From a416ab17ecf9f2cb0f1e3f7bd645a8d1ce690ca2 Mon Sep 17 00:00:00 2001
From: rpj <rpj>
Date: Mon, 18 Feb 2002 03:16:52 +0000
Subject: Major reorganisation of source code; new routine and tests added.

---
 ptw32_rwlock_check_need_init.c | 93 ++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 93 insertions(+)
 create mode 100644 ptw32_rwlock_check_need_init.c

(limited to 'ptw32_rwlock_check_need_init.c')

diff --git a/ptw32_rwlock_check_need_init.c b/ptw32_rwlock_check_need_init.c
new file mode 100644
index 0000000..626cf23
--- /dev/null
+++ b/ptw32_rwlock_check_need_init.c
@@ -0,0 +1,93 @@
+/*
+ * pthread_rwlock_check_need_init.c
+ *
+ * Description:
+ * This translation unit implements read/write lock primitives.
+ *
+ * --------------------------------------------------------------------------
+ *
+ *      Pthreads-win32 - POSIX Threads Library for Win32
+ *      Copyright(C) 1998 John E. Bossom
+ *      Copyright(C) 1999,2002 Pthreads-win32 contributors
+ * 
+ *      Contact Email: rpj@ise.canberra.edu.au
+ * 
+ *      The current list of contributors is contained
+ *      in the file CONTRIBUTORS included with the source
+ *      code distribution. The list can also be seen at the
+ *      following World Wide Web location:
+ *      http://sources.redhat.com/pthreads-win32/contributors.html
+ * 
+ *      This library is free software; you can redistribute it and/or
+ *      modify it under the terms of the GNU Lesser General Public
+ *      License as published by the Free Software Foundation; either
+ *      version 2 of the License, or (at your option) any later version.
+ * 
+ *      This 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
+ *      Lesser General Public License for more details.
+ * 
+ *      You should have received a copy of the GNU Lesser General Public
+ *      License along with this library in 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 "implement.h"
+
+INLINE int
+ptw32_rwlock_check_need_init(pthread_rwlock_t *rwlock)
+{
+  int result = 0;
+
+  /*
+   * The following guarded test is specifically for statically
+   * initialised rwlocks (via PTHREAD_RWLOCK_INITIALIZER).
+   *
+   * Note that by not providing this synchronisation we risk
+   * introducing race conditions into applications which are
+   * correctly written.
+   *
+   * Approach
+   * --------
+   * We know that static rwlocks will not be PROCESS_SHARED
+   * so we can serialise access to internal state using
+   * Win32 Critical Sections rather than Win32 Mutexes.
+   *
+   * If using a single global lock slows applications down too much,
+   * multiple global locks could be created and hashed on some random
+   * value associated with each mutex, the pointer perhaps. At a guess,
+   * a good value for the optimal number of global locks might be
+   * the number of processors + 1.
+   *
+   */
+  EnterCriticalSection(&ptw32_rwlock_test_init_lock);
+
+  /*
+   * We got here possibly under race
+   * conditions. Check again inside the critical section
+   * and only initialise if the rwlock is valid (not been destroyed).
+   * If a static rwlock has been destroyed, the application can
+   * re-initialise it only by calling pthread_rwlock_init()
+   * explicitly.
+   */
+  if (*rwlock == PTHREAD_RWLOCK_INITIALIZER)
+    {
+      result = pthread_rwlock_init(rwlock, NULL);
+    }
+  else if (*rwlock == NULL)
+    {
+      /*
+       * The rwlock has been destroyed while we were waiting to
+       * initialise it, so the operation that caused the
+       * auto-initialisation should fail.
+       */
+      result = EINVAL;
+    }
+
+  LeaveCriticalSection(&ptw32_rwlock_test_init_lock);
+
+  return result;
+}
-- 
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