From ec8547aec9f145e5ead34b9f55a78d5ff238df47 Mon Sep 17 00:00:00 2001
From: Gleb Koval <gleb@koval.net>
Date: Fri, 8 Nov 2024 03:31:48 +0000
Subject: [PATCH] Implement creation of process results

---
 src/threads/thread.c | 21 +++++++++++++++++++++
 1 file changed, 21 insertions(+)

diff --git a/src/threads/thread.c b/src/threads/thread.c
index 457f7b9..ee76718 100644
--- a/src/threads/thread.c
+++ b/src/threads/thread.c
@@ -9,6 +9,7 @@
 #include "threads/flags.h"
 #include "threads/interrupt.h"
 #include "threads/intr-stubs.h"
+#include "threads/malloc.h"
 #include "threads/palloc.h"
 #include "threads/switch.h"
 #include "threads/synch.h"
@@ -68,6 +69,7 @@ static void kernel_thread (thread_func *, void *aux);
 static void idle (void *aux UNUSED);
 static struct thread *running_thread (void);
 static struct thread *next_thread_to_run (void);
+static void init_process_result (struct thread *t);
 static void init_thread (struct thread *, const char *name, int nice,
                          int priority, fp32_t recent_cpu);
 static bool is_thread (struct thread *) UNUSED;
@@ -110,6 +112,7 @@ thread_init (void)
                initial_thread_recent_cpu);
   initial_thread->status = THREAD_RUNNING;
   initial_thread->tid = allocate_tid ();
+  initial_thread->result = NULL; /* Main thread cannot be waited for. */
 }
 
 /* Starts preemptive thread scheduling by enabling interrupts.
@@ -236,6 +239,7 @@ thread_create (const char *name, int priority,
   struct thread *parent_thread = thread_current ();
   init_thread (t, name, parent_thread->nice, priority, parent_thread->recent_cpu);
   tid = t->tid = allocate_tid ();
+  init_process_result (t);
 
   /* Prepare thread for first run by initializing its stack.
      Do this atomically so intermediate values for the 'stack' 
@@ -259,6 +263,10 @@ thread_create (const char *name, int priority,
 
   intr_set_level (old_level);
 
+  /* No need to synchronise child_results since it is only ever accessed by one
+     thread. */
+  list_insert (&parent_thread->child_results, &t->result->elem);
+
   /* Add to run queue. */
   thread_unblock (t);
 
@@ -632,6 +640,18 @@ is_thread (struct thread *t)
   return t != NULL && t->magic == THREAD_MAGIC;
 }
 
+/* Allocate and initialise a process result for given thread. */
+static void
+init_process_result (struct thread *t)
+{
+  struct process_result *result = malloc (sizeof (struct process_result));
+  result->tid = t->tid;
+  result->exit_status = t->exit_status;
+  lock_init (&result->lock);
+  sema_init (&result->sema, 0);
+  t->result = result;
+}
+
 /* Does basic initialization of T as a blocked thread named
    NAME. */
 static void
@@ -660,6 +680,7 @@ init_thread (struct thread *t, const char *name, int nice, int priority,
   t->priority = t->base_priority;
 
   t->exit_status = -1;
+  list_init (&t->child_results);
 
   old_level = intr_disable ();
   list_push_back (&all_list, &t->allelem);