internal::VectorOperations::TBBReduceFunctor< Operation, ResultType > Struct Template Reference

#include <deal.II/lac/vector_operations_internal.h>

Public Member Functions
	TBBReduceFunctor (const Operation &op, const size_type start, const size_type end)
void	operator() (const tbb::blocked_range< size_type > &range) const
ResultType	do_sum () const

Public Attributes
const Operation &	op
const size_type	start
const size_type	end
unsigned int	n_chunks
unsigned int	chunk_size
ResultType	small_array [threshold_array_allocate]
std::vector< ResultType >	large_array
ResultType *	array_ptr

Static Public Attributes
static const unsigned int	threshold_array_allocate = 512

Detailed Description

template<typename Operation, typename ResultType>
struct internal::VectorOperations::TBBReduceFunctor< Operation, ResultType >

This struct takes the loop range from the tbb parallel for loop and translates it to the actual ranges of the reduction loop inside the vector. It encodes the grain size but might choose larger values of chunks than the minimum grain size. The minimum grain size given to tbb is 1. For affinity reasons, the layout in this loop must be kept in sync with the respective class for plain for loops further up.

Due to this construction, TBB usually only sees a loop of length 4*num_threads with grain size 1. The actual ranges inside the vector are computed outside of TBB because otherwise TBB would split the ranges in some unpredictable position which destroys exact bitwise reproducibility. An important part of this is that inside TBBReduceFunctor::operator() the recursive calls to accumulate are done sequentially on one item a time (even though we could directly run it on the whole range given through the tbb::blocked_range times the chunk size

• but that would be unpredictable). Thus, the values we cannot control are the positions in the array that gets filled - but up to that point the algorithm TBB sees is just a parallel for and nothing unpredictable can happen.

To sum up: Once the number of threads and the vector size are fixed, we have an exact layout of how the calls into the recursive function will happen. Inside the recursive function, we again only depend on the length. Finally, the concurrent threads write into different positions in a result vector in a thread-safe way and the addition in the short array is again serial.

Definition at line 1312 of file vector_operations_internal.h.

Constructor & Destructor Documentation

TBBReduceFunctor()

template<typename Operation , typename ResultType >

internal::VectorOperations::TBBReduceFunctor< Operation, ResultType >::TBBReduceFunctor ( const Operation &  op, const size_type  start, const size_type  end  )

inline

Definition at line 1316 of file vector_operations_internal.h.

Member Function Documentation

operator()()

template<typename Operation , typename ResultType >

void internal::VectorOperations::TBBReduceFunctor< Operation, ResultType >::operator() ( const tbb::blocked_range< size_type > &  range ) const

inline

An operator used by TBB to work on a given range of chunks [range.begin(), range.end()).

Definition at line 1358 of file vector_operations_internal.h.

do_sum()

template<typename Operation , typename ResultType >

ResultType internal::VectorOperations::TBBReduceFunctor< Operation, ResultType >::do_sum ( ) const

inline

Definition at line 1368 of file vector_operations_internal.h.

Member Data Documentation

threshold_array_allocate

template<typename Operation , typename ResultType >

const unsigned int internal::VectorOperations::TBBReduceFunctor< Operation, ResultType >::threshold_array_allocate = 512

static

Definition at line 1314 of file vector_operations_internal.h.

op

template<typename Operation , typename ResultType >

const Operation& internal::VectorOperations::TBBReduceFunctor< Operation, ResultType >::op

Definition at line 1381 of file vector_operations_internal.h.

start

template<typename Operation , typename ResultType >

const size_type internal::VectorOperations::TBBReduceFunctor< Operation, ResultType >::start

Definition at line 1382 of file vector_operations_internal.h.

end

template<typename Operation , typename ResultType >

const size_type internal::VectorOperations::TBBReduceFunctor< Operation, ResultType >::end

Definition at line 1383 of file vector_operations_internal.h.

n_chunks

template<typename Operation , typename ResultType >

unsigned int internal::VectorOperations::TBBReduceFunctor< Operation, ResultType >::n_chunks

mutable

Definition at line 1385 of file vector_operations_internal.h.

chunk_size

template<typename Operation , typename ResultType >

unsigned int internal::VectorOperations::TBBReduceFunctor< Operation, ResultType >::chunk_size

Definition at line 1386 of file vector_operations_internal.h.

small_array

template<typename Operation , typename ResultType >

ResultType internal::VectorOperations::TBBReduceFunctor< Operation, ResultType >::small_array[threshold_array_allocate]

Definition at line 1387 of file vector_operations_internal.h.

large_array

template<typename Operation , typename ResultType >

std::vector<ResultType> internal::VectorOperations::TBBReduceFunctor< Operation, ResultType >::large_array

Definition at line 1388 of file vector_operations_internal.h.

array_ptr

template<typename Operation , typename ResultType >

ResultType* internal::VectorOperations::TBBReduceFunctor< Operation, ResultType >::array_ptr

mutable

Definition at line 1391 of file vector_operations_internal.h.

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The documentation for this struct was generated from the following file:

• include/deal.II/lac/vector_operations_internal.h