MultiThreaded Demo:

- fixing various race conditions throughout (usage of static vars, etc)
 - addition of a few lightweight mutexes (which are compiled out by default)
 - slight code rearrangement in discreteDynamicsWorld to facilitate multithreading
 - PoolAllocator::allocate() can now be called when pool is full without
     crashing (null pointer returned)
 - PoolAllocator allocate and freeMemory, are OPTIONALLY threadsafe
     (default is un-threadsafe)
 - CollisionDispatcher no longer checks if the pool allocator is full
     before calling allocate(), instead it just calls allocate() and
     checks if the return is null -- this avoids a race condition
 - SequentialImpulseConstraintSolver OPTIONALLY uses different logic in
     getOrInitSolverBody() to avoid a race condition with kinematic bodies
 - addition of 2 classes which together allow simulation islands to be run
   in parallel:
    - btSimulationIslandManagerMt
    - btDiscreteDynamicsWorldMt
 - MultiThreadedDemo example in the example browser demonstrating use of
   OpenMP, Microsoft PPL, and Intel TBB
 - use multithreading for other demos
 - benchmark demo: add parallel raycasting

examples/ExampleBrowser/ExampleEntries.cpp

@@ -8,6 +8,7 @@
 #include "../RenderingExamples/TinyRendererSetup.h"
 #include "../RenderingExamples/DynamicTexturedCubeDemo.h"
 #include "../ForkLift/ForkLiftDemo.h"
+#include "../MultiThreadedDemo/MultiThreadedDemo.h"
 #include "../BasicDemo/BasicExample.h"
 #include "../Planar2D/Planar2D.h"
 #include "../Benchmarks/BenchmarkDemo.h"
@@ -284,7 +285,13 @@ static ExampleEntry gDefaultExamples[]=
 	ExampleEntry(1,"Fracture demo", "Create a basic custom implementation to model fracturing objects, based on a btCompoundShape. It explicitly propagates the collision impulses and breaks the rigid body into multiple rigid bodies. Press F to toggle fracture and glue mode.", FractureDemoCreateFunc),
 
 	ExampleEntry(1,"Planar 2D","Show the use of 2D collision shapes and rigid body simulation. The collision shape is wrapped into a btConvex2dShape. The rigid bodies are restricted in a plane using the 'setAngularFactor' and 'setLinearFactor' API call.",Planar2DCreateFunc),
-
+#if BT_USE_OPENMP || BT_USE_TBB || BT_USE_PPL
+    // only enable MultiThreaded demo if a task scheduler is available
+    ExampleEntry( 1, "Multithreaded Demo",
+    "Stacks of boxes that do not sleep. Good for testing performance with large numbers of bodies and contacts. Sliders can be used to change the number of stacks (restart needed after each change)."
+    ,
+    MultiThreadedDemoCreateFunc ),
+#endif
 
 
 	ExampleEntry(0,"Rendering"),