Unregister collision detectors when the darstim plugin is unloaded (#529

)

Fixes a segfault that occurs due to destructors being removed from memory before they're called.
---------

Signed-off-by: Addisu Z. Taddese <[email protected]>

dartsim/src/plugin.cc

@@ -57,6 +57,31 @@ class Plugin :
     public virtual ShapeFeatures,
     public virtual SimulationFeatures { };
 
+namespace {
+
+// This is done as a partial fix for
+// https://github.com/gazebosim/gz-physics/issues/442. The issue seems like the
+// destructors for the concrete collision detectors get unloaded and deleted
+// from memory before the destructors run. When it's time to actually call the
+// destructors, a segfault is generated.
+//
+// It's not clear why the destructors are deleted prematurely. It might be a
+// compiler optimization in new compiler versions.
+//
+// The solution here is to call the `unregisterAllCreators` function from the
+// plugins translation unit in the hopes that it will force the compiler to keep
+// the destructors.
+struct UnregisterCollisionDetectors
+{
+  ~UnregisterCollisionDetectors()
+  {
+    dart::collision::CollisionDetector::getFactory()->unregisterAllCreators();
+  }
+};
+
+UnregisterCollisionDetectors unregisterAtUnload;
+}
+
 IGN_PHYSICS_ADD_PLUGIN(Plugin, FeaturePolicy3d, DartsimFeatures)
 
 }