Appendix B Mixing With Other Threading Packages

oneAPI Threading Building Blocks (oneTBB) can be mixed with other threading packages. No special effort is required to use any part of oneTBB with other threading packages.

Here is an example that parallelizes an outer loop with OpenMP and an inner loop with oneTBB.

int M, N;


struct InnerBody {
    ...
};


void TBB_NestedInOpenMP() {
#pragma omp parallel
    {
#pragma omp for
        for( int i=0; i<M; ++ ) {
            parallel_for( blocked_range<int>(0,N,10), InnerBody(i) );
        }
    }
}

The details of InnerBody are omitted for brevity. The #pragma omp parallel causes the OpenMP to create a team of threads, and each thread executes the block statement associated with the pragma. The #pragma omp for indicates that the compiler should use the previously created thread team to execute the loop in parallel.

Here is the same example written using POSIX* Threads.

int M, N;


struct InnerBody {
    ...
};


void* OuterLoopIteration( void* args ) {
    int i = (int)args;
    parallel_for( blocked_range<int>(0,N,10), InnerBody(i) );
}


void TBB_NestedInPThreads() {
    std::vector<pthread_t> id( M );
    // Create thread for each outer loop iteration
    for( int i=0; i<M; ++i )
        pthread_create( &id[i], NULL, OuterLoopIteration, NULL );
    // Wait for outer loop threads to finish
    for( int i=0; i<M; ++i )
        pthread_join( &id[i], NULL );
}