From 0ff197d4061f96b9a6b39af06264d4c73843b3fc Mon Sep 17 00:00:00 2001
From: Andrew Noyes <andrew@weaselab.dev>
Date: Sat, 30 Aug 2025 17:57:16 -0400
Subject: [PATCH] Fix static initialization order fiasco

---
 src/metric.cpp | 54 +++++++++++++++++++++++++++-----------------------
 1 file changed, 29 insertions(+), 25 deletions(-)

diff --git a/src/metric.cpp b/src/metric.cpp
index 9e12a38..f131bcf 100644
--- a/src/metric.cpp
+++ b/src/metric.cpp
@@ -23,8 +23,6 @@
 
 #include "format.hpp"
 
-// TODO fix static initialization order fiasco
-
 // Verify that malloc provides sufficient alignment for atomic 128-bit
 // operations
 static_assert(__STDCPP_DEFAULT_NEW_ALIGNMENT__ >= 16,
@@ -193,15 +191,27 @@ struct Histogram::State {
 struct Metric {
   static std::mutex mutex;
 
-  // Two-level map: name -> Family
-  static std::unordered_map<std::string,
-                            std::unique_ptr<Family<Counter>::State>>
-      counterFamilies;
-  static std::unordered_map<std::string, std::unique_ptr<Family<Gauge>::State>>
-      gaugeFamilies;
-  static std::unordered_map<std::string,
-                            std::unique_ptr<Family<Histogram>::State>>
-      histogramFamilies;
+  // Function-local statics to avoid static initialization order fiasco
+  static auto &get_counter_families() {
+    static std::unordered_map<std::string,
+                              std::unique_ptr<Family<Counter>::State>>
+        counterFamilies;
+    return counterFamilies;
+  }
+
+  static auto &get_gauge_families() {
+    static std::unordered_map<std::string,
+                              std::unique_ptr<Family<Gauge>::State>>
+        gaugeFamilies;
+    return gaugeFamilies;
+  }
+
+  static auto &get_histogram_families() {
+    static std::unordered_map<std::string,
+                              std::unique_ptr<Family<Histogram>::State>>
+        histogramFamilies;
+    return histogramFamilies;
+  }
 
   // Thread cleanup for per-family thread-local storage
   struct ThreadInit {
@@ -214,7 +224,7 @@ struct Metric {
       auto thread_id = std::this_thread::get_id();
 
       // Accumulate counter families
-      for (auto &[name, family] : counterFamilies) {
+      for (auto &[name, family] : Metric::get_counter_families()) {
         auto thread_it = family->perThreadState.find(thread_id);
         if (thread_it != family->perThreadState.end()) {
           for (auto &[labels_key, instance] : thread_it->second.instances) {
@@ -236,7 +246,7 @@ struct Metric {
       }
 
       // Accumulate histogram families
-      for (auto &[name, family] : histogramFamilies) {
+      for (auto &[name, family] : Metric::get_histogram_families()) {
         auto thread_it = family->perThreadState.find(thread_id);
         if (thread_it != family->perThreadState.end()) {
           for (auto &[labels_key, instance] : thread_it->second.instances) {
@@ -490,7 +500,7 @@ Family<Counter> create_counter(std::string name, std::string help) {
                     name.c_str());
 
   std::unique_lock<std::mutex> _{Metric::mutex};
-  auto &familyPtr = Metric::counterFamilies[name];
+  auto &familyPtr = Metric::get_counter_families()[name];
   if (!familyPtr) {
     familyPtr = std::make_unique<Family<Counter>::State>();
     familyPtr->name = std::move(name);
@@ -511,7 +521,7 @@ Family<Gauge> create_gauge(std::string name, std::string help) {
                     name.c_str());
 
   std::unique_lock<std::mutex> _{Metric::mutex};
-  auto &familyPtr = Metric::gaugeFamilies[name];
+  auto &familyPtr = Metric::get_gauge_families()[name];
   if (!familyPtr) {
     familyPtr = std::make_unique<Family<Gauge>::State>();
     familyPtr->name = std::move(name);
@@ -533,7 +543,7 @@ Family<Histogram> create_histogram(std::string name, std::string help,
                     name.c_str());
 
   std::unique_lock<std::mutex> _{Metric::mutex};
-  auto &familyPtr = Metric::histogramFamilies[name];
+  auto &familyPtr = Metric::get_histogram_families()[name];
   if (!familyPtr) {
     familyPtr = std::make_unique<Family<Histogram>::State>();
     familyPtr->name = std::move(name);
@@ -724,7 +734,7 @@ std::span<std::string_view> render(ArenaAllocator &arena) {
   };
 
   // Render counters
-  for (const auto &[name, family] : Metric::counterFamilies) {
+  for (const auto &[name, family] : Metric::get_counter_families()) {
     output.push_back(
         format(arena, "# HELP %s %s\n", name.c_str(), family->help.c_str()));
     output.push_back(format(arena, "# TYPE %s counter\n", name.c_str()));
@@ -777,7 +787,7 @@ std::span<std::string_view> render(ArenaAllocator &arena) {
   }
 
   // Render gauges
-  for (const auto &[name, family] : Metric::gaugeFamilies) {
+  for (const auto &[name, family] : Metric::get_gauge_families()) {
     output.push_back(
         format(arena, "# HELP %s %s\n", name.c_str(), family->help.c_str()));
     output.push_back(format(arena, "# TYPE %s gauge\n", name.c_str()));
@@ -810,7 +820,7 @@ std::span<std::string_view> render(ArenaAllocator &arena) {
   }
 
   // Render histograms
-  for (const auto &[name, family] : Metric::histogramFamilies) {
+  for (const auto &[name, family] : Metric::get_histogram_families()) {
     output.push_back(
         format(arena, "# HELP %s %s\n", name.c_str(), family->help.c_str()));
     output.push_back(format(arena, "# TYPE %s histogram\n", name.c_str()));
@@ -995,12 +1005,6 @@ void Family<Gauge>::register_callback(
 
 // Static member definitions
 std::mutex Metric::mutex;
-std::unordered_map<std::string, std::unique_ptr<Family<Counter>::State>>
-    Metric::counterFamilies;
-std::unordered_map<std::string, std::unique_ptr<Family<Gauge>::State>>
-    Metric::gaugeFamilies;
-std::unordered_map<std::string, std::unique_ptr<Family<Histogram>::State>>
-    Metric::histogramFamilies;
 thread_local Metric::ThreadInit Metric::thread_init;
 
 } // namespace metric