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commit 65edaf3b3b0ea2d26bed884549b29b9e6b01a768
Author: Martin Kloeckner <mjkloeckner@gmail.com>
Date:   Fri, 21 Aug 2026 21:31:19 -0300

Add `ejs/process_unidir_pipe.c`

Diffstat:
A
ejs/process_unidir_pipe.c
 | 
124
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

1 file changed, 124 insertions(+), 0 deletions(-)
diff --git a/ejs/process_unidir_pipe.c b/ejs/process_unidir_pipe.c
@@ -0,0 +1,124 @@
+/*
+ * Process Ping Pong
+ * Martin Klöckner - mklockner@fi.uba.ar
+ *
+ * Based on example given in wait(2) man page
+ */
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+#include <sys/wait.h>
+#include <stdint.h>
+
+#define LOG_ENABLE     true
+#define PIPE_READ_END  0
+#define PIPE_WRITE_END 1
+
+#if true == LOG_ENABLE
+#define LOG(fmt, ...) do {                                      \
+        printf("[LOG] "fmt, ##__VA_ARGS__); \
+    } while (0)
+#define LOG_ID(fmt, ...) do {                                 \
+        printf("[LOG][%ld] "fmt, proc_count, ##__VA_ARGS__); \
+    } while (0)
+#else
+#define LOG(fmt, ...)
+#define PROC_LOG(fmt, ...)
+#endif
+
+int main (void)
+{
+    int wstatus, cpid, proc_count;
+    int pipefd[2];
+    char buf;
+
+    proc_count = 0;
+
+    if (pipe(pipefd) == -1)
+    {
+        perror("pipe");
+        exit(EXIT_FAILURE);
+    }
+
+    cpid = fork();
+
+    if (cpid == -1)
+    {
+        perror("fork");
+        exit(EXIT_FAILURE);
+    }
+    else if (cpid == 0)
+    {
+        // Child
+
+        proc_count++;
+        LOG_ID("PID is %jd\n", (intmax_t) getpid());
+
+        if (close(pipefd[1]) == -1) {
+            // Close unused write end
+            perror("close");
+            exit(EXIT_FAILURE);
+        }
+
+        while (read(pipefd[0], &buf, 1) > 0) {
+            if (write(STDOUT_FILENO, &buf, 1) != 1)
+            {
+                perror("write");
+                exit(EXIT_FAILURE);
+            }
+
+            if(buf == '\n')
+            {
+                break;
+            }
+        }
+
+        exit(EXIT_SUCCESS);
+    }
+    else
+    {
+        // Parent
+
+        if (close(pipefd[0]) == -1) {
+            // Close unused read end
+            perror("close");
+            exit(EXIT_FAILURE);
+        }
+
+        LOG_ID("PID is %jd\n", (intmax_t) getpid());
+        const char *str = "Hello, World!\n\0";
+        write(pipefd[PIPE_WRITE_END], str, strlen(str));
+
+        do
+        {
+            if(waitpid(cpid, &wstatus, WUNTRACED | WCONTINUED) == -1)
+            {
+                perror("waitpid");
+                exit(EXIT_FAILURE);
+            }
+
+            if (WIFEXITED(wstatus))
+            {
+                LOG_ID("Child exited with status %d\n", WEXITSTATUS(wstatus));
+            }
+            else if (WIFSIGNALED(wstatus))
+            {
+                LOG_ID("Child killed by signal %d\n", WTERMSIG(wstatus));
+            }
+            else if (WIFSTOPPED(wstatus))
+            {
+                LOG_ID("Child stopped by signal %d\n", WSTOPSIG(wstatus));
+            }
+            else if (WIFCONTINUED(wstatus))
+            {
+                LOG_ID("Child continued\n");
+            }
+
+        } while (!WIFEXITED(wstatus) && !WIFSIGNALED(wstatus));
+        exit(EXIT_SUCCESS);
+    }
+
+    exit(EXIT_SUCCESS);
+}