- // Ask a lesser priority train to free the block for us
- if(link->get_train()->get_priority()<priority)
- if(link->get_train()->free_block(*link))
- reserved = link->reserve(this);
+ /* We've found another train. If it wants to exit the block from the
+ same endpoint we're trying to enter from or the other way around,
+ treat it as coming towards us. Otherwise treat it as going in the
+ same direction. */
+ Train *other_train = link->get_train();
+ int other_entry = other_train->get_entry_to_block(*link);
+ if(other_entry<0)
+ throw LogicError("Block reservation inconsistency");
+
+ int other_prio = other_train->get_priority();
+
+ bool entry_conflict = (static_cast<unsigned>(entry)==link->traverse(other_entry));
+ bool exit_conflict = (link->traverse(entry)==static_cast<unsigned>(other_entry));
+ if(!entry_conflict && !exit_conflict)
+ {
+ /* Same direction, keep the blocks we got so far and wait for the
+ other train to pass */
+ good = last;
+ good_sens = nsens;
+
+ // Ask a lesser priority train to free the block for us
+ if(other_train->get_priority()<priority)
+ if(other_train->free_block(*link))
+ reserved = link->reserve(this);
+ }
+ else if(other_prio<priority || (other_prio==priority && other_train!=yielding_to && entry_conflict))
+ {
+ /* A lesser priority train is coming at us, we must ask it to free
+ enough blocks to get clear of it to avoid a potential deadlock */
+ blocking_train = other_train;
+ contested_blocks.clear();
+ contested_blocks.push_back(BlockRef(link, entry));
+ last = &contested_blocks.back();
+ continue;
+ }