(svn r13974) -Fix [YAPP]: A train crash could lead to stale reservations. (michi_cc)

3 files changed, 24 insertions, 13 deletions

diff --git a/src/pbs.cpp b/src/pbs.cpp
index 089591e9b..bf3913bc4 100644
--- a/src/pbs.cpp
+++ b/src/pbs.cpp
@@ -204,13 +204,24 @@ static PBSTileInfo FollowReservation(Owner o, RailTypes rts, TileIndex tile, Tra
 	return PBSTileInfo(tile, trackdir, false);
 }
 
+/** Callback for VehicleFromPos to find a train on a specific track. */
+static Vehicle *FindTrainOnTrackEnum(Vehicle *v, void *data)
+{
+	PBSTileInfo info = *(PBSTileInfo *)data;
+
+	if (v->type == VEH_TRAIN && !(v->vehstatus & VS_CRASHED) && HasBit((TrackBits)v->u.rail.track, TrackdirToTrack(info.trackdir))) return v;
+
+	return NULL;
+}
+
 /**
  * Follow a train reservation to the last tile.
  *
  * @param v the vehicle
+ * @param train_on_res Is set to a train we might encounter
  * @returns The last tile of the reservation or the current train tile if no reservation present.
  */
-PBSTileInfo FollowTrainReservation(const Vehicle *v)
+PBSTileInfo FollowTrainReservation(const Vehicle *v, Vehicle **train_on_res)
 {
 	assert(v->type == VEH_TRAIN);
 
@@ -221,19 +232,10 @@ PBSTileInfo FollowTrainReservation(const Vehicle *v)
 
 	PBSTileInfo res = FollowReservation(v->owner, GetRailTypeInfo(v->u.rail.railtype)->compatible_railtypes, tile, trackdir);
 	res.okay = IsSafeWaitingPosition(v, res.tile, res.trackdir, true, _settings_game.pf.forbid_90_deg);
+	if (train_on_res != NULL) *train_on_res = VehicleFromPos(res.tile, &res, FindTrainOnTrackEnum);
 	return res;
 }
 
-/** Callback for VehicleFromPos to find a train on a specific track. */
-static Vehicle *FindTrainOnTrackEnum(Vehicle *v, void *data)
-{
-	PBSTileInfo info = *(PBSTileInfo *)data;
-
-	if (v->type == VEH_TRAIN && !(v->vehstatus & VS_CRASHED) && HasBit((TrackBits)v->u.rail.track, TrackdirToTrack(info.trackdir))) return v;
-
-	return NULL;
-}
-
 /**
  * Find the train which has reserved a specific path.
  *
diff --git a/src/pbs.h b/src/pbs.h
index 8a6a5533f..d01123ed1 100644
--- a/src/pbs.h
+++ b/src/pbs.h
@@ -27,7 +27,7 @@ struct PBSTileInfo {
 	PBSTileInfo(TileIndex _t, Trackdir _td, bool _okay) : tile(_t), trackdir(_td), okay(_okay) {}
 };
 
-PBSTileInfo FollowTrainReservation(const Vehicle *v);
+PBSTileInfo FollowTrainReservation(const Vehicle *v, Vehicle **train_on_res = NULL);
 bool IsSafeWaitingPosition(const Vehicle *v, TileIndex tile, Trackdir trackdir, bool include_line_end, bool forbid_90deg = false);
 bool IsWaitingPositionFree(const Vehicle *v, TileIndex tile, Trackdir trackdir, bool forbid_90deg = false);
 
diff --git a/src/train_cmd.cpp b/src/train_cmd.cpp
index efdbd5c2a..dc7ff694c 100644
--- a/src/train_cmd.cpp
+++ b/src/train_cmd.cpp
@@ -3059,7 +3059,8 @@ bool TryPathReserve(Vehicle *v, bool mark_as_stuck, bool first_tile_okay)
 		}
 	}
 
-	PBSTileInfo origin = FollowTrainReservation(v);
+	Vehicle *other_train = NULL;
+	PBSTileInfo origin = FollowTrainReservation(v, &other_train);
 	/* If we have a reserved path and the path ends at a safe tile, we are finished already. */
 	if (origin.okay && (v->tile != origin.tile || first_tile_okay)) {
 		/* Can't be stuck then. */
@@ -3067,6 +3068,14 @@ bool TryPathReserve(Vehicle *v, bool mark_as_stuck, bool first_tile_okay)
 		ClrBit(v->u.rail.flags, VRF_TRAIN_STUCK);
 		return true;
 	}
+	/* The path we are driving on is alread blocked by some other train.
+	 * This can only happen when tracks and signals are changed. A crash
+	 * is probably imminent, don't do any further reservation because
+	 * it might cause stale reservations. */
+	if (other_train != NULL && v->tile != origin.tile) {
+		if (mark_as_stuck) MarkTrainAsStuck(v);
+		return false;
+	}
 
 	/* If we are in a depot, tentativly reserve the depot. */
 	if (v->u.rail.track & TRACK_BIT_DEPOT) {