Intel® Advisor User Guide

ID 766448
Date 12/16/2022

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Parallelize Data - Intel® oneAPI Threading Building Blocks (oneTBB) Counted Loops

When tasks are loop iterations, and the iterations are over a range of values that are known before the loop starts, the loop is easily expressed in Intel® oneAPI Threading Building Blocks (oneTBB) .

Consider the following serial code and the need to add parallelism to this loop:

        for (int i = lo; i < hi; ++i) {

Here is the serial example converted to use oneTBB , after you remove the Intel Advisor annotations:

#include <tbb/tbb.h>
    tbb::parallel_for( lo, hi, 
        [&](int i) {statement;}

The first two parameters are the loop bounds. As is typical in C++ (especially STL) programming, the lower bound is inclusive and the upper bound is exclusive. The third parameter is the loop body, wrapped in a lambda expression. The loop body will be called in parallel by threads created by oneTBB . As described before in Create the Tasks, Using C++ structs Instead of Lambda Expressions, the lambda expressions can be replaced with instances of explicitly defined class objects.