hotspot/src/share/vm/memory/defNewGeneration.inline.hpp
author ysr
Wed, 07 Sep 2011 13:55:42 -0700
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4965777: GC changes to support use of discovered field for pending references Summary: If and when the reference handler thread is able to use the discovered field to link reference objects in its pending list, so will GC. In that case, GC will scan through this field once a reference object has been placed on the pending list, but not scan that field before that stage, as the field is used by the concurrent GC thread to link discovered objects. When ReferenceHandleR thread does not use the discovered field for the purpose of linking the elements in the pending list, as would be the case in older JDKs, the JVM will fall back to the old behaviour of using the next field for that purpose. Reviewed-by: jcoomes, mchung, stefank
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/*
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 * Copyright (c) 2001, 2010, Oracle and/or its affiliates. All rights reserved.
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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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 *
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 * This code is free software; you can redistribute it and/or modify it
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 * under the terms of the GNU General Public License version 2 only, as
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 * published by the Free Software Foundation.
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 *
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 * This code is distributed in the hope that it will be useful, but WITHOUT
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 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
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 * version 2 for more details (a copy is included in the LICENSE file that
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 * accompanied this code).
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 *
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 * You should have received a copy of the GNU General Public License version
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 * 2 along with this work; if not, write to the Free Software Foundation,
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 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
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 *
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 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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 * or visit www.oracle.com if you need additional information or have any
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 * questions.
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 *
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 */
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#ifndef SHARE_VM_MEMORY_DEFNEWGENERATION_INLINE_HPP
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#define SHARE_VM_MEMORY_DEFNEWGENERATION_INLINE_HPP
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#include "memory/cardTableRS.hpp"
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#include "memory/defNewGeneration.hpp"
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#include "memory/space.hpp"
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// Methods of protected closure types
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template <class T>
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inline void DefNewGeneration::KeepAliveClosure::do_oop_work(T* p) {
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#ifdef ASSERT
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  {
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    // We never expect to see a null reference being processed
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    // as a weak reference.
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    assert (!oopDesc::is_null(*p), "expected non-null ref");
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    oop obj = oopDesc::load_decode_heap_oop_not_null(p);
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    assert (obj->is_oop(), "expected an oop while scanning weak refs");
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  }
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#endif // ASSERT
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  _cl->do_oop_nv(p);
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  // Card marking is trickier for weak refs.
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  // This oop is a 'next' field which was filled in while we
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  // were discovering weak references. While we might not need
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  // to take a special action to keep this reference alive, we
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  // will need to dirty a card as the field was modified.
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  //
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  // Alternatively, we could create a method which iterates through
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  // each generation, allowing them in turn to examine the modified
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  // field.
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  //
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  // We could check that p is also in an older generation, but
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  // dirty cards in the youngest gen are never scanned, so the
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  // extra check probably isn't worthwhile.
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  if (Universe::heap()->is_in_reserved(p)) {
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    oop obj = oopDesc::load_decode_heap_oop_not_null(p);
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    _rs->inline_write_ref_field_gc(p, obj);
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  }
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}
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template <class T>
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inline void DefNewGeneration::FastKeepAliveClosure::do_oop_work(T* p) {
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#ifdef ASSERT
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  {
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    // We never expect to see a null reference being processed
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    // as a weak reference.
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    assert (!oopDesc::is_null(*p), "expected non-null ref");
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    oop obj = oopDesc::load_decode_heap_oop_not_null(p);
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    assert (obj->is_oop(), "expected an oop while scanning weak refs");
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  }
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#endif // ASSERT
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  _cl->do_oop_nv(p);
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  // Optimized for Defnew generation if it's the youngest generation:
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  // we set a younger_gen card if we have an older->youngest
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  // generation pointer.
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  oop obj = oopDesc::load_decode_heap_oop_not_null(p);
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  if (((HeapWord*)obj < _boundary) && Universe::heap()->is_in_reserved(p)) {
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    _rs->inline_write_ref_field_gc(p, obj);
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  }
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}
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#endif // SHARE_VM_MEMORY_DEFNEWGENERATION_INLINE_HPP