BranchGraph: Add a read-write-lock to prevent rendering during rebuild.

Read and write accesses to the branch graph are now protected by a
read-write-lock. The LineageTreeLayoutImp acquires a read-lock during
rendering. And ModelBranchGraph write-locks itself during graphRebuilt().

This commit fixes a ConcurrentModificationException that occurred on some
datasets, when the "TrackScheme Hierarchy" window was shown for the first
time.

src/main/java/org/mastodon/mamut/MamutBranchViewTrackSchemeHierarchy.java

@@ -113,7 +113,7 @@ public TrackSchemeGraph< BranchSpot, BranchLink > createViewGraph( final MamutAp
 			final GraphIdBimap< BranchSpot, BranchLink > idmap = graph.getGraphIdBimap();
 			final ModelGraphProperties< BranchSpot, BranchLink > properties = new MyModelGraphProperties( graph );
 			final TrackSchemeGraph< BranchSpot, BranchLink > trackSchemeGraph =
-					new TrackSchemeGraph<>( graph, idmap, properties );
+					new TrackSchemeGraph<>( graph, idmap, properties, graph.getLock() );
 			return trackSchemeGraph;
 		}
 

src/main/java/org/mastodon/mamut/model/branch/ModelBranchGraph.java

@@ -37,6 +37,8 @@
 
 import net.imglib2.RealLocalizable;
 
+import java.util.concurrent.locks.ReentrantReadWriteLock;
+
 /**
  * A branch-graph specific for {@link ModelGraph}, whose vertices implements the
  * {@link RealLocalizable} and {@link HasTimepoint} interfaces, exposing the
@@ -48,6 +50,7 @@
 public class ModelBranchGraph
 		extends BranchGraphImp< Spot, Link, BranchSpot, BranchLink, BranchSpotPool, BranchLinkPool, ByteMappedElement >
 {
+	private final ReentrantReadWriteLock lock = new ReentrantReadWriteLock();
 
 	public ModelBranchGraph( final ModelGraph graph )
 	{
@@ -60,6 +63,11 @@ public ModelBranchGraph( final ModelGraph graph, final int initialCapacity )
 				new BranchSpotPool( initialCapacity, graph.vertices().getRefPool() ) ) );
 	}
 
+	public ReentrantReadWriteLock getLock()
+	{
+		return lock;
+	}
+
 	@Override
 	public BranchSpot init( final BranchSpot branchVertex, final Spot branchStart, final Spot branchEnd )
 	{
@@ -71,4 +79,31 @@ public BranchLink init( final BranchLink branchEdge, final Link edge )
 	{
 		return branchEdge.init();
 	}
+
+	@Override
+	public void graphRebuilt()
+	{
+		if ( lock == null )
+		{
+			// NB: graphRebuilt() is called the first time, even before the lock
+			// is initialized. This is because the super class (BranchGraphImp)
+			// calls graphRebuilt() in its constructor.
+			// But that's not a problem. We don't need to use the lock while the
+			// constructor is run, since no other thread can access the
+			// branch graph before the constructor finished.
+			super.graphRebuilt();
+		}
+		else
+		{
+			lock.writeLock().lock();
+			try
+			{
+				super.graphRebuilt();
+			}
+			finally
+			{
+				lock.writeLock().unlock();
+			}
+		}
+	}
 }