4 files changed, 87 insertions, 0 deletions
diff --git a/src/threads/synch.c b/src/threads/synch.c
index 317c68a..e714ce0 100644
--- a/src/threads/synch.c
+++ b/src/threads/synch.c
@@ -336,3 +336,43 @@ cond_broadcast (struct condition *cond, struct lock *lock)
   while (!list_empty (&cond->waiters))
     cond_signal (cond, lock);
 }
+
+void
+rwlock_init (struct rwlock *rwlock)
+{
+  sema_init (&rwlock->resource, 1);
+  lock_init (&rwlock->rmutex);
+  rwlock->readcount = 0;
+}
+
+void
+rwlock_write_p (struct rwlock *rwlock)
+{
+  sema_down (&rwlock->resource);
+}
+
+void
+rwlock_write_v (struct rwlock *rwlock)
+{
+  sema_up (&rwlock->resource);
+}
+
+void
+rwlock_read_p (struct rwlock *rwlock)
+{
+  lock_acquire (&rwlock->rmutex);
+  rwlock->readcount ++;
+  if (rwlock->readcount == 1)
+    sema_down (&rwlock->resource);
+  lock_release (&rwlock->rmutex);
+}
+
+void
+rwlock_read_v (struct rwlock *rwlock)
+{
+  lock_acquire (&rwlock->rmutex);
+  rwlock->readcount --;
+  if (rwlock->readcount == 0)
+    sema_up (&rwlock->resource);
+  lock_release (&rwlock->rmutex);
+}
diff --git a/src/threads/synch.h b/src/threads/synch.h
index a19e88b..a76eecc 100644
--- a/src/threads/synch.h
+++ b/src/threads/synch.h
@@ -41,6 +41,23 @@ void cond_wait (struct condition *, struct lock *);
 void cond_signal (struct condition *, struct lock *);
 void cond_broadcast (struct condition *, struct lock *);
 
+/* Readers-writers lock.
+
+   Implementation of "First readers-writers problem" from
+   https://en.wikipedia.org/wiki/Readers%E2%80%93writers_problem. */
+struct rwlock
+  {
+    struct semaphore resource;
+    struct lock rmutex;
+    unsigned readcount;
+  };
+
+void rwlock_init (struct rwlock *);
+void rwlock_write_p (struct rwlock *);
+void rwlock_write_v (struct rwlock *);
+void rwlock_read_p (struct rwlock *);
+void rwlock_read_v (struct rwlock *);
+
 /* Optimization barrier.
 
    The compiler will not reorder operations across an
diff --git a/src/threads/thread.c b/src/threads/thread.c
index 92d1aa8..3112a71 100644
--- a/src/threads/thread.c
+++ b/src/threads/thread.c
@@ -13,6 +13,7 @@
 #include "threads/vaddr.h"
 #ifdef USERPROG
 #include "userprog/process.h"
+#include "threads/malloc.h"
 #endif
 
 /* Random value for struct thread's `magic' member.
@@ -435,6 +436,9 @@ init_thread (struct thread *t, const char *name, int priority)
   strlcpy (t->name, name, sizeof t->name);
   t->stack = (uint8_t *) t + PGSIZE;
   t->priority = priority;
+#ifdef USERPROG
+  list_init (&t->children);
+#endif
   t->magic = THREAD_MAGIC;
 }
 
diff --git a/src/threads/thread.h b/src/threads/thread.h
index 0039560..a3bc814 100644
--- a/src/threads/thread.h
+++ b/src/threads/thread.h
@@ -4,6 +4,9 @@
 #include <debug.h>
 #include <list.h>
 #include <stdint.h>
+#include "threads/synch.h"
+
+#define MAX_FDS 128  /* Max number of file descriptors per thread */
 
 /* States in a thread's life cycle. */
 enum thread_status
@@ -19,6 +22,23 @@ enum thread_status
 typedef int tid_t;
 #define TID_ERROR ((tid_t) -1)          /* Error value for tid_t. */
 
+/* The relationship between a parent and child process.
+   The child reports its exit status by setting exit_status.
+   The parent places the parent_child element in its list of children.
+*/
+struct parent_child
+  {
+    struct list_elem elem; // owned by the parent
+
+    // exit_status is readable by the parent
+    struct semaphore exit_sema;
+    int exit_status;
+
+    struct lock l;
+    int alive_count;
+    tid_t child_tid;
+  };
+
 /* Thread priorities. */
 #define PRI_MIN 0                       /* Lowest priority. */
 #define PRI_DEFAULT 31                  /* Default priority. */
@@ -80,6 +100,7 @@ typedef int tid_t;
    only because they are mutually exclusive: only a thread in the
    ready state is on the run queue, whereas only a thread in the
    blocked state is on a semaphore wait list. */
+
 struct thread
   {
     /* Owned by thread.c. */
@@ -95,6 +116,11 @@ struct thread
 #ifdef USERPROG
     /* Owned by userprog/process.c. */
     uint32_t *pagedir;                  /* Page directory. */
+    struct file **fds;                  /* Pointer to array of file descriptors. */
+    bool load_success;
+
+    struct parent_child *parent; // one parent
+    struct list children; // multiple children
 #endif
 
     /* Owned by thread.c. */