Optimize local time printing using new formatters

src/utils/logging.cc

@@ -27,6 +27,11 @@
 
 #include "utils/logging.h"
 
+#include <version>
+#if __cpp_lib_format >= 201907L
+#include <chrono>
+#include <format>
+#endif
 #include <iomanip>
 #include <iostream>
 #include <thread>
@@ -100,8 +105,26 @@ std::chrono::time_point<std::chrono::system_clock> SteadyClockToSystemClock(
              time - std::chrono::steady_clock::now());
 }
 
+namespace {
+#if __cpp_lib_format >= 201907L
+const std::chrono::time_zone* GetCurrentTimeZone() {
+  try {
+    return std::chrono::current_zone();
+  } catch (const std::runtime_error&) {
+    // If the current time zone cannot be determined, fall back to UTC.
+    return nullptr;
+  }
+}
+#endif
+}  // namespace
+
 std::string FormatTime(
     std::chrono::time_point<std::chrono::system_clock> time) {
+#if __cpp_lib_format >= 201907L
+  static auto* zone = GetCurrentTimeZone();
+  return zone ? std::format("{0:%m%d %T}", zone->to_local(time))
+              : std::format("{0:%m%d %T}", time);
+#else
   static Mutex mutex;
 
   std::ostringstream ss;
@@ -121,6 +144,7 @@ std::string FormatTime(
        << std::setfill('0') << std::setw(6) << us;
   }
   return ss.str();
+#endif
 }
 
-}  // namespace lczero
+}  // namespace lczero