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reduce.h
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24 #ifndef WORK_REDUCE_H
25 #define WORK_REDUCE_H
26 
28 #include "pxr/pxr.h"
29 #include "pxr/base/work/threadLimits.h"
30 #include "pxr/base/work/api.h"
31 
32 #include <tbb/blocked_range.h>
33 #include <tbb/parallel_reduce.h>
34 #include <tbb/task.h>
35 
36 PXR_NAMESPACE_OPEN_SCOPE
37 
38 
98 template <typename Fn, typename Rn, typename V>
99 V
101  const V &identity,
102  size_t n,
103  Fn &&loopCallback,
104  Rn &&reductionCallback,
105  size_t grainSize)
106 {
107  if (n == 0)
108  return identity;
109 
110  // Don't bother with parallel_reduce, if concurrency is limited to 1.
111  if (WorkGetConcurrencyLimit() > 1) {
112 
113  class Work_Body_TBB
114  {
115  public:
116  Work_Body_TBB(Fn &fn) : _fn(fn) { }
117 
118  V operator()(
119  const tbb::blocked_range<size_t> &r,
120  const V &value) const {
121  // Note that we std::forward _fn using Fn in order get the
122  // right operator().
123  // We maintain the right type in this way:
124  // If Fn is T&, then reference collapsing gives us T& for _fn
125  // If Fn is T, then std::forward correctly gives us T&& for _fn
126  return std::forward<Fn>(_fn)(r.begin(), r.end(), value);
127  }
128  private:
129  Fn &_fn;
130  };
131 
132  // In most cases we do not want to inherit cancellation state from the
133  // parent context, so we create an isolated task group context.
134  tbb::task_group_context ctx(tbb::task_group_context::isolated);
135  return tbb::parallel_reduce(tbb::blocked_range<size_t>(0,n,grainSize),
136  identity,
137  Work_Body_TBB(loopCallback),
138  std::forward<Rn>(reductionCallback),
139  tbb::auto_partitioner(),
140  ctx);
141  }
142 
143  // If concurrency is limited to 1, execute serially.
144  return std::forward<Fn>(loopCallback)(0, n, identity);
145 }
146 
155 template <typename Fn, typename Rn, typename V>
156 V
158  const V &identity,
159  size_t n,
160  Fn &&loopCallback,
161  Rn &&reductionCallback)
162 {
163  return WorkParallelReduceN(identity, n, loopCallback, reductionCallback, 1);
164 }
165 
166 PXR_NAMESPACE_CLOSE_SCOPE
167 
168 #endif // WORK_REDUCE_H
V WorkParallelReduceN(const V &identity, size_t n, Fn &&loopCallback, Rn &&reductionCallback, size_t grainSize)
Recursively splits the range [0, n) into subranges, which are then reduced by invoking loopCallback i...
Definition: reduce.h:100
WORK_API unsigned WorkGetConcurrencyLimit()
Return the current concurrency limit, always &gt;= 1.