hotspot/src/share/vm/code/nmethod.hpp
changeset 38133 78b95467b9f1
parent 38043 6d3cae25efbb
child 42040 70ec5a09a0d5
--- a/hotspot/src/share/vm/code/nmethod.hpp	Mon Apr 25 21:25:22 2016 +0300
+++ b/hotspot/src/share/vm/code/nmethod.hpp	Tue Apr 26 10:28:51 2016 +0200
@@ -25,67 +25,10 @@
 #ifndef SHARE_VM_CODE_NMETHOD_HPP
 #define SHARE_VM_CODE_NMETHOD_HPP
 
-#include "code/codeBlob.hpp"
-#include "code/pcDesc.hpp"
-#include "oops/metadata.hpp"
-
-class DirectiveSet;
-
-// This class is used internally by nmethods, to cache
-// exception/pc/handler information.
-
-class ExceptionCache : public CHeapObj<mtCode> {
-  friend class VMStructs;
- private:
-  enum { cache_size = 16 };
-  Klass*   _exception_type;
-  address  _pc[cache_size];
-  address  _handler[cache_size];
-  volatile int _count;
-  ExceptionCache* _next;
-
-  address pc_at(int index)                     { assert(index >= 0 && index < count(),""); return _pc[index]; }
-  void    set_pc_at(int index, address a)      { assert(index >= 0 && index < cache_size,""); _pc[index] = a; }
-  address handler_at(int index)                { assert(index >= 0 && index < count(),""); return _handler[index]; }
-  void    set_handler_at(int index, address a) { assert(index >= 0 && index < cache_size,""); _handler[index] = a; }
-  int     count()                              { return OrderAccess::load_acquire(&_count); }
-  // increment_count is only called under lock, but there may be concurrent readers.
-  void    increment_count()                    { OrderAccess::release_store(&_count, _count + 1); }
-
- public:
-
-  ExceptionCache(Handle exception, address pc, address handler);
+#include "code/compiledMethod.hpp"
 
-  Klass*    exception_type()                { return _exception_type; }
-  ExceptionCache* next()                    { return _next; }
-  void      set_next(ExceptionCache *ec)    { _next = ec; }
-
-  address match(Handle exception, address pc);
-  bool    match_exception_with_space(Handle exception) ;
-  address test_address(address addr);
-  bool    add_address_and_handler(address addr, address handler) ;
-};
-
-
-// cache pc descs found in earlier inquiries
-class PcDescCache VALUE_OBJ_CLASS_SPEC {
-  friend class VMStructs;
- private:
-  enum { cache_size = 4 };
-  // The array elements MUST be volatile! Several threads may modify
-  // and read from the cache concurrently. find_pc_desc_internal has
-  // returned wrong results. C++ compiler (namely xlC12) may duplicate
-  // C++ field accesses if the elements are not volatile.
-  typedef PcDesc* PcDescPtr;
-  volatile PcDescPtr _pc_descs[cache_size]; // last cache_size pc_descs found
- public:
-  PcDescCache() { debug_only(_pc_descs[0] = NULL); }
-  void    reset_to(PcDesc* initial_pc_desc);
-  PcDesc* find_pc_desc(int pc_offset, bool approximate);
-  void    add_pc_desc(PcDesc* pc_desc);
-  PcDesc* last_pc_desc() { return _pc_descs[0]; }
-};
-
+class DepChange;
+class DirectiveSet;
 
 // nmethods (native methods) are the compiled code versions of Java methods.
 //
@@ -108,26 +51,14 @@
 //  [Implicit Null Pointer exception table]
 //  - implicit null table array
 
-class DepChange;
-class Dependencies;
-class ExceptionHandlerTable;
-class ImplicitExceptionTable;
-class AbstractCompiler;
-class xmlStream;
-
-class nmethod : public CodeBlob {
+class nmethod : public CompiledMethod {
   friend class VMStructs;
   friend class JVMCIVMStructs;
   friend class NMethodSweeper;
   friend class CodeCache;  // scavengable oops
  private:
 
-  // GC support to help figure out if an nmethod has been
-  // cleaned/unloaded by the current GC.
-  static unsigned char _global_unloading_clock;
-
   // Shared fields for all nmethod's
-  Method*   _method;
   int       _entry_bci;        // != InvocationEntryBci if this nmethod is an on-stack replacement method
   jmethodID _jmethod_id;       // Cache of method()->jmethod_id()
 
@@ -140,13 +71,6 @@
   // To support simple linked-list chaining of nmethods:
   nmethod*  _osr_link;         // from InstanceKlass::osr_nmethods_head
 
-  union {
-    // Used by G1 to chain nmethods.
-    nmethod* _unloading_next;
-    // Used by non-G1 GCs to chain nmethods.
-    nmethod* _scavenge_root_link; // from CodeCache::scavenge_root_nmethods
-  };
-
   static nmethod* volatile _oops_do_mark_nmethods;
   nmethod*        volatile _oops_do_mark_link;
 
@@ -158,13 +82,7 @@
   address _osr_entry_point;                  // entry point for on stack replacement
 
   // Offsets for different nmethod parts
-  int _exception_offset;
-  // All deoptee's will resume execution at this location described by
-  // this offset.
-  int _deoptimize_offset;
-  // All deoptee's at a MethodHandle call site will resume execution
-  // at this location described by this offset.
-  int _deoptimize_mh_offset;
+  int  _exception_offset;
   // Offset of the unwind handler if it exists
   int _unwind_handler_offset;
 
@@ -179,6 +97,8 @@
   int _nul_chk_table_offset;
   int _nmethod_end_offset;
 
+  int code_offset() const { return (address) code_begin() - header_begin(); }
+
   // location in frame (offset for sp) that deopt can store the original
   // pc during a deopt.
   int _orig_pc_offset;
@@ -189,27 +109,12 @@
   // protected by CodeCache_lock
   bool _has_flushed_dependencies;            // Used for maintenance of dependencies (CodeCache_lock)
 
-  enum MarkForDeoptimizationStatus {
-    not_marked,
-    deoptimize,
-    deoptimize_noupdate };
-
-  MarkForDeoptimizationStatus _mark_for_deoptimization_status; // Used for stack deoptimization
-
   // used by jvmti to track if an unload event has been posted for this nmethod.
   bool _unload_reported;
 
-  // set during construction
-  unsigned int _has_unsafe_access:1;         // May fault due to unsafe access.
-  unsigned int _has_method_handle_invokes:1; // Has this method MethodHandle invokes?
-  unsigned int _lazy_critical_native:1;      // Lazy JNI critical native
-  unsigned int _has_wide_vectors:1;          // Preserve wide vectors at safepoints
-
   // Protected by Patching_lock
   volatile unsigned char _state;             // {in_use, not_entrant, zombie, unloaded}
 
-  volatile unsigned char _unloading_clock;   // Incremented after GC unloaded/cleaned the nmethod
-
 #ifdef ASSERT
   bool _oops_are_stale;  // indicates that it's no longer safe to access oops section
 #endif
@@ -242,9 +147,6 @@
   // counter is decreased (by 1) while sweeping.
   int _hotness_counter;
 
-  ExceptionCache * volatile _exception_cache;
-  PcDescCache     _pc_desc_cache;
-
   // These are used for compiled synchronized native methods to
   // locate the owner and stack slot for the BasicLock so that we can
   // properly revoke the bias of the owner if necessary. They are
@@ -302,18 +204,21 @@
   // Returns true if this thread changed the state of the nmethod or
   // false if another thread performed the transition.
   bool make_not_entrant_or_zombie(unsigned int state);
+  bool make_entrant() { Unimplemented(); return false; }
   void inc_decompile_count();
 
-  // Used to manipulate the exception cache
-  void add_exception_cache_entry(ExceptionCache* new_entry);
-  ExceptionCache* exception_cache_entry_for_exception(Handle exception);
-
   // Inform external interfaces that a compiled method has been unloaded
   void post_compiled_method_unload();
 
   // Initailize fields to their default values
   void init_defaults();
 
+  // Offsets
+  int content_offset() const                  { return content_begin() - header_begin(); }
+  int data_offset() const                     { return _data_offset; }
+
+  address header_end() const                  { return (address)    header_begin() + header_size(); }
+
  public:
   // create nmethod with entry_bci
   static nmethod* new_nmethod(const methodHandle& method,
@@ -334,7 +239,7 @@
                               , Handle installed_code = Handle(),
                               Handle speculation_log = Handle()
 #endif
-                             );
+  );
 
   static nmethod* new_native_nmethod(const methodHandle& method,
                                      int compile_id,
@@ -347,13 +252,10 @@
                                      OopMapSet* oop_maps);
 
   // accessors
-  Method* method() const                          { return _method; }
   AbstractCompiler* compiler() const              { return _compiler; }
 
   // type info
   bool is_nmethod() const                         { return true; }
-  bool is_java_method() const                     { return !method()->is_native(); }
-  bool is_native_method() const                   { return method()->is_native(); }
   bool is_osr_method() const                      { return _entry_bci != InvocationEntryBci; }
 
   bool is_compiled_by_c1() const;
@@ -363,22 +265,17 @@
 
   // boundaries for different parts
   address consts_begin          () const          { return           header_begin() + _consts_offset        ; }
-  address consts_end            () const          { return           header_begin() +  code_offset()        ; }
-  address insts_begin           () const          { return           header_begin() +  code_offset()        ; }
-  address insts_end             () const          { return           header_begin() + _stub_offset          ; }
+  address consts_end            () const          { return           code_begin()                           ; }
   address stub_begin            () const          { return           header_begin() + _stub_offset          ; }
   address stub_end              () const          { return           header_begin() + _oops_offset          ; }
   address exception_begin       () const          { return           header_begin() + _exception_offset     ; }
-  address deopt_handler_begin   () const          { return           header_begin() + _deoptimize_offset    ; }
-  address deopt_mh_handler_begin() const          { return           header_begin() + _deoptimize_mh_offset ; }
   address unwind_handler_begin  () const          { return _unwind_handler_offset != -1 ? (header_begin() + _unwind_handler_offset) : NULL; }
   oop*    oops_begin            () const          { return (oop*)   (header_begin() + _oops_offset)         ; }
   oop*    oops_end              () const          { return (oop*)   (header_begin() + _metadata_offset)     ; }
 
   Metadata** metadata_begin   () const            { return (Metadata**)  (header_begin() + _metadata_offset)     ; }
-  Metadata** metadata_end     () const            { return (Metadata**)  (header_begin() + _scopes_data_offset)  ; }
+  Metadata** metadata_end     () const            { return (Metadata**)  _scopes_data_begin; }
 
-  address scopes_data_begin     () const          { return           header_begin() + _scopes_data_offset   ; }
   address scopes_data_end       () const          { return           header_begin() + _scopes_pcs_offset    ; }
   PcDesc* scopes_pcs_begin      () const          { return (PcDesc*)(header_begin() + _scopes_pcs_offset   ); }
   PcDesc* scopes_pcs_end        () const          { return (PcDesc*)(header_begin() + _dependencies_offset) ; }
@@ -390,16 +287,9 @@
   address nul_chk_table_end     () const          { return           header_begin() + _nmethod_end_offset   ; }
 
   // Sizes
-  int consts_size       () const                  { return            consts_end       () -            consts_begin       (); }
-  int insts_size        () const                  { return            insts_end        () -            insts_begin        (); }
-  int stub_size         () const                  { return            stub_end         () -            stub_begin         (); }
   int oops_size         () const                  { return (address)  oops_end         () - (address)  oops_begin         (); }
   int metadata_size     () const                  { return (address)  metadata_end     () - (address)  metadata_begin     (); }
-  int scopes_data_size  () const                  { return            scopes_data_end  () -            scopes_data_begin  (); }
-  int scopes_pcs_size   () const                  { return (intptr_t) scopes_pcs_end   () - (intptr_t) scopes_pcs_begin   (); }
   int dependencies_size () const                  { return            dependencies_end () -            dependencies_begin (); }
-  int handler_table_size() const                  { return            handler_table_end() -            handler_table_begin(); }
-  int nul_chk_table_size() const                  { return            nul_chk_table_end() -            nul_chk_table_begin(); }
 
   int     oops_count() const { assert(oops_size() % oopSize == 0, "");  return (oops_size() / oopSize) + 1; }
   int metadata_count() const { assert(metadata_size() % wordSize == 0, ""); return (metadata_size() / wordSize) + 1; }
@@ -411,15 +301,10 @@
   int  hotness_counter() const      { return _hotness_counter; }
 
   // Containment
-  bool consts_contains       (address addr) const { return consts_begin       () <= addr && addr < consts_end       (); }
-  bool insts_contains        (address addr) const { return insts_begin        () <= addr && addr < insts_end        (); }
-  bool stub_contains         (address addr) const { return stub_begin         () <= addr && addr < stub_end         (); }
   bool oops_contains         (oop*    addr) const { return oops_begin         () <= addr && addr < oops_end         (); }
   bool metadata_contains     (Metadata** addr) const   { return metadata_begin     () <= addr && addr < metadata_end     (); }
   bool scopes_data_contains  (address addr) const { return scopes_data_begin  () <= addr && addr < scopes_data_end  (); }
   bool scopes_pcs_contains   (PcDesc* addr) const { return scopes_pcs_begin   () <= addr && addr < scopes_pcs_end   (); }
-  bool handler_table_contains(address addr) const { return handler_table_begin() <= addr && addr < handler_table_end(); }
-  bool nul_chk_table_contains(address addr) const { return nul_chk_table_begin() <= addr && addr < nul_chk_table_end(); }
 
   // entry points
   address entry_point() const                     { return _entry_point;             } // normal entry point
@@ -434,24 +319,11 @@
 
   // flag accessing and manipulation
   bool  is_in_use() const                         { return _state == in_use; }
-  bool  is_alive() const                          { unsigned char s = _state; return s == in_use || s == not_entrant; }
+  bool  is_alive() const                          { unsigned char s = _state; return s < zombie; }
   bool  is_not_entrant() const                    { return _state == not_entrant; }
   bool  is_zombie() const                         { return _state == zombie; }
   bool  is_unloaded() const                       { return _state == unloaded; }
 
-  // returns a string version of the nmethod state
-  const char* state() const {
-    switch(_state) {
-      case in_use:      return "in use";
-      case not_entrant: return "not_entrant";
-      case zombie:      return "zombie";
-      case unloaded:    return "unloaded";
-      default:
-        fatal("unexpected nmethod state: %d", _state);
-        return NULL;
-    }
-  }
-
 #if INCLUDE_RTM_OPT
   // rtm state accessing and manipulating
   RTMState  rtm_state() const                     { return _rtm_state; }
@@ -466,30 +338,15 @@
     assert(!method()->is_method_handle_intrinsic(), "Cannot make MH intrinsic not entrant");
     return make_not_entrant_or_zombie(not_entrant);
   }
+  bool  make_not_used()    { return make_not_entrant(); }
   bool  make_zombie()      { return make_not_entrant_or_zombie(zombie); }
 
   // used by jvmti to track if the unload event has been reported
   bool  unload_reported()                         { return _unload_reported; }
   void  set_unload_reported()                     { _unload_reported = true; }
 
-  void set_unloading_next(nmethod* next)          { _unloading_next = next; }
-  nmethod* unloading_next()                       { return _unloading_next; }
-
-  static unsigned char global_unloading_clock()   { return _global_unloading_clock; }
-  static void increase_unloading_clock();
-
-  void set_unloading_clock(unsigned char unloading_clock);
-  unsigned char unloading_clock();
-
-  bool  is_marked_for_deoptimization() const      { return _mark_for_deoptimization_status != not_marked; }
-  void  mark_for_deoptimization(bool inc_recompile_counts = true) {
-    _mark_for_deoptimization_status = (inc_recompile_counts ? deoptimize : deoptimize_noupdate);
-  }
-  bool update_recompile_counts() const {
-    // Update recompile counts when either the update is explicitly requested (deoptimize)
-    // or the nmethod is not marked for deoptimization at all (not_marked).
-    // The latter happens during uncommon traps when deoptimized nmethod is made not entrant.
-    return _mark_for_deoptimization_status != deoptimize_noupdate;
+  int get_state() const {
+    return _state;
   }
 
   void  make_unloaded(BoolObjectClosure* is_alive, oop cause);
@@ -502,18 +359,6 @@
     _has_flushed_dependencies = 1;
   }
 
-  bool  has_unsafe_access() const                 { return _has_unsafe_access; }
-  void  set_has_unsafe_access(bool z)             { _has_unsafe_access = z; }
-
-  bool  has_method_handle_invokes() const         { return _has_method_handle_invokes; }
-  void  set_has_method_handle_invokes(bool z)     { _has_method_handle_invokes = z; }
-
-  bool  is_lazy_critical_native() const           { return _lazy_critical_native; }
-  void  set_lazy_critical_native(bool z)          { _lazy_critical_native = z; }
-
-  bool  has_wide_vectors() const                  { return _has_wide_vectors; }
-  void  set_has_wide_vectors(bool z)              { _has_wide_vectors = z; }
-
   int   comp_level() const                        { return _comp_level; }
 
   // Support for oops in scopes and relocs:
@@ -538,9 +383,6 @@
   void copy_values(GrowableArray<jobject>* oops);
   void copy_values(GrowableArray<Metadata*>* metadata);
 
-  Method* attached_method(address call_pc);
-  Method* attached_method_before_pc(address pc);
-
   // Relocation support
 private:
   void fix_oop_relocations(address begin, address end, bool initialize_immediates);
@@ -549,10 +391,6 @@
 public:
   void fix_oop_relocations(address begin, address end) { fix_oop_relocations(begin, end, false); }
   void fix_oop_relocations()                           { fix_oop_relocations(NULL, NULL, false); }
-  void verify_oop_relocations();
-
-  bool is_at_poll_return(address pc);
-  bool is_at_poll_or_poll_return(address pc);
 
   // Scavengable oop support
   bool  on_scavenge_root_list() const                  { return (_scavenge_root_state & 1) != 0; }
@@ -576,15 +414,6 @@
   long  stack_traversal_mark()                    { return _stack_traversal_mark; }
   void  set_stack_traversal_mark(long l)          { _stack_traversal_mark = l; }
 
-  // Exception cache support
-  // Note: _exception_cache may be read concurrently. We rely on memory_order_consume here.
-  ExceptionCache* exception_cache() const         { return _exception_cache; }
-  void set_exception_cache(ExceptionCache *ec)    { _exception_cache = ec; }
-  void release_set_exception_cache(ExceptionCache *ec) { OrderAccess::release_store_ptr(&_exception_cache, ec); }
-  address handler_for_exception_and_pc(Handle exception, address pc);
-  void add_handler_for_exception_and_pc(Handle exception, address pc, address handler);
-  void clean_exception_cache(BoolObjectClosure* is_alive);
-
   // implicit exceptions support
   address continuation_for_implicit_exception(address pc);
 
@@ -595,24 +424,8 @@
   nmethod* osr_link() const                       { return _osr_link; }
   void     set_osr_link(nmethod *n)               { _osr_link = n; }
 
-  // tells whether frames described by this nmethod can be deoptimized
-  // note: native wrappers cannot be deoptimized.
-  bool can_be_deoptimized() const { return is_java_method(); }
-
-  // Inline cache support
-  void clear_inline_caches();
-  void clear_ic_stubs();
-  void cleanup_inline_caches(bool clean_all = false);
-  bool inlinecache_check_contains(address addr) const {
-    return (addr >= code_begin() && addr < verified_entry_point());
-  }
-
   // Verify calls to dead methods have been cleaned.
   void verify_clean_inline_caches();
-  // Verify and count cached icholder relocations.
-  int  verify_icholder_relocations();
-  // Check that all metadata is still alive
-  void verify_metadata_loaders(address low_boundary, BoolObjectClosure* is_alive);
 
   // unlink and deallocate this nmethod
   // Only NMethodSweeper class is expected to use this. NMethodSweeper is not
@@ -653,20 +466,19 @@
  public:
 #endif
 
-  // GC support
-  void do_unloading(BoolObjectClosure* is_alive, bool unloading_occurred);
-  //  The parallel versions are used by G1.
-  bool do_unloading_parallel(BoolObjectClosure* is_alive, bool unloading_occurred);
-  void do_unloading_parallel_postponed(BoolObjectClosure* is_alive, bool unloading_occurred);
+ protected:
+  virtual bool do_unloading_oops(address low_boundary, BoolObjectClosure* is_alive, bool unloading_occurred);
+#if INCLUDE_JVMCI
+  virtual bool do_unloading_jvmci(BoolObjectClosure* is_alive, bool unloading_occurred);
+#endif
 
  private:
+  bool do_unloading_scopes(BoolObjectClosure* is_alive, bool unloading_occurred);
   //  Unload a nmethod if the *root object is dead.
   bool can_unload(BoolObjectClosure* is_alive, oop* root, bool unloading_occurred);
   bool unload_if_dead_at(RelocIterator *iter_at_oop, BoolObjectClosure* is_alive, bool unloading_occurred);
 
  public:
-  void preserve_callee_argument_oops(frame fr, const RegisterMap *reg_map,
-                                     OopClosure* f);
   void oops_do(OopClosure* f) { oops_do(f, false); }
   void oops_do(OopClosure* f, bool allow_zombie);
   bool detect_scavenge_root_oops();
@@ -678,49 +490,20 @@
   static bool oops_do_marking_is_active() { return _oops_do_mark_nmethods != NULL; }
   bool test_oops_do_mark() { return _oops_do_mark_link != NULL; }
 
-  // ScopeDesc for an instruction
-  ScopeDesc* scope_desc_at(address pc);
-
  private:
   ScopeDesc* scope_desc_in(address begin, address end);
 
   address* orig_pc_addr(const frame* fr) { return (address*) ((address)fr->unextended_sp() + _orig_pc_offset); }
 
-  PcDesc* find_pc_desc_internal(address pc, bool approximate);
-
-  PcDesc* find_pc_desc(address pc, bool approximate) {
-    PcDesc* desc = _pc_desc_cache.last_pc_desc();
-    if (desc != NULL && desc->pc_offset() == pc - code_begin()) {
-      return desc;
-    }
-    return find_pc_desc_internal(pc, approximate);
-  }
-
- public:
-  // ScopeDesc retrieval operation
-  PcDesc* pc_desc_at(address pc)   { return find_pc_desc(pc, false); }
-  // pc_desc_near returns the first PcDesc at or after the givne pc.
-  PcDesc* pc_desc_near(address pc) { return find_pc_desc(pc, true); }
-
  public:
   // copying of debugging information
   void copy_scopes_pcs(PcDesc* pcs, int count);
   void copy_scopes_data(address buffer, int size);
 
-  // Deopt
-  // Return true is the PC is one would expect if the frame is being deopted.
-  bool is_deopt_pc      (address pc) { return is_deopt_entry(pc) || is_deopt_mh_entry(pc); }
-  bool is_deopt_entry   (address pc);
-  bool is_deopt_mh_entry(address pc) { return pc == deopt_mh_handler_begin(); }
   // Accessor/mutator for the original pc of a frame before a frame was deopted.
   address get_original_pc(const frame* fr) { return *orig_pc_addr(fr); }
   void    set_original_pc(const frame* fr, address pc) { *orig_pc_addr(fr) = pc; }
 
-  static address get_deopt_original_pc(const frame* fr);
-
-  // MethodHandle
-  bool is_method_handle_return(address return_pc);
-
   // jvmti support:
   void post_compiled_method_load_event();
   jmethodID get_and_cache_jmethod_id();
@@ -770,7 +553,7 @@
   // are numbered in an independent sequence if CICountOSR is true,
   // and native method wrappers are also numbered independently if
   // CICountNative is true.
-  int  compile_id() const                         { return _compile_id; }
+  virtual int compile_id() const { return _compile_id; }
   const char* compile_kind() const;
 
   // tells if any of this method's dependencies have been invalidated
@@ -789,7 +572,7 @@
   // Fast breakpoint support. Tells if this compiled method is
   // dependent on the given method. Returns true if this nmethod
   // corresponds to the given method as well.
-  bool is_dependent_on_method(Method* dependee);
+  virtual bool is_dependent_on_method(Method* dependee);
 
   // is it ok to patch at address?
   bool is_patchable_at(address instr_address);
@@ -807,12 +590,7 @@
   static int osr_entry_point_offset()             { return offset_of(nmethod, _osr_entry_point); }
   static int state_offset()                       { return offset_of(nmethod, _state); }
 
-  // RedefineClasses support.   Mark metadata in nmethods as on_stack so that
-  // redefine classes doesn't purge it.
-  static void mark_on_stack(nmethod* nm) {
-    nm->metadata_do(Metadata::mark_on_stack);
-  }
-  void metadata_do(void f(Metadata*));
+  virtual void metadata_do(void f(Metadata*));
 };
 
 // Locks an nmethod so its code will not get removed and it will not
@@ -821,26 +599,43 @@
 // needs to be done, then lock_nmethod() is used directly to keep the
 // generated code from being reused too early.
 class nmethodLocker : public StackObj {
-  nmethod* _nm;
+  CompiledMethod* _nm;
 
  public:
 
   // note: nm can be NULL
   // Only JvmtiDeferredEvent::compiled_method_unload_event()
   // should pass zombie_ok == true.
-  static void lock_nmethod(nmethod* nm, bool zombie_ok = false);
-  static void unlock_nmethod(nmethod* nm); // (ditto)
+  static void lock_nmethod(CompiledMethod* nm, bool zombie_ok = false);
+  static void unlock_nmethod(CompiledMethod* nm); // (ditto)
 
   nmethodLocker(address pc); // derive nm from pc
   nmethodLocker(nmethod *nm) { _nm = nm; lock_nmethod(_nm); }
-  nmethodLocker() { _nm = NULL; }
-  ~nmethodLocker() { unlock_nmethod(_nm); }
+  nmethodLocker(CompiledMethod *nm) {
+    _nm = nm;
+    lock(_nm);
+  }
+
+  static void lock(CompiledMethod* method) {
+    if (method == NULL) return;
+    lock_nmethod(method);
+  }
 
-  nmethod* code() { return _nm; }
-  void set_code(nmethod* new_nm) {
-    unlock_nmethod(_nm);   // note:  This works even if _nm==new_nm.
+  static void unlock(CompiledMethod* method) {
+    if (method == NULL) return;
+    unlock_nmethod(method);
+  }
+
+  nmethodLocker() { _nm = NULL; }
+  ~nmethodLocker() {
+    unlock(_nm);
+  }
+
+  CompiledMethod* code() { return _nm; }
+  void set_code(CompiledMethod* new_nm) {
+    unlock(_nm);   // note:  This works even if _nm==new_nm.
     _nm = new_nm;
-    lock_nmethod(_nm);
+    lock(_nm);
   }
 };