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+/*
+Bullet Continuous Collision Detection and Physics Library
+Copyright (c) 2003-2009 Erwin Coumans  http://bulletphysics.org
+
+This software is provided 'as-is', without any express or implied warranty.
+In no event will the authors be held liable for any damages arising from the use of this software.
+Permission is granted to anyone to use this software for any purpose, 
+including commercial applications, and to alter it and redistribute it freely, 
+subject to the following restrictions:
+
+1. The origin of this software must not be misrepresented; you must not claim that you wrote the original software. If you use this software in a product, an acknowledgment in the product documentation would be appreciated but is not required.
+2. Altered source versions must be plainly marked as such, and must not be misrepresented as being the original software.
+3. This notice may not be removed or altered from any source distribution.
+*/
+
+#ifndef BT_DISCRETE_DYNAMICS_WORLD_MT_H
+#define BT_DISCRETE_DYNAMICS_WORLD_MT_H
+
+#include "btDiscreteDynamicsWorld.h"
+#include "btSimulationIslandManagerMt.h"
+#include "BulletDynamics/ConstraintSolver/btConstraintSolver.h"
+
+///
+/// btConstraintSolverPoolMt - masquerades as a constraint solver, but really it is a threadsafe pool of them.
+///
+///  Each solver in the pool is protected by a mutex.  When solveGroup is called from a thread,
+///  the pool looks for a solver that isn't being used by another thread, locks it, and dispatches the
+///  call to the solver.
+///  So long as there are at least as many solvers as there are hardware threads, it should never need to
+///  spin wait.
+///
+class btConstraintSolverPoolMt : public btConstraintSolver
+{
+public:
+	// create the solvers for me
+	explicit btConstraintSolverPoolMt(int numSolvers);
+
+	// pass in fully constructed solvers (destructor will delete them)
+	btConstraintSolverPoolMt(btConstraintSolver** solvers, int numSolvers);
+
+	virtual ~btConstraintSolverPoolMt();
+
+	///solve a group of constraints
+	virtual btScalar solveGroup(btCollisionObject** bodies,
+								int numBodies,
+								btPersistentManifold** manifolds,
+								int numManifolds,
+								btTypedConstraint** constraints,
+								int numConstraints,
+								const btContactSolverInfo& info,
+								btIDebugDraw* debugDrawer,
+								btDispatcher* dispatcher) BT_OVERRIDE;
+
+	virtual void reset() BT_OVERRIDE;
+	virtual btConstraintSolverType getSolverType() const BT_OVERRIDE { return m_solverType; }
+
+private:
+	const static size_t kCacheLineSize = 128;
+	struct ThreadSolver
+	{
+		btConstraintSolver* solver;
+		btSpinMutex mutex;
+		char _cachelinePadding[kCacheLineSize - sizeof(btSpinMutex) - sizeof(void*)];  // keep mutexes from sharing a cache line
+	};
+	btAlignedObjectArray<ThreadSolver> m_solvers;
+	btConstraintSolverType m_solverType;
+
+	ThreadSolver* getAndLockThreadSolver();
+	void init(btConstraintSolver** solvers, int numSolvers);
+};
+
+///
+/// btDiscreteDynamicsWorldMt -- a version of DiscreteDynamicsWorld with some minor changes to support
+///                              solving simulation islands on multiple threads.
+///
+///  Should function exactly like btDiscreteDynamicsWorld.
+///  Also 3 methods that iterate over all of the rigidbodies can run in parallel:
+///     - predictUnconstraintMotion
+///     - integrateTransforms
+///     - createPredictiveContacts
+///
+ATTRIBUTE_ALIGNED16(class)
+btDiscreteDynamicsWorldMt : public btDiscreteDynamicsWorld
+{
+protected:
+	btConstraintSolver* m_constraintSolverMt;
+
+	virtual void solveConstraints(btContactSolverInfo & solverInfo) BT_OVERRIDE;
+
+	virtual void predictUnconstraintMotion(btScalar timeStep) BT_OVERRIDE;
+
+	struct UpdaterCreatePredictiveContacts : public btIParallelForBody
+	{
+		btScalar timeStep;
+		btRigidBody** rigidBodies;
+		btDiscreteDynamicsWorldMt* world;
+
+		void forLoop(int iBegin, int iEnd) const BT_OVERRIDE
+		{
+			world->createPredictiveContactsInternal(&rigidBodies[iBegin], iEnd - iBegin, timeStep);
+		}
+	};
+	virtual void createPredictiveContacts(btScalar timeStep) BT_OVERRIDE;
+
+	struct UpdaterIntegrateTransforms : public btIParallelForBody
+	{
+		btScalar timeStep;
+		btRigidBody** rigidBodies;
+		btDiscreteDynamicsWorldMt* world;
+
+		void forLoop(int iBegin, int iEnd) const BT_OVERRIDE
+		{
+			world->integrateTransformsInternal(&rigidBodies[iBegin], iEnd - iBegin, timeStep);
+		}
+	};
+	virtual void integrateTransforms(btScalar timeStep) BT_OVERRIDE;
+
+public:
+	BT_DECLARE_ALIGNED_ALLOCATOR();
+
+	btDiscreteDynamicsWorldMt(btDispatcher * dispatcher,
+							  btBroadphaseInterface * pairCache,
+							  btConstraintSolverPoolMt * solverPool,        // Note this should be a solver-pool for multi-threading
+							  btConstraintSolver * constraintSolverMt,      // single multi-threaded solver for large islands (or NULL)
+							  btCollisionConfiguration * collisionConfiguration);
+	virtual ~btDiscreteDynamicsWorldMt();
+
+	virtual int stepSimulation(btScalar timeStep, int maxSubSteps, btScalar fixedTimeStep) BT_OVERRIDE;
+};
+
+#endif  //BT_DISCRETE_DYNAMICS_WORLD_H