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hotspot/src/share/vm/runtime/handles.hpp

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+/*
+ * Copyright 1997-2007 Sun Microsystems, Inc.  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 Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
+ * CA 95054 USA or visit www.sun.com if you need additional information or
+ * have any questions.
+ *
+ */
+
+//------------------------------------------------------------------------------------------------------------------------
+// In order to preserve oops during garbage collection, they should be
+// allocated and passed around via Handles within the VM. A handle is
+// simply an extra indirection allocated in a thread local handle area.
+//
+// A handle is a ValueObj, so it can be passed around as a value, can
+// be used as a parameter w/o using &-passing, and can be returned as a
+// return value.
+//
+// oop parameters and return types should be Handles whenever feasible.
+//
+// Handles are declared in a straight-forward manner, e.g.
+//
+//   oop obj = ...;
+//   Handle h1(obj);              // allocate new handle
+//   Handle h2(thread, obj);      // faster allocation when current thread is known
+//   Handle h3;                   // declare handle only, no allocation occurs
+//   ...
+//   h3 = h1;                     // make h3 refer to same indirection as h1
+//   oop obj2 = h2();             // get handle value
+//   h1->print();                 // invoking operation on oop
+//
+// Handles are specialized for different oop types to provide extra type
+// information and avoid unnecessary casting. For each oop type xxxOop
+// there is a corresponding handle called xxxHandle, e.g.
+//
+//   oop           Handle
+//   methodOop     methodHandle
+//   instanceOop   instanceHandle
+//
+// For klassOops, it is often useful to model the Klass hierarchy in order
+// to get access to the klass_part without casting. For each xxxKlass there
+// is a corresponding handle called xxxKlassHandle, e.g.
+//
+//   klassOop      Klass           KlassHandle
+//   klassOop      methodKlass     methodKlassHandle
+//   klassOop      instanceKlass   instanceKlassHandle
+//
+
+//------------------------------------------------------------------------------------------------------------------------
+// Base class for all handles. Provides overloading of frequently
+// used operators for ease of use.
+
+class Handle VALUE_OBJ_CLASS_SPEC {
+ private:
+  oop* _handle;
+
+ protected:
+  oop     obj() const                            { return _handle == NULL ? (oop)NULL : *_handle; }
+  oop     non_null_obj() const                   { assert(_handle != NULL, "resolving NULL handle"); return *_handle; }
+
+ public:
+  // Constructors
+  Handle()                                       { _handle = NULL; }
+  Handle(oop obj);
+#ifndef ASSERT
+  Handle(Thread* thread, oop obj);
+#else
+  // Don't inline body with assert for current thread
+  Handle(Thread* thread, oop obj);
+#endif // ASSERT
+
+  // General access
+  oop     operator () () const                   { return obj(); }
+  oop     operator -> () const                   { return non_null_obj(); }
+  bool    operator == (oop o) const              { return obj() == o; }
+  bool    operator == (const Handle& h) const          { return obj() == h.obj(); }
+
+  // Null checks
+  bool    is_null() const                        { return _handle == NULL; }
+  bool    not_null() const                       { return _handle != NULL; }
+
+  // Debugging
+  void    print()                                { obj()->print(); }
+
+  // Direct interface, use very sparingly.
+  // Used by JavaCalls to quickly convert handles and to create handles static data structures.
+  // Constructor takes a dummy argument to prevent unintentional type conversion in C++.
+  Handle(oop *handle, bool dummy)                { _handle = handle; }
+
+  // Raw handle access. Allows easy duplication of Handles. This can be very unsafe
+  // since duplicates is only valid as long as original handle is alive.
+  oop* raw_value()                               { return _handle; }
+  static oop raw_resolve(oop *handle)            { return handle == NULL ? (oop)NULL : *handle; }
+};
+
+
+//------------------------------------------------------------------------------------------------------------------------
+// Base class for Handles containing klassOops. Provides overloading of frequently
+// used operators for ease of use and typed access to the Klass part.
+class KlassHandle: public Handle {
+ protected:
+  klassOop    obj() const                        { return (klassOop)Handle::obj(); }
+  klassOop    non_null_obj() const               { return (klassOop)Handle::non_null_obj(); }
+  Klass*      as_klass() const                   { return non_null_obj()->klass_part(); }
+
+ public:
+  // Constructors
+  KlassHandle ()                                 : Handle()            {}
+  KlassHandle (oop obj) : Handle(obj) {
+    assert(SharedSkipVerify || is_null() || obj->is_klass(), "not a klassOop");
+  }
+  KlassHandle (Klass* kl) : Handle(kl ? kl->as_klassOop() : (klassOop)NULL) {
+    assert(SharedSkipVerify || is_null() || obj()->is_klass(), "not a klassOop");
+  }
+
+  // Faster versions passing Thread
+  KlassHandle (Thread* thread, oop obj) : Handle(thread, obj) {
+    assert(SharedSkipVerify || is_null() || obj->is_klass(), "not a klassOop");
+  }
+  KlassHandle (Thread *thread, Klass* kl)
+    : Handle(thread, kl ? kl->as_klassOop() : (klassOop)NULL) {
+    assert(is_null() || obj()->is_klass(), "not a klassOop");
+  }
+
+  // General access
+  klassOop    operator () () const               { return obj(); }
+  Klass*      operator -> () const               { return as_klass(); }
+};
+
+
+//------------------------------------------------------------------------------------------------------------------------
+// Specific Handles for different oop types
+#define DEF_HANDLE(type, is_a)                   \
+  class type##Handle;                            \
+  class type##Handle: public Handle {            \
+   protected:                                    \
+    type##Oop    obj() const                     { return (type##Oop)Handle::obj(); } \
+    type##Oop    non_null_obj() const            { return (type##Oop)Handle::non_null_obj(); } \
+                                                 \
+   public:                                       \
+    /* Constructors */                           \
+    type##Handle ()                              : Handle()                 {} \
+    type##Handle (type##Oop obj) : Handle((oop)obj) {                         \
+      assert(SharedSkipVerify || is_null() || ((oop)obj)->is_a(),             \
+             "illegal type");                                                 \
+    }                                                                         \
+    type##Handle (Thread* thread, type##Oop obj) : Handle(thread, (oop)obj) { \
+      assert(SharedSkipVerify || is_null() || ((oop)obj)->is_a(), "illegal type");  \
+    }                                                                         \
+    \
+    /* Special constructor, use sparingly */ \
+    type##Handle (type##Oop *handle, bool dummy) : Handle((oop*)handle, dummy) {} \
+                                                 \
+    /* Operators for ease of use */              \
+    type##Oop    operator () () const            { return obj(); } \
+    type##Oop    operator -> () const            { return non_null_obj(); } \
+  };
+
+
+DEF_HANDLE(instance         , is_instance         )
+DEF_HANDLE(method           , is_method           )
+DEF_HANDLE(constMethod      , is_constMethod      )
+DEF_HANDLE(methodData       , is_methodData       )
+DEF_HANDLE(array            , is_array            )
+DEF_HANDLE(constantPool     , is_constantPool     )
+DEF_HANDLE(constantPoolCache, is_constantPoolCache)
+DEF_HANDLE(objArray         , is_objArray         )
+DEF_HANDLE(typeArray        , is_typeArray        )
+DEF_HANDLE(symbol           , is_symbol           )
+
+//------------------------------------------------------------------------------------------------------------------------
+// Specific KlassHandles for different Klass types
+
+#define DEF_KLASS_HANDLE(type, is_a)             \
+  class type##Handle : public KlassHandle {      \
+   public:                                       \
+    /* Constructors */                           \
+    type##Handle ()                              : KlassHandle()           {} \
+    type##Handle (klassOop obj) : KlassHandle(obj) {                          \
+      assert(SharedSkipVerify || is_null() || obj->klass_part()->is_a(),      \
+             "illegal type");                                                 \
+    }                                                                         \
+    type##Handle (Thread* thread, klassOop obj) : KlassHandle(thread, obj) {  \
+      assert(SharedSkipVerify || is_null() || obj->klass_part()->is_a(),      \
+             "illegal type");                                                 \
+    }                                                                         \
+                                                 \
+    /* Access to klass part */                   \
+    type*        operator -> () const            { return (type*)obj()->klass_part(); } \
+                                                 \
+    static type##Handle cast(KlassHandle h)      { return type##Handle(h()); } \
+                                                 \
+  };
+
+
+DEF_KLASS_HANDLE(instanceKlass         , oop_is_instance_slow )
+DEF_KLASS_HANDLE(methodKlass           , oop_is_method        )
+DEF_KLASS_HANDLE(constMethodKlass      , oop_is_constMethod   )
+DEF_KLASS_HANDLE(klassKlass            , oop_is_klass         )
+DEF_KLASS_HANDLE(arrayKlassKlass       , oop_is_arrayKlass    )
+DEF_KLASS_HANDLE(objArrayKlassKlass    , oop_is_objArrayKlass )
+DEF_KLASS_HANDLE(typeArrayKlassKlass   , oop_is_typeArrayKlass)
+DEF_KLASS_HANDLE(arrayKlass            , oop_is_array         )
+DEF_KLASS_HANDLE(typeArrayKlass        , oop_is_typeArray_slow)
+DEF_KLASS_HANDLE(objArrayKlass         , oop_is_objArray_slow )
+DEF_KLASS_HANDLE(symbolKlass           , oop_is_symbol        )
+DEF_KLASS_HANDLE(constantPoolKlass     , oop_is_constantPool  )
+DEF_KLASS_HANDLE(constantPoolCacheKlass, oop_is_constantPool  )
+
+
+//------------------------------------------------------------------------------------------------------------------------
+// Thread local handle area
+
+class HandleArea: public Arena {
+  friend class HandleMark;
+  friend class NoHandleMark;
+  friend class ResetNoHandleMark;
+#ifdef ASSERT
+  int _handle_mark_nesting;
+  int _no_handle_mark_nesting;
+#endif
+  HandleArea* _prev;          // link to outer (older) area
+ public:
+  // Constructor
+  HandleArea(HandleArea* prev) {
+    debug_only(_handle_mark_nesting    = 0);
+    debug_only(_no_handle_mark_nesting = 0);
+    _prev = prev;
+  }
+
+  // Handle allocation
+ private:
+  oop* real_allocate_handle(oop obj) {
+#ifdef ASSERT
+    oop* handle = (oop*) (UseMallocOnly ? internal_malloc_4(oopSize) : Amalloc_4(oopSize));
+#else
+    oop* handle = (oop*) Amalloc_4(oopSize);
+#endif
+    *handle = obj;
+    return handle;
+  }
+ public:
+#ifdef ASSERT
+  oop* allocate_handle(oop obj);
+#else
+  oop* allocate_handle(oop obj) { return real_allocate_handle(obj); }
+#endif
+
+  // Garbage collection support
+  void oops_do(OopClosure* f);
+
+  // Number of handles in use
+  size_t used() const     { return Arena::used() / oopSize; }
+
+  debug_only(bool no_handle_mark_active() { return _no_handle_mark_nesting > 0; })
+};
+
+
+//------------------------------------------------------------------------------------------------------------------------
+// Handles are allocated in a (growable) thread local handle area. Deallocation
+// is managed using a HandleMark. It should normally not be necessary to use
+// HandleMarks manually.
+//
+// A HandleMark constructor will record the current handle area top, and the
+// desctructor will reset the top, destroying all handles allocated in between.
+// The following code will therefore NOT work:
+//
+//   Handle h;
+//   {
+//     HandleMark hm;
+//     h = Handle(obj);
+//   }
+//   h()->print();       // WRONG, h destroyed by HandleMark destructor.
+//
+// If h has to be preserved, it can be converted to an oop or a local JNI handle
+// across the HandleMark boundary.
+
+// The base class of HandleMark should have been StackObj but we also heap allocate
+// a HandleMark when a thread is created.
+
+class HandleMark {
+ private:
+  Thread *_thread;              // thread that owns this mark
+  HandleArea *_area;            // saved handle area
+  Chunk *_chunk;                // saved arena chunk
+  char *_hwm, *_max;            // saved arena info
+  NOT_PRODUCT(size_t _size_in_bytes;) // size of handle area
+  // Link to previous active HandleMark in thread
+  HandleMark* _previous_handle_mark;
+
+  void initialize(Thread* thread);                // common code for constructors
+  void set_previous_handle_mark(HandleMark* mark) { _previous_handle_mark = mark; }
+  HandleMark* previous_handle_mark() const        { return _previous_handle_mark; }
+
+ public:
+  HandleMark();                            // see handles_inline.hpp
+  HandleMark(Thread* thread)                      { initialize(thread); }
+  ~HandleMark();
+
+  // Functions used by HandleMarkCleaner
+  // called in the constructor of HandleMarkCleaner
+  void push();
+  // called in the destructor of HandleMarkCleaner
+  void pop_and_restore();
+};
+
+//------------------------------------------------------------------------------------------------------------------------
+// A NoHandleMark stack object will verify that no handles are allocated
+// in its scope. Enabled in debug mode only.
+
+class NoHandleMark: public StackObj {
+ public:
+#ifdef ASSERT
+  NoHandleMark();
+  ~NoHandleMark();
+#else
+  NoHandleMark()  {}
+  ~NoHandleMark() {}
+#endif
+};
+
+
+class ResetNoHandleMark: public StackObj {
+  int _no_handle_mark_nesting;
+ public:
+#ifdef ASSERT
+  ResetNoHandleMark();
+  ~ResetNoHandleMark();
+#else
+  ResetNoHandleMark()  {}
+  ~ResetNoHandleMark() {}
+#endif
+};