GH-530 use startReading() instead of rewind() since it also closes 'writeStream'; asserts added to delete()

Author: thurka

visualvm/libs.profiler/lib.profiler.heap/src/org/graalvm/visualvm/lib/jfluid/heap/DominatorTree.java

@@ -80,7 +80,7 @@ synchronized void computeDominators() {
         boolean igonoreDirty;
         try {
             do {
-                currentMultipleParents.rewind();
+                currentMultipleParents.startReading();
                 igonoreDirty = !changed;
                 changed = computeOneLevel(igonoreDirty);
                 switchParents();

visualvm/libs.profiler/lib.profiler.heap/src/org/graalvm/visualvm/lib/jfluid/heap/LongBuffer.java

@@ -67,6 +67,8 @@ class LongBuffer {
 
     void delete() {
         if (backingFile != null) {
+            assert writeStream == null;
+            assert readStreamClosed || readStream == null;
             backingFile.delete();
             useBackingFile = false;
             backingFile = null;