add rwlock implementation

1 files changed, 17 insertions, 0 deletions

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