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/*
* Copyright (c) 2014, 2021, 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.
*
*/
#ifndef SHARE_GC_G1_G1STRINGDEDUP_HPP
#define SHARE_GC_G1_G1STRINGDEDUP_HPP
//
// G1 string deduplication candidate selection
//
// An object is considered a deduplication candidate if all of the following
// statements are true:
//
// - The object is an instance of java.lang.String
//
// - The object is being evacuated from a young heap region
//
// - The object is being evacuated to a young/survivor heap region and the
// object's age is equal to the deduplication age threshold
//
// or
//
// The object is being evacuated to an old heap region and the object's age is
// less than the deduplication age threshold
//
// Once an string object has been promoted to an old region, or its age is higher
// than the deduplication age threshold, is will never become a candidate again.
// This approach avoids making the same object a candidate more than once.
//
#include "gc/g1/g1HeapRegionAttr.hpp"
#include "gc/shared/stringdedup/stringDedup.hpp"
#include "memory/allStatic.hpp"
#include "oops/oopsHierarchy.hpp"
class G1StringDedup : AllStatic {
public:
// Candidate selection policy for full GC, returning true if the given
// String is a candidate for string deduplication.
// precondition: StringDedup::is_enabled()
// precondition: java_string is a Java String
static bool is_candidate_from_mark(oop java_string);
// Candidate selection policy for young/mixed GC.
// If to is young then age should be the new (survivor's) age.
// if to is old then age should be the age of the copied from object.
static bool is_candidate_from_evacuation(const Klass* klass,
G1HeapRegionAttr from,
G1HeapRegionAttr to,
uint age) {
return StringDedup::is_enabled_string(klass) &&
from.is_young() &&
(to.is_young() ?
StringDedup::is_threshold_age(age) :
StringDedup::is_below_threshold_age(age));
}
};
#endif // SHARE_GC_G1_G1STRINGDEDUP_HPP
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