1 files changed, 111 insertions, 0 deletions
diff --git a/libthreads/rwlock.h b/libthreads/rwlock.h
new file mode 100644
index 00000000..1a61eeea
--- /dev/null
+++ b/libthreads/rwlock.h
@@ -0,0 +1,111 @@
+/* Simple reader/writer locks.
+
+   Copyright (C) 1994, 1995, 1996 Free Software Foundation, Inc.
+
+   This program is free software; you can redistribute it and/or
+   modify it under the terms of the GNU General Public License as
+   published by the Free Software Foundation; either version 2, or (at
+   your option) any later version.
+
+   This program is distributed in the hope that it will be useful, but
+   WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program; if not, write to the Free Software
+   Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA. */
+
+#ifndef _RWLOCK_H
+#define _RWLOCK_H 1
+
+#include <cthreads.h>
+#include <assert.h>
+
+struct rwlock
+{
+  struct mutex master;
+  struct condition wakeup;
+  int readers;
+  int writers_waiting;
+  int readers_waiting;
+};
+
+#ifndef RWLOCK_EI
+#define RWLOCK_EI extern inline
+#endif
+
+/* Get a reader lock on reader-writer lock LOCK for disknode DN */
+RWLOCK_EI void
+rwlock_reader_lock (struct rwlock *lock)
+{
+  mutex_lock (&lock->master);
+  if (lock->readers == -1 || lock->writers_waiting)
+    {
+      lock->readers_waiting++;
+      do
+	condition_wait (&lock->wakeup, &lock->master);
+      while (lock->readers == -1 || lock->writers_waiting);
+      lock->readers_waiting--;
+    }
+  lock->readers++;
+  mutex_unlock (&lock->master);
+}
+
+/* Get a writer lock on reader-writer lock LOCK for disknode DN */
+RWLOCK_EI void
+rwlock_writer_lock (struct rwlock *lock)
+{
+  mutex_lock (&lock->master);
+  if (lock->readers)
+    {
+      lock->writers_waiting++;
+      do
+	condition_wait (&lock->wakeup, &lock->master);
+      while (lock->readers);
+      lock->writers_waiting--;
+    }
+  lock->readers = -1;
+  mutex_unlock (&lock->master);
+}
+
+/* Release a reader lock on reader-writer lock LOCK for disknode DN */
+RWLOCK_EI void
+rwlock_reader_unlock (struct rwlock *lock)
+{
+  mutex_lock (&lock->master);
+  assert (lock->readers);
+  lock->readers--;
+  if (lock->readers_waiting || lock->writers_waiting)
+    condition_broadcast (&lock->wakeup);
+  mutex_unlock (&lock->master);
+}
+
+/* Release a writer lock on reader-writer lock LOCK for disknode DN */
+RWLOCK_EI void
+rwlock_writer_unlock (struct rwlock *lock)
+{
+  mutex_lock (&lock->master);
+  assert (lock->readers == -1);
+  lock->readers = 0;
+  if (lock->readers_waiting || lock->writers_waiting)
+    condition_broadcast (&lock->wakeup);
+  mutex_unlock (&lock->master);
+}
+
+/* Initialize reader-writer lock LOCK */
+RWLOCK_EI void
+rwlock_init (struct rwlock *lock)
+{
+  mutex_init (&lock->master);
+  condition_init (&lock->wakeup);
+  lock->readers = 0;
+  lock->readers_waiting = 0;
+  lock->writers_waiting = 0;
+}
+
+#define RWLOCK_INITIALIZER \
+  { MUTEX_INITIALIZER, CONDITION_INITIALIZER, 0, 0, 0 }
+
+
+#endif /* rwlock.h */