineNum);
}
}
  
// Newline at the end
write(output, " ", 1);
}
void readline(char *line) {
char *input;
int amt = read(0, input, 255);
int index;
for (index = 0; index < amt; index++) {
line[index] = input[index];
}
line[index] = 0;
}
void readInput(int output, char numLines) {
char *line;
char **input;
int inputIndex = 0;
while (1) {
readline(line);
if (!strcmp(line, ":q ")) { break; }
input[inputIndex] = line;
inputIndex++;
}
while (*input) {
write(output, *input, strlen(*input));
input++;
}
}
int main(int argc, char** argv) {
char numberLines = 0;
int output = 0; // By default, write to standard out
// Must have at least two arguments
if (argc < 2) {
write(0, USAGE, strlen(USAGE));
}
// Pre parse arguments
int argIndex;
for (argIndex = 1; argIndex < argc; argIndex++) {
if (!strcmp(argv[argIndex], "-n")) {
numberLines = 1;
}
else if(*argv[argIndex] == '@') {
// Jump to next character (from @ to ...)
argv[argIndex]++;
// If form is @filename
if (*argv[argIndex]) {
output = open(argv[argIndex], OPENFLAGS, OPENMODE);
}
// Else, from is @ filename (separate argument)
else {
output = open(argv[argIndex + 1], OPENFLAGS, OPENMODE);
}
  
// If output file cannot be opened
if (output < 0) {
output = 0;
write(output, "Couldn't open file to write to ", 31);
}
}
}
// Drop first argument
argv++;
// Now loop through and actually read
while (*argv) {
// If the argument is not -n
if (strcmp(*argv, "-n")) {
// If its an @ (specify write file)
// We skip it, and optionally jump an arugment
if (**argv == '@') {
// If the write file is not attached, skip the next argument
if (!*argv[1]) { argv++; }
}
// If just a dash, read a line of input
else if (!strcmp(*argv, "-")) {
readInput(output, numberLines);
}
// Else, just read the specified file
else {
readfile(*argv, output, numberLines);
}
}
  
// Go to next argument
argv++;
}
return 0;
}

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