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/*=========================================================================
Program: Visualization Toolkit
Module: vtkAtomicMutex.cxx
Copyright (c) Ken Martin, Will Schroeder, Bill Lorensen
All rights reserved.
See Copyright.txt or http://www.kitware.com/Copyright.htm for details.
This software is distributed WITHOUT ANY WARRANTY; without even
the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR
PURPOSE. See the above copyright notice for more information.
=========================================================================*/
#include "vtkAtomicMutex.h"
#if defined(__i386__) || defined(__x86_64__)
#include <immintrin.h>
#elif (defined(__ARM_FEATURE_SIMD32) || defined(__ARM_NEON)) && __ARM_ARCH_ISA_THUMB > 1
// https://github.com/DLTcollab/sse2neon
static inline __attribute__((always_inline)) void _mm_pause()
{
__asm__ __volatile__("isb\n");
}
#else
#define _mm_pause()
#endif
VTK_ABI_NAMESPACE_BEGIN
//------------------------------------------------------------------------------
vtkAtomicMutex::vtkAtomicMutex()
: Locked(false)
{
}
//------------------------------------------------------------------------------
vtkAtomicMutex::vtkAtomicMutex(const vtkAtomicMutex& other)
: Locked(other.Locked.load(std::memory_order_acquire))
{
}
//------------------------------------------------------------------------------
vtkAtomicMutex& vtkAtomicMutex::operator=(const vtkAtomicMutex& other)
{
this->Locked.store(other.Locked.load(std::memory_order_acquire), std::memory_order_release);
return *this;
}
//------------------------------------------------------------------------------
void vtkAtomicMutex::lock()
{
while (true)
{
// The default memory ordering of C++ atomics std::memory_order_seq_cst
// (sequentially-consistent ordering) is overly restrictive and can be changed
// to std::memory_order_acquire for operations that acquires the lock and
// std::memory_order_release for operations that releases the lock2.
if (!this->Locked.exchange(true, std::memory_order_acquire))
{
return;
}
// The memory_order_relaxed is used to avoid of continuous futile attempts to acquire
// the held lock, and we wait for the lock holder to first release the lock. This
// eliminates cache coherency traffic during spinning:
while (this->Locked.load(std::memory_order_relaxed))
{
// The pause instruction provides a hint that a spin-wait loop is running and
// throttles the CPU core in some architecture specific way in order to reduce
// power usage and contention on the load-store units
_mm_pause();
}
}
}
//------------------------------------------------------------------------------
void vtkAtomicMutex::unlock()
{
this->Locked.store(false, std::memory_order_release);
}
VTK_ABI_NAMESPACE_END
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