Improve performance of JSON rendering

.github/workflows/osrm-backend.yml

@@ -715,6 +715,7 @@ jobs:
  pushd ${OSRM_BUILD_DIR}
  make --jobs=${JOBS} benchmarks
  ./src/benchmarks/alias-bench 
+ ./src/benchmarks/json-render-bench
  ./src/benchmarks/match-bench ../test/data/ch/monaco.osrm
  ./src/benchmarks/packedvector-bench
  ./src/benchmarks/rtree-bench ../test/data/monaco.osrm.ramIndex ../test/data/monaco.osrm.fileIndex ../test/data/monaco.osrm.nbg_nodes

include/util/json_renderer.hpp

@@ -27,18 +27,32 @@ namespace
 constexpr int MAX_FLOAT_STRING_LENGTH = 256;
 }
 
-struct Renderer
+template <typename Out> struct Renderer
 {
- explicit Renderer(std::ostream &_out) : out(_out) {}
+ explicit Renderer(Out &_out) : out(_out) {}
 
- void operator()(const String &string) const
+ void operator()(const String &string)
  {
- out << "\"";
- out << escape_JSON(string.value);
- out << "\"";
+ write('"');
+ // here we assume that vast majority of strings don't need to be escaped,
+ // so we check it first and escape only if needed
+ auto size = SizeOfEscapedJSONString(string.value);
+ if (size == string.value.size())
+ {
+ write(string.value);
+ }
+ else
+ {
+ std::string escaped;
+ escaped.reserve(size);
+ EscapeJSONString(string.value, escaped);
+
+ write(escaped);
+ }
+ write('"');
  }
 
- void operator()(const Number &number) const
+ void operator()(const Number &number)
  {
  char buffer[MAX_FLOAT_STRING_LENGTH] = {'\0'};
  ieee754::dtoa_milo(number.value, buffer);
@@ -64,131 +78,95 @@ struct Renderer
  }
  ++pos;
  }
- out << buffer;
+ write(buffer);
  }
 
- void operator()(const Object &object) const
+ void operator()(const Object &object)
  {
- out << "{";
+ write('{');
  for (auto it = object.values.begin(), end = object.values.end(); it != end;)
  {
- out << "\"" << it->first << "\":";
+ write('\"');
+ write(it->first);
+ write("\":");
  mapbox::util::apply_visitor(Renderer(out), it->second);
  if (++it != end)
  {
- out << ",";
+ write(',');
  }
  }
- out << "}";
+ write('}');
  }
 
- void operator()(const Array &array) const
+ void operator()(const Array &array)
  {
- out << "[";
+ write('[');
  for (auto it = array.values.cbegin(), end = array.values.cend(); it != end;)
  {
  mapbox::util::apply_visitor(Renderer(out), *it);
  if (++it != end)
  {
- out << ",";
+ write(',');
  }
  }
- out << "]";
+ write(']');
  }
 
- void operator()(const True &) const { out << "true"; }
+ void operator()(const True &) { write("true"); }
 
- void operator()(const False &) const { out << "false"; }
+ void operator()(const False &) { write("false"); }
 
- void operator()(const Null &) const { out << "null"; }
+ void operator()(const Null &) { write("null"); }
 
  private:
- std::ostream &out;
+ void write(const std::string &str);
+ void write(const char *str);
+ void write(char ch);
+
+ private:
+ Out &out;
 };
 
-struct ArrayRenderer
+template <> void Renderer<std::vector<char>>::write(const std::string &str)
 {
- explicit ArrayRenderer(std::vector<char> &_out) : out(_out) {}
-
- void operator()(const String &string) const
- {
- out.push_back('\"');
- const auto string_to_insert = escape_JSON(string.value);
- out.insert(std::end(out), std::begin(string_to_insert), std::end(string_to_insert));
- out.push_back('\"');
- }
+ out.insert(out.end(), str.begin(), str.end());
+}
 
- void operator()(const Number &number) const
- {
- const std::string number_string = cast::to_string_with_precision(number.value);
- out.insert(out.end(), number_string.begin(), number_string.end());
- }
+template <> void Renderer<std::vector<char>>::write(const char *str)
+{
+ out.insert(out.end(), str, str + strlen(str));
+}
 
- void operator()(const Object &object) const
- {
- out.push_back('{');
- for (auto it = object.values.begin(), end = object.values.end(); it != end;)
- {
- out.push_back('\"');
- out.insert(out.end(), it->first.begin(), it->first.end());
- out.push_back('\"');
- out.push_back(':');
+template <> void Renderer<std::vector<char>>::write(char ch) { out.push_back(ch); }
 
- mapbox::util::apply_visitor(ArrayRenderer(out), it->second);
- if (++it != end)
- {
- out.push_back(',');
- }
- }
- out.push_back('}');
- }
+template <> void Renderer<std::ostream>::write(const std::string &str) { out << str; }
 
- void operator()(const Array &array) const
- {
- out.push_back('[');
- for (auto it = array.values.cbegin(), end = array.values.cend(); it != end;)
- {
- mapbox::util::apply_visitor(ArrayRenderer(out), *it);
- if (++it != end)
- {
- out.push_back(',');
- }
- }
- out.push_back(']');
- }
+template <> void Renderer<std::ostream>::write(const char *str) { out << str; }
 
- void operator()(const True &) const
- {
- const std::string temp("true");
- out.insert(out.end(), temp.begin(), temp.end());
- }
+template <> void Renderer<std::ostream>::write(char ch) { out << ch; }
 
- void operator()(const False &) const
- {
- const std::string temp("false");
- out.insert(out.end(), temp.begin(), temp.end());
- }
+template <> void Renderer<std::string>::write(const std::string &str) { out += str; }
 
- void operator()(const Null &) const
- {
- const std::string temp("null");
- out.insert(out.end(), temp.begin(), temp.end());
- }
+template <> void Renderer<std::string>::write(const char *str) { out += str; }
 
- private:
- std::vector<char> &out;
-};
+template <> void Renderer<std::string>::write(char ch) { out += ch; }
 
 inline void render(std::ostream &out, const Object &object)
 {
- Value value = object;
- mapbox::util::apply_visitor(Renderer(out), value);
+ Renderer renderer(out);
+ renderer(object);
+}
+
+inline void render(std::string &out, const Object &object)
+{
+ Renderer renderer(out);
+ renderer(object);
 }
 
 inline void render(std::vector<char> &out, const Object &object)
 {
- Value value = object;
- mapbox::util::apply_visitor(ArrayRenderer(out), value);
+ Renderer renderer(out);
+ renderer(object);
 }
 
 } // namespace json

include/util/string_util.hpp

@@ -58,11 +58,32 @@ template <int length, int precision> char *printInt(char *buffer, int value)
  return buffer;
 }
 
-inline std::string escape_JSON(const std::string &input)
+inline size_t SizeOfEscapedJSONString(const std::string &string)
+{
+ size_t size = 0;
+ for (const char letter : string)
+ {
+ switch (letter)
+ {
+ case '\\':
+ case '"':
+ case '/':
+ case '\b':
+ case '\f':
+ case '\n':
+ case '\r':
+ case '\t':
+ size += 2;
+ break;
+ default:
+ size += 1;
+ }
+ }
+ return size;
+}
+
+inline void EscapeJSONString(const std::string &input, std::string &output)
 {
- // escape and skip reallocations if possible
- std::string output;
- output.reserve(input.size() + 4); // +4 assumes two backslashes on avg
  for (const char letter : input)
  {
  switch (letter)
@@ -96,7 +117,6 @@ inline std::string escape_JSON(const std::string &input)
  break;
  }
  }
- return output;
 }
 
 inline std::size_t URIDecode(const std::string &input, std::string &output)

src/benchmarks/CMakeLists.txt

@@ -30,6 +30,18 @@ target_link_libraries(match-bench
  ${TBB_LIBRARIES}
  ${MAYBE_SHAPEFILE})
 
+add_executable(json-render-bench
+ EXCLUDE_FROM_ALL
+ json_render.cpp
+ $<TARGET_OBJECTS:UTIL>)
+
+target_link_libraries(json-render-bench
+ osrm
+ ${BOOST_BASE_LIBRARIES}
+ ${CMAKE_THREAD_LIBS_INIT}
+ ${TBB_LIBRARIES}
+ ${MAYBE_SHAPEFILE})
+
 add_executable(alias-bench
  EXCLUDE_FROM_ALL
  ${AliasBenchmarkSources}
@@ -41,6 +53,8 @@ target_link_libraries(alias-bench
  ${TBB_LIBRARIES}
  ${MAYBE_SHAPEFILE})
 
+
+
 add_executable(packedvector-bench
  EXCLUDE_FROM_ALL
  ${PackedVectorBenchmarkSources}
@@ -58,4 +72,5 @@ add_custom_target(benchmarks
  rtree-bench
  packedvector-bench
  match-bench
+ json-render-bench
  alias-bench)