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114 lines
4.2 KiB
C++
114 lines
4.2 KiB
C++
/*
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* Copyright (c) 2022, 2023, 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_OOPS_SYMBOLHANDLE_HPP
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#define SHARE_OOPS_SYMBOLHANDLE_HPP
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#include "memory/allocation.hpp"
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#include "oops/symbol.hpp"
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class TempSymbolCleanupDelayer : AllStatic {
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static Symbol* volatile _queue[];
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static volatile uint _index;
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public:
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static const uint QueueSize = 128;
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static void delay_cleanup(Symbol* s);
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static void drain_queue();
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};
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// TempNewSymbol acts as a handle class in a handle/body idiom and is
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// responsible for proper resource management of the body (which is a Symbol*).
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// The body is resource managed by a reference counting scheme.
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// TempNewSymbol can therefore be used to properly hold a newly created or referenced
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// Symbol* temporarily in scope.
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//
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// Routines in SymbolTable will initialize the reference count of a Symbol* before
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// it becomes "managed" by TempNewSymbol instances. As a handle class, TempNewSymbol
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// needs to maintain proper reference counting in context of copy semantics.
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//
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// In SymbolTable, new_symbol() will create a Symbol* if not already in the
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// symbol table and add to the symbol's reference count.
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// probe() and lookup_only() will increment the refcount if symbol is found.
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template <bool TEMP>
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class SymbolHandleBase : public StackObj {
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Symbol* _temp;
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public:
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SymbolHandleBase() : _temp(nullptr) { }
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// Conversion from a Symbol* to a SymbolHandleBase.
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SymbolHandleBase(Symbol *s) : _temp(s) {
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if (!TEMP) {
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Symbol::maybe_increment_refcount(_temp);
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return;
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}
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// Delay cleanup for temp symbols. Refcount is incremented while in
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// queue. But don't requeue existing entries, or entries that are held
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// elsewhere - it's a waste of effort.
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if (s != nullptr && s->refcount() == 1) {
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TempSymbolCleanupDelayer::delay_cleanup(s);
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}
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}
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// Copy constructor increments reference count.
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SymbolHandleBase(const SymbolHandleBase& rhs) : _temp(rhs._temp) {
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Symbol::maybe_increment_refcount(_temp);
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}
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// Assignment operator uses a c++ trick called copy and swap idiom.
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// rhs is passed by value so within the scope of this method it is a copy.
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// At method exit it contains the former value of _temp, triggering the correct refcount
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// decrement upon destruction.
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void operator=(SymbolHandleBase rhs) {
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Symbol* tmp = rhs._temp;
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rhs._temp = _temp;
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_temp = tmp;
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}
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// Decrement reference counter so it can go away if it's unused
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~SymbolHandleBase() {
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Symbol::maybe_decrement_refcount(_temp);
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}
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// Symbol* conversion operators
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Symbol* operator -> () const { return _temp; }
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bool operator == (Symbol* o) const { return _temp == o; }
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operator Symbol*() const { return _temp; }
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static unsigned int compute_hash(const SymbolHandleBase& name) {
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return (unsigned int) name->identity_hash();
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}
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};
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// TempNewSymbol is a temporary holder for a newly created symbol
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using TempNewSymbol = SymbolHandleBase<true>;
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// SymbolHandle is a non-temp symbol used to hold a symbol in a semi permanent place,
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// like in a hashtable. The only difference is that the constructor increments the refcount.
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using SymbolHandle = SymbolHandleBase<false>;
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#endif // SHARE_OOPS_SYMBOLHANDLE_HPP
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