add assertunlocked() call

src/stasis/rw.c

@@ -39,7 +39,9 @@ rwl *initlock (void)
 void assertlocked(rwl * lock) {
   assert(lock->writers || lock->readers);
 }
-
+void assertunlocked(rwl * lock) {
+  assert(!(lock->writers || lock->readers));
+}
 void readlock (rwl *lock, int d)
 {
   /*  printf("reader %d\n", d);

stasis/rw.h

@@ -48,6 +48,8 @@ void writelock (rwl *lock, int d);
 int trywritelock(rwl *lock, int d);
 /** aborts if called when no thread holds this latch. */
 void assertlocked(rwl *lock);
+/** aborts if called when a thread holds this latch. */
+void assertunlocked(rwl *lock);
 void downgradelock(rwl * lock);
 void unlock(rwl * lock);
 /** @deprecated in favor of unlock() */