Mercurial > hg > graal-jvmci-8
view src/share/vm/runtime/handles.hpp @ 1716:be3f9c242c9d
6948538: CMS: BOT walkers can fall into object allocation and initialization cracks
Summary: GC workers now recognize an intermediate transient state of blocks which are allocated but have not yet completed initialization. blk_start() calls do not attempt to determine the size of a block in the transient state, rather waiting for the block to become initialized so that it is safe to query its size. Audited and ensured the order of initialization of object fields (klass, free bit and size) to respect block state transition protocol. Also included some new assertion checking code enabled in debug mode.
Reviewed-by: chrisphi, johnc, poonam
author | ysr |
---|---|
date | Mon, 16 Aug 2010 15:58:42 -0700 |
parents | c18cbe5936b8 |
children | f95d63e2154a |
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/* * Copyright (c) 1997, 2009, 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. * */ //------------------------------------------------------------------------------------------------------------------------ // 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"); } // Direct interface, use very sparingly. // Used by SystemDictionaryHandles to create handles on existing WKKs. // The obj of such a klass handle may be null, because the handle is formed // during system bootstrapping. KlassHandle(klassOop *handle, bool dummy) : Handle((oop*)handle, dummy) { assert(SharedSkipVerify || is_null() || obj() == 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 };