From 42191da2512b6f48f7ccd7765a416a7bc9aeeca6 Mon Sep 17 00:00:00 2001
From: scratko <m@scratko.xyz>
Date: Sat, 8 Jun 2024 01:44:31 +0300
Subject: Pipe

Added unidirectional data channel for process communication (pipe).
---
 parallel_progs_by_args.c | 28 ++++++++++++++++++++++------
 1 file changed, 22 insertions(+), 6 deletions(-)

diff --git a/parallel_progs_by_args.c b/parallel_progs_by_args.c
index 97505ab..71d09b2 100644
--- a/parallel_progs_by_args.c
+++ b/parallel_progs_by_args.c
@@ -24,9 +24,10 @@ static void fill_in_item(char *arg, int pid, struct item **list)
     *list = tmp_item;
 }
 
-static void make_new_fork(char **begin_pos, struct item **list,
+static void make_new_fork(int fd[2], char **begin_pos, struct item **list,
                           int *process_counter)
 {
+    static int first_process_flag = 0;
     int pid = fork();
     if(pid == -1) {
         perror("fork error");
@@ -35,12 +36,23 @@ static void make_new_fork(char **begin_pos, struct item **list,
     if(pid) {
         fill_in_item(*begin_pos, pid, list);
         ++*process_counter;
-    }
-    else {
+    } else {
+        /* first process writes to pipeline */
+        if(first_process_flag == 0) {
+            close(fd[0]);
+            dup2(fd[1], 1);
+            close(fd[1]);
+        /* second process reads */
+        } else {
+            close(fd[1]);
+            dup2(fd[0], 0);
+            close(fd[0]);
+        }
         execvp(*begin_pos, begin_pos);
         perror(*begin_pos);
         exit(1);
     }
+    ++first_process_flag;
 }
 
 static char* find_name_by_pid(int pid, struct item *list)
@@ -65,10 +77,12 @@ static void clear_list(struct item *list)
 
 int main(int argc, char **argv)
 {
+    int fd[2];
     int status, pid, process_counter;
+    char **begin_pos, **end_pos;
     struct item *list = NULL;
     process_counter = 0;
-    char **begin_pos, **end_pos;
+    pipe(fd);
     if(argc == 1) {
         fprintf(stderr, "too few arguments\n");
         return 1;
@@ -77,13 +91,15 @@ int main(int argc, char **argv)
     for(begin_pos = argv, end_pos = begin_pos + 1; *end_pos != NULL; ) {
         if(check_delimiter(*end_pos)) {
             *end_pos = NULL;
-            make_new_fork(begin_pos, &list, &process_counter);
+            make_new_fork(fd, begin_pos, &list, &process_counter);
             begin_pos = end_pos + 1;
             end_pos = begin_pos + 1;
         } else
             ++end_pos;
     }
-    make_new_fork(begin_pos, &list, &process_counter);
+    make_new_fork(fd, begin_pos, &list, &process_counter);
+    close(fd[0]);
+    close(fd[1]);
     for( ; process_counter; --process_counter) {
         pid = wait(&status);
         if(WIFEXITED(status) && WEXITSTATUS(status) == 0)
-- 
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