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/*
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* Copyright (c) 2017, 2018, 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_JFR_UTILITIES_JFRREFCOUNTPOINTER_HPP
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#define SHARE_VM_JFR_UTILITIES_JFRREFCOUNTPOINTER_HPP
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#include "jfr/utilities/jfrAllocation.hpp"
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#include "runtime/atomic.hpp"
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template <typename T>
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class RefCountHandle {
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template <typename, typename>
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friend class RefCountPointer;
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private:
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const T* _ptr;
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RefCountHandle(const T* ptr) : _ptr(ptr) {
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assert(_ptr != NULL, "invariant");
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_ptr->add_ref();
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}
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public:
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RefCountHandle() : _ptr(NULL) {}
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RefCountHandle(const RefCountHandle<T>& rhs) : _ptr(rhs._ptr) {
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if (_ptr != NULL) {
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_ptr->add_ref();
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}
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}
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~RefCountHandle() {
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if (_ptr != NULL) {
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const T* temp = _ptr;
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_ptr = NULL;
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temp->remove_ref();
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}
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}
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// The copy-and-swap idiom upholds reference counting semantics
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void operator=(RefCountHandle<T> rhs) {
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const T* temp = rhs._ptr;
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rhs._ptr = _ptr;
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_ptr = temp;
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}
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bool operator==(const RefCountHandle<T>& rhs) const {
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return _ptr == rhs._ptr;
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}
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bool operator!=(const RefCountHandle<T>& rhs) const {
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return !operator==(rhs);
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}
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bool valid() const {
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return _ptr != NULL;
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}
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const T & operator->() const {
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return *_ptr;
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}
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T& operator->() {
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return *const_cast<T*>(_ptr);
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}
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};
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class MultiThreadedRefCounter {
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private:
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mutable volatile int _refs;
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public:
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MultiThreadedRefCounter() : _refs(0) {}
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void inc() const {
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Atomic::add(1, &_refs);
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}
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bool dec() const {
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return 0 == Atomic::add((-1), &_refs);
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}
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int current() const {
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return _refs;
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}
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};
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template <typename T, typename RefCountImpl = MultiThreadedRefCounter>
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class RefCountPointer : public JfrCHeapObj {
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template <typename>
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friend class RefCountHandle;
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typedef RefCountHandle<RefCountPointer<T, RefCountImpl> > RefHandle;
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private:
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const T* _ptr;
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mutable RefCountImpl _refs;
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// disallow multiple copies
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RefCountPointer(const RefCountPointer<T, RefCountImpl>& rhs);
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void operator=(const RefCountPointer<T, RefCountImpl>& rhs);
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~RefCountPointer() {
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assert(_refs.current() == 0, "invariant");
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delete const_cast<T*>(_ptr);
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}
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void add_ref() const {
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_refs.inc();
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}
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void remove_ref() const {
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if (_refs.dec()) {
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delete this;
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}
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}
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RefCountPointer(const T* ptr) : _ptr(ptr), _refs() {
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assert(_ptr != NULL, "invariant");
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}
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public:
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const T* operator->() const {
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return _ptr;
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}
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T* operator->() {
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return const_cast<T*>(_ptr);
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}
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static RefHandle make(const T* ptr) {
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assert(ptr != NULL, "invariant");
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return RefHandle(new RefCountPointer<T, RefCountImpl>(ptr));
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}
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};
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#endif // SHARE_VM_JFR_UTILITIES_JFRREFCOUNTPOINTER_HPP
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