Add process collector

src/metric.cpp

@@ -12,6 +12,7 @@
 #include <cstring>
 #include <functional>
 #include <map>
+#include <memory>
 #include <mutex>
 #include <set>
 #include <string>
@@ -451,6 +452,12 @@ struct Metric {
     return *threadArenas;
   }
 
+  static auto &get_collectors() {
+    using CollectorRegistry = std::vector<std::shared_ptr<Collector>>;
+    static CollectorRegistry *collectors = new CollectorRegistry();
+    return *collectors;
+  }
+
   // Thread cleanup for per-family thread-local storage
   struct ThreadInit {
     ArenaAllocator arena;
@@ -1697,6 +1704,11 @@ std::span<std::string_view> render(ArenaAllocator &arena) {
   // prevents races during static member initialization at program startup
   std::unique_lock<std::mutex> _{Metric::mutex};
 
+  // Call all registered collectors to update their metrics
+  for (const auto &collector : Metric::get_collectors()) {
+    collector->collect();
+  }
+
   // Phase 1: Compile - generate static text and instructions
   // Safe: cached_plan access/initialization protected by mutex above
   if (!Metric::cached_plan || Metric::cached_plan->registration_version !=
@@ -1800,4 +1812,10 @@ void reset_metrics_for_testing() {
   // when threads exit naturally
 }
 
+void register_collector(std::shared_ptr<Collector> collector) {
+  std::unique_lock<std::mutex> _{Metric::mutex};
+  ++Metric::registration_version;
+  Metric::get_collectors().push_back(std::move(collector));
+}
+
 } // namespace metric