Replace nlohmann json with simdjson

src/CMakeLists.txt

@@ -33,7 +33,7 @@ target_link_libraries(gpudrive_mgr
     PUBLIC
         madrona_python_utils
     PRIVATE
-        nlohmann_json::nlohmann_json
+        madrona_json
         gpudrive_cpu_impl
         madrona_mw_cpu
         madrona_common

src/MapReader.cpp

@@ -36,8 +36,13 @@ madrona_gpudrive::Map *copyToArrayOnHostOrDevice(const madrona_gpudrive::Map *in
 
 namespace madrona_gpudrive {
 
-MapReader::MapReader(const std::string &pathToFile) : in_(pathToFile) {
-  assert(in_.is_open());
+simdjson::dom::parser& MapReader::getParser() {
+  static simdjson::dom::parser parser;
+  return parser;
+}
+
+MapReader::MapReader(const std::string &pathToFile){
+  in_ = pathToFile;
   map_ = new madrona_gpudrive::Map();
 }
 
@@ -46,10 +51,13 @@ MapReader::~MapReader() {
 }
 
 void MapReader::doParse(float polylineReductionThreshold) {
-  nlohmann::json rawJson;
-  in_ >> rawJson;
+    // Parse with simdjson
+    auto& parser = getParser();
+    simdjson::dom::element doc;
+    auto error = parser.load(in_).get(doc);
 
-  from_json(rawJson, *map_, polylineReductionThreshold);
+    // Parse the document into the map
+    from_json(doc, *map_, polylineReductionThreshold);
 }
 
 madrona_gpudrive::Map* MapReader::parseAndWriteOut(const std::string &path,

src/MapReader.hpp

@@ -2,7 +2,7 @@
 
 #include <fstream>
 #include <madrona/exec_mode.hpp>
-
+#include <simdjson.h>
 #include "init.hpp"
 
 namespace madrona_gpudrive {
@@ -14,11 +14,12 @@ class MapReader {
   static madrona_gpudrive::Map* parseAndWriteOut(const std::string &path, madrona::ExecMode executionMode, float polylineReductionThreshold);
 
 private:
+  static simdjson::dom::parser& getParser();
   MapReader(const std::string &pathToFile);
   ~MapReader();
   void doParse(float polylineReductionThreshold);
 
-  std::ifstream in_;
+  std::string in_;
   madrona_gpudrive::Map *map_;
 };
 

src/headless.cpp

@@ -35,9 +35,7 @@ int main(int argc, char *argv[])
 
     uint64_t num_steps = std::stoul(argv[2]);
     std::vector<std::string> scenes = {
-        "../data/processed/examples/tfrecord-00000-of-00150_78.json",
-        "../data/processed/examples/tfrecord-00043-of-00150_223.json",
-        "../data/processed/examples/tfrecord-00149-of-00150_111.json"
+        "../data/processed/examples/tfrecord-00000-of-01000_325.json",
     };
     uint64_t num_worlds = scenes.size();