232 lines
8.0 KiB
C++
232 lines
8.0 KiB
C++
// ____ ______ __
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// / __ \ / ____// /
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// / /_/ // / / /
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// / ____// /___ / /___ PixInsight Class Library
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// /_/ \____//_____/ PCL 2.4.23
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// ----------------------------------------------------------------------------
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// pcl/ReferenceCounter.h - Released 2022-03-12T18:59:29Z
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// ----------------------------------------------------------------------------
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// This file is part of the PixInsight Class Library (PCL).
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// PCL is a multiplatform C++ framework for development of PixInsight modules.
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//
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// Copyright (c) 2003-2022 Pleiades Astrophoto S.L. All Rights Reserved.
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//
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// Redistribution and use in both source and binary forms, with or without
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// modification, is permitted provided that the following conditions are met:
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//
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// 1. All redistributions of source code must retain the above copyright
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// notice, this list of conditions and the following disclaimer.
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//
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// 2. All redistributions in binary form must reproduce the above copyright
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// notice, this list of conditions and the following disclaimer in the
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// documentation and/or other materials provided with the distribution.
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//
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// 3. Neither the names "PixInsight" and "Pleiades Astrophoto", nor the names
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// of their contributors, may be used to endorse or promote products derived
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// from this software without specific prior written permission. For written
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// permission, please contact info@pixinsight.com.
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//
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// 4. All products derived from this software, in any form whatsoever, must
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// reproduce the following acknowledgment in the end-user documentation
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// and/or other materials provided with the product:
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//
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// "This product is based on software from the PixInsight project, developed
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// by Pleiades Astrophoto and its contributors (https://pixinsight.com/)."
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//
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// Alternatively, if that is where third-party acknowledgments normally
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// appear, this acknowledgment must be reproduced in the product itself.
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//
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// THIS SOFTWARE IS PROVIDED BY PLEIADES ASTROPHOTO AND ITS CONTRIBUTORS
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// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
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// TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
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// PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL PLEIADES ASTROPHOTO OR ITS
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// CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
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// EXEMPLARY OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, BUSINESS
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// INTERRUPTION; PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; AND LOSS OF USE,
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// DATA OR PROFITS) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
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// CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
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// ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
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// POSSIBILITY OF SUCH DAMAGE.
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// ----------------------------------------------------------------------------
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#ifndef __PCL_ReferenceCounter_h
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#define __PCL_ReferenceCounter_h
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/// \file pcl/ReferenceCounter.h
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#include <pcl/Defs.h>
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#include <pcl/Atomic.h>
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#ifdef __PCL_REFCOUNT_CHECK_DETACHMENT
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# include <pcl/Exception.h>
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#else
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# include <pcl/Diagnostics.h>
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#endif
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namespace pcl
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{
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// ----------------------------------------------------------------------------
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/*!
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* \class ReferenceCounter
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* \brief Thread-safe reference counter for copy-on-write data structures.
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*
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* %ReferenceCounter is used internally by most PCL container and image classes
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* to implement reference-counted, copy-on-write <em>shared data</em>.
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*
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* %ReferenceCounter is a thread-safe reference counter because it implements
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* its internal counter as an instance of the AtomicInt class. This means that
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* counter increment and decrement are implemented as atomic operations.
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*
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* Copy-on-write is a fundamental technique for optimization of resources and
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* execution speed by preventing unnecessary duplication of data, especially
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* when objects are copied and aliased frequently but seldom modified.
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* Basically, a set of objects can share the same data with the condition that
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* the data remains unmodified. In this case, the set of objects is said to be
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* \e referencing a single data item, and all objects in the set are considered
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* as \e aliases of the data. When an alias object tries to modify its
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* referenced data, a new copy is generated on-demand and the object uniquely
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* references the newly generated data, which can then be freely modified. This
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* mechanism works in a completely automatic and transparent way, and
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* %ReferenceCounter just provides a thread-safe counter to keep track of the
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* number of aliased objects that reference the same data structure at a given
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* time, plus a number of useful related functions.
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*
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* \sa AtomicInt
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*/
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class PCL_CLASS ReferenceCounter
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{
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public:
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/*!
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* Constructs a new %ReferenceCounter object. The reference counter is
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* initialized to one, which means that only one object (the caller) is
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* referencing the data associated with this object.
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*/
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ReferenceCounter() = default;
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/*!
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* Destroys a %ReferenceCounter object.
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*/
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~ReferenceCounter()
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{
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}
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/*!
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* Copy constructor. This constructor is equivalent to the default
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* constructor because reference counters are unique objects. In other
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* words, the reference counter is always initialized to one for newly
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* constructed %ReferenceCounter objects.
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*
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* This constructor exists and is not disabled to allow reference-counted
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* data structures to have copy constructors.
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*/
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ReferenceCounter( const ReferenceCounter& )
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: ReferenceCounter()
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{
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}
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/*!
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* Copy assignment. This operator is disabled because reference counters are
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* unique objects.
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*/
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ReferenceCounter& operator =( const ReferenceCounter& ) = delete;
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/*!
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* Increments the reference counter by one unit. This happens when a new
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* object references the data being controlled with this counter.
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*
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* \note This attachment operation is thread-safe: the internal increment
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* operation is atomic.
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*
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* \sa Detach()
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*/
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void Attach()
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{
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m_count.Increment();
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}
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/*!
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* Decrements the reference counter by one unit. This happens when an object
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* ceases to reference the data being controlled with this counter.
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*
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* Returns true if the reference counter is greater than zero after the
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* decrement; false if the reference counter becomes zero. When the
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* reference counter is zero, the data being controlled with this counter is
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* no longer referenced by any object and thus can be safely destroyed.
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*
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* \note This detachment operation is thread-safe: the internal dereference
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* operation is atomic.
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*
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* \sa Attach()
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*/
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bool Detach()
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{
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PCL_CHECK( m_count.Load() > 0 )
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return m_count.Dereference();
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}
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/*!
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* Returns the current value of this reference counter.
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*
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* \sa RefCountAtomic(), IsUnique()
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*/
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int RefCount() const
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{
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return m_count;
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}
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/*!
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* Returns the current value of this reference counter.
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*
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* \note This operation is thread-safe: the integer load has been
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* implemented as an atomic operation.
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*
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* \sa RefCount(), IsUniqueAtomic()
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*/
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int RefCountAtomic() const
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{
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return m_count.Load();
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}
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/*!
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* Returns true iff the data being controlled with this counter is not being
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* referenced by more than one object.
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*
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* \sa IsUniqueAtomic(), Attach(), Detach()
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*/
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bool IsUnique() const
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{
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return RefCount() < 2;
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}
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/*!
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* Returns true iff the data being controlled with this counter is not being
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* referenced by more than one object.
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*
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* \note This operation is thread-safe: the integer comparison has been
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* implemented as an atomic operation.
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*
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* \sa IsUnique(), Attach(), Detach()
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*/
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bool IsUniqueAtomic() const
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{
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return RefCountAtomic() < 2;
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}
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private:
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mutable AtomicInt m_count = 1;
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};
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// ----------------------------------------------------------------------------
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} // pcl
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#endif // __PCL_ReferenceCounter_h
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// ----------------------------------------------------------------------------
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// EOF pcl/ReferenceCounter.h - Released 2022-03-12T18:59:29Z
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