internal RangeWorker(IndexRange[] ranges, int nInitialRange, long nStep)
{
this.m_indexRanges = ranges;
this.m_nCurrentIndexRange = nInitialRange;
this.m_nStep = nStep;
this.m_nIncrementValue = nStep;
this.m_nMaxIncrementValue = 0x10L * nStep;
}
/// <summary>
/// Initializes a RangeWorker struct
/// </summary>
internal RangeWorker(IndexRange[] ranges, int nInitialRange, long nStep)
{
m_indexRanges = ranges;
m_nCurrentIndexRange = nInitialRange;
m_nStep = nStep;
m_nIncrementValue = nStep;
m_nMaxIncrementValue = Parallel.DEFAULT_LOOP_STRIDE * nStep;
}
/// <summary>
/// Implements the core work search algorithm that will be used for this range worker.
/// </summary>
///
/// Usage pattern is:
/// 1) the thread associated with this rangeworker calls FindNewWork
/// 2) if we return true, the worker uses the nFromInclusiveLocal and nToExclusiveLocal values
/// to execute the sequential loop
/// 3) if we return false it means there is no more work left. It's time to quit.
///
internal bool FindNewWork(out long nFromInclusiveLocal, out long nToExclusiveLocal)
{
// since we iterate over index ranges circularly, we will use the
// count of visited ranges as our exit condition
int numIndexRangesToVisit = m_indexRanges.Length;
do
{
// local snap to save array access bounds checks in places where we only read fields
IndexRange currentRange = m_indexRanges[m_nCurrentIndexRange];
if (currentRange.m_bRangeFinished == 0)
{
if (m_indexRanges[m_nCurrentIndexRange].m_nSharedCurrentIndexOffset == null)
{
Interlocked.CompareExchange(ref m_indexRanges[m_nCurrentIndexRange].m_nSharedCurrentIndexOffset, new Shared <long>(0), null);
}
// this access needs to be on the array slot
long nMyOffset;
if (IntPtr.Size == 4 && _use32BitCurrentIndex)
{
// In 32-bit processes, we prefer to use 32-bit interlocked operations, to avoid the possibility of doing
// a 64-bit interlocked when the target value crosses a cache line, as that can be super expensive.
// We use the first 32 bits of the Int64 index in such cases.
unsafe
{
fixed(long *indexPtr = &m_indexRanges[m_nCurrentIndexRange].m_nSharedCurrentIndexOffset.Value)
{
nMyOffset = Interlocked.Add(ref *(int *)indexPtr, (int)m_nIncrementValue) - m_nIncrementValue;
}
}
}
else
{
nMyOffset = Interlocked.Add(ref m_indexRanges[m_nCurrentIndexRange].m_nSharedCurrentIndexOffset.Value, m_nIncrementValue) - m_nIncrementValue;
}
if (currentRange.m_nToExclusive - currentRange.m_nFromInclusive > nMyOffset)
{
// we found work
nFromInclusiveLocal = currentRange.m_nFromInclusive + nMyOffset;
nToExclusiveLocal = nFromInclusiveLocal + m_nIncrementValue;
// Check for going past end of range, or wrapping
if ((nToExclusiveLocal > currentRange.m_nToExclusive) || (nToExclusiveLocal < currentRange.m_nFromInclusive))
{
nToExclusiveLocal = currentRange.m_nToExclusive;
}
// We will double our unit of increment until it reaches the maximum.
if (m_nIncrementValue < m_nMaxIncrementValue)
{
m_nIncrementValue *= 2;
if (m_nIncrementValue > m_nMaxIncrementValue)
{
m_nIncrementValue = m_nMaxIncrementValue;
}
}
return(true);
}
else
{
// this index range is completed, mark it so that others can skip it quickly
Interlocked.Exchange(ref m_indexRanges[m_nCurrentIndexRange].m_bRangeFinished, 1);
}
}
// move on to the next index range, in circular order.
m_nCurrentIndexRange = (m_nCurrentIndexRange + 1) % m_indexRanges.Length;
numIndexRangesToVisit--;
} while (numIndexRangesToVisit > 0);
// we've visited all index ranges possible => there's no work remaining
nFromInclusiveLocal = 0;
nToExclusiveLocal = 0;
return(false);
}
/// <summary>
/// Implements the core work search algorithm that will be used for this range worker.
/// </summary>
///
/// Usage pattern is:
/// 1) the thread associated with this rangeworker calls FindNewWork
/// 2) if we return true, the worker uses the nFromInclusiveLocal and nToExclusiveLocal values
/// to execute the sequential loop
/// 3) if we return false it means there is no more work left. It's time to quit.
///
internal bool FindNewWork(out long nFromInclusiveLocal, out long nToExclusiveLocal)
{
// since we iterate over index ranges circularly, we will use the
// count of visited ranges as our exit condition
int numIndexRangesToVisit = _indexRanges.Length;
do
{
// local snap to save array access bounds checks in places where we only read fields
IndexRange currentRange = _indexRanges[_nCurrentIndexRange];
if (currentRange._bRangeFinished == 0)
{
if (_indexRanges[_nCurrentIndexRange]._nSharedCurrentIndexOffset == null)
{
Interlocked.CompareExchange(ref _indexRanges[_nCurrentIndexRange]._nSharedCurrentIndexOffset, new Box <long>(0), null);
}
// this access needs to be on the array slot
long nMyOffset = Interlocked.Add(ref _indexRanges[_nCurrentIndexRange]._nSharedCurrentIndexOffset.Value,
_nIncrementValue) - _nIncrementValue;
if (currentRange._nToExclusive - currentRange._nFromInclusive > nMyOffset)
{
// we found work
nFromInclusiveLocal = currentRange._nFromInclusive + nMyOffset;
nToExclusiveLocal = nFromInclusiveLocal + _nIncrementValue;
// Check for going past end of range, or wrapping
if ((nToExclusiveLocal > currentRange._nToExclusive) || (nToExclusiveLocal < currentRange._nFromInclusive))
{
nToExclusiveLocal = currentRange._nToExclusive;
}
// We will double our unit of increment until it reaches the maximum.
if (_nIncrementValue < _nMaxIncrementValue)
{
_nIncrementValue *= 2;
if (_nIncrementValue > _nMaxIncrementValue)
{
_nIncrementValue = _nMaxIncrementValue;
}
}
return(true);
}
else
{
// this index range is completed, mark it so that others can skip it quickly
Interlocked.Exchange(ref _indexRanges[_nCurrentIndexRange]._bRangeFinished, 1);
}
}
// move on to the next index range, in circular order.
_nCurrentIndexRange = (_nCurrentIndexRange + 1) % _indexRanges.Length;
numIndexRangesToVisit--;
} while (numIndexRangesToVisit > 0);
// we've visited all index ranges possible => there's no work remaining
nFromInclusiveLocal = 0;
nToExclusiveLocal = 0;
return(false);
}