OpenVDB: nanovdb/util/Reduce.h Source File

OpenVDB 9.0.0

Reduce.h
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1// Copyright Contributors to the OpenVDB Project
2// SPDX-License-Identifier: MPL-2.0
3
4/*!
5 \file Reduce.h
6
7 \author Ken Museth
8
9 \date March 4, 2021
10
11 \brief A unified wrapper for tbb::parallel_reduce and a naive std::future analog
12*/
13
14#ifndef NANOVDB_REDUCE_H_HAS_BEEN_INCLUDED
15#define NANOVDB_REDUCE_H_HAS_BEEN_INCLUDED
16
17#include "Range.h"// for Range1D
18
19#ifdef NANOVDB_USE_TBB
20#include <tbb/parallel_reduce.h>
21#else
22#include <thread>
23#include <future>
24#include <vector>
25#endif
26
27namespace nanovdb {
28
29/// @return reduction
30///
31/// @param range RangeT can be Range<dim,T>, CoordBBox, tbb::blocked_range, blocked_range2D, or blocked_range3D.
32/// @param func functor with signature T FuncT::operator()(const RangeT& range, const T& a) const
33/// @param join functor with the signature T JoinT::operator()(const T& a, const T& b) const
34/// @code
35/// std::vector<int> array(100, 1);
36/// auto func = [&array](auto &r, int a){for (auto i=r.begin(); i!=r.end(); ++i) a+=array[i]; return a;};
37/// int sum = reduce(array, 0, func, [](int a, int b){return a + b;});
38/// @endcode
39
40template <typename RangeT, typename T, typename FuncT, typename JoinT>
41 inline T reduce(RangeT range, const T& identity, const FuncT &func, const JoinT &join)
42{
43 if (range.empty()) return identity;
44#ifdef NANOVDB_USE_TBB
45 return tbb::parallel_reduce(range, identity, func, join);
46#else// naive and likely slow alternative based on std::future
47 if (const size_t threadCount = std::thread::hardware_concurrency()>>1) {
48 std::vector<RangeT> rangePool{ range };
49 while(rangePool.size() < threadCount) {
50 const size_t oldSize = rangePool.size();
51 for (size_t i = 0; i < oldSize && rangePool.size() < threadCount; ++i) {
52 auto &r = rangePool[i];
53 if (r.is_divisible()) rangePool.push_back(RangeT(r, Split()));
54 }
55 if (rangePool.size() == oldSize) break;// none of the ranges were divided so stop
56 }
57 std::vector< std::future<T> > futurePool;
58 for (auto &r : rangePool) {
59 auto task = std::async(std::launch::async, [&](){return func(r, identity);});
60 futurePool.push_back( std::move(task) );// launch tasks
61 }
62 T result = identity;
63 for (auto &f : futurePool) {
64 result = join(result, f.get());// join results
65 }
66 return result;
67 } else {// serial
68 return static_cast<T>(func(range, identity));
69 }
70#endif
71 return identity;// should never happen
72}
73
74/// @brief Simple wrapper to the function defined above
75template <typename T, typename FuncT, typename JoinT >
76 inline T reduce(size_t begin, size_t end, size_t grainSize, const T& identity, const FuncT& func, const JoinT& join)
77{
78 Range1D range(begin, end, grainSize);
79 return reduce( range, identity, func, join );
80}
81
82/// @brief Simple wrapper that works with std::containers
83template <template<typename...> class ContainerT, typename... ArgT, typename T, typename FuncT, typename JoinT >
84 inline T reduce(const ContainerT<ArgT...> &c, const T& identity, const FuncT& func, const JoinT& join)
85{
86 Range1D range(0, c.size(), 1);
87 return reduce( range, identity, func, join );
88
89}
90
91/// @brief Simple wrapper that works with std::containers
92template <template<typename...> class ContainerT, typename... ArgT, typename T, typename FuncT, typename JoinT >
93 inline T reduce(const ContainerT<ArgT...> &c, size_t grainSize, const T& identity, const FuncT& func, const JoinT& join)
94{
95 Range1D range(0, c.size(), grainSize);
96 return reduce( range, identity, func, join );
97}
98
99}// namespace nanovdb
100
101#endif // NANOVDB_REDUCE_H_HAS_BEEN_INCLUDED
Range.h
Custom Range class that is compatible with the tbb::blocked_range classes.
nanovdb::Range
Definition: Range.h:28
nanovdb::Split
Definition: Range.h:25
nanovdb
Definition: Camera.h:16
nanovdb::reduce
T reduce(RangeT range, const T &identity, const FuncT &func, const JoinT &join)
Definition: Reduce.h:41