--- a/hotspot/src/share/vm/runtime/globals.hpp	Mon May 16 14:21:16 2011 -0700
+++ b/hotspot/src/share/vm/runtime/globals.hpp	Mon May 16 22:16:44 2011 -0700
@@ -2909,6 +2909,12 @@
   product(intx, NmethodSweepCheckInterval, 5,                               \
           "Compilers wake up every n seconds to possibly sweep nmethods")   \
                                                                             \
+  notproduct(bool, LogSweeper, false,                                       \
+            "Keep a ring buffer of sweeper activity")                       \
+                                                                            \
+  notproduct(intx, SweeperLogEntries, 1024,                                 \
+            "Number of records in the ring buffer of sweeper activity")     \
+                                                                            \
   notproduct(intx, MemProfilingInterval, 500,                               \
           "Time between each invocation of the MemProfiler")                \
                                                                             \

--- a/hotspot/src/share/vm/runtime/sweeper.cpp	Mon May 16 14:21:16 2011 -0700
+++ b/hotspot/src/share/vm/runtime/sweeper.cpp	Mon May 16 22:16:44 2011 -0700
@@ -37,6 +37,94 @@
 #include "utilities/events.hpp"
 #include "utilities/xmlstream.hpp"
 
+#ifdef ASSERT
+
+#define SWEEP(nm) record_sweep(nm, __LINE__)
+// Sweeper logging code
+class SweeperRecord {
+ public:
+  int traversal;
+  int invocation;
+  int compile_id;
+  long traversal_mark;
+  int state;
+  const char* kind;
+  address vep;
+  address uep;
+  int line;
+
+  void print() {
+      tty->print_cr("traversal = %d invocation = %d compile_id = %d %s uep = " PTR_FORMAT " vep = "
+                    PTR_FORMAT " state = %d traversal_mark %d line = %d",
+                    traversal,
+                    invocation,
+                    compile_id,
+                    kind == NULL ? "" : kind,
+                    uep,
+                    vep,
+                    state,
+                    traversal_mark,
+                    line);
+  }
+};
+
+static int _sweep_index = 0;
+static SweeperRecord* _records = NULL;
+
+void NMethodSweeper::report_events(int id, address entry) {
+  if (_records != NULL) {
+    for (int i = _sweep_index; i < SweeperLogEntries; i++) {
+      if (_records[i].uep == entry ||
+          _records[i].vep == entry ||
+          _records[i].compile_id == id) {
+        _records[i].print();
+      }
+    }
+    for (int i = 0; i < _sweep_index; i++) {
+      if (_records[i].uep == entry ||
+          _records[i].vep == entry ||
+          _records[i].compile_id == id) {
+        _records[i].print();
+      }
+    }
+  }
+}
+
+void NMethodSweeper::report_events() {
+  if (_records != NULL) {
+    for (int i = _sweep_index; i < SweeperLogEntries; i++) {
+      // skip empty records
+      if (_records[i].vep == NULL) continue;
+      _records[i].print();
+    }
+    for (int i = 0; i < _sweep_index; i++) {
+      // skip empty records
+      if (_records[i].vep == NULL) continue;
+      _records[i].print();
+    }
+  }
+}
+
+void NMethodSweeper::record_sweep(nmethod* nm, int line) {
+  if (_records != NULL) {
+    _records[_sweep_index].traversal = _traversals;
+    _records[_sweep_index].traversal_mark = nm->_stack_traversal_mark;
+    _records[_sweep_index].invocation = _invocations;
+    _records[_sweep_index].compile_id = nm->compile_id();
+    _records[_sweep_index].kind = nm->compile_kind();
+    _records[_sweep_index].state = nm->_state;
+    _records[_sweep_index].vep = nm->verified_entry_point();
+    _records[_sweep_index].uep = nm->entry_point();
+    _records[_sweep_index].line = line;
+
+    _sweep_index = (_sweep_index + 1) % SweeperLogEntries;
+  }
+}
+#else
+#define SWEEP(nm)
+#endif
+
+
 long      NMethodSweeper::_traversals = 0;   // No. of stack traversals performed
 nmethod*  NMethodSweeper::_current = NULL;   // Current nmethod
 int       NMethodSweeper::_seen = 0 ;        // No. of nmethods we have currently processed in current pass of CodeCache
@@ -137,6 +225,13 @@
     if (old != 0) {
       return;
     }
+#ifdef ASSERT
+    if (LogSweeper && _records == NULL) {
+      // Create the ring buffer for the logging code
+      _records = NEW_C_HEAP_ARRAY(SweeperRecord, SweeperLogEntries);
+      memset(_records, 0, sizeof(SweeperRecord) * SweeperLogEntries);
+    }
+#endif
     if (_invocations > 0) {
       sweep_code_cache();
       _invocations--;
@@ -213,10 +308,29 @@
   }
 }
 
+class NMethodMarker: public StackObj {
+ private:
+  CompilerThread* _thread;
+ public:
+  NMethodMarker(nmethod* nm) {
+    _thread = CompilerThread::current();
+    _thread->set_scanned_nmethod(nm);
+  }
+  ~NMethodMarker() {
+    _thread->set_scanned_nmethod(NULL);
+  }
+};
+
 
 void NMethodSweeper::process_nmethod(nmethod *nm) {
   assert(!CodeCache_lock->owned_by_self(), "just checking");
 
+  // Make sure this nmethod doesn't get unloaded during the scan,
+  // since the locks acquired below might safepoint.
+  NMethodMarker nmm(nm);
+
+  SWEEP(nm);
+
   // Skip methods that are currently referenced by the VM
   if (nm->is_locked_by_vm()) {
     // But still remember to clean-up inline caches for alive nmethods
@@ -224,8 +338,10 @@
       // Clean-up all inline caches that points to zombie/non-reentrant methods
       MutexLocker cl(CompiledIC_lock);
       nm->cleanup_inline_caches();
+      SWEEP(nm);
     } else {
       _locked_seen++;
+      SWEEP(nm);
     }
     return;
   }
@@ -247,6 +363,7 @@
       }
       nm->mark_for_reclamation();
       _rescan = true;
+      SWEEP(nm);
     }
   } else if (nm->is_not_entrant()) {
     // If there is no current activations of this method on the
@@ -257,6 +374,7 @@
       }
       nm->make_zombie();
       _rescan = true;
+      SWEEP(nm);
     } else {
       // Still alive, clean up its inline caches
       MutexLocker cl(CompiledIC_lock);
@@ -265,6 +383,7 @@
       // request a rescan.  If this method stays on the stack for a
       // long time we don't want to keep rescanning the code cache.
       _not_entrant_seen_on_stack++;
+      SWEEP(nm);
     }
   } else if (nm->is_unloaded()) {
     // Unloaded code, just make it a zombie
@@ -273,10 +392,12 @@
     if (nm->is_osr_method()) {
       // No inline caches will ever point to osr methods, so we can just remove it
       MutexLockerEx mu(CodeCache_lock, Mutex::_no_safepoint_check_flag);
+      SWEEP(nm);
       nm->flush();
     } else {
       nm->make_zombie();
       _rescan = true;
+      SWEEP(nm);
     }
   } else {
     assert(nm->is_alive(), "should be alive");
@@ -293,6 +414,7 @@
     // Clean-up all inline caches that points to zombie/non-reentrant methods
     MutexLocker cl(CompiledIC_lock);
     nm->cleanup_inline_caches();
+    SWEEP(nm);
   }
 }
 

--- a/hotspot/src/share/vm/runtime/sweeper.hpp	Mon May 16 14:21:16 2011 -0700
+++ b/hotspot/src/share/vm/runtime/sweeper.hpp	Mon May 16 22:16:44 2011 -0700
@@ -57,6 +57,13 @@
  public:
   static long traversal_count() { return _traversals; }
 
+#ifdef ASSERT
+  // Keep track of sweeper activity in the ring buffer
+  static void record_sweep(nmethod* nm, int line);
+  static void report_events(int id, address entry);
+  static void report_events();
+#endif
+
   static void scan_stacks();      // Invoked at the end of each safepoint
   static void sweep_code_cache(); // Concurrent part of sweep job
   static void possibly_sweep();   // Compiler threads call this to sweep

--- a/hotspot/src/share/vm/runtime/thread.cpp	Mon May 16 14:21:16 2011 -0700
+++ b/hotspot/src/share/vm/runtime/thread.cpp	Mon May 16 22:16:44 2011 -0700
@@ -2942,12 +2942,22 @@
   _queue = queue;
   _counters = counters;
   _buffer_blob = NULL;
+  _scanned_nmethod = NULL;
 
 #ifndef PRODUCT
   _ideal_graph_printer = NULL;
 #endif
 }
 
+void CompilerThread::oops_do(OopClosure* f, CodeBlobClosure* cf) {
+  JavaThread::oops_do(f, cf);
+  if (_scanned_nmethod != NULL && cf != NULL) {
+    // Safepoints can occur when the sweeper is scanning an nmethod so
+    // process it here to make sure it isn't unloaded in the middle of
+    // a scan.
+    cf->do_code_blob(_scanned_nmethod);
+  }
+}
 
 // ======= Threads ========
 

--- a/hotspot/src/share/vm/runtime/thread.hpp	Mon May 16 14:21:16 2011 -0700
+++ b/hotspot/src/share/vm/runtime/thread.hpp	Mon May 16 22:16:44 2011 -0700
@@ -439,7 +439,7 @@
   // GC support
   // Apply "f->do_oop" to all root oops in "this".
   // Apply "cf->do_code_blob" (if !NULL) to all code blobs active in frames
-  void oops_do(OopClosure* f, CodeBlobClosure* cf);
+  virtual void oops_do(OopClosure* f, CodeBlobClosure* cf);
 
   // Handles the parallel case for the method below.
 private:
@@ -1381,7 +1381,7 @@
   void trace_frames()                            PRODUCT_RETURN;
 
   // Print an annotated view of the stack frames
-  void print_frame_layout(int depth = 0, bool validate_only = false) PRODUCT_RETURN;
+  void print_frame_layout(int depth = 0, bool validate_only = false) NOT_DEBUG_RETURN;
   void validate_frame_layout() {
     print_frame_layout(0, true);
   }
@@ -1698,6 +1698,8 @@
   CompileQueue* _queue;
   BufferBlob*   _buffer_blob;
 
+  nmethod*      _scanned_nmethod;  // nmethod being scanned by the sweeper
+
  public:
 
   static CompilerThread* current();
@@ -1726,6 +1728,11 @@
     _log = log;
   }
 
+  // GC support
+  // Apply "f->do_oop" to all root oops in "this".
+  // Apply "cf->do_code_blob" (if !NULL) to all code blobs active in frames
+  void oops_do(OopClosure* f, CodeBlobClosure* cf);
+
 #ifndef PRODUCT
 private:
   IdealGraphPrinter *_ideal_graph_printer;
@@ -1737,6 +1744,12 @@
   // Get/set the thread's current task
   CompileTask*  task()                           { return _task; }
   void          set_task(CompileTask* task)      { _task = task; }
+
+  // Track the nmethod currently being scanned by the sweeper
+  void          set_scanned_nmethod(nmethod* nm) {
+    assert(_scanned_nmethod == NULL || nm == NULL, "should reset to NULL before writing a new value");
+    _scanned_nmethod = nm;
+  }
 };
 
 inline CompilerThread* CompilerThread::current() {