Add file descriptor (nfds) monitoring to countmon

package/src/countmon.cpp

@@ -3,6 +3,7 @@
 
 #include "countmon.h"
 
+#include <dirent.h>
 #include <string.h>
 #include <unistd.h>
 
@@ -49,6 +50,19 @@ void countmon::update_stats(const std::vector<pid_t>& pids,
           std::stol(stat_entries[prmon::num_threads]);
     }
     stat_entries.clear();
+
+    std::stringstream fd_dir_name{};
+    fd_dir_name << read_path << "/proc/" << pid << "/fd" << std::ends;
+    DIR* fd_dir = opendir(fd_dir_name.str().c_str());
+    if (fd_dir) {
+      struct dirent* entry;
+      while ((entry = readdir(fd_dir)) != nullptr) {
+        if (entry->d_name[0] != '.') {
+          count_stat_update["nfds"] += 1L;
+        }
+      }
+      closedir(fd_dir);
+    }
   }
 
   // Update the statistics with the new snapshot values

package/src/countmon.h

@@ -1,7 +1,7 @@
 // Copyright (C) 2018-2025 CERN
 // License Apache2 - see LICENCE file
 
-// Process and thread number monitoring class
+// Process, thread and file descriptor number monitoring class
 //
 
 #ifndef PRMON_COUNTMON_H
@@ -21,7 +21,8 @@ class countmon final : public Imonitor, public MessageBase {
  private:
   // Setup the parameters to monitor here
   const prmon::parameter_list params = {{"nprocs", "1", "1"},
-                                        {"nthreads", "1", "1"}};
+                                        {"nthreads", "1", "1"},
+                                        {"nfds", "1", "1"}};
 
   // Dynamic monitoring container for value measurements
   // This will be filled at initialisation, taking the names
@@ -46,6 +47,7 @@ class countmon final : public Imonitor, public MessageBase {
   void const get_unit_info(nlohmann::json& unit_json);
   bool const is_valid() { return true; }
 };
-REGISTER_MONITOR(Imonitor, countmon, "Monitor number of processes and threads")
+REGISTER_MONITOR(Imonitor, countmon,
+                 "Monitor number of processes, threads and file descriptors")
 
 #endif  // PRMON_COUNTMON_H

package/tests/test_count.py

@@ -65,6 +65,17 @@ def test_run_test_with_params(self):
                     f"(expected {expect_thread}, got {total_thread}",
                 )
 
+                # File descriptor count sanity check: every process
+                # has at least stdin, stdout, stderr open
+                total_nfds = prmon_json["Max"]["nfds"]
+                min_expected_nfds = 3 * procs
+                self.assertGreaterEqual(
+                    total_nfds,
+                    min_expected_nfds,
+                    msg="File descriptor count too low "
+                    f"(expected >= {min_expected_nfds}, got {total_nfds})",
+                )
+
     return ConfigurableProcessMonitor
 
 

package/tests/test_values.cpp

@@ -28,6 +28,37 @@ std::shared_ptr<spdlog::sinks::basic_file_sink_st> f_sink{
 
 bool prmon::sigusr1 = false;
 
+TEST(CountmonTest, CountmonValueTestFixed) {
+  std::string cur_path = base_path + "drop";
+  std::vector<pid_t> fake_pids = mother_pid;
+
+  std::unique_ptr<Imonitor> monitor(
+      registry::Registry<Imonitor>::create("countmon"));
+
+  const int iterationCount = 3;
+
+  std::map<std::string, unsigned long long> store_stats;
+  for (int iteration = 1; iteration <= iterationCount; ++iteration) {
+    std::stringstream iteration_path{};
+    iteration_path << cur_path << "/" << iteration;
+    monitor->update_stats(fake_pids, iteration_path.str());
+    store_stats = monitor->get_text_stats();
+    ASSERT_EQ(store_stats["nprocs"], 1);
+    ASSERT_EQ(store_stats["nthreads"], 1);
+    if (iteration == 1) {
+      ASSERT_EQ(store_stats["nfds"], 3);
+    } else if (iteration == 2) {
+      ASSERT_EQ(store_stats["nfds"], 5);
+    } else {
+      ASSERT_EQ(store_stats["nfds"], 2);
+    }
+  }
+
+  // Verify that the peak value reflects the maximum across iterations
+  auto max_stats = monitor->get_json_total_stats();
+  ASSERT_EQ(max_stats["nfds"], 5);
+}
+
 TEST(IomonTest, IomonMonitonicityTestFixed) {
   std::string cur_path = base_path + "drop";
   std::vector<pid_t> fake_pids = mother_pid;