• 2021.4
• 09/27/2021
• Public Content
Contents

# Use Nested Algorithms to Increase Scalability

One powerful way to increase the scalability of a flow graph is to nest other parallel algorithms inside of node bodies. Doing so, you can use a flow graph as a coordination language, expressing the most coarse-grained parallelism at the level of the graph, with finer grained parallelism nested within.
In the example below, five nodes are created: an
input_node
,
matrix_source
, that reads a sequence of matrices from a file, two
function_nodes
,
n1
and
n2
, that receive these matrices and generate two new matrices by applying a function to each element, and two final
function_nodes
,
n1_sink
and
n2_sink
, that process these resulting matrices. The
matrix_source
is connected to both
n1
and
n2
. The node
n1
is connected to
n1_sink
, and
n2
is connected to
n2_sink
. In the lambda expressions for
n1
and
n2
, a
parallel_for
is used to apply the functions to the elements of the matrix in parallel. The functions
,
f1
,
f2
,
consume_f1
and
consume_f2
are not provided below.
``````graph g;
input_node< double * > matrix_source( g, [&]( oneapi::tbb::flow_control &fc ) -> double* {
if ( a ) {
return a;
} else {
fc.stop();
return nullptr;
}
} );
function_node< double *, double * > n1( g, unlimited, [&]( double *a ) -> double * {
double *b = new double[N];
parallel_for( 0, N, [&](int i) {
b[i] = f1(a[i]);
} );
return b;
} );
function_node< double *, double * > n2( g, unlimited, [&]( double *a ) -> double * {
double *b = new double[N];
parallel_for( 0, N, [&](int i) {
b[i] = f2(a[i]);
} );
return b;
} );
function_node< double *, double * > n1_sink( g, unlimited,
[]( double *b ) -> double * {
return consume_f1(b);
} );
function_node< double *, double * > n2_sink( g, unlimited,
[]( double *b ) -> double * {
return consume_f2(b);
} );
make_edge( matrix_source, n1 );
make_edge( matrix_source, n2 );
make_edge( n1, n1_sink );
make_edge( n2, n2_sink );
matrix_source.activate();
g.wait_for_all();``````

#### Product and Performance Information

1

Performance varies by use, configuration and other factors. Learn more at www.Intel.com/PerformanceIndex.