--- a/hotspot/src/share/vm/memory/referencePolicy.cpp	Tue Oct 11 10:21:36 2011 +0200
+++ b/hotspot/src/share/vm/memory/referencePolicy.cpp	Wed Oct 12 10:25:51 2011 -0700
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2000, 2010, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2000, 2011, 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
@@ -41,8 +41,9 @@
 
 // The oop passed in is the SoftReference object, and not
 // the object the SoftReference points to.
-bool LRUCurrentHeapPolicy::should_clear_reference(oop p) {
-  jlong interval = java_lang_ref_SoftReference::clock() - java_lang_ref_SoftReference::timestamp(p);
+bool LRUCurrentHeapPolicy::should_clear_reference(oop p,
+                                                  jlong timestamp_clock) {
+  jlong interval = timestamp_clock - java_lang_ref_SoftReference::timestamp(p);
   assert(interval >= 0, "Sanity check");
 
   // The interval will be zero if the ref was accessed since the last scavenge/gc.
@@ -71,8 +72,9 @@
 
 // The oop passed in is the SoftReference object, and not
 // the object the SoftReference points to.
-bool LRUMaxHeapPolicy::should_clear_reference(oop p) {
-  jlong interval = java_lang_ref_SoftReference::clock() - java_lang_ref_SoftReference::timestamp(p);
+bool LRUMaxHeapPolicy::should_clear_reference(oop p,
+                                             jlong timestamp_clock) {
+  jlong interval = timestamp_clock - java_lang_ref_SoftReference::timestamp(p);
   assert(interval >= 0, "Sanity check");
 
   // The interval will be zero if the ref was accessed since the last scavenge/gc.

--- a/hotspot/src/share/vm/memory/referencePolicy.hpp	Tue Oct 11 10:21:36 2011 +0200
+++ b/hotspot/src/share/vm/memory/referencePolicy.hpp	Wed Oct 12 10:25:51 2011 -0700
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2000, 2010, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2000, 2011, 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
@@ -31,19 +31,27 @@
 
 class ReferencePolicy : public CHeapObj {
  public:
-  virtual bool should_clear_reference(oop p)       { ShouldNotReachHere(); return true; }
+  virtual bool should_clear_reference(oop p, jlong timestamp_clock) {
+    ShouldNotReachHere();
+    return true;
+  }
+
   // Capture state (of-the-VM) information needed to evaluate the policy
   virtual void setup() { /* do nothing */ }
 };
 
 class NeverClearPolicy : public ReferencePolicy {
  public:
-  bool should_clear_reference(oop p) { return false; }
+  virtual bool should_clear_reference(oop p, jlong timestamp_clock) {
+    return false;
+  }
 };
 
 class AlwaysClearPolicy : public ReferencePolicy {
  public:
-  bool should_clear_reference(oop p) { return true; }
+  virtual bool should_clear_reference(oop p, jlong timestamp_clock) {
+    return true;
+  }
 };
 
 class LRUCurrentHeapPolicy : public ReferencePolicy {
@@ -55,7 +63,7 @@
 
   // Capture state (of-the-VM) information needed to evaluate the policy
   void setup();
-  bool should_clear_reference(oop p);
+  virtual bool should_clear_reference(oop p, jlong timestamp_clock);
 };
 
 class LRUMaxHeapPolicy : public ReferencePolicy {
@@ -67,7 +75,7 @@
 
   // Capture state (of-the-VM) information needed to evaluate the policy
   void setup();
-  bool should_clear_reference(oop p);
+  virtual bool should_clear_reference(oop p, jlong timestamp_clock);
 };
 
 #endif // SHARE_VM_MEMORY_REFERENCEPOLICY_HPP

--- a/hotspot/src/share/vm/memory/referenceProcessor.cpp	Tue Oct 11 10:21:36 2011 +0200
+++ b/hotspot/src/share/vm/memory/referenceProcessor.cpp	Wed Oct 12 10:25:51 2011 -0700
@@ -36,14 +36,19 @@
 ReferencePolicy* ReferenceProcessor::_always_clear_soft_ref_policy = NULL;
 ReferencePolicy* ReferenceProcessor::_default_soft_ref_policy      = NULL;
 bool             ReferenceProcessor::_pending_list_uses_discovered_field = false;
+jlong            ReferenceProcessor::_soft_ref_timestamp_clock = 0;
 
 void referenceProcessor_init() {
   ReferenceProcessor::init_statics();
 }
 
 void ReferenceProcessor::init_statics() {
-  // Initialize the master soft ref clock.
-  java_lang_ref_SoftReference::set_clock(os::javaTimeMillis());
+  jlong now = os::javaTimeMillis();
+
+  // Initialize the soft ref timestamp clock.
+  _soft_ref_timestamp_clock = now;
+  // Also update the soft ref clock in j.l.r.SoftReference
+  java_lang_ref_SoftReference::set_clock(_soft_ref_timestamp_clock);
 
   _always_clear_soft_ref_policy = new AlwaysClearPolicy();
   _default_soft_ref_policy      = new COMPILER2_PRESENT(LRUMaxHeapPolicy())
@@ -57,6 +62,28 @@
   _pending_list_uses_discovered_field = JDK_Version::current().pending_list_uses_discovered_field();
 }
 
+void ReferenceProcessor::enable_discovery(bool verify_disabled, bool check_no_refs) {
+#ifdef ASSERT
+  // Verify that we're not currently discovering refs
+  assert(!verify_disabled || !_discovering_refs, "nested call?");
+
+  if (check_no_refs) {
+    // Verify that the discovered lists are empty
+    verify_no_references_recorded();
+  }
+#endif // ASSERT
+
+  // Someone could have modified the value of the static
+  // field in the j.l.r.SoftReference class that holds the
+  // soft reference timestamp clock using reflection or
+  // Unsafe between GCs. Unconditionally update the static
+  // field in ReferenceProcessor here so that we use the new
+  // value during reference discovery.
+
+  _soft_ref_timestamp_clock = java_lang_ref_SoftReference::clock();
+  _discovering_refs = true;
+}
+
 ReferenceProcessor::ReferenceProcessor(MemRegion span,
                                        bool      mt_processing,
                                        int       mt_processing_degree,
@@ -122,17 +149,21 @@
   // Update (advance) the soft ref master clock field. This must be done
   // after processing the soft ref list.
   jlong now = os::javaTimeMillis();
-  jlong clock = java_lang_ref_SoftReference::clock();
+  jlong soft_ref_clock = java_lang_ref_SoftReference::clock();
+  assert(soft_ref_clock == _soft_ref_timestamp_clock, "soft ref clocks out of sync");
+
   NOT_PRODUCT(
-  if (now < clock) {
-    warning("time warp: %d to %d", clock, now);
+  if (now < _soft_ref_timestamp_clock) {
+    warning("time warp: "INT64_FORMAT" to "INT64_FORMAT,
+            _soft_ref_timestamp_clock, now);
   }
   )
   // In product mode, protect ourselves from system time being adjusted
   // externally and going backward; see note in the implementation of
   // GenCollectedHeap::time_since_last_gc() for the right way to fix
   // this uniformly throughout the VM; see bug-id 4741166. XXX
-  if (now > clock) {
+  if (now > _soft_ref_timestamp_clock) {
+    _soft_ref_timestamp_clock = now;
     java_lang_ref_SoftReference::set_clock(now);
   }
   // Else leave clock stalled at its old value until time progresses
@@ -150,6 +181,16 @@
   // Stop treating discovered references specially.
   disable_discovery();
 
+  // If discovery was concurrent, someone could have modified
+  // the value of the static field in the j.l.r.SoftReference
+  // class that holds the soft reference timestamp clock using
+  // reflection or Unsafe between when discovery was enabled and
+  // now. Unconditionally update the static field in ReferenceProcessor
+  // here so that we use the new value during processing of the
+  // discovered soft refs.
+
+  _soft_ref_timestamp_clock = java_lang_ref_SoftReference::clock();
+
   bool trace_time = PrintGCDetails && PrintReferenceGC;
   // Soft references
   {
@@ -486,7 +527,8 @@
   while (iter.has_next()) {
     iter.load_ptrs(DEBUG_ONLY(!discovery_is_atomic() /* allow_null_referent */));
     bool referent_is_dead = (iter.referent() != NULL) && !iter.is_referent_alive();
-    if (referent_is_dead && !policy->should_clear_reference(iter.obj())) {
+    if (referent_is_dead &&
+        !policy->should_clear_reference(iter.obj(), _soft_ref_timestamp_clock)) {
       if (TraceReferenceGC) {
         gclog_or_tty->print_cr("Dropping reference (" INTPTR_FORMAT ": %s"  ") by policy",
                                iter.obj(), iter.obj()->blueprint()->internal_name());
@@ -1117,7 +1159,7 @@
     // time-stamp policies advance the soft-ref clock only
     // at a major collection cycle, this is always currently
     // accurate.
-    if (!_current_soft_ref_policy->should_clear_reference(obj)) {
+    if (!_current_soft_ref_policy->should_clear_reference(obj, _soft_ref_timestamp_clock)) {
       return false;
     }
   }

--- a/hotspot/src/share/vm/memory/referenceProcessor.hpp	Tue Oct 11 10:21:36 2011 +0200
+++ b/hotspot/src/share/vm/memory/referenceProcessor.hpp	Wed Oct 12 10:25:51 2011 -0700
@@ -201,7 +201,6 @@
     assert(_ref != _first_seen, "cyclic ref_list found");
     NOT_PRODUCT(_processed++);
   }
-
 };
 
 class ReferenceProcessor : public CHeapObj {
@@ -209,6 +208,9 @@
   // Compatibility with pre-4965777 JDK's
   static bool _pending_list_uses_discovered_field;
 
+  // The SoftReference master timestamp clock
+  static jlong _soft_ref_timestamp_clock;
+
   MemRegion   _span;                    // (right-open) interval of heap
                                         // subject to wkref discovery
 
@@ -456,19 +458,7 @@
   void      set_span(MemRegion span) { _span = span; }
 
   // start and stop weak ref discovery
-  void enable_discovery(bool verify_disabled, bool check_no_refs) {
-#ifdef ASSERT
-    // Verify that we're not currently discovering refs
-    assert(!verify_disabled || !_discovering_refs, "nested call?");
-
-    if (check_no_refs) {
-      // Verify that the discovered lists are empty
-      verify_no_references_recorded();
-    }
-#endif // ASSERT
-    _discovering_refs = true;
-  }
-
+  void enable_discovery(bool verify_disabled, bool check_no_refs);
   void disable_discovery()  { _discovering_refs = false; }
   bool discovery_enabled()  { return _discovering_refs;  }