From 83b6103986c65ad580b4b7f038660bfa01f1d087 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Gustav=20S=C3=B6rn=C3=A4s?= <gustav@sornas.net>
Date: Sun, 21 Feb 2021 19:55:30 +0100
Subject: push child to parents list of children

---
 src/threads/thread.c   |  3 +++
 src/threads/thread.h   | 24 +++++++++++++++++++++++-
 src/userprog/process.c | 24 +++++++++++++++++++-----
 3 files changed, 45 insertions(+), 6 deletions(-)

diff --git a/src/threads/thread.c b/src/threads/thread.c
index 43dd8e3..3112a71 100644
--- a/src/threads/thread.c
+++ b/src/threads/thread.c
@@ -436,6 +436,9 @@ init_thread (struct thread *t, const char *name, int priority)
   strlcpy (t->name, name, sizeof t->name);
   t->stack = (uint8_t *) t + PGSIZE;
   t->priority = priority;
+#ifdef USERPROG
+  list_init (&t->children);
+#endif
   t->magic = THREAD_MAGIC;
 }
 
diff --git a/src/threads/thread.h b/src/threads/thread.h
index e3c426d..b822b64 100644
--- a/src/threads/thread.h
+++ b/src/threads/thread.h
@@ -4,6 +4,7 @@
 #include <debug.h>
 #include <list.h>
 #include <stdint.h>
+#include "threads/synch.h"
 
 #define MAX_FDS 128  /* Max number of file descriptors per thread */
 
@@ -21,6 +22,24 @@ enum thread_status
 typedef int tid_t;
 #define TID_ERROR ((tid_t) -1)          /* Error value for tid_t. */
 
+/* The relationship between a parent and child process.
+   It is setup by the child in 
+   The child reports its exit status by setting exit_status
+   and upping exit_sema. 
+   The parent places the parent_child element in its list of children.
+*/
+struct parent_child
+  {
+    struct list_elem elem; // owned by the parent
+
+    struct semaphore exit_sema;
+
+    struct lock l;
+    int exit_status;
+    int alive_count;
+
+  };
+
 /* Thread priorities. */
 #define PRI_MIN 0                       /* Lowest priority. */
 #define PRI_DEFAULT 31                  /* Default priority. */
@@ -98,7 +117,10 @@ struct thread
 #ifdef USERPROG
     /* Owned by userprog/process.c. */
     uint32_t *pagedir;                  /* Page directory. */
-    struct file **fds;                     /* Pointer to array of file descriptors. */
+    struct file **fds;                  /* Pointer to array of file descriptors. */
+
+    struct parent_child parent; // one parent
+    struct list children; // multiple children
 #endif
 
     /* Owned by thread.c. */
diff --git a/src/userprog/process.c b/src/userprog/process.c
index 5897c84..5f7448b 100644
--- a/src/userprog/process.c
+++ b/src/userprog/process.c
@@ -28,6 +28,7 @@ struct start_process_args
 
     // child -> parent
     bool success;
+    struct list_elem *child_elem;  // list_elem to insert into list of children
   };
 
 static thread_func start_process NO_RETURN;
@@ -41,9 +42,11 @@ tid_t
 process_execute (const char *file_name) 
 {
   struct start_process_args args;  // stack allocated since we know we wait for thread_create to finish reading
+  struct thread *t;
   tid_t tid;
 
-  printf("%s starting %s\n", thread_current ()->name, file_name);
+  t = thread_current ();
+  printf("%s starting %s\n", t->name, file_name);
 
   sema_init (&args.sema, 0);
 
@@ -64,9 +67,11 @@ process_execute (const char *file_name)
   if (tid != TID_ERROR) {
     sema_down (&args.sema);
 
-    //TODO push to list of children
-    if (!args.success)
+    if (args.success) {
+      list_push_back (&t->children, args.child_elem);
+    } else {
       tid = -1;
+    }
   }
   palloc_free_page (args.file_name);
   return tid;
@@ -79,17 +84,26 @@ start_process (void *args_)
 {
   struct start_process_args *args = args_;
   struct intr_frame if_;
+  struct thread *t;
   bool success;
 
+  t = thread_current ();
+
   /* Initialize interrupt frame and load executable. */
   memset (&if_, 0, sizeof if_);
   if_.gs = if_.fs = if_.es = if_.ds = if_.ss = SEL_UDSEG;
   if_.cs = SEL_UCSEG;
   if_.eflags = FLAG_IF | FLAG_MBS;
-  printf("reading\n");
   success = load (args->file_name, &if_.eip, &if_.esp);
-
   args->success = success;
+
+  if (success) {
+    sema_init (&t->parent.exit_sema, 0);
+    lock_init (&t->parent.l);
+
+    args->child_elem = &t->parent.elem;
+  }
+
   sema_up (&args->sema);
 
   /* If load failed, quit. */
-- 
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