Add an program option to specify the number of threads.

With the latest changes, we can do calculation in parallel in multiple different threads.

The updateCache API call is not thread-safe yet. We need to add locks around the transitData object and the updateCache
call. But in the majority of cases, we do not use this api call, so it's safe to use as is for the moment.

connection_scan_algorithm/include/program_options.hpp

@@ -18,6 +18,7 @@ namespace TrRouting
     bool        debug;
     bool        cacheAllConnectionSets;
     bool        useEuclideanDistance;
+    int         numberOfThreads;
     std::string algorithm;
     std::string dataFetcherShortname;
     std::string osrmWalkingPort;

connection_scan_algorithm/src/program_options.cpp

@@ -20,6 +20,8 @@ namespace TrRouting {
       ("cacheAllConnectionSets",                            boost::program_options::value<bool>()       ->default_value(false), "cache all connections set instead of the ones from the last used scenario");
     options.add_options()
       ("useEuclideanDistance",                              boost::program_options::value<bool>()       ->default_value(false), "Use euclidean distance calculation instead of OSRM for access and egress calculations");
+    options.add_options()
+      ("threads",                                           boost::program_options::value<int>()        ->default_value(1), "Number of threads to use to serve requests");
     options.add_options()
       ("osrmPort,osrmWalkPort,osrmWalkingPort",             boost::program_options::value<std::string>()->default_value("5000"), "osrm walking port");
     options.add_options()
@@ -46,6 +48,7 @@ namespace TrRouting {
     cachePath            = "cache";
     cacheAllConnectionSets = false;
     useEuclideanDistance = false;
+    numberOfThreads      = 1;
     osrmWalkingPort      = "5000";
     osrmCyclingPort      = "8000";
     osrmDrivingPort      = "7000";
@@ -85,6 +88,10 @@ namespace TrRouting {
     {
       useEuclideanDistance = variablesMap["useEuclideanDistance"].as<bool>();
     }
+    if(variablesMap.count("threads") == 1)
+    {
+      numberOfThreads = variablesMap["threads"].as<int>();
+    }
 
     if(variablesMap.count("osrmWalkPort") == 1)
     {

connection_scan_algorithm/src/transit_routing_http_server.cpp

@@ -136,13 +136,11 @@ int main(int argc, char** argv) {
     spdlog::info("Using OSRM for access/egress node time/distance");
   }
 
-  spdlog::info("preparing server...");
+  spdlog::info("preparing server with {} threads...", programOptions.numberOfThreads);
 
-  //HTTP-server using 1 thread
-  //Unless you do more heavy non-threaded processing in the resources,
-  //1 thread is usually faster than several threads
   HttpServer server;
   server.config.port = programOptions.port;
+  server.config.thread_pool_size = programOptions.numberOfThreads;
 
   // updateCache:
   server.resource["^/updateCache[/]?$"]["GET"]=[&server, &transitData](std::shared_ptr<HttpServer::Response> serverResponse, std::shared_ptr<HttpServer::Request> request) {