Provide a mechanism for querying and printing system load.

+ Add class `CPUinfo` that has member functions `report_load_average` and `report_cpu_utilization`.
  These functions only work on Linux.  They query `/proc/loadavg` and `/proc/stat` respectively to
  retrieve the current machine status.

src/c4/test/tstOMP.cc

@@ -386,6 +386,15 @@ void MandelbrotDriver(rtt_dsxx::UnitTest &ut) {
 int main(int argc, char *argv[]) {
   rtt_c4::ParallelUnitTest ut(argc, argv, rtt_dsxx::release);
   try {
+
+#ifndef MSVC
+    if (rtt_c4::node() == 0) {
+      // Machine load:
+      CPUinfo().report_load_average();
+      CPUinfo().report_cpu_utilization();
+    }
+#endif
+
     // One MPI rank per machine node?
     bool omrpn(false);
 

src/ds++/SystemCall.hh

@@ -9,7 +9,13 @@
 #define rtt_dsxx_SystemCall_hh
 
 #include "ds++/config.h"
+#include <array>
+#include <chrono>
+#include <fstream>
+#include <iostream>
+#include <sstream>
 #include <string>
+#include <thread>
 #ifdef WIN32
 #define _WINSOCKAPI_
 #include <WinSock2.h>
@@ -97,6 +103,127 @@ void draco_remove(std::string const &path);
 #define draco_setenv(k, v) setenv(k, v, 1)
 #endif
 
+#ifndef MSVC
+//================================================================================================//
+/*!
+ * \class CPUinfo
+ * \brief Read information from /proc/stat and provide information about CPU states.
+ *
+ * \example c4/test/tstOMP.cc
+ * The main() reports the average load and cpu utilization (for Linux).
+ */
+//================================================================================================//
+class CPUinfo {
+
+private:
+  //! The cpudata has 10 values (ref: /proc/stat)
+  static constexpr size_t cpudata_num_values{10};
+  /*!
+   * \struct CPUData
+   *
+   * Data struct for cpu information that will be captured.  The format for /proc/stat is something
+   * like this example:
+   * <code>
+   *    cpu  764699971 57752895 158644540 75321983666 67359813 0 736586 0 0 0
+   * </code>
+   * A string followed by 10 size_t values.
+   *
+   * The 10 values represent cpu states:
+   * - user (0)
+   * - nice (1)
+   * - system (2)
+   * - idle (3)
+   * - iowait (4)
+   * - irg (5)
+   * - softirq (6)
+   * - steal (7)
+   * - guest (8)
+   * - guest_nice (9)
+   * .
+   */
+  struct CPUData {
+    std::string cpu;
+    size_t num_cpus;
+    std::array<size_t, cpudata_num_values> times;
+  };
+
+  /* Maniulators */
+
+  //! Read /proc/stat to determine the system load.
+  CPUData ReadStatsCPU() {
+    CPUData cpu_all_entry;
+    const std::string label_cpu_all("cpu");
+    std::ifstream fileStat("/proc/stat");
+    std::string line("");
+    size_t num_cpu(0);
+    while (std::getline(fileStat, line)) { // Read a line
+      // cpu stats line found
+      if (!line.compare(0, label_cpu_all.length(), label_cpu_all)) {
+        std::istringstream ss(line);
+        // read cpu label
+        ss >> cpu_all_entry.cpu;
+        // read times
+        if (cpu_all_entry.cpu == "cpu") {
+          for (auto &t : cpu_all_entry.times)
+            ss >> t;
+        } else {
+          num_cpu++;
+        }
+      }
+      cpu_all_entry.num_cpus = num_cpu;
+    }
+    return cpu_all_entry;
+  }
+
+  /* Private accessors */
+
+  size_t machIdleTime(CPUData const &c) const { return c.times[3] + c.times[4]; }
+  size_t machActiveTime(CPUData const &c) const {
+    return c.times[0] + c.times[1] + c.times[2] + c.times[5] + c.times[6] + c.times[7] +
+           c.times[8] + c.times[9];
+  }
+
+  //! Read /proc/loadavg data.
+  std::array<float, 3> ReadLoadAvg() {
+    std::array<float, 3> retvalue;
+    std::ifstream fileStat("/proc/loadavg");
+    std::string line("");
+    while (std::getline(fileStat, line)) { // Read a line
+      std::istringstream ss(line);
+      for (auto &t : retvalue)
+        ss >> t;
+    }
+    return retvalue;
+  }
+
+public:
+  //! Report cpu usage
+  void report_cpu_utilization() {
+    // initial state
+    CPUData entry1 = ReadStatsCPU();
+    std::this_thread::sleep_for(std::chrono::milliseconds(500));
+    // state after 0.1 sec.
+    CPUData entry2 = ReadStatsCPU();
+
+    float const activeTime = static_cast<float>(machActiveTime(entry2) - machActiveTime(entry1));
+    float const idleTime = static_cast<float>(machIdleTime(entry2) - machIdleTime(entry1));
+    float const totalTime = activeTime + idleTime;
+    std::cout.width(6);
+    std::cout.precision(2);
+    std::cout << "Average CPU Utilization      : " << 100.0f * activeTime / totalTime << "%\n"
+              << "Number of cores (hw threads) :" << entry1.num_cpus << std::endl;
+  }
+
+  //! Report load average
+  void report_load_average() {
+    // 1, 5, and 15 minute load averages reported by /proc/loadavg.
+    std::array<float, 3> loadAvg = ReadLoadAvg();
+    std::cout << "Load Average: " << loadAvg[0] << ", " << loadAvg[1] << ", " << loadAvg[2]
+              << " (1 min, 5 min, 15 min)" << std::endl;
+  }
+};
+#endif
+
 #endif // rtt_dsxx_SystemCall_hh
 
 //------------------------------------------------------------------------------------------------//