Add process collector

src/main.cpp

@@ -1,10 +1,10 @@
 #include "config.hpp"
 #include "connection.hpp"
-#include "connection_handler.hpp"
 #include "http_handler.hpp"
+#include "metric.hpp"
 #include "perfetto_categories.hpp"
+#include "process_collector.hpp"
 #include "server.hpp"
-#include <atomic>
 #include <csignal>
 #include <cstring>
 #include <fcntl.h>
@@ -176,6 +176,9 @@ int main(int argc, char *argv[]) {
   perfetto::TrackEvent::Register();
 #endif
 
+  // Register the process collector for default metrics.
+  metric::register_collector(std::make_shared<ProcessCollector>());
+
   std::string config_file = "config.toml";
 
   // Parse command line arguments

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

src/metric.hpp

@@ -45,6 +45,7 @@
 
 #include <functional>
 #include <initializer_list>
+#include <memory>
 #include <span>
 #include <type_traits>
 #include <vector>
@@ -231,6 +232,36 @@ bool is_valid_label_value(std::string_view value);
 // when no metric objects are in use and no concurrent render() calls.
 void reset_metrics_for_testing();
 
+/**
+ * @brief Interface for a custom collector that can be registered with the
+ * metrics system.
+ *
+ * This is used for complex metric gathering, such as reading from /proc, where
+ * multiple metrics need to be updated from a single data source.
+ */
+struct Collector {
+  /**
+   * @brief Virtual destructor.
+   */
+  virtual ~Collector() = default;
+
+  /**
+   * @brief Called by the metrics system to update the metrics this collector is
+   * responsible for.
+   */
+  virtual void collect() = 0;
+};
+
+/**
+ * @brief Register a collector with the metrics system.
+ *
+ * The system will hold a shared_ptr to the collector and call its collect()
+ * method during each metric rendering.
+ *
+ * @param collector A shared_ptr to the collector to be registered.
+ */
+void register_collector(std::shared_ptr<Collector> collector);
+
 // Note: Histograms do not support callbacks due to their multi-value nature
 // (buckets + sum + count). Use static histogram metrics only.
 

src/process_collector.cpp

@@ -0,0 +1,154 @@
+#include "process_collector.hpp"
+
+#include <cstdio>
+#include <cstring>
+#include <dirent.h>
+#include <sys/resource.h>
+#include <unistd.h>
+#include <vector>
+
+namespace {
+// Helper function to read the system boot time from /proc/stat.
+// Returns boot time in seconds since epoch, or 0 on error.
+double get_boot_time() {
+  FILE *fp = std::fopen("/proc/stat", "r");
+  if (!fp) {
+    return 0;
+  }
+
+  char line[256];
+  double boot_time = 0;
+  while (std::fgets(line, sizeof(line), fp)) {
+    if (std::strncmp(line, "btime ", 6) == 0) {
+      if (std::sscanf(line + 6, "%lf", &boot_time) != 1) {
+        boot_time = 0;
+      }
+      break;
+    }
+  }
+
+  std::fclose(fp);
+  return boot_time;
+}
+} // namespace
+
+ProcessCollector::ProcessCollector()
+    : cpu_seconds_total_(metric::create_counter(
+                             "process_cpu_seconds_total",
+                             "Total user and system CPU time spent in seconds")
+                             .create({})),
+      resident_memory_bytes_(
+          metric::create_gauge("process_resident_memory_bytes",
+                               "Resident memory size in bytes")
+              .create({})),
+      virtual_memory_bytes_(metric::create_gauge("process_virtual_memory_bytes",
+                                                 "Virtual memory size in bytes")
+                                .create({})),
+      open_fds_(metric::create_gauge("process_open_fds",
+                                     "Number of open file descriptors")
+                    .create({})),
+      max_fds_(metric::create_gauge("process_max_fds",
+                                    "Maximum number of open file descriptors")
+                   .create({})),
+      start_time_seconds_(
+          metric::create_gauge(
+              "process_start_time_seconds",
+              "Start time of the process since unix epoch in seconds")
+              .create({})) {
+  // Set the constant max_fds metric.
+  struct rlimit rlim;
+  if (getrlimit(RLIMIT_NOFILE, &rlim) == 0) {
+    max_fds_.set(rlim.rlim_cur);
+  }
+
+  // Perform an initial collection to populate the other metrics and set the
+  // initial counter values.
+  collect();
+}
+
+void ProcessCollector::collect() {
+  // --- CPU Time, Memory, and Start Time from /proc/self/stat ---
+  FILE *fp = std::fopen("/proc/self/stat", "r");
+  if (!fp) {
+    return;
+  }
+
+  char buf[2048];
+  if (std::fgets(buf, sizeof(buf), fp) == nullptr) {
+    std::fclose(fp);
+    return;
+  }
+  std::fclose(fp);
+
+  // Find the end of the command name, which is in parentheses
+  const char *stats_start = std::strrchr(buf, ')');
+  if (!stats_start) {
+    return;
+  }
+  stats_start += 2; // Skip the ')' and the space
+
+  // Tokenize the rest of the string
+  std::vector<const char *> stats;
+  char *p = const_cast<char *>(stats_start);
+  while (*p) {
+    stats.push_back(p);
+    while (*p && *p != ' ') {
+      p++;
+    }
+    if (*p) {
+      *p = '\0';
+      p++;
+    }
+  }
+
+  // We need at least 22 fields for starttime, 24 for rss
+  if (stats.size() < 24) {
+    return;
+  }
+
+  long clk_tck = sysconf(_SC_CLK_TCK);
+
+  // --- CPU Time ---
+  unsigned long long utime_ticks = std::strtoull(stats[11], nullptr, 10);
+  unsigned long long stime_ticks = std::strtoull(stats[12], nullptr, 10);
+  unsigned long long current_total_ticks = utime_ticks + stime_ticks;
+
+  if (last_total_ticks_ > 0) { // If we have a previous value
+    if (current_total_ticks > last_total_ticks_) {
+      double delta_seconds =
+          (double)(current_total_ticks - last_total_ticks_) / clk_tck;
+      cpu_seconds_total_.inc(delta_seconds);
+    }
+  } else { // First run, initialize the counter
+    cpu_seconds_total_.inc((double)current_total_ticks / clk_tck);
+  }
+  last_total_ticks_ = current_total_ticks;
+
+  // --- Memory ---
+  unsigned long long vsize = std::strtoull(stats[20], nullptr, 10);
+  long rss_pages = std::strtol(stats[21], nullptr, 10);
+  virtual_memory_bytes_.set(vsize);
+  resident_memory_bytes_.set(rss_pages * sysconf(_SC_PAGESIZE));
+
+  // --- Start Time (only needs to be set once) ---
+  if (!start_time_set_) {
+    long long start_time_ticks = std::strtoll(stats[19], nullptr, 10);
+    double boot_time = get_boot_time();
+    if (boot_time > 0) {
+      start_time_seconds_.set(boot_time + (double)start_time_ticks / clk_tck);
+      start_time_set_ = true;
+    }
+  }
+
+  // --- File Descriptors ---
+  int fd_count = 0;
+  DIR *dp = opendir("/proc/self/fd");
+  if (dp) {
+    while (readdir(dp) != nullptr) {
+      fd_count++;
+    }
+    closedir(dp);
+    // Subtract 3 for '.', '..', and the opendir handle itself
+    open_fds_.set(fd_count > 3 ? fd_count - 3 : 0);
+  }
+}

src/process_collector.hpp

@@ -0,0 +1,34 @@
+#pragma once
+
+#include "metric.hpp"
+
+/**
+ * @brief A metric collector for standard process-level statistics.
+ *
+ * Gathers metrics like CPU usage, memory, and file descriptors by reading
+ * files from the /proc filesystem.
+ */
+struct ProcessCollector : public metric::Collector {
+  /**
+   * @brief Constructs the collector and initializes the process metrics.
+   */
+  ProcessCollector();
+
+  /**
+   * @brief Called by the metrics system to update the process metrics.
+   */
+  void collect() override;
+
+private:
+  // Metrics for process statistics
+  metric::Counter cpu_seconds_total_;
+  metric::Gauge resident_memory_bytes_;
+  metric::Gauge virtual_memory_bytes_;
+  metric::Gauge open_fds_;
+  metric::Gauge max_fds_;
+  metric::Gauge start_time_seconds_;
+
+  // Last observed values for calculating counter increments
+  unsigned long long last_total_ticks_ = 0;
+  bool start_time_set_ = false;
+};