Fix for a rare but fatal sleeping/contact graph bug.

include/chipmunk/chipmunk_private.h

@@ -257,6 +257,12 @@ cpArbiterThreadForBody(cpArbiter *arb, cpBody *body)
 	return (arb->body_a == body ? &arb->thread_a : &arb->thread_b);
 }
 
+static inline cpBool
+cpArbiterIsFiltered(cpArbiter *arb)
+{
+	return (arb->contacts == NULL);
+}
+
 void cpArbiterUnthread(cpArbiter *arb);
 
 void cpArbiterUpdate(cpArbiter *arb, cpContact *contacts, int numContacts, struct cpCollisionHandler *handler, cpShape *a, cpShape *b);

src/cpArbiter.c

@@ -221,7 +221,7 @@ void
 cpArbiterUpdate(cpArbiter *arb, cpContact *contacts, int numContacts, cpCollisionHandler *handler, cpShape *a, cpShape *b)
 {
 	// Arbiters without contact data may exist if a collision function rejected the collision.
-	if(arb->contacts){
+	if(!cpArbiterIsFiltered(arb)){
 		// Iterate over the possible pairs to look for hash value matches.
 		for(int i=0; i<arb->numContacts; i++){
 			cpContact *old = &arb->contacts[i];

src/cpSpace.c

@@ -340,8 +340,13 @@ cachedArbitersFilter(cpArbiter *arb, struct arbiterFilterContext *context)
 		// Call separate when removing shapes.
 		if(shape && arb->state != cpArbiterStateCached) cpArbiterCallSeparate(arb, context->space);
 
-		cpArbiterUnthread(arb);
-		cpArrayDeleteObj(context->space->arbiters, arb);
+		// If the arbiter is active (non-sensor/filtered) it will have a contacts array.
+		// TODO is this too much of a hack?...
+		if(!cpArbiterIsFiltered(arb)){
+			cpArbiterUnthread(arb);
+			cpArrayDeleteObj(context->space->arbiters, arb);
+		}
+
 		cpArrayPush(context->space->pooledArbiters, arb);
 
 		return cpFalse;