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

src/LinearMath/btQuickprof.cpp

@@ -16,6 +16,9 @@
 #include "btQuickprof.h"
 
 
+#if BT_THREADSAFE
+#include "btThreads.h"
+#endif //#if BT_THREADSAFE
 
 
 #ifdef __CELLOS_LV2__
@@ -455,6 +458,14 @@ unsigned long int			CProfileManager::ResetTime = 0;
  *=============================================================================================*/
 void	CProfileManager::Start_Profile( const char * name )
 {
+#if BT_THREADSAFE
+    // profile system is not designed for profiling multiple threads
+    // disable collection on all but the main thread
+    if ( !btIsMainThread() )
+    {
+        return;
+    }
+#endif //#if BT_THREADSAFE
 	if (name != CurrentNode->Get_Name()) {
 		CurrentNode = CurrentNode->Get_Sub_Node( name );
 	}
@@ -468,6 +479,14 @@ void	CProfileManager::Start_Profile( const char * name )
  *=============================================================================================*/
 void	CProfileManager::Stop_Profile( void )
 {
+#if BT_THREADSAFE
+    // profile system is not designed for profiling multiple threads
+    // disable collection on all but the main thread
+    if ( !btIsMainThread() )
+    {
+        return;
+    }
+#endif //#if BT_THREADSAFE
 	// Return will indicate whether we should back up to our parent (we may
 	// be profiling a recursive function)
 	if (CurrentNode->Return()) {