- fixed: Both main and worker thread were modifying the portal state.

The parts in the main thread have been offloaded to a new worker job to avoid having to use a mutex to protect the portal state.

src/hwrenderer/scene/hw_bsp.cpp

@@ -56,6 +56,7 @@ struct RenderJob
 		WallJob,
 		SpriteJob,
 		ParticleJob,
+		PortalJob,
 		TerminateJob	// inserted when all work is done so that the worker can return.
 	};
 	
@@ -177,7 +178,12 @@ void HWDrawInfo::WorkerThread()
 			RenderParticles(job->sub, front);
 			SetupSprite.Unclock();
 			break;
+
+		case RenderJob::PortalJob:
+			AddSubsectorToPortal((FSectorPortalGroup *)job->seg, job->sub);
+			break;
 		}
+
 	}
 }
 
@@ -706,16 +712,35 @@ void HWDrawInfo::DoSubsector(subsector_t * sub)
 				// This is for portal coverage.
 				FSectorPortalGroup *portal;
 
+				// AddSubsectorToPortal cannot be called here when using multithreaded processing,
+				// because the wall processing code in the worker can also modify the portal state.
+				// To avoid costly synchronization for every access to the portal list,
+				// the call to AddSubsectorToPortal will be deferred to the worker.
+				// (GetPortalGruop only accesses static sector data so this check can be done here, restricting the new job to the minimum possible extent.)
 				portal = fakesector->GetPortalGroup(sector_t::ceiling);
 				if (portal != nullptr)
 				{
-					AddSubsectorToPortal(portal, sub);
+					if (multithread)
+					{
+						jobQueue.AddJob(RenderJob::PortalJob, sub, (seg_t *)portal);
+					}
+					else
+					{
+						AddSubsectorToPortal(portal, sub);
+					}
 				}
 
 				portal = fakesector->GetPortalGroup(sector_t::floor);
 				if (portal != nullptr)
 				{
-					AddSubsectorToPortal(portal, sub);
+					if (multithread)
+					{
+						jobQueue.AddJob(RenderJob::PortalJob, sub, (seg_t *)portal);
+					}
+					else
+					{
+						AddSubsectorToPortal(portal, sub);
+					}
 				}
 			}
 		}