From: Simon McVittie <simon.mcvittie@collabora.co.uk>
Date: Mon, 13 Aug 2012 17:00:23 +0000 (+0100)
Subject: Use InterlockedExchange to get a full memory barrier on Windows
X-Git-Tag: dbus-1.7.0~34
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=1e494ecc6094d412c3ae4ce25f51946b9278f3dd;p=thirdparty%2Fdbus.git

Use InterlockedExchange to get a full memory barrier on Windows

See the bug for extensive discussion.

Bug: https://bugs.freedesktop.org/show_bug.cgi?id=41423
Reviewed-by: Ralf Habacker <ralf.habacker@freenet.de>
---

diff --git a/dbus/dbus-sysdeps-win.c b/dbus/dbus-sysdeps-win.c
index bc4951b5c..5a2fb209f 100644
--- a/dbus/dbus-sysdeps-win.c
+++ b/dbus/dbus-sysdeps-win.c
@@ -3121,8 +3121,18 @@ _dbus_atomic_dec (DBusAtomic *atomic)
 dbus_int32_t
 _dbus_atomic_get (DBusAtomic *atomic)
 {
-  /* this is what GLib does, hopefully it's right... */
-  MemoryBarrier ();
+  /* In this situation, GLib issues a MemoryBarrier() and then returns
+   * atomic->value. However, mingw from mingw.org (not to be confused with
+   * mingw-w64 from mingw-w64.sf.net) does not have MemoryBarrier in its
+   * headers, so we have to get a memory barrier some other way.
+   *
+   * InterlockedIncrement is older, and is documented on MSDN to be a full
+   * memory barrier, so let's use that.
+   */
+  long dummy = 0;
+
+  InterlockedExchange (&dummy, 1);
+
   return atomic->value;
 }