From 291996a60567617f17aeb5e96159290b1ba22340 Mon Sep 17 00:00:00 2001
From: "Neal H. Walfield" <neal@gnu.org>
Date: Thu, 10 Oct 2002 23:05:06 +0000
Subject: Import libpthread.

---
 sysdeps/generic/pt-rwlock-unlock.c | 90 ++++++++++++++++++++++++++++++++++++++
 1 file changed, 90 insertions(+)
 create mode 100644 sysdeps/generic/pt-rwlock-unlock.c

(limited to 'sysdeps/generic/pt-rwlock-unlock.c')

diff --git a/sysdeps/generic/pt-rwlock-unlock.c b/sysdeps/generic/pt-rwlock-unlock.c
new file mode 100644
index 00000000..fb23a0b9
--- /dev/null
+++ b/sysdeps/generic/pt-rwlock-unlock.c
@@ -0,0 +1,90 @@
+/* Unlock a rwlock.  Generic version.
+   Copyright (C) 2000,02 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Library General Public License as
+   published by the Free Software Foundation; either version 2 of the
+   License, or (at your option) any later version.
+
+   The GNU C Library 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
+   Library General Public License for more details.
+
+   You should have received a copy of the GNU Library General Public
+   License along with the GNU C Library; see the file COPYING.LIB.  If not,
+   write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
+   Boston, MA 02111-1307, USA.  */
+
+#include <pthread.h>
+
+#include <pt-internal.h>
+
+/* Unlock *RWLOCK, rescheduling a waiting writer thread or, if there
+   are no threads waiting for a write lock, rescheduling the reader
+   threads.  */
+int
+pthread_rwlock_unlock (pthread_rwlock_t *rwlock)
+{
+  struct __pthread *wakeup;
+  
+  __pthread_spin_lock (&rwlock->__lock);
+
+  assert (__pthread_spin_trylock (&rwlock->__held) == EBUSY);
+
+  if (rwlock->readers > 1)
+    /* There are other readers.  */
+    {
+      rwlock->readers --;
+      __pthread_spin_unlock (&rwlock->__lock);
+      return 0;
+    }
+
+  if (rwlock->readers == 1)
+    /* Last reader.  */
+    rwlock->readers = 0;
+      
+
+  /* Wake someone else up.  Try the writer queue first, then the
+     reader queue if that is empty.  */
+
+  if (rwlock->writerqueue)
+    {
+      wakeup = rwlock->writerqueue;
+      __pthread_dequeue (wakeup);
+
+      /* We do not unlock RWLOCK->held: we are transferring the ownership
+	 to the thread that we are waking up.  */
+
+      __pthread_spin_unlock (&rwlock->__lock);
+      __pthread_wakeup (wakeup);
+
+      return 0;
+    }
+
+  if (rwlock->readerqueue)
+    {
+      __pthread_queue_iterate (rwlock->readerqueue, wakeup)
+	rwlock->readers ++;
+
+      wakeup = rwlock->readerqueue;
+      rwlock->readerqueue = 0;
+
+      __pthread_spin_unlock (&rwlock->__lock);
+
+      /* We can safely walk the list of waiting threads without holding
+	 the lock since it is now decoupled from the rwlock.  */
+      __pthread_dequeuing_iterate (wakeup, wakeup)
+	__pthread_wakeup (wakeup);
+
+      return 0;
+    }
+
+
+  /* Noone is waiting.  Just unlock it.  */
+
+  __pthread_spin_unlock (&rwlock->__held);
+  __pthread_spin_unlock (&rwlock->__lock);
+  return 0;
+}
-- 
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