commit 46b1283d18d27bcbcfe4298ed074e81dac081fe2
author Lukas Barth <Lukas Barth barth@mentz.net> Fri May 12 14:53:53 2023 +0200
committer Jens Geyer <Jens-G@users.noreply.github.com> Sat Jun 10 14:48:30 2023 +0200
tree 13a48ebd46bed53edcf8c4001a602d226b473868
parent dd2e0d4ae21d2123d2136e43ce81f668d89690b7

Don't create a new locale on every to_string() call.

Creating locales is surprisingly expensive. We have an application where we - especially during tests - write large amounts of Thrift dumps to disk, and is this application we currently spend around 17% of total CPU time in std::locale's constructor. With this change, it's basically down to zero.

lib/cpp/src/thrift/TToString.h

diff --git a/lib/cpp/src/thrift/TToString.h b/lib/cpp/src/thrift/TToString.h
index 79743fd..474429d 100644
--- a/lib/cpp/src/thrift/TToString.h
+++ b/lib/cpp/src/thrift/TToString.h
@@ -35,7 +35,8 @@
 template <typename T>
 std::string to_string(const T& t) {
   std::ostringstream o;
-  o.imbue(std::locale("C"));
+  const static auto locale = std::locale("C");
+  o.imbue(locale);
   o << t;
   return o.str();
 }
@@ -44,7 +45,8 @@
 // is enabled.
 inline std::string to_string(const float& t) {
   std::ostringstream o;
-  o.imbue(std::locale("C"));
+  const static auto locale = std::locale("C");
+  o.imbue(locale);
   o.precision(static_cast<std::streamsize>(std::ceil(static_cast<double>(std::numeric_limits<float>::digits * std::log10(2.0f) + 1))));
   o << t;
   return o.str();
@@ -52,7 +54,8 @@
 
 inline std::string to_string(const double& t) {
   std::ostringstream o;
-  o.imbue(std::locale("C"));
+  const static auto locale = std::locale("C");
+  o.imbue(locale);
   o.precision(static_cast<std::streamsize>(std::ceil(static_cast<double>(std::numeric_limits<double>::digits * std::log10(2.0f) + 1))));
   o << t;
   return o.str();
@@ -60,7 +63,8 @@
 
 inline std::string to_string(const long double& t) {
   std::ostringstream o;
-  o.imbue(std::locale("C"));
+  const static auto locale = std::locale("C");
+  o.imbue(locale);
   o.precision(static_cast<std::streamsize>(std::ceil(static_cast<double>(std::numeric_limits<long double>::digits * std::log10(2.0f) + 1))));
   o << t;
   return o.str();