Deterministic render ordering

src/metric.cpp

@@ -11,6 +11,7 @@
 #include <cstdlib>
 #include <cstring>
 #include <functional>
+#include <map>
 #include <mutex>
 #include <string>
 #include <thread>
@@ -168,6 +169,21 @@ struct LabelsKey {
     }
     return true;
   }
+
+  bool operator<(const LabelsKey &other) const {
+    if (labels.size() != other.labels.size()) {
+      return labels.size() < other.labels.size();
+    }
+    for (size_t i = 0; i < labels.size(); ++i) {
+      if (labels[i].first != other.labels[i].first) {
+        return labels[i].first < other.labels[i].first;
+      }
+      if (labels[i].second != other.labels[i].second) {
+        return labels[i].second < other.labels[i].second;
+      }
+    }
+    return false; // They are equal
+  }
 };
 
 } // namespace metric
@@ -214,9 +230,8 @@ template <> struct Family<Counter>::State {
       global_accumulated_values;
 
   // Callback-based metrics (global, not per-thread)
-  std::unordered_map<
-      LabelsKey, MetricCallback<Counter>, std::hash<LabelsKey>,
-      std::equal_to<LabelsKey>,
+  std::map<
+      LabelsKey, MetricCallback<Counter>, std::less<LabelsKey>,
       ArenaStlAllocator<std::pair<const LabelsKey, MetricCallback<Counter>>>>
       callbacks;
 
@@ -238,10 +253,8 @@ template <> struct Family<Gauge>::State {
       instances;
 
   // Callback-based metrics
-  std::unordered_map<
-      LabelsKey, MetricCallback<Gauge>, std::hash<LabelsKey>,
-      std::equal_to<LabelsKey>,
-      ArenaStlAllocator<std::pair<const LabelsKey, MetricCallback<Gauge>>>>
+  std::map<LabelsKey, MetricCallback<Gauge>, std::less<LabelsKey>,
+           ArenaStlAllocator<std::pair<const LabelsKey, MetricCallback<Gauge>>>>
       callbacks;
 
   State(ArenaAllocator &arena)
@@ -321,9 +334,8 @@ struct Metric {
 
   // Function-local statics to avoid static initialization order fiasco
   static auto &get_counter_families() {
-    using FamilyMap = std::unordered_map<
-        std::string_view, Family<Counter>::State *, std::hash<std::string_view>,
-        std::equal_to<std::string_view>,
+    using FamilyMap = std::map<
+        std::string_view, Family<Counter>::State *, std::less<std::string_view>,
         ArenaStlAllocator<
             std::pair<const std::string_view, Family<Counter>::State *>>>;
     static FamilyMap *counterFamilies = new FamilyMap(
@@ -334,9 +346,8 @@ struct Metric {
   }
 
   static auto &get_gauge_families() {
-    using FamilyMap = std::unordered_map<
-        std::string_view, Family<Gauge>::State *, std::hash<std::string_view>,
-        std::equal_to<std::string_view>,
+    using FamilyMap = std::map<
+        std::string_view, Family<Gauge>::State *, std::less<std::string_view>,
         ArenaStlAllocator<
             std::pair<const std::string_view, Family<Gauge>::State *>>>;
     static FamilyMap *gaugeFamilies = new FamilyMap(
@@ -347,11 +358,11 @@ struct Metric {
   }
 
   static auto &get_histogram_families() {
-    using FamilyMap = std::unordered_map<
-        std::string_view, Family<Histogram>::State *,
-        std::hash<std::string_view>, std::equal_to<std::string_view>,
-        ArenaStlAllocator<
-            std::pair<const std::string_view, Family<Histogram>::State *>>>;
+    using FamilyMap =
+        std::map<std::string_view, Family<Histogram>::State *,
+                 std::less<std::string_view>,
+                 ArenaStlAllocator<std::pair<const std::string_view,
+                                             Family<Histogram>::State *>>>;
     static FamilyMap *histogramFamilies = new FamilyMap(
         ArenaStlAllocator<
             std::pair<const std::string_view, Family<Histogram>::State *>>(
@@ -997,9 +1008,8 @@ std::span<std::string_view> render(ArenaAllocator &arena) {
     }
 
     // Aggregate all counter values (thread-local + global accumulated)
-    std::unordered_map<LabelsKey, double, std::hash<LabelsKey>,
-                       std::equal_to<LabelsKey>,
-                       ArenaStlAllocator<std::pair<const LabelsKey, double>>>
+    std::map<LabelsKey, double, std::less<LabelsKey>,
+             ArenaStlAllocator<std::pair<const LabelsKey, double>>>
         aggregated_values{
             ArenaStlAllocator<std::pair<const LabelsKey, double>>(&arena)};
 
@@ -1094,9 +1104,8 @@ std::span<std::string_view> render(ArenaAllocator &arena) {
       AggregatedHistogram(ArenaAllocator &arena)
           : thresholds(&arena), counts(&arena), sum(0.0), observations(0) {}
     };
-    std::unordered_map<
-        LabelsKey, AggregatedHistogram *, std::hash<LabelsKey>,
-        std::equal_to<LabelsKey>,
+    std::map<
+        LabelsKey, AggregatedHistogram *, std::less<LabelsKey>,
         ArenaStlAllocator<std::pair<const LabelsKey, AggregatedHistogram *>>>
         aggregated_histograms{ArenaStlAllocator<
             std::pair<const LabelsKey, AggregatedHistogram *>>(&arena)};
@@ -1295,4 +1304,31 @@ void Family<Gauge>::register_callback(
 std::mutex Metric::mutex;
 thread_local Metric::ThreadInit Metric::thread_init;
 
+void reset_metrics_for_testing() {
+  std::lock_guard _{Metric::mutex};
+
+  // WARNING: This function assumes no metric objects are in use!
+  // Clear all family maps - this will leak the Family::State objects but
+  // that's acceptable for testing since they were allocated in the global arena
+
+  // Get references to the maps
+  auto &counter_families = Metric::get_counter_families();
+  auto &gauge_families = Metric::get_gauge_families();
+  auto &histogram_families = Metric::get_histogram_families();
+  auto &interned_labels = Metric::get_interned_labels();
+
+  // Clear all family registrations
+  counter_families.clear();
+  gauge_families.clear();
+  histogram_families.clear();
+  interned_labels.clear();
+
+  // Reset the global arena - this will invalidate all arena-allocated strings
+  // but since we're clearing everything, that's OK
+  Metric::get_global_arena().reset();
+
+  // Note: Thread-local arenas will be cleaned up by ThreadInit destructors
+  // when threads exit naturally
+}
+
 } // namespace metric

src/metric.hpp

@@ -218,6 +218,11 @@ bool is_valid_metric_name(std::string_view name);
 bool is_valid_label_key(std::string_view key);
 bool is_valid_label_value(std::string_view value);
 
+// Reset all metrics state - WARNING: Only safe for testing!
+// This clears all registered families and metrics. Should only be called
+// when no metric objects are in use and no concurrent render() calls.
+void reset_metrics_for_testing();
+
 // Note: Histograms do not support callbacks due to their multi-value nature
 // (buckets + sum + count). Use static histogram metrics only.