From 4207f9c279e832e3afcb3f5fc6cd8d84cb4cfe4c Mon Sep 17 00:00:00 2001
From: Sven Gothel <sgothel@jausoft.com>
Date: Sat, 28 Mar 2015 01:43:35 +0100
Subject: Bump OculusVR RIFT SDK to 0.5.0.1
---
LibOVRKernel/Src/Kernel/OVR_Lockless.h | 117 +++++++++++++++++++++++++++++++++
1 file changed, 117 insertions(+)
create mode 100644 LibOVRKernel/Src/Kernel/OVR_Lockless.h
(limited to 'LibOVRKernel/Src/Kernel/OVR_Lockless.h')
diff --git a/LibOVRKernel/Src/Kernel/OVR_Lockless.h b/LibOVRKernel/Src/Kernel/OVR_Lockless.h
new file mode 100644
index 0000000..f9043a9
--- /dev/null
+++ b/LibOVRKernel/Src/Kernel/OVR_Lockless.h
@@ -0,0 +1,117 @@
+/************************************************************************************
+
+PublicHeader: OVR_Kernel.h
+Filename : OVR_Lockless.h
+Content : Lock-less classes for producer/consumer communication
+Created : November 9, 2013
+Authors : John Carmack
+
+Copyright : Copyright 2014 Oculus VR, LLC All Rights reserved.
+
+Licensed under the Oculus VR Rift SDK License Version 3.2 (the "License");
+you may not use the Oculus VR Rift SDK except in compliance with the License,
+which is provided at the time of installation or download, or which
+otherwise accompanies this software in either electronic or hard copy form.
+
+You may obtain a copy of the License at
+
+http://www.oculusvr.com/licenses/LICENSE-3.2
+
+Unless required by applicable law or agreed to in writing, the Oculus VR SDK
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+
+*************************************************************************************/
+
+#ifndef OVR_Lockless_h
+#define OVR_Lockless_h
+
+#include "OVR_Atomic.h"
+
+// Define this to compile-in Lockless test logic
+//#define OVR_LOCKLESS_TEST
+
+namespace OVR {
+
+
+// ***** LocklessUpdater
+
+// For single producer cases where you only care about the most recent update, not
+// necessarily getting every one that happens (vsync timing, SensorFusion updates).
+//
+// This is multiple consumer safe, but is currently only used with a single consumer.
+//
+// The SlotType can be the same as T, but should probably be a larger fixed size.
+// This allows for forward compatibility when the updater is shared between processes.
+
+// FIXME: ExchangeAdd_Sync() should be replaced with a portable read-only primitive,
+// so that the lockless pose state can be read-only on remote processes and to reduce
+// false sharing between processes and improve performance.
+
+template<class T, class SlotType = T>
+class LocklessUpdater
+{
+public:
+ LocklessUpdater() : UpdateBegin( 0 ), UpdateEnd( 0 )
+ {
+ OVR_COMPILER_ASSERT(sizeof(T) <= sizeof(SlotType));
+ }
+
+ T GetState() const
+ {
+ // Copy the state out, then retry with the alternate slot
+ // if we determine that our copy may have been partially
+ // stepped on by a new update.
+ T state;
+ int begin, end, final;
+
+ for(;;)
+ {
+ // We are adding 0, only using these as atomic memory barriers, so it
+ // is ok to cast off the const, allowing GetState() to remain const.
+ end = UpdateEnd.Load_Acquire();
+ state = Slots[ end & 1 ];
+ begin = UpdateBegin.Load_Acquire();
+ if ( begin == end ) {
+ break;
+ }
+
+ // The producer is potentially blocked while only having partially
+ // written the update, so copy out the other slot.
+ state = Slots[ (begin & 1) ^ 1 ];
+ final = UpdateBegin.Load_Acquire();
+ if ( final == begin ) {
+ break;
+ }
+
+ // The producer completed the last update and started a new one before
+ // we got it copied out, so try fetching the current buffer again.
+ }
+ return state;
+ }
+
+ void SetState( const T& state )
+ {
+ const int slot = UpdateBegin.ExchangeAdd_Sync(1) & 1;
+ // Write to (slot ^ 1) because ExchangeAdd returns 'previous' value before add.
+ Slots[slot ^ 1] = state;
+ UpdateEnd.ExchangeAdd_Sync(1);
+ }
+
+ AtomicInt<int> UpdateBegin;
+ AtomicInt<int> UpdateEnd;
+ SlotType Slots[2];
+};
+
+
+#ifdef OVR_LOCKLESS_TEST
+void StartLocklessTest();
+#endif
+
+
+} // namespace OVR
+
+#endif // OVR_Lockless_h
+
--
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