i'm trying to do a homework where i need to count the lines, words and characters of n files.
Each file in the list must be processed (counted) by a distinct process;
The hierarchical relationship between processes must be such that the i+1 process is created by the process i;
Example:
PID PPID
child1 parent1 File1 l=2 w=5 c=20
child2 child1 File2 l=3 w=6 c=30
Total: l=5 w=11 c=50
Each process sends the numbers to the parent with a pipe and the parent will sum them in 3 different variables. (totLines/totWords/totChars).
The problem is here, this 3 variables will reset to 0 in each fork() so my total will only show the last numbers sent to the pipe (Total: l=3 w=6 c=30) and i can't find a solution to this... I think the problem is on the break; of the parent, when i remove it the sum works but the program will repeat the prints 3/4 times.
Here's some of my code:
int send[3];
int get[3];
int fd[2];
for (i = 0; i < n; i++)
{
pipe(fd);
pid = fork();
if (pid < 0)
{
perror("fork");
exit(1);
}
else if (pid == 0)
{
countFile(filename, send);
printf("PID: %d - PPID: %d - %d %d %d\n", send[0], send[1], send[2]);
close(fd[0]);
write(fd[1], send, sizeof(send));
close(fd[1]);
}
if (pid != 0)
{
close(fd[1]);
read(fd[0], get, sizeof(get));
totLines += get[0];
totWords += get[1];
totChars += get[2];
close(fd[0]);
break; // <--- removing this break makes the sum work but will print
//the total and the print in the child process multiple times
}
}
int status;
for (i = 0; i < n; i++){
wait(&status);
}
if(i+1 == n){
printf("Total: %d %d %d\n", totLines, totWords, totChars);
}
Thanks for your help!
As I noted in a comment, given that the parent can only read from pipes it creates, the transfer of information from a child of a child of a child (as required by the "hierarchical relationship between processes must be such that the i+1 process is created by the process i" requirement) means that only one pipe is in use.
Further, the initial process has no sensible way of determining the PID of any process except its immediate child. Therefore, more information must be passed back from the children. The children can all use the same pipe as long as the data written per child is small enough and written in a single operation and the size can be determined. Since the parental code must print the file name, PID and PPID, it seems reasonable to pass 6 data items back to the parent:
These observations lead me to write this code — which substantially ignores what you have so far. Note that I use my preferred error reporting code, which is available in my SOQ (Stack Overflow Questions) repository on GitHub as files stderr.c and stderr.h in the src/libsoq sub-directory.
There's one sneaky twist in the code — the use of the random_children() function to generate a random number of processes so that the PID values do not (in general) increment monotonically by 1. You'd probably want to leave that out.
Note that the output format leaves the most variable bit — the file name — at the end of the line rather than embedding it in the middle. It would be feasible to find the length of the longest name and format the file name after the two PID value and before the counts — consider it an exercise for the reader.
pipe83.c/* SO 7020-7788 */
/*
** Count the lines, words and characters of n files.
**
** - Each file in the list must be processed (counted) by a distinct
** process;
** - The hierarchical relationship between processes must be such that
** the i+1 process is created by the process i;
**
** Example:
**
** PID PPID
** child1 parent1 File1 l=2 w=5 c=20
** child2 child1 File2 l=3 w=6 c=30
**
** Total: l=5 w=11 c=50
**
** Each process sends the numbers to the parent with a pipe and the
** parent will sum them in 3 different variables.
*/
#include <ctype.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include "stderr.h"
static void count_file(const char *file, int counts[3])
{
FILE *fp = fopen(file, "r");
if (fp == NULL)
err_syserr("failed to open file '%s' for reading: ", file);
int lines =0;
int words = 0;
int bytes = 0;
int in_word = 0;
int c;
while ((c = getc(fp)) != EOF)
{
bytes++;
if (c == '\n')
lines++;
if (isspace(c))
{
in_word = 0;
}
else
{
if (!in_word)
words++;
in_word = 1;
}
}
counts[0] = lines;
counts[1] = words;
counts[2] = bytes;
fclose(fp);
}
static void random_children(void)
{
srand(getpid());
int n = rand() % 10;
for (int i = 0; i < n; i++)
{
pid_t pid = fork();
if (pid < 0)
err_syserr("failed to fork: ");
if (pid == 0)
exit(EXIT_SUCCESS);
}
}
static void child_at_work(int fd, int argc, char **argv, int n)
{
int data[6] = { n, getpid(), getppid(), 0, 0, 0 };
random_children();
count_file(argv[n], &data[3]);
if (write(fd, data, sizeof(data)) != sizeof(data))
err_syserr("failed to write data to pipe: ");
if (n >= argc - 1)
exit(0);
pid_t pid = fork();
if (pid < 0)
err_syserr("failed to fork: ");
if (pid == 0)
child_at_work(fd, argc, argv, n + 1);
close(fd);
exit(EXIT_SUCCESS);
}
int main(int argc, char **argv)
{
err_setarg0(argv[0]);
if (argc < 2)
err_usage("file [...]");
int p[2];
if (pipe(p) != 0)
err_syserr("failed to create pipe: ");
pid_t pid = fork();
if (pid < 0)
err_syserr("failed to fork: ");
if (pid == 0)
{
err_setlogopts(ERR_LOG|ERR_MILLI);
close(p[0]);
child_at_work(p[1], argc, argv, 1);
err_error("function child_at_work() returned unexpectedly\n");
}
close(p[1]);
int data[6];
/*
** 0 = file number
** 1 = PID
** 2 = PPID
** 3 = lines
** 4 = words
** 5 = bytes
*/
int lines = 0;
int words = 0;
int bytes = 0;
printf("%5s %5s\n", "PID", "PPID");
while (read(p[0], data, sizeof(data)) == sizeof(data))
{
lines += data[3];
words += data[4];
bytes += data[5];
printf("%5d %5d l=%5d w=%5d c=%5d %s\n",
data[1], data[2], data[3], data[4], data[5], argv[data[0]]);
}
printf("%-14.14sl=%5d w=%5d c=%5d\n", "Total:", lines, words, bytes);
close(p[0]);
return 0;
}
Running that on the C files in my 'Stack Overflow Questions' directory yields:
$ pipe83 *.c
PID PPID
56980 56979 l= 97 w= 251 c= 2206 checkeuid.c
56981 56980 l= 17 w= 55 c= 480 ex97.c
56989 56981 l= 36 w= 119 c= 752 fgets_delim67.c
56993 56989 l= 29 w= 61 c= 532 glob61.c
56995 56993 l= 35 w= 127 c= 993 lcs47.c
57001 56995 l= 195 w= 577 c= 4784 pipe13.c
57009 57001 l= 98 w= 322 c= 2906 pipe43.c
57013 57009 l= 143 w= 447 c= 3213 pipe83.c
57015 57013 l= 12 w= 36 c= 256 pragma83.c
57021 57015 l= 23 w= 66 c= 670 pth43.c
57029 57021 l= 41 w= 115 c= 908 rd83.c
57033 57029 l= 134 w= 460 c= 3461 revdigits.c
57035 57033 l= 34 w= 101 c= 593 rot71.c
57041 57035 l= 32 w= 115 c= 1076 scan13.c
57049 57041 l= 51 w= 131 c= 1033 scan67.c
57053 57049 l= 88 w= 297 c= 2946 sigcont17.c
57055 57053 l= 65 w= 139 c= 1732 sigcont31.c
57061 57055 l= 51 w= 148 c= 1384 sigcont43.c
57069 57061 l= 101 w= 194 c= 2383 so-6886-8740-1.c
57073 57069 l= 84 w= 257 c= 1938 test-strsep.c
Total: l= 1366 w= 4018 c=34246
$ wc *.c
97 251 2206 checkeuid.c
17 55 480 ex97.c
36 119 752 fgets_delim67.c
29 61 532 glob61.c
35 127 993 lcs47.c
195 577 4784 pipe13.c
98 322 2906 pipe43.c
143 447 3213 pipe83.c
12 36 256 pragma83.c
23 66 670 pth43.c
41 115 908 rd83.c
134 460 3461 revdigits.c
34 101 593 rot71.c
32 115 1076 scan13.c
51 131 1033 scan67.c
88 297 2946 sigcont17.c
65 139 1732 sigcont31.c
51 148 1384 sigcont43.c
101 194 2383 so-6886-8740-1.c
84 257 1938 test-strsep.c
1366 4018 34246 total
$