Intel Threading Building Blocks

Name

parallel_reduce<Range,Body> Template Function — Computes reduction over a range of values.

Synopsis

#include "tbb/parallel_reduce.h"

template<typename Range, typename Body>

void parallel_reduce( const Range& range, Body& body );

template<typename Range, typename Body, typename Partitioner>

  void parallel_reduce( const Range& range, Body& body,

                      Partitioner &partitioner );

Description

A parallel_reduce<Range,Body> performs parallel reduction of Body over each value in Range. Type Range must model the Range Concept. The body must model the requirements in Table 3-7.

Table 3-7. Requirements for parallel_reduce body

Pseudosignature	Semantics
Body::Body( Body& ,split );	Splitting constructor. Must be able to run the operator() and join methods concurrently.
Body::~Body()	Destructor.
void Body::operator()( Range& range );	Accumulate results for the subrange.
void Body::join( Body& rhs );	Join results. The result in rhs should be merged into the result of this.

A parallel_reduce recursively splits the range into subranges to the point where is_divisible() returns false for each subrange. A parallel_reduce uses the splitting constructor to make one or more copies of the body for each thread. It may copy a body while the body’s operator() or join method runs concurrently. You are responsible for ensuring the safety of such concurrency. In typical usage, the safety requires no extra effort.

When worker threads are available, parallel_reduce invokes the splitting constructor ...