Programming

Hi,

I'm studying for an exam coming up soon and I'm trying to figure out what is the functional difference between these two approaches:

#pragma omp parallel for
	for(unsigned int i = 0; i < G.Out.bucket_count(); i++){
		for(auto itv = G.Out.begin(i); itv != G.Out.end(i); itv++){

			unsigned int v = itv->first;

			#pragma omp parallel for
			for(unsigned int j = 0; j < G.Out[v]._map.bucket_count(); j++){
				for(auto ite = G.Out[v]._map.begin(j); ite != G.Out[v]._map.end(j); ite++){

					unsigned int w = ite->first;

					if(o[v] > o[w])
					 #pragma omp critical
					 p[o[v]] = min(p[o[v]],o[w]);

				}
			}

		}

and

	#pragma omp parallel for
	for(unsigned int i = 0; i < G.Out.bucket_count(); i++){
		for(auto itv = G.Out.begin(i); itv != G.Out.end(i); itv++){

			unsigned int v = itv->first;

			if(p[v] == v){

				unsigned int parent = v; //=p[v]

				#pragma omp parallel for reduction(min : parent)
				for(unsigned int j = 0; j < G.Out[v]._map.bucket_count(); j++){
					for(auto ite = G.Out[v]._map.begin(j); ite != G.Out[v]._map.end(j); ite++){
						unsigned int w = ite->first;
						if(v > w)
						 parent = min(parent,w);
					}
				}

				p[v] = parent;
				if(p[v] != v) changes = 1;

			}

		}
	}

In the first example, the minimum between the two values is calculated using a critical section, while the second one uses a reduction. Both work, and they seem equivalent to me, when would one choose one or the other?

Thanks, and sorry if the question is too niche. Any other info about OpenMP is greatly appreciated :D