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// Copyright (c) 1999
// Utrecht University (The Netherlands),
// ETH Zurich (Switzerland),
// INRIA Sophia-Antipolis (France),
// Max-Planck-Institute Saarbruecken (Germany),
// and Tel-Aviv University (Israel). All rights reserved.
//
// This file is part of CGAL (www.cgal.org)
//
// $URL: https://github.com/CGAL/cgal/blob/v6.1/STL_Extension/include/CGAL/Handle.h $
// $Id: include/CGAL/Handle.h b26b07a1242 $
// SPDX-License-Identifier: LGPL-3.0-or-later OR LicenseRef-Commercial
//
//
// Author(s) : Sylvain Pion
#ifndef CGAL_HANDLE_H
#define CGAL_HANDLE_H
#include <cstddef>
#include <cstdint>
#include <atomic>
#include <CGAL/Handle_for.h>
#include <CGAL/assertions.h>
namespace CGAL {
class Rep
{
friend class Handle;
protected:
Rep(int count = 1)
: count(count)
{}
virtual ~Rep() {}
std::atomic_int count;
};
class Handle
{
public:
typedef std::ptrdiff_t Id_type ;
Handle() noexcept
: PTR(static_cast<Rep*>(0)) {}
Handle(const Handle& x) noexcept(!(CGAL_PRECONDITIONS_ENABLED || CGAL_ASSERTIONS_ENABLED))
{
CGAL_precondition( x.PTR != static_cast<Rep*>(0) );
PTR = x.PTR;
//CGAL_assume (PTR->count > 0);
incref();
}
Handle(Handle&& x) noexcept : PTR(x.PTR) { x.PTR = 0; }
~Handle() { reset(); }
Handle&
operator=(const Handle& x) noexcept(!CGAL_PRECONDITIONS_ENABLED)
{
CGAL_precondition( x.PTR != static_cast<Rep*>(0) );
x.incref();
if(PTR) decref(); // not reset() in case this==&x
PTR = x.PTR;
return *this;
}
Handle&
operator=(Handle&& x) noexcept
{
swap(*this, x);
return *this;
}
friend void swap(Handle& a, Handle& b) noexcept { std::swap(a.PTR, b.PTR); }
private:
void incref() const noexcept
{
if (is_currently_single_threaded()) {
PTR->count.store(PTR->count.load(std::memory_order_relaxed) + 1, std::memory_order_relaxed);
} else {
PTR->count.fetch_add(1, std::memory_order_relaxed);
}
}
void decref()
{
if (is_currently_single_threaded()) {
auto c = PTR->count.load(std::memory_order_relaxed);
if (c == 1)
delete PTR;
else
PTR->count.store(c - 1, std::memory_order_relaxed);
} else {
// TSAN does not support fences :-(
#if !defined __SANITIZE_THREAD__ && !__has_feature(thread_sanitizer)
if (PTR->count.load(std::memory_order_relaxed) == 1
|| PTR->count.fetch_sub(1, std::memory_order_release) == 1) {
std::atomic_thread_fence(std::memory_order_acquire);
#else
if (PTR->count.fetch_sub(1, std::memory_order_acq_rel) == 1) {
#endif
delete PTR;
}
}
}
public:
void reset()
{
if (PTR)
{
decref();
PTR=0;
}
}
int
refs() const noexcept { return PTR->count.load(std::memory_order_relaxed); }
Id_type id() const noexcept { return static_cast<Id_type>(reinterpret_cast<std::intptr_t>(static_cast<void*>(PTR)) / sizeof(Rep)); }
bool identical(const Handle& h) const noexcept { return PTR == h.PTR; }
void * for_compact_container() const { return PTR; }
void for_compact_container(void* p) { PTR = static_cast<Rep*>(p); }
protected:
Rep* PTR;
};
//inline Handle::Id_type id(const Handle& x) { return x.id() ; }
inline bool identical(const Handle &h1, const Handle &h2) noexcept { return h1.identical(h2); }
} //namespace CGAL
#endif // CGAL_HANDLE_H
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