From 2c58ceb889efd1483f3986827134135d6d977a4a Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Gustav=20S=C3=B6rn=C3=A4s?= <gustav@sornas.net>
Date: Fri, 12 Mar 2021 16:13:28 +0100
Subject: implement wait

---
 src/userprog/process.c | 39 +++++++++++++++++++++++++++++----------
 src/userprog/syscall.c | 12 ++++++++++--
 2 files changed, 39 insertions(+), 12 deletions(-)

(limited to 'src/userprog')

diff --git a/src/userprog/process.c b/src/userprog/process.c
index 589b48b..fadd14d 100644
--- a/src/userprog/process.c
+++ b/src/userprog/process.c
@@ -93,11 +93,12 @@ start_process (void *args_)
   if_.eflags = FLAG_IF | FLAG_MBS;
   success = load (args->file_name, &if_.eip, &if_.esp);
   args->success = success;
+  t->load_success = success;
 
   if (success) {
     t->parent = malloc (sizeof (struct parent_child));
 
-    // sema_init (&t->parent.exit_sema, 0);
+    sema_init (&t->parent->exit_sema, 0);
     lock_init (&t->parent->l);
 
     t->parent->child_tid = t->tid;
@@ -132,9 +133,22 @@ start_process (void *args_)
    This function will be implemented in problem 2-2.  For now, it
    does nothing. */
 int
-process_wait (tid_t child_tid UNUSED) 
+process_wait (tid_t child_tid)
 {
-  for (;;) {}
+  struct thread *t = thread_current ();
+  struct list_elem *e;
+  for (e = list_begin (&t->children); e != list_end (&t->children);
+       e = list_next (e))
+  {
+    struct parent_child *pc = list_entry (e, struct parent_child, elem);
+    if (child_tid == pc->child_tid) {
+      sema_down (&pc->exit_sema);
+      int exit_status = pc->exit_status;
+      pc->exit_status = -1;
+      return exit_status;
+    }
+  }
+  return -1;
 }
 
 static void
@@ -157,14 +171,18 @@ process_exit (void)
   struct thread *cur = thread_current ();
   uint32_t *pd;
 
-  free_pc (cur->parent);
+  if (cur->load_success) {
+    sema_up (&cur->parent->exit_sema);
+    free_pc (cur->parent);
+    printf("%s: exit(%d)\n", cur->name, cur->parent->exit_status);
 
-  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);
+    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
@@ -318,6 +336,7 @@ load (const char *file_name, void (**eip) (void), void **esp)
   }
 
   file_name = esp_cmd;
+  strlcpy (thread_current ()->name, file_name, 16);
 
   /* argv entries are pointers so they need to be aligned to the pointer size. */
   size_t psize = sizeof (char *);
diff --git a/src/userprog/syscall.c b/src/userprog/syscall.c
index 177cf02..52526aa 100644
--- a/src/userprog/syscall.c
+++ b/src/userprog/syscall.c
@@ -88,11 +88,15 @@ exit (int status)
   thread->parent->exit_status = status;
   lock_release (&thread->parent->l);
 
-  printf("%s: exit(%d)\n", thread->name, status);
-
   thread_exit ();
 }
 
+static int
+wait (tid_t child_tid)
+{
+  return process_wait (child_tid);
+}
+
 static int
 read (int fd_i, void *buf, unsigned size)
 {
@@ -178,6 +182,10 @@ syscall_handler (struct intr_frame *f UNUSED)
       // exec
       f->eax = exec (INTR_ESP (1, char *));
       break;
+    case 3:
+      // wait
+      f->eax = wait (INTR_ESP (1, tid_t));
+      break;
     case 4:
       // create
       f->eax = create (INTR_ESP (1, char *), INTR_ESP (2, off_t));
-- 
cgit v1.2.1