adding standalone C++ code for CPU monitoring of a process (#1658)

Author: sawenzel

UTILS/monitorCPU.cpp

@@ -0,0 +1,92 @@
+// A small, standalone code, to quickly record CPU-vs-T
+// for a running process, so that one can make plots.
+// Simply compile with g++ -O2 monitorCPU.cpp -o monitor.exe and run.
+
+#include <iostream>
+#include <fstream>
+#include <sstream>
+#include <chrono>
+#include <thread>
+#include <unistd.h>
+
+double getProcessCpuUtilization(int pid)
+{
+  std::ifstream statFile("/proc/" + std::to_string(pid) + "/stat");
+  if (!statFile.is_open()) {
+    std::cerr << "Failed to open stat file for PID " << pid << std::endl;
+    return -1.0; // Error indicator
+  }
+
+  std::string line;
+  std::getline(statFile, line);
+  statFile.close();
+
+  std::istringstream iss(line);
+  std::string token;
+  // We only need the 14th and 15th fields: utime and stime
+  for (int i = 0; i < 13; ++i) {
+    iss >> token;
+  }
+  unsigned long utime, stime;
+  iss >> utime >> stime;
+
+  unsigned long process_total = utime + stime;
+  static unsigned long last_process_total = 0;
+
+  // Read total CPU time from /proc/stat
+  unsigned long total_cpu_time = 0;
+  std::ifstream stat("/proc/stat");
+  if (stat.is_open()) {
+    std::string cpuLabel;
+    while (stat >> cpuLabel && cpuLabel != "cpu") {
+      // Skip non-cpu lines
+      stat.ignore(std::numeric_limits<std::streamsize>::max(), '\n');
+    }
+    unsigned long value;
+    for (int i = 0; i < 10; ++i) {
+      stat >> value;
+      total_cpu_time += value;
+    }
+  } else {
+    std::cerr << "Failed to open /proc/stat" << std::endl;
+    return -1.0; // Error indicator
+  }
+  stat.close();
+
+  // Calculate CPU utilization over the last 5 seconds
+  static unsigned long last_total_cpu_time = total_cpu_time;
+  double utilization = (process_total - last_process_total) * 1.0 / (total_cpu_time - last_total_cpu_time);
+
+  // Update last total CPU time for next calculation
+  last_total_cpu_time = total_cpu_time;
+  last_process_total = process_total;
+
+  return utilization;
+}
+
+int getNumberOfCores()
+{
+  return sysconf(_SC_NPROCESSORS_ONLN);
+}
+
+int main(int argc, char* argv[])
+{
+  int pid = -1;
+
+  if (argc > 1) {
+    pid = atoi(argv[1]);
+  }
+
+  while (true) {
+    double cpuUtilization = getProcessCpuUtilization(pid);
+    if (cpuUtilization >= 0.0) {
+      std::cerr << "CPU(" << pid << ") " << cpuUtilization * 100 * getNumberOfCores() << "\n";
+    } else {
+      std::cerr << "Error retrieving CPU utilization." << std::endl;
+    }
+
+    // Wait for 2 seconds
+    std::this_thread::sleep_for(std::chrono::seconds(2));
+  }
+  return 0;
+}