Added SpinLock class.

Engine/Core/SpinLock.h

@@ -0,0 +1,77 @@
+//
+// Urho3D Engine
+// Copyright (c) 2008-2011 Lasse Öörni
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in
+// all copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+// THE SOFTWARE.
+//
+
+#pragma once
+
+/// Non-reentrant userspace mutual exclusion primitive.
+class SpinLock
+{
+public:
+    /// Construct.
+    SpinLock() :
+        locked_(0)
+    {
+    }
+    
+    /// Acquire the lock. Spin in a loop while waiting.
+    void Acquire()
+    {
+        for (;;)
+        {
+            if (TestAndSet(&locked_, 1) == 0)
+                break;
+        }
+    }
+    
+    /// Try to acquire the lock without waiting. Return true if successfully acquired.
+    bool TryAcquire()
+    {
+        return TestAndSet(&locked_, 1) == 0;
+    }
+    
+    /// Release the lock.
+    void Release()
+    {
+        TestAndSet(&locked_, 0);
+    }
+    
+private:
+    /// Test-and-set a value atomically and return the previous value.
+    static unsigned TestAndSet(unsigned* dest, unsigned newValue)
+    {
+        #ifdef _MSC_VER
+        __asm
+        {
+            mov edx, dest
+            mov eax, newValue
+            lock xchg eax, dword ptr [edx]
+        }
+        #else
+        return __sync_lock_test_and_set(ptr, newValue);
+        #endif
+    }
+    
+    /// Locked flag.
+    unsigned locked_;
+};
+