1 files changed, 38 insertions, 15 deletions

diff --git a/src/userprog/process.c b/src/userprog/process.c
index 45aaaa4..c0a770b 100644
--- a/src/userprog/process.c
+++ b/src/userprog/process.c
@@ -18,6 +18,11 @@
 #include "threads/thread.h"
 #include "threads/vaddr.h"
 
+struct start_process_args
+  {
+    char *file_name;
+  };
+
 static thread_func start_process NO_RETURN;
 static bool load (const char *cmdline, void (**eip) (void), void **esp);
 
@@ -28,29 +33,43 @@ static bool load (const char *cmdline, void (**eip) (void), void **esp);
 tid_t
 process_execute (const char *file_name) 
 {
-  char *fn_copy;
+  struct start_process_args args;  // stack allocated since we know we wait for thread_create to finish reading
   tid_t tid;
 
+  printf("%s starting %s\n", thread_current ()->name, file_name);
+
+  sema_init (&args.sema);
+
   /* Make a copy of FILE_NAME.
      Otherwise there's a race between the caller and load(). */
-  fn_copy = palloc_get_page (0);
-  if (fn_copy == NULL)
+  args.file_name = palloc_get_page (0);
+  if (args.file_name == NULL)
     return TID_ERROR;
-  strlcpy (fn_copy, file_name, PGSIZE);
-
-  /* Create a new thread to execute FILE_NAME. */
-  tid = thread_create (file_name, PRI_DEFAULT, start_process, fn_copy);
-  if (tid == TID_ERROR)
-    palloc_free_page (fn_copy); 
+  strlcpy (args.file_name, file_name, PGSIZE);
+
+  /* Create a new thread to execute FILE_NAME.
+     If thread_create fails we free and return immediately since we know
+     that the thread didn't start.
+     Otherwise, the child thread can be scheduled freely so we explicitly
+     wait for the child to signal that it has read the args. Only then can
+     we free resources and return the tid. */
+  tid = thread_create (file_name, PRI_DEFAULT, start_process, &args);
+  if (tid == TID_ERROR) {
+    palloc_free_page (args.file_name); 
+  } else {
+    //TODO thread created, wait to see if start_process worked
+    //     return -1 if failed
+  }
+  printf("woops\n");
   return tid;
 }
 
 /* A thread function that loads a user process and starts it
    running. */
 static void
-start_process (void *file_name_)
+start_process (void *args_)
 {
-  char *file_name = file_name_;
+  struct start_process_args *args = args_;
   struct intr_frame if_;
   bool success;
 
@@ -59,13 +78,17 @@ start_process (void *file_name_)
   if_.gs = if_.fs = if_.es = if_.ds = if_.ss = SEL_UDSEG;
   if_.cs = SEL_UCSEG;
   if_.eflags = FLAG_IF | FLAG_MBS;
-  success = load (file_name, &if_.eip, &if_.esp);
+  printf("reading\n");
+  success = load (args->file_name, &if_.eip, &if_.esp);
 
   /* If load failed, quit. */
-  palloc_free_page (file_name);
-  if (!success) 
+  palloc_free_page (args->file_name);
+  if (success) {
+    //TODO report success
+  } else {
+    //TODO report failure
     thread_exit ();
-
+  }
   /* Start the user process by simulating a return from an
      interrupt, implemented by intr_exit (in
      threads/intr-stubs.S).  Because intr_exit takes all of its