My program uses systems calls to count number of words in a file, and I need a way to check when all child have exited so that I can print a statement saying "x files have been counted". So I need a way to stop it from printing the print statement twice, and it should only print once at the end.
My output:
Child process for input_file_1.txt: word count is: 6
All 2 files have been counted
Child process for input_file_2.txt: word count is: 14
All 2 files have been counted
my main code (assume the wordCount function is correct):
int main(int argc , char *argv[]){
int *pid;
int parentPid, status;
if (argc < 2){
printf("Usage: a.out(./a.out) filename1 filename2 ..\n");
return -1;
}
pid = (int*)malloc(argc-1 * sizeof(int));
parentPid = getpid();
for (int i = 1; i < argc; i++){
pid = fork();
if (pid == 0){
if (countWord(parentPid,argv[i]) > 0)
printf("Child process for %s: word count is: %d\n",argv[i],countWord(parentPid,argv[i]));
}
else{
if(parentPid == getpid()){
wait(&status);
if (WIFEXITED(status) != 0)
printf("All %d files have been counted\n",argc - 1);
}
}
}
return 0;
}
Related
The code I've written finds out the number of words in multiple text files by creating multiple processes with each process being responsible for one file to count its words.
What I want to do is using pipes to find out total number of words in all files.
So the parent should:
creates a pipe between the each child and itself so it can get the number of words from each child
reports the total number of words in all the files by adding the numbers received through pipes
checks the exit status of each child and prints out how that child
exited
also let each child:
sends the number of the words to the parent via the pipe
send 0 as word count through the pipe to the parent if the file does
not exist or any other error happens
returns/exits with 0 if it is successfull in opening the file and
counting the words in that file, returns/exits with 1 if there is an
error (e.g., file does not exist etc.)
#include <stdio.h>
#include <stdlib.h>
#include <sys/types.h>
#include <unistd.h>
#define MAX_CHAR 100
pid_t getpid(void);
pid_t getppid(void);
char* itoa(int i, char b[]){
char const digit[] = "0123456789";
char* p = b;
if(i<0){
*p++ = '-';
i *= -1;
}
int shifter = i;
do{ //Move to where representation ends
++p;
shifter = shifter/10;
}while(shifter);
*p = '\0';
do{ //Move back, inserting digits as u go
*--p = digit[i%10];
i = i/10;
}while(i);
return b;
}
int countWords(char * fp, int pid) {
FILE * file;
int words = 0;
char word[MAX_CHAR];
//execute this function only if child process of parent, no gradchild is allowed to execute this function!
if (pid == getppid()) {
file = fopen(fp, "r");
if (file == NULL) {
return -1;
}
//find string in the file and count the words.
while (fscanf(file, "%s", word) != EOF) {
words++;
}
return words;
} else {
return -1;
}
return 0;
}
int main(int argc, char * arvg[]) {
//if invalid arguments
if (argc < 2) {
fprintf(stderr, "ERROR: INVALID ARGUMENTS");
exit(-1);
}
int count = 0, pid, ppid, status, totalwords;
int result = -1;
int fd[2];
char string[100];
char readbuffer[80];
int *write_fd = &fd[1];
int *read_fd = &fd[0];
result = pipe(fd);
if(-1 == result){
perror("pipe");
return -1;
}
//creates (argc - 1) child processes using fork()
pid = (int) malloc((argc - 1) * sizeof(int));
//parent pid
ppid = getpid();
//each child process to count the number of words in each file
for (int i = 1; i < argc; i++) {
//child process
pid = fork();
if( pid == -1){
perror("failed to fork");
return -1;
}else if (pid == 0) {
// call a function to count the number of words in file arvg[i]
int words = countWords(arvg[i], ppid);
close(*read_fd);
if (words >= 0) {
printf("Child process pid_%d for %s :number of words is %d\n", i, arvg[i], words);
//I don't know how to write int into the pipe,so below might be wrong
write(*write_fd, words, 1);
return 0;
} else if (words == -1) {
printf("Child process pid_%d for %s :does not exists\n", i, arvg[I]);
//I don't know how to write int into the pipe,so below might be wrong
write(STDOUT_FILENO, words, 1);
exit(1);
}
} else {
close(*write_fd);
//and I have no idea how to read int from pipes
read(*read_fd, &readbuffer, 1);
totalwords += ???
close(*read_fd);
//Wait until all child processes exit/return
if (ppid == getpid()) {
wait( & status);
}
//inspect their exit codes, WEXITSTATUS = return code when child exits
if (WEXITSTATUS(status) == 1) {
count++;
}
}
}
printf("Main process created %d child processes to count words in %d files\n", argc - 1, argc - 1);
printf("Total words is %d", totalwords);
printf("%d files have been counted sucessfully!\n", argc - 1 - count);
printf("%d files did not exist.\n", count);
return 0;
}```
Can someone help me to figure out this? I don't really know how to achieve my goal with pipe.
found some issues with the code. I fixed them for you (however, I would have done the same thing slight differently)
reading and writing int from a pipe is pretty straight forward, just typecast correctly while reading or writing to an int.
malloc to a pid was not necessary. Also malloc returns a pointer and should have been typecasted with (int*)
always add the right includes while using calls. Manual page or reading about the calls while trying to understand the parameters passed and return values is extremely useful.
Enough said, here is your working code
#include <stdio.h>
#include <stdlib.h>
#include <sys/types.h>
#include <unistd.h>
#include <sys/wait.h>
#define MAX_CHAR 100
pid_t getpid(void);
pid_t getppid(void);
char* itoa(int i, char b[]){
char const digit[] = "0123456789";
char* p = b;
if(i<0){
*p++ = '-';
i *= -1;
}
int shifter = i;
do{ //Move to where representation ends
++p;
shifter = shifter/10;
}while(shifter);
*p = '\0';
do{ //Move back, inserting digits as u go
*--p = digit[i%10];
i = i/10;
}while(i);
return b;
}
int countWords(char * fp, int pid) {
FILE * file;
int words = 0;
char word[MAX_CHAR];
//execute this function only if child process of parent, no gradchild is allowed to execute this function!
if (pid == getppid()) {
file = fopen(fp, "r");
if (file == NULL) {
return -1;
}
//find string in the file and count the words.
while (fscanf(file, "%s", word) != EOF) {
words++;
}
return words;
} else {
return -1;
}
return 0;
}
int main(int argc, char * arvg[]) {
//if invalid arguments
if (argc < 2) {
fprintf(stderr, "ERROR: INVALID ARGUMENTS");
exit(-1);
}
int count = 0, pid, ppid, status, totalwords = 0;
int result = -1;
int fd[2];
char string[100];
char readbuffer[80];
int *write_fd = &fd[1];
int *read_fd = &fd[0];
int recvd = 0;
result = pipe(fd);
if(-1 == result){
perror("pipe");
return -1;
}
//creates (argc - 1) child processes using fork()
//pid = (int) malloc((argc - 1) * sizeof(int));
//parent pid
ppid = getpid();
//each child process to count the number of words in each file
for (int i = 1; i < argc; i++) {
//child process
pid = fork();
if( pid == -1){
perror("failed to fork");
return -1;
}else if (pid == 0) {
printf ("%d child running \n", i);
// call a function to count the number of words in file arvg[i]
int words = countWords(arvg[i], ppid);
close(*read_fd);
if (words >= 0) {
printf("Child process pid_%d for %s :number of words is %d\n", i, arvg[i], words);
//I don't know how to write int into the pipe,so below might be wrong
write(*write_fd, (void *)&words, 1);
return 0;
} else if (words == -1) {
printf("Child process pid_%d for %s :does not exists\n", i, arvg[i]);
//I don't know how to write int into the pipe,so below might be wrong
write(STDOUT_FILENO, (void *)&words, 1);
exit(1);
}
} else {
close(*write_fd);
//and I have no idea how to read int from pipes
read(*read_fd, (void*)&recvd, 1);
totalwords += recvd;
printf("recvd %d \n", totalwords);
close(*read_fd);
//Wait until all child processes exit/return
if (ppid == getpid()) {
wait( & status);
}
//inspect their exit codes, WEXITSTATUS = return code when child exits
if (WEXITSTATUS(status) == 1) {
count++;
}
}
}
printf("Main process created %d child processes to count words in %d files\n", argc - 1, argc - 1);
printf("Total words is %d\n", totalwords);
printf("%d files have been counted sucessfully!\n", argc - 1 - count);
printf("%d files did not exist.\n", count);
return 0;
}
Well, the first time around, I did not focus on the algo. I fixed all of it. The problem is forking in a loop and reading and writing it would lead to wrong results. Moreover, Parent needs to look for EOF to ensure all read has happened. Anyways, Here is the code that should work
#include <stdio.h>
#include <stdlib.h>
#include <sys/types.h>
#include <unistd.h>
#include <sys/wait.h>
#define MAX_CHAR 100
pid_t getpid(void);
pid_t getppid(void);
char* itoa(int i, char b[]){
char const digit[] = "0123456789";
char* p = b;
if(i<0){
*p++ = '-';
i *= -1;
}
int shifter = i;
do{ //Move to where representation ends
++p;
shifter = shifter/10;
}while(shifter);
*p = '\0';
do{ //Move back, inserting digits as u go
*--p = digit[i%10];
i = i/10;
}while(i);
return b;
}
// count word from file provided
int countWords(char * fp, int pid) {
FILE * file;
int words = 0;
char word[MAX_CHAR];
//execute this function only if child process of parent, no gradchild is allowed to execute this function!
if (pid == getppid()) {
file = fopen(fp, "r");
if (file == NULL) {
return -1;
}
//find string in the file and count the words.
while (fscanf(file, "%s", word) != EOF) {
words++;
}
return words;
} else {
return -1;
}
return 0;
}
//do everything related to child here in this function
void child_process(int write_fd, char *filename, int ppid)
{
// call a function to count the number of words in file argv[i]
printf("counting words of %s\n", filename);
int words = countWords(filename, ppid);
if (words >= 0) {
printf("Child process pid for %s :number of words is %d\n", filename, words);
write(write_fd, (void *)&words, 1);
close(write_fd);
exit(0);
} else if (words == -1) {
printf("Child process pid for %s :does not exist\n", filename);
write(STDOUT_FILENO, (void *)&words, 1);
close(write_fd);
exit(1);
}
return;
}
int main(int argc, char * argv[]) {
//if invalid arguments
if (argc < 2) {
fprintf(stderr, "ERROR: INVALID ARGUMENTS");
exit(-1);
}
int pid = 0;
int ppid = 0;
int totalwords = 0;
int fd[2] = {0};
int write_fd = 0;
int read_fd = 0;
int recvd = 0;
// open a pipe
if(-1 == pipe(fd)){
perror("pipe");
return -1;
}
// assign write_fd and read_fd
write_fd = fd[1];
read_fd = fd[0];
//parent pid
ppid = getpid();
//each child process to count the number of words in each file
pid = fork();
for (int i = 0; i < argc-1; i++)
{
//child process
if (pid == 0) {
close(read_fd);
child_process(write_fd, argv[i+1], ppid);
break;
} else {
pid = fork();
}
}
// don't let child run beyond this point
if (pid == 0) {
exit(0);
}
// parent only code
if (pid > 0)
{
close(write_fd);
while (read(read_fd, (void*)&recvd, 1) > 0)
{
wait(NULL);
totalwords += recvd;
}
close(read_fd);
}
printf("Main process created %d child processes to count words in %d files\n", argc - 1, argc - 1);
printf("Total words is %d\n", totalwords);
printf("%d files have been counted sucessfully!\n", argc - 1);
}
I'm trying to use exec to execute a list of commands given as arguments.
Example input when In run the program would be ./assn2 ls date.
When I do this only the first command is executed.
#include<stdio.h>
#include<stdlib.h>
#include<sys/wait.h>
#include<unistd.h>
int main(int argc, char *argv[])
{
int args = argc-1;
pid_t childpid = fork();
// error
if (childpid < 0)
{
perror("fork() error");
exit(-1);
}
// parent process
if (childpid != 0)
{
printf("Parent Process started, now waiting for ID: %d\n", childpid);
wait(NULL);
printf("Parent Process resumeed. Child exit code 0. Now terminating\n");
exit(0);
}
// child process
if (args > 0)
{
printf("Child process has begun. %d argument/s provided\n", args);
int i;
for (i = 1; i <= argc; i++)
{
execlp(argv[i], argv[i], NULL);
}
execvp(argv[1], argv);
}
else
{
printf("No arguments provided, terminating child\n");
}
return 0;
}
Once the first child process execs (and succeeds), the for loop no longer continues because the an execlp would just replace the current process image with the command being exec'ed.
What you want to do is to loop over the command line arguments in the parent process and exec once for each of the command. Something like is probably what you're after:
for(int i = 1; i < argc; i++) {
pid_t pid = fork();
if (pid == 0) {
execlp(argv[i] ,argv[i], (char*)0);
perror("exec");
} else if (pid > 0) {
wait(NULL);
} else {
perror("fork");
exit(1);
}
}
What are you trying to achieve with the sequential calls to execlp() and execvp()? These functions are not meant to return. I think you should read the ref:
The exec() family of functions replaces the current process image with a new process image. [..] The exec() functions only return if an error has occurred.
As a result you cannot execute them one after another in the same process.
Read about fork():
fork() creates a new process by duplicating the calling process.
Moreover, here:
for(i = 1; i <= argc; i++)
you go out of bounds, since argv starts indexing from 0, and ends at argc - 1.
Chnage it to:
for(i = 1; i < argc; i++)
I want to do that 2 child processes will put their names and wait until other process put his name. For instance, if there are first and second process, first will put her name and will wait for other's name in screen. So I want to work with processes and I wanna to see they are working sequentially.
Output:
first
second
first
second
first
second
I just tried something about C(linux).
int main(void)
{
pid_t child_a, child_b;
int pipe1[2], pipe2[2];
char mesazhi1[] = "first";
char mesazhi2[] = "second";
char buf[1024];
int first_pipe = pipe(pipe1);
pipe(pipe2);
if(first_pipe == -1){
perror("pipe");
exit(1);
}
child_a = fork();
if (child_a == 0)
{
/* Child A code */
int i;
for (i = 0; i < 3; i++)
{
write(pipe1[1],mesazhi1, strlen(mesazhi1) + 1);
//printf("first\n");
int a = read(pipe2[0], buf, strlen(mesazhi2) + 1);
printf("%s - %d\n", buf, a);
}
}
else
{
child_b = fork();
if (child_b == 0)
{
int i;
for (i = 0; i < 3; i++)
{
write(pipe2[1],mesazhi2, strlen(mesazhi2) + 1);
//printf("second\n");
int a = read(pipe1[0], buf, strlen(mesazhi1) + 1);
printf("%s - %d\n", buf, a);
}
}
else
{
/* Parent Code */
int returnStatusA,returnStatusB;
waitpid(child_a, &returnStatusA, 0); // Parent process waits here for child to terminate.
waitpid(child_b, &returnStatusB, 0); // Parent process waits here for child to terminate.
if (returnStatusA == 0 && returnStatusB == 0) // Verify child process terminated without error.
{
printf("%s\n", "The child processes terminated normally.\n");
}
if (returnStatusA == 1 && returnStatusB == 1)
{
printf("%s\n", "The child processes terminated with an error!. \n" );
}
}
}
}
It is putting name randomly. I mean that I think, sometimes second process works faster than first. Output like that:
first
second
second
first
second
...
So why second process doesn't wait for first one, because I think that read() function should wait until there is something in pipe1.
In the posted code, both processes write to their respective pipes, and then read. After that, it's a race to see which process gets to print first.
For a more controlled situation, have child B call read and printf before calling write. That way B has to wait for A before printing, and vice versa.
if (child_b == 0)
{
int i;
for (i = 0; i < 3; i++)
{
int a = read(pipe1[0], buf, strlen(mesazhi1) + 1);
printf("%s - %d\n", buf, a);
write(pipe2[1],mesazhi2, strlen(mesazhi2) + 1);
}
}
I am trying to find a way to make this algorithm run concurrent and be simultaneous. So far it has only 1 for-loop that reads each file and then makes a process for each file.
I believe this algorithm runs sequentially which is not what I want...
I thought about creating an outer for-loop where I put the wait(null) and read command. But when I tried it did not work, didn't produce output. Currently I have the wait(null) command in the parent process.
Any suggestions?
Code:
int main(int argc, char *argv[])
{
// ATTRIBUTES //
int freq[argc-1], ipc[argc][2], nbytes, i;// freq of words, pipes, counters
ssize_t errorfi;
char readbuffer[9999];
char** k = malloc(50);
char** op = malloc(50);
if(argc == ONE) { // there are no files given, throw error and close
fprintf(stderr, "There are no files found from %s\n", argv[0]);
exit(0);
}
for(i = 1; i < argc; i++) // creates pipes for ipc
pipe(ipc[i]);
pid_t pids[argc-1]; // array of pids
for(i = 1; i < argc; i++) { // reads input after position 0(a.out)
pid_t pid = fork(); // creates process
pids[i-1] = pid;
if( pid < 0 ) { // bad fork process: error
perror("bad fork");
exit(0);
}
else if(pid > 0) { //parent process
close(ipc[i][1]);
wait(NULL);
nbytes = read(ipc[i][0], readbuffer, sizeof(readbuffer));
if(nbytes > 0)
printf("%s\n", readbuffer);
}
else if(pid == 0) { // child process
close(ipc[i][0]);
k = inputReader(argv[i]); // finds filename,w1,w2,w3,uniqueWords
char info[50] = "";
strcat(info, k[0]);
strcat(info, " ");
strcat(info, k[1]);
strcat(info, " ");
strcat(info, k[2]);
strcat(info, " ");
strcat(info, k[3]);
strcat(info, " ");
strcat(info, k[4]);
int uniqueWordint = atoi(k[4]);
freq[i-1] = uniqueWordint; // freq of all uniqueWords
errorfi = write(ipc[i][1], info, strlen(info)+1); // writes info to pipe i
if (errorfi < 0 ) {
fprintf(stderr, "error found when writing in pipe errofi: %d\n", errorfi);
exit(0);
}
exit(0); // close process
} // closes child process
} // closes for-loop for each process
for(j = 0; j < argc-1; j++) {
wait(2); // if i put read command here it won't work
}
return(0); // close main
}
This is pretty much a sequential execution indeed. The parent-process enters a loop, forks a child-process, and then it won't continue to the next loop until that child-process is done.
What you could do is create a pid_t array of size argc, to store each fork()'s return value.
Also create a new loop after "for-loop for each process", where the parent-process would wait for all of his children, using wait(2) or waitpid(2), depending on whether you need to process each child's result in the specific order or not, and continue processing them (reading or whatever needed.
Would this code be considered concurrent or sequential? I think it is concurrent because there a for-loop and it creates processes and for each process there a child,parent, etc... so they all run in parallel. Would this be right?
Code:
int main(int argc, char *argv[])
{
// ATTRIBUTES //
int freq[argc-1], ipc[argc][2], nbytes, i;// freq of words, pipes, counters
ssize_t errorfi;
char readbuffer[9999];
char** k = malloc(50);
char** op = malloc(50);
if(argc == ONE) { // there are no files given, throw error and close
fprintf(stderr, "There are no files found from %s\n", argv[0]);
exit(0);
}
for(i = 1; i < argc; i++) // creates pipes for ipc
pipe(ipc[i]);
for(i = 1; i < argc; i++) { // reads input after position 0(a.out)
pid_t pid = fork(); // creates process
if( pid < 0 ) { // bad fork process: error
perror("bad fork");
exit(0);
}
else if(pid > 0) { //parent process
close(ipc[i][1]);
wait(NULL);
nbytes = read(ipc[i][0], readbuffer, sizeof(readbuffer));
if(nbytes > 0)
printf("%s\n", readbuffer);
}
else if(pid == 0) { // child process
close(ipc[i][0]);
k = inputReader(argv[i]); // finds filename,w1,w2,w3,uniqueWords
char info[50];
strcat(info, k[0]);
strcat(info, " ");
strcat(info, k[1]);
strcat(info, " ");
strcat(info, k[2]);
strcat(info, " ");
strcat(info, k[3]);
strcat(info, " ");
strcat(info, k[4]);
int uniqueWordint = atoi(k[4]);
freq[i-1] = uniqueWordint; // freq of all uniqueWords
errorfi = write(ipc[i][1], info, strlen(info)+1); // writes info to pipe i
if (errorfi < 0 ) {
fprintf(stderr, "error found when writing in pipe errofi: %d\n", errorfi);
exit(0);
}
exit(0); // close process
}// closes child process
} // closes for-loop for each process
return(0); // close main
} // closes main