Add helper functions to initialise the memory-mapped files table and counter

src/threads/thread.c

@@ -16,6 +16,7 @@
 #include "threads/synch.h"
 #include "threads/vaddr.h"
 #include "vm/page.h"
+#include "vm/mmap.h"
 #ifdef USERPROG
 #include "userprog/process.h"
 #include "userprog/syscall.h"
@@ -274,6 +275,8 @@ thread_create (const char *name, int priority,
     }
 #endif
 
+  mmap_init ();
+
   /* Prepare thread for first run by initializing its stack.
      Do this atomically so intermediate values for the 'stack' 
      member cannot be observed. */