summaryrefslogtreecommitdiff
path: root/libthreads
diff options
context:
space:
mode:
Diffstat (limited to 'libthreads')
-rw-r--r--libthreads/rwlock.h95
1 files changed, 95 insertions, 0 deletions
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;
+}