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/**
* @file
* @author Aapo Kyrola <akyrola@cs.cmu.edu>
* @version 1.0
*
* @section LICENSE
*
* Copyright [2012] [Aapo Kyrola, Guy Blelloch, Carlos Guestrin / Carnegie Mellon University]
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*
* @section DESCRIPTION
* Minimum spanning forest based on Boruvska steps. Also alternatively implementation using
* star contraction.
*
* This application demonstrates how graph contraction algorithms can be implemented efficiently
* with GraphChi.
*/
#define GRAPHCHI_DISABLE_COMPRESSION
#include <string>
#include "graphchi_basic_includes.hpp"
using namespace graphchi;
enum ContractionType {
STAR = 1, BORUVSKA = 2
};
ContractionType contractionType;
#define MAX_VIDT 0xffffffff
struct bidirectional_component_weight {
vid_t smaller_component;
vid_t larger_component;
vid_t orig_src, orig_dst;
bool in_mst;
double weight;
bidirectional_component_weight() {
smaller_component = larger_component = MAX_VIDT;
in_mst = false;
weight = 0.0f;
orig_src = orig_dst = 0;
}
bidirectional_component_weight(double x) {
smaller_component = larger_component = MAX_VIDT;
in_mst = false;
weight = x;
orig_src = orig_dst = 0;
}
vid_t neighbor_label(vid_t myid, vid_t nbid) {
vid_t label = (myid < nbid ? larger_component : smaller_component);
if (label == MAX_VIDT) label = nbid; // NOTE: important optimization (for random orders!)
return label;
}
vid_t & my_label(vid_t myid, vid_t nbid) {
if (myid < nbid) {
return smaller_component;
} else {
return larger_component;
}
}
bool labels_agree() {
return smaller_component == larger_component;
}
};
class AcceptMinimum : public DuplicateEdgeFilter<bidirectional_component_weight> {
bool acceptFirst(bidirectional_component_weight &first, bidirectional_component_weight &second) {
return (first.weight < second.weight);
}
};
/**
* Type definitions. Remember to create suitable graph shards using the
* Sharder-program.
*/
typedef vid_t VertexDataType;
typedef bidirectional_component_weight EdgeDataType;
graphchi_engine<VertexDataType, EdgeDataType> * gengine;
size_t MST_OUTPUT;
size_t CONTRACTED_GRAPH_OUTPUT;
FILE * complog;
/**
* GraphChi programs need to subclass GraphChiProgram<vertex-type, edge-type>
* class. The main logic is usually in the update function.
*/
struct BoruvskaStarContractionStep : public GraphChiProgram<VertexDataType, EdgeDataType> {
// Hash parameters, always chosen randomly
uint64_t a, b;
size_t num_edges;
int num_contract, num_tails, num_heads, num_active_vertices;
BoruvskaStarContractionStep() {
a = (uint64_t) std::rand();
b = (uint64_t) std::rand();
num_edges = 0;
num_contract = num_tails = num_heads = num_active_vertices = 0;
logstream(LOG_INFO) << "Chose random hash function: a = " << a << " b = " << b << std::endl;
}
bool heads(vid_t vertex_id) {
const long prime = 7907; // Courtesy of Wolfram alpha
return ((a * vertex_id + b) % prime) % 2 == 0;
}
/**
* Vertex update function. Note: we assume fresh edge values.
*/
void update(graphchi_vertex<VertexDataType, EdgeDataType> &vertex, graphchi_context &gcontext) {
if (vertex.num_edges() == 0) {
return;
}
if (gcontext.iteration == 0) {
num_active_vertices ++;
num_edges += vertex.num_inedges();
double min_edge_weight = 1e30f;
int min_edge_idx = 0;
// TODO: replace with reductions
/* Get minimum edge */
for(int i=0; i < vertex.num_edges(); i++) {
bidirectional_component_weight edata = vertex.edge(i)->get_data();
// Remember the original edge identity
if (edata.orig_src == edata.orig_dst) {
edata.orig_src = vertex.id();
edata.orig_dst = vertex.edge(i)->vertex_id(); // Note: forgets direction
vertex.edge(i)->set_data(edata);
}
double w = edata.weight;
if (w < min_edge_weight || (w == min_edge_weight && edata.in_mst)) { // Tie-breaking
min_edge_idx = i;
min_edge_weight = w;
}
}
if (!vertex.edge(min_edge_idx)->get_data().in_mst) {
bidirectional_component_weight edata = vertex.edge(min_edge_idx)->get_data();
edata.in_mst = true;
vertex.edge(min_edge_idx)->set_data(edata);
}
}
if (contractionType == STAR && gcontext.iteration > 0) {
// Communicate label and check if want to contract
// Tails collapse into Heads
bool meTails = !heads(vertex.id());
vid_t my_id = vertex.id();
if (meTails) {
num_tails++;
// Find minimum edge with a heads
for(int i=0; i < vertex.num_edges(); i++) {
graphchi_edge<EdgeDataType> * e = vertex.edge(i);
if (heads(e->vertex_id())) {
if (e->get_data().in_mst) {
my_id = e->vertex_id();
num_contract++;
break;
}
}
}
} else {
num_heads++;
}
// Write my label
for(int i=0; i < vertex.num_edges(); i++) {
graphchi_edge<EdgeDataType> * e = vertex.edge(i);
bidirectional_component_weight edata = e->get_data();
edata.my_label(vertex.id(), e->vertex_id()) = my_id;
e->set_data(edata);
}
}
if (contractionType == BORUVSKA) {
/* Get my component id. It is the minimum label of a neighbor via a mst edge (or my own id) */
vid_t min_component_id = vertex.id();
for(int i=0; i < vertex.num_edges(); i++) {
graphchi_edge<EdgeDataType> * e = vertex.edge(i);
if (e->get_data().in_mst) {
min_component_id = std::min(e->get_data().neighbor_label(vertex.id(), e->vertex_id()), min_component_id);
}
}
/* Set component ids and schedule neighbors */
for(int i=0; i < vertex.num_edges(); i++) {
graphchi_edge<EdgeDataType> * e = vertex.edge(i);
bidirectional_component_weight edata = e->get_data();
if (edata.my_label(vertex.id(), e->vertex_id()) != min_component_id) {
edata.my_label(vertex.id(), e->vertex_id()) = min_component_id;
e->set_data(edata);
}
}
}
}
/**
* Called before an iteration starts.
*/
void before_iteration(int iteration, graphchi_context &gcontext) {
logstream(LOG_INFO) << "Start iteration " << iteration << ", scheduled tasks=" << gcontext.scheduler->num_tasks() << std::endl;
}
void after_iteration(int iteration, graphchi_context &gcontext) {
logstream(LOG_INFO) << "To contract: " << num_contract << ", tails=" << num_tails << " heads=" << num_heads <<
" active=" << num_active_vertices << std::endl;
if (iteration == 1) {
fprintf(complog, "%d,%d,%ld\n", num_contract, num_active_vertices, num_edges);
}
}
void before_exec_interval(vid_t window_st, vid_t window_en, graphchi_context &gcontext) {}
void after_exec_interval(vid_t window_st, vid_t window_en, graphchi_context &gcontext) {}
};
double totalMST = 0.0;
mutex lock;
/**
* Update function that writes the contracted graph for next iteration and
* outputs also the minimum spanning edges.
*/
struct ContractionStep : public GraphChiProgram<VertexDataType, EdgeDataType> {
bool new_edges;
ContractionStep() {
new_edges = false;
}
/**
* Vertex update function. Note: we assume fresh edge values.
*/
void update(graphchi_vertex<VertexDataType, EdgeDataType> &vertex, graphchi_context &gcontext) {
if (vertex.num_inedges() == 0) {
return;
}
// Loop over only in-edges
for(int i=0; i < vertex.num_inedges(); i++) {
graphchi_edge<EdgeDataType> * e = vertex.inedge(i);
bidirectional_component_weight edata = e->get_data();
if (e->get_data().in_mst) {
lock.lock();
if (edata.weight >= 0.0) totalMST += edata.weight;
lock.unlock();
}
if (e->get_data().in_mst && edata.labels_agree()) {
if (edata.weight >= 0.0) {
gengine->output(MST_OUTPUT)->output_edge(edata.orig_src, edata.orig_dst, edata.weight);
}
} else if (!edata.labels_agree()) {
// Output the contracted edge
vid_t a = edata.my_label(vertex.id(), e->vertex_id());
vid_t b = edata.neighbor_label(vertex.id(), e->vertex_id());
// NOTE: If in MST, we need to emit it but will set it to -1 ("invalid") so it will be
// picked up on next round for sure and the component is kept in-tact, but will
// not affect the MST as it is zero weight.
if (edata.in_mst) {
if (edata.weight >= 0.0)
gengine->output(MST_OUTPUT)->output_edge(edata.orig_src, edata.orig_dst, edata.weight);
edata.weight = -1.0;
}
edata.smaller_component = MAX_VIDT;
edata.larger_component = MAX_VIDT;
new_edges = true;
gengine->output(CONTRACTED_GRAPH_OUTPUT)->output_edgeval(std::min(a, b),
std::max(a, b),
edata);
} else {
// Otherwise: discard the edge
}
}
}
/**
* Called before an iteration starts.
*/
void before_iteration(int iteration, graphchi_context &gcontext) {
logstream(LOG_INFO) << "Contraction: Start iteration " << iteration << std::endl;
}
void after_iteration(int iteration, graphchi_context &gcontext) {
}
void before_exec_interval(vid_t window_st, vid_t window_en, graphchi_context &gcontext) {}
void after_exec_interval(vid_t window_st, vid_t window_en, graphchi_context &gcontext) {}
};
int main(int argc, const char ** argv) {
/* GraphChi initialization will read the command line
arguments and the configuration file. */
graphchi_init(argc, argv);
/* Metrics object for keeping track of performance counters
and other information. Currently required. */
metrics m("minimum-spanning-forest");
m.start_time("msf-total-runtime");
/* Basic arguments for application */
std::string filename = get_option_string("file"); // Base filename
bool scheduler = false; // Whether to use selective scheduling
/* Detect the number of shards or preprocess an input to create them */
int nshards = get_option_int("nshards", 0);
delete_shards<EdgeDataType>(filename, nshards);
convert_if_notexists<double, EdgeDataType>(filename, get_option_string("nshards", "10"));
contractionType = get_option_string("algo", "boruvska") == "boruvska" ? BORUVSKA : STAR;
if (contractionType == BORUVSKA) {
complog = fopen("msflog_boruvska.txt", "w");
} else {
complog = fopen("msflog_star.txt", "w");
}
for(int MSF_iteration=0; MSF_iteration < 100; MSF_iteration++) {
logstream(LOG_INFO) << "MSF ITERATION " << MSF_iteration << " contraction: " << contractionType << std::endl;
/* Step 1: Run boruvska step */
BoruvskaStarContractionStep boruvska_starcontraction;
graphchi_engine<VertexDataType, EdgeDataType> engine(filename, nshards, scheduler, m);
engine.set_disable_vertexdata_storage();
gengine = &engine;
engine.set_save_edgesfiles_after_inmemmode(true);
engine.set_modifies_inedges(true);
engine.set_modifies_outedges(true);
engine.set_disable_outedges(false);
engine.run(boruvska_starcontraction, 2);
/* Step 2: Run contraction */
/* Initialize output */
basic_text_output<VertexDataType, EdgeDataType> mstout(filename + ".mst", "\t");
int orig_numshards = (int) engine.get_intervals().size();
std::string contractedname = filename + "C";
sharded_graph_output<VertexDataType, EdgeDataType> shardedout(contractedname, new AcceptMinimum());
MST_OUTPUT = engine.add_output(&mstout);
CONTRACTED_GRAPH_OUTPUT = engine.add_output(&shardedout);
ContractionStep contraction;
engine.set_disable_vertexdata_storage();
engine.set_modifies_inedges(true);
engine.set_modifies_outedges(false);
engine.set_disable_outedges(true);
engine.set_save_edgesfiles_after_inmemmode(true);
engine.run(contraction, 1);
// Clean up
delete_shards<EdgeDataType>(filename, orig_numshards);
std::cout << "Total MST now: " << totalMST << std::endl;
if (contraction.new_edges == false) {
logstream(LOG_INFO) << "MSF ready!" << std::endl;
break;
}
nshards = (int)shardedout.finish_sharding();
filename = contractedname;
}
m.stop_time("msf-total-runtime");
/* Report execution metrics */
metrics_report(m);
fclose(complog);
return 0;
}
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