From d33fe03b2fd2ba0fd559c52a1598593238767bbc 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 21:18:13 +0100
Subject: free parent_child when possible

---
 src/userprog/process.c | 41 +++++++++++++++++++++++++++++++++--------
 src/userprog/syscall.c | 10 +++++++++-
 2 files changed, 42 insertions(+), 9 deletions(-)

(limited to 'src/userprog')

diff --git a/src/userprog/process.c b/src/userprog/process.c
index e99374b..39f063b 100644
--- a/src/userprog/process.c
+++ b/src/userprog/process.c
@@ -14,6 +14,7 @@
 #include "threads/flags.h"
 #include "threads/init.h"
 #include "threads/interrupt.h"
+#include "threads/malloc.h"
 #include "threads/palloc.h"
 #include "threads/synch.h"
 #include "threads/thread.h"
@@ -42,12 +43,8 @@ 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;
 
-  t = thread_current ();
-  printf("%s starting %s\n", t->name, file_name);
-
   sema_init (&args.sema, 0);
 
   /* Make a copy of FILE_NAME.
@@ -68,7 +65,7 @@ process_execute (const char *file_name)
     sema_down (&args.sema);
 
     if (args.success) {
-      list_push_back (&t->children, &args.child->elem);
+      list_push_back (&thread_current ()->children, &args.child->elem);
     } else {
       tid = -1;
     }
@@ -98,10 +95,15 @@ start_process (void *args_)
   args->success = success;
 
   if (success) {
-    sema_init (&t->parent.exit_sema, 0);
-    lock_init (&t->parent.l);
+    t->parent = malloc (sizeof (struct parent_child));
+
+    // sema_init (&t->parent.exit_sema, 0);
+    lock_init (&t->parent->l);
 
-    args->child = &t->parent;
+    t->parent->child_tid = t->tid;
+    t->parent->alive_count = 2;
+
+    args->child = t->parent;
   }
 
   sema_up (&args->sema);
@@ -135,6 +137,19 @@ process_wait (tid_t child_tid UNUSED)
   for (;;) {}
 }
 
+static void
+free_pc (struct parent_child *pc)
+{
+  lock_acquire (&pc->l);
+
+  pc->alive_count--;
+  if (pc->alive_count == 0) {
+    free (pc);
+  } else {
+    lock_release (&pc->l);
+  }
+}
+
 /* Free the current process's resources. */
 void
 process_exit (void)
@@ -142,6 +157,16 @@ process_exit (void)
   struct thread *cur = thread_current ();
   uint32_t *pd;
 
+  free_pc (cur->parent);
+
+  struct list_elem *e;
+  struct parent_child *child;
+  while (!list_empty (&cur->children)) {
+    e = list_pop_front (&cur->children);
+    child = list_entry (e, struct parent_child, elem);
+    free_pc (child);
+  }
+
   /* Destroy the current process's page directory and switch back
      to the kernel-only page directory. */
   pd = cur->pagedir;
diff --git a/src/userprog/syscall.c b/src/userprog/syscall.c
index 0df46f4..177cf02 100644
--- a/src/userprog/syscall.c
+++ b/src/userprog/syscall.c
@@ -69,7 +69,7 @@ get_fd (struct thread *thread, int fd_i)
 }
 
 static void
-exit (int status UNUSED)
+exit (int status)
 {
   struct thread *thread = thread_current ();
 
@@ -83,6 +83,14 @@ exit (int status UNUSED)
     }
     free (thread->fds);
   }
+
+  lock_acquire (&thread->parent->l);
+  thread->parent->exit_status = status;
+  lock_release (&thread->parent->l);
+
+  printf("%s: exit(%d)\n", thread->name, status);
+
+  thread_exit ();
 }
 
 static int
-- 
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