From f0b144e5999441e5bf328991ef9fe2268d112687 Mon Sep 17 00:00:00 2001
From: Marcin Chrzanowski <marcin.j.chrzanowski@gmail.com>
Date: Wed, 4 Jan 2017 23:09:53 -0500
Subject: Implement concurrent Brandes's algorithm

---
 src/brandes.cc | 98 ++++++++++++++++++++++++++++++++++++++++++++++++++++++----
 1 file changed, 92 insertions(+), 6 deletions(-)

diff --git a/src/brandes.cc b/src/brandes.cc
index 809ccd4..776b263 100644
--- a/src/brandes.cc
+++ b/src/brandes.cc
@@ -1,24 +1,110 @@
+#include <algorithm>
 #include <fstream>
 #include <iostream>
+#include <thread>
+#include <queue>
+#include <mutex>
 
 #include "parse.h"
 #include "graph.h"
+#include "dependency_calculator.h"
 
-int main(int argc, char *argv[]) {
+int threads;
+std::string input_file;
+std::string output_file;
+
+Graph graph;
+std::map<int, double> betweenness;
+std::queue<int> vertices_to_process;
+std::mutex queue_mutex;
+std::mutex betweenness_mutex;
+std::vector<std::thread> threads_list;
+
+void parse_args(int argc, char *argv[]) {
     if (argc < 4) {
         std::cerr
             << "USAGE: ./brandes <number-threads> <input-file> <output-file>"
             << std::endl;
-        return 1;
+        exit(1);
     }
 
-    int threads = std::stoi(argv[1]);
-    std::string input_file = argv[2];
-    std::string output_file = argv[3];
+    threads = std::stoi(argv[1]);
+    input_file = argv[2];
+    output_file = argv[3];
+}
 
+void parse_input() {
     Parser parser(input_file);
+    graph = parser.get_graph();
+}
+
+void init() {
+    for (int vertex : graph.get_vertices()) {
+        betweenness[vertex] = 0;
+        vertices_to_process.push(vertex);
+    }
+}
+
+int next_vertex() {
+    std::lock_guard<std::mutex> lock(queue_mutex);
+    if (vertices_to_process.empty()) {
+        return -1;
+    }
+    int vertex;
+    vertex = vertices_to_process.front();
+    vertices_to_process.pop();
+    return vertex;
+}
+
+void update_betweenness(int vertex, DependencyCalculator & dc) {
+    std::lock_guard<std::mutex> lock(betweenness_mutex);
+    for (int v : graph.get_vertices()) {
+        if (v != vertex ) {
+            betweenness[v] += dc.get_dependency(v);
+        }
+    }
+}
+
+void launch_threads() {
+    for (int i = 0; i < threads; i++) {
+        threads_list.emplace_back([&] () {
+            int vertex = next_vertex();
+            while(vertex != -1) {
+                DependencyCalculator dc(graph, vertex);
+                update_betweenness(vertex, dc);
+
+                vertex = next_vertex();
+            }
+        });
+    }
+}
+
+void join_threads() {
+    for (std::thread& thread : threads_list) {
+        thread.join();
+    }
+}
+
+void print_betweenness() {
+    std::ofstream fout(output_file);
+
+    for (int vertex : graph.get_vertices()) {
+        if (graph.has_out_edges(vertex)) {
+            fout << vertex << " " << betweenness[vertex] << std::endl;
+        }
+    }
+}
+
+int main(int argc, char *argv[]) {
+    parse_args(argc, argv);
+    parse_input();
+
+    init();
+
+    launch_threads();
+    join_threads();
 
-    const Graph &graph = parser.get_graph();
+    print_betweenness();
 
     return 0;
 }
-- 
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