From be3a784665464e0a32fdf915556d8e77ada5cb7f Mon Sep 17 00:00:00 2001
From: Miles Bader <miles@gnu.org>
Date: Mon, 8 May 1995 19:21:51 +0000
Subject: Initial revision

---
 libthreads/rwlock.h | 95 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 95 insertions(+)
 create mode 100644 libthreads/rwlock.h

(limited to 'libthreads')

diff --git a/libthreads/rwlock.h b/libthreads/rwlock.h
new file mode 100644
index 00000000..8241dfff
--- /dev/null
+++ b/libthreads/rwlock.h
@@ -0,0 +1,95 @@
+/* Simple reader/writer locks.
+
+   Copyright (C) 1994, 1995 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. */
+
+struct rwlock
+{
+  struct mutex master;
+  struct condition wakeup;
+  int readers;
+  int writers_waiting;
+  int readers_waiting;
+};
+
+/* Get a reader lock on reader-writer lock LOCK for disknode DN */
+extern inline 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 */
+extern inline 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 */
+extern inline 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 */
+extern inline 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 */
+extern inline 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;
+}
-- 
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