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/*=========================================================================
*
* Copyright NumFOCUS
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* https://www.apache.org/licenses/LICENSE-2.0.txt
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*
*=========================================================================*/
/*=========================================================================
*
* Portions of this file are subject to the VTK Toolkit Version 3 copyright.
*
* Copyright (c) Ken Martin, Will Schroeder, Bill Lorensen
*
* For complete copyright, license and disclaimer of warranty information
* please refer to the NOTICE file at the top of the ITK source tree.
*
*=========================================================================*/
#ifndef itkTimeStamp_h
#define itkTimeStamp_h
#include "itkMacro.h"
#include "itkIntTypes.h"
#include <atomic>
#include "itkSingletonMacro.h"
namespace itk
{
/** \class TimeStamp
* \brief Generate a unique, increasing time value.
*
* TimeStamp records a unique time when the method Modified() is
* executed. This time is guaranteed to be monotonically increasing.
* Classes use this object to record modified and/or execution time.
* There is built in support for the binary < and > comparison
* operators between two TimeStamp objects.
*
* \warning On most platforms, this class uses a lock-free incremental
* counter. The Modified function can safely be called simultaneously
* by multiple threads on different instances of the class. However,
* calling the Modified function by different threads on the same
* instance of the class can lead to some unexpected behavior. The
* global counter will always be correct but the local m_ModifiedTime
* might not (see
* https://www.itk.org/mailman/private/insight-developers/2009-February/011732.html
* for more detail).
*
* \ingroup ITKSystemObjects
* \ingroup ITKCommon
*/
class ITKCommon_EXPORT TimeStamp
{
public:
/** Standard class type aliases. */
using Self = TimeStamp;
using GlobalTimeStampType = std::atomic<ModifiedTimeType>;
/** Create an instance of this class. We don't want to use reference
* counting. */
static Self *
New();
/** Destroy this instance. */
void
Delete()
{
delete this;
}
/** The class name as a string. */
static const char *
GetNameOfClass()
{
return "TimeStamp";
}
/** Set this objects time to the current time. The current time is just a
* monotonically increasing unsigned long integer. It is possible for this
* number to wrap around back to zero. This should only happen for
* processes that have been running for a very long time, while constantly
* changing objects within the program. When this does occur, the typical
* consequence should be that some filters will update themselves when
* really they don't need to. */
void
Modified();
/** Return this object's Modified time. */
ModifiedTimeType
GetMTime() const
{
return m_ModifiedTime;
}
/** Support comparisons of time stamp objects directly. */
bool
operator>(TimeStamp & ts) const
{
return (m_ModifiedTime > ts.m_ModifiedTime);
}
bool
operator<(TimeStamp & ts) const
{
return (m_ModifiedTime < ts.m_ModifiedTime);
}
/** Allow for typecasting to unsigned long. */
operator ModifiedTimeType() const { return m_ModifiedTime; }
private:
/** Set/Get the pointer to GlobalTimeStamp.
* Note that SetGlobalTimeStamp is not concurrent thread safe. */
itkGetGlobalDeclarationMacro(GlobalTimeStampType, GlobalTimeStamp);
ModifiedTimeType m_ModifiedTime{ 0 };
/** The static GlobalTimeStamp. This is initialized to NULL as the first
* stage of static initialization. It is then populated on the first call to
* itk::TimeStamp::Modified() but it can be overridden with SetGlobalTimeStamp().
* */
static GlobalTimeStampType * m_GlobalTimeStamp;
};
} // end namespace itk
#endif
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