Fixed #560: if a rigid body has more than one collision (and one collision can be

reported p to 4 times by bullet), a crash would be caused when the rigid body is
removed (meaning that all further collisions with this body are invalid/removed,
while the loop in physics still tries to access them).
This patches removes bodies only when it is safe to do so, i.e. after the collision
loop. Removals done in the loop will be stored and executed later.


git-svn-id: svn+ssh://svn.code.sf.net/p/supertuxkart/code/main/trunk@11198 178a84e3-b1eb-0310-8ba1-8eac791a3b58

src/physics/physics.cpp

@@ -38,8 +38,8 @@
  */
 Physics::Physics() : btSequentialImpulseConstraintSolver()
 {
-    m_collision_conf = new btDefaultCollisionConfiguration();
-    m_dispatcher     = new btCollisionDispatcher(m_collision_conf);
+    m_collision_conf      = new btDefaultCollisionConfiguration();
+    m_dispatcher          = new btCollisionDispatcher(m_collision_conf);
 }   // Physics
 
 //-----------------------------------------------------------------------------
@@ -49,11 +49,13 @@ Physics::Physics() : btSequentialImpulseConstraintSolver()
  */
 void Physics::init(const Vec3 &world_min, const Vec3 &world_max)
 {
-    m_axis_sweep     = new btAxisSweep3(world_min, world_max);
-    m_dynamics_world = new STKDynamicsWorld(m_dispatcher,
-                                            m_axis_sweep,
-                                            this,
-                                            m_collision_conf);
+    m_physics_loop_active = false;
+    m_axis_sweep          = new btAxisSweep3(world_min, world_max);
+    m_dynamics_world      = new STKDynamicsWorld(m_dispatcher,
+                                                 m_axis_sweep,
+                                                 this,
+                                                 m_collision_conf);
+    m_karts_to_delete.clear();
     m_dynamics_world->setGravity(
         btVector3(0.0f,
                   -World::getWorld()->getTrack()->getGravity(),
@@ -100,9 +102,26 @@ void Physics::addKart(const AbstractKart *kart)
  */
 void Physics::removeKart(const AbstractKart *kart)
 {
-    m_dynamics_world->removeRigidBody(kart->getBody());
-    m_dynamics_world->removeVehicle(kart->getVehicle());
-    m_dynamics_world->removeConstraint(kart->getUprightConstraint());
+    // We can't simply remove a kart from the physics world when currently
+    // loops over all kart objects are active. This can happen in collision
+    // handling, where a collision of a kart with a cake etc. removes
+    // a kart from the physics. In this case save pointers to the kart
+    // to be removed, and remove them once the physics processing is done.
+    if(m_physics_loop_active)
+    {
+        // Make sure to remove each kart only once.
+        if(std::find(m_karts_to_delete.begin(), m_karts_to_delete.end(), kart)
+                     == m_karts_to_delete.end())
+        {
+            m_karts_to_delete.push_back(kart);
+        }
+    }
+    else
+    {
+        m_dynamics_world->removeRigidBody(kart->getBody());
+        m_dynamics_world->removeVehicle(kart->getVehicle());
+        m_dynamics_world->removeConstraint(kart->getUprightConstraint());
+    }
 }   // removeKart
 
 //-----------------------------------------------------------------------------
@@ -111,6 +130,7 @@ void Physics::removeKart(const AbstractKart *kart)
  */
 void Physics::update(float dt)
 {
+    m_physics_loop_active = true;
     // Bullet can report the same collision more than once (up to 4
     // contact points per collision). Additionally, more than one internal
     // substep might be taken, resulting in potentially even more
@@ -207,6 +227,14 @@ void Physics::update(float dt)
             p->getUserPointer(1)->getPointerFlyable()->hit(NULL);
         }
     }  // for all p in m_all_collisions
+
+    m_physics_loop_active = false;
+    // Now remove the karts that were removed while the above loop
+    // was active. Now we can safely call removeKart, since the loop
+    // is finished and m_physics_world_active is not set anymore.
+    for(unsigned int i=0; i<m_karts_to_delete.size(); i++)
+        removeKart(m_karts_to_delete[i]);
+    m_karts_to_delete.clear();
 }   // update
 
 //-----------------------------------------------------------------------------

src/physics/physics.hpp

@@ -60,7 +60,6 @@ private:
 
         /** The contact point for each object (in local coordincates). */
         Vec3               m_contact_point[2];
-
     public:
         /** The entries in Collision Pairs are sorted: if a projectile
          * is included, it's always 'a'. If only two karts are reported
@@ -124,6 +123,18 @@ private:
     };  // CollisionList
     // ========================================================================
 
+    /** This flag is set while bullets time step processing is taking
+    *  place. It is used to avoid altering data structures that might
+    *  be used (e.g. removing a kart while a loop over all karts is
+    *  taking place, as can happen in collision handling). */
+    bool               m_physics_loop_active;
+
+    /** If kart need to be removed from the physics world while physics
+    *  processing is taking place, store the pointers to the karts to
+    *  be removed here, and remove them once the physics processing
+    *  is finished. */
+    std::vector<const AbstractKart*> m_karts_to_delete;
+
     /** Pointer to the physics dynamics world. */
     STKDynamicsWorld                *m_dynamics_world;