--- /dev/null	2017-11-09 09:38:01.297999907 +0100
+++ new/src/hotspot/share/jfr/leakprofiler/chains/edgeUtils.cpp	2018-04-09 14:38:26.621806332 +0200
@@ -0,0 +1,312 @@
+/*
+ * Copyright (c) 2014, 2018, Oracle and/or its affiliates. All rights reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ *
+ */
+
+#include "precompiled.hpp"
+#include "classfile/javaClasses.hpp"
+#include "jfr/leakprofiler/chains/edge.hpp"
+#include "jfr/leakprofiler/chains/edgeStore.hpp"
+#include "jfr/leakprofiler/chains/edgeUtils.hpp"
+#include "jfr/leakprofiler/utilities/unifiedOop.hpp"
+#include "oops/fieldStreams.hpp"
+#include "oops/instanceKlass.hpp"
+#include "oops/objArrayOop.inline.hpp"
+#include "oops/oopsHierarchy.hpp"
+#include "runtime/handles.inline.hpp"
+
+bool EdgeUtils::is_leak_edge(const Edge& edge) {
+  return (const Edge*)edge.pointee()->mark() == &edge;
+}
+
+bool EdgeUtils::is_root(const Edge& edge) {
+  return edge.is_root();
+}
+
+static int field_offset(const Edge& edge) {
+  assert(!edge.is_root(), "invariant");
+  const oop ref_owner = edge.reference_owner();
+  assert(ref_owner != NULL, "invariant");
+  const oop* reference = UnifiedOop::decode(edge.reference());
+  assert(reference != NULL, "invariant");
+  assert(!UnifiedOop::is_narrow(reference), "invariant");
+  assert(!ref_owner->is_array(), "invariant");
+  assert(ref_owner->is_instance(), "invariant");
+  const int offset = (int)pointer_delta(reference, ref_owner, sizeof(char));
+  assert(offset < (ref_owner->size() * HeapWordSize), "invariant");
+  return offset;
+}
+
+static const InstanceKlass* field_type(const Edge& edge) {
+  assert(!edge.is_root() || !EdgeUtils::is_array_element(edge), "invariant");
+  return (const InstanceKlass*)edge.reference_owner_klass();
+}
+
+const Symbol* EdgeUtils::field_name_symbol(const Edge& edge) {
+  assert(!edge.is_root(), "invariant");
+  assert(!is_array_element(edge), "invariant");
+  const int offset = field_offset(edge);
+  const InstanceKlass* ik = field_type(edge);
+  while (ik != NULL) {
+    JavaFieldStream jfs(ik);
+    while (!jfs.done()) {
+      if (offset == jfs.offset()) {
+        return jfs.name();
+      }
+      jfs.next();
+    }
+    ik = (InstanceKlass*)ik->super();
+  }
+  return NULL;
+}
+
+jshort EdgeUtils::field_modifiers(const Edge& edge) {
+  const int offset = field_offset(edge);
+  const InstanceKlass* ik = field_type(edge);
+
+  while (ik != NULL) {
+    JavaFieldStream jfs(ik);
+    while (!jfs.done()) {
+      if (offset == jfs.offset()) {
+        return jfs.access_flags().as_short();
+      }
+      jfs.next();
+    }
+    ik = (InstanceKlass*)ik->super();
+  }
+  return 0;
+}
+
+bool EdgeUtils::is_array_element(const Edge& edge) {
+  assert(!edge.is_root(), "invariant");
+  const oop ref_owner = edge.reference_owner();
+  assert(ref_owner != NULL, "invariant");
+  return ref_owner->is_objArray();
+}
+
+static int array_offset(const Edge& edge) {
+  assert(!edge.is_root(), "invariant");
+  const oop ref_owner = edge.reference_owner();
+  assert(ref_owner != NULL, "invariant");
+  const oop* reference = UnifiedOop::decode(edge.reference());
+  assert(reference != NULL, "invariant");
+  assert(!UnifiedOop::is_narrow(reference), "invariant");
+  assert(ref_owner->is_array(), "invariant");
+  const objArrayOop ref_owner_array = static_cast<const objArrayOop>(ref_owner);
+  const int offset = (int)pointer_delta(reference, ref_owner_array->base(), heapOopSize);
+  assert(offset >= 0 && offset < ref_owner_array->length(), "invariant");
+  return offset;
+}
+
+int EdgeUtils::array_index(const Edge& edge) {
+  return is_array_element(edge) ? array_offset(edge) : 0;
+}
+
+int EdgeUtils::array_size(const Edge& edge) {
+  if (is_array_element(edge)) {
+    const oop ref_owner = edge.reference_owner();
+    assert(ref_owner != NULL, "invariant");
+    assert(ref_owner->is_objArray(), "invariant");
+    return ((objArrayOop)(ref_owner))->length();
+  }
+  return 0;
+}
+
+const Edge* EdgeUtils::root(const Edge& edge) {
+  const Edge* current = &edge;
+  const Edge* parent = current->parent();
+  while (parent != NULL) {
+    current = parent;
+    parent = current->parent();
+  }
+  return current;
+}
+
+// The number of references associated with the leak node;
+// can be viewed as the leak node "context".
+// Used to provide leak context for a "capped/skipped" reference chain.
+static const size_t leak_context = 100;
+
+// The number of references associated with the root node;
+// can be viewed as the root node "context".
+// Used to provide root context for a "capped/skipped" reference chain.
+static const size_t root_context = 100;
+
+// A limit on the reference chain depth to be serialized,
+static const size_t max_ref_chain_depth = leak_context + root_context;
+
+const RoutableEdge* skip_to(const RoutableEdge& edge, size_t skip_length) {
+  const RoutableEdge* current = &edge;
+  const RoutableEdge* parent = current->physical_parent();
+  size_t seek = 0;
+  while (parent != NULL && seek != skip_length) {
+    seek++;
+    current = parent;
+    parent = parent->physical_parent();
+  }
+  return current;
+}
+
+#ifdef ASSERT
+static void validate_skip_target(const RoutableEdge* skip_target) {
+  assert(skip_target != NULL, "invariant");
+  assert(skip_target->distance_to_root() + 1 == root_context, "invariant");
+  assert(skip_target->is_sentinel(), "invariant");
+}
+
+static void validate_new_skip_edge(const RoutableEdge* new_skip_edge, const RoutableEdge* last_skip_edge, size_t adjustment) {
+  assert(new_skip_edge != NULL, "invariant");
+  assert(new_skip_edge->is_skip_edge(), "invariant");
+  if (last_skip_edge != NULL) {
+    const RoutableEdge* const target = skip_to(*new_skip_edge->logical_parent(), adjustment);
+    validate_skip_target(target->logical_parent());
+    return;
+  }
+  assert(last_skip_edge == NULL, "invariant");
+  // only one level of logical indirection
+  validate_skip_target(new_skip_edge->logical_parent());
+}
+#endif // ASSERT
+
+static void install_logical_route(const RoutableEdge* new_skip_edge, size_t skip_target_distance) {
+  assert(new_skip_edge != NULL, "invariant");
+  assert(!new_skip_edge->is_skip_edge(), "invariant");
+  assert(!new_skip_edge->processed(), "invariant");
+  const RoutableEdge* const skip_target = skip_to(*new_skip_edge, skip_target_distance);
+  assert(skip_target != NULL, "invariant");
+  new_skip_edge->set_skip_edge(skip_target);
+  new_skip_edge->set_skip_length(skip_target_distance);
+  assert(new_skip_edge->is_skip_edge(), "invariant");
+  assert(new_skip_edge->logical_parent() == skip_target, "invariant");
+}
+
+static const RoutableEdge* find_last_skip_edge(const RoutableEdge& edge, size_t& distance) {
+  assert(distance == 0, "invariant");
+  const RoutableEdge* current = &edge;
+  while (current != NULL) {
+    if (current->is_skip_edge() && current->skip_edge()->is_sentinel()) {
+      return current;
+    }
+    current = current->physical_parent();
+    ++distance;
+  }
+  return current;
+}
+
+static void collapse_overlapping_chain(const RoutableEdge& edge,
+                                       const RoutableEdge* first_processed_edge,
+                                       size_t first_processed_distance) {
+  assert(first_processed_edge != NULL, "invariant");
+  // first_processed_edge is already processed / written
+  assert(first_processed_edge->processed(), "invariant");
+  assert(first_processed_distance + 1 <= leak_context, "invariant");
+
+  // from this first processed edge, attempt to fetch the last skip edge
+  size_t last_skip_edge_distance = 0;
+  const RoutableEdge* const last_skip_edge = find_last_skip_edge(*first_processed_edge, last_skip_edge_distance);
+  const size_t distance_discovered = first_processed_distance + last_skip_edge_distance + 1;
+
+  if (distance_discovered <= leak_context || (last_skip_edge == NULL && distance_discovered <= max_ref_chain_depth)) {
+    // complete chain can be accommodated without modification
+    return;
+  }
+
+  // backtrack one edge from existing processed edge
+  const RoutableEdge* const new_skip_edge = skip_to(edge, first_processed_distance - 1);
+  assert(new_skip_edge != NULL, "invariant");
+  assert(!new_skip_edge->processed(), "invariant");
+  assert(new_skip_edge->parent() == first_processed_edge, "invariant");
+
+  size_t adjustment = 0;
+  if (last_skip_edge != NULL) {
+    assert(leak_context - 1 > first_processed_distance - 1, "invariant");
+    adjustment = leak_context - first_processed_distance - 1;
+    assert(last_skip_edge_distance + 1 > adjustment, "invariant");
+    install_logical_route(new_skip_edge, last_skip_edge_distance + 1 - adjustment);
+  } else {
+    install_logical_route(new_skip_edge, last_skip_edge_distance + 1 - root_context);
+    new_skip_edge->logical_parent()->set_skip_length(1); // sentinel
+  }
+
+  DEBUG_ONLY(validate_new_skip_edge(new_skip_edge, last_skip_edge, adjustment);)
+}
+
+static void collapse_non_overlapping_chain(const RoutableEdge& edge,
+                                           const RoutableEdge* first_processed_edge,
+                                           size_t first_processed_distance) {
+  assert(first_processed_edge != NULL, "invariant");
+  assert(!first_processed_edge->processed(), "invariant");
+  // this implies that the first "processed" edge is the leak context relative "leaf"
+  assert(first_processed_distance + 1 == leak_context, "invariant");
+
+  const size_t distance_to_root = edge.distance_to_root();
+  if (distance_to_root + 1 <= max_ref_chain_depth) {
+    // complete chain can be accommodated without constructing a skip edge
+    return;
+  }
+
+  install_logical_route(first_processed_edge, distance_to_root + 1 - first_processed_distance - root_context);
+  first_processed_edge->logical_parent()->set_skip_length(1); // sentinel
+
+  DEBUG_ONLY(validate_new_skip_edge(first_processed_edge, NULL, 0);)
+}
+
+static const RoutableEdge* processed_edge(const RoutableEdge& edge, size_t& distance) {
+  assert(distance == 0, "invariant");
+  const RoutableEdge* current = &edge;
+  while (current != NULL && distance < leak_context - 1) {
+    if (current->processed()) {
+      return current;
+    }
+    current = current->physical_parent();
+    ++distance;
+  }
+  assert(distance <= leak_context - 1, "invariant");
+  return current;
+}
+
+/*
+ * Some vocabulary:
+ * -----------
+ * "Context" is an interval in the chain, it is associcated with an edge and it signifies a number of connected edges.
+ * "Processed / written" means an edge that has already been serialized.
+ * "Skip edge" is an edge that contains additional information for logical routing purposes.
+ * "Skip target" is an edge used as a destination for a skip edge
+ */
+void EdgeUtils::collapse_chain(const RoutableEdge& edge) {
+  assert(is_leak_edge(edge), "invariant");
+
+  // attempt to locate an already processed edge inside current leak context (if any)
+  size_t first_processed_distance = 0;
+  const RoutableEdge* const first_processed_edge = processed_edge(edge, first_processed_distance);
+  if (first_processed_edge == NULL) {
+    return;
+  }
+
+  if (first_processed_edge->processed()) {
+    collapse_overlapping_chain(edge, first_processed_edge, first_processed_distance);
+  } else {
+    collapse_non_overlapping_chain(edge, first_processed_edge, first_processed_distance);
+  }
+
+  assert(edge.logical_distance_to_root() + 1 <= max_ref_chain_depth, "invariant");
+}